Research Document 1998/16

Acoustic survey of cod spawning aggregations in Placentia Bay, May 1997

By G.A. Rose, and G.L. Lawson

Abstract

An adaptive 2-stage survey design was used to estimate the abundance of cod on major spawning grounds in Placentia Bay in May 1997. Surveys were conducted from the RV Innovation (10 m) using BioSonics DT4000 digital echosounders (120 and 38 kHz). Two spawning aggregations were located in May, at Perch Rock and Bar Haven, and another at Oderin Bank in June. Only the Perch Rock aggregation will be reported on here. Acoustic transects were run on days 143, 144, and 146, during the peak in spawning (approximately 50% of mature females had hydrated oocytes). A full grid of the entire aggregation was run on day 144, consisting of 9 transects across the aggregation at nominally 0.5 nmiles apart. Fish of ages 8, 7, and 5 (1989, 1990 and 1992 year classes) were heavily represented in catches by feather hooks deployed from automatic jigging reels. Transect densities ranged from 0.1 to 0.9 fish m-2 re: TS of -31.6 dB. The mean biomass estimate was approximately 38,000 t comprising approximately 18 million fish.)

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