Research Document - 2005/023

2005 Evaluation of 4VWX Herring

By Power, M.J., R.L. Stephenson, S. Gavaris, K.J. Clark, F.J. Fife, D. Knox, L.M. Annis

Abstract

Landings in the southwest Nova Scotia/Bay of Fundy spawning component in 2004 (78,000t) were about 10,000t lower than the previous year and near the average of the last decade. There continues to be signs of deterioration in the state of the stock. The 2004 catch was dominated by age 2 and 3 recruits and there was an absence of older fish. SSB on both Trinity Ledge and Seal Island spawning areas remain well below historical levels. The truncated catch at age and the rapid decline of individual year-classes indicates that total mortality may be considerably higher than estimated. There has also been little progress towards defined conservation objectives in recent years.

Acoustic surveys of spawning grounds indicate a relatively stable spawning stock biomass (SSB) in recent years. Combination of the absolute SSB estimate from acoustic surveys with fishery catch at age data in a virtual population analysis (VPA) implies a rapid and substantial biomass increase (5-fold over the past 5 years) which has not been seen in the surveys and is inconsistent with the truncated age composition. A VPA calibrated with the trend in acoustic surveys suggests a relatively stable SSB of less than 200kt and a high fishing mortality (F). The pattern of residuals is acceptable, and this scenario matches observations recorded in the fishery (i.e. no large increase in biomass, high fishing mortality leading to truncated age structure).

Landings of 4,050t from the 2004 offshore Scotian Shelf banks were below average since the fishery was reactivated in 1996. The 2004 fishery was dominated by catches of age 4 and 5 fish. In contrast, bottom trawl research survey catches from the past seven years have been the highest on record and herring were widely distributed on banks west of Sable Island.

Biomass estimates from acoustic surveys of the major coastal Nova Scotia spawning components were substantially lower for all surveyed areas in 2004 with large decreases for the Little Hope and Eastern Shore areas. There was no surveying from the Glace Bay area due to technical problems. Recorded landings showed a relatively large increase for the Eastern Shore area and decreases in the other main areas. The Bras d’Or lakes fishery was closed in 2004 and there was also no sampling.

There was an increase in landings in the traditional New Brunswick weir and shutoff juvenile herring fishery to 20,700t from 9,000t in 2003 but there is still a trend of decreasing landings over the past ten years.

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