Examination of spatial heterogeneity in population age frequency and recruitment in the ocean quahog (Arctica islandica Linnaeus 1767)

Abstract

The ocean quahog, Arctica islandica, is a commercially important species on the northwestern Atlantic continental shelf. This species can live over 200 years with ages varying widely per 5-mm size class (shell length), making study of age-related demographics difficult. To determine how the demography of this species differs across its range, including age frequencies, age-at-length relationships, and sex ratios, ocean quahogs from multiple sites distributed from the Mid-Atlantic Bight to Georges Bank were studied. The age and length frequencies from two populations collected in 2019 from New Jersey, north and south of Hudson Canyon (39.840556 N, 72.821667 W and 39.33 N, 73.545 W, respectively), were analyzed and compared to two other populations from Long Island (40.09658 N, 73.01057 W) and Georges Bank (40.72767 N, 67.79850 W), previously collected in 2015 and 2017. Sex-specific differences were also analyzed to determine how said differences influenced a range of demographic metrics. Though some similarities in recruitment trends exist, likely caused by large-geographic-scale environmental conditions, each site contains a distinct population with distinct demographics. Recruitment is consistent over hundreds of years, but year-to-year and decadal-length variations are apparent. One age–length key may potentially be used to represent Long Island and northern New Jersey, but the remaining sites are significantly dissimilar. Sex ratios also vary, potentially caused by differential survival of one sex during certain times in the past. Mortality rates for Georges Bank are distinctly higher compared to the other populations. Based on these results, the use of separate age–length keys would seem necessary for each population and each sex.