A Mako’s Last Meal Part II: The Shark Bite Effect
[music and rushing water] [music] Narrator: In 2013, headlines swept the nation about the 12-foot, 1,300 pound record breaking mako shark caught off the coast of southern California, which scientists discovered had eaten a whole California sea lion. Not only did scientists learn more about what makos eat by analyzing everything in this shark’s stomach, but a sea lion biologist in Seattle closely inspected the shark’s meal to help him understand a recent phenomenon in the Channel Islands. So here we are out on San Miguel Island. This is Point Bennett, which is the main rookery for both California sea lions and Northern fur seals in southern California. During the height of the breeding season, there are over a hundred thousand California sea lions here. Also there’s about twelve thousand Northern fur seals, and the populations here have been basically increasing exponentially since they were protected in 1972. And during that time we’ve seen very little evidence of predation on these guys. But in the last three years starting in 2011, we’ve seen huge increase in shark lesions on living animals. So we’re interested in trying to learn as much as we can about it. And the sea lion we got out of the mako shark stomach is of real significance because it’s one of the first times that we’ve actually had a sea lion in good enough shape where it still has the bite marks associated with the shark on both the flippers and on the body. So, you can see here on the femur, on the hind flipper here, we actually have quite a bit of scarring here. You can see a lesion here, here, on the backside. Probably what she did was immobilize the animal from the hind end. And then it looks as though at some point it went and thrashed the neck of this animal. So it’s almost as if the sea lion were moving when it were taken, which makos are pursuit predators so that’s not all that far fetched. And you can see just all this hide here has tooth rakes and punctures, holes. And oh, yea, these are perfect right here. This is exactly what we’re looking for, because you can actually measure these and make an inference about the size of the shark. Narrator: Because of this rare opportunity of having access to both predator and prey, Jeff knows the spacing of the mako’s teeth, which can be correlated with bite marks on the sea lion. Together with documenting the distinctive rake patterns, these data can be applied to observations in the field. Jeff Harris: Okay, so I’ve just spotted a really good example of what a mako lesion looks like on a sea lion. It’s on an adult female. It appears to be both the top and bottom jaw imprinted on her side and the whole bottom jaw comes across her belly and the lesion on this female actually really matches up well with the young animal we pulled out of the mako shark stomach. We can actually compare these types of lesions and you can actually assign this one to a shark species, a known shark species. With the Mako shark lesions what you see is a lot of fine really fine punctures where the teeth are actually inserting into the flesh. They stay the same diameter as they rake across, which is more of a slashing bite, whereas with a white shark, their teeth are actually more designed to take flesh. So if a white shark had bitten this animal, there would be a whole lot more tissue missing, and most likely it would have been a fatal wound for her. Narrator: Since 2011, Jeff and others have also documented many signs of white shark attacks, and they are fairly obvious versus the tell-tale raking pattern of a mako’s bite. The evidence of sharks attacking and eating these fully grown animals suggests that California sea lions are becoming a more important prey item for sharks in the Southern California Bight. It also suggests that large sharks are making their way back into the ecosystem, which begs the question, why were they absent in the first place? Jeff Harris: Well, one of the hypotheses is that it’s been about 30 years since the closure of a gill net fishery that was targeting large sharks here in the California Bight and during that time sea lions have been growing exponentially. And so just now we are starting to see the sharks coming back, and not only sharks but large sharks here, that are large enough to consume a sea lion. So now this is kind of the first evidence we have of a predator coming back to actually predate these animals and take them in more of a regular fashion that will help balance our ecosystem and allow for more of a natural state in the California Bight.