Search

Ability to quantify connectivity among spawning subpopulations and their relative contribution of recruits to the broader population is a critical fisheries management need. By combining microsatellite and age information from larval yellow perch ( Perca flavescens) collected in the Lake St. Clair - Detroit River system (SC-DRS) and western Lake Erie with a hydrodynamic backtracking approach, we quantified subpopulation structure, connectivity, and contributions of recruits to the juvenile stage in western Lake Erie during 2006-2007. After finding weak (yet stable) genetic structure between the SC-DRS and two western Lake Erie subpopulations, microsatellites also revealed measurable recruitment of SC-DRS larvae to the juvenile stage in western Lake Erie (17%-21% during 2006-2007). Consideration of precollection larval dispersal trajectories, using hydrodynamic backtracking, increased estimated contributions to 65% in 2006 and 57% in 2007. Our findings highlight the value of complementing subpopulation discrimination methods with hydrodynamic predictions of larval dispersal by revealing the SC-DRS as a source of recruits to western Lake Erie and also showing that connectivity through larval dispersal can affect the structure and dynamics of large lake fish populations. [ABSTRACT FROM AUTHOR]

Climate change has caused shifts in seasonal timing of climatic events such as the onset of spring upwelling, which can lead to temporal mismatches between fish spawning and production of zoopklankton prey. Fishing may exacerbate mismatches through age truncation, particularly when offspring survival is dependent on maternal age, but no-take reserves or harvest reductions might buffer this effect. To quantify the potential for management to buffer synergistic interactions between fishing and climate, we developed a dynamic population model of a harvested species where larval survival depended on spring transition timing and maternal age. We applied this model to rockfishes ( Sebastes spp.) after verifying empirically that spring transition timing affects their recruitment success. We found that yield and persistence changed more with maternal-age-dependent larval provisioning than maternal-age-dependent spawning timing across a range of spring transition timings, especially with environmental stochasticity. Either implementing reserves or reducing fishing can mitigate impacts on larval survival, but reserves convey the added benefit of decreased sensitivity of yield and persistence to fishing. However, reserve buffering effects decreased with the inclusion of environmental stochasticity. [ABSTRACT FROM AUTHOR]

Timing of spawning and hatching of shortnose sturgeon, Acipenser brevirostrum, in the Saint John River, New Brunswick, Canada, was estimated using inverse prediction. We examined egg incubation periods at 5, 9, and 13 °C to back-calculate spawning dates. No larvae hatched at 5 °C. At 9 and 13 °C, hatching began after 18 and 8 days post fertilization, respectively. Lengths of yolk-sac larvae reared in the laboratory at 13-21 °C were used to develop a temperature-mediated Gompertz growth model. The inverted Gompertz model, predicting larval age from larval size and water temperature, was applied to 671, 164, and 746 larvae captured in the wild in 2008, 2009, and 2010, respectively. Estimated hatching distributions peaked in late May, and mean spawning events were predicted to occur in late April - early May (9 °C scenario) and middle to late May (13 °C scenario). Larval ages at the two sampling transects, 4.5 km apart, were similar, while catch per unit effort was lower downstream, indicating mortality during dispersal. Inverse prediction of larval ages provides fast and cost-effective estimates of the timing of spawning, hatching, and larval migration in the wild. [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]

Population mean egg size of salmonids increases with the mean size of gravels in which a population spawns. A long-standing hypothesis is that large larvae cannot navigate small-gravel interstices, so mothers must decrease per-offspring investment when spawning gravels are small. We manipulated the size of incubation gravels and egg size of Atlantic salmon ( Salmo salar) to test whether size-related entombment of larvae occurs. We find little evidence of size-related entombment, but we find evidence that gravel size does not affect all larval sizes equally. Larger larvae emerge from small gravels before development is complete and with a visible yolk sac, possibly due to oxygen limitation in small gravels. Smaller larvae always complete development in the gravel and emerge without a yolk sac. Although growth and survival may increase with juvenile size following yolk-sac absorption, juveniles with yolk sacs may fare worse when depredation rates are high. The egg size - gravel size correlation may therefore reflect increased postemergence mortality among larger offspring in small-gravel environments. Alternatively, compaction stress in fine gravels coupled with size asymmetries in larval strength may have caused the patterns that we observed, in which case our data may not help explain the egg size - gravel size correlation. [ABSTRACT FROM AUTHOR]