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Naturalist Notebook May 12 to May 17

By May 12 the winds had shifted to the northeast, making it a choppier day out on the water.  Luckily, the morning trip found fin whales in the bay, making a trip to rougher water unnecessary.  The steep drop-off of the land provides an ideal geographical structure for upwellings to occur, making the area just off of Provincetown beaches excellent locations for finding feeding fin whales.  Like humpbacks, fin whales will sometimes, although less frequently, use bubbles to trap fish.  Fin whales also tend to swim in circles as they feed on small schooling fish, stealthily lunging through their prey, frequently on their sides.


As the wind died down in the northeast, the afternoon trip ventured to the southern edge of Stellwagen Bank where dozens of humpback whales were feeding away.  A group of four whales, including Scratch and her calf, created bubble nets, while the calf lobtailed and rolled around on its side while mom fed on sand lance.  Still feeding on its mother’s milk, the calf didn’t participate in the bubble feeding, but rather played nearby, practicing gestures and behaviors that it will likely use as an adult humpback. 


On May 13th we were lucky enough to catch a glimpse of the highly endangered North Atlantic right whale.   Once heavily exploited by whalers for their blubber and baleen, their current population is estimated to be between 300 and 400 individuals.  In the spring and the fall, right whales take advantage of the vast concentrations of copepods—flea sized crustaceans which mature in Cape Cod Bay and provide a source of food for these enormous whales.  In the summer, many members of the population, particularly mother and calf pairs, head further north to the Bay of Fundy.  However,there is a lot that we don’t know about the migration patterns of right whales, as a significant portion of the population is largely undocumented in the summer months.  Where do these animals go?  Are their numbers so few that they disperse widely across the North Atlantic Ocean, or is there another population hotspot that scientists have yet to discover?  Answering these questions could be the key to the future preservation of this highly threatened species.


Glassy seas and light winds made May 14th a very pleasant day for whale watching.  Anvil and Buckshot, two humpback whales who brought calves back to Stellwagen Bank last summer, were seen kickfeeding and lunging through schools of sand lance at the surface of the water.  Giving birth to calves is a huge energetic expense and it’s likely that these recent moms are still recovering by building up their blubber layers after a winter of fasting and sending their calves out on their own.  Mother and calves stay together for about a year before they go their separate ways, so it’s likely that Anvil and Buckshot both recently went through this parting. 


May 16th’s afternoon trip brought us to three different species of baleen whales, including many feeding humpback whales, several stealthily traveling finbacks, and even the elusive minke whale. Though thought to be plentiful in the Gulf of Maine, minke whales are one of the more challenging animals to watch.  While they are similar in shape to the streamlined, sleek finback whale, they are approximately one third their length.  Most of the minkes found in the Gulf of Maine are thought to be juveniles, reaching lengths of approximately 20 feet, and are rarely seen associating with other minkes in this area.


The three species seen today are all classified as “rorquals”, which refers to the pleats running down the undersides of their bodies from their jaws all the way to their navels.  These pleats expand as the whales engulf mouthfuls of food and water, allowing them to temporarily increase the volume of their mouths to maximize their food intake. 


On May 17th we experienced one of the most dramatic bouts of humpback whale feeding that many of us had ever seen.  Upon stopping the boat near the southwest corner of Stellwagen Bank, a frequent hotbed of humpback feeding activity, we could see at least fifty to sixty humpback whales within a half mile radius.  Everywhere we looked humpback whales were feasting on the millions of sand lance that had amassed near the edge of Stellwagen.  


As we moved into the area we started to recognize familiar whales and their characteristic feeding styles.  Coral is a male humpback that we’ve been watching since 1988.  Coral’s characteristic kickfeeding style is easily recognizable to those of us who have been seeing him year after year.  Other humpbacks prefer cooperatively blowing bubble nets—concentric rings of bubble columns which trap and stun fish.  Looking down into the center of the bubble net we could actually see the sand lance group together before being swallowed whole by the humpbacks that had formed the net.  Generally when we see a lot of humpbacks in one area we assume that they’re there for the food.  Even then is it rare to see groups of more than three or four whales associated with one another, so imagine our surprise to see a total of nine animals work together to form one enormous bubble net!