Research Document - 2006/047

An Examination of Turnover Rate of Herring on the Spawning Grounds of Scots Bay and German Bank using Tagging Data

By Clark, K.J.

Abstract

A tagging study was undertaken on the spawning grounds of Scots Bay and German Bank to examine the residency time of herring on the grounds during spawning season. Tagging was attempted on as close to a weekly basis as possible, although weather or a lack of fishing activity sometimes prevented this. A total of 8,580 tags were applied to herring from Scots Bay on four occasions and a total of 5,047 tags were applied to herring on German Bank on five occasions. The overall tag return rate for Scots Bay was 4.5%, whereas the return rate from German Bank was only 0.6%. Returns from both spawning grounds indicated that, although the majority of tag returns came from within the first three weeks after tagging, some fish remained on the spawning grounds for up to five to six weeks after tagging. The possibility that some herring remain on the spawning grounds for longer than the previously assumed 10 to 14 day interval has implications for the timing of the repeated acoustic surveys of the spawning grounds used in the 4VWX herring assessment in recent years.

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