Log for April 27, 2015

Our whale watch yesterday was a very special and unforgettable experience. We had a few usual suspects out there including Atlantic white-sided dolphins, harbor porpoises, minke whales and fin whales. But more importantly, we had a scattered group of about 10 skim feeding sei whales.

Sei whales skim with the Boston skyline in the distance

This was my very first time seeing sei whales, so it was an especially exciting trip for me! Sei whales are large, 40-60 foot baleen whales that rarely, but occasionally visit the inner waters of Massachusetts Bay.

Look at that baleen! 
Synchronized skim feeding

Calanus copepod, sei whale food
While they are rorquals like fin, humpback and minke whales, their prey and feeding habits are more like right whales. Sei whales, like North Atlantic right whales, feed primarily on copepods, a type of zooplankton. When large patches of copepods are present, they sometimes swim through this area in groups taking advantage of this feeding opportunity. I had a lot of guests asking me about these copepods so I thought I'd add a photo to give our readers an idea of what type of animals these sei whales are filtering out of the water (see photo). Considering how small these animals are, you can imagine they have to filter a very large volume of water to get the biggest bang for their buck. They do this by opening their enormous mouths and swimming very slowly across the surface of the water for extended periods of time. This is what we call skim feeding. You can see from the photos that this type of feeding is very different from the powerful lunge feeding we are used to seeing humpback and fin whales displaying.

Open mouth, coming our way

Skim feeding is a very tranquil and beautiful behavior to watch and something, in four years of coming out to Stellwagen Bank, I have never been able to experience. This slow and graceful feeding gave guests the opportunity to observe, in slow motion, the function of ventral pleats and baleen. As these sei whales fed, they filtered seawater on their sides allowing guests to watch their ventral pleats stretch, their throats expanding as they slowly filled with seawater (see photos). We then observed this water flow through their baleen as they filtered their food out of the water.

Baleen and ventral pleats on full display

We watched these whales feeding in awe the entire trip and enjoyed listening to them breathe against the silence of a calm sea. I felt very lucky to have been on our whale watch yesterday and I know our guests did as well! It was an experience I know I will never forget!

Flat calm and peaceful skim feeding

I promised I would provide an update regarding an entangled whale we heard about over the VHF radio on Sunday. Fortunately, the humpback whale was successfully disentangled by the Center for Coastal Studies disentanglement team. However, with deep wounds and being underweight, it is likely still suffering from the effects of the entanglement.

— Tasia Blough

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