Gone Fishin' : Basking shark migration traced
Greg Skomal, a Massachusetts Division of Marine Fisheries (DMF) biologist and Martha's Vineyard resident, does some very interesting work. Recently, he led a study that shed new light on the migratory routes of basking sharks.
Greg is the state's resident shark expert. Every July some sun-baked fisherman swears he saw a great white, and that sets off a round of "just when you thought it was safe to go in the water" news reports. In turn, Greg takes on his most visible public responsibility, which is to reassure summer visitors that it is safe to swim in state waters.
A basking shark opens its mouth very, very wide. Photo by Nick Caloyianis
Greg dutifully appears on CNN or FOX and tells people that there are sharks swimming in the ocean but that sharks prefer to snack on blubbery seals, not blubbery humans (research has shown it is the difference between a diet rich in fish and one heavy on ice cream cones).
But most of the time, Greg and his fellow biologists work to understand more about a species that presents a number of questions and is threatened by overfishing in many areas of the world. Recently, their work unlocked one of the mysteries associated with basking sharks, the world's second largest fish.
Greg is the lead author of a study, "Transequatorial migrations by basking sharks in the western Atlantic ocean," published in the June 23 issue of Current Biology. It is not exactly People Magazine material, but it is interesting.
The study identifies the shark's previously unknown winter habitat. It is a discovery that has implications for the species' conservation, according to state environmental officials.
"The Commonwealth is proud to employ high-caliber staff, such as biologist Greg Skomal, who work on behalf of Massachusetts citizens helping us to understand and act as good stewards of the environment," Energy and Environmental Affairs Secretary Ian Bowles said in a press release.
State officials are understandably proud and grateful to have something positive to announce in connection with the work of state employees. I am certain the head of the MBTA wishes he could have found a way to get in on the action.
The basking shark grows in excess of 20 feet up to a maximum length of 32 feet. It has a huge mouth and tiny teeth. The shark uses comb-like gillrakers to filter small shrimp-like creatures from the huge volume of water it takes in when it opens its mouth.
Island fishermen are familiar with basking sharks. It is not unusual to see one of these huge fish cruising off Gay Head or just off Lobsterville Beach. But little has been known about where these fish wintered. For years scientists believed the shark moved to deeper water and hibernated.
The study, which relied on satellite technology, revealed that Atlantic basking sharks, which were previously believed to inhabit only the waters of the United States and Canada, have a range that stretches the length of the Atlantic Ocean.
The study team included Stephen Zeeman of the Univ. of New England in Biddeford, Maine; John Chisholm, DMF; Erin Summers of the Maine Dept. of Marine Resources; and Harvey Walsh, Kelton McMahon, and Simon Thorrold of the Woods Hole Oceanographic Institution.
One of the most important members of the team is not listed among the authors. He is Bill Chaprales, said Greg, a commercial harpoon fisherman from Cape Cod. He helped the biologists develop the techniques they needed to locate and get close to the fish, and use a harpoon to plant a tag that would remain in a free-swimming fish.
The tags are basically small computers that can be programmed to disengage after a specific time period and transmit data via a satellite back to the researcher. Each tag costs approximately $3,500.
The development of the tags and the willingness of Bill Chaprales to contribute his time and practical knowledge was a key to adding to the body of knowledge about these fish. Greg said, "Not only did the technology not exist to any great degree, but people did not know how to go about tagging these fish."
Greg makes it a point to work with fishermen, recreational or commercial. "They are on the water all the time and I am not," he said.
One of the challenges the team faced was placing the tag so that it would stay on a fish that swims thousands of miles, is known to breach out of the water and routinely swims more than one half mile deep.
Beginning in 2004 and continuing through 2005 and 2006 the team tagged 25 fish in Cape and Island waters in the summer and fall, including a big female within a stone's throw of Gay Head in June 2006 that Greg estimated to be 28 feet long. The team spent the last two years collecting and analyzing data.
One of the challenges the team faced was to minimize tag-shedding, the loss of the tag prematurely. The inability to collect data over long periods is a problem with tuna and some species of sharks.
"Short-term deployments don't give you big-picture type of results," said Greg. "Because of our tagging techniques we have been able to keep tags on for more than a year and that is why we have gotten big-picture results. It really boils down to some of the simplest things and that is keeping a tag in a shark. In this study 18 of the tags transmitted data after deployment for periods of 12 to 423 days.
The migratory paths of the sharks were estimated by coupling tag data with a novel geo-positioning technology technique. The researchers found that basking sharks travel from the coast of southern New England to the Bahamas, the Caribbean Sea and off the coast of South America, swimming at depths of 600 to 3,000 feet for several weeks or months.
The shark that moved the longest distance in the study remained off Cape Cod in the waters of the continental shelf through the end of September before moving rapidly south and across the Windward and Leeward Islands in the Caribbean in late November and early December. By January, this shark was offshore in the vicinity of the Amazon River mouth, where it remained for approximately one month before resuming a southward migration parallel to the coast of Brazil when the tag popped up in early May.
The findings show that tropical waters are not a barrier to migration and highlight the need for global conservation efforts throughout the species' range, said the study.
Greg said the National Science Foundation is continuing to fund the study with the aim of trying to learn more about basking shark movements through long-term tag deployments and its reproductive cycle.
The basking shark has little food value, but was once fished heavily in the early part of the 20th century in the waters surrounding Great Britain, primarily for the oil found in its huge liver.
It is now listed as a vulnerable species. Estimates place the global population at 10,000 individuals.
Greg has described the basking shark as a whale trapped in a shark's body. He said a close encounter with a feeding basking shark while diving in waters off England made him feel like a piece of plankton. Perhaps the next study will rewrite the story of Jonah and the whale.
Fish stories
Reports from around the Island indicate that shore fishing is quite good. Bluefish are off East Beach and fishermen are hooking into striped bass around the Island.
The bass are quite big for this early in the season. One night I saw Lucas Mercier land a very fat fish that was 40 inches long. Boat fishermen are having a great time in the rips with blues and bass.
The 18th annual Martha's Vineyard Rod and Gun Club Fly Rod Striped Bass Catch and Release Tournament is on for this Saturday night. Fishermen must register Saturday between noon and 3 pm at the high school cafeteria. On Sunday the culinary arts program provides breakfast. The awards ceremony begins at 9:30 am.
In anticipation of the tournament, Coop's will host an Orvis Day Friday afternoon from noon to 2 pm. Orvis reps will be on hand to show off the latest rods and reels, provide casting tips, and generally share advice.
There will be hot dogs, fish talk and prize giveaways as well. Coop's is on Edgartown-West Tisbury Road just outside of Edgartown next to Cottle's. Call 508-627-3909 for more information.
Lost tackle box
Steve Maxner found a tackle box filled with gear and a pair of sneakers at the Lagoon boat ramp Saturday. If you know the sneaker size, call Steve at 508-696-7248.
