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Naturalist Notebook 26 May to 1 June
During the weeks leading up to May 26, we had witnessed intense surface feeding behaviors from our summer population of humpback whales, and we wondered whether or not they would keep it up. Sure enough, we soon came across eight humpback whales feeding on the Southwest corner of Stellwagen Bank. Because feeding behavior often happens near the surface, we don’t always see the fluking dives that we see when whales go for deeper dives. Humpback whales are generally identified as individuals based on the black and white patterns on the underside of their tail or fluke, but when they don’t raise their tails in a fluking dive, we have to rely on other methods. The white scar running up Abrasion’s tailstock easily identifies this whale, even without the fluke pattern, but what about the others? Fortunately, the size and the shape of the dorsal fin can also be a reliable indicator of a whale’s identity. Note the difference in the size, shapes, and markings on the dorsal fins pictured below.
Ember’s Dorsal Flounder’s Dorsal Tunguska’s Dorsal
May 27 brought us more feeding humpback whales and several long, slender finbacks. At one point during the trip, passengers started to ask about the smaller dorsal fin that periodically appeared and disappeared among the feeding humpbacks, and wondered whether or not they were seeing dolphins. This creature turned out not to be a dolphin at all, but rather, a smaller type of baleen whale—the minke whale.
Smallest of the baleen whales in Cape Cod waters, this seemingly small whale is actually about 20 feet (6.1 meters) long! The Minke whale is also known as the little piked whale, because of the pointed snout visible when the whale first surfaces. In the waters off Cape Cod, Minkes are sighted year round, yet, little is known about their lives. Sightings on Stellwagen are primarily of one individual or small groups of two or three. Unlike other species in the area, it is rare to see mothers with calves. Some researchers speculate that the Minkes of Cape Cod are primarily juveniles.
Abundant in number world-wide, Minkes are the most heavily hunted baleen whale. Despite a moratorium on commercial whaling, over 1400 Minkes are killed each year in commercial hunts off Iceland, Norway, in the North pacific and the Southern Ocean Whale Sanctuary.
On May 28, as is standard, we advised our passengers to participate in the intial whale-finding mission by scanning the horizon and looking for a “spout”— the visible exhalation of a whale. This technique is often our best bet for finding whales on days with moderate to high visibility. Today, however, this became unnecessary as soon as we got to the Southern edge of Stellwagen Bank. The unmistakable body of a humpback whale leaping and spinning out of the water was visible above the waterline, and was soon followed by a lingering mound of whitewater from the whale’s impact with the water surface. A breach!
Normally, it’s unlikely to see a breach at all, which is why we could hardly believe our eyes when we saw not one, not two, but three humpback whales all breaching side-by-side! Tongs, Abrasion, and Flounder, named for the distinct markings on their flukes or tails, continued to breach synchronously as we watched, awestruck.
Why whales breach in the feeding ground is still unknown; however, the fact that these three humpbacks were doing so in such proximity to one another made us consider how little we know about the social structure of these mysterious creatures.
On May 29 we returned to the southern portion of Stellwagen Bank where we came acrossBuckshot and Trident, two humpback whales who brought calves back to Stellwagen Bank last year. Having a calf tends to be a two year commitment for a female humpback, as the gestation period and the time that the calf spends in close proximity to mom each last approximately a year. For this reason, a two year calving interval tends to be standard for a healthy, mature female humpback, although a one year calving interval is not unheard of.
Trident
To our current knowledge, there is no way to tell whether or not a female is pregnant with the naked eye—only hormonal analyses will suffice. Therefore it is possible that next year, either of these whales could come back with another calf. However, it is important to keep in mind that giving birth to a calf is an enormous energetic investment, and in doing so, the female might lose up to 1/3 of her body weight. These females, even more so than the other humpbacks, are especially concerned with acquiring the appropriate amount of calories during their summer feeding season.
Buckshot and Trident’s respective calves have since left their mothers sides and are now on their own to find food for the summer season, but as humpback whales tend to return to the same feeding ground their mothers brought them to in their first year of life, we are hoping to see them on their own this summer.
May 30 Was as an ideal day for a whale watch. The light and variable winds made for calm, glassy seas, and whale watch passengers were clearly enjoying basking in the sun on the upper deck of the Dolphin VIII. Once we got to Stellwagen Bank, the productivity of the ecosystem was immediately evident. Humpback whales and birds alike were busily feeding on sand lance, which is a small schooling fish found in the billions in Stellwagen Bank. It is frequently used as a bait fish, but it also happens to be the favorite food of certain types of birds and whales alike.
As humpback whales displayed their variety of feeding behaviors—bubble nets, kickfeeding, and bubble clouds—herring gulls flew low over the water causing the fish to leap out of the water in a cascade of miniscule, shimmering splashes. The pattering sound of the fish hitting the water as the whales loudly exhaled echoed off the stillness of the water as we watched striped bass swim under our bow. A copepod-rich plankton tow performed at that moment revealed to us yet another important component of the predator-prey ecosystem interactions of this highly productive area.
On May 31, the Southern edge of Stellwagen bank was the place to find active humpbacks, including Trident and Circus. A splash in the distance led us to a lobtailing humpback, who, on closer inspection of the fluke, turned out to be an individual named Habeñero. In general, humpback whales are named after a distinctive marking on their fluke. Indeed, the black shape on this whale’s left fluke closely resembles a habeñero pepper. However, in this case, the name is closely related to the whale’s lineage. Habeñero was born in the year 2000 to a whale named Pepper. Pepper herself was named because she was frequently seen in the presence of Salt, who was the first humpback to officially receive a name in the Gulf of Maine.
Habeñero
June 1 provided an ideal photo opportunity with a humpback whale breaching with the Pilgrim Monument of Provincetown looming the background. This was a striking reminder that these whales are experiencing their drastically different lifestyles in our very backyards!
A humpback whale breaches with the Pilgrim Monument in the background
The backdrop of Provincetown as seen from the whalewatching boat also highlighted the dramatic shift in how visitors and residents of Provincetown view the nearby whale population. Once home to a major whaling fleet, Provincetown is now a very conservation-minded community, and is home to a whalwatching industry which emphasizes the appreciation and protection of our precious marine resources.
Students keep track of the trip’s sightings