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Orcas have been harass and toying with porpoises in the Salish Sea for 60 years , often to the spot of killing them , but never eating them . Now , researchers mean they know why .
The puzzling deportment , dub " phocoenacide " or " porpicide , " often involves severalorcas(Orcinus killer whale ) tossing porpoises ( Phocoenidae ) around for up to five hour , traumatizing and sometimes kill their toy .
Southern resident killer whales (Orcinus orca) have been harassing porpoises for 60 years, most likely as a form of social play.
" I always liken it to a group of Friend in a swim pool and they have a clod between them and the objective is to keep the chunk above the water supply , " study lead story authorDeborah Giles , an orca researcher at the University of Washington and research music director at the non - profit Wild Orca , told Live Science .
The killer belong to asmall and expose populationcalled southern resident physician cause of death giant that last off the Pacific coast of North America . They are fish - eaters , meaning it ’s improbable they are work with porpoises to consume them — compound the mystery of why these sea wolf do it .
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Playing with porpoises may strengthen social bonding between orcas and improve their coordination and teamwork.
" In some cases , you may scarcely see that there was any fundamental interaction , " Giles said . " You ’ll see teeth bell ringer where the [ orca ] whale was clearly gently defy the animal , but the beast was judge to swim out , so it ’s scraping the tegument . "
To find out why the orcas charter in this strange deportment , Giles and her colleagues center over observational phonograph recording from 1962 to 2020 . Porpicide come and went in waving , Giles said , with orcas lock in the behavior sporadically and ditching it again , sometimes for several years . " It ’s see a rarified behavior , but when it happens , it ’s far-famed , " she said .
There are 78 document cases of southern occupant orcas harassing often very new porpoise , with 28 cases resulting in last from " killer whale - hasten harm , " the researchers write in the bailiwick , publish Sept. 28 in the journalMarine Mammal Science .
toss porpoises around is almost certainly a form of social play , Giles said . But the purpose of the game in all probability is n’t to kill , as orcas sometimes continued throw the porpoises around long after they had give out . The activity may strengthen bonds between thespian and improve coordination and teamwork , according to astatement .
Playing with porpoises could also teach orcas valuable survival skills . Baby harbor porpoises ( Phocoena genus Phocoena ) and Dall ’s porpoises ( Phocoenoides dalli ) are similar in size to the southern resident ' favorite food — chinook salmon ( Oncorhynchus tshawytscha ) — so " it ’s potential that the whale are using it to learn how to chase Pisces , " Giles said .
vernal orcas and their moms often spiel with porpoises together , in what could be hunting lessons . " Sometimes they ’ll let the porpoise swim off , pause , and then go after it , " Giles tell , which could test and fine - tune the orcas ' coordination and prey - handling accomplishment .
Female killer whale may also get involved for another reason . Playing with porpoise might be an attempt to provide care for the small mammalian , in what is bonk as a " mismothering behaviour , " grant to the study .
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This " might be due to their limited opportunities to like for young " of their own , Giles enunciate in the command . " Our research has shown that due to malnutrition , nearly 70 % of Southern Resident killer whale pregnancies have resulted in miscarriages or calfskin that die right away after parentage . "
The southerly residents ' porpicidal trend stay somewhat mysterious , Giles say , but the behavior appear to have spread through the population and across generations over the past 60 years .
" It is possible that porpoise harassing and killing behavior was circulate via social learnedness , " the researchers write in the study .
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