| Dungeness (s’áaw), King, and Tanner (x’éix̲) crabs are all commonly caught subsistence species for tribal members and are an important traditional and nutritional resource for community members. While less commonly harvested, community members also catch shrimp (s’éex’át). Crabs in Hoonah are already dealing with the effects of climate change. One community member reported that he used to pull his pots out with so many crabs in them they could barely fit through the holes, now he struggles to catch more than a dozen at a time. The same man said he noticed them migrating to other places and that the traditional spots where he used to crab weren’t as plentiful now as they were. Other tribal citizens were concerned about competition with commercial crabbers and overfishing. |
Primary Risks
Increasing ocean temperatures will disrupt molting and growth, resulting in smaller and fewer crabs.
Waters in Alaska have already warmed approximately 2 °C, which is believed to be the major driver behind issues such as the collapse of the snow crab fishery. In normal conditions, small cold traps remain at the bottom of the ocean where crabs can take refuge on hot days, but as waters warm and mixing patterns change, those spots are harder to find. Dungeness need waters between 38 and 65 °F, and in warmer waters they burn more energy, meaning they’ll need to eat more to survive, which is a problem if in the future there is likely to be fewer of the shellfish crab eat.
WARMER WATERS REDUCE THE AMOUNT OF OXYGEN IN THE WATER, SUFFOCATING CRABS.
Cold water can hold more dissolved oxygen than warm water, so when the water gets warmer, the oxygen levels drop. Low oxygen events most commonly occur in the spring and summer, when there aren’t many larvae in the water, and can kill off adult crabs. Crabs are particularly vulnerable to low oxygen events because they’re stuck on the seafloor and can’t just swim to another area where it’s easier to breathe.
WARMER WATERS WILL ALSO WORSEN HARMFUL ALGAL BLOOMS, KILLING CRABS OR MAKING THEM TOXIC.
Since crabs eat shellfish, the toxins caused by certain types of harmful algal blooms can be concentrated in the guts of crabs and lead to illness and death if consumed.Algal blooms can also lead to extremely low oxygen conditions and mass die offs. Tanner crabs are also vulnerable to bitter crab syndrome, which makes the meat toxic and commercially non-viable.
OCEAN ACIDIFICATION IS LIKELY TO DAMAGE CRABS’ ABILITIES TO GROW SHELLS AND INTERRUPT THEIR BREEDING.
Crab shells are built out of chitin calcium carbonate, which is harder to find as the ocean gets more acidic. Without the building blocks crabs need, larvae have been observed with pitted and folded shells. Crabs use their shells to swim, control their buoyancy and protect themselves from predators, all of which are crucial for their survival. The whiskers that crabs use to navigate underwater and search for prey can also dissolve off their faces, leaving them practically blind while they forage, and at low enough pH can kill larvae before they hatch. Acidic waters also slow the release of crab larvae, leading to a mismatch between the time when the crabs hatch and when the phytoplankton for them to eat is favailable. Lower pH can also disrupt their movement within the water.
INVASIVE SPECIES, SUCH AS EUROPEAN GREEN CRABS, CAN DAMAGE CRUCIAL CRAB HABITAT AND OUTCOMPETE NATIVE CRABS FOR FOOD.
Green crabs can eat up to 40 juvenile clams and mussels per day, outcompeting native Dungeness for food. They also shred eelgrass beds while foraging, which provide critical nursery habitat for young crabs. While green crabs have not yet been detected in Hoonah waters, they were discovered as far north as Metlakatla in the summer of 2022 and are predicted to reach Hoonah in the coming years.
Adaptation strategies
SHORT-TERM GOALS:
1.1: Continue water quality monitoring program to look for harmful phytoplankton with SEATOR partners
1.2: Develop European green crab monitoring program in collaboration with other tribal, state, federal and international partners
1.3: Support changes to commercial fishing regulations to protect subsistence harvest of crabs in Port Fredrick
1.4: Educate the community about the negative impacts of increasing water temperatures on crabs and other crustaceans
MID-TERM GOALS:
2.1: Establish protocols to monitor crab habitat (e.g. eelgrass beds)
2.2: Assess the need for monitoring biotoxins in crab meat
2.3: Establish environmental restoration practices to improve crab habitats around Port Frederick
2.4: Develop crustacean biomass monitoring program to look for changes in larval, juvenile and adult life stages of relevant crab species.
2.5: Establish programs and capacities necessary to participate in advocacy efforts around climate change, just transitions, and maintaining Indigenous rights
2.6: Investigate relationship between crab and other crustaceans and electromagnetic fields
2.6.1: If relevant, develop adaptation strategies using this relationship in order to reduce crustacean bycatch
LONG-TERM GOALS:
3.1: Support regional efforts to understand the effects of climate change on relevant crab species
3.2: Research shellfish resiliency – physiological costs of resilience, non-traditional shellfish harvesting and aquaculture strategies, options to mitigate paralytic shellfish poisoning, and more
3.3: Develop and support policy protections for small-scale and local resident fisherman and subsistence fishermen to maintain access to diminishing resources, while limiting large-scale shellfish and fishing harvests
3.4: Participate in natural resource management decisions / processes to eliminate adverse impacts on crabs and other crustaceans in Southeast Alaska