Sharks Are Color Blind: new study shows they live in a world of contrast

According to a new study by scientists from Australia, sharks are color blind.  This puts them in the same category as whales and dolphins as sea creatures that may have had color vision at one time but evolved to a black and white world, perhaps as a more effective means of hunting.

Previous studies of several species of rays, part of the same general family as sharks, were found to have several types of ospins or light sensitive proteins in the photoreceptors of their retinas which provide them with the ability to see in color.  But studies of wobbegong sharks showed them to not have the necessary levels of ospins for color, only black and white.

Dr. Susan Theiss, University of Queensland (yes, we're related - she is my niece), and her colleagues studied two different species of wobbegong sharks; each of which prefer different levels of depth in the sea as their normal habitat.  Because of those differences in depth, the vision of the two species is more sensitive to different wavelengths of light.  Each species is better attuned to the type of light that predominantly penetrates their environment.  One wobbegong shark species preferred deeper water where it is penetrated by shorter wavelengths - a bluish kind of light.  Sharks in shallower water can be more sensitive to red or green spectrums of light.

Color blind as they are then, sharks live in a world of contrast.  Their other senses of sound and scent can aid them in their search for prey then, at some point, contrasting visual stimuli kicks in, and at close range sensing electrical impulses can come into play.

Sometimes color can be a distraction and can prevent the shark from staying focused on a potential target.  Color exists in nature for a variety of reasons and in some environments it can actually act as a kind of camouflage.  Oddly enough, as a filmmaker, I typically use a black and white viewfinder with my camera as it can often provide a sharper image for focusing purposes.

Playing off that sense of visual contrast, it might be possible to help keep sharks from becoming accidental bycatch by camouflaging or making hooks less visually interesting.  And the same could possibly be said for surfers who provide considerable contrast (as does a seal) in their black wetsuits. 

"If we can use this knowledge to design longline fishing lures that are less visible to sharks then we will be able to reduce the amount of shark bycatch. We may also be able to make wetsuits less attractive, and make the water safer for surfers and divers," says co-author Associate professor Nathan Hart of the University of Western Australia and reported in Australia's ABC Science. 

Source: ABC Science

Orcas vs. Sharks: whales hunt deep sea sharks in New Zealand

Thought I would pass along this interesting blog post from marine biologist Candace Calloway Whiting, writing in the Seattle PI. She did some digging in regards to a recent event documented in New Zealand of pod of orcas corralling what appear to be some juvenile cowsharks (six- or seven-gill) in a sort of hunting/feeding technique.

Orcas have been known to prey upon sharks, but what makes this news item so noteworthy is that these New Zealand orcas were after deep water sharks and that they managed to bring them to the surface, disorienting the sharks which played to the orcas' advantage. It also appears that the orcas were able to capitalize on the fact that these sharks will stick together - brothers and sisters - which is not a common shark behavior.

Pod of Orcas Rounds Up a Group of Sharks - Were These Sharks Related to Each Other?

Update: 12/28/11 - In reply to my request to identify the shark species involved, Seattle Aquarium shark biologist Jeff Christiansen sent the following :

"It is difficult to make a definitive ID from a partial view and with only one photo but I would hazard a guess the shark in the photo is a sevengill shark Notorynchus cepedianus or possibly even Heptranchias perlo. While I can’t rule out a sixgill the spotting pattern visible on the dorsal surface of the shark is characteristic of the sevengill. The photo is not sharp enough to tell if there are six or seven gill slits. Its definitely one of the Cowsharks as the six and sevengill sharks are called and finding them in groups is not unusual for that species… pack hunting and association is documented in sevengills. The Sevengill can tolerate much higher light levels than its deep water cousin the sixgill."

I’ll update again when I hear back from a New Zealand orca researcher who may have more information on the orca pod that appeared to be hunting the sharks.

On Boxing Day (the day after Christmas) in New Zealand a pod of orcas managed to corral at least a half dozen sharks and apparently gave them a good thrashing in the shallows off the beach. Orcas are known to kill and eat sharks in many parts of their range – often eating the nutrient dense livers and discarding the rest – so although witnessing the interaction must have been amazing, the news that the whales went after the sharks was in and of itself not surprising.

But the fact that the orcas managed to get several sharks together in a group for the presumed mayhem is fairly astounding, and I was as curious about the sharks as I was the orcas as I read the article.

Copyright protection prohibits me from being able to use the photo of one of the sharks thought to have been involved in the altercation with the orcas, but it is similar to this one, and is one of the few species that is easily identified with just a head shot. If you look carefully you will see that the shark has six gills [note update above, this may have been a related species of cowshark, not a sixgill] instead of the usual five, and logically is called a six-gill shark (the sixth gill is thought to help extract oxygen from the deep water where the adult sharks are found).

The following video shows both the massive size this species can attain, and the depth to which it can be found. “This six-gill shark (Hexanchus) was filmed during a submersible dive off the northeast coast of Molokai at a depth of 1000m (3280ft). The 2 red laser dots are 6 inches apart, resulting in a length of about 18 ft for the shark.”

But if they were chasing this deep sea species of shark, how did the orcas manage to get several, albeit smaller, of these sharks rounded up in the shallows off the beach?

I found the answer through the Seattle Aquarium’s shark research program, and though I have not gotten a confirmation that this is the shark species involved in the New Zealand fracas, what I learned about six-gill sharks is fascinating and over-turns much of what we believe to be true about sharks in general.

The biologists have discovered that in this local population, sibling six-gill sharks stay together for many years, at least until they become large enough to move out of the protected environment of the Salish Sea.

The mother shark can give birth to over 100 baby sharks (called pups), and each litter of brothers and sisters remains together for years in “loosely associated groups”, possibly finding food together and avoiding predators.

The eyes of six-gill sharks are adapted to low light conditions and they shun the bright light of the surface during daylight hours, so the orcas might have managed to find a group of the sharks in deeper water, driven them to the surface where the sharks would have been blinded and disoriented causing them to swim up onto the beach (the news article reported that observers thought the sharks swam up to get out of the water, certainly possible but not likely.)

Although six-gill sharks are opportunistic feeders often scavenging about anything they can find, humans are not on the menu, and fortunately for them these sharks aren’t usually on our menu either – what a shame it would be to kill off the sharks of the world without ever knowing their secrets.

Brother and sister sharks growing up together, who knew?

For more on orcas and sharks, please see “Orcas and sharks, just who is hunting whom?” Also this report on New Zealand orca expert Ingrid Visser’s discovery of orcas hunting thresher sharks.

Source: SeattlePI.com
Source: Stuff.co.nz

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.

Wolves & Sharks: key predators at risk from sport

From time to time in this blog, I have cited the role that ocean predators such as sharks play in maintaining a balanced ecosystem - whether we personally care for the animal or not. In fact when I would speak to groups about sharks, I would acknowledge the fears and distaste that some people in the audience might have but would then focus on the critical importance of the shark. You may not love them, but they are indispensable.

And from time to time, I have mentioned the ongoing situation regarding endangered wolves in the U.S. The designation of wolves as endangered in the Yellowstone and Rocky Mountain areas has been a flip-flopping issue with certain populations faced with extinction at the hands of hunters, backed by the support of concerned ranchers who have lost cattle to predation.

There are strong parallels between sharks and wolves both socially, with their interaction with mankind, and ecologically. First, ecologically, they serve the same functions as apex predators, maintaining a proper balance of fauna and even flora within their respective ecosystems. Without sharks, the numbers of their primary prey would increase, feeding on smaller prey that are often herbivores. And so there is a potential shift in a marine community and a potential increase in vegetation and algae that can threaten other life forms like coral - all part of the non-linear cascade effect.

Wolves serve a similar function, maintaining balance between prey ranging from small "varmints" to deer, elk, and moose. In the past when the wolves were not provided protection as endangered species, there was both an explosion in the small animal or rodent population and a decline in grazing land as more and more large animals like deer and elk would de-nude the grasslands.

Secondly, sharks have been exposed to senseless hunting through "shark tournaments" wherein large numbers of both juvenile and mature breeding sharks were hauled in, often times the catch being sharks of no tournament or commercial value. With organizations like the Shark-Free Marinas Initiative, there are efforts being made to at least alter the decisively fatal outcome generated by shark tournaments through the implementation of catch-and-release techniques. With the current state of regulations and protections for wolves being in somewhat disarray (see prior post), there are now similar tournaments, "wolf-killing derbies," that leave dwindling populations of wolves in the Greater Yellowstone and Northern Rocky areas, including Idaho and Montana, at great risk.

The Defenders of Wildlife, through their www.savewolves.org campaign, are working to protect these threatened land predators by educating people to their importance and by focusing public awareness towards the businesses and corporations that sponsor or support the wolf-killing derbies.

According to Defenders of Wildlife president, Rodger Schlickeisen, "Since wolves were reintroduced to Greater Yellowstone and central Idaho fifteen years ago, we’ve seen local ecosystems rebound as these top predators helped prevent overgrazing of foliage by elk and deer. According to the Rocky Mountain Elk Foundation, there are 150,000 elk in Montana, compared to 90,000 in the mid 1980s when wolves started to make their way back to the state. Wyoming's elk population is up 35% since then to 95,000, while Idaho's is up 5% to 115,000."

Sharks and wolves - critically important predators that bring balance to nature's ecosystems but whose image, from Jaws to Little Miss Riding Hood, have placed them on a collision course with man - are at risk of extinction. And, because of the complexity of nature's web, man's attempts to artificially achieve balance (eliminate the predator, then control the increasing prey populations) have not been particularly productive. The challenge is to find methods not to control nature's balance but to work with it, allowing it to flourish in it's infinitely more successful ways.

To learn more about the campaign to save the wolves, click here.
To learn more about the campaign to eliminate wolf-killing derbies, click here.

Crocodile Hunting: Australia rejects safaris to manage population

Sharks are not the only predators subject to discussions regarding their numbers and possible interactions with man. In the Northern Territory of Australia, crocodile populations have increased from a record low of 3000 in the 1970's, for both salt and fresh water species, to an estimated number today of 80,000 for just the saltwater species alone. The increase was the result of legislation that protected the crocodiles and limited any government-sanctioned culling to 600 per year.

But with that apparent ecological success story and the unfortunate deaths of four people by crocodiles, all in the month of March of this year, the Northern Territory government proposed "crocodile safaris" to allow tourists and trophy hunters to increase the number of crocodiles hunted with the idea that would correct the problem of crocodile-human interactions.

The proposal was rejected by Australia's environment minister who has, instead, increased the number of eggs that can be harvested and the number of crocodiles that can be legally culled.

Peter Garrett, environment minister, said, “I am of the view that safari hunting is not a suitable approach for the responsible management of crocodiles.” The prime minister of the Northern Territory has said that he would continue to press for the safaris.

This situation brings into question the entire issue of how does one "manage" any species to sustain its population, if management is required at all? With tourists and hunters entering the picture, one could not guarantee that the most "appropriate" animals would be taken - appropriate meaning older mature males or females who have had the opportunity to reproduce (if this is applicable to crocodiles; and I must admit I know little about them).

Another issue to consider is the circumstances behind the rash of human fatalities. Are crocodiles encroaching upon humans? Are humans, through increasing development or urbanization, encroaching upon the reptiles? Is the Northern Territory, when in a healthy environmental condition, an area where these and other types of animal interactions are to be expected? (A crocodile cruising down the main street in Miami is one thing; a croc resting near the green at the 9th hole of a golf course next to the Everglades is a different story.)

And then there's the concept, suggested by some, to let nature take its course, that the growing population of crocodiles would ultimately self-regulate based on available prey and natural selection (an increased population can also mean more sick and less "successful" crocodiles which would, over time, ultimately impact the population and balance it out in line with the overall ecosystem). The counter-argument would question how long this natural selection would take, since the current Northern Territory crocodile population has been growing steadily for over 30 years.

Sharks in the oceans, mountain lions and coyotes in the hills, even lions in the savannahs - all have populations at risk and all have the potential for human interaction. If we choose to regulate the species ourselves, we must do it with an eye on the entire health of the ecosystem in which they live and to remind ourselves who is encroaching on who.
Read entire article in Embrace Australia.

Northern Rockies Wolves: once again under the gun

Wolves are under the gun again, literally.

Until recently, Northern Rockies gray wolves had been on the Endangered Species List and therefore protected from extermination. While their numbers had been recovering, many conservation organizations felt the the government's decision to remove the wolf from the endangered species list was premature. It was questionable as to whether there are sufficient number of breeding pairs. But, with the increasing numbers there is the inevitable occasional loss of livestock, and so the future fate of the wolf was put into question once again as pressure mounted to find a way to placate ranchers with some sort of "acceptable" sustainable population figure.

Unfortunately, it was decided that the magic number was to be less than the current population. In August, it was reported that Idaho was issuing over 10,000 hunting licenses for the taking of 220 wolves - out of a population reported to be somewhere between 846 and 1,000. Conservation organizations rallied their legal forces to reinstate the wolves' former status and a final decision is in the hands of a judge as to an injunction against the Idaho hunt.

But in the meantime, the hunt has begun and the first kills have been reported.

And the issue is spilling over into other states. Montana is preparing to open up wolf hunting on September 15th. And there has been concern emanating from Oregon where a very small number of wolves exists, a fledgling splinter group from the larger Northern Rockies population. Conservationists are concerned that, with the reduction of wolves through open hunting, the populations ranging across all these states will be threatened due to a lack of mating prospects and lost continuum of a healthy genetic pool.

Interestingly, this is the same issue expressed regarding the loss of oceanic predators like great whites - that the loss of one population can impact another population many miles away, perhaps a population even in so-called "protected" waters, due to a loss of the gene pool mix within these migratory animals.

According to Suzanne Stone, Northern Rockies representative of the Defenders of Wildlife, "Idaho hosts the core of the Northern Rockies wolf population, with approximately 1,000 wolves. By wiping out 220 wolves, the state will cripple the regional wolf population by isolating wolves into disconnected subgroups incapable of genetic or ecological sustainability."

"It's only a matter of time," warned Stone, "before Idaho's state legislature enforces their demand that all wolves be removed 'by whatever means necessary,' which is still the state's official policy on wolves."

Read story in Environmental News Service.

Lionfish and Pythons: invasive species paying the ultimate price

Well, I'm back from a very successful trip to Chattanooga, Tennessee. Hopefully I will have impressed a few listeners before they watch shark television programming that seems to be obsessed with one thing this year: shark attacks.

I caught two interesting news bits on invasive species. The introduction of foreign animal and plant life into an ecosystem can have disastrous effects either on the ecosystem itself - as in the case of invasive seaweeds or predators like the lionfish - or on our man-made infrastructures - like the damage caused to water pipes from freshwater mussels.

1. Speaking of lionfish: their population has been exploding in the warm waters off Florida and the Caribbean, ever since their introduction by aquarists who could no longer care for them at home and released them into the wild. Voracious by nature, the beautiful lionfish was thought to possibly be held in check through predation by larger animals like groupers. While that still may be the case someday, at the moment it's a losing battle. One that has prompted the development of "lionfish tournaments" which have netted as many as 1200+ lionfish in a single event.

2. TIME magazine just reported on a government-sanctioned program to rid the Florida Everglades of exotic Asian pythons - again, introduced into the wild by owners who could no longer manage them at home. These reptiles, like the Burmese python, can reach a length of up to 18 feet and can disrupt the Everglade's predator-prey hierarchy by feeding on everything from small rodents all the way up to the typical apex predator of the Everglades, the alligator. Officials from the Florida Fish and Wildlife Conservation are working with snake experts to round up some of the estimated 150,000 pythons and are considering even issuing bounty hunter permits.

It's a sad price that has to be paid by all invasive species, whether plant or animal, when the result is their wholesale destruction. But the real villain lies with man either through his thoughtlessness, negligence, or perverse need to own exotic animals as pets. And because of it, we must then cover our tracks at the end of a spear or the barrel of a gun.