The National Oceanic and Atmospheric Administration reported Sunday that the last of the three killer whales that had swum upstream in Alaska's Nushagak River earlier this month has died. From the NOAA:
The carcass of the juvenile killer whale was found Friday near Grass Island, an island in the Nushagak River across from Dillingham in an area that is tidally influenced. Based on the description of the location where the animal was found by a local resident, biologists believe the juvenile whale would've had to have swum there, rather than having been carried there by the tide.
The report states that there is no word on a plan for a necropsy of the animal. The whale's two companions had been found dead one week earlier, and a necropsy conducted on those animals revealed that one of them, an adult female, was pregnant. Biologists had held out hope that the last orca may have made it back to sea after it had been spotted swimming back downriver.
The distance upriver that the whales had traveled -- nearly 30 miles -- was an "unprecedented" occurrence, according to one NOAA biologist. The whales may have been chasing prey when they found themselves outside of their normal saltwater environment and into the freshwater of the river, causing stress to the whales' systems that likely led to their deaths.