572 
Growth of juvenile red king crab ( Paralithodes 
camtschaticus ) in Bristol Bay (Alaska) elucidated 
from field sampling and analysis of trawl-survey data 
Timothy Loher 
David A. Armstrong 
School of Fisheries and Aquatic Sciences 
Box 355020 
University of Washington 
Seattle, Washington 98195 
Present address (for T Loher): International Pacific Halibut Commission 
P.O. Box 95009 
Seattle, Washington 98145-2009 
E-mail address (for T. Loher): loher@u washington.edu 
Bradley G. Stevens 
AFSC Kodiak Laboratory 
Kodiak Fisheries Research Center 
National Marine Fisheries Service 
301 Research Court 
Kodiak, Alaska 99615 
Abstract— An analysis of in situ 
growth rate was conducted for juvenile 
red king crab ( Paralithodes camtschat- 
icus) in Bristol Bay, Alaska. Growth 
of early juveniles (-2-40 mm CL; age 
0-3 yr) was determined by fitting sea- 
sonalized Gompertz growth models to 
length-frequency data. The parame- 
ters 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 growth model to published 
length-frequency data from separate 
sources. Growth of late juvenile and 
early reproductive crabs, -30-100 mm 
carapace length (CL), was examined by 
analyzing length-frequency data from 
the National Marine Fisheries Service 
annual Bering Sea trawl survey from 
1975 through 1999. Mean CL associ- 
ated with strong size modes of crabs in 
Bristol Bay length-frequency distribu- 
tions was resolved by using the FiSAT 
software package (FAO-ICLARM Stock 
Assessment Tools) to track the modal 
size progression of strong year classes 
and assign mean size-at-age character- 
istics to 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 
after settlement were estimated to be 
-9 mm, 23 mm, and 47 mm CL in 
Bristol 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 modes were identified for 
both males and females <-100 mm CL, 
which included the modal progression 
of two year classes that presumably 
settled in 1976 and 1990. The 1976 year 
class grew slowly and would not have 
recruited to the reproductive stock until 
-9 years after settlement, whereas the 
1990 year class appeared to recruit at 
-8 years after settlement. Both esti- 
mates indicate that Bristol Bay red 
king crabs are older at reproductive 
maturity than the -6 years after settle- 
ment presently assumed. An attempt 
to resolve discrete mean size-at-age 
from the length-frequency data met 
with little success because variability 
in growth between year classes mark- 
edly obscured size-at-age characteris- 
tics in the stock. 
Manuscript accepted 20 March 2001. 
Fish. Bull. 99:572-587 (2001). 
Population abundance of red king crab 
(Paralithodes camtschaticus ) in Bristol 
Bay, Alaska (Fig. 1) is typified by great 
variability. The maximum abundance 
of harvestable male crabs in the stock 
over the last 25 years has fluctuated 
by over an order of magnitude, peak- 
ing at nearly 60 million individuals in 
1977, and has fallen to less than 3 mil- 
lion from 1983 to 1985 (Loher et al., 
1998; Zheng and Kruse 1 ). Strong fish- 
eries in the late 1970s and early 1980s 
were followed by substantially reduced 
abundance in recent years, and fishery 
closures in 1981 and 1994, leading to 
concern over the status of the popula- 
tion by both management agencies and 
fishermen. Such concern prompted the 
Alaska Department of Fish and Game 
to develop a detailed harvest-based 
recovery plan for the fishery (Zheng et 
al. 2 ) that considers the stock to be fully 
recovered once it reaches an effective 
spawning biomass of 55 million pounds. 
This biomass has not occurred in Bris- 
tol Bay since 1981 (Zheng and Kruse 1 ; 
Zheng et al. 2 ), but it was chosen as an 
appropriate rebuilding level primarily 
on the basis of length-based recruit- 
ment models that, in turn, rely on the 
inferred underlying stock-recruitment 
relationship for the population (Zheng 
et al., 1995a, 1995b). 
Present assumptions regarding red 
king crab growth rates suggest that 
Bristol Bay crabs recruit to the re- 
productive stock at an age of approx- 
imately 6 years after settlement (i.e. 
-seven years following egg fertilization; 
Zheng et al., 1995a, 1995b), which cor- 
responds to mean sizes of 105 mm car- 
apace length (CL) and 97 mm CL for 
males and females, respectively. These 
size-at-age values are based on Ste- 
vens and Munk (1990), Weber (1967), 
and Balsiger (1974). However, none of 
these sources represents a comprehen- 
sive treatment of growth from settle- 
ment through maturity based entirely 
on field-collected data from the Bristol 
Bay region. Balsiger’s (1974) growth 
1 Zheng, J., and G. H. Kruse. 1999. Status 
of king crab stocks in the eastern Bering 
Sea in 1999. Alaska Department of Fish 
and Game, Reg. Inf. Rep. 5J99-09. Division 
of Commercial Fisheries, Alaska Depart- 
ment of Fish and Game, RO. Box 25526, 
Juneau, Alaska, 99801. 
2 Zheng, J., M. C. Murphy, and G. H. Kruse. 
996. Overview of population estimation 
methods and recommended harvest strat- 
egy for red king crabs in Bristol Bay. 
Alaska Department of Fish and Game, 
Reg. Inf. Rep. 5J96-04. Division of Com- 
mercial Fisheries, Alaska Department of 
Fish and Game, P.O. Box 25526, Juneau, 
Alaska, 99801. 
