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R.M. Dorazio

Publications and source records attributed to R.M. Dorazio.

29 records · Page 2Linked to original sources
USGS1993

Prerelease stratification in tag-recovery models with time dependence

A statistical model is developed for estimating time-dependent survival and recovery rates of tagged populations that are stratified into groups at release. For populations of fish, the groups might include different sexes or stocks, or they might be distinguished by the location or method of capture. In the model developed here, survival and recovery rates are formulated as linear combinations of parameters that include the effects of time, group, and time–group interactions. Methods of testing the statistical significance of these potential sources of variation are described and illustrated with the recoveries of different stocks of anadromous striped bass ( Morone saxatilis ). For the striped bass data, elimination of time- and stock-specific sources of variation substantially improved the precision of survival estimates without introducing important bias. During 1988–89 the average survival of both stocks was 0.78 ( SE = 0.04). Calculations of statistical power indicate that stock-specific differences in survival of ± 0.2 could have been detected about 50% of the time, given the low rates of recovery and numbers of fish released.

Canadian Journal of Fisheries and Aquatic Sciences↗
USGS1991

Evaluation of a mark-recapture method for estimating mortality and migration rates of stratified populations

We simulated mark–recapture experiments to evaluate a method for estimating fishing mortality and migration rates of populations stratified at release and recovery. When fish released in two or more strata were recovered from different recapture strata in nearly the same proportions, conditional recapture probabilities were estimated outside the [0, 1] interval. The maximum likelihood estimates tended to be biased and imprecise when the patterns of recaptures produced extremely "flat" likelihood surfaces. Absence of bias was not guaranteed, however, in experiments where recapture rates could be estimated within the [0, 1] interval. Inadequate numbers of tag releases and recoveries also produced biased estimates, although the bias was easily detected by the high sampling variability of the estimates. A stratified tag–recapture experiment with sockeye salmon ( Oncorhynchus nerka ) was used to demonstrate procedures for analyzing data that produce biased estimates of recapture probabilities. An estimator was derived to examine the sensitivity of recapture rate estimates to assumed differences in natural and tagging mortality, tag loss, and incomplete reporting of tag recoveries.

Canadian Journal of Fisheries and Aquatic Sciences↗
USGS1991

Stocking of hatchery-reared striped bass in the Patuxent River, Maryland: Survival, relative abundance, and cost‐effectiveness

Hatchery‐reared fingerlings of striped bass Morone saxatilis were tagged, stocked, and recovered in the Patuxent River, Maryland, to estimate their survival and abundance relative to wild young of the year and to compare the costs and benefits of stocking phase‐I (35–50 mm, total length) and phase‐II (150–200 mm) fish. About 100,000 phase‐I fingerlings were tagged and released each year during midsummer 1988 and 1989. Both tagged and untagged (wild) young of the year were recovered by alongshore seining in the river through 80 d poststocking. Mortality rates of wild and hatchery‐reared young of the year were not significantly different‐about 3%/d. Wild young of the year were more abundant in 1989 than in 1988. In 1988, phase‐I fingerlings composed 56% of all young‐of‐the‐year striped bass in the river. In 1989 wild young‐of‐the‐year striped bass outnumbered hatchery‐reared fingerlings by about 11 to 1. Whether phase‐I or phase‐II stocking was more cost‐effective depended on the relative magnitudes of fingerling survival and on hatchery production costs. The range of phase‐II survival (5–50%) observed among different hatcheries and years of production was too broad to support generalizations about cost‐effectiveness, given the fivefold difference in the unit costs of phase‐I and phase‐II production.

Maryland↗
USGS1990

Immunological discrimination of Atlantic striped bass stocks

Stocks of Atlantic striped bass Morone saxatilis that were assumed to be geographically isolated during spawning showed strong antigenic differences in blood serum albumin. A discriminant function was estimated from the immunologic responses of northern (Canadian and Hudson River) and southern (Chesapeake Bay and Roanoke River) stocks to two reference antisera. The function correctly classified 92% of the northern and 95% of the southern fish in the training set. Cross-validation revealed similar percentages of correct classification for fish that were of known origin but not used to estimate the discriminant function. Monte Carlo experiments were used to evaluate the ability of the discriminant function to predict the relative contribution of northern fish in samples of various size and stock composition. Averages of predicted proportions of northern fish in the samples agreed well with actual proportions. Coefficients of variation (100 × SD/mean) in the predicted proportions ranged from 1.5 to 36% for samples of 50–400 fish that contained at least 10% northern stock. In samples that contained only 2% northern stock, however, at least 1,600 fish were required to achieve similar levels of precision.

Transactions of the American Fisheries Society↗