Abundance, recruitment, and environmental forcing of Kodiak red king crab

Commercial harvests of red king crab Paralithodes camtschaticus around Kodiak Island, Alaska increased rapidly in the 1960s to a peak of 42,800 mt in 1965. Stock abundance declined sharply in the late 1960s, moderated in the 1970s, and crashed in the early 1980s. The stock has not recovered despite a commercial fishery closure since 1983. To better understand the rise, collapse, and continued depleted status of the red king crab stock around Kodiak Island, I conducted a retrospective analysis with three primary objectives: (1) reconstruct spawning stock abundance and recruitment during 1960-2004; (2) explore stock-recruit relationships; and (3) examine ecological influences on crab recruitment.;A population dynamics model was used to estimate abundance, recruitment, and fishing and natural mortalities. Three male and four female "stages" were estimated using catch composition data from the fishery (1960-1982) and pot (1972-1986) and trawl (1986-2004) surveys. Male abundance was estimated for 1960-2004, but limited data constrained female estimates to 1972-2004. Strong crab recruitment facilitated increased fishery capitalization during the 1960s, but the high harvest rates were not sustainable, likely due to reproductive failure associated with sex ratios skewed toward females.;To examine spawner-recruitment (S-R) relationships for the Kodiak stock, I considered lags of 5-8 years between reproduction and recruitment and, due to limited female data, two currencies of male abundance as a proxy for spawners: (1) all males ≥125 mm carapace length (CL); and (2) legal males (≥145 mm CL). Model selection involved AICc, the Akaike Information Criterion corrected for small sample size. An autocorrelated Ricker model using all males and a 5-year lag, with the time series separated into three productivity periods corresponding to different ecological regimes, minimized AIC c values. Depensation at low stock sizes was not detected.;Potential effects of selected biotic and abiotic factors on early life survival by Kodiak red king crab were examined by extending the S-R relationship. Results suggested a strong negative influence of Pacific cod Gadus macrocephalus on crab recruitment. Thus, increased cod abundance and a nearshore shift in cod distribution likely impeded crab stock rebuilding.