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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]