Coastal seals are highly adaptable marine mammals inhabiting temperate and subarctic shorelines. Their presence often overlaps with commercially sought-after crustaceans like the lobster. This shared environment leads to curiosity about whether these agile predators include the hard-shelled invertebrates in their diet. Understanding this interaction requires examining the seals’ opportunistic hunting behavior and the ecological factors influencing their menu.
The Specifics of Lobster Predation
Seals, including species like the Grey seal and Harbor seal, occasionally consume lobsters. However, this predation is generally considered an infrequent and secondary food source for the overall population. Scientific analysis of seal diets, often conducted by examining stomach contents and scat samples, consistently shows that crustaceans make up a very small fraction of their total intake.
When a seal preys on a lobster, it must account for the crustacean’s tough exoskeleton and large claws. Seals are not equipped to chew; they typically swallow smaller prey whole or tear larger items into manageable chunks. To process a lobster, a seal may use its powerful jaw to crush the shell of smaller individuals. Alternatively, they employ a forceful shaking action to tear off the tail and claws before consuming the softer muscle tissue.
This behavior highlights that seals are opportunistic predators that take advantage of available food, even if processing requires effort. However, the energy expenditure required to pursue, subdue, and dismantle an armored lobster makes it a less attractive dietary choice compared to softer-bodied prey. The consumption of lobsters by seals is typically a situational response rather than a consistent hunting strategy.
The Typical Diet of Coastal Seals
The vast majority of a coastal seal’s diet consists of fish, classifying them primarily as piscivores. Their preferred prey are species that school in large numbers or are found on the seafloor, providing an easily accessible and calorically dense meal. Common fish items include bottom-dwelling species like cod and flounder, as well as pelagic species such as herring and sand lance.
Fish are preferred because they are soft-bodied, making them easy to capture, tear, and swallow quickly while hunting underwater. Seals also regularly supplement their diet with cephalopods, like squid and octopus. These similarly offer high nutritional value without the defensive armor of a crustacean. A Harbor seal typically consumes a daily amount of food equal to five to six percent of its body weight, requiring high-yield prey.
The consistent focus on fish and cephalopods is a matter of energetic efficiency. Soft-bodied prey offers a higher caloric return on investment and requires less time and force to ingest than cracking a lobster’s thick shell. The inclusion of crustaceans is usually a fallback, filling a temporary gap in their primary food supply.
Environmental Factors Affecting Prey Choice
A seal’s decision to consume a lobster is often a direct result of environmental pressures and local prey availability. Coastal ecosystems are dynamic, and the abundance of primary fish prey can fluctuate significantly due to seasonal migrations or localized depletion. As highly adaptable foragers, seals shift their diet to whatever is most abundant and easiest to catch in their immediate area.
When preferred fish species migrate or become scarce—due to natural cycles or human activities like overfishing—seals become more opportunistic. They focus on secondary prey items, which can include lobsters if the crustacean population is dense and easily accessible on the seabed. This habitat overlap is important, as seals frequently forage in the benthic zone where lobsters reside.
The diet of a seal is highly regional and temporal, reflecting the immediate conditions of its foraging grounds. This explains why seals in one area may show very little evidence of lobster consumption, while those in another area with depleted fish stocks and a high lobster density may prey on them more frequently. The shift to a crustacean diet is not a preference but a flexible ecological response to changes in the local food web.