RISSO'S DOLPHIN PREDATION - very rare documentation!
Today we had an absolutely incredible encounter with 7-8 Bigg's transient killer whales that included an adult male, a large juvenile, and a calf. We have only documented a fatal Risso's dolphin attack in Monterey Bay once before! We also once observed Risso's dolphin CHASING off killer whales. Interactions between these two species are rare.
These individuals have never been documented in Monterey Bay, and (to our knowledge) are not in any published catalog. However, several have been sighted at least once before (Central California, 2019). The attack was already underway when we arrived at the canyon edge. The killer whales had separated one Risso's dolphin away from its pod of about 10-15 dolphin (who porpoised away). All were engaged in the attack except for two female-types who stayed on the perimeter. Two killer whales breached in the beginning: the male breached once, and so did a female-type. About 15 minutes after we arrived, one whale grabbed the Risso's dolphin by its fluke and dragged it down! The killer whales stayed underwater for a long time, likely feeding for several minutes. About 15 minutes later, a pool of blood appeared in the water. One whale did two spyhops after the predation event; Bigg's transients frequently spyhop, breach, or do other surface behaviors in what seems like a celebration after a kill. They then shifted from feeding to traveling, about 10 minutes later. They were porpoising at 9.5 knots for 45 minutes - and came up to our boat twice! A VERY exciting day! Check out these photos and stay tuned for some videos as a post and in our story!
Photos by Daniel Bianchetta and Colleen Talty
Here is some more detail on our latest orca encounter (Wed, Aug 25)! The orcas seen predating on the Risso's dolphin are a very rarely seen group; we only know of one other sighting. We matched three of the 7-8 whales we saw (the male and two females) to a sighting we were alerted to off Morro Bay in October of 2019, where they were hunting a fin whale about 12 miles offshore! There was no confirmed kill from that sighting; however, there was a big bite taken out of the fin whale's jaw. As we have only recorded these whales two times in over 30 years of research, and have now documented them hunting both Risso's dolphin and a fin whale - most likely these orcas are not part of our regular CA transient killer whale population. We do not know for sure where they came from - but since we do not regularly encounter them, they could POSSIBLY be from an offshore group of killer whales that normally target sperm whales and other offshore species. A few of these whales have a couple of black cookiecutter shark bite scars in their saddles; the male's scar was acquired since their 2019 sighting. They most likely obtained these injuries while in warmer offshore waters; we have documented other killer whales with similar scars, encountered well offshore. One of the females also had a stalked barnacle on the trailing edge of her dorsal fin, which is likely a Xenobalanus barnacle (thank you @Diane Alps) - found on a variety of cetaceans. We do not often see these barnacles on our California transient killer whales; they are generally seen on whales like those from the Eastern Tropical Pacific (ETPs), from warmer water regions. Check out our photos to see some of these details - plus a great look into an orca's eye and underwater view of their teeth!
Photos by intern Morgan Quimby