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From December 2012 to June 2014, 796 Pacific guitarfish were caught in 183 fishing sets in northern Peru. Catch occurred in 86.3% of sets. Most individuals caught were mature with a bias toward males. The mean total length for females and males was 83.4 cm, and 91.1 cm, respectively. The capture per unit effort (CPUE) was 12.6 ± 3.4 guitarfish (km.12 h)−1. The length–weight relationships showed that this species presents a sexual dimorphism in growth. These results support the importance of Sechura Bay as a key area for this species. This study represents the first species‐specific fishery data for the Pacific guitarfish. [ABSTRACT FROM AUTHOR]

The present study addressed the population dynamics of the grey-leaved Cordia sinensis to evaluate its status and contribute to the understanding of the demographic behaviour and reproductive performance of this important semi-desert tree. Twenty permanent quadrats (25 × 25 m) were visited seasonally to investigate the variations in C. sinensis population in 5 different habitats (desert, fallow land, cultivated plots, roadsides, and ruderal areas) in Kharga Oasis, Egypt to estimate its phenology, vegetative and reproductive characteristics. The seedling and vegetative phases attained their highest activity during winter, while flowering during spring and fruiting during summer. The highest plants (H) and largest diameter at breast height (D), size index, and tree volume were recorded in autumn, while the highest H/D ratio was recorded during winter. Two size distributions were recognized all over the year: positive skewed distribution in winter and bell shape distribution in autumn, summer and spring. The highest number of new branches was recorded during autumn, while the maximum number of dead branches was recorded in summer. The highest number of branches and leaves were recorded in cultivated plots. The sub-branches produced the highest number of inflorescences, flowers, and fruits during spring, associated with the highest reproductive success. C. sinensis had the longest and widest fruits as well as the highest fresh and dry weights in the ruderal areas characterized with the highest number of seeds and aborted embryos. The present study provides baseline information on C. sinensis, which could help in putting a valuable management plan for monitoring and controlling this plant. [ABSTRACT FROM AUTHOR]

The Irtysh River, which stretches for 633 km, is the second longest river in Xinjiang. The valley forests within its basin are unique forest resources that exhibit crucial ecological functions and form an integral part of China's "Three North" Shelterbelt Forest Project. However, previous studies mainly focused on individual tributaries or main streams, lacking comprehensive research on the overall river and valley forest resources and their ecological functions. To address this research gap based on comprehensive investigations, this study analyzed the dominant species composition, spatial distribution patterns, and influencing factors of valley forests across various branches of the Irtysh River basin plain. The results revealed the presence of 10 local tree species in the area, with Populus laurifolia, Populus alba, Salix alba, and Betula pendula as the dominant species. However, seedling regeneration was relatively weak. P. laurifolia, P. alba, and S. alba were widely distributed across tributaries and main streams, whereas B. pendula was primarily found in the tributaries. The four dominant species exhibited distinct clustering patterns. The concentration intensity of these dominant species in the main stream of the Irtysh River basin was significantly higher than those in other tributaries, with P. laurifolia showing a lower concentration intensity across the entire basin than the other dominant species. Negative density dependence was the primary biological factor influencing species aggregation intensity, with significant positive effects on P. alba and S. alba and significant negative effects on B. pendula. Among the abiotic factors, elevation had a significant positive effect on the aggregation intensities of P. alba, S. alba, and B. pendula, indicating that these species tend to aggregate more densely at higher elevations. Conversely, slope had a significant negative impact on the aggregation intensities of P. laurifolia, P. alba, and S. alba, suggesting that increasing slope steepness leads to a decrease in the clustering of these species. Similarly, the distance from the river channel had a significant negative effect on the aggregation intensities of S. alba and B. pendula, implying that as the distance from the river increases, the clustering patterns of these species become less pronounced. This study aimed to detail the current state of valley forest resources and their ecological functions, thereby laying a foundation for their effective protection. [ABSTRACT FROM AUTHOR]

During cruise 89 of the R/V Akademik Mstislav Keldysh in September–October 2022, search for the snow crab Chionoecetes opilio were conducted in benthic communities of the Kara Sea using a Sigsby bottom trawl and the TUV Videomodule; as well, plankton samples were collected with a Bongo net in order to record crab larvae in the water column. Single large individuals of snow crab were found for the first time in the eastern Kara Sea, on a transect from the Voronin Trough towards the coast of Taimyr, starting at a depth of 490 m. At the same time, not a single crab larva was caught, which indicates penetration of mature crabs into these areas across the bottom. Conversely, in the western part of the sea and in Blagopoluchiya Bay, large numbers of all size groups of C. opilio on the bottom, as well as crab larvae in the water column, were observed. The differences in the speed and nature of the snow crab invasion are explained by the contrast in the ice conditions in the western and eastern Kara Sea. The snow crab population is likely to spread further in the eastern Kara Sea due to trends towards an increase in the ice-free period in the Arctic. [ABSTRACT FROM AUTHOR]

This study examines an optimal contraception control problem for a nonlinear competitive vermin population model that is dependent on size structure and spatial diffusion in a polluted environment. The control variables are the average number of female sterilant and the input rate of exogenous toxicant. It has a good guiding effect on curbing environmental pollution and controlling the number of vermin. These results provide a theoretical basis for controlling and preventing vermin and curbing environmental pollution. The hybrid system belongs to the class of separable models, and its solution is separable in terms of size and spatial location. Therefore, we transform the system into two subsystems and prove the existence and uniqueness of non-negative solutions via the comparison principle and fixed point theorem, respectively. The necessary conditions for the optimal contraception strategy are derived by constructing an adjoint system and using tangent-normal cones. The method of characteristics and the finite difference method approximate the non-negative solutions of the two subsystems, and some numerical examples illustrate the theoretical results. [ABSTRACT FROM AUTHOR]

The distribution characteristics of size-fractionated Chlorophyll a (Chl-a) and the environmental factors were studied in the coastal area of the Leizhou Peninsula in January 2022. The result showed that Chl-a ranged from 0.39 to 4.78 mg/m3 (averaging 1.21 mg/m3) at the surface and 0.43 to 2.78 mg/m3 (averaging 1.04 mg/m3) at the bottom layer, respectively. The spatial distribution of Chl-a concentration was associated with salinity. High Chl-a concentration was observed in the eastern part of the Leizhou Peninsula characterized by lower salinity, and low Chl-a concentration in Qiongzhou Strait with higher salinity. Nanophytoplankton (2–20 µm) was the dominant contributor, accounting for 61.3% and 63.7% of the total Chl-a at the surface and bottom layer, respectively. Both microphytoplankton (>20 µm) and nanophytoplankton displayed increased Chl-a with the increase in total Chl-a. Salinity, nutrients and temperature appear to influence the phytoplankton size structure in the coastal area of the Leizhou Peninsula. Additionally, the regulation of nutrient varied among phytoplankton of different sizes. This study contributed to our understanding of coastal ecosystem processes and has potential implications for coastal management and monitoring efforts.

Abstract Background During a field survey of urban flora in Alexandria city in 2019–2022, an interesting species belonging to the Solanaceae was collected from a newly archaeological excavation site and identified as Nicotiana glutinosa L. Many visits were made to the herbaria of Egypt to confirm the species records, but no single record was found. Reviewing the available literature revealed that this tropical American taxon was never recorded in the flora of Egypt. Aims The present study was focused on N. glutinosa growth structure and plant macro- and micromorphology. Methods Ten sampling sites were covered for N. glutinosa size structure. Plant samples were examined for stem anatomy, leaf, seed, and pollen morphology. Results The species size structure reveals that the individual size index ranges from 1.33 to 150 cm, while its density ranges from 4 to 273 individuals /100 m−2. N. glutinosa has successfully established itself in one of the archaeological sites in Egypt, showing a “healthy” population with a high degree of size inequality, characterized by a relative majority of the juvenile individuals. Voucher specimens were deposited in the Herbarium of Alexandria University (ALEX) Faculty of Science, another specimen is processed to make herbarium specimens at the Herbarium of the Botanic Garden (Heneidy et al. collection, deposition number. 5502). Conclusions From our observations, N. glutinosa seems to have invasive potential, as it shows characteristics shared by most invasive species that are thought to help in their successful establishment in new habitats. This article emphasizes the importance of monitoring and regularly reporting the threats of alien invasive species to avoid any possible negative impacts on indigenous biodiversity in the future.

In this paper, we consider the optimal boundary control problem of a two-species competitive system with time delay and size structure in a polluted environment. First, the well posedness of the system is studied by using the characteristic line method and the fixed point principle. Second, the necessary conditions for optimal boundary control are obtained by conjugate system and normal cone property. Finally, the existence and uniqueness of the optimal strategy are proved by Ekeland variational principle. [ABSTRACT FROM AUTHOR]

Most likely, the alien snow crab Chionoecetes opilio entered the Kara Sea from the Barents Sea, both due to the migration of adults and with currents at the larval stage. Currently, all bottom stages, including mature individuals and a large number of pelagic larvae, are present in the Kara Sea. However, the origin of larvae has not yet been clarified. The larvae hatched in the Kara Sea should be at an earlier stage of development compared with the larvae arrived here from the Barents Sea due to later development of phytoplankton and, accordingly, later hatching. The larvae of the snow crab Chionoecetes opilio and the spider crab Hyas araneus were collected in the central and southwestern Kara Sea in July–early August 2019 by a Bongo zooplankton net with a diameter of 60 cm. It was established that the larvae were unevenly distributed across the Kara Sea. The most populus region was the border with the Barents Sea in the St. Anna Trough (up to 860 ind./m2), and relatively high concentrations of larvae were recorded in the southwestern part, where their abundance at stations varied from 18 to 302 ind./m2. In the zone of the Ob–Yenisei plume, crab larvae were absent or their abundance was minimal. Using molecular genetic methods, the species identity of 361 larvae (344 C. opilio and 17 H. araneus) was reliably determined, and measurements of a number of morphological structures were made for 401 larvae. Significant differences in size were found at the zoea II stage between C. opilio and H. araneus. In July 2019, in most of the Kara Sea, in zooplankton samples, crab larvae were represented by zoea I of C. opilio with rare specimens of zoea I of H. araneus of the Kara Sea origin. Only in the southwestern part, at the boundary with the Barents Sea, was the presence of zoea II of C. opilio and H. araneus observed in samples with an increased share of the latter species in catches, which probably originated from the Barents Sea. [ABSTRACT FROM AUTHOR]

Estuary reopening is a means of restoring estuarine habitats, which has recently been implemented in a few developed countries. The regeneration of a brackish zone in the Nakdong River Estuary (NRE), South Korea, were tested through a series of barrage reopening. During the same period, we conducted extensive fish surveys in the upper part of the NRE barrage on a monthly basis from 2017 to 2021, and subsequently determined whether fish populations and communities were affected by the reopening. The results showed that the reopening of the NRE hardly affected the fish community structure, as non-native species such as Erythroculter erythropterus and Lepomis macrochirus maintained their dominance. Still, we discovered that certain euryhaline species are positively affected by estuary reopening, as total 46 Japanese eels (Anguilla japonica) were captured after the reopening, which had not been detected before the reopening. By comparing the size structure of various fish species, we discovered that size distribution of native and migratory species presented more positively skewed pattern after the reopening, while size structure in non-native species remained relatively unchanged normally distributed pattern. Piecewise structural equation modelling revealed that the NRE had become more complex ecosystem, as migratory fish species abundance and biomass started to show a positive correlation with hydraulic factors such as discharge and negative correlation with seasonality after the reopening. We concluded that estuary reopening created some changes in migratory and native freshwater species but such changes were not notably detected in non-native species. Therefore, appropriate sluice operation methodologies, such as considering the migration seasons of migratory species, should be developed. Additionally, human-involved management policies are required to regulate non-native species populations. [ABSTRACT FROM AUTHOR]

Blue mussels Mytilus have returned to the high Arctic region of Svalbard in the beginning of twenty-first century after being absent for almost a 1000 years. Not only M. edulis had arrived in Svalbard, but also a complex of sympatric species including M. edulis, M. galloprovincialis, M. trossulus, and some of their hybrids, which may have a wide range of origins from both sides of the North Atlantic. Mussels were first found in the sublittoral at the entrance to Isfjorden, west coast of Spitsbergen island, and are spreading in other areas, and recently were also found in the intertidal zone. Here, we report viable larvae that were recovered from within the mantle cavity of mussels from the lower intertidal shore collected in late July 2019 and 2021 in Trygghamna, Isfjorden. The identity of larval and adult mussels was confirmed by sequencing of barcode region. Larvae ranged in size from 178 to 376 µm, from mussels 21 to 57 mm in shell length, and estimated to range over 3 to 12 years. It remains unclear whether the larval retention within the mantle cavity results from an intake of near shore concentrations and whether this may lead to larviphagy. [ABSTRACT FROM AUTHOR]

Food web projections are critical for evaluating potential risks to ecosystems and fisheries under global warming. The temperature dependence of biological processes and regional differences in food web structure are two important sources of uncertainty and variation in climate forced projections of fish communities, but we do not know their magnitude or relative contribution. Here we systematically evaluated a range of different assumptions about temperature‐dependence on rates, including size‐dependent effects, controlling food intake, metabolism, and non‐predation mortality in fishes using species‐resolved size spectrum food web models that link individual‐level physiological processes to population and community dynamics. We simulated the physiological effect of warming in a range of size‐structured food web models calibrated to different marine ecosystems and in simplified trait‐based models. Higher food intake in warmed conditions increased total fish biomass, catches, and mean body weight, but these effects were offset by the negative effects of warming on metabolism and mortality, which combined resulted in lower total biomasses and catches for most food webs. These effects were enhanced when warming increased metabolic rates more than food intake, and the outcomes were also sensitive to size dependency of temperature responses. Importantly, these general patterns were not uniform across all food webs—individual functional groups and fish species within food webs responded to warming in different ways depending on their position in the food web and its structure. Hence, caution is warranted when generalizing food web or species outcomes to warming because they are mediated by community interactions. Uncertainty related to temperature dependence and ecological interactions will impact food web projections and should be represented in climate change projections. Plain Language Summary: Multi‐species models are often used to predict how climate change will affect marine ecosystems, fisheries yields and conservation. However, temperature can affect species in a variety of ways, making predictions challenging. Moreover, warming driven changes in a fish community will also depend on species interactions, potentially amplifying or dampening warmingdriven effects in individual species. We explored how 2°C of warming may impact fish biomasses, yields and sizes using six models developed for different marine food webs and three theoretical models with different assumptions about species interactions. We found that, overall, warming tended to result in lower biomasses and fisheries yields, but slightly larger average fish sizes. Yet, results differed depending on how we modeled temperature effects on species food intake and energy expenditure. Moreover, even under the same assumptions about temperature impacts, models developed for different ecosystems behaved differently showing that species interactions will modify warming effects, making general predictions difficult. To make better predictions on warming impacts and more informed adaptation strategies we urgently need more work to understand how temperature affects individual species and communities. Meanwhile, models predicting ecosystems responses to warming should more clearly account for the uncertainty in temperature effects on fishes. Key Points: Assumptions regarding how temperature drives biological rates strongly influence food web responses to warmingCommunity interactions further modify outcomes to warming which complicate efforts to generalize warming responses across food websUncertainty in food web temperature dependences should be represented in climate change projections [ABSTRACT FROM AUTHOR]

Growth in individual body size amongst different species can to a greater or lesser extent depend on environmental factors such as resource availability. Individual growth curves can therefore be largely fixed or more plastic. Classic theory about phenotypic plasticity assumes that such plasticity has associated costs. In contrast, according to dynamic energy budget theory, maintaining a fixed growth rate in the face of variable resource availability would incur additional energetic costs. In this article, we explore the simultaneous evolution of the degree of plasticity in individual growth curves and the rate of non-plastic, environment-independent individual growth. We explore different relations between possible additional energetic costs and the degree of growth curve plasticity. To do so, we use adaptive dynamics to analyze a size-structured population model that is based on dynamic energy budget theory to account for the energetic trade-offs within an individual. We show that simultaneous evolution of the degree of growth curve plasticity and the rate of non-plastic individual growth will drive these traits to intermediate values at first. Afterwards, the degree of growth curve plasticity might evolve slowly towards extreme values depending on whether energetic costs increase or decrease with the degree of plasticity. In addition, the analysis shows that it is unlikely to encounter species in which individual growth is entirely fixed or entirely plastic, opposing general assumptions in dynamic energy budget theory. [ABSTRACT FROM AUTHOR]

Background: During a field survey of urban flora in Alexandria city in 2019–2022, an interesting species belonging to the Solanaceae was collected from a newly archaeological excavation site and identified as Nicotiana glutinosa L. Many visits were made to the herbaria of Egypt to confirm the species records, but no single record was found. Reviewing the available literature revealed that this tropical American taxon was never recorded in the flora of Egypt. Aims: The present study was focused on N. glutinosa growth structure and plant macro- and micromorphology. Methods: Ten sampling sites were covered for N. glutinosa size structure. Plant samples were examined for stem anatomy, leaf, seed, and pollen morphology. Results: The species size structure reveals that the individual size index ranges from 1.33 to 150 cm, while its density ranges from 4 to 273 individuals /100 m−2. N. glutinosa has successfully established itself in one of the archaeological sites in Egypt, showing a "healthy" population with a high degree of size inequality, characterized by a relative majority of the juvenile individuals. Voucher specimens were deposited in the Herbarium of Alexandria University (ALEX) Faculty of Science, another specimen is processed to make herbarium specimens at the Herbarium of the Botanic Garden (Heneidy et al. collection, deposition number. 5502). Conclusions: From our observations, N. glutinosa seems to have invasive potential, as it shows characteristics shared by most invasive species that are thought to help in their successful establishment in new habitats. This article emphasizes the importance of monitoring and regularly reporting the threats of alien invasive species to avoid any possible negative impacts on indigenous biodiversity in the future. [ABSTRACT FROM AUTHOR]

Macrozoobenthos of the littoral of Lake Onego is represented by 22 units of different taxonomic rank. The invasive species Gmelinoides fasciatus (Stebbing 1899) (CRUSTACEA: AMPHIPODA) plays a dominant role by biomass in the littoral macrozoobenthos community during the subglacial period. The peculiarities of the size and sex composition of the G. fasciatus population are studied. It was shown for the first time that in the subglacial period on the littoral of Lake Onego the population of amphipods contains young individuals from 2.1 mm, in contrast to the size composition of this species in Lake Ladoga. Apparently, these are crustaceans that appeared in the summer of the previous year, as we did not discover any breeding females. The sexual structure of the G. fasciatus population in Lake Onego is stable, with the ratio of females to males being 1:1.

Introduction: Irregular echinoids are characterized by having a selection of the substrate mainly on soft bottoms. In El Salvador, seven species of irregular echinoids have been recorded on the main sandy beaches of the country, M. stokesii is one of them. Objective: Determine the abundance, density and size structure of M. stokesii on beaches at the mouth of the El Tamarindo estuary, El Salvador. Methods: The research was carried out in the dry season in the east of the country on the beaches of the El Tamarindo estuary, which is characterized by large extensions of sand mixed with organic matter. At each site, band transects parallel to the coast were plotted by 9 quadrants of 10 m2 separated from each other by 10 m (total area of 90 m2), where individuals of M. stokesii found within the delimited area were counted and measured. Results: 958 individuals of M. stokesii were counted with a total density of 10.64 ± 13.22 ind/m2. The size range was 1-6.5 cm. The habitat was characterized by presenting sand with organic matter in the first mm of the substrate in the company of other invertebrates. Conclusions: The abundance and density of M. stokesii are similar to the ones recorded in other studies in the region. [ABSTRACT FROM AUTHOR]

The Yellow Sea (YS) and East China Sea (ECS) are highly dynamic marginal seas of the northwestern Pacific Ocean. To gain an in-depth understanding of zooplankton community structure, zooplankton abundance, biovolume, and size structure in summer 2017 in the YS and ECS were assessed using ZooScan imaging analysis. Zooplankton abundance and biovolume ranged 2.94–1 187.14 inds./m3 and 3.13–3 438.51 mm3/m3, respectively. Based on the biovolume data of the categorized size classes of 26 identified taxonomic groups, the zooplankton community was classified into five groups, and each group was coupled with distinctive oceanographic features. Under the influence of the Yellow Sea Cold Water Mass, the Yellow Sea offshore group featured the lowest bottom temperature (10.84±3.42 °C) and the most abundant Calanoids (mainly in the 2–3 mm size class). In the Yellow Sea inshore group, Hydrozoans showed the largest biovolume and dominated in the 3–4-mm and > 5-mm size classes. The East China Sea offshore group, which was affected by the Kuroshio Branch Current, featured high temperature and salinity, and the lowest bottom dissolved oxygen (2.58±0.5 mg/L). The lowest values of zooplankton abundance and biovolume in the East China Sea offshore group might be attributed to the bottom dissolved oxygen contents. The East China Sea inshore group, which was mainly influenced by the Zhejiang-Fujian Coastal Current and Changjiang Diluted Water, was characterized by high chlorophyll a and the largest biovolume of carnivorous Siphonophores (280.82±303.37 mm3/m3). The Changjiang River estuary offshore group showed the most abundant Cyclopoids, which might be associated with the less turbid water mass in this region. Seawater temperature was considered the most important factor in shaping the size compositions of Calanoids in different groups. [ABSTRACT FROM AUTHOR]

The current status of the stocks, the dynamics of commercial fisheries, and the distribution of the saffron cod Eleginus gracilis in the fishery areas of the Far East are analyzed. In the Far Eastern basin, saffron cod makes the greatest contribution to the total catch of aquatic biological resources in the Karaginsky subzone (8.1%) and off western Kamchatka (3.6%). The total saffron cod catch from the Far Eastern seas in 2003–2022 ranged within 16 700–50 600 tons, with an average of 33 900 t. According to the data of bottom trawl surveys conducted in 2016–2023, the largest saffron cod aggregations are traditionally observed in the shelf waters off western Kamchatka, in the southwestern and northwestern Bering Sea, where the catch per unit effort reaches 4500 kg per trawling hour. Off western Kamchatka, the biomass of this species was estimated at 197 400 t; in the Karaginsky subzone, 100 400 t; in the West Bering Sea zone, 32 800 t; in the East Sakhalin and Petropavlovsk-Commander subzones, the values were similar, 17 100 and 17 200 t, respectively; and in the North Okhotsk Sea area, 8700 t. Almost all the exploited stocks in recent years have been above their average long-term annual level or fluctuated within its range. In general, the status of the saffron cod stocks in the fishery subzones at the present time can be considered satisfactory. [ABSTRACT FROM AUTHOR]

While it is well‐accepted that predation plays a key role in shaping both size structure and species composition in natural ecosystems, fine‐scale variation in predation risk within ecosystems has been largely neglected. The objective of this study was to use normalised size spectra (NSS) to investigate whether small‐scale spatial variation in predation risk (by fish) can modulate zooplankton community structure at the within‐lake level in a small temperate lake.We tested the difference in the NSS between two hydrologically well‐connected basins of a lake exhibiting contrasting thermal regimes. The first is a well‐mixed shallow basin (max. depth 2.5 m) that is inaccessible to brook charr (Salvelinus fontinalis) during summer because the temperature is too warm. The second is a deeper basin (max. depth 18 m) offering a thermal refuge during summer because of lake stratification. As a consequence of these differences in fish accessibility, the fishless basin should contain larger and more abundant zooplankters, inducing a change in NSS slope and height.Our results showed that both the zooplankton size structure and taxonomic composition were distinct in the two basins, with a higher proportion of small individuals and a higher abundance of zooplankton in the shallow basin compared to the deep one. Furthermore, following cooling of the epilimnion in late summer, the zooplankton communities of both basins exhibited a clear shift in size structure and species composition: in autumn, there were smaller individuals and larger proportions of Bosminidae and Daphniidae compared to colonial rotifers than in summer. These results suggest a potential effect of the change in the spatial distribution of brook charr which feed preferentially on large individuals, reducing the average body size of the zooplankton community.Our results show that predation risk by fish can induce a spatial and temporal variation in zooplankton community structure within small temperate lake ecosystems exhibiting contrasted thermal regimes. Other potential predators also influenced the zooplankton community structure, creating a complex interplay that has to be taken into account to disentangle ecological processes and predict their future changes. [ABSTRACT FROM AUTHOR]

Demographic studies that quantify species' performances for survival, growth, and reproduction are powerful means to characterize sources of demographic bottlenecks and predict community dynamics. However, they require fine-scale surveys of populations in the field, and are often too effort-intensive to be replicable at a large scale and in the long term. We developed a standardized digital approach for extracting demographic data on species' abundances, sizes, and positions within video transects, enabling back-from-the-field data acquisition and therefore optimizing time spent in the field. The approach is based on manual species identification, size measurements, and mapping in video transects, mimicking what is traditionally performed in the field, though it can be automated in the future with the deployment of artificial intelligence. We illustrate our approach using video surveys of a reef-building coral community in New Caledonia. The results characterize the composition of the coral community and demographic performances as key ecological indicators of coral reef health, shed light on species' life strategies and constraints to their demographics, and open paths for further quantitative investigations. Key findings include the diversity of life strategies with contrasting levels of investment in survival, growth, and reproduction found among the six taxa dominating the coral community (Acropora, Montipora, Porites, Galaxea, Favia, Millepora), indicating the diversity of demographic paths to ecological success. Our results also indicate that several species have adapted mechanisms to prevail under limiting hydrodynamic environments through the propagation of coral fragments. Our approach facilitates image-based demographic investigations, supporting endeavors in ecology and ecosystem management. [ABSTRACT FROM AUTHOR]

Abstract Food web projections are critical for evaluating potential risks to ecosystems and fisheries under global warming. The temperature dependence of biological processes and regional differences in food web structure are two important sources of uncertainty and variation in climate forced projections of fish communities, but we do not know their magnitude or relative contribution. Here we systematically evaluated a range of different assumptions about temperature‐dependence on rates, including size‐dependent effects, controlling food intake, metabolism, and non‐predation mortality in fishes using species‐resolved size spectrum food web models that link individual‐level physiological processes to population and community dynamics. We simulated the physiological effect of warming in a range of size‐structured food web models calibrated to different marine ecosystems and in simplified trait‐based models. Higher food intake in warmed conditions increased total fish biomass, catches, and mean body weight, but these effects were offset by the negative effects of warming on metabolism and mortality, which combined resulted in lower total biomasses and catches for most food webs. These effects were enhanced when warming increased metabolic rates more than food intake, and the outcomes were also sensitive to size dependency of temperature responses. Importantly, these general patterns were not uniform across all food webs—individual functional groups and fish species within food webs responded to warming in different ways depending on their position in the food web and its structure. Hence, caution is warranted when generalizing food web or species outcomes to warming because they are mediated by community interactions. Uncertainty related to temperature dependence and ecological interactions will impact food web projections and should be represented in climate change projections.

New data on biology of hair crab Erimacrus isenbeckii are presented and ecological and geographical variability of this species is discussed. Molting, growth, sex and size structure of the crab are considered on the data collected in the Shelikhov Bay of the Okhotsk Sea in September-October, 2022. The male : female ratio of E. isenbeckii in the trap catches was 14 : 1. Gender differences in their age, weight, and carapace width were not significant (p < 0.05). The maximum size of E. isenbeckii in the Shelikhov Bay was 104 mm that is less the size values at the western coast of Kamchatka, southward from Kamchatka, and in the Aniva Bay of Sakhalin Island, and much smaller the crabs from the waters of Hokkaido Island and Alaska Peninsula. Rather high portion of the males on the 3rd intermolting stage was detected (57 %). The age composition of males varied significantly in dependence on stage of molting (p < 0.05). A freshly molted female on the 1st intermolting stage with an unoccluded genital opening was caught together with its exuvia. After molting, within the crab trap, it had increased the width of carapace in 6 mm. This new information could be used in monitoring of the E. isenbeckii population in the Shelikhov Bay.

The Irtysh River, which stretches for 633 km, is the second longest river in Xinjiang. The valley forests within its basin are unique forest resources that exhibit crucial ecological functions and form an integral part of China’s “Three North” Shelterbelt Forest Project. However, previous studies mainly focused on individual tributaries or main streams, lacking comprehensive research on the overall river and valley forest resources and their ecological functions. To address this research gap based on comprehensive investigations, this study analyzed the dominant species composition, spatial distribution patterns, and influencing factors of valley forests across various branches of the Irtysh River basin plain. The results revealed the presence of 10 local tree species in the area, with Populus laurifolia, Populus alba, Salix alba, and Betula pendula as the dominant species. However, seedling regeneration was relatively weak. P. laurifolia, P. alba, and S. alba were widely distributed across tributaries and main streams, whereas B. pendula was primarily found in the tributaries. The four dominant species exhibited distinct clustering patterns. The concentration intensity of these dominant species in the main stream of the Irtysh River basin was significantly higher than those in other tributaries, with P. laurifolia showing a lower concentration intensity across the entire basin than the other dominant species. Negative density dependence was the primary biological factor influencing species aggregation intensity, with significant positive effects on P. alba and S. alba and significant negative effects on B. pendula. Among the abiotic factors, elevation had a significant positive effect on the aggregation intensities of P. alba, S. alba, and B. pendula, indicating that these species tend to aggregate more densely at higher elevations. Conversely, slope had a significant negative impact on the aggregation intensities of P. laurifolia, P. alba, and S. alba, suggesting that increasing slope steepness leads to a decrease in the clustering of these species. Similarly, the distance from the river channel had a significant negative effect on the aggregation intensities of S. alba and B. pendula, implying that as the distance from the river increases, the clustering patterns of these species become less pronounced. This study aimed to detail the current state of valley forest resources and their ecological functions, thereby laying a foundation for their effective protection.

Groupers (Family Epinephelidae) are commonly caught in data-poor small-scale multi-species fisheries for sale on both export and domestic markets. This study presents data on the species composition and size/life-stage structure of Epinephelus spp. groupers caught by small-scale fishers and sold locally in the Indonesian province of South Sulawesi. Data were collected from fishing ports and local markets at 12 sites representing the three seaways around South Sulawesi (Makassar Strait, Flores Sea, Gulf of Bone). Each specimen (n = 3,398) was photographed alongside an object of known length, and total length (TL) was obtained using the Rapid Scaling on Object (RASIO). Of the 23 species identified, four (Epinephelus areolatus, Epinephelus ongus, Epinephelus quoyanus, and Epinephelus fasciatus) collectively comprised 69% of the catch, while the 13 least abundant species contributed less than 5%. The catch was dominated (67%) by the subadult life-stage, with just under 20% in the adult class. Juveniles dominated the catch of Epinephelus fuscoguttatus, a valuable export commodity. Observations of early maturity as well as the sizeable gap between length at first capture (Lc) and length at first maturity (Lm) indicate recruitment overfishing of most species, with the notable exception of Epinephelus rivulatus. The proportion of adult fish was low (≈5%–30%) for the twelve most abundant species (E. areolatus, E. ongus, Epinephelus quoyanus, E. fasciatus, Epinephelus coioides, Epinephelus faveatus, Epinephelus sexfasciatus, Epinephelus maculatus, Epinephelus bleekeri, Epinephelus corallicola, E. fuscoguttatus, Epinephelus polyphekadion). For two moderately abundant species (E. faveatus and E. malabaricus), TL < Lm for all specimens. The limited data available indicate spawning ratio is lower than reported from deep-water fisheries of E. areolatus and E. coioides. The results call for targeted research to fill knowledge gaps regarding the biology and ecology of groupers exploited mainly for domestic markets; highlight the need for species-level data to inform management policies such as minimum legal size regulations; and can contribute towards species-level status assessments.

Peltogyne mexicana Martínez is a commercially attractive purple-hued hardwood tree of demographic, environmental and biogeographic rarity in southern Mexico. Despite P. mexicana’s status as a threatened species in Mexico, its populations are rarely managed and subject to open harvesting. Due to the limited number of P. mexicana studies that account for the influence of local tree extraction, we analyzed population-level parameters and community-level associations in two sites - one site called Tepehuaje with active P. mexicana extraction and another called Acahuizotla without extraction due to an ongoing P. mexicana moratorium. Using three 500 m2 plots per site, we characterized P. mexicana population size structure, abundance, spatial distribution, composition, and diversity of associated flora. In both sites, P. mexicana populations exhibited a type one size structure dominated by seedlings. Tepehuaje had 52% fewer saplings and juveniles and three times fewer adults when compared to the site without extraction. P. mexicana juvenile survival in Tepehuaje, a site with warmer climate and lower canopy cover, occurred mainly under trees with heavy foliage (including conspecifics). In Acahuizotla, a site with cooler climate and greater canopy cover, sapling and juvenile abundance was higher in open spaces and under small trees like Cascabela ovata. Although species richness was greater in Acahuizotla, species diversity was higher in Tepehuaje likely due to regularly opened gaps from artisanal logging that limited dominance of certain species. An importance value index (IVI) analysis based on dominance, abundance, and foliar coverage of associated P. mexicana plant communities revealed differences between Acahuizotla (Tetrapterys spp., followed by Plumeria rubra L) and Tepehuaje (Citharexylum affine D. Don, and Bauhinia ungulata L). All species associated with P. mexicana were found to be characteristic of tropical subdeciduous forests. Studying P. mexicana demography and ecology expands the limited knowledge we have of a rare, yet biologically important, species, and sheds light on local practices that can improve persistence.

Floodplains are highly complex ecosystems representing high biodiversity and conservation values, but they are also one of the world's most threatened ecosystems due to extensive development and anthropogenic activities. Lake Tempe is a lowland riverine floodplain lake in Sulawesi Island, Indonesia, that is subject to multiple stressors such as flow alteration, eutrophication and invasive species. In this study, the dynamics of the zooplankton community size structure was investigated in Lake Tempe. Five size-based metrics, including zooplankton mean body size, total abundance, total, biomass, and normalised biomass size spectra (NBSS) slope and intercept were assessed from net-sampled zooplankton collected monthly from March to December 2016, and the role of environmental variables in shaping these size-based metrics were also examined. Zooplankton community size structure is a useful metric as it is less labour intensive than traditional approaches, provides more data accuracy and does not require highly specialised taxonomic expertise. The zooplankton community in Lake Tempe was characterised by high density of small-sized zooplankton with an average mean body size < 500 µm equivalent spherical diameter. While the zooplankton density was characterised by the dominance of the size class 300–700 µm, there was evidence of a significant contribution of the size > 700 µm towards total biomass. Seasonal hydrological regimes, water temperature and eutrophication parameters, as indicated by total phosphorus and chlorophyll-a concentration, had a significant role in driving the variability of zooplankton community size structure in this system. The results of this study are not only a significant step in providing critical baseline information on the zooplankton assemblage of Lake Tempe, but is also a significant contribution to the overall understanding of zooplankton community structure in tropical lakes, and will aid in improving lake management plans in these regions. [ABSTRACT FROM AUTHOR]

Space‐for‐time approaches are often used to indicate current or future changes over time. A European gillnet standard facilitates spatial‐scale comparisons of fish communities in European lakes. Fish size was generally lower and densities higher in warmer lakes, but less is known about trends over decadal time scales. We analysed the size of European perch (Perca fluviatilis L.) in 2121 Swedish lakes sampled during 1996–2021. The aim was to test whether size changed over time, and whether trends were similar in southern and northern regions. We analysed mean length and occurrence or relative abundance of size classes from the smallest (<100 mm) to the largest individuals (≥350 mm), and length at 1 and 5 years. The large data set was used to find general trends over time within regions, and within‐lake trends were tested for 40 time‐series lakes. The mean length of perch decreased in the southern and increased in the northern region. The proportion of the smallest perch increased in the southern, but not in the northern region. The most general trend was an increasing occurrence and proportion of the largest‐sized perch in both regions in the large dataset. The average trends in the southern region of the large dataset also appeared as predominant trends within time‐series lakes, although opposite trends occurred within some lakes in each region. This study also revealed that perch size at age 1 often increased within lakes over time, while more variable trends were found for size at age 5. The duration of the growth season has generally increased during the time frame of the present study, while other changes may differ between lakes in the same region. We recommend more studies based on time series of fish monitoring, including studies on possible reasons for the increased occurrence of very large perch in Swedish lakes. [ABSTRACT FROM AUTHOR]

Objective: Three competing hypotheses might explain the widely documented intrapopulation larger‐fish‐upstream phenomenon. The age‐phased recruitment hypothesis posits that fish spawn downstream and move upstream as they age and grow, the static population with growth and mortality gradients hypothesis posits that fish spawn throughout a riverscape and growth is greater upstream while recruitment is greater downstream, and the colonization cycle hypothesis posits that fish spawn upstream, larvae drift downstream, and individuals move upstream as they age and grow. Methods: We tested for the larger‐fish‐upstream pattern using populations of Silver Chub Macrhybopsis storeriana in the Arkansas and Ohio rivers, as well as investigated longitudinal variation in reproductive investment (Arkansas River), age structure for adult fish (Arkansas River), and number and occurrence of age‐0 fish (Ohio River). Result: The larger‐fish‐upstream pattern was temporally persistent in both riverscapes. In the Arkansas River, reproductive investment was greatest upstream, where initiation of spawning likely occurred based on gonadosomatic indices. Adult fish were most numerous in the Arkansas River 125–175 km upstream from Kaw Reservoir, with age‐2 fish numbers peaking farther upstream compared with age‐1 fish. In the Ohio River, age‐0 fish counts increased downstream and were rare among the shortest river fragments (<100 km) between lock‐and‐dam structures. These findings are inconsistent with the age‐phased recruitment hypothesis based on upstream spawning in the Arkansas River and inconsistent with the static population with growth and mortality gradients hypothesis based on virtual absence of age‐2 fish downstream (Arkansas River) and age‐0 fish upstream (Ohio River). The most likely explanation for longitudinal variation in Silver Chub size distribution is downstream drift of ichthyoplankton followed by net upstream movement (i.e., colonization cycle hypothesis), but formal assessments of movement and ova characteristics require more research. Conclusion: Managing multidimensional riverscapes requires insight into the mechanisms that regulate upstream‐to‐downstream patterns in fish populations, and our work underscores a potential size‐related benefit to maintaining broadscale longitudinal connectivity. Impact statementLarger Silver Chub occur farther upstream in two North American rivers and tests of competing hypotheses suggest this pattern is maintained by broad‐scale movement. Indices based on fish lengths could be used to inform management of longitudinal connectivity in large rivers. [ABSTRACT FROM AUTHOR]

The size structure of microeukaryotic plankton communities exerts a fundamental control on marine ecosystem functions, such as food web dynamics and element flows. The global expansion of nitrogen (N) and phosphorus (P) nutrient pollutants into estuaries and coastal waters is causing public health and environmental concerns associated with microeukaryotic plankton activities. In the context of eutrophication, understanding how size structure and biotic activities of microeukaryotic plankton communities responds to anthropogenic nutrient inputs is vital to evaluate the future fate of coastal ecosystems. Here, we conducted onboard incubation experiments to provide the first investigation of how size structure and co-occurrence network of microeukaryotic plankton communities change under the dynamic nutrient conditions in the Pearl River Estuary. Our study revealed (1) a transition from P limitation to N limitation or potential NP co-limitation for the growth of pigmented protists along the Pearl River-South China Sea continuum, and isohaline ∼ 31.5 being the geographic boundary; (2) P availability drove the microeukaryotic plankton community size structure that the increased P inputs favored the dominance of nano-sized (3–20 μm) protists due to the increased relative abundance of Chlorophyta; (3) increased P inputs enhanced the species competition among phototrophic protists and improved the network stability of microeukaryotic plankton communities. In the future, if there is an increase in anthropogenic input of P in the Pearl River Estuary during summer, which would alleviate the pressure of P-deficiency, it is expected to increase the biomass of microeukaryotic plankton, with a dominance of nano-sized Chlorophyta. Altogether, this study advances our understanding of the geographic nutrient limitation pattern for pigmented protist plankton in the Pearl River Estuary, an urbanized estuarine ecosystem. Moreover, it enhances our knowledge regarding the response of marine microeukaryotic plankton communities to future environmental changes.

Abstract The present study provides some parameters of the population biology of Charybdis (Charybdis) hellerii (A. Milne-Edwards, 1867), an invasive swimming crab inhabiting the estuarine portion of the Sergipe River, northeastern Brazilian coast. Samplings were carried out monthly from July 2015 to June 2016 with baited traps. The species was the second most abundant caught organism and its relative abundance ranged over the time from 11 to 59%. Sex ratio was 1:1 and all individuals were morphologically mature. Males were bigger than females. Ovigerous females were observed year-round and the smallest one was 31.35 mm carapace width. These findings show that the population is well established on the Sergipe coast. The entire distribution, and possible impacts, of C. (C.) hellerii on local environments need to be evaluated in further studies.

The Atlantic sea scallop supports one of the most lucrative fisheries on the Northeast U.S. shelf. Understanding the interannual variability of sea scallop size structure and associated drivers is critically important for projecting the response of population dynamics to climate change and designing coherent fishery management strategies. In this study, we constructed time series of sea scallop size structures in three rotationally closed areas in the Mid-Atlantic Bight (MAB) and decomposed their total variances using the variance partitioning method. The results suggested that the interannual variances in sea scallop size structures were associated more with thermal stress in regions shallower than 60 m but more with fishing mortality in regions deeper than 60 m. The percentages of small (large) size groups increased (decreased) with elevated thermal stress and fishing pressure. We adopted a scope for growth model to build a mechanistic link between temperature and sea scallop size. Model results suggested a gradual decrease in maximum shell height and habitat contraction under warming. This study quantified the relative contributions of thermal stress and fishing mortality to the variance of scallop size structure and discussed the need for adaptive management plans to mitigate potential socioeconomic impacts caused by size structure changes. [ABSTRACT FROM AUTHOR]

This paper investigates the basic reproductive parameters, ecology, and size structure of the common cuttlefish Sepia officinalis. A total of 1217 individuals were sampled monthly from both offshore bottom trawling and inshore small-scale fishery off Mallorca Island's coast (western Mediterranean) during 2017–2019. Inshore individuals were larger than the individuals inhabiting offshore and males were more abundant than females both inshore and offshore waters. The estimated size at first maturity (L50) was 87 mm for females and 78 mm for males. S. officinalis has a semi-continuous reproduction cycle throughout the year with a spawning peak between March and June. Oocyte size-frequency distribution (OSFD) analysis showed an asynchronous oocyte development. Advanced mode fecundity (FAM) ranged between 8 and 326 oocyte/female with a mean of 158 ± 14 oocyte/female. The Stomach Fullness Index (SFI) was found to decrease during reproductive development in inshore specimens, while the stomach vacuity index (SVI) followed the opposite trend for both inshore and offshore individuals, indicating a lessening of the feeding activity specially during spawning. However, once at shallower waters, spawning females displayed higher SFI values compared to males, which was probably linked to the higher energetic demand associated with reproduction. Digestive gland index (DGI) showed little variation in females across maturation stages, while males' values decreased, especially during spawning, reflecting sexual differences in the energy allocation strategy. Those results suggest that common cuttlefish fulfil the cost of reproduction through both current food intake and accumulated somatic reserves. [ABSTRACT FROM AUTHOR]

Striped catfish Pangasianodon hypopthalmus (Sauvage, 1878) is a flagship catfish species of the Mekong River region, a commercially valuable food fish that is important in freshwater fisheries, and a popular aquaculture species in many Asian countries. The species was assessed as "Endangered" by the International Union for Conservation of Nature (IUCN) due to range contraction and declining abundance, though the status of the species' wild population in Cambodia, a critical habitat for the species, is not well understood. Here, we assess the population status of the striped catfish in Cambodia using multiple sources, including time-series catch data and length frequency distribution data from a commercial fishery (stationary trawl bagnet or dai) operated in the Tonle Sap River from 1998/99 to 2017/18 and larval drift data monitored in the Mekong River in Phnom Penh from 2004 to 2018. We found that there was a significant decline (R2 = 0.54, p = 0.0002) in the catch (metric tonnes) of the striped catfish from the commercial dai fishery over the last two decades. Similarly, length-based indicator analysis indicates that striped catfish mean length and abundance have both declined over the study period, raising concerns about the sustainability of river catfish fisheries. Moreover, long-term larval drift monitoring in Mekong River shows that there was a marginally significant decline in the quantity of striped catfish larvae/juvenile drifting downstream to the lower floodplain over the last decade. Changes in flood index (extent and duration of flood) in the Tonle Sap floodplain affected by the Mekong's flow are likely key factors driving the decline of the wild populations of the striped catfish. Both larval fish abundance and floodplain fish harvests have a significant positive relationship with Mekong flow and flood extent. Indiscriminate fishing exacerbates pressures on striped catfish stocks. Therefore, actions such as maintaining natural seasonal flows (flood timing, extent, and duration) to the Tonle Sap floodplain and protecting migratory fish stocks from overharvest and habitat fragmentation are essential to the persistence of stocks of striped catfish and other large-bodied migratory fishes that utilize both the Cambodian Mekong and Tonle Sap floodplains. [ABSTRACT FROM AUTHOR]

Catostomidae (catostomids) are suckers of the order Cypriniformes, and the majority of species are native to North America; however, species in this group are understudied and rarely managed. The popularity in bowfishing and gigging for suckers in the United States has increased concerns related to overfishing. Little information exists about the relative gear effectiveness for sampling catostomids. We sought to evaluate the relative effectiveness of boat electrofishing for sampling Black Redhorse Moxostoma duquesnei, Golden Redhorse M. erythrurum, Northern Hogsucker Hypentelium nigricans, White Sucker Catostomus commersonii, and Spotted Sucker Minytrema melanops populations in Lake Eucha, Oklahoma. We used an information theoretic approach to determine the abiotic variables related to sucker catch per effort (C/f). Our analysis indicated that sucker C/f was highest during the night and decreased with increasing water temperature. Sucker size structure was significantly different between daytime and nighttime samples; however, effect size estimates for size structure comparisons indicated that size distributions exhibited moderate overlap. Distributional comparisons indicated that daytime and nighttime samples were similar for fish greater than 180 mm in total length. Effect size estimates also indicated little association between the proportion of each species captured and time of day or water temperature. Night electrofishing in reservoirs at water temperatures from 16 to 25°C yielded the most precise C/f estimates, with the highest numbers of suckers collected at water temperatures from 6 to 15°C. Further study of the relationship between abiotic variables and catostomid catchability using various gears will be beneficial to agencies interested in these populations. [ABSTRACT FROM AUTHOR]

During the last decades, a decrease in the nutrients and an increase in marine temperature on the surface of the Varna Bay of the Black Sea have been registered. The main aim of this study was to establish the influence of some environmental factors (SST, TP, DIN) on the structure of the phytoplankton and to define what part of these dynamics results from the changes in temperature. Bivariate correlation and Nonlinear regression analyses were used to establish the connection between factors of the environment and the quality parameters of different size and taxonomic groups of phytoplankton. The rising SST proved to statistically significantly influence the decrease in the abundance of nano-phytoplankton (50.9%), the abundance and biomass of micro-phytoplankton (53%; 33.2%), the Bacillariophyceae (49.5%; 35.6%), and the biomass of the species of group "Other" (51.4%). The decreasing TP has a significant influence on the decrease in the abundance and biomass of the diatoms and the biomass of group "Other". The decreasing DIN significantly affects the decrease in the abundance and biomass of Dinophyceae. The analyses showed that rising temperatures had a leading role in the changes in the taxonomic and size structure of phytoplankton during the period 1992–2019. [ABSTRACT FROM AUTHOR]

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Body size–dependent physiological effects of temperature influence individual growth, reproduction, and survival, which govern animal population responses to global warming. Considerable knowledge has been established on how such effects can affect population growth and size structure, but less is known of their potential role in temperature‐driven adaptation in life‐history traits. In this study, we ask how warming affects the optimal allocation of energy between growth and reproduction and disentangle the underlying fitness trade‐offs. To this end, we develop a novel dynamic energy budget integral projection model (DEB–IPM), linking individuals' size‐ and temperature‐dependent consumption and maintenance via somatic growth, reproduction, and size‐dependent energy allocation to emergent population responses. At the population level, we calculate the long‐term population growth rate (fitness) and stable size structure emerging from demographic processes. Applying the model to an example of pike (Esox lucius), we find that optimal energy allocation to growth decreases with warming. Furthermore, we demonstrate how growth, fecundity, and survival contribute to this change in optimal allocation. Higher energy allocation to somatic growth at low temperatures increases fitness through survival of small individuals and through the reproduction of larger individuals. In contrast, at high temperatures, increased allocation to reproduction is favored because warming induces faster somatic growth of small individuals and increased fecundity but reduced growth and higher mortality of larger individuals. Reduced optimum allocation to growth leads to further reductions in body size and an increasingly truncated population size structure with warming. Our study demonstrates how, by incorporating general physiological mechanisms driving the temperature dependence of life‐history traits, the DEB–IPM framework is useful for investigating the adaptation of size‐structured organisms to warming. [ABSTRACT FROM AUTHOR]

Most small-scale inland fisheries in the Global South prohibit fishing gear with smaller meshes than is legally permitted. Nonetheless, in most instances, this is not strictly enforced. But starting in 2017, Uganda and Tanzania ramped up enforcement on Lake Victoria. We used time series hydro-acoustic data to determine whether the strict enforcement achieved the management goal of increased biomass (t) of commercial species and an increase in the biomass of big Nile perch (> 50 cm). The biomass for 2018–2021 (under strict enforcement) was expected to be greater than in 2007–2017 (prior to strict enforcement). The biomass of key species fluctuated annually, but no spatial or temporal differences in biomass associated with strict enforcement were evident. Similarly, the biomass of big Nile perch did not increase. Our findings suggest that mesh sizes may have limited influence on fish biomass dynamics in Lake Victoria, and that high primary productivity of the lake, high turnover rates of fish species, and limited compliance by fishers likely counteract the effects of high fishing effort on biomass and size structure of fish. Therefore, the high cost of strict top-down enforcement and the societal cost of lost lives, jobs, and livelihoods may not be justified. [ABSTRACT FROM AUTHOR]

Measurements of body length play an important role in the assessment of size and population structure of whales, allowing estimation of population parameters such as age at sexual and physical maturity. Uniquely, sperm whales can be measured from the interpulse interval (IPI) of their echolocation clicks, which contain information on the length of the head, which is allometrically related to body length. Measurements of IPI were taken from 424 acoustic recordings made between 1996 and 2019 at Kaikōura, New Zealand. Extrapolation to total length, using a new regression equation calculated from this population, revealed a significant increase in the mean length of whales visiting Kaikōura during summer in recent years (2014–2019), with no trend in the mean length for those visiting in winter. Increasing size during summer months appears to be driven by the growth of the same individuals returning summer after summer, combined with declining recruitment of new, smaller individuals. Thus, we hypothesise that the whales that visit in summer may represent an aging population. This is significant as sperm whales are a taonga [Of special significance to NZ Māori] species, top predators in the Kaikōura ecosystem, and the primary focus of the tourism industry at Kaikōura. [ABSTRACT FROM AUTHOR]

Research on Bluegills, Lepomis macrochirus R., is abundant but typically focuses on water bodies with similar environmental conditions. We assessed Bluegill density, relative abundance (catch per unit effort [CPUE] by electrofishing), growth, and size structure in 60 lakes with wide-ranging surface areas (2–12,412 ha), trophic states (oligotrophic–hypereutrophic), and macrophyte abundances (0.3–100 percent of lake volume inhabited [PVI]) across Florida, USA. Bluegill density and CPUE increased with lake productivity and decreased with macrophyte abundance. Bluegill growth increased with lake productivity and CPUE of stock-length Florida Bass, Micropterus floridanus L., a Bluegill predator. Bluegill size structure increased with lake productivity and decreased with Bluegill density. Results indicate that Bluegill fisheries with abundant individuals of quality size (≥150 mm) require productive (>25 μg/L chlorophyll-a concentration) lakes with moderate to high macrophyte coverage (PVI 50–100), abundant stock-length Florida Bass (>40 fish/h of electrofishing), and Bluegill densities <300 fish/ha. This study provides an approach to predict Bluegill population demographics based on abiotic and biotic factors, establish fisheries management expectations, and develop regional and lake-specific management tools. [ABSTRACT FROM AUTHOR]

The seasonal and spatial variability of the size structure of Calanus sp. populations was compared in two fjords of Western Spitsbergen. The size structure of the copepodite stages IV and V differed significantly in summer and late autumn. The differences between the populations from Grenfjord and Billefjord were less pronounced due to the local heterogeneity of environmental factors. Selective elimination of large individuals by the animals of a higher trophic levels, individual changes in the body size of individuals as fat reserves were accumulated/metabolized, and the presence of two generations with different size characteristics were considered the reasons of seasonal variability described above. [ABSTRACT FROM AUTHOR]

This paper reports the results of a 15-year trawl ban imposed in 1990 in the Gulf of Castellammare (GCAST: NW Sicily, central Mediterranean Sea) and its effects on the biomass and size structure of demersal finfish and shellfish and on the proportion of different commercial categories of fish. Data were collected by experimental trawl surveys conducted in the GCAST and in two trawled areas before and after 1990. The biomass of the total assemblage and of a number of selected species was significantly higher in the GCAST after the ban. Highly commercial species had the largest increase in the same gulf after the ban, particularly at the depths used by artisanal fishermen. The results from size-based indicators were not as clear-cut as those from biomass though. Although the length frequency distributions obtained in the GCAST were significantly different from the other gulfs, in several cases, the values of the size indicators were higher in the trawled gulfs. Our results suggest that, at the temporal and spatial scale adopted, trawl bans may drive full biomass recovery but only partial size structure recovery of the fish populations subject to trawl exclusion, at least in the Mediterranean. The trawl ban in the Gulf of Castellammare provides an example of an effective ecosystem-based fisheries management tool that offers the potential for fish stock rebuilding and for the economic sustainability of artisanal, small-scale fisheries. [ABSTRACT FROM AUTHOR]

We conducted an annual monthly sampling in the aquaculture areas of Lianjiang and Zhangpu, Fujian province, in the west coast of the Taiwan Strait, to gain insight into the effects of shellfish aquaculture on total phytoplankton biomass and its distribution in phytoplankton size fractions. We observed that the total chlorophyll-a (TChl-a) concentration was higher in Zhangpu (annual mean 2.690 ± 2.375 μg/L) than in Lianjiang (annual mean 1.700 ± 1.500 μg/L) and that Lianjiang had a high N/P ratio during the study, which may have been the main reason for the differences in phytoplankton biomass between the two shellfish aquaculture areas. The response of phytoplankton to shellfish aquaculture was different in the northern versus southern areas. During the aquaculture period of Lianjiang, the TChl-a concentration of surface water was approximately 14% lower than that of bottom water, and such a decreasing trend of Chl-a concentration was consistently present in micro-, nano-, and pico-size fractions. Phytoplankton depletion was not observed during investigation in Zhangpu, which showed highly variable in environmental factors. The contribution of pico-sized Chl-a to TChl-a is evaluated by shellfish aquaculture to some extent in Lianjiang. The shift from the dominance of nano-phytoplankton to the dominance of micro- phytoplankton and pico-phytoplankton was caused mainly by seasonal variation in environmental conditions. In complex marine environments, the distribution of phytoplankton biomass in phytoplankton size fractions showed no significant response to shellfish aquaculture.

As a renewable resource, biological population not only has direct economic value to people's lives, but also has important ecological and environmental value. This study examines an optimal harvesting problem for a periodic, competing hybrid system of three species that is dependent on size structure in a polluted environment. The existence and uniqueness of the nonnegative solution are proved via an operator theory and fixed point theorem. The necessary optimality conditions are derived by constructing an adjoint system and using the tangent-normal cone technique. The existence of unique optimal control pair is verified by means of the Ekeland variational principle and a feedback form of the optimal policy is presented. The finite difference scheme and the chasing method are used to approximate the nonnegative T-periodic solution of the state system corresponding to a given initial datum. The objective functional represents the total profit obtained from harvesting three species. The results obtained in this work can be extended to a wide variety of fields.

This study examines an optimal harvesting problem for a periodic n-dimensional food chain model that is dependent on size structure in a polluted environment. This is closely related to the protection of biodiversity, as well as the development and utilization of renewable resources. The model contains state variables representing the density of the ith population, the concentration of toxicants in the ith population, and the concentration of toxicants in the environment. The well-posedness of the hybrid system is proved by using the fixed point theorem. The necessary optimality conditions are derived by using the tangent-normal cone technique in nonlinear functional analysis. The existence and uniqueness of the optimal control pair are verified via the Ekeland variational principle. The finite difference scheme and the chasing method are used to approximate the nonnegative T-periodic solution of the state system corresponding to a given initial datum. Some numerical tests are given to illustrate that the numerical solution has good periodicity. The objective functional here represents the total profit obtained from harvesting n species.

Predicting whether, how, and to what degree communities recover from disturbance remain major challenges in ecology. To predict recovery of coral communities we applied field survey data of early recovery dynamics to a multi-species integral projection model that captured key demographic processes driving coral population trajectories, notably density-dependent larval recruitment. After testing model predictions against field observations, we updated the model to generate projections of future coral communities. Our results indicated that communities distributed across an island landscape followed different recovery trajectories but would reassemble to pre-disturbed levels of coral abundance, composition, and size, thus demonstrating persistence in the provision of reef habitat and other ecosystem services. Our study indicates that coral community dynamics are predictable when accounting for the interplay between species life-history, environmental conditions, and density-dependence. We provide a quantitative framework for evaluating the ecological processes underlying community trajectory and characteristics important to ecosystem functioning.

Plankton size structure is crucial for understanding marine ecosystem dynamics and the associated biogeochemical processes. A fixation step by acid Lugol's solution has been commonly employed to preserve plankton samples in the field. However, the acid Lugol's solution can bias the estimation of size structure and the preserved plankton size structure can vary with time. Here, we explore the impact of sample storage time on the size-structure of the plankton community preserved by Lugol's solution. Two short-term experiments and one long-term experiment were conducted to explore the change of plankton community size structure with the storage time: covering from a week to a month, and to nearly seven months based on particle-size data obtained by continuous Flow Cytometer and Microscope (FlowCAM) measurements. We found a linear change of plankton size with the storage time in short-term periods (less than 3 months) with a decrease of the slope but an increase of the intercept for the normalized biomass size spectrum (NBSS). However, there were opposite trends for NBSS with increasing slope but decreasing intercept after 3 months. The potential causes of the distinct patterns of the NBSS parameters are addressed in terms of the interplay between particle aggregation and fragmentation. We found large changes in plankton biovolume and abundance among different size classes, which may indicate a distinct effect of acid Lugol's solution on various plankton size classes. The mechanism driving temporal change in the size-structure of the Lugol-fixed plankton community was further discussed in terms of particle aggregation and fragmentation. Finally, we emphasize that the effect of storage time should be taken into account when interpreting or comparing data of plankton community acquired from samples with various storage durations. [ABSTRACT FROM AUTHOR]

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