Research Document - 1999/120
An evaluation of the western Newfoundland herring acoustic abundance index from 1989-1997.
By I.H. McQuinn, and L. Lefebvre
Abstract
A hydroacoustic survey was conducted aboard the F.G. Creed in the fall of 1997 as part of a fishery-independent abundance index for the west coast of Newfoundland herring stocks. Systematic-parallel transects were chosen along the coast and were surveyed during night-time hours. Biological sampling was accomplished in collaboration with the western Newfoundland large purse seine fleet, which also took temperature, salinity and depth (STD) profiles. Raw volume backscatter data (Sv) were collected from a 38 kHz transducer, as well as split-beam phase data. This survey revealed that herring concentrations were more schooled than in 1995, closer to shore, more in the upper layers, and displaced towards the north and the south where warmer waters were available at all depths. The vast majority of herring echoes (80%) were recorded north of New Ferrole (stratum 10) and along the coast towards the Strait of Belle Isle. The total combined spring and autumn stock size in 1997 (88,000 t) was relatively stable compared to the 1995 estimate (89,500 t), although the spring-spawning stock decreased by 37% and the autumn-spawning stock increased by 20% over the past two years.
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