(CNN) Scientists are worried another orca whale may be dead, and that may spell trouble for a group of whales that live off the coast of the Pacific Northwest.

The whale, named L41, was not with his family when researchers encountered them off Washington's coast last week. The last time they had seen him, he was looking thin and not healthy, according to Shari Tarantino, president of the Orca Conservancy.

If L41 is not just missing, but in fact dead, that would bring the population of Southern Resident orcas to just 72 whales. It hasn't been that low since 1974 when 71 whales remained, according to the National Oceanic and Atmospheric Administration.

L41 was significant to the Southern Resident population because he and one other male, J1, fathered a majority of the whales born since 1990. J1 fathered 16 whales, and L41 fathered 20 whales, according to NOAA.

"He was just a really big personality, and a big whale, and of course he was an important member of his family," Deborah Giles, research scientist for University of Washington's Center for Conservation Biology told The Seattle Times. "I am going to miss seeing him."

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