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Research Document - 2014/068

Estimating German Bank and Scots Bay Herring Spawning Ground Turnover Rates from Tag Returns

By G.D. Melvin, R. Martin, and M.J. Power

Abstract

The biomass of herring on individual spawning grounds in the Maritimes Region is determined from the total of multiple acoustic surveys conducted throughout the spawning season. A minimum elapsed time of 14 days between surveys was established to avoid double counting of fish from one survey to another. Data from several tagging studies were combined to estimate the temporal turnover for two of the main spawning grounds in Bay of Fundy/Southwest Nova Scotia area. Between 1998 and 2011, 51,432 herring were released on German Bank and 11,214 in Scots Bay, with a return rate of 0.5% and 1.9%, respectively. A strongly correlated log linear relationship between cumulative proportions of returns and elapsed time was found for both spawning grounds; r² = 0.97 for German Bank and 0.83 for Scots Bay. Based on a 14 day interval between surveys, approximately 13% in the former and 19% on the latter of herring remained on the spawning grounds between surveys. The equations were then used to adjust individual survey biomass estimates based on the elapsed time between surveys. Estimates of the proportion of spawning herring remaining on both spawning grounds during subsequent surveys were made and the total spawning stock biomass adjusted accordingly for the entire time series (1999-2012).

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