Research Document 1998/81

Quantitative acoustic surveys of 4WX herring in 1997

By G.D. Melvin, K.J. Clark, F.J. Fife, M.J. Power, S.D. Paul, and R.L. Stephenson

Abstract

An automated acoustic logging system installed aboard two commercial herring seiners was used to document the abundance and the distribution of herring in NAFO Division 4WX during the 1996/97 fishing season. The data were collected during standard fishing operations and structured surveys. The former were used to document the general distribution of fish throughout the season, while the latter followed standard acoustic survey protocol for quantitative assessment. Biomass estimates were determined for several major spawning components within the 4WX stock complex. Prior to the fishing season it was estimated that 7-10 days must elapse between spawning surveys to ensure a new wave of fish had occupied the spawning grounds and to avoid double counting. Unfortunately, large and presumably new schools of fish were observed and surveyed by the fishing industry in Scots Bay and on German Bank with only 6 days between surveys. Examination of length frequencies, gonad stages and distribution of catches did not provide conclusive evidence that the observations were made on a new and/or different group of fish. To avoid double counting the estimate from the second survey was discounted by the percent of stage 5 pre-spawning herring observed in the first. Total biomass estimate for a spawning component was determined by summing the surveys after discounting. Based on this approach the German Bank spawning component was estimate to be 370,356t between September 18 and October and the Scots Bay component 160,168t between July 29 and August 18.

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