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Feeding ecology of white perchMorone americanalarvae, a major component of the ichthyoplankton community in the estuarine turbidity maximum(ETM) region of upper Chesapeake Bay, was evaluated in years of contrasting physical conditions. In 1998, high river flow led to an ETM with high turbidity and pronounced salinity stratification. In 1999, under low river flow conditions, turbidities in the ETM region were lower and the salt front was located 15 km up-stream of its location in 1998. Copepodites and adults ofEurytemora affiniswere the predominant prey in guts of all length classes of larvae(3·2–9·8 mm standard length,LS) that were examined. Repeated-measures, multiple regression analyses were conducted to evaluate the influence of several factors on feeding success by determining if physical conditions(temperature, current velocity, salinity, turbidity and light) and prey concentrations explained variability in mean gut fullness(gut contents mass per body mass) of small(<5 mmLS) and large(>5 mmLS) white perch larvae.Eurytemora affinisconcentrations were significant in the statistical models for both small and large larvae. High concentrations ofE. affinis, which enhanced encounter rates of white perch larvae with prey, may have been the most important factor determining feeding success in the ETM region. Larval feeding incidence(percentage of guts with food) was higher in 1998, suggesting that annual variability in river flow influenced larval feeding success by controlling physical and biological conditions in the ETM region. [ABSTRACT FROM AUTHOR]

After the collapse of striped bass Morone saxatilis stocks in the late 1970s, hatchery programs and release experiments were instituted to evaluate the potential to restore striped bass in Chesapeake Bay. Because survival of striped bass larvae to first feeding (7 d after hatch) is low in Chesapeake tributaries, ranging from 0.2 to 5.2% of eggs spawned, it is possible to enhance survival through hatchery propagation of eggs and yolk-sac larvae, and it may be feasible to supplement recruitment by stocking post-yolk-sac larvae. During 1991–1993, otoliths of 31.7 million hatchery-produced striped bass larvae (5–13 d after hatch) were chemically marked and released into two tributaries of Chesapeake Bay. In years of moderate to poor natural larval production (1991, 1992), stocked larvae contributed 20 to 30% to overall juvenile abundance. In 1993, a year of high natural production, stocked larvae contributed only 5% to juvenile abundance, although numbers contributed were higher than in previous years. Using field and hatchery estimates of larval and juvenile growth and mortality, enhancement strategies were compared in which fish were released at three different ages: larvae (7 d post-hatch), summer-stocked juveniles (55 d post-hatch), or fall-stocked juveniles (220 d post-hatch). Based upon hatchery records, reared larvae and juveniles experienced substantially higher rates of growth and survival than did wild larvae and juveniles of similar age. In years of low natural egg production, cohort biomass at 220 d post-hatch was highest when juveniles were stocked in summer or fall. When approximate costs were incorporated into the analysis, the efficacy of stocking 7-d-old larvae was higher than summer and fall stocking of juveniles if stocked larvae encountered favourable conditions. In years of poor natural recruitment, stocking post yolk-sac larvae into estuarine tributaries could supplement stocks of striped bass and possibly other anadromous species which experience high embryo and yolk-sac larva mortality. [ABSTRACT FROM PUBLISHER]

A larval mark-recapture experiment was undertaken to compare dispersal patterns and vital rates of hatchery-produced and wild larvae. The potential of larval stocking to enhance recruitment in an estuarine tributary was also evaluated. Approximately 6.5 million striped bass Morone saxatilis larvae (5–7 mm, SL) were marked by immersion in 25 mg l−1 alizarin complexone, which was deposited in their otoliths. Following release on two dates, the dispersal of marked larvae from release sites was rapid and their distribution 4 days after release resembled that of wild larvae. Growth rates of four release groups ranged from 0.20 to 0.25 mm day−1 and mortality rates ranged from 0.09 to 0.19 day−1. The rates were similar to those of wild larvae. More than 70% mortality of released groups occurred from 0 to 3 days after release and larvae stocked at one down-river site apparently suffered complete mortality due to advective down-estuary loss. Hatchery-produced larvae were released during a period when temperatures were favorable for growth and survival. Survivors of released larvae were estimated to account for 10 to 35% of the age 0+ juvenile striped bass in the Patuxent River in 1991. The success of this experiment indicated that marked larvae can serve as “probes” to examine environmental and habitat factors that affect recruitment of striped bass and other anadromous species. In the case of striped bass, large-scale stocking of larvae could contribute significantly to recruitment in Chesapeake Bay tributaries. [ABSTRACT FROM PUBLISHER]

A mesocosm system was developed to be deployed from a research vessel and set adrift with its enclosed plankton, including fish eggs, larvae, and gelatinous predators. The system consists of an array of mesocosms that are 1 m diameter, 5 m long, and 3.2 m3 capacity, and which are constructed of 20-μm porosity dacron. Deployment and harvesting procedures are described. The mesocosms "capture" a sample of the water column and provide an assay method to examine planktonic processes in experiments of a few hours' to a few days' duration. Mortality rates of bay anchovy, Anchoa mitchilli, eggs and yolk-sac larvae were estimated from drifting mesocosm experiments in 1989 and 1991. Overall mean instantaneous rates were 0.073 h−1 for eggs and 0.051 h−1 for larvae, indicating that 95% of a cohort had died within 2 days of hatching. Egg and larval mortality rates were variable due to the variability in the initial numbers of captured eggs and larvae and to the complex mix of predator sizes and biovolumes that were enclosed in different deployments. An attempt (only partially successful) was made to relate observed mortalities to the abundance of two enclosed gelatinous predators, a ctenophore Mnemiopsis leidyi and a scyphomedusan Chrysaora quinquecirrha. The mesocosm results are compared with those from an encounter model that predicts predation mortality. The results are also compared with synoptic ichthyoplankton surveys and an analysis of predator gut contents, which provide independent estimates of egg/larvae mortality and their consumption by gelatinous predators. The drifting mesocosm methods holds promise and, with modifications of experimental design, can be a valuable tool to study zooplankton population processes, including those of early life stages of marine estuarine fishes. [ABSTRACT FROM PUBLISHER]

Differences in the dynamics (growth and mortality) and energetics properties of marine and freshwater fish larvae have important implications for determining the life stages at which year-class size is established. After correcting for temperature effects, marine fish larvae, which typically weigh less at hatch, can be shown to experience mortality rates, have higher metabolic requirements, and have longer larval stage durations than do freshwater fish larvae. Growth rates and growth efficiencies are similar for the two categories of larvae. The difference in body size between typically small marine and typically large freshwater fish larvae is an important factor affecting their dynamics and energetics. Predicted mean survivorship to metamorphosis of a cohort of freshwater fish larvae is 5.30%, while that of marine larvae is only 0.12%. The probability of significant density-dependent regulation during the larval stage could be relatively high for marine species, based upon their life-history properties. The probability that episodic mortalities of larvae will have significant impacts on recruitment may be higher for freshwater fish than for marine fish. Starvation mortality is more probable for marine larvae, primarily because of their small body size, associated high metabolic demands, and possibly higher ingestion requirements. Because expected mean survivorship of freshwater larvae is 44 times higher than that of marine larvae, juvenile-stage dynamics will be relatively important in controlling/regulating recruitment levels of freshwater fishes. In contrast, properties of marine species indicate that larval-stage dynamics will have a greater influence on recruitment success. [ABSTRACT FROM PUBLISHER]

Variable recruitments of striped bass were hypothesized to be causedby factors influencing growth and survival of larvae. Eggs and larvae were collected in the Potomac River from 1987 to 1989 and in the Upper Chesapeake Bay in 1988 and 1989 to estimate abundances larval growth and survival rates, and environmental variability. Larval hatch dates, ages, and growth and mortality rates were estimated from analysis of otolith daily increments. A retrospective analysis of Potomac River ichthyoplankton data from 1974--1977 and 1980--1982 provided additional estimates of larval abundances and vital rates for comparative purposes. Significant correlations between vital rates (growth and mortality) and abundances of striped bass larvae, and the Maryland juvenile recruitment index indicated that recruitment level may be fixed during the larval stage. The ratio of mean daily growth and mortality rates (G:Z) of larvae in the Potomac River for 1987--1989 was highest in 1987 when the juvenile index was relatively high, and was lower in 1988 and 1989 when juvenile indices were low. In the Upper Bay, mean larval growth rate, survival rate, and the G:Z ratio were highest in 1989 when the juvenile index also was high. In both tributaries,abundances of late-stage larvae (8 mm SL) were correlated with juvenile-stage recruitment indices. The retrospective analysis provided additional evidence that Potomac River larval abundances and G:Z ratioswere positively correlated with juvenile recruitment indices in the 1974--1977 and 1980--1982 periods. Conditions favoring striped bass larval abundance and Potential recruitment differed between the Potomac River and the Upper Bay. In the Potomac, late-stage larval abundances coincided with late-season water temperatures that were relativelywarm, low river discharges and high, late-season densities of zooplankton prey, which favored larval growth. In the Upper Bay, the high abundance of late-stage larvae in 1989 relative to 1988 was attributedto a [ABSTRACT FROM AUTHOR]

Exogenous anomalies induced by contemporary climate change may severely impact dynamics of early life stages of fish. Here, we modelled how growth rate and abundance of postflexion larvae, and recruitment of Baltic spring-spawning herring (Clupea harengus membras) in the Pärnu Bay, Gulf of Riga (GoR) may respond to shifting climate variables. Higher larval growth rates were aligned with later seasonal emergence of yolk-sac larvae, while lower abundance of postflexion larvae occurred in years of earlier seasonal seawater warming. Cooler temperatures (<16 °C) in spring expanded the optimal thermal window for first-feeding herring larvae, attributable to the absence of early seasonal water temperature warming. Higher recruitment levels emerged in years of seasonally delayed warming and were associated with higher abundance of postflexion larvae. In recent decades, the trend towards earlier warming of the Baltic Sea in spring threatens to create a bottleneck to successful recruitment of herring. The existing paradigm that abundant Baltic herring year-classes occur only in the years following mild winters no longer stands as environmental conditions undergo rapid change. The relative contribution of Pärnu Bay larval nursery areas to recruitment has diminished as the suitable thermal window has been dramatically reduced in recent decades. Evolving thermal dynamics in the GoR have developed relatively recently and in future present a bottleneck for herring production., (Copyright © 2022 Elsevier Ltd. All rights reserved.)