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

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 Cana ry Islands. Population structure, reproduction, growth, and mortality of th e species were studied from sampling undertaken from August 1992 to July 19 95. Range of length of fish in the catches was between 36 and 80 cm TL, wit h a main distribution between 56 and 66 cm. The overall ratio of males to f emales was 1:1.74. Females predominated in all sizes. The sex ratio varied throughout the period of study; the lowest discrepancy between males and fe males, however, was during the reproductive period. A vertical space partit ioning 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 w as 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 relatio nship for all fish were a = 0.004521 and b = 2.98932. Age readings of otoli ths indicated that the exploited population consisted of nine age groups (I II-XI years). The von Bertalanffy growth parameters for all individuals wer e 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.