The primary food source for the Southern Resident orcas is salmon. In fact, approximately 80-90% of a Resident orca’s diet is composed of these fish. A National Marine Fisheries Service study in March 2010 found that orca whales consume a specific species, the Chinook salmon.
Also known as King or Tyee salmon, the Chinook salmon (Oncorhynchus tshawystscha) stocks originate in rivers from central California to northwest Alaska. These salmon are anadromous, which means that they spend the majority of their life in the ocean but return to their natal freshwater streams to spawn, or reproduce. Chinook are typically the largest of the Pacific salmon species and average 36 inches in length and 30 pounds, with larger fish reaching up to 58 inches and 129 pounds. Although the spawning cycle takes place yearly, most Chinook salmon have a lifespan of 5-7 years and do not return to spawn until the end of their lives. The adult fish die after spawning, leaving valuable nutrients in the freshwater and saltwater ecosystems. Salmon represent an integral piece of the coastal food chain, and as such have been honored as a staple food and icon of the native communities in the Pacific Northwest.
Since orcas are at the top of the food chain, much of their food is likely to carry high contamination from water pollution. The Southern Residents’ prey (salmon) consumes marine invertebrates, which in turn consume plankton and other microorganisms in the saltwater environment. These tiny creatures are susceptible to waste generated by humans in the form of heavy metals, pesticides, herbicides, medications, solvents, petroleum products, and other toxins that make their way from populated areas into the ecosystem. Each creature in the food chain carries this contamination as it is consumed and ingested by the next predator, until the salmon upon which the orcas are dependent are also carrying a remnant of human-made pollution.
According to the National Marine Fisheries Service, “Salmon are affected by a wide variety of factors in the ocean and on land, including ocean and climatic conditions, dams, habitat loss, urbanization, agricultural and logging practices, presence of wood in streams, water diversion, and predators (including humans). Wild Chinook salmon populations have disappeared from large areas where they once flourished, and several evolutionarily significant units (ESUs) have been listed or proposed for listing as at risk for extinction under the Endangered Species Act” (NOAA, 2010).
Adult orcas must eat approximately 3-4% of their body weight each day just to stay healthy. For a 5-ton mammal, this means eating about 300-400 pounds of fish daily. And since each salmon is usually caught independently, (unlike baleen whales that siphon large mouthfuls of food at once), this means that Resident orca pods spend the majority of each day seeking and hunting their prey. As responsible kayakers, we do our best to give them space and allow them to focus on their main priority: eating.
© Copyright 2015 Outdoor Odysseys | Kayaking the San Juans for 24 years.