On the Hunt: study looks at great white shark's ambush capabilities

If you have shown even a passing interest in great white sharks, you have probably heard or read descriptions of these powerful sharks as ambush predators which feed primarily on seals and sea lions. And you may have seen images of white sharks on the hunt, leaping out of the water as they hope to catch an unsuspecting seal - striking images of one of the ocean's truly most magnificent predators.

In a recent scientific paper, Neil Hammerschlag, Ph.D. of the University of Miami's RJ Dunlap Marine Conservation Program and R. Aidan Martin, Ph.D. of the University of British Columbia examined the nuts and bolts of what transpires when a great white shark is in a predation mode. "Marine predator-prey contests: ambush and speed versus vigilance and agility," published in Marine Biology Research, details the optical and physical advantages and disadvantages for both predator and prey.

Camouflage, Vision, and Speed
The researchers studied great white shark predatory behavior at South Africa's Seal Island, famed for its spectacular breaching white sharks. They observed several elements that play into the shark's ability to affect a successful ambush. First, the time of day: we have heard that many sharks like to hunt at early dusk or sunrise. This is a time period that provides the shark with a workable degree of light to see prey at the surface, but also provides maximum camouflage using its natural counter-shading (dark coloration on top, light underneath). In low light levels, the shark's gray upper body reflects very little light and easily blends in with the dark rocky bottom below.

I have seen this personally where, during bright sun, the shark is illuminated with dancing rays of sunlight and can take on a slight metallic sheen to its skin. But as the sun falls and the dappled light fades, the shark's skin becomes strikingly flat and non-reflective - its cloak of invisibility now at work.

The researchers also noted that the great white shark's ability to see a seal moving along the surface is linked to the shark's depth. A principle call Snell's Law restricts the shark's range of vision to a formula based on depth - a common depth exhibited by the sharks in gaining an ideal horizontal view of the surface (150 to 170m/490 to 550ft) is around 26 to 30m (85 to 98ft).

Finally, there is the great white shark's speed. The muscles of a great white are incredible storehouses of energy, capable of very powerful bursts that can hurtle the shark to speeds of 35km/h (22 mph) at the surface, over 1.5x the speed of breaching blacktip sharks and enough to lift a 2000 pound shark clear of the water. To reach that maximum velocity, the white shark requires a depth - a running start, as it were - of a little over 25m (82ft) and can cover that distance in less than 3 seconds! That leaves the seal with precious little time to escape.

An Opportunity for the Prey
Nature has certainly allowed the great white shark to evolve into an extraordinarily efficient hunter. But does its prey have anything up its sleeve? In the early dusk light, the seal's vision is limited to about 3m (9ft) in depth which can provide it with just a split second to spot an ambushing shark at top speed. However, with that small window of time, nature has provided the seal with a chance to escape. Seals are very agile in the water, with a very tight turning radius and the ability to change direction quickly. So if the seal is not injured in the initial charge, it can utilize its maneuverability to make a hasty getaway. The seal's vigilance and agility can give it an edge in survival. And as one can expect, those seals that are less experienced (ie: young) or slowed by illness or age are often prey for the great white shark because their awareness and agility is diminished.

We know the great white shark is a powerful hunter with capabilities that put it near the very pinnacle of the food chain. Hammerschlag's and Martin's study looks at the actual mechanics of those amazing abilities and makes for an interesting quick read. It proves, once again, how truly fascinating and magnificent these animals are.

Click here to download a PDF of the report.

Cambodia's Tigers and the Banteng: protecting a predator can also mean protecting its prey

In Cambodia, international conservation groups and the Cambodian government are working to restore the eastern plains as a primary habitat for the country's dwindling population of tigers. The number of tigers worldwide is perilously low, with totals estimated at around 3,200 to perhaps 5,000. Poaching has been the primary threat to the tiger, but to develop a comprehensive conservation and management program, the World Wildlife Fund (WWF) recognizes that more must be done than just eliminate poaching. One must also protect its food source.

The Cambodian tigers feed on wild pigs, muntjac deer, and banteng - an endangered species of cattle. All have suffered declines in number in the past few decades. In particular, the banteng, estimated at 2,700 to 5,700 in number residing in the eastern plains, has seen a decrease of 50% in the last 30 years. Due to its scarcity worldwide, the banteng is listed as globally endangered by the IUCN.

While the banteng suffered at the hands of poachers seeking its meat and horns, the WWF has recently issued a report based on surveys taken in 2009 and 2011 that identify social and agricultural land concessions and infrastructure as the primary threat. Human development is encroaching upon the banteng, and their loss threatens the future of one of its primary predators: the tiger.

“For the tiger population to recover, one of the most important things needed is a sustainable source of prey, such as banteng,” read a statement from the WWF regarding the need for a comprehensive and effective conservation management plan in Cambodia. “Anything less threatens to unravel a decade of conservation progress and with each passing day diminishes the Eastern Plains’ value as a national and global ecological asset for current and future generations.”

Because of the complex web of inter-dependencies that make up a healthy ecosystem, simple "silver bullet" solutions are far and few between. Should we stop the commercial killing of, say, whales or sharks, we must then also consider the health and status of the animals upon which they feed - from the smallest krill to large commercial fish. And for the remaining Cambodian tigers, should we protect their numbers we must also provide an environment within which they can feed and flourish.

“For tigers and prey species- including a globally endangered banteng population to recover within the landscape, stronger protected area management and a commitment to conservation from high levels of Cambodian government are essential,” WWF species conservation manager Nick Cox said.

Read about the banteng in the Phnom Penh Post.

Predators and Prey: study finds important changes in behavior from overfishing

When explaining the impact of commercial overfishing (or, for that matter, terrestrial hunting) on the predator-prey relationships in an ecosystem, conservationists will often talk in terms of changes in population of various species and it is often portrayed as a domino-like effect. This may make it easier for the layperson to understand - a singular, straight line chain of events - but scientists know that the reality of it is a lot more complex. They will speak in terms of a cascade effect, a bit like a nuclear chain reaction, where one event impacts several others, each impacting several others, and so on.

Because of that complexity, there is still a lot that we do not know as to what happens to an entire marine ecosystem when key predators are eliminated through overfishing. We have a tendency to look at just population numbers, but a recent paper in Ecology documented evidence of changes in prey foraging behavior and how this can have a pervasive effect across an entire reef system.

Researchers focused on the northern Line Islands in the South Pacific and studied the foraging behavior patterns of numerous species, using one pristine reef as a baseline for comparison to other areas that were impacted in various degrees by a loss of key predators through local fishing.

The predator-prey relationship is much more than "the big fish eats the little fish." Fundamentally, that may be true but there are also factors such as when and where prey forage that enter into the equation. Some animals maintain certain depth ranges or preferred areas around the reef, or they had particular times of day when they would venture out to feed - all offering a certain level of risk and effecting behavior designed to give them the best chance of survival.

The researchers in the Line Islands found that, with the loss of a predator, prey behavior changed over multiple species, and this, in essence, really upsets the applecart of ecological balance. In fact, the article proposed that, while there can certainly be changes in population numbers of various prey species (which can include predators of smaller species - remember, just about everybody is eating somebody else in the ocean), the changes in foraging behavior could be the more important issue with its effects rippling through the entire complex web of relationships that help to make up a healthy marine ecosystem.

We live in a very complex world, but we have a tendency to prefer our answers or solutions to be neat and simple. Unfortunately, nature hasn't successfully evolved over millions of years in a straight "A + B = C" fashion. With each day, scientists are learning more about that complexity and what profound effects we are having on it.

You can order the complete article from Ecology.

Meddling With the Predator vs. Prey Relationship: man must pay up in sometimes surprising ways

When we selectively eliminate critical species from ecosystems, there is a price to be paid not only by the animal itself and the ecology. Man too must pony up - but our price may not be so obvious. It may be a price that is paid years down the road or is one we choose to ignore in the face of immediate personal or commercial gain.

This is what was once faced by cattlemen with regard to the hunting of wolves in the northern United States. Whatever was gained by cattle ranchers in eliminating a key predator, it ultimately came back to haunt them when the deer and varmint population exploded and competition between nature and the cattlemen for suitable grazing land necessitated bringing back the wolf population. But now the pendulum seems to be swinging back and the hunt for wolves is once again beginning in earnest - with no lessons apparently learned.

Many commercial fisheries stand on the brink of collapse, but sometimes the reason is not the obvious one: overfishing of a particular species. In some cases, it is rather the domino-like effect of our actions - as in the case of the hake fishery in Chile which has been severely impacted by the expansion of the Humboldt squid population, a voracious predator whose numbers have grown because of the commercial elimination of the squid's primary natural predators: sharks, tuna, and billfish.

This secondary effect is now being seen in other regions along the eastern Pacific coast: in the Sea of Cortez, where catches of grouper are in decline; and Northern California, where local fishermen are switching from catching rockfish to hauling up huge quantities of squid.

Here's a short video from my recent assignment in the Sea of Cortez.



The filming was for an important future program about which I have to be tight lipped for the time being. But the issue regarding Humboldt squid, which represents one of the multiple effects of disrupting once-balanced marine ecosystems, is an ongoing and growing one.

You fish. The fish are all gone. You move on. It's not that simple anymore.

Humboldt Squid: continues to appear outside its traditional range

Where I live in Southern California, it's been making the news that Humboldt squid, also known as jumbo squid, have been showing up in greater numbers and local sportfishermen having been having a field day, catching the squid in the early evening hours. In just the past few days, over 400 squid have been reeled in. While edible (if you like calamari rings the size of small tires!), the squid are more known for putting up quite a fight. These are very large and aggressive squid, reaching a body length of as much as 6 feet and weighing 100 pounds.

There's a very important developing story behind these occasional encounters with Humboldt squid along the eastern Pacific coast. Their traditional range was along the Mexican coast at a depth of about 500 to 600 feet. What determined their range was temperature and natural predators - two factors that dictate territories for many ocean species. But those factors have been changing.

Humboldt squid have been reported now as far south as Chile and as far north as Alaska. And they have been reported more and more in shallower waters, disrupting the populations of several commercially fished species like Salmon in the Pacific Northwest. These squid are particularly ravenous, with a very high metabolism, and they have been a major disruption to fishermen - not to mention what these predators are doing to their newly targeted prey populations.

It has been theorized that changes in ocean temperatures and loss of natural predators, like sharks and whales, are the root causes behind the squids' appearance in areas never before seen. And it poses a risk to fish populations and even divers - these squid are very fast, hit hard, and are very aggressive - even cannibalistic when a squid is injured in a feeding frenzy.

Scott Cassell, head of the Undersea Voyager Project, has become a sort of unofficial "squid guy," having spent considerable time observing and filming these animals. He has appeared in several documentaries talking about these animals and has a healthy respect for them and a measure of concern as to how they can disrupt local ecosystems along the eastern Pacific coast.



I have been working with Scott on several projects and we plan on diving with the squid shortly in Northern California. It's not something to be taken lightly. If he knows he will be having some close encounters, Scott typically wears a set of protective armor and chain mail and he has had broken bones thanks to these powerful cephlapods.

Ocean climate change through global warming and a disrupted predator-prey relationship through overfishing - two man-made changes that could have unintended ecological consequences with the expansion of the Humbodlt squid's hunting territory.

Read Los Angeles Times news article.

Orcas: new studies show changes in killer whales

When discussions of Arctic or Antarctic species come up, they often focus on polar bears, penguins, and walruses - all animals worthy of our concern and whose populations are at risk from changes in their environment due to climate change, pollution, or oil drilling development.

Orcas - or, if you like, Killer Whales - are also being impacted by environmental changes, some good and some not so good.

In a report from Canadian scientists, there is evidence that orcas are able to manage changes in their ocean environment by moving more northward, extending their uppermost boundaries in the Arctic Circle. This is made possible by the reduction of sea ice, particularly in the summer months.

Orcas typically cruise the thinner edges of the Arctic ice but avoid the thicker ice where access to the surface for breathing would be more limited. The scientists reviewed data of orca sightings dating back centuries and saw a definite increase since 1900 in the Arctic region, including into the Hudson Bay, that coincides with the recorded reduction of the Arctic sea ice. It remains to be seen whether this will disrupt the marine ecosystem as the orcas possibly begin to prey more and more on northern Arctic species like bowhead whales, belugas, and narwhals.

In another study, orcas were cited as a probable cause for the decline of sea otters, seals, and sea lions along southwest Alaska over a period of several decades. Not to completely blame the orcas, the study points to a cause for this change in the orcas' diet as the result of industrialized whaling. Whaling decimated whale populations and deprived orcas of an important food source. Hence the shift to other marine mammals as prey.

Orcas are extremely social animals, living in family units or pods, that can exist for many years, complete with elaborate and close social hierarchies. External stressors (ie: changes in their environment and/or food source) that produced changes in populations have been cited in a recent report as a possible cause for changes in the social structure of orcas in Canadian/U.S. waters. It opens the door for more study as to the impact of habitat change on the social order and survivability of this highly social marine mammal.

And lastly, according to a scientific report, the population of orcas that inhabit the Antarctic's Ross Sea, has apparently been decreasing both in terms of frequency (when observed) and in numbers and the primary culprit is, once again, commercial overfishing. In this case, the overfishing of the Antarctic Toothfish, a primary food source for this particular orca population. Whether the orcas have declined or are moving on to better hunting grounds has yet to be determined. But it is another example of the struggle between man and nature over available marine resources. And if the ocean's animals keep losing - from the smallest feeder fish to large predators like orcas - then ultimately we lose.

Humboldt Squid: the "red demon" moves into Southern California

Like something from Disney's Twenty Thousand Leagues Under the Sea, the humboldt squid is a formidable predator typically found in deep Pacific waters off of Mexico and Central America. Reaching up to five feet in length and as much as 100 pounds, it is fast and aggressive with a voracious appetite.

And it is beginning to appear in shallower water off of Southern California. In San Diego, during night dives, scuba divers are encountering groups of humboldt squid, and several have moved too close into the shallows and been washed up on the beach.

According to a recent AP news report,

"Research suggests the squid may have established a year-round population off California at depths of 300 to 650 feet, said Nigella Hillgarth, executive director of the Birch Aquarium at Scripps Institution of Oceanography. Divers this summer have been encountering them at about 60 to 80 feet down, they said. No one knows how many squid are in the shallow waters, but one biologist estimated they could number in the hundreds, or possibly thousands.

'Usually where there's one squid, there's a lot of squid, so I would assume that there's a good number,' said John Hyde, a biologist with the National Marine Fisheries Service in San Diego."

Scientists are not sure why the squid have moved further north or are entering shallower waters. Explanations range from global warming to loss of prey to a reduction of natural predators. On this last point, I have read studies that have explained the bio-dispersion of various species based on the predators that feed upon them. When the predators are gone, then the species in question is no longer "corralled" as it normally would and changes in bio-dispersion or migrations can occur. In the case of humboldt squid, sharks are one of its key predators.

Whatever the explanation for the squid's movement north, there is reason for some concern. They can pose a serious risk to unsuspecting divers and their voracious appetites can severely impact local fisheries. Scott Cassell, CEO of the Undersea Voyager Project, who has spent many years studying and filming humboldt squid, recently told me that in his studies he had predicted the potential for this danger as much as ten years ago.

Another possible example of the ramifications either climate change, overfishing, or loss of apex predators - or all of the above.

Care for a calamari ring the size of your dinner plate?

Forage Fish: challenged to support aquafarming and the marine ecosystem balance

In previous posts I have referred to the challenges and potential of aquafarming. While it holds considerable promise in meeting the commercial demand for seafood, it is an industry in its infancy and is experiencing its technological growing pains as it addresses issues from parasite control to pollution from the waste products of concentrated, confined fish populations.

Another challenge cited in a recent issue of Annual Review of Environment and Resources has to do with the feeding of aquafarmed fish. Small to medium-size fish like anchovies, sardines, and mackerel - often referred to as forage fish - are being harvested in great numbers to feed poultry, pigs and other terrestrial animals. That puts enough pressure on the populations of forage fish as it is, but now there is the added pressure of supplying them to the growing aquafarm industry. This further deprives pelagic predators and many seabirds of a primary food source.

When I engage audiences in discussing the importance of apex predators like sharks, I often refer to the predator-prey pyramid. This hierarchy of survival is depicted as a pyramid because at the wide base of the pyramid are the plankton and small forage fish - available in large numbers because of a high reproductive rate - which serve as a foundation. And as you ascend up the pyramid to larger and larger predators, the pyramid narrows, representing nature's ability to control those populations through reduced reproductivity.

All well and good but as we continue to harvest more and more forage fish, which are relatively easy to catch, we begin to undermine the foundations of that pyramid. This not only impacts nature's balance and reduces the forage fish populations and potentially the animals that feed on them, but it also affects commercial demand and the price of forage fish can increase - which hampers developing nations who rely on forage fish for food and to build aquafarming as a viable alternative to other negative fishing practices.

As we jockey resources in an attempt to fulfill our needs, we may ultimately have to address the 800-pound gorilla in the room that we have tried to ignore: 6.7 billion people and rising.

Sharks and Shellfish: a common thread

I was reading about two seemingly disparate animals: sharks and shellfish. And I came to realize there was a common thread to the life-threatening situations these animals are facing.

A recent report in the Norwegian scientific journal, Oikos, analyzed the impact on changes in seal predation behavior if the shark populations that preyed on the seals declined ("Do shark declines create fear-released systems?"). Pretty heady stuff, but through the researchers' computer models it was theorized that there could be major shifts in diets from shallower prey like herring to deeper water prey like pollock - where local sharks frequent, when the decline in shark populations has removed an element of fear that dictates a good measure of the seal's hunting behavior. Bottom line was that a decline in shark populations could produce a more significant change in the predator-prey hierarchy relationship than previously thought.

With shellfish, scientists are seeing an impact of warmer waters on various species that is producing population declines from deadly bacteria, among other factors. Oyster beds along the west coast of the U.S. are now seeing the effect (read recent article). The east coast has seen this effect, too. A platter full of shucked oysters may not be your cup of tea (it's not mine), but as filter feeders, shellfish play a critical role in maintaining water quality. When shellfish populations whither, bacteria and various types of algae explode and push out a wide range of sealife through water degradation and loss of habitat.

So, what's the connection? One is that both of these situations represent the domino effect that occurs within any complex marine eco-system. For every action, there is a reaction - sometimes a very severe or unexpected one. Another connection is that these are basically man-made problems - over-fishing and global warming - and will have an effect on commercial operations that involve these animals. So our actions come back to haunt us.

Certain marine issues can gain more traction and get more media attention or public sympathy and support. But in the end, we need to consider the overall complexity of this ecological jigsaw puzzle we call the oceans and give every issue its due.