Shark News: important research in the Gulf of Mexico, California, and more

Several news items have been swirling around the shark conservation news outlets and blogs of late - from the big picture, population view to the more drilled down, scientifically-studied behavioral aspects.

Research in the Gulf of Mexico
In the aftermath of the Gulf Oil Spill, many research organizations are studying the current and long-term effects on the marine environment. Much of those effects can be very subtle and on a microscopic level that can slowly work its way up the food chain. Similar to the pollution from methylmercury that can work its way into larger ocean fish where it can accumulate, oil and the toxic brew generated from the massive use of dispersants could end up in sharks.

Oceana, one of the larger non-profit ocean conservation organizations, is embarking on a study of sharks in the Gulf through tagging and long-term monitoring of the tagged sharks health and migratory behaviors to detect any significant changes. In addition to sharks, Oceana will be studying the impact on many of the smaller organisms - the building blocks of a marine ecosystem.

As reported in Tampa Bay Online, Oceana's chief scientist Michael Hirshfield said, "We all notice the sharks and the whales and the turtles and the seabirds when an accident like this happens. If they die, it's pretty visible. It's the worms and the little tiny things that are at the bottom of the food chain that matter a lot to the rest of the Gulf ecosystem. If they die, we're not going to notice it.''

Sea Otter Predation in Central California
On the western coast of the United States, scientists with the California Department of Fish and Game have been recording an increase in the number of great white shark predations on sea otters along the state's Central Coast. From Pismo Beach to Monterey Bay, there has been a recorded 26 cases since August.

In most cases, these attacks are considered investigative bites and probably coming from juvenile white sharks who are in the transition process from feeding on fish to mammals (adult white sharks primarily feed on marine mammals like seals and sea lions). Not finding the sufficient taste and texture of fat that the white shark needs, it moves on. But even with an investigative nibble, that can prove fatal for the sea otter. Of the 26 reported cases, only one sea otter apparently survived.

The ten-year average for sea otter predations by white sharks is only seven in August; six in September. This year's spike could lead to a new record, surpassing 2009's annual record total of sixty-three.

Fish and Game scientists are studying the increase but a definitive reason has not been established. A mild summer with cooler ocean temperatures could be a cause - making conditions closer to shore (and closer to the sea otters) more tolerable. But it could also be indicative of an increase in the overall white shark population, as mentioned in an earlier post, which would be good for the white sharks, but poses a quandary for Fish and Game officials who are entrusted with protecting sea otter populations that have been negatively impacted from decades of overhunting and encroachment by man on their natural habitat.

The Monterey County Herald discussed the issue with Fish and Game scientist Michael Harris. "Shark attacks on otters are part of nature, Harris said, but they concern researchers who want to preserve healthy populations. 'It becomes complicated,' he said. 'They are both protected species.'"

Studying Electrical Sensitivity
Just a little further north along the California coast, the University of San Francisco was extolling the work of one of their own, Dr. Brandon Brown, the university's winner of the 2010 Distinguished Research Award. Dr. Brown has focused much of his recent work on the characteristics of the hydrogel in sharks and other elasmobranchs that gives these animals a type of sixth sense - the ability to detect faint electrical fields given often by other animals.

Many shark enthusiasts are familiar with this feature of a shark's hunting capability. The Ampullae de Lorenzini are the pores - a kind of five-o'clock shadow seen around the nose area of a shark - that contain the hydrogel, Dr. Brown has been studying. Through his research, one of the interesting results has been his analysis of how experienced and inexperienced sharks use the hydrogel in their hunting patterns.

According to a news release from the University's news room, "By comparing mathematical models to actual shark behavior, Brown has been able to witness sharks who use their “sixth sense” to make a beeline for the source while some, thought to be less experienced hunters, spiral in toward the source of the electrical impulses. Spiraling allows them to maintain the same orientation to the impulses as they approach, so as not to lose the scent, so to speak."

The research goes on and these amazing animals continue to fascinate us all.

Read the Tampa Bay Online article on shark research in the Gulf of Mexico.
Read the Monterey County Herald article on white shark predation of sea otters.
Read the USF article on Dr. Brown's research on elasmobranch's hydrogel.

Great White Sharks and Boats: do they stalk small boats?

Great white sharks are known for their ability to ambush and capture large prey, like seals, sea lions, or elephant seals - a common prey because of their high fat content that provides the shark with the energy it needs. But do they selectively hunt and attack boats?

This is the question that The Dorsal Fin blog was asking in response to a recent press release covering the upcoming trans-Atlantic voyage of Wave Vidmar as he prepares for a solo-rowboat expedition this summer. Apparently, previous solo boaters have reported being followed by white sharks for hours, even days, and have experienced shark bites on their vessels.

The press release stated, "Typically Atlantic Great White sharks (Carcharodon carcharias) will follow the tiny ocean row boats for hours to days, then attack by biting the backs of the boats."

That's a pretty bold statement to make and one that The Dorsal Fin rightfully questioned. He received additional information from Wave Vidmar to clarify that four solo boaters had anecdotal experiences of white sharks following them, but that it was not necessarily "typical" behavior. Perhaps an over-ambitious public relations person felt that Vidmar's upcoming voyage needed a little extra sizzle, but let's put it in perspective based on what we do know about white shark predatory behavior.

First of all, great white sharks have two roles as predators: hunters and scavengers. As hunters, besides feeding on marine pinnipeds (seals) and large fish (like tuna), white sharks have been known to feed on cetaceans like dolphins, porpoises, and small whales on rare occasions. Studies have shown that their primary point of attack is on the caudal, or tail, area, as this will immobilize the cetacean.

As scavengers, white sharks have been shown to feed on a variety of cetacean carcasses including much larger whales. The sharks, attracted by the scent of the decomposing animal, will make a slow and careful investigation, and then commence feeding on the remains.

So, could either of these behaviors come into play involving a small boat? Perhaps. The shark may be first attracted to the vibrations given off by the rowing motion. Then the visual of a large dark body floating on the surface may further pique its curiosity - is this a floating carcass? The shark may very well follow the boat for some distance, making a determination as to whether this is viable prey. Bumping the boat or engaging in an investigative bite or nibble, often at the stern (the carcass' "tail"), is not uncommon. But a full-on rush from underneath, as when ambushing a seal, is highly unlikely.

From Great White Sharks: The Biology of Carcharodon carcharias, "While predation by sharks on cetaceans is relatively rare, many sharks scavenge dead cetaceans. White sharks are frequently observed feeding on carcasses of whales off Australia and the eastern United States."

I have had the personal experience of being bumped by a great white shark while sitting in a Zodiac inflatable, during filming. Of course, the "bump" from a 15-foot white shark is no little pat - the shark pushed the inflatable, and the two of us on board, a good foot out of the water. But the shark was merely checking out whether this black mass floating on the surface was a dead whale - it was in its scavenger mode and certainly was not trying to sink the inflatable to get after the two occupants aboard.

So, would a great white shark trail behind a boat and bump or bite it? It's possible. Would it track the boat for several hours? That's also possible; I have seen white sharks spend a considerable amount of time cautiously investigating a tuna head suspended in the water, used by shark divers as an attractant. Would a shark spend days tracking the boat? My gut feeling tells me that's a bit of a stretch. The boaters may be seeing more than one shark over a period of several days. Or it may be the same shark returning, its curiosity once again piqued. But the press release statement seems to imply that the shark is round-the-clock relentless in its pursuit. Sensational but unlikely.

Like the oceanic white tip shark I wrote about earlier, great white sharks are important ocean predators. But we must not think of them as only hunters, continually on the prowl. Their roles as scavengers is critically important and can be the source of their curiosity with surface objects like small boats.

Read the entire press release.
To get some detailed information on white shark hunting and scavenging behavior, read Great White Shark: The Biology of Carcharodon carcharias, edited by Drs. Peter Klimley and David Ainley. Of particular interest is Chapter 27: White Shark Predation and Scavenging on Cetaceans in the East North Pacific Ocean.