Research Document - 2000/118

Saturation Index for longlines and gill nets in Sentinel Fisheries of cod in the Northern Gulf of St. Lawrence.

By S. Brulotte and A. Fréchet

Abstract

Catch rates from cod directed fixed gear Sentinel Fisheries thus complement other tools available for the assessment of the northern Gulf of St. Lawrence cod stock. The saturation index was estimated for longlines and gill nets used in the cod directed Sentinel Fisheries from 1994 to 1998. The areas covered by these surveys are the West Coast of Newfoundland and North Shore of Quebec, 49 fishing sites. Since the onset of Sentinel Fisheries by fixed gear, fishers have used their traditional fishing sites and traditional fishing gear as prior to the moratorium on the cod fishery. The number of cod (Atlantic and Ogac) caught was generally calculated from the number of Atlantic cod sampled. For the other species caught (fish, sharks, crustacean, etc.) an average individual weight was used. The index saturation of the longline was calculated from the total number of specimens caught divided by number of hooks used. For the gill nets, the index was calculated from the total number of specimens caught divided by number of nets used.

A total of 2985 trips were done with longlines between 1994 and 1998, of which 2591 were done in Newfoundland and 394 in Quebec. Out of a total of 2985 trips done, 104 had no catch, 1113 had only cod, 1663 had mixed catches of cod and other species and only 105 without cod but with other species caught. Cod represents more than 60 % of the numbers caught in over of the trips (62.4 %). The index of saturation (all species) in the longline is low for most observations; 80.8 % of the trips had saturation indices between 0 and 20 %. A total of 4311 trips were done between 1994 and 1998 with gill nets of which 1709 were done in Newfoundland and 2602 in Quebec. Out of the 4311 trips done only 81 had no catch, 838 trips had caught only cod, 3192 had cod and other species and only 200 trips had species other than cod caught. In Newfoundland, the proportion of cod caught in gill nets are similar to longline with 57.3 % of trips having over 60 % cod in their catches. In Quebec, this proportion drops to 30,3 % of the trips with over 60 % of cod catches. In Newfoundland and Quebec, the frequency of a saturation of 25 individuals or less per net is generally over 80 % of the trips.

The gear saturation is a measure of loss of efficiency of a gear as the number of fish caught increases. Saturation has thus a very direct effect on catch rates. In the case of Sentinel Fisheries, for most trips with longlines and gill nets, the saturation indices are likely too low to bias catch rates.

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