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Black sea bass undergo seasonal movements from coastal habitats to offshore waters in the autumn, with a return migration during spring months. Our knowledge of the migratory patterns has been based upon seasonal distribution information gathered from NEFSC survey and fishery data, however, little is known about offshore mixing among the coastal components of the population.
After completion of our first full year of tagged black sea bass recaptures, we have been able to observe several trends in the data reported. Our overall release range (Cape Cod, MA to Cape Hatteras, NC) has been divided into four regions to examine differences in movement as you change latitude over the range; within each region, recaptured tags were grouped according to the number of days at liberty. Distance traveled and linear angle of movement were calculated based on the release and recapture coordinates, and vectors were formed for each region based on five periods of liberty (see the key below). It should be noted, for consistent comparison, only tags released during the fall seasons were used in the development of these vectors. In this case the "Days at Liberty" periods can be approximated in months and have been shown in parenthesis on the key.
The colored diagrams to either side of the Vector Coloring key below, demonstrate the expected vector pattern for the listed type of movement. The Random Movement diagram shows short distance movements over time, with little directionality; there is no indication of a migratory behavior. When examining the expected pattern for Seasonal Migration, there is little movement shortly after release followed by directional movements. In this 'ideal' example, we are able to see that fish released in late September show steps of movement away from their release location (in this example SSE) and after 225 days at liberty they begin movement back towards their coastal residence location. The following maps describe the trends found within the regions and how average movements change as days at liberty increases. The black circles represent a 25 nautical mile radius from the origin to present a sense of scale for the map and the average distance traveled by the fish during an interval.
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New England Region (MA, RI, CT)
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Long Is./Northern New Jersey Region
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Cape May Region (sNJ, DE, MD, nVA)
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Virginia Beach Region
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Several patterns become apparent when these maps are compared and contrasted. As latitude decreases, the mean distance traveled also decreases. In support of this pattern, the movements also contain less directionality and appear more random throughout their time at liberty. The black sea bass released from New England move the furthest distance with distinct southern and western components in their migration. At the other end of our release range, fish released off Virginia Beach, show some directionality to the south and east, but the distances they travel are much smaller and more uniform throughout the year.
The northern portion of the stock moves long distances with a distinct seasonal migration while southern region fish move shorter distances with no apparent migration to a winter residence. These observations are based on one year's collection of data (fish released in September 2002 and recaptured before December 2003). The Black Sea Bass Tagging Project continues to collect data on a weekly basis and will contribute additional observations as the data becomes more complete. Vectors shown above are based on preliminary data and will become more detailed with additional recapture reports.
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