A conceptual life history of the Atlantic croaker (Micropogonias undulatus) identifies the effects of the environment on juvenile recruitment. In a multi-disciplinary approach to modelling, the major effects are investigated, quantified and presented in a flow chart. The model is divided into three sub models, each representing a major component which affects juvenile recruitment. North/south spawning location in the Mid-Atlantic Bight is affected by the bottom water temperature as influenced by the cessation of the summer winds in relation to timing of croaker migration. The pelagic phase is the most critical time in the life history of a larval croaker as they are subjected to wind-induced transport which may cause direct loss off the shelf and entrainment in the Gulf Stream, or indirect loss by prolonging time in transit to the nursery area. The magnitude of this wind-included effect is a function of the direction, strength, duration and time relative to spawning and is incorporated in an equation to predict year-class strength of croaker. The juvenile croaker overwinter in the Chesapeake Bay system. Winter temperature is shown to be the predominant variable affecting year-class survival to the following summer in very cold years. However, in very warm years, the predictive capabilities of the model are improved when a measure of fall recruitment, i.e. wind-induced transport, is incorporated. Croaker is basically a density-independent stock as, juvenile recruitment is erratic and dependent upon these environmental parameters. The effect of spawning stock size is only apparent after accounting for density-independent effects, and slightly improves the explained variance of the statistical relationship. Year-class strength and fishing pressure cause interannual variability in commercial catch. Overfishing a weak year class reduce spawning potential, and several poor year classes in a row magnify this. The moel, tested for the 1982-83 data, predicts a strong year class.

Numerical classification analyses (clustering) of spring, summer and fall National Marine Fisheries Service bottom trawl catches on the inshore continental shelf between Cape Ann, Ma. and Cape Fear, N.C., showed consistent species associations and faunal zones over a three year period. Analysis of a data set created by combining all nine survey cruises also produced consistent species associations, however sites clustered by seasons as well as by geographic area. The three faunal provinces of the U.S. east coast (Gulf of Maine, Middle Atlantic Bight and South Atlantic Bight) were represented in the study area, as were the seasonal faunal barriers at Nantucket Shoals and Cape Hatteras. Generally, the faunal zones correlated well with the thermal regimes of each province and respected the faunal barriers when strong thermal gradients were present. Only south of Cape Hatteras did depth appear to define a boundary between faunal zones. During the spring, when bottom water temperatures were lowest, four species associations and three faunal zones were identified. The species associations consisted of a cold water boreal group (affiliated only with the faunal zone between Cape Ann and Cape May, N.J.), a less cryophilic boreal group, a eurythermal warm temperate group and a warm temperate group which was restricted to waters south of Cape Hatteras. With vernal warming, a northerly and onshore migration of warm temperate species increased to five the number of species associations in summer. Beside the four groups found in spring, a more thermophilic association was identified. Separations between the northern three summer faunal zones occurred at Nantucket Shoals and northern New Jersey. The other two summer zones were restricted to south of Cape Hatteras and were separated longitudinally (inshore and offshore). In fall, when bottom temperatures were highest, a sixth species group of primarily southern species was identified. This group appeared restricted to the inshore faunal zone south of Cape Hatteras. The five faunal zones recognized in summer were also identified in fall.

The effects of AroclorRTM1242 exposure on developing amphibians were examined by exposing southern leopard frogs, Rana sphenocephala, to a contaminated diet throughout the larval period. Treatment groups consisted of an untreated control, a solvent control, 17beta-estradiol, and three PCB doses (10, 100, and 1000 mug/g). PCB accumulation and biotransformation were examined. Effects of PCB exposure on metamorphosis and sexual differentiation were assessed. PCB accumulation was not statistically different between the egg masses. Levels of PCBs in the tissues differed in a dose related manner. Within treatments, body weight appeared to be the major factor correlated with PCB concentration. Congener patterns varied between AroclorRTM1242 and tadpole tissues. Hydroxybiphenyls were not detected in individual tadpoles, but were present in pooled samples. Mortality was similar among the treatment groups. The untreated food control had slightly higher mortality. The effects of AroclorRTM 1242 exposure differed between the egg masses. From the first egg mass, there were no treatment differences in the proportion of survivors metamorphosing. Treatment with 17beta-estradiol affected sexual differentiation relative to the controls. Exposure to AroclorRTM1242 had no effect. This may be due to the nature of gonadal maturation in this population, which was entirely female. In the second egg mass, PCB treatment was associated with an increased rate of metamorphosis in the highest dose. The high dose significantly (alpha = .05) altered sexual differentiation relative to the solvent control (88% female). This effect was similar to 17beta-estradiol treatment (94% female). Exposure to high and medium doses of PCBs produced five individuals with asynchronous gonads. The effect of body weight on PCB levels may be a result of greater ingestion of the contaminated diet by larger animals, relative to their smaller siblings. The apparent stimulation of metamorphosis in the second egg mass by PCB exposure may be due to an endocrine disrupting effect on the corticosterone "stress" axis. A thyroid-mediated mechanism of effect is also possible. While the effects on sexual differentiation may be due to estrogenic activity, a corticosterone-like effect cannot be ruled out. Higher level endocrine function, such as feedback regulation, could also be affected.

Laboratory experiments determined the effects of two levels of habitat complexity upon pipefish (Syngnathus fuscus) foraging for amphipods. Habitats were composed of equal densities of either narrow (low complexity) or wide (high complexity) leafed artificial seagrass. The response to habitat, as measured by rate of encounter with amphipods, probability of attack after encounter, probability of success after attack, and overall rate of amphipod consumption, was determined for combinations of two fish size classes and three amphipod size classes. Small fish did not experience visually inhibitive effects in either habitat, while large fish had their visual fields impinged upon in the wide leaf habitat and encountered fewer amphipods. There was a general trend for encounter rate to increase with amphipod size. Large fish attack probability was positively related to amphipod size in the narrow leaf habitat, but negatively related to amphipod size in the wide leaf habitat. Small fish attack probability was negatively related to amphipod size in both habitats. Success was negatively related to a ratio of prey size to fish size, and showed no overall effect of habitat. Pipefish have flexible behaviors, allowing them to minimize unsuccessful attacks. Due to their position in the structure of vegetation, amphipods have a distribution of vulnerabilities; a criterion by which pipefish select prey. Size-selective predation on gammarid amphipods by pipefish was examined utilizing simulation modeling and laboratory experimentation. Three computer simulation models were developed: (1) a mechanistic model based on empirically derived size-dependent mechanisms of pipefish-amphipod interaction, (2) an optimal diet breadth model in which the rate of energy intake is maximized, and (3) an optimal diet breadth model where switching from energy maximization to time minimization occurs as consumption becomes limited by gastric processing (i.e. satiation). None of these models successfully accounted for the observed pattern of prey size selection. Pipefish concentrated their feeding upon smaller, energetically more profitable amphipods, in excess of what was predicted by either the mechanistic or optimal diet breadth models. This pattern of selection was evident through out 4 hour feeding bouts, indicating that diet breadth compression did not occur.

Spatial management of marine resources requires population dynamic parameters in much greater spatial detail than traditional stock assessments provide. This dissertation presents a suite of methods to improve the spatial prediction of population abundance, fishing and natural mortality and to make greater use of commercial catch data. The main objectives of this dissertation are to determine the efficacy of using the vast amount of data collected by on-board observers on commercial vessels in model-based estimation of abundance and to use the spatial autocorrelation to improve resource mapping and abundance estimation. The first paper presents a methodology for improving variogram estimation when samples exist from multiple years or regions sharing a similar process for generating spatial autocorrelation. In both simulations and in real datasets of oyster abundance the method proposed here reduced the likelihood of failing to obtain a variogram from a set of samples and improved the efficiency of variogram estimation. The second paper presents a simulation of the efficacy of using biased samples for geostatistical predictions. By creating and sampling spatially-autocorrelated datasets in a manner similar to a commercial fishery we found that model-based geostatistics provided a means of obtaining relatively unbiased predictions of abundance using this data. The next paper used catches obtained by onboard observers in the scallop fishery in Georges Bank Closed Area II in 1999 to obtain geostatistical abundance estimates. We used Vessel Monitoring System (VMS) effort data to obtain tows with less than 10% of the total effort. These tows provided geostatistical estimates of initial scallop abundance similar to a preseason fishery-independent survey. Local differences between the observer and survey predictions were driven primarily by data gaps. The last paper obtained spatially-explicit DeLury depletion estimates of dredge efficiency and scallop abundance using VMS data to correct for the actual fished area. Corrected-area efficiency estimates ranged between 20 and 55% with a mean of 45% and maps of abundance closely matched fishery-independent survey estimates. These results indicate that the there is tremendous potential to incorporate commercial fishery data for the purposes of obtaining quantitative resource assessment information.

Five fishery independent data sets were used to investigate multispecies fish recruitment patterns in Chesapeake Bay (1966--1997). Despite differences in sampling gear, sampled habitat, collection methods, and sampling sites, the strongest multispecies recruitment patterns within each data set (revealed by separate principal components analyses) depict a negative relationship between recruitment of spring spawning anadromous fishes and fall-winter continental shelf spawning species. This pattern dominates both low and high frequency components of the multispecies data. Because these two species groups utilize freshwater and oligohaline reaches of the Bay and its tributaries as springtime nursery areas, this Chesapeake Bay Anadromous-Shelf Spawner (CBASS) recruitment pattern was compared to spring climatic variability in the Mid Atlantic region. Using principal components analysis, cluster analysis, and a gridded sea level pressure (SLP) data set, an objective circulation classification technique identified ten synoptic-scale SLP patterns responsible for spring (Mar--May) weather conditions and interannual seasonal climate variability. Classification and regression tree modeling, ordinary least squares, and least trimmed squares regression were used to compare covariability between the CBASS recruitment pattern and the thirty (3 months x 10 patterns) monthly frequency pressure pattern time series. March frequencies of two regional pressure patterns, the Azores-Bermuda and Ohio Valley high pressure systems, were found to account for a large portion of the CBASS pattern's variability. Spring conditions in March, brought on by an early appearance of the Azores-Bermuda High, favor recruitment of shelf spawners while prolonged winter conditions, brought on by a relative dominance of the Ohio Valley high, favor anadromous spawning success. These observations are supported by an analysis of March temperature and precipitation anomaly patterns for the continental U.S. Analyses of hydro-climatic, species specific zooplankton density, and juvenile fish abundance variables for three Bay tributaries demonstrate that the timing of the winter--spring transition differentially influences nursery area habitat suitability in a pattern consistent with the climate-CBASS recruitment relationships described in this study. The climate-recruitment relationships described in this study represent a multivariate variant of Cushing's Match-Mismatch hypothesis.

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