Population dynamics and fishery of dolphinfish (<i>Coryphaena hippurus</i>) in the western Mediterranean

Abstract

SUMMARY: The dolphinfish (Coryphaena hippurus) fishery based on the island of Mallorca (western Mediterranean) and the population dynamics of the species were studied between 1995 and 1996. Fishing effort, landings and length composition of the catches during the sampling period, as well as the historic catch data series and fleet were analysed. Virtual Population Analysis (VPA), taking as the time unit the week in 1995 and the fortnight in 1996, were also carried out. Dolphinfish is fished from August to December, with main catches in September-October, using anchored fish aggregation devices (FADs) and 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 46 boats took part in this fishery in 1995 and 37 in 1996, with a catch of 128 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 than 120 metric tons, showing a slightly increasing trend (4 tons per year). The comparison of different measures of effort (FADs, days and hours) showed similar values of CPUE, although the number of FADs showed the lowest variation, 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 rather than absolute values, showed that the available population and the recruitment 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 fishing season, while biomass increased during the first 5 weeks. The fact that the exploited fraction of the dolphinfish population is composed of 0-age class suggests that catch fluctuations might be related to environmental parameters and to the migratory behaviour pattern of the species. These two interrelated factors can produce failures of its annual spawning in the western Mediterranean, and/or of the recruitment of the species to the fishery.