A high prevalence of intersex or testicular oocytes (TO) in male smallmouth bass within the Potomac River drainage has raised concerns as to the health of the river. Studies were conducted to document biomarker responses both temporally and spatially to better understand the influence of normal physiological cycles, as well as water quality and land-use influences. Smallmouth bass were collected over a 2-year period from three tributaries of the Potomac River: the Shenandoah River, the South Branch Potomac and Conococheague Creek, and an out-of-basin reference site on the Gauley River. The prevalence of TO varied seasonally with the lowest prevalence observed in July, post-spawn. Reproductive maturity and/or lack of spawning the previous spring, as well as land-use practices such as application of manure and pesticides, may influence the seasonal observations. Annual, seasonal, and site differences were also observed in the percentage of males with measurable concentrations of plasma vitellogenin, mean concentration of plasma vitellogenin in females, and plasma concentrations of 17β-estradiol and testosterone in both sexes. Bass collected in the South Branch Potomac (moderate to high prevalence of TO) had less sperm per testes mass with a lower percentage of those sperm being motile when compared to those from the Gauley River (low prevalence of TO). An inverse relationship was noted between TO severity and sperm motility. An association between TO severity and wastewater treatment plant flow, percent of agriculture, total number of animal feeding operations, the number of poultry houses, and animal density within the catchment was observed.

The paper brings together major inferences from: (1) classical limnology—lake and stream typology, the role of major abiotic variables; (2) fisheries limnology—Ryderˈs morphoedaphic index, Jenkinsˈ reservoir findings, concepts of habitat niches; (3) studies of ecological structure of communities—succession, diversity, stability, variability, regulation; (4) recent developments concerning the effects of major cultural stresses on fish communities. A model is proposed to interrelate these and other concepts, and then relate them all to conventional fisheries practices and objectives. The model is directed at events and processes at the community level of organization and it is argued that much of fisheries theory and management practices of the future will perforce need to be directed at the community level.

A small ultrasonic fish tag is described, which is useful in studies of the game and pan fishes of freshwater lakes. The device emits a continuous signal of from 14 to 20 hr duration, at a frequency of 65 kilohertz. With the receiving equipment described, 37 white bass, Roccus chrysops (Raf.), have been successfully tracked in Lake Mendota for periods up to 13 hr. A study of the frequency of recapture of spawning white bass, marked with “dummy” transmitters in various ways, suggested that implantation in the stomach provided the more satisfactory tagging procedure. Of 672 fish tagged in various ways, 8.1% of those tagged externally, 6.2% of those with the tag implanted in the body cavity, and 18.8% of those with the tag placed in the stomach were recovered. In comparison, 17.5% of those marked with a hole punched in the soft dorsal fin were recaptured.

Timeliness in estimating fishery potentials seems more important than precision, at least in the earlier periods of development of specific fisheries. Comparative studies of several sets of lakes, particularly of those supporting developing fisheries in Africa, suggest that potential yield may be related to several simple indices of production. The morphoedaphic index, derived from measures of total dissolved solids and the mean depth, has provided the simplest and most general approach to the problem of initial estimates of potential yield in lakes and reservoirs. Other methods of relating yield to nutrient concentration and primary production reinforce the concept of the dependence of potential yield on lake productivity. During the developing phase of a fishery more direct methods of estimating potential yield, through estimates of the production of the extant stocks, are also being used with some success. These have been adapted from fishery models developed for single stocks. In keeping with the need for rapid assessments during development, the simplest models have been emphasized. An equivalence between production and the product of biomass and mortality rate, along with the assumption that from 30 to 50% of the production of a stock is potentially harvestable, appears particularly useful. The problem of additivity of the potential yields of individual stocks seems relatively unimportant in first-order estimates, though the question of interactions is being examined, particularly in Lake Tanganyika. Programs of monitoring relative abundance of stocks over time have also been useful, both in indicating the approach of actual yield to potential yield and, after "calibration" against actual yields, as indices of stock and total biomasses.

In the spring and summer of 1965, 26 white bass, Roccus chrysops (Rafinesque), were displaced to open water on Lake Mendota, Wisconsin, and their paths traced by means of ultrasonic transmitters carried in the stomachs of the fish and receiving gear located on boats. Seventeen fish captured by fyke nets on their spawning ground were displaced 1.6 km west-southwest to a mid lake release point. Two months after the spawning season nine fish, captured by hook-and-line, were displaced 3.1 km east-northeast from their capture area to the same release point. The mean tracking time for all 26 fish was 7.31 hr.Both the spawning and nonspawning fish maintained steady courses over long distances, and both groups showed a distinct directional preference for the eastern half of the lake where the spawning grounds are located. This open-water orientation helps explain the rapid homing performance, observed in previous experiments, of displaced spawning white bass, and also demonstrates that white bass possess mechanisms for orienting to directional cues present in their natural environment.Water currents, wind-generated surface waves, and the sun were examined as possible directional cues used by the fish. Although there was some evidence supporting the use of each of these cues, the problem of orientation mechanisms remains obscure. It was determined, however, that the observed movements of the fish cannot be explained as simply passive drift by the water currents.

Available biological and hydrographic information on Lake Nasser was examined to provide guidelines for future development of the fisheries. Not enough consistent data were available to allow precise estimates of fishing-stock interrelations; however, an approximation of potential yield was derived from subjective evaluation of limnological characteristics of the lake. Morphoedaphic factors were utilized to establish a numerical expectation of yield in relation to other tropical lakes and reservoirs. Two other models based on estimated zooplankton biomass and an assumed net gain in productivity in Lake Nasser at the expense of a yield loss to the Mediterranean fishery provided order-of-magnitude agreement. Potential yield estimates for Lake Nasser (including its southern portion, Lake Nubia, Sudan) were 23,000 metric tons (MT) of fish annually, providing the reservoir fills to its expected maximum (180 m), or 12,000 MT if it remains at its 1973 level of about 160 m. These estimates are considered sufficiently reliable to guide future development of the fishery.There is little evidence to support the existence of stock overexploitation. Tilapia nilotica, however, the major species entering the fishery, has been subjected to potentially damaging fishing practices on its breeding grounds. These practices combined with water level drawdown, inadvertently timed to perturb Tilapia fry inhabiting the shallow nursery areas, may unduly stress a prime species largely responsible for the current success of the fishery.Management recommendations for the Nasser–Nubia Reservoir include a regular program of monitoring both stocks and harvest, especially for Tilapia. Development emphasis should be placed on improving the logistics of the fishery rather than increasing the number of fishermen, at least until the lake area expands substantially.