Following consecutive years of record warm temperatures, scientists in 2021 saw the lowest abundance of adult snow crabs and immature female crabs ever observed in the nearly 50 years of NOAA Fisheries’ annual bottom trawl survey of the eastern Bering Sea. Data collected during these surveys are used, along with data compiled by trained observers on commercial fishing vessels, and laboratory analysis of age and growth data to estimate the population abundance and sustainably manage commercially important crab and groundfish species.The survey measures biomass indices — that’s the amount of crab by weight in metric tons, or mt caught.
This year, despite a return to cooler temperatures, the survey estimates for mature male (20,403 mt) and female snow crab (20,941 mt) are even lower. They are 22 percent and 33 percent lower, respectively, than the 2021 estimates. This is the lowest estimate in the time series for mature male abundance and the third lowest for mature female abundance.
The results are not surprising given what scientists observed last year. It often takes several years to see population and ecosystem shifts after significant environmental events like what occurred during the heatwave events of 2016, 2018, and 2019 in the Bering Sea.
“The positive news is that we saw a significant increase in immature snow crab abundance, both males and females. Depending on how many of these young crabs actually survive to adulthood, this could be one bright spot for the fishing industry in a few years,” said Mike Litzow, survey lead and director of the Alaska Fisheries Science Center’s Kodiak Laboratory. “We are providing these early results to stock assessment scientists and resource managers to inform science and management discussions that will occur over the next few months to identify fishery management measures for the 2023 fishing year.”
A Closer Look at 2022 Eastern Bering Sea Survey Results for All Alaska Crab
We develop survey abundance estimates for the seven commercial crab stocks sampled during the eastern Bering Sea bottom trawl survey. These estimates have fluctuated dramatically over the 1975–2022 time series. Overall, mature male biomass of commercial crab stocks decreased from approximately 300,000 mt to below 100,000 mt in the mid-1980s. This was followed by an increase to nearly 500,000 mt in the early 1990s, attributed to increases in snow and Tanner crab. Total mature male biomass then leveled out around 200,000 mt between 2005 and 2015, but has been steadily dropping since. The 2022 total estimated mature male biomass for all stocks was 64,894 mt, 11 percent higher than the record-low estimate from 2021.
Snow Crab
Legal male snow crab estimated biomass was approximately 33,447 mt. This represents a 44 percent decline in estimated biomass since 2021. It is less than one third of the previous 20-year average of approximately 110,299 mt.
Bristol Bay Red King Crab
In 2022, mature and immature male and female biomass estimates were higher than in 2021. However compared with historic values, male and female populations remain low across all size classes. Estimated legal size male biomass was approximately 18,060 mt. This estimate is higher than 2021, but less than the previous 20-year average of 27,106 mt. The majority of legal males were concentrated around central Bristol Bay and south to the Black Hills. Mature and immature male Bristol Bay red king crab biomass estimates were 21,832 mt and 3,129 mt, respectively. The 2022 mature female red king crab biomass estimate was 10,280 mt and the immature female biomass estimate was 946 mt. The mature female biomass estimate in 2022 increased by 3 percent from the 2021 estimate, but was well below the 20-year average of approximately 31,771 mt. Estimates for immature female biomass were greater than 2021 values. However, female abundance across all size classes remains low compared with historic values. The majority of mature female red king crab were in central Bristol Bay, while immature females were generally in shallower waters closer to shore.
Tanner Crab
Estimated abundance generally increased in waters east 166°W (with the exception of mature females), but declined or remained constant in the west compared to 2021. The biomass estimate for legal male Tanner crab east of 166° W (those with a shell wider than 120 mm) was approximately 6,450 mt. The 2022 estimated biomass of legal Tanner crab in the eastern area was higher than in 2021, but well below the previous 20-year average biomass of approximately 12,885 mt. Estimated mature male biomass was 8,725 mt and the immature male biomass estimate was 6,036 mt. Mature and immature biomass estimates increased over 2021 values, but remain relatively low. Estimated biomass for mature female Tanner crab was 1,800 mt, while the immature female Tanner crab estimated biomass was 690 mt. Estimated mature female biomass declined from 2021 and was below the previous 20-year average of approximately 3,692 mt.
The 2022 biomass estimate for legal male Tanner crab west of 166°W (shells wider than 110 mm) was approximately 5,131 mt. The 2022 estimated biomass of legal Tanner crab in the western area was well below the previous 20-year average biomass of approximately 19,373 mt. Estimated mature male biomass was 6,816 mt and the immature male biomass estimate was 7,676 mt. Both mature and immature male biomass decreased for western Tanner crab from 2021 values. Estimated biomass for mature female Tanner crab was 4,767 mt, while the immature female Tanner crab estimated biomass was 1,975 mt.
St. Matthew Island Blue King Crab
Abundance estimates increased from 2021 estimates across all size and sex categories. The St. Matthew blue king crab population has gone through three peaks in abundance and corresponding fishery openings and closures. The fishery has been closed since 2016. Legal male crab biomass was estimated at 1,467 mt. The legal male biomass estimate was similar to 2021 and well below the previous 20-year average of around 2,373 mt. The mature male biomass estimate was 1,902 mt and the immature male biomass estimate was 1,352 mt. One or two stations often greatly affect the population estimates for St. Matthew Island blue king crab. The mature female blue king crab biomass estimate was 549 mt and the immature female biomass estimate was 360 mt. The 2022 mature female biomass estimate is similar to 2021 and higher than the previous 20 year average (142 mt). In 2022 immature male biomass and abundance estimates are the highest they have been in a decade, although mature male estimates are depressed. Female abundance and biomass estimates have been elevated over the past four years.
Pribilof Islands Red King Crab
Estimated abundance for mature females declined, while estimated abundance for mature males showed a moderate increase. Legal male biomass was approximately 5,075 mt, which was higher than in 2021. This is similar to the previous 20-year average of approximately 4,982 mt. The biomass estimate for mature males was 5,105 mt and 0.1 mt for immature males. The biomass estimate for mature females was 989 mt and no immature females were caught. Historically, red king crab were not abundant in the Pribilof District and they were caught as bycatch in the blue king crab fishery.
Pribilof Islands Blue King Crab
Male and female abundance remains low. Legal male crab biomass was estimated at 111 mt, which was below the average of approximately 270 mt for the previous 20 years. Only two males were caught in the Pribilof District, both of which were of legal size. The biomass estimate for mature females was 145 mt and no immature females were caught. Mature female biomass in 2022 was less than the previous 20-year average of approximately 380 mt.
Northern District Red King Crab
There is no commercial fishery currently operating for this area. The 2022 biomass estimate of legal-sized males (shells larger than 135 mm) was 1,754 mt. The biomass estimates for mature and immature males were 2,335 mt and 423 mt respectively. Estimated mature male biomass increased from 2021 and was the second highest on record. Estimated biomass of mature and immature female red king crab was 1,550 mt and 15 mt, respectively. The 2022 biomass and abundance of mature females declined from 2021, but was higher than any other year in the time series.
Other Information Collected to Inform Management
The State of Alaska manages the Bering Sea/Aleutian Islands King and Tanner Crabs Federal Fishery. State regulations are subject to the provisions of the management plan, the Magnuson-Stevens Act national standards, and other applicable federal laws.
Each year, NOAA Fisheries conducts research surveys to collect biological information to inform crab and fish stock assessments that are used to support management decisions. Specifically, all crab sampled in the survey are sorted by species and sex, and a total catch weight is obtained for each species.
Key Studies This Year
- Using pop-up satellite tags to learn more about Bristol Bay red king crab and commercial size snow crab movements
- Collecting biological samples to estimate age and body condition of snow crab
- Collecting and analyzing blood samples from immature snow crab to monitor the prevalence of bitter crab syndrome
- Collecting snow crabs for laboratory experiments to quantify the impact of temperature on bitter crab syndrome and black eye syndrome progression
- Collecting Tanner crab to better understand the impacts of ocean acidification
Data are still being analyzed for the northern Bering Sea. That data will be presented during the North Pacific Fishery Management Council Crab Plan Team meeting the week of September 12.
