Cape Cod has seen an increase in shark sightings in recent years, prompting both interest and concern. This rise stems from specific ecological shifts in the region’s marine environment. Understanding these changes clarifies why these ocean inhabitants are more common in the Cape’s waters, pointing to environmental factors and conservation successes.
The Return of the Seals
A primary reason for increased shark presence off Cape Cod is the recovery of the seal population. Decades ago, hunting severely depleted seal numbers in New England waters. The federal Marine Mammal Protection Act of 1972 halted this, allowing populations to rebound.
Gray seals, a key prey species for large sharks, have grown from near extinction in the 1970s to an estimated 30,000 to 50,000 individuals in southeastern Massachusetts today. These seals congregate on beaches and sandbars along the Outer Cape, making them an available food source. This rebound has directly attracted their primary predators, great white sharks, to the region.
Favorable Ocean Conditions
Cape Cod’s ocean conditions also contribute to its attractiveness as a shark habitat. Great white sharks prefer water temperatures ranging from 55 to 73 degrees Fahrenheit (12 to 24 degrees Celsius), provided by the Cape’s waters in warmer months. This temperature range aligns with their seasonal migration patterns.
Geographical features also play a role. The Outer Cape, with its shallow waters and proximity to deeper migratory routes, creates an environment where sharks can efficiently hunt. Studies show that great white sharks off Cape Cod spend up to 47% of their time in waters shallower than 15 feet. Areas like Monomoy Islands, Chatham, Nauset Beach, and North Truro are frequented due to high concentrations of seals.
Apex Predator: The Great White
The great white shark is the species most associated with increased shark sightings. These apex predators undertake predictable annual migrations, spending summer and fall in coastal waters off New England and Atlantic Canada. They feed predominantly on seals before migrating south to warmer winter waters from South Carolina to the Gulf of Mexico. Individual sharks exhibit site fidelity, returning to the same locations, including Cape Cod, in multiple years.
Globally classified as vulnerable to extinction by the International Union for Conservation of Nature (IUCN), conservation efforts, including federal protection since 1997, have contributed to a slow rebuilding of their Atlantic population. Cape Cod has emerged as the only known aggregation site for white sharks in the western North Atlantic, largely due to the abundant seal population. This re-establishment of the predator-prey relationship is a significant factor in their increased presence.
Coexisting with Sharks
The increased presence of sharks in Cape Cod waters necessitates public awareness and safety measures. Organizations like the Atlantic White Shark Conservancy (AWSC) fund scientific research, educate the public, and enhance safety initiatives. Their efforts help people understand shark behavior and how to coexist with these animals.
Practical safety guidelines are promoted to minimize encounters:
- Avoid swimming near seals or in areas with visible schools of fish, as these attract sharks.
- Staying close to shore, where rescuers can easily reach individuals and feet can touch the bottom, is recommended.
- Swimming, paddling, kayaking, and surfing in groups, while avoiding isolated areas, enhances safety.
- Avoiding murky water, limiting excessive splashing, and refraining from wearing shiny jewelry can reduce attraction.
- Beaches frequently use signage and flag warning systems; a purple flag indicates shark risk.
- The Sharktivity App, developed by AWSC, provides real-time shark sightings and tracking data to help beachgoers make informed decisions.