Research Document - 2000/066
Summary of the 1999 herring acoustic surveys in NAFO Division 4VWX.
By G.D. Melvin, T. Scheidl, F.J. Fife, M.J. Power, K.J. Clark, R.L. Stephenson, C.L. Waters, and S.D. Arsenault
Abstract
The distribution and abundance of Atlantic herring in NAFO Division 4WX was documented and estimated from data collected by automated acoustic logging systems deployed on five purse seiners and research surveys. As in previous years, the data originated from fishing operations and structured (DFO- directed mapping and acoustic) surveys. The number of recording nights from both fishing excursions (92 to 184) and structured surveys (8 to 29) increased from 1998 to 1999. Adherence to the survey design for structured surveys proposed for the 1999 fishing season was mixed. Approximately 50% of the structured surveys were considered to have met the criteria for a successful/completed survey. Although survey coverage of the main spawning grounds improved, the coverage was not considered adequate for inter-year comparisons. The total biomass for each of the main spawning components was estimated by summing the results of surveys separated by more than 10 days during the spawning season. In 1999, the observed biomass was based almost exclusively on data collected during structured surveys. Biomass estimates for Scots Bay, Trinity Ledge and German Bank were 41,000t, 3,900t, and 460,800t. For the stock complex, the minimum spawning stock biomass estimate was estimated to be 505,700t. Although the minimum SSB's do not directly reflect trends in stock abundance, the decline in observed biomass in Scots Bay and on Trinity Ledge is cause for some concern, given the extent/increase of survey coverage.
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