Biology of a deep benthopelagic fish, roudi escolar Promethichthys prometheus (Gempylidae), off the Canary Islands

Abstract

The roudi escolar Promethichthys prometheus is common in deep hook-and-line and longline catches of a small-scale fishery along the slope off the Canary Islands. Population structure, reproduction, growth, and mortality of the species were studied from sampling undertaken from August 1992 to July 1995. Range of length of fish in the catches was between 36 and 80 cm TL, with a main distribution between 56 and 66 cm. The overall ratio of males to females was 1:1.74. Females predominated in all sizes. The sex ratio varied throughout the period of study; the lowest discrepancy between males and females, however, was during the reproductive period. A vertical space partitioning among sexes was observed, with males predominating from 600 to 800 m depth, females from 300 to 500 m. The reproductive period of the species was from April to September, with a peak in spawning in June-July. The size at first maturity was 47.41 cm. The parameters of the length-weight relationship for all fish were a = 0.004521 and b = 2.98932. Age readings of otoliths indicated that the exploited population consisted of nine age groups (III-XI years). The von Bertalanffy growth parameters for all individuals were L-infinity = 93.61 cm, k = 0.18/years, and t(0) = -1.54 years. The rates of mortality for all fish were Z = 0.49/years, M = 0.35/years, and F = 0.14/years. The length at first capture for the whole population was 51.57 cm.