The following supplementary material is available for this article:
Appendix S1. Trends in the mean numerical abundance of adult fishes sampled on the North Sea groundfish survey. Continuous lines represent mean abundance estimates for all sites and broken lines represents abundance estimates from fixed sites.
Appendix S2. Relationship between the powers to detect annual percentage increases and decreases in abundance.
Appendix S3. Total number of stations sampled in each year of the survey. Twenty three stations were sampled every year.
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