Determinants of mean length at age of spring spawning herring off the coast of Hokkaido, Japan

The stock of Hokkaido spring spawning herring Clupea pallasii collapsed in the middle of the 20th century. In the first half of the 20th century, large amounts of spawning herring were caught by set nets at coastal spawning grounds off the coast of Hokkaido, Japan. Using the catch data, we analyzed the mean length at age with respect to sea-surface temperature and density-dependent growth during the years 1910 to 1954 by generalized additive modeling (GAM). This stock is distributed at the southern boundary of the distribution range of Pacific herring, and we thus hypothesized that high temperatures have a negative effect on growth. Our study shows that length of Hokkaido spring spawning herring is highly dependent on growth during the first years of life and on temperatures preceding and during the feeding season. Higher temperatures during winter have a negative effect on growth. We found only weak indications of density-dependent growth in the stock of Hokkaido spring spawning herring.