Updated: Jun 27, 2021
It’s hard to ignore the presence of great white sharks during a visit to a Cape Cod beach in Massachusetts. Large signs encourage beachgoers to be “shark smart” when swimming, and echoes of attacks from previous years are still heard. With local grey seal numbers (one of the sharks’ prey) estimated to be 30,000 to 50,000 strong, many blame the increased presence of Great Whites on bounding seal populations. However, why does this only seem to be a problem of recent years?
There are archaeological records of seals in New England dating to 4,000 years ago. However, from the 1890’s to the 1960’s, New England states offered a bounty for grey seals in an attempt to recover struggling fish stocks, until the local population all but disappeared. Now under federal protection through the Marine Mammal Protection Act of 1972, grey seal populations have rebounded. Similar to their pinniped prey, known as a family including seals and sea lions, great whites faced anthropogenic threats until the 1990’s, when they became federally protected. With direct threats from humans minimized, both populations have filled spaces in the local ecosystem.
The return of an apex predator can have beneficial implications for a marine ecosystem. Sharks help control the number of mesopredators like seals or rays, thereby maintaining healthy populations of smaller prey, such as cod or scallops. They also promote healthy nutrient cycling throughout the ocean, feeding on prey in deeper waters and bringing carbon back near the surface. Seals also have this effect, excreting nearly 90% of their nitrogen intake throughout the water column, potentially benefiting phytoplankton, important photosynthesizers in the marine environment. However, with seals swimming closer to Cape Cod shores in an attempt to evade their predators, Great White interactions with humans are becoming more common.
There’s been five attacks on swimmers in Cape Cod waters since 2012. Some are calling for another seal cull to reduce both species’ proximity to the shore, while others perceive the return of seals and sharks as a successful conservation effort. Up to 100 million sharks are killed each year worldwide for the shark fin trade and other markets. As apex predators, they help maintain healthy ecosystems, but are still susceptible to extinction due to their slow growth.
With more shark sightings around Cape Cod each year, there’s a unique opportunity to educate locals and tourists alike on the critical role of sharks and seals in marine ecosystems. Perhaps in allowing these important marine relationships to exist naturally, we can respect their fragility and coexist in our coastal communities.