C. Phillip Goodyear

Assessing the Impact of Power Plant Mortality on the Compensatory Reserve of Fish Populations

ABSTRACT A technique is presented to quantify the concepts of compensation and compensatory reserve in exploited fish populations. The technique was used to examine the impact of power plant mortality on a hypothetical striped bass population. Power plant mortality had a more severe impact on the compensation ratio and compensatory reserve for an exploited stock than for an unexploited stock. The technique can be applied to determine a critical compensation ratio which could serve as a standard against which additional sources of mortality, such as those caused by power plants, could be measured.

On the Ability to Detect the Influence of Spawning Stock on Recruitment

Abstract Simulated observations of spawning stock size, recruitment, and two random environmental variables were obtained from a density-independent Leslie matrix model. Recruitment to Age 1 was directly proportional to population fecundity but strongly influenced by the effects of the random environmental variables. The simulated observations were subjected to multiple regression analysis which detected the influence of the random environmental variables but did not reliably detect the influence of spawning stock. These results indicate that multiple regression is unreliable in detecting the influence of stock on recruitment when annual variations in recruitment are primarily due to environmental factors.

Relationship between reported commercial landings and abundance of young striped bass in Chesapeake Bay, Maryland

Abstract The ability to predict subsequent landings of striped bass Morone saxatilis from the indices of abundance of juveniles (young of the year) determined annually by the Maryland Department of Natural Resources was evaluated by multiple-regression techniques. About 57% of the variation in reported landings could be accounted for by the juvenile indices 2, 3, 4, and 5 years prior to the year of the landings for the period 1959–1983. Elimination of the first 4 years of record (1959–1962) increased the R2 to 0.83. The regressions of reported landings on the indices of ages 2–5 striped bass for the periods 1964–1973 and 1974–1983 indicated that mortality in the fishable stock increased between the two periods. These results support the use of the juvenile indices for monitoring recruitment into the population and as a basis for management decisions.

Maryland Striped Bass: Recruitment Declining below Replacement

Abstract 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 ...

An Empirical Methodology for Estimating Entrainment Losses at Power Plants Sited on Estuaries

Abstract A model based on empirically derived age-, time-, and space-variant entrainment susceptibility data may be used for estimating conditional entrainment mortality of aquatic organisms, particularly fish and shellfish, caused by operation of one or more power plants on an estuary. Model application requires knowledge of the morphometry of the water body, the power-plant flow rates, the probability of entrainment survival, and the duration, distribution, and abundance of entrainable age-groups. A novel feature of the model is that organism distribution and movement within the model are defined by information derived from field samples rather than by hydrodynamic principles and equations.

Toxic Materials, Fishing, and Environmental Variation: Simulated Effects on Striped Bass Population Trends

Abstract 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.

Use of Catenary Geometry to Estimate Hook Depth during Near-Surface Pelagic Longline Fishing: Theory versus Practice

Abstract Management and conservation of many highly migratory fish species are based on population assessments that rely heavily on catch and effort data from the pelagic longline fishing industry. In 2003, we monitored hook time at depth for shallow-set commercial longlines (i.e., four hooks between surface buoys) targeting swordfish Xiphias gladius in the Windward Passage between Haiti and Cuba. We deployed temperature–depth recorders (TDRs) on about every 13th hook and attached them to branchlines just above the hook. Most TDRs were placed on branchlines that were predicted by catenary geometry to be at the deepest hook position between floats. Additional TDRs were also placed at the shallowest predicted hook position. We monitored 10 pelagic longline sets with a length (mean ± SE) of 44.9 ± 2.0 km. Time at depth for each TDR was binned into 5-m depth intervals. The expected bimodal distributions of hook time at depth were not observed; modes were 40 m for both the shallowest and deepest predicted hook...

Sun compass orientation of immature bluegill

Abstract Immature bluegills, Lepomis macrochirus (N = 389), were collected from Par Pond, a 1,120-hectare impoundment on the United States Department of Energys Savannah River Plant near Aiken, South Carolina, and tested individually by observing their directional movement from the center of a circular testing facility. Bluegills captured 10–20 m from shore in areas lacking extensive submerged vegetation swam in a direction which would have taken them to shore at the area of their capture, whereas those taken from areas having submerged vegetation offshore swam in the direction opposite from shore. The directional responses of fish that were phase-shifted by 6 hours demonstrated that they were using time-compensated sun orientation. Fish exposed to a predator oriented in the direction of shore in their training facility, but if no predators had been present during training, moved in the direction of deep water. Present evidence indicates that immature bluegills use their sun compass mechanism in oriented...

Effects of Mixed-Metric Data on Production Model Estimation: Simulation Study of a Blue-Marlin-Like Stock

Abstract An underlying assumption of surplus-production modeling is that the models two basic data streams (indices of abundance and records of catch) are expressed in the same metric, either biomass or numbers. For lack of data, that assumption is sometimes violated; recent assessments of blue marlin Makaira nigricans and white marlin Tetrapturus albidus in the Atlantic Ocean, for example, have used indices of abundance based on numbers with indices of catch based on biomass. We examined the effects of using mixed-metric data in production modeling. Our method was a simulation study based on the life history and fishery characteristics of blue marlin in the Atlantic Ocean. Populations were simulated over a range of growth patterns and with either increasing or declining abundance by the use of a simulation model incorporating sex, size, and age structure; sexually dimorphic growth; variation of size at age; age-varying natural mortality; and deterministic or stochastic recruitment. Simulated abundance d...

Oscillatory Behavior of a Striped Bass Population Model Controlled by a Ricker Function

Abstract The oscillatory properties of a striped bass (Morone saxatilis) population model controlled by a Ricker function were examined by plotting the value of the parameter alpha above which the population will oscillate with an amplitude equal to or greater than 1% of the equilibrium stock size. The value of alpha required for persistent oscillation was affected by the age distribution and the reproductive age structure of the model population. The most stable age structure was found to exist at an instantaneous mortality rate of about 1.0. The results support the notion that fluctuations in the abundance of striped bass stock are largely due to density-independent influences on survival.