Importance of Juvenile Striped Bass Food Habits in the Potomac Estuary

132

Low dissolved oxygen concentrations, caused by density stratification of the water column and excess nutrient inputs, occur in many aquatic habitats. Laboratory experiments we conducted indicated that low dissolved oxygen has the potential to strongly alter the absolute and relative importance of a suite of estuarine predators of fish larvae. At dissolved oxygen concentrations 22 mg l-', predation on naked goby Gobiosolna bosc larvae by an important invertebrate predator of plankton in Chesapeake Bay [the sea nettle scyphoinedusa Chrysaora quinqueclrrha) increased. In contrast, at the same oxygen concentrations, predation by 2 vertebrate predators, juvenile striped bass Morone saxatllis and adult naked goby, decreased. Changes in consumption of larvae most likely resulted from impaired ability of larvae to escape the scyphornedusa, and decreased attack rates by adult and juvenile fishes. Fish predators increased gill ventilation rates even at oxygen levels higher than those leading to decreased predation. However, we could detect no comparable change in behavior of the sea nettle even at 1 mg 1-', the lowest oxygen concentration tested The observed changes in trophic interactions occurred at dissolved oxygen concentrations that are not lethal during short exposures, and that commonly occur in the Chesapeake Bay and other eutrophic estuaries during summer. Thus, low oxygen has the potential to cause significant changes in the importance of alternate trophic pathways in estuarine systems.

Section: Study Organismsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Effects of low dissolved oxygen on predation on estuarine fish larvae

Breitburg¹,

Steinberg²,

DuBeau³

et al. 1994

132

“…Although daily mortality of Chesapeake Bay fish larvae due to fish predation has not been estimated, mesocosm experiments (Cowan & Houde 1993) and field collections (e.g. Markle & Grant 1970, Boynton et al 1981 indicate that juvenile and small adult fishes are important consumers of fish larvae. For example, fish larvae (primarily naked goby) can, at times, comprise over 40% of the diet of juvenile striped bass Morone saxatiljs in Chesapeake Bay tributaries (Markle & Grant 1970, Boynton et al 1981.…”

Section: Introductionmentioning

confidence: 99%

“…Markle & Grant 1970, Boynton et al 1981 indicate that juvenile and small adult fishes are important consumers of fish larvae. For example, fish larvae (primarily naked goby) can, at times, comprise over 40% of the diet of juvenile striped bass Morone saxatiljs in Chesapeake Bay tributaries (Markle & Grant 1970, Boynton et al 1981. Two hypothetical fish predators are used in the simulations: 'sensitive' and 'tolerant' fish that differ in the dissolved oxygen concentrations that affect their predation rates and distributions.…”

Section: Introductionmentioning

confidence: 99%

Linking water quality to larval survival:predation mortality of fish larvae in an oxygen-stratified water column

Breitburg¹,

Rose²,

Cowan³

1999

Low dissolved oxygen concentrations can affect growth rates, distribut~ons and predatorprey interactions of aquatic organisms. Each of these potential effects is generally examined separately in laboratory and field studies. As a result, it is often difficult to determine the net influence of low oxygen on survival and which individual effect of low oxygen contributes most to mortality. We used a spatially explicit individual-based predation model to predict how effects of low dissolved oxygen on vertical distributions, predation rates, and larval growth combine to influence survival of estuarine fish larvae in a water colun~n where the subpycnocline (bottom) and pycnocline layers are subject to oxygen depletion We analyzed simulations involving 3 predators (scyphomedusae based on Chrysaora quinquecirrha, and fish that were relatively sensitive to, or tolerant of, low dissolved oxygen), water columns that dlffered in the relative thickness of the subpycnocline layer, and bottom dissolved oxygen concentrations ranging from < l mg 1-' to no-effect concentrations. The effect of dissolved oxygen on larval and predator vertical &stributions, predator capture success and larval growth rates In simulations were based on previous experiments and field sampling in the Patuxent River, a tributary of the Chesapeake Bay. USA. Simulations indicated that bottom dissolved oxygen can strongly affect predation mortality of fish larvae. Thus, there is the potential for eutrophication to have a large effect on larval fish survival, and possibly recruitment, even in the absence of direct effects of low oxygen-induced mortality of larvae or the effects of nutrient enrichment on the abundance of larval prey or predators. Depending on predator characteristics and water column depth, lowest larval survival occurred when oxygen concentrations were either < l mg I-' or sufficiently high that oxygen concentratlon had no effect on distributions or capture rates; hlghest survival generally occurred with hypoxic bottom layers (1 to 2 mg 1-' dissolved oxygen). Bottom dissolved oxygen concentration also strongly affected the relative importance of fish and sea nettle predation in simulations that included both types of predators. Differences among predator types had important consequences for the magnitude and location of predation. Bottom-layer oxygen depletion shifted the focus of trophic interactions into the pycnocline and surface layers. Additional simulations indicated that distributional and capture success effects on larval survival were more important than growth rate effects, and that the direction of effects depended on the predator type and dissolved oxygen concentrations. Limitations of the model as well as implications of results for efforts to reduce nutrient loadings into estuaries are discussed.

“…These fish are top predators in coastal systems, feeding on aquatic invertebrates at small sizes, but generally becoming more piscivorous with age (Boynton et al 1981, Gardinier and Hoff 1982, Rulifson & McKenna 1987, Hartman & Brandt 1995a. Further, striped bass may be important in controlling populations of prey species (Hartman & Brandt 1995b) and shortages of appropriate-sized food have been suggested as a reason for coastal migration of adult striped bass in Chesapeake Bay (Hartman 1993).…”

Section: Introductionmentioning

confidence: 99%

The influence of size on striped bass foraging

Hartman¹

2000

Striped bass Morone saxahhs is an abundant piscivorous fish in estuaries and coastal systems along the US Atlantic coast and has also been stocked into systems in Cahfornia and the continental US. Despite the widespread distnbution of striped bass and their relative importance as a predator in these systems, little is known about how relative size of prey affects their prey capture success. This study measured the capture success and handling times of striped bass fed live shiners Notropis athennoides and N. chrysocephalus and the results are expressed in terms of size (prey-to-predator size ratio, PPR). Striped bass capture success declined with increasing PPR. It was best described (p < 0.01) by the equation: attack success = 0.861-1.82PPR. Handling time (h) increased with increasing PPR (p < 0.01) and was described by the equation: h = 0 . 3 3 9 e " .~~~~. Comparison of prey profitability curves showed that the relative size of prey suggested as most profitable (mass/time) was similar to that found in the stomachs of wild striped bass in Chesapeake Bay from 1990 to 1992. The peak in frequency of PPR from stomachs occurred at PPR = 0.12 (mean PPR = 0.14) and was identical to the peak in profitability from model results (PPR = 0.12), although both the diet PPR and model profitability distnbutions were skewed towards larger relative prey sizes. Comparison of the results of this study with a simliar study for small bluefish suggests that profitable prey sizes for striped bass overlap with those of much smaller bluefish.