Bering Sea King Crab Headed for a Steep Decline-Incomplete Knowledge Leads To Overfishing

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As we have argued before, incomplete science, cherry picked data, bum projections, and plain old fashioned dishonesty are a problem in the North Pacific fisheries.  Although our focus is the Gulf of Alaska, problems in the Bering Sea king crab fisheries demonstrate dangerous faults in fisheries management.

According to Deckboss:

 "Results from this summer's eastern Bering Sea trawl survey is fueling fears of a painful cut in the catch limit for the state's most valuable crab. The estimated biomass of legal-sized male Bristol Bay red king crabs is 15,412 metric tons, down 27.8 percent from the 2010 estimate. It's the fourth consecutive year the biomass has fallen."


But faulty modelling by the State of Alaska, according to Braxton Dew, may be one of the reasons for the collapse.

Reinventing the Wheel (and Getting It Wrong)

Braxton Dew

Fisheries Research Scientist

NMFS, Ret.

Today’s crab managers and modelers have reinvented red king crab biology to assume that all adult (≥120 mm carapace length) males are capable of mating each year with multiple females. However, back in the 1950s and 1960s, fishermen, processors, and researchers knew that adult male red king crab do not molt and mate in the same year. For example:

1) Based on the results of Bering Sea tagging studies, male red king crab do not molt and mate in the same year and only about 50% of the population’s mature males move inshore to participate in mating in any given year (Fujita et al. 1973; Takeshita et al. 1990).

2) Molting males, because of profound physiological changes associated with the molting process, undergo a severe reduction in muscle mass and meat content. They are unsuitable for processing and canning from December to March (USFWS 1942; Wallace et al. 1949).

3) Newly molted males were largely absent from catches in the spring Japanese tangle-net fishery, which caught mostly old-shell, non-molting males during April-June as they moved to nearshore Bristol Bay spawning grounds (Kawasaki 1959; Miyahara and Shippen 1965).

4) Consistent with the female-predominated populations found on the spawning grounds (Dew 2008), winter-molting males remain offshore as non-participants in the migration to inshore spawning grounds (Korolev 1964; Chebanov 1965; Rodin 1970, 1990).

Meatless and Mateless

The above graphic shows that adult males molt in winter, mainly during February. Japanese research shows that meat recovery is a slow process, continuing through spring, summer, and fall. Until they regain a reasonable complement of muscle mass, it is unlikely that recently molted males can participate in mating.

Crab Cannot Be In Two Places At Once

Below is a map (from Dew, 2010) showing the Bering Sea ‘bachelor grounds’ centered on Station F6, which is more than 200 km from nearshore spawning grounds. In any given year millions of newly molted mature males can be found on these bachelor grounds, while viable old-shell males are servicing females on distant spawning grounds. During a half-century of sampling, less than 1% of the more than 12,000 mature crab collected at these stations were females; 99% were large, new-shell males. At Station F6, only a single female has been collected in 26 years of sampling. Clearly, there’s not much mating going on here. Why are these hollowed-out, relatively meatless males, far from any known spawning grounds, counted in the model as viable spawners? Clueless managers, oblivious to the reproductive implications of the molting bottleneck common to all crab species, used this same kind of counting during the years leading up to the Bristol Bay population’s ‘mysterious’ collapse in 1980-81.

Bering Sea Bachelor Grounds

All of these data and observations from Japanese, Soviet, and US researchers, indicating that Bering Sea red king crab do not molt and mate in the same year, were compiled and published in 2005 by Dew and McConnaughey for the convenience of red king crab managers and modelers. However, despite the concurrence of scientists from three nations, the information has been ignored by ADF&G’s red king crab model-maker, Dr. Jie Zheng.

In 2009 an independent review of the Zheng model by the Center for Independent Experts (CIE) recommended the following:

Assess mature male molting time. If a fraction of mature males are not capable of mating during the survey time (Dew 2008), then the current calculation of mature males available for mating (>120 mm) would be overestimated.

Dr. Zheng’s non-response to this CIE review comment, which can be found in the 2011 Crab SAFE on the North Pacific Fishery Management Council (NPFMC) web site, is that Dew (2008) is wrong. Fair enough, but what about the work of USFWS (1942), Wallace et al. (1949), Kawasaki (1959), Korolev (1964), Chebanov (1965), Miyahara and Shippen (1965), Rodin (1970), Fujita et al. (1973), Rodin (1990), and Takeshita et al. (1990)? Unlike Dr. Zheng, these were research scientists who worked in the Bering Sea. Dr Zheng is not a research scientist but is an ADF&G biometrician, whose job it is to acknowledge reliable information and data from biological research scientists and to incorporate such into his statistical model. It is unlikely that Dr. Zheng can produce credible data that contradicts a half-century of Bering Sea findings by Japanese, US, and Soviet scientists, as discussed in Dew and McConnaughey (2005), Dew (2008), and Dew (2010).

Incomplete Knowledge Leads To Overfishing

Why does the Zheng model assume that all male red king crab greater than 120 mm CL can and do mate each and every year with 1-3 females? What about the 25-50% of the adult male population that molts in late winter (Jan-Mar), shortly before the mating season (Feb-Jul)? Counting newly molted crab as fully functional males, as is done in Dr. Zheng’s length-based model, results in a substantial (33-100%) overestimate of annual male reproductive potential. In a male-only fishery, such miscalculation can be fatal, as understood by Canadian managers who make allowance for the fact that snow crab (Chionoecetes opilio) cannot participate in mating in the same year they molt (Sainte-Marie et al. 1999, 2002).



It would be interesting to know how the model’s flawed representation of king crab reproductive biology passes muster each year with the Crab Plan Team (CPT) and the Council’s Scientific and Statistical Committee (SSC), both of which are advisory bodies whose primary duty is to prevent overfishing. If it is true that a substantial proportion of the adult male population does not participate in mating each year, then management safeguards such as MSST (Minimum Stock Size Threshold), ESB (Effective Spawning Biomass), etc. are compromised and the Bristol Bay red king crab stock is most likely overfished.


In response to recent questions about why Bering Sea red king crab abundance is declining, Dr. Zheng offered his expert opinion that “Something’s happening out there that we don’t understand.” Perhaps Dr. Zheng, along with his CPT and SSC overseers, should begin by understanding that Bering Sea red king crab males do not molt and mate in the same year.

Literature Cited

Chebanov, S. M. 1965. Biology of the king crab, Paralithodes camtschatica (Tilesius), in Bristol Bay. Soviet Fisheries Investigations in the Northeast Pacific, part 4. TINRO 53:82–84.



Dew, C.B. 2008. Red king crab mating success, sex ratio, spatial distribution, and abundance estimates as artifacts of survey timing in Bristol Bay, Alaska. North American Journal of Fisheries Management 25:1618-1637. doi:10.1577/M07-038.1


Dew, C.B. 2010. Historical Perspective on Habitat Essential to Bristol Bay Red King Crab. In: G.H. Kruse, G.L. Eckert, R.J. Foy, R.N. Lipcius, B. Sainte-Marie, D.L. Stram, and D. Woodby (eds.), Biology and Management of Exploited Crab Populations under Climate Change. Alaska Sea Grant, University of Alaska Fairbanks. doi:10.4027/bmecpcc.2010.04


Dew, C. B., and R. A. McConnaughey. 2005. Did trawling on the broodstock contribute to the collapse of Alaska’s king crab? Ecological Applications 15:919–941.


Fujita, H., K. Takeshita, and K. Kawasaki. 1973. Seasonal movement of adult male king crab in the eastern Bering Sea revealed by tagging experiment. Bulletin of the Far East Fisheries Research Lab 9:89–107.


Kawasaki, S. 1959. Report on the research by Japan on the king crab in the eastern Bering Sea. International North Pacific Fisheries Commission 322(1):1–8, Vancouver, B.C.


Korolev, N. G. 1964. The biology and commercial exploitation of the king crab, Paralithodes camtschatica (Tilesius), in the southeastern Bering Sea, Soviet Fisheries Investigations in the Northeast Pacific, part 2. TINRO 49:102–108.


Miyahara, T., and H. H. Shippen. 1965. Preliminary report of the effect of varying levels of fishing on eastern Bering Sea king crabs, Paralithodes camtschatica (Tilesius). Rapports et Proce`s-Verbaux des Reunions, Conseil Permanent International pour l’Exploration de la Mer 156:51–58.


Rodin, V. E. 1970. Some data on the distribution of king crab, Paralithodes camtschatica (Tilesius), in the southeastern Bering Sea, Soviet Fisheries Investigations in theNortheast Pacific, part 5. TINRO 72:143–148.


Rodin, V. E. 1990. Population biology of the king crab, Paralithodes camtschatica Tilesius, in the north Pacific ocean. Pages 133–144 in Proceedings of the International Symposium on King and Tanner Crabs. University of Alaska Sea Grant Program, Report AK-SG-90-04, Fairbanks.


Sainte-Marie, B., J.-M. Sevigny, and M. Carpentier. 2002. Interannual variability of sperm reserves and fecundity of primiparous females of the snow crab (Chionoecetes opilio) in relation to sex ratio. Canadian Journal of Fisheries and Aquatic Sciences 59:1932–1940.


Sainte-Marie, B., N. Urbani, J.-M. Sevigny, F. Hazel, and U. Kuhnlein. 1999. Multiple choice criteria and the dynamics of assortive mating during the first breeding season of female snow crab, Chionoecetes opilio (Brachyura, Majidae). Marine Ecology Progress Series 181:141–153.


Takeshita, K., H. Fujita, and S. Matsuura. 1990. A note on population structure in the eastern Bering Sea adult red king crab, Paralithodes camtschatica. Pages 427–433 in Proceedings of the International Symposium on King and Tanner Crabs. University of Alaska Sea Grant College Program, Report AK-SG-90-04, Fairbanks.


USFWS (U.S. Fish and Wildlife Service). 1942. Report of the Alaska crab investigation. Fishery Market News 4(5a).

Wallace, M. M., C. J. Pertuit, and A. H. Hvatum. 1949. Contributions to the biology of the king crab, Paralithodes camtschatica (Tilesius). U.S. Fish and Wildlife Service Fishery Leaflet 340.


Keep yer flippers wet.