Maternal effects on recruitment of five gadoid species

Commercial fishing is almost always non‐random and generally removes large and old individuals from fish stocks, thereby reducing age diversity among spawners. Reduced age diversity may result in less stable recruitment. Here, we explore the influence of age diversity (H), mean age of the spawning stock (MA) and sea surface temperature (SST) on recruitment‐per‐spawning biomass (RSSB) for five commercial gadoid species (Atlantic cod, haddock, ling, saithe and tusk) by using data from analytical stock assessment spanning 4–7 decades. In the past 10–20 years, spawning stock biomass of these species (except for tusk) has increased due to lower fishing pressure. Concurrently, H and MA increased, especially for cod. However, our results did not indicate long term either positive or negative correlation between the maternal factors (H and MA) and RSSB for four of the studied species. Cod was the only species that showed significant positive correlation between H and RSSB, but the correlation did not hold during the most recent period of high SST. The conflicting outcomes underscore the difficulty in identifying a constant and direct maternal and/or environmental influence on RSSB.