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Virginia Sea Grant funded research

Chesapeake Bay Striped Bass Mycobacteriosis: Should we care?

John Hoenig, Wolfgang Vogelbein (VIMS)

Our objectives are to: 1) determine prevalence and severity of internal and external mycobacterial lesions in striped bass in the Rappahannock River; 2) procure, photograph, measure and tag striped bass with and without mycobacterial lesions from the Rappahannock River, and hold them in a large enclosure (holding pen) until water temperatures drop to unfavorable levels; evaluate progression of the disease and note all mortalities; sacrifice remaining fish for internal examination and histopathology at the end of the field season; 3) measure, tag, and release approximately 800-1000 striped bass in the Rappahanock River; those fish with external lesions will be noted and photographed; obtain tag returns in order to estimate survival rates; 4) evaluate a model for estimating survival rates of fish with and without (visceral) mycobacteriosis and apply the model to project data to estimate survival rates; and 5) prepare manuscripts for publication and present results to management agencies.

Fifty small (18-22”) striped bass will be held in a large holding pen in the Rappahannock River during the autumn. Half will have external lesions consistent with mycobacteriosis and half will be asymptomatic. Progression of the disease and mortality rates will be monitored over the course of the study to determine impact of the disease. 800 to 1000 striped bass will be tagged and released in the Rappahannock River. Those fish (up to 30%) with mycobacterial lesions will be photographed before release. Relative and absolute survival rates will be estimated to determine impact of the disease on Rappahannock River striped bass.

Mortality rates of striped bass appear to be increasing but the causes of this increase are unclear. Three possibilities include increased fishing mortality, increased natural mortality due to mycobacteriosis, and increased natural mortality due to lack of forage food. If the increase in mortality rate is due to fishing, then the mandated response is to regulate the fishing mortality. Therefore, the nature of the mortality has immediate management implications. Mycobacterial infections of striped bass in Chesapeake Bay are becoming more common, with some fish exhibiting emaciation and skin lesions. Striped bass are an important component in the Chesapeake Bay ecosystem and represent a valuable fishery resource. Therefore, it is important to understand whether mycobacteriosis is a major factor in determining population productivity, ecosystem dynamics, and appropriate management measures. This project is designed to answer the question of antifying mortality rates associated with the disease.