Distribution and abundance of larval tunas (Scombridae) associated with the Loop Current, pelagic Sargassum, and oceanic frontal zones in the Gulf of Mexico

Information is lacking on the distribution and abundance of tuna larvae in relation to their seasonal occurrence at oceanic pelagic habitats in the northern Gulf of Mexico. Atlantic bluefin (Thunnus thynnus), yellowfin (Thunnus albacares), blackfin (Thunnus atlanticus), and unidentified tuna larvae (Thunnus spp.) were collected during a 2000-2003 investigation of larval and juvenile fishes associated with pelagic Sargassum and oceanic frontal zones in the northern Gulf of Mexico, as well as with the Loop Current. Tuna larvae (n = 380) occurred in 49% (n = 77) of the collections taken during the study (n = 158). Larvae were collected from surface and subsurface waters by neuston net (505 mu m), bongo net (333 mu m), and Tucker trawl (333 mu m). Sampling occurred only during day time, and tuna larvae were not collected shoreward of the 300m isobath. Mean abundance of bluefin larvae (3.4 - 8.6 mm; n = 124) was highest in collections from the Loop Current boundary and were collected only in May, providing further documentation of a compressed spring spawning season for this species in the Gulf of Mexico. Larvae of yellowfin (3.7 - 7.9 mm; n = 18) and blackfin tuna (3.6 - 7.3 mm; n = 47) were present in northern Gulf collections at Sargassum and frontal zones (none from the Loop Current) from May through August of all years, indicating a protracted spawning season in the region for these species. No tuna larvae were collected in fall and winter. Unidentified larvae (Thunnus spp.) require further examination for purposes of species identification. Continued research is critical to advance the scientific understanding of the biology, ecology, and habitat requirements of young tunas in the northern Gulf of Mexico.