The extensive distribution of blue whiting (Micromesistius poutassou) spans 35 degrees of latitude in the NE Atlantic. Strong recruitments in the early 2000s made blue whiting one of the world’s largest fisheries; 2.5 million tonnes were landed in 2004. Recruitment dropped sharply in 2006, but the fishery maintained catches of 1m tonnes until 2008. Subsequent fluctuations in stock status and TAC reductions to less than 2% of the 2004 landings (40,000t in 2011) have created strong imperatives for improved assessments and management advice.

A robust index of recruitment for blue whiting does not exist. Indices previously used in assessment are problematic due to poor survey coverage and unreliable acoustic detection for small fish in the demersal zone. Whilst these indices were useful during high recruitment events, they were ineffective during periods of low recruitment (estimating zero recruitment in some years), and were subsequently excluded from the stock assessment. Current assessments are consequently over reliant on model-derived recruitment indices.

We present a robust, standardised recruitment index derived from a combination of under-utilised ground-fish surveys. Integrating over a million data-points across three decades, we apply advanced modelling techniques to estimate the recruitment of blue whiting in the Southern region of its distribution. Recruitment signals are evident in the surveyed area, and indicate less variability than suggested by the previous problematic indices. This study demonstrates the utility of examining previously neglected data sources to help resolve critical issues in fisheries resource assessment.