Abstract
SUMMARY: The pilotfish (Naucrates ductor) is mainly caught as a by-catch of the dolphinfish fishery using FADs deployed around Mallorca (western-Mediterranean) from the end of August to December. The age and growth parameters of this species were estimated by length frequency analysis and daily growth increments observed in the otoliths. To validate the daily formation of the ring observed in the sagittae otoliths, a marking otoliths experiment with SrCl 2 was carried out with juvenile specimens kept in laboratory conditions. The growth parameters obtained from otolith interpretation were based on age at length of 99 specimens ranging between 15 and 31.2 cm FL. Length frequency analyses were based on the monthly length distribution obtained in 1990, 1991, 1995 and 1996. The results obtained from the two methods were similar and showed rapid growth during the first 6 months of life. The von Bertalanffy growth equation from otoliths was FL= 28.97 (1-e (-6.87(t - 0.055) ). Positive allometric growth was observed in the length-weight relationship, with no differences existing between sexes: W (g)= 0.0147*FL3.040 (cm).
Highlights
The pilotfish (Naucrates ductor Linnaeus, 1758)(Pisces: Carangidae) is an epipelagic oceanic species that is almost cosmopolitan in tropical and subtropical seas
Specimens smaller than 12 cm fork length were obtained with a dip net in different months under drifting objects or under the fish aggregating devices (FADs) used in the fishery
In the majority of cases, otoliths were polished before reading in a grinder-polisher with 3 mm micropolish alumina
Summary
The pilotfish (Naucrates ductor Linnaeus, 1758)(Pisces: Carangidae) is an epipelagic oceanic species that is almost cosmopolitan in tropical and subtropical seas. N. ductor inhabits the Mediterranean, and has occasionally been caught in the Black Sea (Bauchot, 1987). This species is one of the most characteristic of the pelagic fish assemblage associated with fish aggregating devices (FADs) in the western and central Mediterranean (Massutí and Reñones, 1994; Relini et al, 1994) and in the central Atlantic (Hunter and Mitchell, 1967). Pers) and Mallorca (Massutí and Morales-Nin, 1995) from the end of summer to the beginning of winter This fishery is directed towards the capture of Coryphaena hippurus (Linnaeus, 1758) and its two principal bycatch species are the carangidae N. ductor and Seriola dumerili (Risso, 1810).
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