Research Document - 2010/110

The 2009 German Bank Spawning Ground Tagging Turnover Rates

By E.E. Maxner, G.D. Melvin, and M.J. Power

Abstract

A tagging study to examine herring turnover rate on the German Bank spawning grounds was conducted during the summer/fall of 2009. The project will continue for the next two years to gain a better understanding of residency time of herring throughout the spawning season. Tagging was conducted whenever possible between August and October with 15 independent tagging events. A total of 10,338 tags were applied with a tag return rate of 0.7% in a 4 month return window. The tag return data were compared to previous turnover studies on German Bank and Scots Bay, which resulted in similar return rates (all under 1%). Tag return and maturity data were used to determine the length of time herring remain on the spawning grounds. Based on daily recoveries from 69 tags recaptured, 52% were recaptured within the first week, 78% by the second week, and 93% by the third week. Although the majority of the tags were returned by the first three weeks after tagging, some fish remained on the spawning grounds for up to five weeks. The relationship between the proportion of fish remaining on the spawning grounds and the days at large was found to be highly correlated (r² = 0.972). Turnover information is critical in the estimate of total spawning stock biomass from multiple acoustic surveys. The current assumes a 10 to 14 day resident period.

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