Gulf of Maine marine mammal populations have fluctuated wildly in the centuries since European explorers first reported seas teaming with cod and seals in their logbooks. Today, populations of many whales, porpoises, dolphins and seals that inhabit the Gulf are steady or increasing, due in large part to protections afforded under the 1972 Marine Mammal Protection Act. Research points to additional reasons for burgeoning populations, particularly of seals, which may soon approach carrying capacity for the region. Meanwhile, a few species remain within a breath of survival, particularly the North Atlantic right whale.

According to Sean Todd, director of Allied Whale at the College of the Atlantic, four types of large whales are common visitors to the Gulf of Maine: the humpback, finback, North Atlantic right whale, and the relatively diminutive minke whale. The blue whale and sei whale are occasional visitors. Joining these behemoths are the smaller cetaceans—the harbor porpoise, Atlantic white-sided dolphin and the common dolphin, among others. Harbor seals and, more recently, grey seals, are present in large numbers. Hooded seals and harp seals—the “ice seals” from Arctic regions to the north—visit seasonally, and the latter has been seen more frequently in the past decade.

The history of these species over the last few centuries is similar in many ways to that of seabirds and terrestrial wildlife: early settlers hunted animals for fur, feathers, meat and oil. The right whale was driven nearly extinct in the Gulf of Maine in the days of sail.

With the emergence of fossil fuels and industrial-scale fishing at the turn of the last century, commercial hunting put continued pressure on other mammals. The harbor seal and grey seal, for example, were hunted for bounties set by Maine towns and the state of Massachusetts. The Massachusetts bounty for grey seals was lifted in 1962, according to Dr. Jim Gilbert, emeritus professor at the University of Maine, who has studied seals in the region for 35 years.

By the second half of the 20th century, attitudes and perceptions about marine mammals shifted. With the removal of the bounty system and the implementation of the Marine Mammal Protection Act since 1972, populations of most of the region’s marine mammals—at least those that are well-studied—are thought to be steady or slowly increasing. Grey seals have increased dramatically in the region in the last two decades, apparently due to range extension from the core population on Sable Island off the coast of Nova Scotia. Yet, the largest marine mammals, which move through vast stretches of the Atlantic on yearly migrations, have only recently been protected from hunting with the international ban on commercial whaling implemented in 1996. The North Atlantic right whales remain critically endangered with a population between 400 and 500, according to Todd.

In order to assess marine mammal populations, researchers count animals via aerial or coast-based surveys, and individual animals are tagged or identified from photographs.

Gilbert has partnered with the National Oceanic and Atmospheric Administration and other researchers around the region to survey seals using a combination of aerial surveys and radio-tagging. This year, they were able to conduct the first regional survey for harbor seals since 2001. During March and April 2012, the team attached radio tags to seals off Cape Cod and the coast of Maine. In May they conducted six days of aerial surveys using two planes, one equipped with cameras and one with radio receivers, to cover approximately 50 percent of the Gulf of Maine coastal region. The resulting photos are currently being processed; each photo must be visually inspected by a human, since digital analysis can’t differentiate seal from rock. Tagging results are used to calculate the percentage of seals that were not hauled out on rocks during the survey. The population estimate in 2001 was 99,000 animals, nearly a third of which were pups— a substantial increase from the 10 to 12 percent found in a 1981 survey. Gilbert notes that seals may be more productive now than in prior decades due to factors beyond management changes, including better food availability for seals.

While the slow but steady success in rebuilding marine mammal populations is a societal success—certainly that was a central goal of the 1972 federal act—not everyone is thrilled to have these large animals rebounding offshore. As throughout the history of European settlement, humans continue to have complicated relationships with marine mammals. Issues arise when mammals encounter fishing gear and risk entanglement, while fishermen and fish farmers take issue with seals tracking their gear and eating fish from nets, lines and pens before they are landed. Shipping companies have had to change routes to reduce the chances of injury to whales; fishermen have been required to change gear, use noise-producing deterrents and cease fishing in certain areas to protect whales and porpoises; and beach-goers and surfers more often need to exercise caution in waters where great white sharks are feeding on seals.

What will future decades mean for the Gulf of Maine’s sea mammals? Under current dedicated protection, some species may rebound to populations that reach regional “carrying capacity”—which, according to the National Marine Fisheries Service, harbor seals in the Oregon-Washington area stock may have reached. Dr. Gilbert notes that scientists expect a population at carrying capacity to have lower productivity due to competition or higher mortality due to disease. The 2012 harbor seal survey results, which will be available by the end of the year, will provide insight into whether productivity has decreased at all in the 11 years since the last New England survey. In Europe, a series of major disease events have decreased seal populations by up to 50 percent on multiple occasions in recent decades, and a similar phenomenon could happen here, especially if populations of apex predators, like killer whales and sharks, continue to shrink. Meanwhile, fishermen along the coast of Maine continue to fear seals are competing with them for fish, inhibiting the rebuilding of historic populations of cod and other groundfish species.

Will seals rebound to the point of nuisance, demanding selective hunting? Will whales benefit from dedicated rebuilding efforts to become a more common sight, like the bald eagle that now flies along our shores? Will other human uses of marine waters find ways to coexist with mammals of the deep? Only one thing is clear. Mammals in the Gulf of Maine will continue to be influenced by environmental change, social norms, economic pressures and our attitude toward nature. q

This article is made possible by funds from Maine Sea Grant.

Heather Deese holds a doctorate in oceanography and is the Island Institute’s vice-president of programs. Catherine Schmitt is communications coordinator for Maine Sea Grant.