Distribution, biomass and size of grooved Tanner crabs (Chionoecetes tanneri) from annual bottom trawl surveys (2003–2010) along the U.S. west coast (Washington to California)

Abstract

Catch and distribution of grooved Tanner crab (Chionoecetes tanneri Rathbun, 1893) from the Northwest Fisheries Science Center's bottom trawl survey (55–1280m) were examined along the U.S. west coast (lat. 32°30′N–48°30′N). Grooved Tanner crabs were present in 28% of tows and occurred primarily at depths from 300 to 1280m. Annual biomass (metric tons, mt) indices and density (kgkm−2) estimates for the population varied significantly throughout the study area and within five International North Pacific Fisheries Commission (INPFC) statistical areas. Highest estimates occurred in the Monterey INPFC area (lat. 36°N–40°30′N) and within the 601–800m depth interval. Depth distribution varied by year and coast-wide catch-weighted average depths (m) were significantly correlated with average annual Pacific Decadal Oscillation (PDO) indices (2003–2010), a measure of Pacific climate variability. Annual mean carapace widths (CW), measured from 2005 to 2010, were always greater for males (96.9–113.9mm) relative to females (85.3–95.8mm). Size frequency distributions varied by year with strong recruitment for both sexes apparent in 2010. Grooved Tanner crabs were partially segregated by depth and stage. Males and females were found in all depth intervals but the average depth of adult females was significantly shallower (756m) than adult males (837m); adults were significantly shallower than subadult female (907m) and subadult male (927m) crabs.