Manta Rays: new study tracks their movements off Yucatan

While marine advocates fret over the plight of sharks and their fate at the hands of commercial fishermen, another of the shark's relatives is heading into perilous waters: the majestic and graceful Manta Ray. 

Given the unfortunate nickname "devil fish" by local fishermen, the manta ray, which can attain an enormous 25-foot wingspan, is a filter-feeder and completely harmless to humans (it does not have a stinger like other rays).  Similar to baleen whales, the manta ray draws water through its mouth and, as it passes through its gills, structures called gill rakers strain zooplankton from the water.

What has put the manta ray at risk - it is currently listed as "vulnerable" to extinction by the International Union for Conservation of Nature (IUCN) - is that they are hunted in some quarters for those gill rakers, a favorite of traditional Chinese medicine, and they are also caught as accidental bycatch.  Part of the elasmobranch subclass that includes sharks, skates, and rays, the manta ray, like their relatives, does not have a high reproductive rate.  So, they are not well-prepared to withstand high losses.

However, there's much we do not know about these large rays that are so popular with scuba divers and snorklers in several tropical resort locations, representing not only a threatened species but a tourism generator as well.  To fill the gap in our knowledge, a recent study which was just published in PLoS One used satellite tags, the ones often used on sharks and other pelagic fish, to learn more about the movement patterns of manta rays.

Organized by the Wildlife Conservation Society, UK's University of Exeter, and the Mexican government, the study involved tagging six manta rays - four females, one male, and one juvenile - over a 13-day period off the coast  of the Yucatan Peninsula.  In that approximate two week period, the manta rays mostly stayed within 200 miles of the shoreline but did travel a good distance.

“The satellite tag data revealed that some of the rays traveled more than 1,100 kilometers during the study period,” said Dr. Matthew Witt of the University of Exeter’s Environment and Sustainability Institute. “The rays spent most of their time traversing coastal areas plentiful in zooplankton and fish eggs from spawning events.”  

Of concern was the fact that, with the rays not necessarily staying centralized to one area but more on the prowl for waters rich in zooplankton, they spent a considerable amount of time outside the boundaries of marine protected areas and, by doing so, putting themselves at risk from commercial fishing, being caught in nets accidentally, and even exposing themselves to the risk of being struck by large ships.   Less than 12 percent of the locations where the tagged animals were tracked were within marine protected areas.

“Almost nothing is known about the movements and ecological needs of the manta ray, one of the ocean’s largest and least-known species,” said Dr. Rachel Graham, lead author on the study and director of the Wildlife Conservation Society's Gulf and Caribbean Sharks and Rays Program. “Our real-time data illuminate the previously unseen world of this mythic fish and will help to shape management and conservation strategies for this species.”  

We can only hope that this and other future studies will provide a base of knowledge that will motivate governments and international agencies to take steps to arrest the apparent decline in manta ray populations.  All filter-feeders play a role in maintaining the proper balance in zooplankton and other microscopic marine animals.  Were we to lose the manta ray, we would be faced with unknown consequences.

Source: Wildlife Conservation Society
 

Turtles and Sharks: long migrations studied in the South Atlantic

Animal migration is one of nature's most mysterious presentations of animal behavior. What makes an animal travel great distances? How are they able to do it in a relatively straight path? Why do they use the same route year after year? Just how are they so good at it, while I can get lost in the local Costco?

One vast body of water where several marine species migrate but where mankind has not spent much time studying these movements is the South Atlantic, between South America and Africa. However, two recent studies have shed some interesting light on the long migration paths taken by leatherback turtles and blue sharks. Both of these species are threatened with possible extinction, so the more we know, the better we can manage our conservation efforts.

As reported in the Proceedings of the Royal Society B, researchers from England tagged and track the migratory routes of leatherback turtles for five years, from a breeding colony in Central Africa to feeding grounds in the southwestern Atlantic. Using satellite tracking tags on 25 females, the researchers found that the turtles followed three migratory paths, often traveling in remarkably straight lines.

One female turtle was tracked along a path that totaled just under 4,700 miles and took about 150 days of nonstop swimming to complete. The researchers are keen to know the "when and where" of these journeys to ensure that commercial fisheries do not take advantage of the turtle's singular purpose and place themselves right in the turtles' paths. The researchers are hoping to avoid a large decline in leatherback turtles in the South Atlantic as has happened to leatherbacks in the Pacific.

"All of the routes we've identified take the leatherbacks through areas of high risk from fisheries, so there's a very real danger to the Atlantic population," said University of Exeter professor Brendan Godley.

At the same time, researchers from the University of Florida were tracking the migratory routes of the blue shark. Working with a Brazilian team of researchers, Felipe Carvalho, under the supervision of renown shark expert Dr. George Burgess, Director of the Florida Program for Shark Research, began tagging blue sharks along the Brazilian coast. The question was whether the tracking results would show a migration that would link shark populations in both the southeastern and southwestern Atlantic.

Blue sharks are heavily fished in the South Atlantic and within coastal territorial waters some nations are trying to determine how to best manage the remaining populations. By showing a migratory link between these separate locations, it emphasizes the need for multinational cooperation. As it turned out, one of Carvalho's blue sharks, tagged off the coast of Brazil, was detected off Africa 87 days later.

“This is the first evidence of the transatlantic migration of a blue shark from the southwestern Atlantic Ocean to the southeastern Atlantic Ocean. We thought this migration might be happening, but we never had the data before to prove it,” Carvalho said.

More and more, we are finding species that travel along oceanic highways, making incredible journeys over and over again. Navigating by prevailing currents, or visual cues, or even by the Earth's magnetic fields - all have been suggested as possible theories that could account for the animal's amazing accuracy.

Whatever the method, it is important for us to understand these migrations and their purpose and use that knowledge to protect rather than take advantage of leatherback turtles, blue sharks, and so many other species that roam the seas.

Read about tracking leatherback turtles from the Associated Press.
Read about tracking blue sharks from Physorg.com

Wintering White Sharks: possible migrations along U.S. east coast

A possible migration corridor has been identified for great white sharks on the east coast of the U.S. A satellite tagging study was initiated in the fall by the Massachusetts Division of Marine Fisheries and some of the early results are intriguing. It is possible that the great white sharks that appear off the New England coast during the summer months - suspected of feeding on seal populations there - travel south during the winter months based on the results of a tagged shark who has appeared as far south as Jacksonville, Florida.

Satellite tagging has been used on great whites and other shark species to record location, speed, depth, and ambient temperature. Typically, a well-placed tag will record data for 30 to as long as 90 days then release itself, float to the surface, and download its data to satellites overhead. Researchers must wait patiently then sift through a mountain of data when it is downloaded all at once. Satellite tags can provide more long-range data than regional telemetry tags (like those documented in my film, Island of the Great White Shark) but are also subject to being dislodged prematurely. A newer technique, SPOT tagging, bolts the tag to the shark to insure a significantly longer monitoring period, but requires that the shark be caught and brought on board; a technique that has raised considerable controversy because of the physical impact imposed on the shark during the procedure.

In the summer months, several species of shark inhabit the New England coastline, from basking sharks to thresher and blue sharks to the great white white (although not in significant numbers). This new tagging study is the first indication that, like their distant cousins throughout the world who exhibit distinct migratory patterns, white sharks could very well be moving up and down the east coast based on seasonal temperature changes and any changes in prey populations that those seasons impose.

Great whites have already been shown to migrate from the west coast Farallon Islands to the mid-Pacific; same for the white sharks at Isla Guadalupe. White sharks have been monitored moving from South Africa all the way to Australia and back. While there can always be the occasional exception, there is continuing evidence that these sharks and other pelagic species develop critical migratory patterns. Our concern would be, what would happen to these sharks if their migrations were intercepted by commercial fishing fleets? Or what would happen to the overall health of their populations with changes in ocean temperature due to global warming? How ingrained are these patterns and what would happen if external factors were altered - could the sharks successfully adjust?

Expedition Great White: reeling in white sharks for research

On November 16, the National Geographic Channel will premiere Expedition Great White, a special program that details satellite tagging research done on great white sharks at Isla Guadalupe. Using rod-and-reel techniques to pull white sharks on board to take blood samples and attach satellite tags, the researchers hope to learn more about the long-range migrations of these sharks. To promote the show, Nat Geo has released a promo video and pictures of the researchers in action. Click here to view a photo gallery from OutdoorLife.com. Here's the promo video:



There are differing views amongst shark advocates as to whether the method used to catch these sharks is appropriate or humane.

"While I don’t doubt the good intentions of the researchers, based on the pictures, it clearly doesn’t appear as if the sharks were "unstressed" throughout the experience. Being hooked, landed, and tied down seems like it would be a fairly stressful situation, although I’m not a 'shark expert,' so don’t quote me on that. Don’t get me wrong. I understand that the knowledge gained from the research could potentially benefit the species as a whole, but I have to wonder if this approach is really the ideal technique for gathering information about the white sharks at Guadalupe." - The Dorsal Fin

"As a commercial shark diving operator I am o.k with credible science done by professionals. This is real science. The fact that National Geographic is there to document does not diminish the effort. There's also a very fine line between 'credible science' and the ad hoc 'experiments' you often see on Discovery Channel Shark Week that have no basis in science, and are often played out so film crews can do questionable and increasingly invasive things with sharks." - Shark Divers

The rod-and-reel approach appears to have come out of the need to attach the satellite tag using a bolt-on method, which requires immobilizing the shark for an extended period of time. While the need to acquire a reliable and viable stream of data over an extended period of time is critical to the success of this type of long-range migration research, one wonders whether the rod-and-reel technique is the best and most humane approach that today’s technology has to offer. Perhaps it is, based on the size and weight of the tag. Perhaps that means we need to re-think the tag itself.

If one considers the trauma placed on the animal, considering both the stress of being hooked and reeled in and the physical stress of an animal this size being removed from the water, it begs the question: could microelectronics devise a smaller, lighter tag that could be attached using methods similar to those used for regional telemetry tags – a simple hooked barb and wire leader attached via a pole spear? Looking at the photos in the Outdoor Life photo gallery and watching the Nat Geo promo video, I get a sense that a very elaborate and expensive mousetrap was devised to catch and hold these sharks out of the water. Could that effort and expense been spent on devising a better mousetrap?

Or would that not have provided exciting enough television programming?

There’s a lot here we don’t know. Was every shark that was hooked, successfully reeled in? Was every shark that was reeled in then successfully brought on board? Was every shark successfully revived? Was there follow up as to the health and behavior of every shark that was caught and released? Were there negative outcomes and would we ever hear about it? If there was any bad news, I question whether we would see it on television, as I would expect there would be some negative reaction from CONAP, the Mexican agency that is charged with maintaining the health of Isla Guadalupe’s flora and fauna.

In June, at the BLUE Ocean Film Festival, I listened to Greg Marshal, the man behind the Crittter Cam, talk about the evolution of his invention. It was clear that the effort was being made to utilize advances in miniaturization to reduce the size of the Critter Cam to improve performance, simplify attachment, and lower the impact on the animal.

It’s an age old argument: what price do we – or the sharks – pay for the sake of scientific research and data? The debate continues.

Galapagos Islands: hi-tech GPS comes to the aid of marine park management

The Galapagos Islands - an oceanic oasis that was one of Darwin's key research sites for his seminal work on evolution - is feeling the pressure of its unique status. With increased tourism and island population, combined with international demands for seafood, the Galapagos has been showing signs of this negative impact on its natural resources.

The Galapagos Marine Reserve (GMR) was created in 1998 to provide protection to the islands' surrounding waters. And in the next few months, through the support of Conservation International and WildAid, the GMR will be taking a hi-tech step forward in managing major ship traffic in the area.

Utilizing GPS satellite tracking equipment, the activities of ships greater than 20 metric tons will be monitored by the Galapagos National Park Service (GNPS). This will provide the GNPS with greater ability to manage and regulate ships in no-take zones, tourism itineraries, and commercial shipping. Besides "tagging" ships, the computer-based system will enable the GNPS to tag and track migratory species and monitor environmental/climate changes.

Hats off to Conservation International and WildAid for supporting this important example of cost-effective marine research and management.