NOAA Fisheries answers questions about what is behind the declines in snow crab and salmon and how we are addressing them.
We have been studying Alaska marine ecosystems for more than 50 years. During 2014–2016, we observed a series of marine heatwaves in the north Pacific focused mostly on the Gulf of Alaska. In 2018 and 2019, additional heatwaves reached the Bering Sea. Sea ice was at an all-time low, and bottom temperatures at an all-time high. These heatwaves were something we had never seen in the history of our fisheries research surveys in the Bering Sea. Marine heatwaves are projected to increase in frequency and duration due to climate change. During and after these recent events, together with federal, state, academic, industry and private sector research partners, and Alaska Indigenous community members, we have observed dramatic declines in some species.
In a number of these situations, changes in the marine food web and prey availability were identified as a leading factor in the declines.
We are going to continue to:
Recent marine heatwave conditions we experienced in the Bering Sea and Gulf of Alaska have helped us to better understand how the animals we have been studying for decades are responding to changing ocean conditions. But we need to work together—scientists, managers, small-scale and large-scale fishing businesses, non-governmental organizations, private industry, local communities, and Indigenous communities. Only through our collective knowledge and understanding will we be able to meet the challenges that lie ahead.
For NOAA Fisheries, bycatch refers to “discarded catch of marine species and unobserved mortality due to a direct encounter with fishing vessels and gear.”
NOAA Fisheries works with the North Pacific Fishery Management Council to implement management measures and refine existing measures to minimize bycatch while also allowing for optimum yield as required by the Magnuson-Stevens Act. We do this by:
The U.S. federal government and the State of Alaska jointly manage the Bering Sea and Aleutian Islands crab stocks listed in the Federal Fishery Management Plan through the North Pacific Fishery Management Council. The State of Alaska solely manages the Gulf of Alaska crab stocks. NOAA Fisheries works closely with the state to provide science to manage federal crab stocks.
The State of Alaska manages the salmon fisheries that occur within 3 nautical miles from shore. The federal government has jurisdiction over salmon fisheries occurring between 3 and 200 nautical miles from shore in the Exclusive Economic Zone (EEZ).
The Council’s Federal Fishery Management Plan (FMP) for the salmon fisheries in the EEZ off Alaska divides management into the West Area and the East Area. The East Area is the area of the EEZ in the Gulf of Alaska east of the longitude of Cape Suckling.
The FMP delegates management authority over the salmon troll and sport fisheries in the U.S. EEZ in the East Area to the State of Alaska. The Southeast Alaska troll fishery is currently the only commercial salmon fishery authorized by the Salmon FMP.
The Salmon FMP prohibits commercial fishing for salmon in the West Area, which is the area of the EEZ off Alaska west of the longitude of Cape Suckling, including the Gulf of Alaska, Bering Sea, Chukchi Sea, and Beaufort Sea.
The West Area has historically excluded three pockets of Federal waters from the FMP, thereby deferring management to the State of Alaska. As a result of litigation, NMFS is currently working to incorporate one of these areas--the EEZ waters of Cook Inlet--into the Salmon FMP. Pursuant to a court order, NOAA Fisheries must implement a new management regime for the Cook Inlet EEZ by May 2024.
In addition to federal salmon fisheries management NOAA Fisheries has responsibilities to conduct research on salmon that return to rivers in Canada as part of the Pacific Salmon Treaty. The Pacific Salmon Treaty was signed by Canada and the United States in 1985. It provides a framework for the two countries to cooperate on the sharing and management of Pacific salmon. The Pacific Salmon Commission, composed of representatives of each country, oversees implementation of the treaty. The commission negotiates salmon fishery management regimes for the stocks of common interest, and the two countries must manage their fisheries consistent with any regimes recommended by the Commission and approved by the United States and Canada. Within the United States, the states (Alaska, Washington, Oregon and Idaho) and the tribes are responsible for regulation of their fisheries consistent with regimes agreed to by the Commission. The treaty includes provisions regulating salmon fisheries from Alaska to mid-Oregon, including the marine waters and Transboundary rivers of Southeast Alaska, and the Yukon River. In 2018, the commission negotiated a new 10-year agreement for the conservation and sharing of Pacific salmon. The new Agreement is in force from 2019 through 2028, with regular review of stock status and regulatory effectiveness throughout that period. The commission includes substantial technical and policy support by the states, tribes, first nations and federal entities, ensures fisheries are in compliance with treaty provisions, and makes adjustments consistent with the needs of the salmon resource.
Salmon bycatch primarily occurs in the pelagic trawl fisheries in Alaska. It is closely monitored by independent fisheries observers and is limited in Federal regulation by caps.
Eastern Bering Sea snow crab stock was declared overfished under federal law once before in 1999. This means that their abundance was too low to support much fishing. Numerous factors can result in this designation, due to both environmental and human activities. But that was a more gradual decline that arose from a lack of recruitment, meaning few juvenile crabs survived to transition to older ages, not a sudden mortality event. The fishery was declared rebuilt in 2011 as new recruitment supported the stock abundance increase. The fishery has never been closed before.
Under federal law, a stock is overfished when the population size gets too low, jeopardizing its ability to produce maximum sustainable yield. Overfishing is when it is harvested at a rate higher than would support maximum sustainable yield.
We have been surveying the same areas, which cover the distribution of crab and other important commercial fish species in the Bering Sea, for four decades. In recent years, we expanded our survey to include the northern Bering Sea. We also have other data that corroborate what we observed in our survey including observer data, which is collected from observers on commercial fishing vessels.
Movement to the northern Bering Sea could account for declines in the eastern Bering Sea. But, surveys in the northern Bering Sea did not find crab in the quantities or of the correct sizes to explain declines in the south. Movement west into Russian waters is another possibility, but Russian scientists reported declines in catch per unit effort in 2020. Catch per unit effort usually increases with higher abundance.
While it is possible that some crab moved into deeper waters, it is unlikely that all of the missing crab from the shelf are on the slope. The amount of available habitat is less than 10 percent of that on the shelf, and fishery catch per unit effort from 2022 was the lowest on record. We also have observer data from fishing vessels that is consistent with what we observed in our survey.
Whenever we look at fishing mortality we have to remember that exploitation only occurs on very large males. Very few females are caught and a large fraction of the mature male biomass is protected from exploitation by size preferences. The vast majority of crab that disappeared in the collapse during 2018–2021 were not large enough to be captured by the directed crab fishery. If captured in the directed fishery, females and smaller males are discarded back into the water and are considered to have relatively low mortality rates. Our management system has rigorous controls in place that track catch and abundance. However, these controls cannot account for unpredictable events like we experienced in the Bering Sea during 2018 and 2019.
Total snow crab abundance (the count of crab numbers) was down 60 percent in 2019 compared with the 2018 high point. Much of the decline was driven by a decline in immature crabs, and in retrospect scientists can see that this was the beginning of the population collapse. However, the biomass (total weight) of the largest males that support the fishery actually increased in 2019, as large numbers of crab grew to the larger sizes that can be fished. Since the fishery is managed according to the biomass of the largest males, this change resulted in an increase in the quota. In 2020–2021 catches were higher. This was a result of not having the 2020 survey, which was canceled due to the COVID-19 pandemic. If we had had those data we could have reacted sooner.
All of these factors cause snow crab mortality. None of these factors alone could account for the full magnitude of the decline in stock abundance observed in fisheries surveys and in observer data. What changed in 2018 and 2019 was a dramatic shift in environmental conditions across snow crab habitat— record high bottom temperatures in the Bering Sea and record low sea ice. It is likely that a combination of factors related to heatwave conditions contributed to the decline. Preliminary studies suggest that starvation was likely a key factor in the decline across juvenile and adult crabs.
Pacific cod are one of the largest predators of snow crab in the Bering Sea. Typically, when we observe crab in cod stomachs, they are primarily smaller than 55 millimeter carapace width, with the majority smaller than 40 millimeter carapace width. The crab that went missing from 2018 to 2019 were 50–70 millimeter in carapace width, largely outside the range of predation risk by cod during those years. In addition, relatively few Pacific cod were present in the eastern Bering Sea when these crab disappeared.
Bitter crab syndrome is a fatal disease caused by a parasitic dinoflagellate. Within Bering Sea monitoring sites, prevalence of bitter crab syndrome increased annually from 2014-2017. Scientists are continuing to monitor disease and efforts are underway to determine the prevalence of bitter crab syndrome in archived Bering Sea snow crab samples from 2018, 2019 and 2022.
The decline in snow crab biomass from the 2018 survey to the 2021 survey was 1.4 billion pounds. Total estimated snow crab bycatch mortality in all groundfish fisheries (trawl and pot) in the three years from July 1, 2018 to June 30, 2021 was 937,078 pounds. That's about 0.06 percent of the total decline.
Bycatch occurs to some degree in both the directed crab pot fisheries and other fisheries for groundfish. Discards of snow crab in groundfish fisheries has been highest in the yellowfin sole trawl fishery. Lesser amounts are taken in the flathead sole trawl fishery, the Pacific cod bottom trawl fishery, rock sole trawl fishery, and the Pacific cod hook-and-line and pot fisheries. Bycatch in other fisheries has historically been low.
Crab disappeared over the entire the survey area, not just in the areas where the cold pool usually sits. Immature male and female snow crab (31–60 millimeter carapace width) are usually found in the area occupied by the cold pool (<2℃). They tend to concentrate in colder, shallow waters of the northern Bering Sea and eastern Bering Sea middle shelves. Mature female snow crabs appear to track near-bottom temperature during a northeast to southwest migration to warmer waters near the shelf break. Large males (larger than 95 millimeter carapace width) typically prefer warmer, deeper water. We saw declines across all of these groups.
In laboratory and field studies, water temperatures above 4-5°C lead to decreased growth, energetic condition and survival of juveniles. Immature snow crab have narrower thermal preferences than adults and seek cold water habitats as refuge from groundfish predators.
Since the mid-2000s, snow crab stock abundance has been increasing and independent fishery observers have closely monitored the pollock fleet. The number of crab taken as bycatch in the pollock fishery is low. The juvenile crab that disappeared, grew and thrived for around 8 years under similar pressure from the pollock and other trawl fisheries. What changed in 2018 and 2019 was the absence of ice and the associated cold pool. Pollock bycatch did not increase during these years, but it did increase during 2020 and declined again in 2021. However, the numbers of crab taken in the fishery at any time were not significant enough to cause the snow crab population decline.
Each year, through the North Pacific Fishery Management Council public process, snow crab bycatch limits are set for the Bering Sea Aleutian Islands groundfish trawl fishery operating in the C. Opilio Bycatch Limitation Zone (COBLZ). This bycatch limit in the groundfish fisheries includes the pollock fishery, which receives a portion of the overall limit. To determine the PSC, the Council uses a formula that accounts for annual survey abundance estimates. The snow crab PSC by the pollock fishery is low and in recent years the fishery has not reached its PSC limit.
There was an increase in snow crab bycatch in the yellowfin sole fishery in 2018–2019 and 2019–2020. The increase in this fishery alone seen during these two years was not significant enough to cause a decline of the magnitude seen in the snow crab survey in 2019 and 2021. The bycatch increase was much lower than historical levels that occurred in the 1990s and the increase was a function of there being more snow crab in the Bering Sea than ever before.
Through our annual northern Bering Sea ecosystem surface trawl survey we monitor abundance, condition, and distribution of juvenile salmon in the ocean.
There is a direct relationship between the abundance of juvenile Chinook salmon that we see in the northern Bering Sea surface trawl and ecosystem survey during the summer and the number of adult fish that return to the Yukon River to spawn 3 to 4 years in the future. Recent increases in freshwater temperature and discharge levels during the spawning migration of Yukon River Chinook salmon have been linked to the decline in the number of juveniles produced per spawner.
Juvenile surveys in the northern Bering Sea have identified key differences in the critical survival periods for chum and Chinook salmon.
The initial forecast model for Yukon River chum salmon is under development by Sabrina Garcia at the Alaska Department of Fish and Game. It identifies that juvenile and adult abundance covaried over time. However, this relationship did not hold up during the marine heatwaves in the Bering Sea and Gulf of Alaska. The survival and condition, or fat reserves, of juvenile chum salmon declined with warming temperatures. Prey quality and quantity are thought to be an important factor in the condition and survival of Yukon River chum during their marine life-history stage.
This is supported in NOAA Fisheries surveys. In 2016–2019, when ocean temperatures were warmer than average, scientists observed low abundance of certain high-fat zooplankton. These small planktonic animals form the base of the northern Bering Sea marine food chain for whales, seals, sea birds, walrus and young fish, like salmon and pollock.
When scientists looked at what juvenile chum salmon were feeding on during warm years, they noticed a high proportion of jellyfish and anemones in their stomachs. This group of species has just half the caloric content of the zooplankton species that chum are known to eat. The chum caught in 2018 and 2019 were also smaller than average. The prey quality, quantity and warm ocean temperatures while young salmon are in the ocean impacts their growth and fat reserves during the summer.
Juvenile western Alaska chum salmon spend their first summer at sea feeding and growing within the shelf waters of the northern Bering Sea. These salmon migrate offshore during late fall, and spend their winter in the Gulf of Alaska. Juvenile chum salmon fed on lower quality prey and were smaller in size during the extreme warm events of 2016 through 2019 along the northern Bering Sea shelf. They then migrated to the Gulf of Alaska where the second marine heatwave was occurring. Reduced fat reserves from summer and higher metabolic rates during winter, a period of reduced prey availability, likely led to high mortality of these fish.
The answer may lie in critical periods during marine residence and the migration pathways that these salmon take during different stages of their marine life. Juvenile western Alaska chum salmon (in the northern Bering Sea) spend their first summer at sea in the northern Bering Sea feeding, growing, and laying down fat reserves. These salmon migrate to the Gulf of Alaska during winter. Survey data from the northern Bering Sea indicate that these juveniles were in poor condition (low fat reserves) at the end of their first summer. They migrated to the Gulf of Alaska for winter, and entered their winter habitat during the second marine heatwave. Low fat reserves from summer, increased competition for limited resources, and higher metabolic rates during winter led to high mortality for these salmon.
Juvenile Bristol Bay sockeye salmon spend their first summer at sea feeding and growing within the southern Bering Sea. Past survey data indicates that these salmon are higher in relative abundance and are in good condition during years with warm sea temperatures. These salmon spend their winters in the central North Pacific Ocean and western Gulf of Alaska, regions that were not as directly impacted by the marine heatwaves.
Bycatch of salmon has been occurring, and has been closely monitored, in the pollock trawl fishery for a number of years.
Between 2011–2021 annual estimates of chum salmon bycatch from Western Alaska ranged from 3,061 to 66,199 with an average of 39,904. Estimates from Yukon River fall stocks ranged from 1,044 to 28,061 with an average of 9,448. In 2021, bycatch from the Western Alaska group was estimated to be 48,656 and bycatch from the Yukon River fall stocks was estimated to be 2,854. Genetic research shows that 9.4 percent of the total chum bycatch was from western Alaska (2021).
The most recent estimate of Chinook salmon bycatch is from 2020 and indicated that 16,796 fish from Coastal Western Alaska stocks, 670 fish from the Middle Yukon River stock, and 729 fish from the Upper Yukon River stock were caught. The majority of Chinook salmon caught as bycatch were from Western Alaska, British Columbia, and lower 48 populations. The proportion of Middle (2 percent) and Upper Yukon (2 percent) stocks in 2020 was similar to the 10-year average (2 and 4 percent respectively).
To address bycatch in foreign fisheries, a fishery management plan amendment established Chinook salmon PSC limits in the early 1980s. The salmon savings areas were created in 1995. The Council has been actively addressing Chinook and chum salmon PSC measures since the mid-1990s. Previously triggered time and area closures (Salmon Savings Areas) have been used to manage chum and Chinook in the Bering Sea. These closures were designed based on analyses of groundfish observer data collected from 1990 through 1995.
Amendment 91, implemented in 2010, created a hard cap for Chinook salmon that varies based on abundance of western Alaska stocks and an incentive program to minimize bycatch of chum salmon. It is an innovative approach to managing Chinook salmon bycatch in the Bering Sea pollock fishery. It combines a prohibited species catch limit on the amount of Chinook salmon that may be caught incidentally with an incentive plan agreement and performance standard designed to minimize salmon bycatch to the extent practicable in all years. This is necessary to minimize Chinook salmon bycatch in the Bering Sea pollock fishery while maintaining the potential for the full harvest of the pollock total allowable catch. Amendment 91 is intended to promote the goals and objectives of the Magnuson-Stevens Act, the Fishery Management Plan, and other applicable laws.
Amendment 110, implemented in 2015, created a comprehensive Chinook and chum salmon bycatch avoidance program. It revised language in the “Chum Salmon” and “Chinook Salmon” entries in the “Prohibited Species Catch (PSC) Limits” section of the Fishery Management Plan.
Efforts continue to reduce chum and Chinook bycatch. The State of Alaska has established a Salmon Bycatch Taskforce. On November 28, 2022, the North Pacific Fishery Management Council held its first Chum Salmon Bycatch Committee meeting to begin discussions to look more closely at chum salmon bycatch, building on the continuing efforts it has undertaken to reduce Chinook bycatch.
More information on chum salmon bycatch
Scientists at the Alaska Fisheries Science Center are engaged in a number of research efforts to provide important information to help resource managers understand and mitigate this issue.
Our Genetics Program is exploring ways to help the fishing industry avoid catching specific stocks of salmon through integrative analyses that combine large datasets to predict stock specific distributions. Additionally, the genetics lab has decreased the analysis time for chum salmon by nearly a year and will do the same for Chinook salmon. This will ensure these important data are made available sooner.
The Center’s Resource Assessment and Conservation Engineering Program also studies fish behavior inside commercial fishing nets. We are working with the commercial pollock fishing industry to develop salmon excluders. Scientists are also collaborating on a study to develop species distribution models to predict Chinook salmon and pollock fleet overlap.
Oceanic whitetip shark. Hawaiʻi longline fishermen use leaders to connect weighed branch lines and baited hooks. A new rule prohibits steel wire leaders in the Hawaiʻi deep-set longline fishery, starting May 31, 2022. The rule aims to increase the survival of hooked oceanic whitetip sharks caught as bycatch in the Pacific Islands region. Credit: Andy Mann
A pod of killer whales in Alaska waters.
