Le Bris A, Millis KE, Wahle RA, Chen Y, Alexander MA, Allyn AJ, Schuetz JG, Scott JD & Pershing AJ (2018) Climate vulnerability and resilience in the most valuable North American fishery. PNAS 115 (8) 1831-1836.
Coastal New England towns have a fascinating relationship with the ocean. It’s difficult to pass through any of these towns lining the coast in the summer without the smell of rich thick clam chowder filling the air or seeing signs advertising clam bakes. Through the years the popularity of the abundant selection of fisheries has changed. Historically groundfish such as cod and haddock, were the most sought-after food from the sea. The American Lobster, Homarus americanus, was more of an afterthought. Since colonial-times, lobster was so low on people’s appetite that it was mostly a food for the poor and served in prisons. However, in the 1900s, as other fisheries declined, lobster came into popularity. Since then it’s been a staple seafood delicacy to most New Englanders.
Today, the American lobster is considered to be the most valuable fishery in both the US and Canada. In 2015 the harvest of lobster in both countries amounted to $1.5 billion.
Gulf of Maine vs. Southern New England
The American Lobster is found from New Jersey and up into Canada. However, the lobster population in Southern New England is not as healthy as the population found in the Gulf of Maine. Specifically, lobster in Southern New England are less abundant and the fishery has nearly collapsed. Meanwhile the population in the Gulf of Maine has increased and the fishery remains. The work by Le Bris and colleagues set out to describe these two ranges and compare why might the populations be different.
By means of historical records, fisheries data and literature about the physiology of the American lobster, the authors were able to discern the success/failure of the lobster population in the two subregions of the Northeast (Fig1).
Lobster Lifestyle & Climate Change
The life of a lobster is quite different than it was several decades ago. Because of over-fishing, the Atlantic Cod population is not what it used to be. Cod prey upon lobster. With a decline in cod populations the abundance of lobster has increased. Whereas the Southern New England region there are many natural predators of lobsters that still persist.
Since the 1980s average water temperatures in New England have increased by 1 or 2°C. This increase in temperature has reduced habitat for the juvenile lobsters who are hypothesized to have expanded their range northward (Fig2). Rising water temperatures also expand the prevalence of epizootic shell disease. In 1998 the Southern New England region experienced an outbreak of the shell disease. Southern New England populations seem to be more affected by both reduction in habitat and disease prevalence primarily due to relatively warmer waters than further north in the Gulf of Maine.
So are populations in Southern New England are declining because of an increase in water temperature and predation. But why might the abundance of individuals from this important fishery be increasing in the Gulf of Maine? Is it simply that the water is colder? Not quite.
Like most fisheries, there are limits that ensure that a healthy population of the species persists over time. In the 1930s legislators in Maine decided to impose a maximum size limit for lobsters whereas a similar rule wasn’t put in place in Southern New England until 2008. In addition, Mainers made it mandatory to identify reproductive female lobsters and return them to the ocean dated all the way back to 1917. This practice is less common in Southern New England and voluntary. The removal of adult females, especially if they’re egg-bearing, could severely set back population growth (recovery). Data from the 1980s to present day associated with water temperatures, fishing strategies and lobster abundance was used to model the status of lobster populations in each region. The authors found that, in addition to climatic changes (temperature), conservation efforts have had a significant input in sustaining a healthy population in the Gulf of Maine.
The American lobster is the most valuable fishery resource in North America. Its population has been threatened from a fishery standpoint as well as a climatic one. However, the research done by Le Bris and colleagues show that through the power of conservation the population can not only remain, it can grow.