Douglas S. Vaughan

Estimating Improvement in Spawning Potential Ratios for South Atlantic Red Drum through Bag and Size Limit Regulations

Abstract Based on a recent stock assessment of red drum Sciaenops ocellatus along the southern U.S. Atlantic coast (South Carolina to Florida), we calculated the possible gains in the static spawning potential ratio (SPR) from fishing mortality reductions (savings) produced by changing slot (size) and bag limits. Our method for calculating savings provides flexibility to address differences in commercial and recreational fishery regulations, regional stock conditions, and specific gear characteristics, and to account for discard mortality. Gear- and age-specific estimates of fishing mortality rates (F) for 1992–1997 resulted in savings from recreational fishery bag limits given a particular slot size. Relative changes in catch-at-age estimates modified the age-specific F estimates and, hence, the calculated SPR values. Additionally, recreational savings was adjusted to account for a release mortality of 10%. Static SPRs were estimated for (1) bag limits with increasing minimum size limits and a fixed maxi...

Biomarkers, natural variability, and risk assessment: Can they coexist?

Abstract This paper is a discussion of the utility of biomarkers as a component of the ecological risk assessment process. Both the pros and the cons of biomarkers are discussed, as well as consideration of some of the sources of variability. In the end, biomarkers are considered useful as long as we are aware of their limitations and sources of uncontrolled variability.

Forecasting Annual Harvests of Atlantic and Gulf Menhaden

Abstract Continuous records of annual landings and fishing effort exist in the Atlantic purse-seine fishery for Atlantic menhaden Brevoortia tyrannus since 1940 and the Gulf of Mexico fishery for Gulf menhaden B. patronus since 1946. Currently, year-ahead forecasts of landings from these species-specific fisheries separated by the Florida peninsula are provided to the industry by means of multiple-linear-regression models that relate landings and effort over the data series. Here, we compare three methods for this purpose—multiple regression, time series, and artificial neural networks—to determine whether forecast accuracy can be increased. Best-fit models were developed with each method for each fishery, and then 10-year retrospective analyses of 1-year-ahead catch forecasts were compared among the three methods. In general, multiple-regression and artificial neural network models were similar in their fit to the data series and both were better than time series models, judging from the Akaike informati...

Assessing Coastwide Effects of Power Plant Entrainment and Impingement on Fish Populations: Atlantic Menhaden Example

Abstract A method was developed for assessing coastwide effects of power plant impingement and entrainment on managed fish stocks. The method imbeds an assessment of anthropogenic effects that occur during the first year of life of fish (the period when most entrainment and impingement occur) into a standard age-structured stock assessment that addresses age-1 and older fish. The method thereby provides a straightforward means for comparing the effects of entrainment and impingement mortality to other forms of anthropogenic mortality affecting coastwide fish stocks. The method uses standard equations from fishery science that represent the relationships among independent competing forces of mortality, stock abundance, and landings. Power plant mortality is treated like fishing mortality, and power plant losses are treated like fishery landings. The total age-0 natural mortality rate is allocated to the individual age-0 life stages based on a power function relating daily natural mortality rates to age-spe...

Impact of impingement on the Hudson River white perch population. Final report

The impact of power plant impingement on the 1974 and 1975 year classes of the Hudson River white perch population is assessed using a simple model derived from Rickers theory of fisheries dynamics. The impact of impingement is expressed in the model as the conditional mortality rate, rather than as the more commonly used exploitation rate. Since the calculated impact is sensitive to errors in the estimation of population size and total mortality, ranges of probable values of these quantities are used to compute upper and lower bounds on the fractional reduction in abundance of each year class. Best estimates of abundance and mortality are used to compute the conditional impingement mortality rate separately for each plant and month. The results are used to assess the relative impacts of white perch impingement at six Hudson River power plants and to identify the seasons during which the impact is highest.