The Reproductive Biology Female Atlantic Herring (Clupea harengus): Validating Classification Schemes to Assess the Importance of ‘Skipped Spawning'

Atlantic herring are iteroparous (repeat spawners) with group-synchronous oocyte development, and determinate fecundity; and are total spawners. In the Gulf of Maine and Georges Bank,  herring are assessed as a single stock complex, where females mature as 3-4 year olds and may live to 11 years. In some marine fishes,  it is becoming evident that mature females may not spawn every year (‘skipped spawning’); therefore,  estimates of spawning stock biomass may overestimate reproductive potential. ‘Skipped spawning’ has been documented in Norwegian spring-spawning herring, but has not yet been evaluated for herring in the northwest Atlantic.  To evaluate the magnitude of ‘skipped spawning’, we collected ovaries in the fall of 2014 and evaluated them histologically to assess imminent (indicated by vitellogenic or mature oocytes) or recent spawning (evidenced by the presence of postovulatory follicles). In addition, we determined  the accuracy of a classification scheme based on macroscopic characters from microscopic (histological) characters of the same individuals.  Challenges of  differentiating among immature, ‘skip spawning’, and regenerating (resting) females both macro- and microscopically will be presented.   Improved identification of these stages is needed to assess the significance of ‘skip spawning’ for Atlantic herring in the Gulf of Maine and on Georges Bank.