Informe de la campaña de investigación biológico-pesquera de palangre de fondo en aguas del Atlántico sur-oriental y en los sectores Atlántico e índico de la CCRVMA (Subárea 48.6 y División 58.4.4)

A bottom-longline research cruise was carried out between 22 of October and 1 of December 1997. During this experience several submarine mountains were surveyed south to Africa close to the Antarctic Convergence (Meteor) and in the CCAMLR region (Shona, Spiess, western slope of the Bouvet Island, Ob and Lena). The general objective of the cruise was to study the fish populations inhabiting these submarine mountains and more especifically those of the toothfish (Dissostichus eleginoides). The specific objectives established according to this were to analyze the species structure variations in a north-south and west-east gradient and to determine the geographical and bathymetrical distribution of the species within the study area. Furthermore, it was planned the obtention of data to study different aspects of the biology of D. eleginoides, to conduct length analysis, to determine the sex structure of the populations and to estimate relative abundance indices for this species analyzing its geographical and vertical variation. The sampling method consisted of longline fishing operations using perpendicular transects to the isobathes, fishing in different depth strata using one or two sets, from the shallower waters down to depths between 1500 and 2000 metres. Catches in numbers were widely dominated by toothfish (D. eleginoides) with 2822 individuals (83.24 %). Macrourus carinatus was the second species in numbers during the cruise (210 individuals). The total catch in weight was 21.43 t, of which 20.502 t (95.63 %) corresponded to toothfish. The submarine mountains showed substantial differences in relation to the topography, the species composition of the catches, and the relative abundance and the size structure of D. eleginoides found in each of them. This fact makes it difficult the extrapolation of results between geographical areas without having prior information from them. Lengths of individuals of D. eleginoides living in the shallower depth strata affect length structure in deeper waters. The general trend to increase length with depth seems to be somehow disturbed by inflections or alterations related to local bottom features. Sex ratio of D. eleginoides is not significantly different from 1: 1 until a total length of around 90 cm which corresponds to the onset of the sexual maturity for males. This could be related to the beginning of migratory movements that make them inaccessible to fishing with bottom longlines. As a result females account for a 70% of individuals bigger than 90 cm of total length. The stratum with highest catch per unit effort was that of 600-800 m though absolute values varied between areas (413.06 kg/1000 hooks in Ob and Lena, 225.10 kg/1000 hooks in Meteor and 58.16 kg/1000 hooks in Subarea 48.6). Total catch per unit effort by region also differed between regions ranging from a maximun value of 359.1 kg1000 hooks in Ob and Lena and a minimun of 185.25 kg/1000 hooks in Meteor.