Platt’s Bank Journal 2005

Platt’s Bank – 07/11 – 07/13/05

by Heather McRae

Portland, Maine – Thirty miles off shore the sun is fading behind what seems to be the edge of the ocean. Herring are breaking the water’s surface, jumping and twisting to feed on dense patches of krill and calanus copepods. Like popcorn, the krill jump into the air as the herring attempt to have dinner. On the edge of these frantic patches a humpback whale lunges from below the surface with its accordion-like ventral pleats fully expanded.

Above Platt’s Bank, in the Gulf of Maine, a group of researchers from the University of Southern Maine, The New England Aquarium, and the Gulf of Maine Research Institute are investigating high productivity areas, known as hot spots.

NEAq's Research Vessel, Galatea, in Portland<br />
Harbor

NEAq’s Research Vessel, Galatea, in Portland Harbor

Hot spots are identifiable based on the concept of recognizing an area with high productivity and high species diversity relative to an area with little productivity and low species diversity. Thus, an area with copepods and krill in dense red mats, herring amongst these patches, whales, and seabirds create a hot spot. In general, the concept is vague and identifies the need to study such activity areas. Researchers are asking how to quantify and identify these hot spots.

These patches of copepods and krill form in circles and river-like patterns across the ocean surface. An aerial survey crew flies to scope out the bank area, and provides any coordinates of potential hot spots to the boat crew. The aerial crew leaves from Biddeford Maine and fly for approximately four hours following pre-defined transects across Platt’s Bank and finishes along Jeffries Ledge. The boat crew leaves from Portland Maine and has 12-14 hour days on the water with a three-hour transportation time to and from the survey area.

Hot spot near Platts Bank

“Hot spot” near Platts Bank

My name is Heather McRae and I am part of both the boat and aerial crews for the Platt’s Bank surveys. I am a 2005 graduate of the University of New Hampshire with a degree in marine and freshwater biology and I am currently working for the New England Aquarium.

The ocean, which can often seem infinite and impersonal may also spring to life and drag you into the mystery underneath the surface. Few people get to study the interconnections between marine organisms, their prey, predators, and daily activity, but in our project we get to spend time looking for the most active areas in our study area to compare to those not-so-active regions you witness at sea. What many of you see on television, such as PBS specials are what we are looking for an area with high productivity and species diversity. At the same time, those areas that can seem boring are the way to measure what hot spots are, and provide insight into what the ocean is like when most of us are at sea.

Humpback fluke

Humpback fluke

My first aerial survey was a unique chance to observe marine life from 750 feet above the ocean’s surface. The perspective of the sea life is a trade off to observations from sea level. Above the surface, the sea life, especially marine mammals such as fin whales ( Balaenoptera physalus ), look like the drawing in guidebooks as far as shape and proportion, a view that is distorted at eye level. The most amazing part of the flight was the realization that whales and some large fish are big enough to identify from great distances. From 750 feet high in the sky, a 70-foot long fin whale appears only six-seven inches long, but its body has a white glow and shows off the features only a fin whale has.

For the duration of my three and a half hour flight we observed humpback (Megaptera novaeangliae), fin, minke ( Balaenoptera acutorostrata ), and pilot whales ( Globicephala sp. ), North Atlantic white-sided dolphins ( Lagenorhynchus acutus ), basking sharks ( Cetorhinus maximus ), and an ocean sunfish ( Mola mola ). Seabirds are also visible from the plane, however, identification of these avians requires the observation of flight pattern and wing beat over shape. On the boat, these wing beats become important with overall body shape and color. My expectation for teeny-tiny size came from flying in commercial airplanes, always looking for sea life and marine mammals when flying over the ocean – something I am still yet to see from a Boeing airplane.

After my first experience as part of an aerial crew and finally seeing whales from the sky I got to encounter another “first”. On the boat, thirty something miles off shore, we are chasing those hot spots that the plane typically identifies. This time, the plane has already landed in Biddeford and we find patches of surface activity popping up all around us.

What we see up close are dense red patches moving in the water column. These red patches are full of Calanus finmarchicus (calanus) copepods and Meganyctiphanes norvegica (krill or euphausiids). Amongst the dense patches of mero- and holoplankton are the silver sides of herring twisting and jumping to eat the calanus and probably catching some krill in there too. Along the edges of the patch lunge the humpbacks targeting the herring and even the krill. The gulls in the area are eating the herring too – and thus we have just witnessed a complex food web, here on the ocean’s surface. This is a hot spot (insert sound of excited scientists here- think kids and water fights).

Dolphins under bow

Dolphins under the bow

To study hot spots and not-so-hot spots we use an observation protocol and log that into a computer program. We observe for marine life (marine mammals, sharks, ocean sunfish, seabirds, etc.) and log into the system a series of coded coordinates as to their location relative to the boat. We also run three oceanographic tests; a CTD (Conductivity, Temperature, Depth), TAPS (Tracor Acoustic Profiling System, using hydroacoustics to measure the size and number of zooplankton in the water column), and the FISH (a towed hydroacoustic system for fish). Each instrument will help to identify the key characteristics in hot spots and potential clues in the patterns that they may follow.

To gain a better understanding of this area over time, we decide to stay the night. By dark, almost two hours after we sighed the patches, they have calmed down and the billowing sound of a whales exhalations echoes not too far off in the distance. This night is calm, the sea surface winding down of activity – the way most of us see the ocean. A few birds here and there, maybe a whale traveling off in the distance. This is no PBS special with only the best of the best clips from a month at sea, this is science, the wait expected, and the hot spots all that more exciting.

Platt’s Bank – July 24, 2005

by Heather McRae

Oftentimes what a whale is feeding on is not clear to an onlooker. In my adventures toward becoming a marine biologist I have witnessed an occasion at sea that suggested an area of high productivity – including humpback and fin whales feeding on herring and dense patches of krill and copepods. However, this one previous experience has been masked by one month off the coast of Portland – where I have now seen this more often than anyone in the project imagined. What makes this particular day so extraordinary is witnessing the feeding patterns of a humpback whale on dense krill patches from the air, aboard a small aircraft well-designed to provide a bird’s-eye view of the Gulf of Maine.

Two humpback whales feeding on the krill patches

Two humpback whales feeding on the krill patches
(Peter Stevick)

We circled on a single humpback for nearly half an hour while witnessing an event that evokes the question “why do they do that?” Simply, it is thought that a baleen whale has a sense of taste for the chemical production of the plankton. There is a lot we know about whales, but there are still pieces of the puzzle left to fill in.

Whales are part of the mammal order Cetacea. There are two main groups of cetaceans, the toothed whales (Odontoceti) and the baleen whales (Mysticeti). The toothed whales include the porpoises, dolphins, and smaller whales such as killer whales (Orcinus orca). The baleen whales, such as a humpback, lack teeth and instead feed with plates of baleen.

Humpback feeding on krill

Humpback feeding on krill (Heather McRae)

Baleen acts like a strainer does for pasta. Keratin (much like what your fingernails are made of) hangs in a rigid plate from the roof of the mouth. The size of the plates can vary between the whales, as does the density and coarseness due to varying food sources. The fringe acts as the catching mechanism inside the mouth while the plates (smooth on the outside) allow the water to easily flow outwards. A feeding whale will take a big gulp of water, slowly close the mouth, and use their tongue to push all the food and water outwards – so as the food catches on the fringe, the water flows past through the plates and back into the ocean.

Whales are highly specialized for their life as marine mammals. In observing the feeding of the humpback from the plane it is evident that their fusiform or streamlined body, paddle-like flippers, and horizontal fluke aide both traveling and foraging. The gracefulness of a whale from the air is something magnificent, because you can observe how streamlined the body truly is. A humpback, whose scientific name, Megaptera novaeangliae, means ‘great winged New Englander’ due to their characteristically long pectoral fins, is easily observed by plane in the Atlantic Ocean. Their long white flippers glow under the surface and on this particular day, they can be seen over twenty feet below the water’s surface.

aerial view of krill

Aerial view of krill (Peter Stevick)

It is clear that the krill were rising and falling in the water column. More than a dozen groups of krill formed like grayish mats under the ocean surface in varying shapes and sizes. As we circled, the krill would rise to the surface, slowly brightening the water to a swirling rich red. As these patches formed, a single humpback whale was on full throttle ahead for this food. Although we counted more whales in the area, this particular whale was the only one feeding on the patches. As the whale drew nearer to the patches we observed a few quick breathes at the surface than a dive. The fun part of circling was trying to guess which patch would be the next victims – and all I could think about was a line from Finding Nemo – “swim away, swim away…” But as the glowing white flippers appears nearing one patch the mouth, gaping open, ventral pleats extended, came right up in the middle of the patch demolishing half or most of that food source. Sure enough, the whale continued. It would take in a mouthful, breathe, and hone in on the next patch – often going for those which we could see were most rich in color. Of course, the whale cleaned up each patch – never leaving half of a patch behind. The whale also was selective, which made guessing patches all the more fun. We watched the whale head for one patch, change direction (at least 45 degrees), then head for another patch just beyond.

Humpback feeding on krill

Humpback feeding on krill (Heather McRae)

What was the deciding factor to eat a patch or not? This piece of the puzzle we have yet to determine, but we can extrapolate that the humpback was selective with foraging patches and, from this observer’s perspective, was one happy whale.

More information:

Animal Diversity Web (ADW) is an online database of animal natural history, distribution, classification, and conservation biology at the University of Michigan.

Provincetown Center for Coastal Studies is a non-profit organization focused on research of marine and coastal habitats and education for the preservation of marine and coastal habitats in Provincetown, MA.