Early life ecology of sailfish, Istiophorus platypterus, in the northern Gulf of Mexico
Simms, Jeffrey R.
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Sailfish, Istiophorus platypterus, are commonly taken by the recreational and commercial fisheries in the Gulf of Mexico (Gulf) and larvae are frequently reported in the region, indicating the Gulf's potential role as spawning and/or nursery ground of sailfish. Five ichthyoplankton surveys were conducted in shelf and slope waters of the northern Gulf during the summers of 2005 (May, July, September) and 2006 (June, August). Surveys were conducted off the Texas and Louisiana coasts from 27 - 28N and 88 - 94W. During the two year study, 2,426 sailfish larvae were collected, ranging in size from 2.0 - 24.3 mm standard length (SL). Sailfish larvae were collected in 45.0% of collections with a peak density ranging of 51.5 larvae per 1000 m-2 of water sampled, and the highest larval abundances were observed within frontal features of the Loop Current. Sagittal otoliths were extracted from 1,236 larvae, and otolith microstructure analysis indicated sailfish ranged in age from 5 - 25 days post-hatch. Hatch-date distributions indicated fish were from early May to mid September spawning and/or hatching events. Instantaneous growth coefficients (g) ranged from 0.113 to 0.127 with intra- and inter-annual variations in growth observed. Growth coefficients correspond to a 10.7 - 11.9% increase in length per day. Instantaneous daily mortality rates (Z) were estimated from regressions of the decline in loge-transformed abundance on age and ranged from 20.4% to 29.2% per day suggesting large losses during the early life interval. Instantaneous weight-specific growth coefficients (G) ranged from 41.5% to 45.9% per day and were indexed to daily mortality to assess intra- and inter-annual variation in recruitment potential. Recruitment indices > 1.0 were observed during all surveys, suggesting cohort biomass was increasing and that conditions were favorable for growth, survival and recruitment. The results of this study indicate that the northern Gulf represents viable spawning and nursery habitat of sailfish and the sustainability of Atlantic sailfish populations may be linked to spawning in the Gulf.