Abstract

Information on the reproduction of large pelagic fishes in the northern Gulf of Mexico is almost non-existent. Species such as blue marlin (Makaira nigricans), yellowfin tuna (Thunnus albacares) and bluefin tuna (T. thynnus) are captured by both commercial and recreational fishers in the northern Gulf. Blue marlin are taken during the summer (May - September), bluefin tuna are found from January through June and yellowfin tuna are captured almost year-round. Histological examination of gonads of blue marlin captured during June 2000, 2001 and 2002 (n = 5) showed ovaries were in the regressed or early maturation classes. Collections of istiophorid larvae in the northern Gulf indicated that spawning by billfish was at a low level in Mayand increased during the summer months. Collections of female bluefin tuna during June 2000 and 2001 (n = 2) showed ovaries in the late maturation class, capable of spawning. Furthermore, the ovaries of one of the specimens examined contained 24 h postovulatory follieles (POF), suggesting spawning occurred within the past 24 h of capture. Male bluefin tuna (n = 1) had testis in the mid matmation class with spermatozoa evident in the sperm ducts. Collections of bluefin tuna larvae reflected a similar temporal pattern of late spring/early summer spawning; all larvae (n= 33) were collected in May. Yellowfin tuna were collected during June 2000 and 2002, and most specimens were male (n = 9). The majority of the males (56 %) were in the mid maturation reproductive class and all males contained spermatozoa in the sperm ducts, indicating all fish were in spawning condition. Yellowfin tuna appear to have a slightly later spawning season than bluefin tuna in the Gulf, as only 50 % of the females were in spawning condition, however, all females in the late maturation class (n = 2) had POF in the ovaries. This is the first report of yellowfin tuna spawning in the northern Gulf. Larvae of yellowfin tuna are more difficult to identify than bluefin tuna and have not yet been recognized in USM/COMS plankton collections. These preliminary results suggest the northern Gulf of Mexico is an important spawning ground for many large pelagic fishes.

PDF Preview