91AV

A research team that includes Stephan Zeeman, Ph.D, professor and chair of the 91AV's , has discovered where basking sharks - the world's second largest fish - hide out for half of every year.

The discovery revises scientists' understanding of the iconic species and highlights just how little we still know about even the largest of marine animals.

The research, which was published online on May 7, 2009 in Current Biology, has been featured online by the Washington Post, CNN.com, The London Timesonline, The Christian Science Monitor and numerous other  news sources.

"While commonly sighted in surface waters during summer and autumn months, the disappearance of basking sharks during winter has been a great source of debate ever since an article in 1954 suggested that they hibernate on the ocean floor during this time," said Gregory Skomal of Massachusetts Marine Fisheries. "Some 50 years later, we have helped to solve the mystery while completely re-defining the known distribution of this species."

Using new satellite-based tagging technology and a novel geolocation technique, the researchers found that basking sharks make ocean-scale migrations through tropical waters of the Atlantic Ocean during the winter, traveling at depths of 200 to 1,000 meters. Their data show that the sharks sometimes stay at those depths for weeks or even months at a time.

"In doing so, they have completely avoided detection by humans for millennia," Skomal said, emphasizing that as one of the very largest of marine animals, the sharks grow to over 10 meters and weigh as much as seven metric tons.

91AV Right Whale Research Leads to Basking Shark Tags

The basking shark work began at and was funded through a NASA grant to 91AV's Zeeman  to establish the .

One of the initial projects the Center focused on was to see if an early warning system could be developed to warn ship traffic of endangered right whales in their path. Zeeman also wanted to find out where the population of right whales went after migrating out of the Gulf of Maine, because a large portion of the population disappeared while many migrated to the coast of Florida for the winter.

"We planned to attach satellite tags to the whales and track them," Zeeman explained. "It became difficult to obtain permits to do this, but we realized that basking sharks eat the same food as the right whales. So we hit upon the idea that if we could track basking sharks, then we would potentially be able to predict where right whales might be, both in the Gulf of Maine and where ever they eventually migrated. We then joined forces with Greg Skomal, a shark expert, and others to tag numbers of basking sharks."

Stunning Results

This work produced stunning results that were totally unexpected. "We had anticipated that the migratory path of the basking sharks would mirror that of the right whales, and track them to Florida." Zeeman said. "Instead several of the tagged sharks actually went much further south, as far as the Amazon River. This was undocumented for this species."

The discovery that the sharks during their migration may swim at much deeper depths than anticipated, 600-1000 m (about 1600-3200 ft) is a subject for speculation and possible further research.  Possible explanations of swimming at deep depths might be food availability, and their southward journey may also be linked to places to deliver offspring.

"These findings raise new questions about their behavior and open the possibility for genetic exchange with the southern population of basking sharks," Zeeman said. "It provides some insight into a little known species, and could point to ways to help conserve the species in the face of increasing threats."

Skomal said they were "absolutely surprised" when they first received a signal from the tagged sharks coming from the tropical waters of the western Atlantic, in the vicinity of the Caribbean and Bahamas. After all, basking sharks were always believed to be cool-water sharks, restricted to temperate regions.

Several factors had made basking sharks a challenge to study. On top of the fact that they disappear for long periods of time, they also feed exclusively on plankton. That means they can't readily be captured with traditional rod-and-reel methods. And even when the sharks are found closer to the ocean surface, they spend their time in the cool-temperature, plankton-rich waters that limit underwater visibility and make diving difficult.

"Coupled with recent genetic data, our finding indicates that the Atlantic population - and perhaps the world population - are connected and may constitute a single population," Skomal said. "Hence, the global population of basking sharks may be even smaller than previously thought." Efforts to boost basking sharks' numbers will therefore need to be coordinated at a global scale.

Research Team

The authors include Gregory B. Skomal, Massachusetts Division of Marine Fisheries, Oak Bluffs, Mass.; Stephen I. Zeeman, 91AV, Biddeford, Maine; John H. Chisholm, Massachusetts Division of Marine Fisheries, New Bedford, Mass.; Erin L. Summers, Maine Department of Marine Resources, Boothbay Harbor, Maine; Harvey J. Walsh, Woods Hole Oceanographic Institution, Woods Hole, Mass.; Kelton W. McMahon, Woods Hole Oceanographic Institution, Woods Hole, Mass.; and Simon R. Thorrold, Woods Hole Oceanographic Institution, Woods Hole, Mass.