Yellow perch stocks in many rivers systems in Maryland's portion of the Chesapeake have declined in recent decades. Rigorous assessment of aquatic habitat health from an ecosystem approach is emerging as a new technique to manage resources. Changes in habitat quality and quantity caused by human impacts are likely to be responsible for at least some declines of aquatic organisms. In particular, impacts that diminish water quality in the watershed can reduce survival during critical life history stages and thus, reduce abundance. Evaluation of survival of egg/larval, juvenile, sub adult and adult fish can be used to determine factors that limit stock abundance.
Stocking marked fish can also be used to collect valuable stock assessment information from the population. Many commonly employed mark-recapture strategies employed in fisheries management lend themselves to this type of assessment. Stocking multiple sizes/ages of fish (larval, juvenile) enable evaluation of survival for these life stages. Survival can be affected by specific habitat/water quality variables. This data can be used to evaluate impediments to recruitment caused by degraded water quality or the environment. Learning how human-induced changes affect recruitment to the population can focus mitigation attention to remedy adverse impacts and improve the habitat.
Selection of tributaries that could benefit from restoration is critical. The tributary must have once had suitable habitat to support the various life history stages of the organism. Selection should be done based on historic and current data on the status of the population. Two rivers that lend themselves to this are the Severn River and South River. These rivers once supported abundant populations of yellow perch. Historic scientific information on the populations exists and current surveys are conducted there on the occurrence of perch in these rivers. Development has been heavy in these watersheds and may significantly affect water quality of the habitat. Evaluation into the quality and potential productivity of these developed watersheds can be valuable as we try to develop an ecosystem approach to managing aquatic resources and fish populations.
Maryland DNR Fisheries Service Hatcheries Division conducted a pilot project for restoration of Severn River and South River yellow perch during the spring of 2001. This included the development of reliable production and marking techniques to produce fish for stocking and to assess the impacts of stocking efforts. Techniques included induced spawning of adult yellow perch using hormonal stimulation, oxytetracycline (OTC) marking trials to determine optimal doses for effective marking, the culture of several ages/sizes of perch for stocking and development of methods to uniquely mark fish stocked at different sizes.
In order to enhance and evaluate river ecosystems we initiated a five-year stocking program starting in 2002. Pre-spawned adults were collected from fyke nets set in targeted tributaries. Adults were transported to Manning State Hatchery and induced to spawn in tanks. Perch were marked and stocked as larvae and juveniles in the Severn River and South River. Approximately 600,000 larvae and 400,000 juveniles were released into these tributaries.
After stocking, a monitoring program was conducted in both watersheds to collect yellow perch. Sampling was conducted over the range of occurrence for juveniles beginning immediately following each stocking event. Approximately 450 yellow perch that were captured in the survey were analyzed to determine hatchery or natural origin. Results indicated that the hatchery fish had good survival to juvenile size. The contribution of wild perch and those stocked as larvae and juveniles were used to determine parameters, such as survival and abundance, using mark-recapture models. These sampling efforts were useful to assess the population status in these rivers and integrate information into data collected concerning the watershed ecosystem health.
Results of the investigation indicated that the major impediments to successful yellow perch populations on the Severn and South rivers are poor recruitment and low juvenile indices. This is due the associations with impervious surface and development with yellow perch health. Until these issues are addressed the successfulness of corrective stocking will be limited. The hatcheries division does not currently stock yellow perch in Maryland waters.