Population dynamics and fishery of dolphinfish (Coryphaena hippurus) in the western Mediterranean

The dolphinfish (Coryphaena hippurus) fishery based on the island of Mallor ca (western Mediterranean) and the population dynamics of the species were studied between 1995 and 1996. Fishing effort, landings and length composit ion of the catches during the sampling period, as well as the historic catc h data series and fleet were analysed. Virtual Population Analysis (VPA), t aking as the time unit the week in 1995 and the fortnight in 1996, were als o carried out. Dolphinfish is fished from August to December, with main cat ches in September-October, using anchored fish aggregation devices (FADs) a nd surrounding net. The mooring areas, placed from 70 to 1200 m depth, are distributed among the boats registered for the year's fishery. A total of 4 6 boats took part in this fishery in 1995 and 37 in 1996, with a catch of 1 28 and 52 metric tons respectively. These wide fluctuations are also shown in the annual catches of the 16year series, which ranged from 2 to more tha n 120 metric tons, showing a slightly increasing trend (4 tons per year). T he comparison of different measures of effort (FADs, days and hours) showed similar values of CPUE, although the number of FADs showed the lowest vari ation, with normal variances and average values not significantly different between harbours. The length composition of the catches ranged from 20 to 64 cm fork length, which corresponds to juveniles between 2 and 6 months of age. The main results of the VPA, which must be regarded in relative rathe r than absolute values, showed that the available population and the recrui tment in 1995 are greater (around one order of magnitude) than in 1996. For both years, the number of individuals declined in the course of the fishin g season, while biomass increased during the first 5 weeks. The fact that t he exploited fraction of the dolphinfish population is composed of 0-age cl ass suggests that catch fluctuations might be related to environmental para meters and to the migratory behaviour pattern of the species. These two int errelated factors can produce failures of its annual spawning in the wester n Mediterranean, and/or of the recruitment of the species to the fishery.