Destructive human behaviour at root of orca plight

photo of David Suzuki

SCIENCE MATTERS
by David Suzuki

News about orca mother Tahlequah carrying her dead newborn for 17 days through the Salish Sea this summer was heartbreaking, and rightfully captured the world’s attention. It highlighted the plight of one of Canada’s most endangered marine mammals. The southern resident killer whale (orca) population has dropped by 25 per cent in two decades. Just 74 remain, and none has successfully given birth in three years.

The southern residents’ survival depends on chinook salmon, their primary food. In the Fraser River, 11 of 15 chinook stocks are highly depleted and require conservation action. Habitat destruction, fisheries, agricultural runoff, warming and acidifying waters from climate change, and disease threats from open net-pen salmon farms all play roles in chinook decline. Commercial and recreational fisheries compete with whales for salmon, and their presence, along with all ocean traffic, disrupts the feeding whales.

Sports fishing groups attribute chinook declines to seals and sea lions and are calling for culls. But blaming seals doesn’t explain low chinook returns.

It’s tempting to look for simple linear solutions such as a cull, but it’s highly unlikely to have the desired outcome. The complexity of marine food webs requires a non-linear view that includes millions of ecological possibilities. According to one study, only four per cent of a harbour seal’s diet is salmon, and an even smaller proportion is chinook. Seals eat all species of juvenile salmon, and only rarely the adult salmon recreational fisheries target. It’s plausible that a seal’s presence increases rather than decreases chinook numbers.

Many people calling for seal and sea lion culls also point to increased hatchery production as the best solution to plummeting wild salmon stocks. But during more than 130 years of West Coast hatcheries, fisheries have collapsed, and wild salmon populations have declined. The proliferation of hatcheries between 1900 and 2014, among other factors, led to a 97 per cent reduction of wild Puget Sound steelhead.

Pacific salmon are an adaptive species, capable of measurable genetic variations within 17 generations and able to adjust to the variable natural environments where they were born. Artificially selecting parents in a hatchery removes much of the natural selection necessary to ensure effective adaptation.

Hatchery fish can never really be wild. Their presence can do more harm than good. Those that survive compete with wild fish for food, and in some cases may eat smaller wild fish. Often the use of hatcheries results in a drive for more fishing to justify hatchery costs or to avoid taking necessary actions such as reducing catch and restoring habitat to rebuild wild fish populations.

Commissioner of the Environment and Sustainable Development Julie Gelfand called the federal government’s measures to protect endangered orcas reactive, limited and late. Humans are the main threat to wildlife. We must take responsibility and change our destructive ways. If we want orcas and other species to survive, we should look in the mirror and change our own behavior.

Excerpted from the original article. David Suzuki is a scientist, broadcaster, author and co-founder of the David Suzuki Foundation. Written with contributions from David Suzuki Foundation senior editor Ian Hanington. Learn more at www.davidsuzuki.org

1 thought on “Destructive human behaviour at root of orca plight”

  1. “According to one study, only four per cent of a harbour seal’s diet is salmon.” What study? Only one? This does not support the argument. If you can find only one study it is probably bogus.

Leave a comment

*