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The views and opinions expressed or implied in this article are those of the author (or authors) and do not necessarily reflect the position of the National Marine Fisheries Service, NOAA. Abstract—Seasonal migration of commercial-size (≥102 mm carapace width [CW]), morphometrically mature (MM) snow crabs (Chionoecetes opilio) from the eastern Bering Sea was examined in relation to the summer distribution of mature females to identify spatiotemporal overlap of males and females and determine the likelihood of mating associations for specific reproductive stages. Depth variation associated with this migration was examined to determine whether seasonal migrations contribute to previously recognized spatial differences in distributions of commercial-size males caught in the winter fishery and in the National Marine Fisheries Service summer bottom trawl survey. Depth data from 33 data storage tags attached to commercial-size MM males during 2010 and 2011 indicated that most males moved inshore during spring—a movement that would allow them to mate with multiparous females but not with pubescent-primiparous females. Smaller tagged males (100–102 mm CW) underwent more extensive inshore migrations, and several of them traveled more than 100 km in one direction. Both tagging and distribution data indicated that most commercial-size MM males remained predominantly on the outer shelf throughout the year (despite some inshore movements during spring) and, therefore, these males did not contribute greatly to the spatial differences observed between winter and summer. Migrations of snow crabs (Chionoecetes opilio) differ between sexes and among different size classes, resulting in distributions that are highly structured and complex (Ernst et al., 2005). In the eastern Bering Sea, these migrations depend partially on bottom temperature gradients (Ernst et al., 2005) and can vary annually depending on the extent of the “cold pool” (Kotwicki and Lauth, 2013), a near bottom layer of cold (<2°C) water that forms across mid-depths (50–100 m) of the eastern Bering Sea shelf. On the basis of data from the eastern Bering Sea shelf collected during the National Marine Fisheries Service (NMFS) annual summer bottom-trawl survey, immature crabs of both sexes undertake down-slope ontogenetic migrations that are generally from the northeast to the southwest (Otto, 1998; Zheng et al., 2001; Ernst et al., 2005). Upon reaching full maturity, both sexes undergo a terminal molt in the spring, after which they are thought to continue to migrate into deeper water (Oresanz et al., 2004; Ernst et al., 2005; Parada et al., 2010). For commercial-size males, ≥102 mm in carapace width (CW), this migration is assumed to culminate on the outer shelf (depths of 100–200 m), where the winter commercial fishery is concentrated (Orensanz et al., 2004). Less is known about smaller terminally molted males, but they are assumed to reside inshore of the commercial-size males. Male migrations likely differ before and after the terminal molt. Because the transformation from a small-clawed “adolescent” stage to a large-clawed morphometrically mature (MM) stage coincides with the terminal molt for males, these stages have been distinguished by using the relationship of carapace width (CW) to chela height (CH) (Comeau and Conan, 1992; Stevens et al., 1993; Rugolo et al.1; Tamone et al., 2007). Because members of a cohort can reach maturity over multiple ages, the size distribution of MM males overlaps that of adolescent males. Although adolescent males are sometimes capable of mating, MM males

Seasonal migrations of morphometrically mature male snow crab (Chionoecetes opilio) in the eastern Bering Sea in relation to mating dynamics