Gestation period and pupping seasonality of female spiny dogfish (Squalus acanthias) off Southern New England

Abstract

Recently, it has been suggested that spiny dogfish (Squalus acanthias) in the western North Atlantic Ocean have a shorter gestation period than the widely cited 2 years, have an asynchronous reproductive cycle, and carry pups in various stages of development. Mature female spiny dogfish were collected monthly from July 2013 through June 2015 to confirm gestation period and pupping seasonality off southern New England, and data on 2545 embryos from 622 females were obtained. Recent postpartum females and females with candled embryos appeared from January through April indicating parturition that was followed closely by mating. Vitellogenesis is concurrent with embryo growth, and therefore ova are ready for fertilization immediately after pupping. Visible embryos were observed in June, and growth continued until the external and internal yolks were absorbed and the umbilical scar was partially healed. Gestation period was approximately 23 months. No individual was observed with first and second year embryos. Average fecundity per female was estimated on the basis of the largest group of oocytes (5.3), free-living embryos (4.3), and total embryos (candled and free-living) (4.5). These values are similar to those of previous studies, but average fecundity by maternal size class has decreased from that of previous studies and is negatively correlated with spawning stock biomass, which provides supporting evidence for density dependent fecundity.