Abundance indices of Greenland halibut in deepwater fishing zones of NAFO Divisions 3LMN

Abstract

Since 1990 a deepwater fishery of Greenland halibut has been developed in the boundary of Divisions 3L and 3M, extended to the North of Division 3N in 1992. The main participants in this fishery are Spain and Portugal. A description of this fishery is found in Junquera et al. (1992). The Spanish fleet is composed by bottom trawlers that fish from depths of 800 m onwards. Catch rates are of the same level as in other areas where Greenland halibut were traditionally exploited (Brodie, 1991). The fishing activity has been monitored by observers on board since the onset of this fishery. Eight observers stayed on board these commercial vessels in 1990, 23 in 1990 and 30 in 1992. They provided a great amount of information on fishing areas, length distributions, catches and effort which would allow us to get a quite clear picture about the trends of this species in the area. The fleet in 1990 was mainly large trawlers, but smaller vessels were incorporated with time. This heterogeneity of the fleet and the differences in the survey intensity at different seasons and years hampered a direct interpretation of the raw information on catch and effort to calculate indices accounting for seasonality or long-trends in catch rates (Junquera et al., 1992). Following a recommendation of the NAFO Scientific Council in 1992 (Anon., 1992), the standardization of the catch rates in the whole available time series of data from the commercial fishery is undertaken in this paper. It allowed us to obtain comparable time series of catch rates, which can be considered as fishery related abundance indices because this is a directed fishery for Greenland halibut.