摘要:

Stocks of striped bass Morone saxatilis have declined in the Chesapeake Bay system over the last decade. We present evidence for the working hypothesis that the decline has resulted, in part, from loss of deep-water habitat for adults, caused by limiting concentrations of dissolved oxygen that are related, in turn, to nutrient enrichment and greater planktonic production. A related hypothesis is that changes in the near-shore habitat for juvenile striped bass, involving severe declines in submerged aquatic vegetation due to nutrient-driven planktonic shading, also have contributed to the decline of striped bass. Nutrients (nitrogen and phosphorus) and chlorophyll a, an indicator of phytoplankton biomass, have increased in many areas of the bay and tributaries over the past 20 to 30 years. These trends are qualitatively correlated with greater deoxygenation of the deep channel in the mid and upper bay. During the late 1970s, summer oxygen concentrations as low as 2 ml/liter approached to within 7–8 m of the surface, allowing water stressful to striped bass to intrude onto shoal areas of the bay. The volume of Chesapeake Bay bottom waters containing 0.5 ml O2/liter or less was about 15 times greater in July 1980 than in July 1950. The combination of the expanding hypoxic pool and summer temperatures above preferred levels for adult striped bass may contribute to an “oxygen-temperature squeeze” that forces adults onto shoal areas of the bay or out of the upper bay. Many of these shoal areas now lack suitable cover for juvenile striped bass and their prey. Strong intraspecific competition among striped bass may be occurring there.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1985)114<97:NEOCBA>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

Decreased survival of larval striped bass Morone saxatilis resulting from toxic chemicals in the environment and decreased survival of adults caused by fishing both are suspected as agents contributing to the decline in the Chesapeake Bay stock since the mid-1970s. The relative power of each type of mortality to cause population declines was evaluated with simulation techniques. Equivalent levels of added mortality induced qualitatively identical and quantitatively similar trends in population simulations for all conditions examined except if strong density-dependent mortality preceded the contaminant toxicity. In this case the contaminant effect caused a greater reduction in yield, but the population did not tend toward extinction. The results indicate that the observed downward trend in the Chesapeake Bay population can be halted or reversed by a reduction in fishing mortality, even if contaminant toxicity is the proximate cause for the decline.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1985)114<107:TMFAEV>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

Swimming stamina and indices of bodily condition were compared among young-of-the-year striped bass Morone saxatilis from the Hudson River, the Potomac and Nanticoke rivers (tributaries of Chesapeake Bay), and three hatchery stocks. Hudson River fish showed one of the poorest swimming performances, Potomac River fish the best. Wild fish as a group differed from hatchery fish as a group in the biochemical compositions of their livers and muscles, but this probably was related to their respective diets. The bones of wild fish generally had lower density, strength, and structural integrity than those of hatchery fish. Among wild fish, those from the Hudson River were exceptional for their high liver-weight: Body-weight ratio, low liver DNA and muscle protein concentrations, high liver (but average muscle) RNA:DNA ratio, poor bone quality, and heavy infestation with cestode larvae, the last being associated with extensive loss of muscle bundles. From previous work, Hudson River striped bass are known to have higher body burdens of chlorinated hydrocarbons, polychlorinated biphenyls, heavy metals, and other contaminants than fish from the Potomac or Nanticoke rivers. A direct cause and effect has yet to be established, but we suggest that the symptoms of poor condition observed in Hudson River striped bass are consistent with exposure of these fish to stress from environmental contaminants.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1985)114<114:CSSBCB>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

Groups of striped bass Morone saxatilis eggs from several parental sources differed in their concentrations of HCB (hexachlorobenzene), DDTs, PCBs (polychlorinated biphenyls) and chlordanes. Survival of both starved and fed larvae was inversely related to concentrations of chlorinated hydrocarbons in these eggs. Changes in body burdens of these organochlorine compounds were calculated among larvae fed Artemia nauplii containing distinctive organochlorine residues. Accumulation from dietary sources of the organochlorines was more pronounced in larvae hatched from eggs with low parental contributions of chlorinated hydrocarbons. Among these larvae, body burdens increased in rough proportion to the cumulative amount of food-borne contaminant ingested. Accumulation rates were highest for DDTs, followed by PCBs, chlordanes, and HCB. In larvae with high initial concentrations, however, only DDTs showed accumulation during the feeding period.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1985)114<125:EOPADO>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

Surveys of larval striped bass Morone saxatilis and zooplankton in the Potomac River upper estuary were made in 1981. In addition to distribution and abundance, nutritional state of larvae was assessed by morphometric, histologic, and two biochemical techniques: RNA:DNA ratio and fatty acid composition and concentration. All four techniques gave evidence of poor nutritional state early in the season but not later. Analyses of distribution indicated a significant correlation among nutritional indices and copepod and cladoceran densities.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1985)114<137:IOFSTN>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

A mathematical technique was developed to examine interrelationships among first-year survival rates, adult fecundity, and adult survival of striped bass Morone saxatilis based on indices of year-class strength. Application of this technique to striped bass in Maryland waters of the Chesapeake Bay provided evidence for reduced survival in the life cycle. If adult fecundity and survival have remained constant, first-year survival declined significantly from 1969 to 1983, and averaged less than that needed for replacement for the last 10 years. Treatment of the individual spawning grounds separately indicated that the downward trend in survival for the pooled data was the result of declines in the upper bay and, to a lesser extent, in the Choptank River. Alternatively, if first-year survival and adult fecundity were assumed to have remained constant, an annual decline of about 1.9% in adult survival would have been required to produce the observed trend in the pooled year-class data. This would be consistent with increased fishing mortality and implies declining recruitment because of declining stock size. Continuing declines in first-year or adult survival would eliminate the Maryland striped bass stock and the fishery it supports. Conversely, an increase in adult survival could offset the effect of the unknown factor or factors responsible for the apparent decline in first-year survival.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1985)114<146:MSB>2.0.CO;2

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

ISSN:0002-8487    

DOI:10.1577/00028487.1985.10493237

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor