Southern Resident orcas are facing an accelerating risk of extinction, a new study has found.
The study, published in Nature, reports that the population, which lives in areas across Alaska, Washington state, Oregon and California, is declining by one percent every year.
The killer whales are under threat for a variety of reasons, including a lack of prey. Orcas feast exclusively on chinook salmon which are declining in their home waters.
"Wildlife species and populations are being driven toward extinction by a combination of historic and emerging stressors (e.g., overexploitation, habitat loss, contaminants, climate change), suggesting that we are in the midst of the planet's sixth mass extinction," says the study.
"The invisible loss of biodiversity before species has been identified and described in scientific literature has been termed, memorably, dark extinction. The critically endangered Southern Resident killer whale population illustrates its contrast, which we term bright extinction; namely the noticeable and documented precipitous decline of a data-rich population toward extinction."
There are only around 75 Southern Resident orcas alive today, making the situation dire. And this number seems only set to decrease.
"Here we use a population viability analysis to test the sensitivity of this killer whale population to variability in age structure, survival rates, and prey-demography functional relationships," the authors write in the study. "Preventing extinction is still possible but will require greater sacrifices on regional ocean use, urban development, and land use practices, than would have been the case had threats been mitigated even a decade earlier."
The main cause for the decline is mainly down to "unsustainable" levels of fishing between 1970 and 1980 the study reports. This severally limited the salmon population, as well as causing noise which "reduces foraging efficient" for the whales, contamination. All these factors also mean calves are less likely to live.
Salmon are also suffering from warming water conditions, meaning their population continues to decline.
Chief scientist and co-founder of Ocean's Initiative, Rob Williams, who worked on the study, told Seattle's King 5 news site that Southern Resident orcas could do with half the amount of noises currently being produced, and 30 percent more salmon than current levels, to boost their numbers.
The Southern Resident killer whale population is important for a number of reasons, and are a protected species. Not only are they culturally important to their region, but they have an important role in the food chain and as a result, the ecosystem.
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