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

Abstract

Atlantic 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.

Variation in energy density of northwest Atlantic forage species: Ontogenetic, seasonal, annual, and spatial patterns

“…The GAM for Atlantic Herring indicated low ED on GB in fall compared to inshore portions of the GOM. Wuenschel and Deroba (2019) showed that spatial distributions differed between immature and mature fish in the region, with immature individuals not migrating out to GB, as reflected here in the higher ED inshore compared to the lower postspawn ED offshore. The size range of Atlantic Herring analyzed included many mature individuals of both spring‐ and fall‐spawning groups, and season explained a relatively small portion of the variation.…”

“…The anadromous Alewife requires large amounts of energy stores to make long migrations upriver in spring to spawn (Munroe 2002). Atlantic Herring also undergo dramatic seasonal cycles in energy allocation to reproduction, with most spawning occurring in the late summer/early fall in the GOM and on GB and more limited spawning in the spring (Melvin et al 2009;Richardson et al 2010;Wuenschel and Deroba 2019). Kenyon et al (2022) reported strong intraannual variation in the fat content of Atlantic Herring in the North Sea that was related to reproductive status.…”

A unified framework and terminology for reproductive traits integral to understanding fish population productivity

“…Given the broad geographic range of many of the coldwater species reported, stock‐specific variations in egg size and spawning duration are expected. For instance, Atlantic Herring from the U.S. Gulf of Maine have a 2 month fall–winter spawning season, with evidence of some individuals spawning during spring (Wuenschel and Deroba 2019), compared with the April and May spawning season in Norway reported in Lønning et al. (1988).…”

Fourier transform near infrared spectroscopy as a tool to predict spawning status in Alaskan fishes with variable reproductive strategies

“…Histological examination of ovaries at different stages of development throughout an annual reproductive cycle provides essential information on the spawning strategy of individual species. 3,4 Spawning strategy can vary among fish species in the rate and timing of oocyte development. Understanding the individual spawning strategy of a fish is important for informing the histological interpretation of ovary collections used to determine proportions of spawning-capable versus non-spawning fish in a population.…”