Exploratory longline fishing around the Kerguelen Islands (Division 58.5.1). Description of the fishing effort; catchability and target size of Dissostichus eleginoides

During the 1990/91 and 1991/92 fishing seasons, two longliners carried out exploratory fishing over the western shelf break of the Kerguelen shelf (Division 58.5.1). Scientific monitoring of fishing carried out by one of these longliners has allowed a description of fishing methods to be made. Bottom longlines are generally used at depths of 400 to 600 m. The mainline (1 to 2 miles long) carries about 2 400 to 3 600 straight hooks, which are from 61 to 75 mm in length. The bait used is either imported fish (horse mackerel) or squid, or species (e.g.Champsocephalus gunnari) which are caught locally by trawlers. The vessel is equipped with an automatic longline baiter which has an efficiency of about 75%. The catch rate has been assessed as being about 10.9%, but this average is reduced by the fact that fish become unhooked along the side of the ship, which leads to a real catchability value in the order of 10.2%. The catch is almost exclusively made up of Dissostichus eleginiodes, by-catches being extremely small (0,28%).
Length frequency distributions (LFD) observed for Dissostichus eleginoides confirm that fish caught are large, their average length being greater than that in catches made previously by trawlers in the same area. This average length is comparable for the two successive fishing seasons (93.4 cm in 1990/91 and 92.95 cm in 1991/92). The fish caught are for the most part adults, and a clear difference can still be observed between the LFD for males (L = 88.09 cm in 1990/91 and 88.13 cm in 1991/92) and that of females (L = 98.70 cm in 1.990/91 and 98.61 cm in 1991/92). The sex ratio is almost equally balanced.