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The Northeast Atlantic mackerel is an income breeder with indeterminate fecundity, spawning in multiple batches at optimal temperatures around 11°C in the upper water column during February–July along the continental shelf from 36–62°N. Based on macroscopic staging of gonads (N ∼62000) collected in 2004–2021, we detected an on-going extension of spawning activities into the Norwegian Sea feeding area (62–75°N), reaching stable levels around 2012 onwards. This poleward expansion increased as more fish entered the area, whilst the maximum proportions of spawners concurrently dropped from about 75 to 15% from May to July. Detailed histological examinations in 2018 confirmed the macroscopic results but clarified that 38% of the spawning-capable females in July terminated their spawning by atresia. We suggest that increased access to suitable spawning areas (≥10°C), following ocean warming from 2002 onwards, functions as a proximate cause behind the noticed expansion, whereas the ultimate trigger was the historic drop in body growth and condition about 10 years later. Driven by these energetic constraints, mackerel likely spawn in the direction of high prey concentrations to rebuild body resources and secure the future rather than current reproduction success. The ambient temperature that far north is considered suboptimal for egg and larval survival. [ABSTRACT FROM AUTHOR]

Climate change threatens fisheries health through changing ecosystem dynamics; however, the impacts on the physiology and ecology of commercial fish populations are unclear. Here, annually deposited growth increments of female yelloweye rockfish (Sebastes ruberrimus) opercula collected in the Gulf of Alaska were used to successfully reconstruct lifetime (∼1-year resolution) steroid hormone, stable isotope, spawning, and stress data. We assessed how hormone profiles, spawning and distress frequencies related to sea surface temperature (SST), chlorophyll a concentrations as well as climate indices. Further, we assessed whether incorporating indicators of foraging depth and diet, stable isotope values (ẟ13C and ẟ15N), would improve model interpretations. Progesterone and estradiol concentrations decreased with increasing SST, suggesting that increasing SSTs may negatively impact juvenile and subadult females' reproductive development. Spawning frequency was positively linked to changes in the North Pacific Gyre Oscillation (NPGO) index, potentially timed with favorable conditions for larval survival. This was supported by juveniles having a lower probability of a distress event during positive NPGO years compared to negative NPGO years. While relationships among environmental data and yelloweye rockfish physiology were weak, this study provides insight into the environmental impacts on the lifetime reproduction and stress of a commercially important teleost species. [ABSTRACT FROM AUTHOR]

Seismic airgun surveys to map petroleum deposits in the seabed may impact behaviour of marine animals over large distances. Understanding whether fish spawning behaviour is affected by this anthropogenic noise source is important because reproductive success may be impacted. The fine-scale behavioural responses of Atlantic cod to airgun exposure over an extended period were investigated using an acoustic telemetry positioning system on a spawning ground in Norway. During 2019 to 2021, 135 spawning cod were equipped with telemetry sensor tags and were exposed to airgun shooting during the spawning periods of 2020 and 2021, with varying received sound levels comparable to a full-scale survey at distances of 5 to >40 km. Cod demonstrated only weak responses to the disturbance from repeated 3-h treatment periods over 5-d, swimming on average slightly deeper during seismic exposure compared to silent control periods. This response varied between individuals. Longer-term effects of seismic exposure on swimming depth were not detected. No changes in swimming acceleration, displacement, or area use occurred. These results suggest that relatively distant seismic surveys do not substantially alter cod behaviour during the spawning period at received sound exposure levels varying between 115 and 145 dB re 1 µPa2s over a 5-d period. [ABSTRACT FROM AUTHOR]

Understanding the genetic differentiation among populations of most marine fish requires investigating the differences among spawning grounds. However, this can be challenging as spawning grounds for some species are not well known, or spawning fish are difficult to collect. An alternative is to collect juvenile fish in nursery habitats closely associated with potential spawning grounds. Greenland halibut is a deep-dwelling, commercially important species with at least two identified major offshore spawning grounds in the North Atlantic and weak genetic differentiation across the Atlantic. In this study, we sampled juveniles from three sites representing the Davis Strait spawning area in the northwest Atlantic and one site in the northeast Atlantic representing the primary spawning area along the western slope of the Barents Sea. We applied genotype by sequencing and discovered 90 genetic markers that could be used to assess genetic differentiation among the four sites. The northeast and northwest Atlantic showed major genetic differentiation, supporting the existence of the two primary spawning clusters. Additionally, we found genetic differentiation between the three northwest Atlantic samples implying the existence of more than one spawning area in the northwest. [ABSTRACT FROM AUTHOR]

Crocodile newts (Echinotriton and Tylototriton) are emblematic of the biodiversity of South-East Asia. In this study, we provide an account of their evolution, diversity and phylogeography based on mitochondrial (16.2 kb) and nuclear sequences (3.2 kb), combining barcoding data from nearly 1200 specimens collected over ~180 localities, representative of all lineages known to date. While phylogenies of nuclear data lacked resolution, the mitochondrial tree showed dynamic allopatric speciation that followed climate cooling during the last 10 million years, a pattern shared with many other tropical and subtropical amphibians. In crocodile newts, this implies weak dispersal and local adaptation as contributing factors of isolation, and was accompanied by macro- and micro-evolutionary changes in reproductive behaviours. Specifically, our resolved phylogeny of Tylototriton allowed the tracing of a major shift from conserved habits of terrestrial clutch-spawning towards more plastic strategies involving both aquatic and land spawning of single eggs. Using this framework, we then revised the taxonomy of crocodile newts by describing a new subgenus and two new species. Our study provides a basis to guide future phylogeographic, speciation and conservation research on these iconic amphibians. [ABSTRACT FROM AUTHOR]

Seismic airgun surveys may disturb and displace fish at large ranges. If such displacement causes fish to abandon spawning grounds, reproductive success could be impacted. To investigate whether airgun sound causes cod (Gadus morhua L.) to leave their spawning grounds, acoustic telemetry arrays were deployed on two cod spawning grounds: a test and a reference site. From 2019 to 2021, 136 mature cod from the test site and 45 from the reference site were tagged with acoustic transmitters. Intermittent seismic shooting of two 40 in.3 airguns for 1 week during the spawning periods of 2020–2021 resulted in fluctuating sound exposure levels (SEL) at the test site, comparable to a full-scale industrial survey 5–>40 km away. Residency and survival of tagged cod were analysed with capture–mark–recapture models fitted to the detection and recapture data. Departure rate of the mature cod varied between spawning seasons but was similar between the test and reference sites. Neither survival nor departure significantly differed between seismic exposure and baseline periods. The results indicated that exposure to airguns at received SEL of up to ∼145 dB re 1 µPa2 s, comparable to a seismic survey occurring several kilometres away, did not displace tagged cod from spawning grounds. [ABSTRACT FROM AUTHOR]

The consequences of fisheries-induced evolution on stock productivity and yield depend, to a large extent, on the general prospects for growth and survival. Here, we compare the selection pressures imposed by two distinct patterns of exploitation—principally targeting spawning or non-spawning aggregations—on age at maturity among 15 Canadian stocks of Atlantic herring (Clupea harengus) that have exhibited a consistent pattern of length-at-age responses to common large-scale environmental drivers since the 1960s. In accordance with expectations for maturity-dependent harvesting, the establishment of a spawner-targeted fishery in the southern Gulf of St. Lawrence coincided with a shift towards delayed maturity in both resident stocks, whereas stocks elsewhere subject to fisheries that also exploited juveniles more commonly exhibited trends towards earlier maturity. Despite these differences, we find that environmentally driven changes in length at maturation, combined with total mortality, may overwhelmingly determine lifetime reproductive success and possibly fitness. By linking phenotypic changes experienced in the juvenile period to simple correlates of egg production in mature age classes, our study highlights the importance of managing fisheries in the context of ubiquitous but contrasting environmental constraints on life histories. [ABSTRACT FROM AUTHOR]

To supplement catch and effort regulations with the purpose to rebuild the cod (Gadus morhua) stock in Kattegat, Sweden and Denmark established a large (426 km2) year-round no-take zone (NTZ) surrounded by partially protected areas (PPAs) in 2009. The purpose of these spatial regulations was to prohibit cod fishing on the spawning grounds and to displace fisheries bycatch of cod from areas where mature cod aggregate in the Kattegat. The aim of this study is to evaluate the effects of the established NTZ and PPAs on the local fish assemblage, including cod. Based on a spatially high-resolution bottom trawl survey in the Kattegat (covering 2008–2021), multivariate analyses revealed significant shifts in the fish assemblage. A closer analysis indicated that six to seven fish species, including cod increased in the NTZ relative to control areas depending on if abundance or biomass was used as dependent variable. Univariate analysis showed that two flatfish species dab (Limanda limanda) and lemon sole (Microstomus kitt), and Norway lobster (Nephrops norvegicus) significantly increased in biomass in the NTZ, and turbot (Scophthalmus maximus) in the PPA relative to the control areas. These results suggest that the NTZ protected even relatively mobile species in an open sea system, such as the Kattegat. However, neither cod abundance nor biomass showed a significant increase as an effect of the NTZ and PPA despite two relatively strong year classes in 2012 and 2013, which possibly would have helped the recovery of the cod stock. As assessed by the International Council for the Exploration of the Sea in 2022, Kattegat cod continuously suffer from being severely overfished with low recruitment, and high discard rates in the mixed N. norvegicus fishery, is considered the major driver behind the reinforced depletion of the stock. [ABSTRACT FROM AUTHOR]

Atlantic bluefin tuna (ABT) (Thunnus thynnus) travel long distances to spawn in oligotrophic regions of the Gulf of Mexico (GoM) which suggests these regions offer some unique benefit to offspring survival. To better understand how larval survival varies within the GoM a spatially explicit, Lagrangian, individual-based model was developed that simulates dispersal and mortality of ABT early life stages within realistic predator and prey fields during the spawning periods from 1993 to 2012. The model estimates that starvation is the largest cumulative source of mortality associated with an early critical period. However, elevated predation on older larvae is identified as the main factor limiting survival to late postflexion. As a result, first-feeding larvae have higher survival on the shelf where food is abundant, whereas older larvae have higher survival in the open ocean with fewer predators, making the shelf break an optimal spawning area. The modeling framework developed in this study explicitly simulates both physical and biological factors that impact larval survival and hence could be used to support ecosystem based management efforts for ABT under current and future climate conditions. [ABSTRACT FROM AUTHOR]

Density-dependent growth, which might influence the effects of fisheries on a population, is often ignored when management strategies are evaluated, mainly due to a lack of appropriate models readily available to be implemented. To improve on this, we investigated if somatic growth in Norwegian spring-spawning herring (Clupea harengus) depends on cohort density using a formulation of the von Bertalanffy growth function on cohorts from 1921 to 2014 and found a significant negative correlation between estimated asymptotic length and density. This clearly indicates density-dependent effects on growth, and we propose a model that can be used to predict the size-at-age of Norwegian spring-spawning herring as a function of herring density (the abundance of two successive cohorts) in short-term predictions of catch advice, and in Management strategy evaluations, including estimation of their reference points such as F MSY. [ABSTRACT FROM AUTHOR]

This study used Spanish Kiko goats as a small ruminant model (SRM) for teaching animal science courses via experiential laboratory-based methods at a small liberal arts college in the Southeastern United State. Perceivably, the SRMs presents an accessible and sustainable teaching tool for undergraduate education at institutions with limited resources, such as cattle facilities. The use of mature (> 3 years old) bucks (male model 1, 2 & 3), does (female model 1 & 2), and kids (kid model 1, 2, 3; 8 months old) as SRMs in 4 courses and resultant learning is reported herein. SRMs were fed, late weaned, and continuously bred to simulate the nutritional and reproductive management practiced in rotationally grazed strictly forage-fed cattle. Growth performances amongst bucks (pre and post pubertal; Figure 1), does (pre- and post-partum Figure 2), and kids (pre and post weaning Figure 3) were recorded and analyzed. Feed intake trials (Figures 4 and 5), fecal analysis, and apparent DMD were conducted. The benefits of continuous suckling and postweaning management of does and kids were realized as 100% of does and kids successfully transited each breeding period. In addition, kids approached market weights (15.53 kg) at 136 days postpartum (Figure 3) and does were rebred at first postpartum estrus (62 days). The use of prebreeding season reproductive tract examinations via ultrasound and BSE in female and male SRMs enabled effective evaluations of the poor reproductive performance of the cattle herd (59.3% pregnancy rate in 2022). The use of SRMs allowed for learning ruminant gastrointestinal and reproductive system physiology. Subsequently, comprehension of the impact of mineral and vitamin deficiencies on the annually declining reproductive performance of rotationally grazed cattle was enhanced. Conclusively, the use of SRMs supported my learning and is recommended for teaching/learning in animal sciences at institutions with limited resources. [ABSTRACT FROM AUTHOR]

Spawning timing in fish is generally cyclical in temperate regions in order to increase the probability of matching larval occurrence with ideal environmental conditions. The capelin stock in Northwest Atlantic Fisheries Organization Divisions 2J3KL collapsed in 1990–1991 and has not recovered. This collapse was concomitant with collapses in groundfish stocks and cold oceanographic conditions. Using citizen science data, newspaper archives, grey and primary literature, and monitoring data, a century of capelin beach spawning times were compiled. Capelin beach spawning has been persistently 3 weeks later since the stock collapse. To identify potential predictors of capelin spawning timing, an exploratory analysis was conducted using environmental and biological variables and a period factor that categorized a year as either pre-collapse (1990 and earlier) or post-collapse (post-1990) in a step-wise multiple regression model. Spawning timing was predicted to be delayed in the post-collapse period when there were negative anomalies in the Newfoundland and Labrador Climate Index and summer (June–August) North Atlantic Oscillation, and when there was a decrease in mean length of the spawning population. The production of weak year-classes is predicted when spawning is delayed, suggesting that late spawning is severely inhibiting the recovery of the stock. [ABSTRACT FROM AUTHOR]

Life history events, from mating and voltinism to migration and emergence, are governed by external and historically predictable environmental factors. The ways humans have altered natural environments during the Anthropocene have created myriad and compounding changes to these historically predictable environmental cues. Over the past few decades, there has been an increased interest in the control temperature exerts on life history events as concern over climate change has increased. However, temperature is not the only life history cue that humans have altered. In stream ecosystems, flow and light serve as important life history cues in addition to temperature. The timing and magnitude of peak flows can trigger migrations, decreases in stream temperature may cause a stream insect to enter diapause, and photoperiod appears to prompt spawning in some species of fish. Two or more of these cues may interact with one another in complex and sometimes unpredictable ways. Large dams and increasing impervious cover in urban ecosystems have modified flows and altered the timing of spawning and migration in fish. Precipitation draining hot impervious surfaces increases stream temperature and adds variability to the general pattern of stream warming from climate change. The addition of artificial light in urban and suburban areas is bright enough to eliminate or dampen the photoperiod signal and has resulted in caddisfly emergence becoming acyclical. The resulting changes in the timing of life history events also have the potential to influence the evolutionary trajectory of an organism and its interactions with other species. This paper offers a review and conceptual framework for future research into how flow, temperature, and light interact to drive life history events of stream organisms and how humans have changed these cues. We then present some of the potential evolutionary and ecological consequences of altered life history events, and conclude by highlighting what we perceive to be the most pressing research needs. [ABSTRACT FROM AUTHOR]

We developed a new type of generalized depletion model adapted to the rapid life cycle of Octopus vulgaris and the data collection framework put in place in its co-managed small-scale fishery (SSF) in Asturias, northwest Spain. The model uses weekly data from 19 seasons to estimate annual recruitment and female spawners emigration out of the vulnerable stock to attend to their broods. The matched annual spawners-recruitment (SR) magnitudes are then used as observations in a non-Bayesian hierarchical inference framework. The Shepherd SR model was selected among three alternatives. The stock has a high degree of density-dependence, leading to overcompensation. The estimated SR model has an unstable equilibrium point, driving the stock to deterministic cyclic fluctuations under small disturbances. Under those conditions the maximum sustainable yield (MSY) is not applicable, lending further credence to Sidney Holt's opposition to the MSY as a basis for the elaboration of fishery management objectives, with potentially wide relevance to the management of SSF and cephalopod fisheries. We argue that harvest rates based on mean latent productivity, a concept that includes the MSY as a special case, are more adequate and sustainable for fluctuating stocks. [ABSTRACT FROM AUTHOR]

Many salmonid populations are of conservation concern, and the release of hatchery-produced juveniles is a frequently used measure to alleviate declines and increase harvest opportunities. While such releases may be of conservation value for some populations, stocking may also decrease the effective population size and subsequently impose additional strain on already threatened populations. In this study, we assessed how the cohort-wise effective number of breeders in five populations of Atlantic salmon (Salmo salar) were affected by supplementation. Altogether, 19 cohorts were studied (2–7 cohorts per population) by estimating the proportion hatchery-released individuals and the effective number of wild and captive breeders in each cohort of the respective populations. We show that the effect of releasing captive-bred individuals varies both between populations and between years within the same population. A Ryman–Laikre effect—where the effective number of breeders has decreased as a consequence of supplementation—was observed for 11 cohorts. We discuss how supplementation can be adapted to optimize the effective population size, demonstrate that evaluation of supplementation can be reliably achieved, and show that supplementation programmes that lead to high proportions of hatchery-origin fish on spawning grounds are more likely to induce a Ryman–Laikre effect. [ABSTRACT FROM AUTHOR]

The spatial distribution of fish early life stages can impact recruitment at later stages and affect population size and resilience. Northeast Arctic (NEA) cod spawning occurs along the Norwegian coast. Eggs, larvae, and pelagic juveniles drift near-surface towards the Barents Sea nursery area. In this study, a 35-year long time series of NEA cod larvae data was analysed in combination with factors that potentially may affect the distribution of eggs and larvae. These factors included biological aspects of the spawning stock, and environmental variables, such as water temperature, wind, ocean current, and prey abundance. Our aim was to shed light on how these factors influence larval abundance and distribution and how larval abundance and distribution influenced recruitment at age 3. We found that biomass and mean weight of the spawners were positively associated with larval abundance and that a high liver condition index of the spawners was associated with a north-easterly distribution of the larvae. The environmental variables showed generally weak or no correlations with abundance or distribution of larvae. Lastly, we found significant association between larval abundance and year-class abundance at age 3, while the spatial distribution metrics of the larvae, i.e. distribution extent, mean longitude, and mean latitude, showed no significant association with future year-class abundance. [ABSTRACT FROM AUTHOR]

Atlantic herring (Clupea harengus) has complex population structure and dynamics including diverse life histories and spawning times with spring and autumn spawning as the most common modes. Originally, spawning herring were phenotypically identified based on their maturity development or otolith microstructure by determining seasonal specific larval growth patterns. Recently, genetic markers have revealed clear genetic differentiation between spring- and autumn-spawning populations. All three methods were applied to herring caught at the same locations during spring and autumn to determine the coherence of methods. In a selected subset, most herring (∼77%) had an otolith microstructure and genetic assignment coinciding with the phenotypically assigned spawning season. Non-spawning herring (<5%) that were classified as belonging to the current spawning season using genotyping and otolith-typing were assigned as skipped spawners. For ∼8% of spawning herring, the genetic and otolith assignment contradicted the phenotypically assigned spawning season, characteristic of straying individuals. Otolith-typing contradicted the genetic and phenotypical assignment in ∼7% of the cases, potentially representing individuals reuniting back to the spawning season favoured by their genotype. Although the viability of offspring from these individuals remains undocumented, it is suggested that the observed switching of spawning season may contribute to gene flow between herring populations. [ABSTRACT FROM AUTHOR]

Fish spawning aggregations (FSAs) are vulnerable to overexploitation, yet quantitative assessments of FSA populations are rare. We document an approach for how to conduct such an assessment, evaluating the response of Critically Endangered Nassau Grouper (Epinephelus striatus) to protections in the Cayman Islands. We assessed pre-protection status on all islands using length data from fishery catch. We then used 17 years of noninvasive length-frequency data, collected via diver-operated laser calipers, to estimate recruitment and spawning biomass of Nassau Grouper on Little Cayman following protection. Bimodal length distributions in 2017–2019 indicated a large recruitment pulse (4–8× average) derived from spawning in 2011. Biomass recovered to 90–106% of the pre-exploitation level after 16 years, largely driven by the strong 2011 year class. Length distributions were also bimodal in 2017–2019 on nearby Cayman Brac, implying a synchronous recruitment pulse occurred on both islands. Our results demonstrate that: (i) in situ length data can be used to monitor protected FSAs; (ii) spatiotemporal FSA closures can be effective, but success takes time if population recovery depends upon sporadic recruitment; and (iii) FSA fishery management targets may need to be higher than commonly recommended (i.e. spawning potential ratio >0.6 instead of 0.4). [ABSTRACT FROM AUTHOR]

Spawn and specimens of Toledonia biplicata comb. nov. were collected from Burdwood Bank during March 2013. Species-level identification was derived from radular, shell and spawn characters. A low number of eggs laid per spawn (one to three), absence of an external gelatinous mass and a considerably thickened capsule wall (~50 µm) constitute a unique combination of spawn characters among heterobranchs. Egg capsules are ovoid in shape and measure 600–763 × 450–656 µm. They are filled with albuminous liquid, allowing complete intracapsular development of a single embryo. The developmental stages recognized are uncleaved eggs (153 µm in average diameter), veliger stages (279–378 µm in maximal length) and prehatchling juveniles (442–609 µm). Toledonia biplicata increases its volume 40-fold during its intracapsular development, whereas other comparable cephalaspids increase ≤ 4-fold. The role of the capsule wall as protection and an additional source of food is discussed. The adaptive value of these characters in relationship to the environmental conditions of the Magellanic region is discussed. A comparison with the spawn of other cephalaspids, nudibranchs and pleurobranchids is conducted, and the taxonomic implications are discussed. This is the first description of the spawn and developmental stages of a representative of the genus Toledonia. [ABSTRACT FROM AUTHOR]

In species with limited opportunities for pre‐ejaculatory sexual selection (behavioural components), post‐ejaculatory mechanisms may provide opportunities for mate choice after gametes have been released. Recent evidence from a range of taxa has revealed that cryptic female choice (i.e., female‐mediated differential fertilization bias), through chemical cues released with or from eggs, can differentially regulate the swimming characteristics of sperm from various males and ultimately determine male fertilization success under sperm competition. We assessed the potential role that such female‐modulated chemical cues play in influencing sperm swimming characteristics in beach‐spawning capelin (Mallotus villosus), an externally fertilizing fish that mates as couples (one male and one female) or threesomes (two males and one female) with presumably limited opportunities for pre‐ejaculatory sexual selection. We assayed sperm swimming characteristics under varying doses and donor origins of egg cues and also examined the possibility of assortative mating based on body size. We found mating groups were not associated by size, larger males did not produce better quality ejaculates, and egg cues (regardless of dosage or donor identity) did not influence sperm swimming characteristics. Our findings suggest that intersexual pre‐ejaculatory sexual selection and cryptic female choice mediated by female chemical cues are poorly developed in capelin, possibly due to unique natural selection constraints on reproduction. [ABSTRACT FROM AUTHOR]

Biomass of the yellowtail Seriola quinqueradiata , an important fishery resource in Japan, has increased about threefold over the past 20 years to ∼300 thousand metric tons. We examined the interannual variations in distribution and abundance of S. quinqueradiata larvae [4.2–7.9 mm body length (BL), ∼7 to 18 days after hatching], based on sampling surveys over a broad area of the shelf-break region of the East China Sea (ECS) in April, the main spawning period, over 15 years (2001–2015). High abundances of larvae were found in the northern ECS off the southwestern coast of Kyushu Island throughout the survey period. After 2010, the larvae began to occur abundantly also in the southern ECS south of 29°30′N, indicating a southward expansion of the spawning ground. There has been a significant positive trend of larval abundance over the whole ECS during the 15 years, which was mainly due to the sharp increase in larval abundance in the southern ECS after 2010. Although interannual variation in larval abundance was not related to environmental conditions (temperature, salinity, and chlorophyll a concentration), it was closely correlated with the spawning stock biomass. This indicates that the increasing trend of larvae was related to the increase in egg production in the ECS. Also, the larval abundance showed a weak positive correlation with recruitment, suggesting that the increased larval abundance has, in part, contributed to high recruitment. [ABSTRACT FROM AUTHOR]

While monitoring fish sounds has enhanced our understanding of spatio-temporal patterns of spawning and acoustic communication, data interpretation often fails to account for environmental effects on acoustic recordings, resulting in uncertainty of whether measures of detected fish sounds correspond to rates of sound production, specific behaviours, and abundance. In this study, we applied acoustic propagation modelling and detection theory to estimate rates of sound production of territorial, male Gulf grouper (Mycteroperca jordani) from passive acoustic recordings and evaluate effective communication distances. To assess behavioural drivers, environmentally calibrated, hourly estimates of sound production rates were compared to diver observations of courtship, spawning, and numbers of females encountered within male territories. Rates of sound production increased before sunset and were correlated to observed rates of spawning and females encountered, indicating that sound production is largely driven by female presence and increased opportunities to spawn. The mean effective communication distance was estimated to be <21 m, supporting the importance of short-range communication within the observed behaviours. Our findings corroborate that fish sounds can be used to infer measures of reproductive activity and the relative abundance of both sexes during spawning periods once properly calibrated for environmental effects and detection capabilities. [ABSTRACT FROM AUTHOR]

Although the management of fish spawning aggregations (FSAs) often requires a precautionary approach that initially emphasizes conservation, understanding the dynamics of spawning and interactions with fishing activities can help identify long-term management solutions that balance conservation with utilization. We designed a parsimonious, per-recruit model to evaluate the potential effects of seven time-closure scenarios implemented during the spawning season on egg-production-per-recruit (EPR; a conservation metric) and yield-per-recruit (YPR; a fisheries metric) of Gulf corvina (Cynoscion othonopterus), a vulnerable marine fish that experiences persistent overfishing at its only known spawning grounds in the Gulf of California, Mexico. Five of seven scenarios provided measurable increases in EPR (11–48%) and were accompanied by proportional increases in YPR (29–36%) that resulted in a sustainable fishery. Increased mortality of juveniles and small adults through targeted fishing or as bycatch in other fisheries, however, would erode both the fisheries and conservation benefits of these time closures. Our results demonstrate that information on spawning and fishing activities can be combined with stakeholder input to identify regulations that permit the sustainable harvesting of FSAs. Furthermore, the implementation of brief, temporal fishing effort restrictions can represent a viable, less restrictive alternative to marine protected areas for the management of FSAs. [ABSTRACT FROM AUTHOR]

Stock assessments historically have used age- and size-independent methods to estimate reproductive output in marine fishes. Recent assessments have used total egg production (TEP), often assuming an invariant spawning frequency (SF) for all females. However, spawning parameters vary with age and size, which invalidates this assumption. This study investigated the age- and size-dependence of female spawning fraction, duration, and frequency in two economically valuable species, gag (Mycteroperca microlepis) and scamp (Mycteroperca phenax), in Atlantic waters off the southeastern United States, with the ultimate objective of quantifying the effect of these dependencies on TEP estimates. Spawning parameters had moderate-to-strong dome-shaped relationships with age and size (r 2 = 0.63–0.94), peaking at intermediate ages and sizes. As larger, older females approach sexual transition, they may increase their lifetime reproductive success by shifting energy resources away from female reproductive investment (i.e. eggs) towards investment that will promote future male reproductive success (i.e. gonad transformation). The estimate of TEP based on age-dependent SF was 38% lower for gag and 41% lower for scamp than the estimate based on age-independent (AI) SF; therefore, the AI method overestimates stock productivity. Incorporating age- and size-based reproductive data into assessments can lead to more reliable stock productivity estimates and potentially improved management. [ABSTRACT FROM AUTHOR]

Effective fishery management measures to protect fish spawning aggregations require reliable information on the spatio-temporal distribution of spawning. Spawning closures have been part of a suite of fishery management actions to rebuild the Gulf of Maine stock of Atlantic cod (Gadus morhua), but difficulties remain with managing rebuilding. The objective of this study was to identify the spatial and temporal distribution of cod spawning during winter in Massachusetts Bay to improve our understanding of cod spawning dynamics and inform fisheries management. Spawning was investigated in collaboration with commercial fishermen during three winter spawning seasons (October 2013–March 2016) using acoustic telemetry and passive acoustic monitoring equipment deployed in fixed-station arrays and mounted on mobile autonomous gliders. Tagged cod exhibited spawning site fidelity and spawning primarily occurred from early November through January with a mid-December peak and some inter-annual variability. The spatial distribution of spawning was generally consistent among years with multiple hotspots in areas >50 m depth. Current closures encompass most of spawning, but important areas are recommended for potential modifications. Utilizing multiple complementary technologies and deployment strategies in collaboration with commercial fishermen enabled a comprehensive description of spawning and provides a valuable model for future studies. [ABSTRACT FROM AUTHOR]

Wild abalone (Family Haliotidae) populations have been severely affected by commercial fishing, poaching, anthropogenic pollution, environment and climate changes. These issues have stimulated an increase in aquaculture production; however production growth has been slow due to a lack of genetic knowledge and resources. We have sequenced a draft genome for the commercially important temperate Australian 'greenlip' abalone (Haliotis laevigata, Donovan 1808) and generated 11 tissue transcriptomes from a female adult abalone. Phylogenetic analysis of the greenlip abalone with reference to the Pacific abalone (Haliotis discus hannai) indicates that these abalone species diverged approximately 71 million years ago. This study presents an in-depth analysis into the features of reproductive dysfunction, where we provide the putative biochemical messenger components (neuropeptides) that may regulate reproduction including gonad maturation and spawning. Indeed, we isolate the egg-laying hormone neuropeptide and under trial conditions induce spawning at 80% efficiency. Altogether, we provide a solid platform for further studies aimed at stimulating advances in abalone aquaculture production. The H. laevigata genome and resources are made available to the public on the abalone 'omics website, http://abalonedb.org. [ABSTRACT FROM AUTHOR]

Diel patterns of different activities arise from adaptations to periodic cycling of environmental parameters and may involve trade-offs between acquiring benefits and minimizing associated costs. In this study, we provide fundamental baseline data on diel activity of natural populations of Nothobranchius fishes, model organisms in laboratory studies, including links between diurnal rhythms and ageing. Initially, we quantified the diel change in activity in wild populations of three African killifish species (Nothobranchius furzeri , Nothobranchius orthonotus and Nothobranchius pienaari) and compared average activity between sexes. In all species, males were more active than females, probably as a result of their active pursuit of females. Swimming activity peaked at midday. In N. furzeri , the only species occurring at all sites, oocytes were ovulated in the early morning, and most spawning events had occurred by the early afternoon. Gut fullness and diet richness increased before spawning activity and peaked in the morning. Daytime diet was dominated by chironomid larvae, whereas notonectid bugs were the dominant prey at night, perhaps as a result of different prey detectability over the diel cycle. Finally, no loyalty to any particular pool section was detected in N. furzeri. Collectively, these data provide the first empirical description of diel activity in three wild populations of African killifish. [ABSTRACT FROM AUTHOR]

Sunfishes or Molidae are a rarely encountered family within the teleost order Tetraodontiformes and most details of their reproductive biology including times and places of spawning and their larval ecology are rather unclear. Spawning of two species of Molidae was suggested in the Sargasso Sea before, yet comprehensive data on larval distribution from this area or elsewhere have never been published. Here we report on the abundance and size distribution of 383 sharptail mola (Masturus lanceolatus) and slender sunfish (Ranzania laevis) larvae, present novel information on their larval growth and development and test correlations with prevailing hydrographic data. Only 18 mostly larger Masturus larvae were caught evenly distributed over the study area and with no obvious hydrographic preferences. We conclude that there was no active spawning of M. lanceolatus in the area during the time of the cruise. In contrast, Ranzania larvae were caught primarily inside and south of a thermal frontal zone with increasing abundances toward warmer surface layers in the southeast of the study area. Due to the consistent presence of young Ranzania , it can be assumed that spawning activity was ongoing throughout the month of April, 2015. Our findings confirm the Sargasso Sea as a spawning area for R. laevis. [ABSTRACT FROM AUTHOR]

In this manuscript, we test how an understanding of geographical variation in larval fitness in relation to temperature and habitat use could be a useful method to improve our understanding of recruitment and develop better indices of annual recruitment. On the basis of the assumption that growth and survival of tuna larvae are influenced by temperature, we have developed a potential larval survival index for Atlantic bluefin tuna (Thunnus thynnus) by combining empirical data from egg and larval rearing experiments with temperature data from hydrodynamic models. The experiments were designed to test the full range of temperature variability that bluefin larvae would experience in the field and provide a mechanistic understanding of the processes driving egg and larval survival. We then developed a biological model using the temperature-related growth expressions and a size-dependent survival function for the larvae. The biological model was applied to a time-series of spatially explicit temperature data for the western Mediterranean from the Strait of Gibraltar to 6°E, which includes the major recognized bluefin tuna eastern stock spawning area, the Balearic Sea. Our results show that areas with high probabilities of larval survival coincide with those that would be considered as optimal based on other data sources (ichthyoplankton surveys, spawning female locations from commercial fisheries data, and adult tracking data). However, evidence of spawning has been found in areas with suboptimal thermal habitats, as predicted by the model, which we discuss regarding sampling effort and salinity fronts. There was a good match between the survival index and recruitment indices from standardized CPUE fisheries data. These results have implications for our understanding of the recruitment process of the eastern stock of Atlantic bluefin tuna, since they suggest that the combined effects of temporal and spatial variability of the environment drive recruitment success, which has important implications for the management of the species. [ABSTRACT FROM AUTHOR]

Many marine fish form spawning aggregations (FSAs) and exhibit meta-population stock structure, affecting reproductive resilience and the optimal spatial scale of management. Red drum use a known FSA site off Tampa Bay (TB FSA site) and another presumed FSA site off Charlotte Harbor (CH FSA site). We studied these sites for 3 years (2012–2014) to assess space use and annual abundance at the TB FSA site using: (i) genetically profiled fish, non-lethally sampled by purse seine (n  = 9087); (ii) aerial surveys (n  = 37); and (iii) acoustic telemetry (n  = 122 fish). Thousands of fish concentrated at the TB FSA site to spawn each year, dispersing afterward to an area of at least ∼150 km along the coast and 90 km offshore. Fish acoustically tagged at the TB FSA site showed strong annual spawning site fidelity (91% in 2013 and 85% in 2014) and the straying rate to the CH FSA site to the south was low (6–13%). Annual abundance at the TB FSA site varied, with the estimated abundance in 2013 being four times greater than that estimated for 2014. Similarly, aerial surveys in 2013 sighted 2.5 times as many aggregations as in 2014. However, fine-scale space use, which typically goes unassessed in abundance estimates (short-term surface behaviour and temporary migration), also differed between these years and needs to be integrated into future capture-mark–recapture models. [ABSTRACT FROM AUTHOR]

Snapper (Chrysophrys auratus) in South Australia spawn over a wide range of daily times and hatch in ∼1.5 d. Traditional estimates of daily egg production (i) divide sampled eggs into daily age cohorts, e.g. days 1 and 2, (ii) compute cohort ages by assuming that all spawning occurs at a fixed daily peak hour, and (iii) link the estimation of spawning egg density with egg mortality rate by regressing cohort egg densities against cohort age. We propose a method for estimating daily egg production, the number of eggs spawned per unit area per day (P 0), without these assumptions. We use a range of estimates of snapper egg mortality rate obtained from prior studies to backcorrect for egg mortality to the age 0 spawning egg density for each stage of eggs individually rather than aggregating into daily cohorts. P 0 is estimated as a mean of sample tow densities rather than as a regression intercept. This stage-based P 0 estimator avoids errors associated with assuming a fixed daily spawning hour and classifying eggs into day 1 or 2. It requires no regressions of sampled daily cohort egg densities against age, which often provide imprecise estimates of mortality rates. Simulation testing showed 1–2% accuracy for this estimator of P 0. The uncertainty of assuming egg mortality rates is moderated by the insensitivity of estimates of P 0 to the input value of egg mortality rate. [ABSTRACT FROM AUTHOR]

The present study contributes to a better understanding of the daily spawning dynamics of southern NEA mackerel (Scomber scombrus) with implications for the estimation of batch fecundity. It shows that there is a time window during the day, mainly in the afternoon, during which the advanced oocyte mode in imminent spawners separates from the remaining, smaller oocytes. This synchronicity in the separation of the spawning batch amongst imminent spawners corroborates evidence for the existence of daily spawning synchronicity in the population. This is particularly important for applications of the daily egg production method, DEPM, because such pattern facilitates both the ageing of eggs for the estimation of the daily egg production at sea and the ageing of postovulatory follicles for the estimation of spawning frequency. For NEA mackerel, batch fecundity could only be measured when a clear hiatus was established between the spawning batch and the smaller oocytes. Hydrated females that do not show such hiatus would not be valid for batch fecundity measurements suggesting that the "hydrated oocytes method" is not fully applicable for this stock. Knowing the time of day at which the batch is separated, will facilitate the sampling of valid females for the estimation of batch fecundity. [ABSTRACT FROM AUTHOR]

The protracted spawning period of broadcast-spawning marine fishes has potential to generate considerable variability in metrics of individual reproductive output. We undertook a temporally detailed genetic study of larvae produced by Atlantic cod (Gadus morhua) from two spatially proximate populations spawning under controlled semi-natural conditions over 94 days. Based on daily samples of larvae (n = 4489 in total), we document fine-scaled temporal changes in, and correlates of, offspring phenotype and reproductive output (egg batches produced or fertilized). Larval length and standardized yolk-sac volume declined 11 and 49% over the spawning period, respectively. The adaptive significance of these trends is unclear. Longer, heavier females produced longer, better-provisioned larvae. Body size affected the number of egg batches to which an individual contributed genetically but not spawning duration. Males contributed gametes to a greater number of egg batches (19.5 vs. 9.2), and spawned over a longer period of time (48.9 vs. 30.8 days), than females. After accounting for body size and condition, egg batch number and spawning duration differed between adjacent populations separated by < 10 km. Our work highlights the need to understand the environmental and adaptive causes of temporal variability in offspring quality and its consequences to individual fitness and per capita population growth in batch-spawning fishes. [ABSTRACT FROM AUTHOR]

European sea bass (Dicentrarchus labrax) is an important target species for recreational and commercial fisheries. In recent years, the spawning stock biomass has declined markedly in some areas, and strict management measures have been introduced. However, the development of appropriate stock assessment and fisheries management has been hampered by a lack of information on post-release mortality. This study investigated post-release mortality of sea bass captured with common recreational fishing gear under experimental conditions in an aquaculture facility over 10 d. Three experiments investigated: (i) the effects of different bait types; (ii) the impact of prolonged air exposure; and (iii) the impact of deep hooking on post-release mortality. By combining the experimental results with country-specific information on sea bass angling practices, estimates of post-release mortality are provided for the northern sea bass stock. No mortality was observed for sea bass captured on artificial baits. The use of natural baits resulted in a mortality of 13.9% (95% CI  = 4.7–29.5%), which was associated with deep hooking, hooking injuries, and prolonged air exposure. The use of artificial baits and short air exposure (≤30 s) increased survival probability, whereas deep hooking resulted in 76.5% (95% CI  = 50.0–93.2%) mortality. Depending on country-specific angling practices, post-release mortality estimates ranged from 2.8% to 9.1% (mean = 5.0%, 95% CI  = 1.7–14.4%) for northern sea bass. Despite these relatively low mortality estimates, post-release mortality should be considered in stock assessments as its cumulative impact may be high. Moreover, post-release mortality can be reduced by implementing species-specific best practice guidelines. [ABSTRACT FROM AUTHOR]

We evaluated the effects of multiple bottom-up processes on the relative condition (an index of length-specific weight) of adult Gulf menhaden Brevoortia patronus sampled from the US commercial fishery, from 1964 to 2011, in the northern Gulf of Mexico (NGOM). A series of Generalized Additive Models (GAMs) were constructed to examine the influence of Mississippi River Discharge (MRD), El Niño Southern Oscillation (ENSO), wind vector components, sea surface temperature (SST), and chlorophyll a concentration. Relative condition was positively correlated with MRD and highest during weak La Nina-like and moderate El Nino-like conditions. The effect of wind vector components was variable across the NGOM. This observation is likely due to geographic differences in wind-related transport of nutrient rich river plume waters. Relative condition was highest at 24°C and declined rapidly when SST was below 23°C or above 29°C. Relative condition exhibited seasonal variability with increasing condition from August until November, likely caused by seasonal provisioning by individuals for winter spawning. We show that multiple bottom-up processes contribute to contrasts in the condition of Gulf menhaden in the NGOM and these results can be used to predict the response of Gulf menhaden to environmental variability. [ABSTRACT FROM AUTHOR]

Juvenile jack mackerel were found in 2009 in the Challenger break and the East Pacific ridge (CHAEPR). This seamount region is ~3500 km from the coastal historic jack mackerel nursery grounds off Chile (north of 30°S). We reviewed historic evidence of juveniles around this seamount and data on several local environmental conditions: sea surface temperature, chlorophyll-a, wind, turbulence levels, and Eddy kinetic energy (EKE). A Lagrangian model for the early life stages of jack mackerel in the eastern South Pacific was used to assess the potential of the seamount region as a permanent nursery ground. Transport/retention mechanisms were assessed by releasing virtual particles coupled to a growth model into the flow simulated by an eddy-resolving ocean model. Model simulations showed high inter-annual variability for particle retention in the seamount region; high retention levels were associated with low EKE such that the particles were retained for several months. Satellite altimetry has shown a local minimum in eddy activity in the region where the juveniles were observed; this minimum was consistent with the above temporal relationship. The inclusion of the CHAEPR oceanic seamount region as a potential nursery ground for jack mackerel expands the current conceptual framework for the spatial population structure of this species in the South Pacific off central Chile proposed by Arcos et al. (The jack mackerel fishery and El Ni~no 1997-98 effects off Chile. Progress in Oceanography 49: 597-617, 2001). Finally, we discuss the relevance of seamounts playing a double role (spawning and nursery grounds) from the standpoint of conservation and biodiversity. [ABSTRACT FROM AUTHOR]

The spawning dynamics of Atlantic cod (Gadus morhua) on Georges Bank and Nantucket Shoals are not well understood. To address this uncertainty, we combined Fishermen's Ecological Knowledge (FEK) with traditional scientific data to develop a more holistic understanding of cod spawning on Georges Bank. Data from historical reports, trawl surveys, fisheries observers, and ichthyoplankton surveys were used to describe the spatial and temporal distribution of cod spawning activity. We also collected FEK regarding cod spawning dynamics through semi-structured interviews (n = 40). The fishermen had detailed knowledge of the spatial and temporal distribution of cod spawning, and identified persistent fine-scale (i.e. <50 km²) spawning grounds that were often associated with specific habitat features, including spawning grounds that were previously unreported in the scientific literature. The spawning seasons and locations identified by fishermen generally agreed with information from traditional scientific data, but it was evident that seasonal scientific surveys lack the spatial and temporal resolution needed to fully characterize the distribution of cod spawning activity. Our results will help inform management measures designed to promote the rebuilding of Georges Bank cod, and also provide a basis for further investigations of cod spawning dynamics and stock structure. [ABSTRACT FROM AUTHOR]

Atlantic Menhaden Brevoortia tyrannus exhibit particularly complex recruitment dynamics as a coastal-spawning species with seasonal migrations along the North American Coast from Nova Scotia, Canada, to Florida, United States. Despite a coast-wide reduction in juvenile production from the 1970s to the 1990s, Atlantic Menhaden continues to support one of the oldest and largest commercial fisheries on the US east coast. We used a stochastic partial differential equation model to estimate spawning location and larval dispersal on the Atlantic Coast over two time periods, with data from the Northeast Fisheries Science Center ichthyoplankton surveys conducted in 1977-1987 and 2000-2013. Within the study area, Atlantic Menhaden spawning appears to occur primarily near shore over a large spatial range, from southern New England to North Carolina over the majority of the year, but at greatest levels during November and December. Larger, older larvae were found over a similar spatial and temporal range, dispersing farther from shore. Between the two periods, we observed an increase in secondary, spring-time spawning events. We observed no major, directional spatial shift in spawning or dispersal. However, estimated spawning activity increased near Delaware Bay. Both small and large larvae were most abundant in the Southern portion of the study area during both periods. Yet, total spatial coverage of all larvae varied greatly among years until the mid-2000s, when the Atlantic Menhaden population was believed to have recovered reduction in juvenile production from the 1970s to the 1990s. In most recent years, we observed consistent and large areas of spawning and larval dispersal. [ABSTRACT FROM AUTHOR]

The location of reproduction is a key life history trait, as it influences the bio-physical conditions that offspring experience and, thus, fitness. Capelin Mallotus villosus is a small (<200mm), short-lived forage fish that spawns in two habitats in coastal Newfoundland: warm beaches and cool, deep water (15-40 m). From 2009 to 2014, we investigated temperature-dependent spawning habitat use by quantifying hourly temperature at spawning sites during July within each habitat along with population-level spawning site use. Capelin did not spawn at sites with temperatures <2 °C or consistently >12 °C, supporting the estimated suitable spawning temperature range (2-12 °C). Spawning typically occurred exclusively at beaches early in July when deep-water habitat was too cold (i.e.<2 °C), and then switched to deep-water habitat later in July when beaches became too warm (i.e.>12 °C). Spawning overlapped for 1-3 d in both habitats when temperatures were within suitable ranges (2011, 2013), but capelin also spawned exclusively in one habitat when temperatures remained suitable in the other. The latter suggests that other factors influence spawning habitat selection, such as conspecific egg densities and other environmental conditions. Overall, the flexible use of spawning habitats, along with wide tolerance ranges of capelin eggs to environmental conditions, are likely key adaptations to maximize fitness and stabilize population dynamics of this important forage fish species in an unpredictable environment. [ABSTRACT FROM AUTHOR]

Warming temperatures caused by climate change have the potential to impact spawning phenology of temperate marine fish as some species have temperature-dependent gonadal development. Inter-annual variation in the timing of Atlantic cod (Gadus morhua) spawning in the northern North Sea, central North Sea and Irish Sea was estimated by calculating an annual peak roe month (PRM) from records of roe landings spanning the last three decades. A trend towards earlier PRM was found in all three regions, with estimates of shifts in PRM ranging from 0.9 to 2.4 weeks per decade. Temperatures experienced by cod during early vitellogenesis correlated negatively with PRM, suggesting that rising sea temperatures have contributed to a shift in spawning phenology. A concurrent reduction in the mean size of spawning females excluded the possibility that earlier spawning was due to a shift in size structure towards larger individuals, as large cod spawn earlier than smaller-sized individuals in the North Sea. Further research into the effects of climate change on the phenology of different trophic levels within the North Sea ecosystem should be undertaken to determine whether climate change-induced shifts in spawning phenology will result in a temporal mismatch between cod larvae and their planktonic prey. [ABSTRACT FROM AUTHOR]

Lagrangian Flow Network (LFN) is a modelling framework in which ocean sub-areas are represented as nodes in a network interconnected by links representing transport of propagules (eggs and larvae) by currents. We asses the sensitivity and robustness of four LFN-derived connectivity metrics measuring retention and exchange. The most relevant parameters are tested over large ranges and a wide region with contrasting hydrodynamics: density of released particles, node size (spatial scale of discretization), Pelagic Larval Duration (PLD) and spawning modality. We find a minimum density of released particles that guarantees reliable values for most of the metrics examined. We also find that node size has a nontrivial influence on them. Connectivity estimates for long PLDs are more robust against biological uncertainties (PLD and spawning date) than for short PLDs. For mass-spawners releasing propagules over short periods (≈ 2-10 days), daily release must be simulated to properly consider connectivity fluctuations due to variable currents. In contrast, average connectivity estimates for species that spawn repeatedly over longer durations (few weeks to few months) remain robust even using longer periodicity (5-10 days). Our results have implications to design connectivity experiments with particle-tracking models and to evaluate the reliability of their results. [ABSTRACT FROM AUTHOR]

Movement patterns of marine fishes can have considerable impacts on their population dynamics. A thorough understanding of fish movements is therefore required for informing stock identification, stock assessment, and fishery management. This study investigated the seasonal movements and connectivity of a spring-spawning component of Atlantic cod (Gadus morhua) in the western Gulf of Maine. From 2010 through 2013, spawning cod were sampled within an inshore spawning closure and tagged with conventional tags (n = 2368), acoustic transmitters (n = 106), and archival data storage tags (n = 266). Acoustic receivers were deployed on three inshore spawning sites to test for connectivity among sites. Data from archival tags were used to describe seasonal habitat occupancy and movement patterns via geolocation to statistical areas. Tagging data indicated that cod were primarily residential in the western Gulf of Maine, moving inshore to spawn during the spring (April-July), followed by an offshore migration to their feeding grounds for summer and fall. Cod generally inhabited waters from 45 to 175 m, with the deep offshore basins (>150 m) serving as overwintering habitat. Occupied water temperatures ranged from 4.0 to 13.3 °C, with the coldest temperatures experienced from March through July and the warmest temperatures experienced from September through January. Results provided evidence of spawning site fidelity and connectivity among spawning sites, with some fish visiting multiple spawning sites within or between years. The movements observed during and after the spring-spawning season serve as important mechanisms influencing metapopulation dynamics in the Gulf of Maine region, including both fine- and broad-scale population structure. The improved understanding of cod movement patterns will assist fishery managers in developing management plans, including spawning protection measures, and help to address remaining uncertainties with respect to cod population structure in the Gulf of Maine and other regions. [ABSTRACT FROM AUTHOR]

Mark-recapture experiments were conducted in the tidal Nanticoke River (Chesapeake Bay) to determine how the salt front retains striped bass larvae and controls nursery production. During two spring spawning seasons, 25.1 million hatchery-produced, first-feeding larvae (5-12 days post-hatch) were released with chemically marked otoliths at selected locations and times. Surveys tracked the spatial and demographic fates of released and naturally spawned larvae. Released larvae dispersed rapidly within the freshwater tidal portion of the estuary and were retained above the salt front. Their distributions overlapped with natural larvae. Growth and mortality rates did not differ with respect to release location, but did vary with day of release, influenced by storm events and seasonal changes in temperature. In 1993, a group released during a storm event did not yield any recaptured larvae. Zooplankton concentrations in both years were likely sufficient for successful larval feeding. In spring 1993, a season of relatively high freshwater flow, nursery volume was 2.1-fold larger and juvenile production from larval releases was fourfold higher than in 1992. We propose that increased nursery volume reduces variance in water quality, enhances retention of larvae within the nursery, thus increasing production of larval striped bass. [ABSTRACT FROM AUTHOR]

The inclusion of biological and ecological aspects in the assessment of fish population status is one of the bases for an ecosystem-based fisheries management. During the past two decades the Eastern Baltic cod has experienced a drastic reduction in growth and body condition that may have affected its survival. We used results from published experimental literature linking cod condition to starvation and mortality, to estimate the annual proportion of cod close to the lethal condition level in the Eastern Baltic cod stock. Thereafter we applied these results to adjust the natural mortality (M) assumed in the analytical stock assessment model. The results in terms of Spawning Stock Biomass (SSB), Fishing mortality (F) and Recruitment (R) in the final year from the stock assessment using M values adjusted for low condition were up to 40% different compared with the assessment assuming a constant M=0.2. This method could be used for adjusting natural mortalities for other cod stocks where changes in condition are observed. [ABSTRACT FROM AUTHOR]

Anadromous fishes often use various survival tactics while migrating through main stem rivers to successfully reach spawning grounds and reproduce. Mixed-stock assemblages of anadromous adult summer steelhead Oncorhynchus mykiss re-enter the Columbia River from late spring through fall including the period of peak summer water temperatures, and previous studies suggest that stocks alter migratory behaviour in response to warm temperatures by seeking cool water refuges. We combined parentage-based tagging with mixed stock analyses to test whether steelhead use a non-natal tributary (Deschutes River, OR, USA) as a thermal refuge and if this migratory behaviour is associated with stock-specific run-timing. Results collected over two migration years indicated that out-of-basin fish in the Deschutes River were disproportionately from specific stocks in the Snake River (Salmon and Grande Ronde) that had migrated through the main stem Columbia River when water temperatures exceeded 21 °C. Stocks migrating through the main stem river during cooler temperature periods were either less frequent (Clearwater River), or not encountered (lower Snake River) in the Deschutes River. This study facilitates an improved understanding of stock-specific migratory characteristics associated with environmental conditions in this system. Results potentially affect fisheries management, hatchery protocols, cool-water refuge maintenance, and conservation of wild Deschutes River populations. [ABSTRACT FROM AUTHOR]

Iteroparity (repeat spawning) is a life history attribute with significant conservation value for at-risk populations of steelhead trout (Oncorhynchus mykiss). However, stock-specific rates of iteroparity and abundance of post-spawned steelhead "kelts" can be difficult to monitor in large river systems where multiple populations are commonly encountered as aggregated mixtures. We used genetic mixed-stock analysis (MSA) to determine steelhead origins and tested for stock-specific differences in the prevalence of an iterparous reproductive strategy. Steelhead from the Snake River, USA were sampled as "returns" migrating upstream to spawn and as emigrating post-spawned "kelts". Fish were assigned between two regions that are characterized by predominant run-type. We observed a larger overall proportion of kelts from region-1 (putative-A run; 82%) compared to kelts from region-2 (putative B-run; 18%), but returns from region-2 (30%) were nearly twice as abundant as kelts. Female kelts were predominant throughout the basin, occurring in similar proportions between regions (72% region-1, 77% region-2). The inferred ocean age distribution of kelts was distinct between regions, and regional differences in body size and emigration timing were significant (P<0.0001). Although the ocean age-classes for kelts and returns within the same region were similarly distributed, kelts were significantly smaller in average body size compared to returns, and the results were temporally consistent. The association between body size and post-spawn survival suggests that strategies to improve overall recovery of steelhead, such as artificial reconditioning, may achieve greater success by targeting smaller kelts. Moreover, monitoring of post-spawn survival, and repeat spawning potential will likely benefit from MSA to augment demographic information and improve the accuracy of differentiating among specific stocks or regions. [ABSTRACT FROM AUTHOR]

Many fish species that are separated into genetically distinct populations are exploited as mixed stocks and this creates challenges for a sustainable management. European whitefish in the Baltic Sea represents one of these species forming sea- and river-spawning ecotypes, which are further divided into local populations. This study evaluated the effect of combining genetic markers with an adaptive meristic trait (gillraker count, GRC) on the performance of mixed-stock analysis (MSA) of Baltic whitefish. Using 586 individuals from 13 spawning locations, a simulated mixtures analysis showed that the combination of GRC and nine microsatellites improves both the accuracy and precision of MSA for distinguishing two sympatric ecotypes. When applied to gill-net fishery samples (758 fish) collected around the Å land Islands, the estimated stock composition showed a large temporal shift in abundance of two ecotypes between June and November, with decreasing frequency of river spawners in autumn. Our results indicate that combining neutral genetic markers with the adaptive meristic trait provides a useful fisheries monitoring tool for conservation and management of two sympatric whitefish ecotypes in the Baltic Sea. [ABSTRACT FROM AUTHOR]

Farmed Atlantic salmon (Salmo salar) escape from net pens and enter rivers to spawn, potentially resulting in genetic introgression and reduced fitness of wild salmon. Here, we quantify genetic introgression of farmed to wild salmon, using molecular genetic markers, in populations from 147 salmon rivers, representing three-quarters of the total wild salmon spawning population in Norway. For 109 rivers with adult modern samples and sample sizes of 20 or more, the average level of farmed genetic introgression was 6.4% (median=2.3%), with a range between 0.0% and 42.2%. Fifty-one of these rivers showed significant farmed genetic introgression when compared with historical reference samples. We observed a highly significant correlation between estimated farmed introgression and average proportion of escaped farmed salmon. We quantify levels of introgression as unweighted averages or weighted by population sizes, to compare geographical regions and to compare levels of introgression in rivers and fjords designated as locations deserving a high level of protection. We found a generally lower level of introgression in National Salmon Rivers and National Salmon Fjords subjected to formal protection by parliament. We conclude that farmed to wild genetic introgression is high in a large proportion of Norwegian salmon rivers, with the highest levels found in the most intensive areas of salmon farming. The extensive genetic introgression documented here poses a serious challenge to the management of farmed and wild Atlantic salmon in Norway and, in all likelihood, in other regions where farmed-salmon escape events occur with regularity. [ABSTRACT FROM AUTHOR]

According to density-dependent habitat selection theory, areas of high density can be indicative of high population productivity and have positive individual fitness consequences. Here, we explore six groundfish populations on the Scotian Shelf, Canada, where a decline in areas of high density beyond a certain threshold is associated with disproportionately large declines in Spawning Stock Biomass (SSB). This is evidenced by empirical, concave, positive relationships between high-density areas (HDAs) and SSB. We introduce a methodology to estimate the threshold below which SSB declines increasingly faster per unit of HDA decline. The spatial threshold among these six stocks was remarkably consistent; when stocks lose 70-80% of HDAs, disproportionately large SSB declines are likely to occur. We propose that spatial thresholds could serve as spatial reference points to complement existing SSB limit reference points (LRPs). For some stocks we identify spatial thresholds which correspond to SSB levels that exceed those associated with the designated SSB LRP, suggesting that a review of these SSB LRPs warrants merit. For other stocks, spatial reference points can be used in concert with SSB reference points, strengthening efforts to incorporate a precautionary approach to fisheries management. Our results warrant further research into the general application of HDA as spatial limit and target reference points for fisheries management in addition to other population status indicators within a broad recovery framework. [ABSTRACT FROM AUTHOR]

Simultaneous hermaphrodites that exchange gametes within pairs allow us to test whether equity of resource exchange is positively associated with duration of cooperative partnerships. The chalk bass (Serranus tortugarum) provides an excellent model system for such research because they spawn daily, trading sex roles with the same mating partners in repeated spawning bouts (a tactic called "egg parceling"). Even so, they live in site-attached aggregations with opportunities for extra-pair matings. We asked whether individuals spawn preferentially with 1 long-term partner and whether partner fidelity was associated with matching in the number of eggs produced in a single day by individuals within pairs. In addition, we observed random focal individuals during spawning to determine whether egg parceling was coordinated within pairs: we asked whether parcel number (per day) was well matched within pairs and whether parcels were exchanged in nonrandom sequences. We did not witness any "break-ups" in our long-term pairs; during each monthly census, all identified pairs were found spawning and courting with their "primary" mating partner until one or both of them disappeared. Daily egg production and the number of egg parcels exchanged within primary partnerships were coordinated. The sequence of parcel exchange was fairly regular, although ca. 20% of focal individuals fertilized or exchanged a few egg parcels with another partner(s); parceling allows individuals the option to exchange eggs outside of the primary pair. Our study provides novel empirical evidence of strong pair bonds and resource matching even in relatively large social groups with extra-pair trading opportunities. [ABSTRACT FROM AUTHOR]