In 2011, fish processors in Dutch Harbor in Alaska's Aleutian Islands, found something interesting inside cod that had been caught in the waters of nearby Unimak Pass:
There were feet, heads, wings, bones and feathers, partially-digested carcasses without heads, and fully intact carcasses that had not yet been digested. There were crested auklets, common Murres, a Cassin's auklet, a thick-billed murre, and a number of remains that could not be specifically identified.
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The fish workers sent the bird parts to researchers at the Alaska SeaLifeCenter, who, with colleagues from the University of Alaska, have published their findings in the journal Marine Ornithology.
This is not the first time that large predatory fish have been recorded as eating birds: previous examples include monkfish eating little auks, catfish grabbing pigeons, and even African freshwater tigerfish leaping out of the water to catch a swallow in flight.
There have also been occasional previous records of seabird parts in Pacific cod caught around the Aleutian Islands. But study co-author Tuula Hollmen told Yereth Rosen of Alaska Dispatch Newsthat "the evidence from Dutch Harbor appears to be the first documentation of Pacific cod making a practice of eating birds."
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Exactly how they go about doing so is uncertain. The authors tested the lung tissue of 33 crested auklets removed from the cods' stomach, and found that three of them had air in them at the time of their death, suggesting that while those three were presumably taken alive, the others had already drowned when they were consumed.
Crested auklets comprised the great majority of the identified bird remains; the authors note that they often forage in large groups but may also dive as deep as 30 meters, and it is possible that in some cases the cod feed on them opportunistically, either at the surface or in the water column, while in other instances they may scavenge carcasses from the seabed.
As for how often this happens, under what circumstances, or what the biological significance might be, Hollmen told Rosen that, for now, there are more questions than answers.
"That's just an area that we didn't know much about," she said.
-via Alaska Dispatch News