Assessing linkages between petroleum platforms and pelagic fishes using telemetry, with emphasis on blue runner (Caranx crysos).

Abstract

Petroleum platforms number greater than 4,200 in the Gulf of Mexico and Caranx crysos (blue runner) is one of the most abundant fish species around these platforms. Forty-six blue runner were tagged with acoustical transmitters in August 2005, though the study was terminated prematurely due to the impending arrival of Hurricane Katrina. Nineteen blue runner were tagged in September 2006 and tracked for up to two months. Blue runner exhibited limited site fidelity around the platforms in 2005. The home range of twenty-three blue runner was calculated in 2005. A significant difference was found between the fork length of the fish and their overall 50% range, but their overall 95% range. The reverse was true when comparing mean daily ranges and fork length. The daytime core ranges were generally larger than the nighttime core ranges, though not significantly so. In 2006 tagged fish were released at unmanned platforms and all but one returned to the main complex and remained there over the course of the study period. The size of blue runner schools was estimated to be 36m. They were found to school more during the day than at night and moved between schools showing no preference for schooling with a particular fish. The blue runner showed a distinct diel vertical migration pattern with a marked descent to about 25m at night and ascent to the surface in the morning. The rate of ascent was significantly greater than the rate of descent. There was no relationship between these rates, the amplitude of migrations and maximum nightly depths with the lunar periodicity. There was a significant difference between the nighttime distribution of blue runner at the unmanned platforms and the manned platforms with fish at the unmanned platforms having a greater mean depth. The swimming speeds of tagged blue runner were greater during the day than at night and were indicative of passive foraging behavior. The lighted manned platforms appear to allow for greater foraging opportunities at night than the unmanned platforms.