Abstract
Skate egg case nursery sites are specific locations on the ocean floor where some species of skates deposit egg cases to incubate for up to 5 yr until hatching. We examined genetic diversity within and among skate egg nursery sites of the Alaska skate Bathyraja parmifera and the Aleutian skate B. aleutica in the eastern Bering Sea to gain a better understanding of how skates utilize these areas. Restriction-site associated DNA (RAD) sequencing libraries were used to obtain single nucleotide polymorphism (SNP) datasets for B. parmifera (5285 SNPs) and B. aleutica (3309 SNPs). We found evidence for significant genetic differentiation among all B. parmifera and B. aleutica nursery areas, with 1 exception. B. parmifera from the spatially proximate Pribilof and Bering Canyons were genetically similar, suggesting that this may represent a large contiguous nursery area. Genetic differences between embryos at distinct developmental stages within nursery areas were not significant. Adult B. parmifera taken from the Bering Sea and Aleutian Islands were genetically distinct from embryo collections, implying that additional genetic types of B. parmifera may exist that were not represented by the nursery areas sampled in this study. Our data also showed evidence for low effective population sizes and low Ne/N ratios. Results indicate that nursery areas support genetically distinct components of each species, which underscores the importance of skate egg nursery areas for conservation of genetic diversity.
Highlights
Egg case nursery sites are localized areas where oviparous skates in the Bering Sea and Aleutian Islands lay egg cases in high densities (> 50 000 eggs km−2) in contact with the ocean bottom or other permanent structure to incubate for up to 5 yr until hatching without parental care (Hoff 2008)
We examined genetic diversity within and among skate egg nursery sites of the Alaska skate Bathyraja parmifera and the Aleutian skate B. aleutica in the eastern Bering Sea to gain a better understanding of how skates utilize these areas
This study revealed new information on the population structure and use of nursery habitats by Alaska skates Bathyraja parmifera and Aleutian skates B. aleutica
Summary
Egg case nursery sites are localized areas where oviparous skates in the Bering Sea and Aleutian Islands lay egg cases in high densities (> 50 000 eggs km−2) in contact with the ocean bottom or other permanent structure to incubate for up to 5 yr until hatching without parental care (Hoff 2008). The Aleutian skate B. aleutica is found from northern Japan to the Aleutian Islands and southeast Alaska, and is the most abundant skate on the eastern Bering Sea slope, representing approximately onethird of the skate biomass in that region (Stevenson et al 2008, Hoff 2016, Ormseth 2020). Fertilization in all skates found in the Bering Sea is internal, and embryos are protected by tough proteinaceous egg cases laid by females in pairs on the seafloor (Matta 2006, Hoff 2009). Ageing is difficult for this species, and a higher maximum age is expected based on observed population dynamics data
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