This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: While the Discovery Channel's annual Shark Week event has given the public greater familiarity with sharks, much about them—from their mysterious love lives to how their eating habits bring them into conflict with recreational anglers—remains a mystery to scientists. Now, two new studies led by researchers from the University of Massachusetts Amherst peer into these important aspects of shark biology to help guide real-world conservation strategies.
In a pair of papers recently published in Environmental Biology of Fishes and Fisheries Research, the teams recorded the first known seasonal breeding ground of the nurse shark in the Virgin Islands and conducted the first survey of recreational anglers who have experienced depredation—when a predator eats the fish they've hooked—in the Northeast Shelf Large Marine Ecosystem, which stretches from northern Maine to North Carolina. Together, the papers will help efforts to protect critical breeding grounds and better educate anglers to sustain recovering marine populations. It is incredibly rare to observe sharks mating in the wild.
While scientists may know how they do it, where they mate is largely a mystery, making it extremely difficult to protect the mating grounds that many species of sharks return to year after year. Given that many species, like the Caribbean's nurse shark, mate infrequently, have long gestation periods and give birth to only a few pups at a time, anything that negatively affects their preferred mating spots risks destabilizing their populations. Which is why, when lead author Grace Casselberry, a postdoctoral researcher at UMass Amherst, got a tip that nurse sharks were mating in the shallow waters off Windlass Bight in the Virgin Islands' Anegada, she was excited.
"The only other place in the world where similar numbers of mating nurse sharks have been recorded is in the Dry Tortugas," she says. "One day we witnessed 27 nurse sharks in tightly packed groups in shallow water, with mating happening throughout the day." "This is the bedroom for these sharks," says Andy Danylchuk, professor of fish conservation at UMass Amherst and one of the paper's senior authors. "There's something quite special about this particular location." It turns out that nurse sharks prefer to mate in the shallows near shore.
"Knee-deep is the sweet spot," says Casselberry, "and it's all happening in an area about 150 meters (490 feet) long, which means that the spot is sensitive to human disruption. If this stretch of shoreline were to be developed, it would erase this group of nurse sharks' mating grounds." In fact, even the researchers' presence seemed to disturb the sharks, who would rather mate unobserved—which means sites like Windlass Bight should be preserved and more work should be undertaken to find and protect shark breeding grounds. "Humans can do terrible things," says Evan Prasky, a doctoral student at UMass Amherst and the author of a new paper on depredation in the Northeast Shelf Large Marine Ecosystem, "but we can also learn how to coexist.
We need to move toward a more coexistent model of ecosystem management and conservation." One unintended consequence of conservation measures that have successfully helped reverse declines in sharks, seals and other marine predators is that the fish recreational anglers love to hook, like striped bass, have become easy targets for hungry animals. "Seals are a great conservation success story," says Prasky. "There were only several hundred left in the Northeast Shelf a few decades ago.
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