Biological features of nine deep-water fishes from the midslope of the Northwest African coast

Abstract

The size distribution, sex ratio, spawning activity, and maturity of Alepocephalus bairdii, Alepocephalus productus, Alepocephalus rostratus, Bathygadus favosus, Bathygadus melanobranchus, Nezumia aequalis, Mora moro, Trachyscorpia echinata and Hoplostethus mediterraneus inhabiting the middle slope off Northwest Africa were analysed. Maturation takes place during the winter months, when a high proportion (>62%) of large individuals were observed in the mature, spawning or postspawning stage, with the exception of H. mediterraneus (57.3%). Negative allometric growth was recorded as a general pattern in both sexes, but isometric growth was recorded in females of A. productus, A. rostratus, and B. melanobranchus. Positive allometric growth was only observed in females of T. echinata. The length frequency distribution showed significant differences between sexes, except in A. productus and A. bairdii. Females of Macrouridae species were found to be larger and heavier than males. Sex ratios were generally unbalanced, but no bias was observed in N. aequalis, T. echinata, and H. mediterraneus. Relative size at sexual maturity ranged mainly between 0.66 and 0.72, but B. favosus, H. mediterraneus, and N. aequalis showed lower values (0.54–0.61). Sexual maturity is reached mainly at a size between 1 and 5 cm smaller in males than in females, except in A. bairdii and T. echinata.