The Reproductive Biology of Female Atlantic Herring in U.S. Waters: Validating Classification Schemes for Assessing the Importance of Spring and Skipped Spawning

Abstract

AbstractAtlantic Herring Clupea harengus are iteroparous (repeat spawners) with group‐synchronous oocyte development and determinate fecundity, and they are total spawners. However, they also exhibit plasticity in other aspects of their reproductive biology including spawning seasonality and skipped spawning. Previous studies in other regions have reported skipped spawning and errors in macroscopic classifications of maturity, both of which could bias estimates of reproductive potential, but a critical assessment of these in U.S. waters is lacking. In the Gulf of Maine and Georges Bank, herring are assessed as a single stock complex, where females typically mature as 3 to 4 year olds and may live up to 11 years. To evaluate the magnitude of skipped spawning, we collected the ovaries of Atlantic Herring from fishery‐dependent and fishery‐independent sources over multiple seasons and evaluated them histologically to assess imminent (indicated by vitellogenic or maturing oocytes) or recent spawning (evidenced by the presence of postovulatory follicles). Gonad histology allowed us to determine spawning seasonality and skipped spawning. Macroscopic maturity classification was more accurate in fall (1–4% incorrect maturity) than in spring (7% incorrect maturity). The spatial distributions of immature and mature fish from both fishery‐dependent and fishery‐independent sources differed, which affected the estimation of maturity at length and age. We estimated 9–14% spring spawners in the region, but we did not find evidence of skipped spawning. The time series of the macroscopic data that were available (1987–2018) showed increases in spring spawning with latitude, but the proportions have not changed much over recent decades. The effects of up to 30% spring or skipped spawning on a stock assessment of Atlantic Herring were evaluated. Spring spawning had little effect relative to assuming 100% fall spawning (the current assumption), and skipped spawning decreased the scale of spawning stock biomass (SSB) and related reference points, with the degree of change increasing with skipped spawning rates, but it had few consequences otherwise.