A key assumption about dwindling numbers of southern resident killer whales pins the blame on a lack of salmon, but a study out of the University of British Columbia has found they have twice the number of chinook available in summer as their much healthier cousins, the northern residents.
Researchers spent months tracking the two whale populationsB次元官网网址� preferred food in the Salish Sea and the waters of northern Vancouver Island and their findings have now been published in the peer-reviewed research journal PLOS One.
Andrew Trites, the reportB次元官网网址檚 co-author and the director of the marine mammal research unit at the university, said they didnB次元官网网址檛 find what they expected.
B次元官网网址淚t was surprising,B次元官网网址� Trites said of his first reaction to their discovery.
B次元官网网址淲hen you find what you donB次元官网网址檛 expect, then you look even harder at your data, and your first thought is, you must have done something wrong.B次元官网网址�
This monthB次元官网网址檚 latest census of the endangered southern residents found they number just 73, compared with the growing population of the northern residents at about 300.
Trites said they double and triple-checked the salmon numbers found during the summer of 2020.
B次元官网网址淚 guess IB次元官网网址檝e learned over time that we have to be careful about jumping to quick conclusions,B次元官网网址� he said.
The report found chinook were twice as prevalent in the southern residentsB次元官网网址� feeding areas compared to those of the northern residents.
B次元官网网址淭his implies that southern resident killer whales have greater access to chinook salmon compared to northern residents during summer B次元官网网址� and that any food shortage southern residents may be encountering is occurring at other times of year, or elsewhere in their range,B次元官网网址� said the study published Oct. 10.
Trites said researchers collaborated with commercial and sport fishermen and whale-watching companies to identify the feeding areas from the entrance of Juan de Fuca Strait off southern Vancouver Island and the mouth of the Fraser River, up to waters off the northern end of Vancouver Island.
The widening population gap between the two groups of fish-eating whales has variously been attributed to ecological and biological differences between regions, such as salmon availability, competition, physical disturbance, underwater noise, contaminants and inbreeding.
B次元官网网址淗owever, food availability likely plays the greatest role in limiting their carrying capacities,B次元官网网址� the study said of southern residents.
Trites said noise is more common in southern waters which prevents southern residents from catching prey.
B次元官网网址淚tB次元官网网址檚 a bit like going into a busy supermarket and you are shopping with somebody else, but you canB次元官网网址檛 tell each other what to get because itB次元官网网址檚 too noisy.
B次元官网网址淚tB次元官网网址檚 so hustling with so many people in it that you canB次元官网网址檛 hear each other, you canB次元官网网址檛 talk about what youB次元官网网址檙e trying to get for dinner,B次元官网网址� said Trites.
The study said vessel noise can B次元官网网址渕ask communicationB次元官网网址� between pod members and interfere with foraging and navigation B次元官网网址� while the physical presence of vessels can also reduce foraging efforts.
B次元官网网址淜iller whales are more likely to encounter greater numbers of vessels in the Salish Sea than in the north (Vancouver) Island waters, which could mean that salmon are less accessible to southern residents than to northern residents despite there being a higher abundance of chinook,B次元官网网址� the study said.
Trites said some may find it difficult to accept the results of the study, but it could make people rethink their assumptions.
B次元官网网址淎nd I think if we really want to save southern resident killer whales, we need to think bigger and not assume that weB次元官网网址檝e solved the problem because if weB次元官网网址檙e wrong, weB次元官网网址檙e dooming them to extinction,B次元官网网址� said Trites.
