Movements of deep-sea red crab (Geryon maritae) off South West AfricalNamibia

Abstract

Of 10246 red crabs tagged between 1979 and 1984 on the continental slope of Namibia, a total of 1604 were recaptured by commercial fishermen. Three tagging methods were tested. The most effective method was by inserting the tag through the epimeral suture. Though tagged crabs were released over a range of depths (from 400 to 900 m), the distances that they covered while at large were found to be unrelated to the depth at which they were released. No significant differences were found for distances moved by males compared to immature females, but differences (P< 0,01) did Indicate that large males (;;, 105 mm carapace width (CW» move farther than small males. Mature females moved significantly farther (P < 0,001) than the other crabs and over 32% moved> 100 km. The farthest distance covered by a single crab was 3BO km. No seasonal trends regarding distances or direction moved were noted for either sex or size groupings examined. Mature females did show a tendency, although unrelated to season, to move northwards. Movements of crabs by depth suggested that, although crabs of all sizes and sexes move freely between depths, small males « 100 mm CW) do tend to favour deeper water than larger males and vice versa. Female crabs tend to favour shallow depths and, of those tagged at 800 and 900 m, over 60% were recaptured shallower than 700 m. Based on the results of this study, it Is considered that the movement pattems of G. maritae. could best be described as nomadic. A possible reason for the fact that mature females display different movement patterns compared to other crabs in the population is discussed, as are possible implications to the fishery of ,crab movements between Namibia and Angola

S. Afr. J. Zool. 1987,22(2)