Evidence Of blue marlin (Makaira nigricans) spawning in Bermuda waters and elevated mercury levels in large specimens

The gonads of 11 adult female blue marlin (Makaira nigricans Lacépède, 1803) caught mostly in July in Bermuda waters (2002–2005), and ranging in weight from 242–465 kg, were evaluated histologically for reproductive status. The gonadosomatic index (GSI) of these specimens ranged from 0.70%–6.22%; specimens with a GSI ≥ 3 were reproductively active. Based on gonad histology, 70% of the females caught in July were actively spawning or in spawning condition, with post-ovulatory follicles (POFs) or in final stages of oocyte maturation. These observations confirm that active spawning occurs in Bermuda waters in July and significantly extends the known northern spawning range of blue marlin in the western Atlantic Ocean. In addition, our largest specimen (465 kg) examined histologically was in spawning condition. This appears to be the first reproductively active specimen of this size ever reported. For the first time, a juvenile blue marlin (256 mm lower jaw fork length) was collected at Bermuda's northerly latitude (32°N). The estimated age of this specimen (42 d), obtained by counting daily growth increments on the sagitta, produced an estimated birth date in mid-July. White muscle tissue samples from 13 blue marlin (50–545 kg) specimens from the western North Atlantic (four from Bermuda), were analyzed for total mercury (THg) and had values from 1.77–12.7 ppm. These values are amongst the highest THg concentrations reported in any teleost. The high reproductive potential of the largest females, as well as their questionable food value due to THg contamination, suggests that consideration be given to reducing fishing mortality.