Why a Seal Cull is Not the Solution for Shark Attacks on Cape Cod


Emma Sullivan, Editor-In-Chief

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Over the past 150 years, the Northwest Atlantic grey and harbor seal populations have been in flux. State led bounties in the mid 1900s decimated seal populations, but, since the enactment of the Marine Mammal Protection Act in 1972, these populations have rebounded. A seal popping its head out of the water near the Chatham Fish Pier is now a common sight. However, these increased seal populations have also helped facilitate the return of great white sharks to Cape waters. Massachusetts Division of Marine Fisheries researcher Greg Skomal led a shark population study that wrapped up in summer 2018; he found increased numbers of great white sharks have traveled to Cape waters in recent summers. The Cape has also seen a corresponding increase of great white shark attacks, culminating in the death of Arthur Medici in early September, 2018. In response, locals have renewed efforts to cull Cape seals. However, officials should not allow these culls because they would be ineffective and potentially threaten the entire Cape ecosystem.

First and foremost, the grey and harbor seals that congregate on Cape beaches are part of a greater pinniped population that spans the Northwest Atlantic. To decrease the seal populations on the Cape, Massachusetts would have to instate bounties similar to those in the mid 1900s. Those original Massachusetts bounties were complimented by similar ones in Maine and Canada, decreasing populations across the Northwest Atlantic, including in Cape waters. Thus, without a coordinated effort from Maine and Canada, a Cape seal cull would be ineffective.

But, if a Northwest Atlantic cull did take place, how would it affect the Cape ecosystem? As most locals know, the Cape Cod ecosystem is much more complex than the swathes of sandy beaches tourists see. Beneath the surface lies a constantly fluctuating system of nutrients, predators and prey in which seals play an intrinsic role. Scientists’ current understanding of the Northwest Atlantic ecosystem suggests that seals have a positive impact and that their extirpation may be detrimental. For example, the seal’s role as an apex predator is important to the diversity of the Cape ecosystem. When seals are present, species in lower trophic levels, like sand lance or cod, must work to avoid their predator, thus adding another layer of complexity to the interactions between species in the ecosystem. The more complex an ecosystem, the stronger and healthier the ecosystem is.

Additionally, seals contribute to the Cape ecosystem in ways that cannot be seen by the human eye. For example, nitrogen from seal waste contributes to the health of the marine ecosystem, in accordance with Joe Roman’s (2010) study on marine mammal’s input of nitrogen into the Gulf of Maine. The complexity of the seal’s role is compounded by the time they spend hauled out in terrestrial environs. While the only study of seal’s effects on Cape terrestrial ecosystems by then college student Michelle Woods (2016) proved inconclusive, increased nitrogen levels from seal waste could facilitate vegetation growth, helping to stabilize the ever eroding dunes on the Cape. Thus, given the positive ways the seals impact the Cape ecosystem, a cull would be not only ineffective, but also irresponsible.

Recent research by Kristina Cammen from the University of Maine has found that seal populations become caught in an seemingly endless cycle. Ecological managers and officials have been plagued by the depletion, then conservation, and finally, recovery of seal populations in the Northwest Atlantic. The continuation of this cycle often results from legislation passed without knowledge of how decreasing or increasing protection for species will impact the entire ecosystem. The historic examples of Northwest Atlantic seal population fluctuations and the lack of recent extensive research clearly demonstrate that we do not fully understand the seal’s role in the Cape ecosystem. Thus, we cannot cull the Northwest Atlantic seal population because we will be sucked back into the endless cycle of depletion, conservation, and recovery.


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