Yesterday around New York Harbor, I spotted a pair of Atlantic Harbor Seals basking under the noonday sun at the end of algae covered rocky groin. They were just relaxing and warming up their body out of chilly bay water.
Water temperatures in New York Harbor range now from the mid 40s to the mid 50s. Air temperatures yesterday were in the mid 60s. Since water, compared to air, conducts heat easily, marine mammals need to find ways to stay warm as they lose a lot of their body heat in water than in air at the same temperature. We share this aspect with marine mammals. This is why people often feel cold when swimming in the water when the temperature is 70 degrees than walking on the beach at the same temperature. We lose our body heat.
For seals, since time spent on land is time not losing heat so quickly as in the water, hauling out is a critical piece of being healthy and happy and to maintain a high-quality energy balance.
One seal was big and long, about 6-feet long. It was almost certainly a male Harbor Seal. Males can weigh 150 to 300 pounds and grow up to 6 feet long. The other seal was smaller, and lighter in color. Perhaps a female seal, as females weigh up to 200 pounds and are generally 4.5 feet long. It could have also been a juvenile though.
I watched them snoozing and sleeping for 15 minutes on green algae surrounded by gulls, brant, and black ducks. Then all of sudden the little seal jumped in the water, soon followed by the bigger seal. Both went for a swim.
About 10 minutes later, the smaller seal showed its head out of water. It had just caught a fish for lunch. In its mouth was a large flat fish, most likely an adult winter flounder.
The body of the winter flounder is oval-shaped, flat, and thick. Adults can reach lengths of about 10 inches. Winter flounder have a small mouth and can change color to blend in with the bottom type, but generally are much darker than most other flatfish.
New York Harbor is an important spawning area for winter flounder. Starting sometime in late fall or when water temperatures decrease around 55 degrees F, mature adults migrate from deeper waters out in the into shallow estuarine waters to spawn from late December into April. They are omnivores and feed on sand shrimp, amphipods, larval fish, mollusks, worms, and some species of seaweeds and plants.
It was the flounder, though that was prey, not predator, this time. Harbor Seals are carnivores and love to eat fresh fish.
Harbor Seals are not picky eaters and will generally feed on a wide variety of fish and crustaceans. According to studies done by NOAA from the scat of Harbor Seals collected on sandy beaches in New England, in general, the most numerous prey species in the samples were sandlance, silver hake, Atlantic herring, and redfish. Other species included cod, haddock, pollock, flounders, mackerel, and squid. They will also consume clams, crabs, and shrimp. A Harbor Seal's diet varies seasonally and regionally and often is subject to local prey availability. Within the span of a single day, they take in between 5 and 6 percent of their full weight.
Little by little the little seal was ripping up the flounder into smaller pieces to swallow. Harbor seals do not generally chew their meals, but will swallow it whole or take in intact pieces. Food will be digested as a seal hauls out of the sea to rest. It was quite a lunchtime experience.