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The eco-hydraulic diversity in a tidal reach is obviously enriched after spur dikes built, such as a turbulent rapid around structures head when tide ebbing and a gently dynamic environment in the back during the whole tide process. It would be much beneficial for adult fishes to spawn eggs and the youngs to fatten. Spur dikes have been utilized as channel regulation structures worldwide, especially in the upstream tidal reach of river estuary, where is a superexcellent habitat for resident fish or migratory fish during different life history stages. However, local hydraulic characters will be altered upon spur dikes establishment, resulting in several influence on fish habitat. The purpose of this paper was to reveal the impacts mechanism of spur dikes on fish habitat in a tidal reach through a comprehensive analysis based on some previous neglected aspects, such as fish physiological characters, hydraulic variations and essential factors alterations of the aquatic ecosystem. Hydraulic information around spur dikes was acquired through a 3D hydrodynamic model, and validations of tidal level, velocity and diversion ratio yielded a high accuracy. Turbulent rapid around spur dikes head and mild nearshore environment behind structures have some potentialities to become new spawning grounds, for fish spawning semi-pelagic eggs and fish laying adhesive eggs respectively. Benefitted from effective mixture of water during a tidal cycle, plenty of planktons and organic matters will be brought in and gradually enriched behind structures, thus a favorable feeding ground will appear there. Meanwhile, deflecting flow induced by spur dikes may cause some hazards for survival probability of migratory larval fish. It is drifted off the nearshore into the river middle, where is a higher turbulent intensity and less phytoplankton concentration. In summary, spur dikes possess tremendous ecological effects, i.e. enriching the eco-hydraulic diversity, not only as a velocity shelter. In addition, research result could afford a sufficient basis for environment conservations to restore aquatic ecosystem with spur dikes. [ABSTRACT FROM AUTHOR]

Understanding the relationship between intraspecific phenotypic variation and habitat is fundamentally important to ecology and evolution. However, it is largely unknown whether the environment drives the morphological variation in riverine fish otoliths, which are potential phenotypic markers. In this study, we investigated morphological variations in the otoliths of an endemic Chinese fish (Schizothorax nukiangensis Tsao) collected from seven sites with varying environmental gradients along the Nu‐Salween River. We compared morphological characters of S. nukiangensis otoliths among sampling sites and identified environmental sources of otolith morphological variation using multivariate regression trees and multiple factor analysis. Results showed that S. nukiangensis otoliths collected from different habitats were significantly different in morphology, mainly at the rostrum, excisura and posterior rim. Variations in otolith morphology (specifically the increase in otolith length) were predominantly governed by average river gradient; this might be a functional response to hydrogeomorphic conditions. Other environmental gradients (i.e., altitude, latitude and average annual temperature) played a minor role in otolith shape. This study highlighted the role of environmental factors in determining the otolith shape in riverine fish; thus, species and population discriminations based on otolith morphology should consider intraspecific variability. [ABSTRACT FROM AUTHOR]

With regard to published data on the ecology of early peled larvae acclimated in lakes or reared under experimental or fish farm conditions, interannual variability of feeding and environmental conditions during the transition to exogenous feeding has been demonstrated for peled larvae in a control water body located in the floodplain of the main spawning tributary of the lower Ob River. The conditions that govern exogenous food consumption by early peled larvae and largely determine the fate of a given generation depend on both biotic (the concentration of food organisms) and abiotic factors (wind regime). The trophic optimum during the transition of larvae to exogenous feeding, which ensures the level of gut filling sufficient for their survival and growth in the control water body, is determined by a complex of natural events. The results of this study may be extrapolated to the entire native range of the Ob River peled population and used for planning the release of peled larvae into natural water bodies of Western Siberia to compensate for losses to their biological resources. [ABSTRACT FROM AUTHOR]

Winter flounder, Pseudopleuronectes americanus, from southern New England and the Gulf of Maine were historically considered to be obligate estuarine spawners. However, recent experiments and observations document that winter flounder in the Gulf of Maine also utilize coastal waters for spawning. An individual-based modeling approach was used to investigate the transport of winter flounder larvae from three hypothesized coastal spawning grounds in the Gulf of Maine. Transport success rates were greatest for larvae released from Ipswich Bay, intermediate for Stellwagen Bank and least successful for those released from Jeffreys Ledge. There was substantial interannual variability in larval transport and geographic patterns of potential connectivity. Furthermore, the date of spawning had an important influence on transport success. Model results suggest that certain coastal spawning grounds used by winter flounder may serve as an important source of larvae to estuaries and nearshore nursery areas. The potential influx of coastal spawned larvae could have implications for the resilience, productivity and gene flow in local populations. Model results provide further support for the conclusion that winter flounder in the Gulf of Maine may not be solely dependent upon estuaries for spawning. Results also suggest that coastal spawning groups should be considered explicitly in the management of winter flounder, and protected under Essential Fish Habitat regulations. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the role of the northern Gulf of Mexico (Gulf) as essential habitat of common dolphinfish ( Coryphaena hippurus) and pompano dolphinfish ( C. equiselis) during early life and to characterize conditions in which they were found. Eight ichthyoplankton surveys were conducted during the summer months from 2007 to 2010 in northern Gulf waters off Texas and Louisiana (26-28°N, 87-93°W), during which 1145 dolphinfish larvae were collected. C. hippurus, the dominant dolphinfish species, were collected in 57% of sampling sites with an overall mean density of 0.73 larvae 1000 m−3, whereas C. equiselis were only collected at 18% of sites with a mean density of 0.12 larvae 1000 m−3. Generalized additive models ( GAMs) were used to examine the relationship between several environmental parameters and C. hippurus presence/absence and density. Both presence/absence and density GAMs indicated that catches of C. hippurus larvae increased near fronts and eddies and that increased abundances were most strongly associated with higher salinities and cooler temperatures. In addition, our models showed that C. hippurus larvae were positively associated with C. equiselis larvae, suggesting that C. hippurus and C. equiselis use similar habitats. Results of this study indicate that the Gulf may represent important spawning and/or nursery habitat of dolphinfishes and that mesoscale features and physicochemical conditions influence the distribution and abundance of C. hippurus larvae in this region. [ABSTRACT FROM AUTHOR]

Little information is available on governing factors of larval fish dispersal in natural river systems. Therefore, we aimed to describe dispersal and retention of marked larval nase carp, Chondrostoma nasus, along a shoreline nursery habitat of the River Danube. Based on a three-dimensional hydrodynamic model, we analyzed the influence of the hydraulic conditions on larval dispersal. We also related observed larval pathways to numerical particle tracing. Clear differences in the temporal drift pattern were due to significant differences in the hydrodynamic characteristics of the release stations. Some larvae remained in the study reach, most upstream of the release point. These were significantly larger than drifting larvae. We conclude that larval dispersal has an active component and that dispersal and retention patterns are dependent on the habitat structure and hydrodynamic characteristics of the releasing points. This emphasizes the importance of links between the location of spawning sites within the river and variation in flow during early development, the combination of which may contribute to successful recruitment of fluvial fish species. [ABSTRACT FROM AUTHOR]

Abstract: Pacific bluefin tuna (Thunnus orientalis) have spawning grounds in waters stretching from south of Okinawa to east of Taiwan. This species is typical of fishes that spawn seasonally in small, limited areas. Any marked change in the marine environment of the spawning grounds is likely to have a direct impact on larval survival and growth. We conducted rearing experiments on larvae to investigate these impacts and found that a reduction in temperature resulted in poor growth during the juvenile stage, even if larval survival rates did not change. In the wild, this reduced growth rate is likely to reduce survival rates because smaller juveniles have poorer swimming ability and their ability to avoid predators is also reduced. This is especially important since the Kuroshio current, which connects the spawning grounds to the nursery grounds, transports larvae rapidly because of its faster surface current (the western boundary current), thus larvae arriving too quickly in coastal waters can be exposed to very cold temperatures. An ocean model (MIROC) simulation under a climate warming scenario () predicted that the temperature in the spawning ground would be 3°C higher in 2100 than in present time, while the transport to nursery grounds would also be faster. In this case, the combination of several mechanisms would control the recruitment of juvenile bluefin. On the spawning grounds, high temperatures exceeding the optimal range would increase larvae mortality and any surviving larvae would reach the nursery grounds more quickly, but warmer coastal waters would have less negative impact on their growth. We forced a model of larval drift with MIROC output fields to study the complex response of bluefin tuna recruitment. As a result, the predicted survival rates of larvae arriving in Japanese coastal waters in 2100 would decline to 36% of present recruitment levels. [Copyright &y& Elsevier]

Abstract: Within the framework of the TUNIBAL project that focused on Atlantic bluefin tuna (Thunnus thynnus) larval ecology, ichthyoplankton surveys were conducted from 2001 to 2005 off the Balearic archipelago, which is recognized as one of the main spawning areas of the eastern Atlantic stock of this species. In each survey, a regular sampling grid of about 200 stations, 10 nautical miles apart were sampled. CTD casts and oblique Bongo 60 and surface Bongo 90 plankton tows were carried out. The occurrence frequencies of Atlantic bluefin tuna, albacore tuna (Thunnus alalunga) and bullet tuna (Auxis rochei) larvae in quantitative Bongo 60 samples were 0.14, 0.29 and 0.49 respectively. Mean larval abundances in these positive samples were relatively high: 31 larvae 10m−2 for Atlantic bluefin tuna, 17 for albacore tuna and 31 for bullet tuna. All species had patchy distributions since more than 90% of the stations showed larval densities under 10 larvae 100m−3 (70% showed even less than 2 larvae 100m−3), whereas in some isolated spots, we recorded abundances as high as 867 (Atlantic bluefin) or 872 (bullet tuna) larvae 10m−2. These results allowed us to relate larval distribution to mesoscale hydrographic features and to characterize the spawning habitat of these species. Single Quotient Parameter analyses were applied to spatial (depth), physical (temperature, salinity, dissolved oxygen and geostrophic current velocities) and biological (mesozooplankton biomass) variables to determine the environmental preferences of each species for spawning. Results showed that the complex hydrodynamic scenarios around the Balearic Islands, due to the interaction between the inflowing surface Atlantic water masses (AW) and Mediterranean surface waters (MW), play a key role in determining the abundance and distribution of tuna larvae in this area, especially in the case of Atlantic bluefin tuna. Spawning of this species seems to take place mainly in offshore mixed waters, as suggested by their preferences for waters with salinities between 36.9 and 37.7, located near frontal areas in the confluence of AW and MW. Atlantic bluefin tuna start to spawn once sea surface temperatures (SST) are over 20.5°C, and preferentially in the range of 21.5–26.5°C. Its larval distribution suggests that spawners reach the Balearic Sea in association with the inflowing AW. However, bullet tuna and albacore tuna larvae, species whose Mediterranean stocks stay in this sea year round, had a more widespread distribution and were found both in MW and AW. Bullet tuna starts to spawn in shallower waters near the shelf break once the SST reaches 19°C, and shows significant preferences for waters over 23.5°C. Similar to Atlantic bluefin tuna, albacore tuna spawn in offshore waters, but its spawning peak is later than its congeneric species, since it has a significant preference for even warmer waters, over 27°C. [Copyright &y& Elsevier]

Abstract: Critical gaps in our understanding of the distributions, interactions, life histories and preferred habitats of large and medium-size pelagic fishes severely constrain the implementation of ecosystem-based, spatially structured fisheries management approaches. In particular, spawning distributions and the environmental characteristics associated with the early life stages are poorly documented. In this study, we consider the diversity, assemblages, and associated habitat of the larvae of large and medium-sized pelagic species collected during 2years of monthly surveys across the Straits of Florida. In total, 36 taxa and 14,295 individuals were collected, with the highest diversity occurring during the summer and in the western, frontal region of the Florida Current. Only a few species (e.g. Thunnus obesus, T. alalunga, Tetrapturus pfluegeri) considered for this study were absent. Small scombrids (e.g. T. atlanticus, Katsuwonus pelamis, Auxis spp.) and gempylids dominated the catch and were orders of magnitude more abundant than many of the rare species (e.g. Thunnus thynnus, Kajikia albida). Both constrained (CCA) and unconstrained (NMDS) multivariate analyses revealed a number of species groupings including: (1) a summer Florida edge assemblage (e.g. Auxis spp., Euthynnus alleterattus, Istiophorus platypterus); (2) a summer offshore assemblage (e.g. Makaira nigricans, T. atlanticus, Ruvettus pretiosus, Lampris guttatus); (3) an ubiquitous assemblage (e.g. K. pelamis, Coryphaena hippurus, Xiphias gladius); and (4) a spring/winter assemblage that was widely dispersed in space (e.g. trachipterids). The primary environmental factors associated with these assemblages were sea-surface temperature (highest in summer-early fall), day length (highest in early summer), thermocline depth (shallowest on the Florida side) and fluorescence (highest on the Florida side). Overall, the results of this study provide insights into how a remarkable diversity of pelagic species spatially and temporally partition spawning within a region that is characterized by dynamic oceanography and strong habitat gradients. [Copyright &y& Elsevier]