Determination of size discrepancies for sailfish (Istiophorus platypterus) in varying ocean basins.

This paper describes an internship project to fulfill the requirements for a Master of Professional Science from the University of Miami. The internship sought out to determine if sailfish grow to larger asymptotic sizes in different areas of the worlds oceans and hypothesize what factors, both environmental and oceanographic, could lead to differences in the length of sailfish. This internship project, in cooperation with the International Game Fish Association (IGFA), focused on using the available size (length and weight) data held by the host organization as well as databases held by regional fishery management councils to compare size frequencies and asymptotic length of sailfish around the globe. A total of 104,949 individual sailfish lengths and locations were used in the analysis of this study. After separating the observations into regions, the largest average sizes of sailfish were determined to be in the eastern Atlantic (n = 199), 204 cm and the eastern Pacific (n = 16,474), 187 cm. Both areas coincide with eastern boundary currents which are known to have some of the most productive ocean systems in the world, holding large accumulations of prey species. Habitat compression, caused by hypoxic zones, in these areas may also force sailfish prey closer to the surface of the water column and therefore congregate the schools of both predators and prey further. Analysis of variance shows there was a significant difference in the size of sailfish between ocean basins (p < 2e-16). The data acquired from the Indian Ocean had over 75,000 observations and in total had an average size of 180 cm. Out of the total observations, 60% came from three fleets, Japan (n = 830), Taiwan (n = 13,368) and Sri Lanka (n = 31,744). The data set reported that the Sri Lankan fleet used gill nets and the Japanese and Taiwanese fleets used longlines. The distribution of the fleets throughout the region also varied. The Sri Lankan fleet reported observations in two grids, 6105075 (western part of Sri Lanka) and 6105080 (eastern part of Sri Lanka). The Japanese fleet reported observations in 13 grids, which had a relatively diverse distribution throughout the ocean, and the Taiwanese fleet reported observations in 98 grids, which spanned mostly in the western part of the ocean and off the southeast coast of Sri Lanka.