Growth of juvenile red king crab (Paralithodes camtschaticus) in Bristol Bay (Alaska) elucidated from field sampling and analysis of trawl-survey data

An analysis of in situ growth rate was conducted for juvenile red king crab (Paralithodes camtschaticus) in Bristol Bay, Alaska. Growth of early juven iles (similar to2-40 mm CL; age 0-3 yr) was determined by fitting seasonali zed Gompertz growth models to length-frequency data. The parameters, of the growth model and resulting size-at-age estimates were compared with those from studies conducted at Unalaska and Kodiak Islands by fitting the same g rowth model to published length-frequency data from separate sources. Growt h of late juvenile and early reproductive crabs, similar to 30-100 mm carap ace length.(CL), was examined by analyzing length-frequency data from the N ational Marine Fisheries Service annual Bering Sea trawl survey from 1975 t hrough 1999. Mean CL associated with strong size, modes of crabs in Bristol Bay length-frequency distributions was resolved by using the FiSAT softwar e package (FAO-ICLARM Stock Assessment Tools) to track the modal size progr ession of strong year classes and assign mean size-at-age characteristics t o the stock. Growth of early juvenile crabs was slower in Bristol Bay than that observed by other researchers at Unalaska or Kodiak. Sizes at 1, 2, and 3 years aft er settlement were estimated to be similar to9 mm, 23 mm, and 47 mm CL in B ristol Bay compared with 16 mm, 38 mm, and 66 mm CL at Unalaska; at Kodiak, estimated sizes of 12 mm and 42 mm were obtained for age-1 and age-2 crabs , respectively. Within the Bristol Bay trawl survey data, a total of 24 mod es were identified for both males. and females <<similar to> 100 mm CL, whi ch included the modal progression of two year classes that presumably settl ed in 1976 and 1990. The 1976 year class grew slowly and would not have rec ruited to the reproductive stock until similar to9 years after settlement, whereas the 1990 year class appeared to recruit at similar to8 years after settlement. Both estimates indicate that Bristol Bay red king crabs are old er at reproductive maturity than the similar to6 years after settlement pre sently assumed. An attempt to resolve discrete mean size-at-age from the le ngth-frequency data met with little success. because variability in growth between year classes markedly obscured size-at-age characteristics in the s tock.