A Larval Striped Bass Habitat Index for Chesapeake Bay Tributaries
A Larval Striped Bass Habitat Index (LSBHI) was developed to assess the suitability of annual environmental conditions in three Chesapeake Bay tributaries with the respect to recruitment of striped bass larvae. LSBHI values were calculated for the Potomac, Patuxent and Choptank Rivers for each year from 1986 through 2000, using Maryland water quality and zooplankton monitoring data from the Chesapeake Bay Program. The LSBHI is intended to provide an indicator of the quality and potential of each tributary’s striped bass spawning and nursery habitat for each year of available data. The LSBHI incorporates components of the Individual Based Model (IBM) of Rose and Cowan (1993) to score annual conditions with regard to initial spawning success, early survival of eggs and pre-feeding larvae, and feeding larval growth and production as a function of zooplankton availability. The annual LSBHI for a tributary is composed of three sub-indices, each calculated for regional semi-monthly cohorts: 1) a spawning sub-index, 2) an early survival sub-index, and 3) a zooplankton (food) availability sub-index. The spawning sub-index uses temperature and salinity data, as well as literature based relationships of these parameters to striped bass spawning to determine the suitability of the habitat for a successful spawn. The early survival sub-index uses temperature to assess the habitat with respect to egg and early larval survival. The zooplankton availability sub-index is based on a comparison of the available zooplankton (a function of zooplankton abundance and predator searching ability given relative sizes of predator versus prey and water clarity), the minimum food requirement based upon metabolic relationships, and the maximum consumption possible. To independently verify the LSBHI, annual values were quantitatively compared with annual juvenile abundance measures from beach seine surveys conducted by Maryland Department of Natural Resources. Application of the LSBHI was successful for the Potomac River (R=0.62, p<0.01), Patuxent River(R=0.55, p=0.03), but did not correlate well with the beach seine data for the Choptank (R=-0.14, p=0.61). Possible reasons for this lack of fit and recommendations for expanding the LSBHI to include additional factors (e.g. flow, pH) are discussed.