Larval Mortality in Marine Fishes and the Critical Period Concept

We investigated the link between hatch date, growth trajectory, estuarine retention and survival of rainbow smelt larvae Osmerus mordax in the St. Lawrence Middle Estuary. Young smelt were collected over their entire distributional range across the salinity gradient of the Middle Estuary (0 to 25 psu) during 2 growing seasons. Individual growth trajectories and hatch-date distributions were reconstructed from otolith microstructure. High abundances of larvae were observed in the upstream region (0 to 10 psu) corresponding to the estuarine turbidity maximum (ETM). Larval rainbow smelt hatched in May during a period of 26 to 27 d, and mortality rates were variable among hatch dates. These variations were related to the feeding conditions experienced by first-feeding larvae (3 to 5 d after hatching) that fluctuated from day to day according to a predictable cycle of 15 d associated with photoperiod and tide. Comparison of growth trajectories of larvae at various ages indicated that older individuals, i.e. survivors, grew faster. Furthermore, smelt larvae collected within the ETM exhibited significantly higher growth rates than those sampled in the downstream area of the Middle Estuary, suggesting that larvae collected in the latter region represented dispersal from the ETM. We concluded that inter-annual variations in year-class strength might not be generally affected by early starvation, as larvae will experience recurrently good, medium and bad first-feeding conditions each year because of the length of the hatching period. However, any factor that reduces growth rate during the larval stage, including parasitism, has the potential to affect interannual variability in year-class strength.KEY WORDS: Hatch date · Growth rate · Survival · Estuarine turbidity maximum · Otolith microstructure · Rainbow smelt larvae 203: 233-245, 2000 and silversides Menidia beryllina (Gleason & Bengtson 1996) have been reported. Resale or republication not permitted without written consent of the publisherMar Ecol Prog SerThe different causes of mortality during the early life history of fishes implies different selective processes acting on the phenotype within generations (Houde 1997). For instance, if survival is governed by predation, larger larvae should be less susceptible to predation (the 'bigger is better' hypothesis; Miller et al. 1988), while faster-growing larvae should be available to predators for a shorter period of time before metamorphosis to the juvenile stage (the 'stage duration' hypothesis; Anderson 1988, Cushing 1990). In the case where starvation is the principal cause of mortality, larger and faster-growing larvae are expected to exhibit the highest feeding rates, and to be less sensitive to starvation (Beyer & Laurence 1980, Rosenberg & Haugen 1982. Finally, if dispersion is mainly responsible for mortality, larger and faster-growing larvae should exhibit better swimming capabilities for retention in favourable nursery areas. However, it is unlikely that only 1 mechanism regulates mortality (Legg...

Section: Survival Related To Hatch Datesupporting

confidence: 91%

Section: Introductionmentioning

confidence: 99%

Critical periods and growth-dependent survival of larvae of an estuarine fish, the rainbow smelt Osmerus mordax

Sirois¹,

Dodson²

2000

“…Spacing of the occurrence of larval fishes reduces potential trophic competition during the critical period (May 1974). Seasonal temperature changes also affect large-scale spatial distributions of juveniles (Day et al 1989).…”

Section: Spatial Scale Seasonality and Ontogenymentioning

confidence: 99%

Patterns of resource use by fishes and macroinvertebrates in Barataria Bay, Louisiana

Jones¹,

Baltz

Allen³

2002

We examined patterns of resource use by size classes of fishes and macroinvertebrates in Barataria Bay, Louisiana. Analyses were based on microhabitat data characterized by water depth, distance from shore, substrate, salinity, dissolved oxygen and temperature. Stratified random samples along the salinity gradient from the nearshore Gulf of Mexico to about 30 km inland were taken monthly with a 1 m beam trawl to characterize distributions of fishes, macroinvertebrates and environmental conditions. From October 1992 through September 1993, 31 602 individuals belonging to 70 species were collected. The 10 most abundant species plus 3 others of special interest were chosen for further analyses. Seasonal differences in environmental variables and differences in resource use among species within ecological groups and within selected species were evaluated by 1-way ANOVAs. A factor analysis resolved 6 environmental variables into 3 orthogonal axes that simplified visualization and comparisons within and among species. Three factors accounted for 70% of the environmental variance and represented seasonality, distance-depth and substrate-salinity axes. Twelve of 13 species showed statistically significant differences between size classes in use of temperature, but some differences were probably due to seasonal temperature changes and the ephemeral nature of life history stages. Within-species differences were less prevalent for variables other than temperature, and the majority were related to use of deeper water as size increased. When seasonal, spatial and size-structured distributions were compared, species with peak abundances during the same seasons had the highest ecological overlaps. Ecological overlaps of 3 closely related species pairs were generally below the mean for the assemblage. Understanding patterns of resource use and the environmental requirements of estuarine-dependent species is an important step in identifying and protecting nursery habitats.

“…Food conditions at the onset of exogenous feeding are hypothesized to be especially important. This has frequently been demonstrated in the laboratory, but field verification has been difficult to achieve (see reviews in May 1974, Leggett 1986). The links between in situ food quantity and quality and survival remain obscure.…”

Section: Introductionmentioning

confidence: 99%

Effect of prey abundance and size on the growth and survival of larval fish: an experimental study employing large volume enclosures

Frank¹,

Leggett²

1986

We examined the effect of natural variations in the concentration and size composition of plankton in coastal waters on the growth and survival of recently hatched larval capelin Mallotus villosus. Known numbers of larvae were stocked into 4 m3 j n sjtu enclosures, containing plankton communities whose size composihon and total particle concentration mirrored those occurnng naturally dunng times when the nearshore waters were alternately dominated by deep upwelled waters, and by warmer surface waters. Daily growth of larvae was unrelated to total plankton concentrahon, but strongly correlated with the concentrahon of plankton in the 40 to 51 pm (esd) size range. Daily mortality was negatively correlated with concentrations of plankton <81 pm (esd). This correlation was strongest with prey in the 32 to 40 pm and 40 to 51 pm (esd) size classes. The in situ concentration of plankton in the optimum size range for growth and survival was temporally dynamic and strongly influenced by wind-driven water mass exchange. The relevance of these findings to previous studies of the effect of prey concentration on growth and survival in larval fishes is discussed.