Abstract
The preferred thermal habitat for juvenile Atlantic bluefin tuna (Thunnus thynnus thynnus), ages 1 - 4, has been determined from analyses of behavioral, hydrographic, and catch data derived from bluefin (ABT) fisheries in the Middle Atlantic Bight (MAB) from 1976 through 1982. The data indicate that both inter-seasonal and intra-seasonal changes in catchability (availability and vulnerability) are affected by the dynamics of the preferred habitat and that catch-per-unit effort (CPUE) data are valid indices of ABT concentration or catchability. Use of CPUE with constant or random catchability results in biased estimates of ABT stock abundance, especially when environmental conditions vary. Inter-seasonal changes in the geographic location of the center of apparent abundance and duration of the various fisheries for ABT from North Carolina to Rhode Island has been interpreted as being a function of the location and condition of the preferred temperature habitat. It appears that relatively cool summers favor the southern fisheries of Virginia and North Carolina and that relatively warm summers favor the northern fisheries of New Jersey, New York and Rhode Island. Since sea surface temperature (SST) is a proxy indicator for the location of the sub-surface preferred habitat, one can monitor the habitat from satellite infrared (IR) data and use the IR and other data to derive models which result in forecasts of the onset, location, and duration of the various ABT fisheries in the MAB.Daily changes in the distribution, concentration, and CPUE of juvenile ABT in the Virginia Beach, Virginia fishery followed the ephemeral changes in the off-shore location, history, and temperature gradients of the Chesapeake Bay plume frontal zone. The effect of bottom topographic features and SST fronts on CPUE were profound, especially when horizontal SST gradients were located within the Rossby radius of internal deformation. The results suggest that the optical characteristics of the water (transparency and chlorophyll concentration) play a greater role in influencing the distribution and relative apparent abundance of tunas than previously thought.Synoptic scale SST data derived from NOAA-series satellites were essential for monitoring the location and orientation of the Chespeake Bay plume frontal zone in relation to observed changes in the fishery. The utility of the Coastal Zone Color Scanner (CZCS) on the NIMBUS satellite could not be extensively evaluated in this research due to problems of obtaining usable data for the Virginia coastal waters for the 1979 and 1980 fishing seasons.