Northwest Herring Acoustic Survey Cruise Report and Abundance Estimate, 2007

Abstract

The northwest and west coast herring acoustic survey programme was first implemented in 1994, with the current winter spawning survey representing the 9th in the time series. The stock in this area is composed of 2 spawning components (autumn and winter), covering a large geographical area. Spawning occurs over a protracted period of over 4-months from late September through to late March. The age profile of the survey stock as generated from trawl samples indicated ages ranging from 1-7 years. Maturity samples indicate the largest proportion of the stock to be in a pre-spawning, spawning or spent state, with small amounts of immature fish, as would be expected at this time. The 2007 survey estimate generated a TSB (total stock biomass) of 14,200 t relating to a SSB (spawning stock biomass) of 13,974 t. Poor weather dominated the survey with almost 25% lost in downtime. As a result the survey area and track lines had to be reduced to compensate and hydrographic stations had to be sacrificed. The poor weather experienced no doubt had an impact on herring schooling behaviour and our detection ability.