Sunday, March 17, 2019

The Heat Is On

Resident Killer Whales
With the resident killer whales starving to death, and much lower than anticipated chinook and sockeye salmon runs this past summer, the finger pointing has begun, with commercial and recreational fishermen, along with some First Nations people, leading the call for a culling of seals and sea lions. Claiming these creatures have upset the ecological balance a group calling themselves the Pacific Balance Pinnipeds Society (PBPS) wants to start hunting seals and sea lions and sell their meat, blubber, and fur on the open market. The DFO (Department of Fisheries & Ocean) estimates there are 100,000 seals in B.C. waters and the PBPS group would like cut this number in half by starting to harvest at least 2,000 of them annually along with 100 sea lions to reduce the pressure on salmon stocks. If only it were that simple....

Stellar Sea Lions

For starters, according to the Marine Mammal Research Consortium, 80% of the Stellar sea lion population has disappeared since 1980 leaving only 50,000 individuals in the wild and causing the U.S. government to declare them an endangered species in the waters of Alaska. While there are a number of theories as to what has caused such a sharp decline the most widely accepted explanation is nutritional stress. The diet of Stellar sea lions was historically made up of 60% herring, which has a very high fat content, some salmon and 30% from the gadidae family of fish which includes cod, hake, and pollock. With the decline of herring due to over-fishing, herring now make up less than 20% of their diet with the balance made up mostly from the gadidae fish family. The gadidae fish have less than 10% of the oil content of herring and this low-fat low-calorie diet has resulted in malnutrition, juvenile mortality, and failed pregnancies in the sea lion population. The amount of salmon in their diet hasn't changed.

California Sea Lions

The other sea lion species common to the B.C. coastline is the slightly smaller California sea lion of which there are an estimated 350,000 individuals. They range from southeast Alaska to central Mexico and, while not considered endangered, it is still a protected species though permits in the U.S. have been granted to kill them when they get too close to certain salmon spawning areas in the Columbia River. The primary fish in their diet however is North Pacific hake/whiting, which they follow up and down the coastline, though they also eat other fish species and squid. The California sea lions in turn make up one of the most common food items for the transient killer whales and great white sharks.

Harbour Seals
Harbour seals are the most common pinniped in B.C. waters and they can live up to 20-30 years and weigh up to 300 lbs. Not surprisingly their diet is made up mostly of fish with herring being the main ingredient from December to March and North Pacific hake/whiting the rest of the year. Only 4% of their diet is salmon. Transient killer whales are their main predators.

Each year in late spring millions of juvenile Pacific salmon leave the fresh water as smolts to enter the ocean and being the process becoming adult salmon which can take 1 - 5 years depending on what species they are. It is at this time in their life cycle they are most vulnerable to a wide range of predators including seals and North Pacific hake/whiting.

North Pacific Hake/Whiting

The North Pacific hake/whiting grows up to 3 feet in length, lives up to 20 years and its diet includes plankton, shrimp, herring, and juvenile salmon. The species supports an important commercial fishery and its population is considered to be very healthy. It's obviously critical to the sea lion and seal populations who follow the fish as it makes its way up north in late spring/summer. Then while it returns via an offshore route to Mexico and California to spawn, the sea lions and seals turn their attention to the migrating herring.

However, since the 1960's collapse of the herring fishery the recovery has been very slow. The importance of the Pacific herring cannot be overstated. Without the herring the Stellar sea lions are dying of malnutrition as are the chinook salmon who depend on it for over 60% of their diet and the southern resident killer whales who, in turn, depend on chinook salmon for 80% of their diet.

Feeding and spawning grounds for B.C. herring
Without herring other fish and mammals have to find alternative things to eat though they don't all have the same adaptability. The Pacific hake/whitefish have no problem eating juvenile salmon but the resident killer whales can't seem to make the switch to other salmon species. Seals and sea lions will eat whatever is available and they seem to be doing quite fine but killing seals and sea lions who eat Pacific hake/whitefish will only aggravate the problem for the salmon and reduce the amount of prey available to the transient killer whales. The obvious solution to this mess is to ban any fishing of herring or Chinook salmon. Trying to solve the problem by selective killing will only create more imbalances.

MV Kaganovsky
In the meantime a group of scientists from Russia, Canada, the United States, Japan, and South Korea have set out on a test fishery in the Gulf of Alaska to try and figure out the secret lives of the 5 Pacific salmon species. Sailing on board the Russian ship Kaganovsky they will be analyzing catches of salmon and other species from Haida Gwaii to Alaska to try and gain a better understanding of what goes on when these fish leave coastal waters. It's the Year of the Salmon and the heat is on to try and get some answers.

Range of Pacific Salmon Species

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