The U.S.-based Northwest Fisheries Science Center says a resident killer whale pod off the West Coast has welcomed a new addition to the family.

The centre said the new orca calf named J55 was spotted while its team was conducting research near Puget Sound on Monday.

"The calf seems to be just a few days old and in good condition," wrote the centre in a Facebook post.

The centre said it wasn't clear who the mother is, but it hopes to find out after a few more encounters with the pod.

Unfortunately, the researchers also said they spotted a 20-year-old female pushing around a deceased newborn — her first documented calf.

At least half of killer whale calves don't make it through their first year, said the centre.

Orca baby boom

After years of population decline, there appears to be somewhat of an orca baby boom on the West Coast.

In December, the Center for Whale Research confirmed the birth of the eighth calf in 2015 for the endangered southern residents, boosting the population to 84.

Part of the decline in population has been blamed on dwindling salmon stocks, which make up most of the diet of the resident orcas. A recent study suggested that Chinook salmon made up more than 98 per cent of the endangered killer whales' summer diet.

The species is listed as endangered and faces triple threats of pollution, noise and food shortages.