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The article presents an investigation of the causes of recruitment variability in striped bass Morone saxatilis from Chesapeake Bay. The authors mention that the investigation documents spatio-temporal variability in abundance of larval striped bass and feeding success of larvae. They observe that recruitments of striped bass were related with matches in space and time of larval striped bass and high presence of zooplankton prey. They also discuss the claim that freshwater flow controls recruitment by its effect on the overlap of temperature/salinity zones, which are preferred by larvae.

The small-scale distribution and retention mechanisms of white perch (Morone americana) and striped bass (M. saxatilis) early-life stages were investigated in the upper Chesapeake Bay estuarine turbidity maximum (ETM). Physical measurements and biological collections were made at fixed-location stations within the ETM during three research cruises in 1998 and two in 1999. Results were compared with mapping surveys of physical properties and organism distributions above, within, and below the ETM. Physical conditions at the fixed stations differed markedly among cruises and between years due to differences in fresh- water flow and wind. In each year, striped bass and white perch larval concentrations were highest in waters of salinity 1-4. Larvae were more abundant in the ETM region in 1998, a high-flow year, suggesting that the ETM provides favorable nursery habitat when low salinity waters and the ETM coincide in high freshwater-flow conditions. In 1998, the earliest pelagic life stages of fish larvae (eggs, yolk-sac larvae) and the copepod Eurytemora affinis, an important prey of feeding larvae, apparently were retained in deep, landward-flowing water within the salt front and ETM region. Statistical analyses indicated that distributions of white perch and striped bass post-yolk-sac larvae were associated with E. affinis distributions and suggested that retention of larval fish could result from tracking prey. Comparing fixed-station and mapping approaches demonstrates the importance of sampling at different spatial scales within the ETM region and suggests that larvae are faced with trade-offs between selecting zones of high retention or high visual-feeding success. [ABSTRACT FROM AUTHOR]

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]