Many Cape Codders and visitors believe that the increased numbers of seals and white sharks in Cape Cod represent new populations of species who did not previously inhabit these waters.  This is not the case, however.  Archeological data and anecdotal evidence suggest that grey seals inhabited the waters between Connecticut and Maine until the end of the 1600s, when the hunting of seals became so widespread that they became extirpated, or extinct at the local level. There is not an abundance of scientific evidence of white shark populations from this time period, however in piecing together catch data, reports of human and white shark interactions, and anecdotal evidence, we can conclude that white shark populations were definitively present in these waters during the 17th century.

The data that we have from the 20th century suggests that white shark populations were not large in the western North Atlantic (WNA) waters. But we do know that bycatch and capture by recreational fisheries, engaging in sport hunting of white sharks, further reduced the small population. It’s estimated that sport hunting of white sharks decreased the population by as much 80% during the 1980s and 1990s.

The hunting and killing of seals was outlawed in Massachusetts in the 1960s and in the entire country in 1972, via the Marine Mammal Protection Act. Harvesting sharks in the US Atlantic became illegal in 1997, and we know from incidental catch records and siting reports that white sharks populations began to recover around this time.  And now, nearly 2 decades later, we have observed a notable increase in the populations of both species. Overall trends in the global populations of both species remains highly uncertain, but we can conclude that local white shark recovery is directly related grey seal recovery in WNA waters at large and in Cape Cod specifically.

This story is a conservation success story.  That said, the resulting conflicts between humans and sharks and humans and seals continue to threaten the conservation and potential survival of both species.