How Humpback Whales Feed Hawai‘i

By Jeannine Rossa

A Hawai‘i humpback whale mother and calf. Photo by Ed Lyman, NOAA permit #782-1719

We can feel it. The air is changing. It’s a little cooler, a little moister. The cloud patterns are shifting. The wiliwili are setting seed. Kolea have returned. The ocean is cooling down. Soon, more whales will return. And when they do, they will bring Hawai‘i incredible gifts — their very bodies — that quite literally feed us all.

How do whales feed us? Let’s go back to fourth grade science, when we learned about the food chain. Plants are eaten by a small animal which is eaten by a bigger animal which in turn is eaten by a still bigger animal. In our ocean, phytoplankton (floating miniscule plants) are eaten by zooplankton (floating tiny animals), which are eaten by small fish which are eaten by bigger fish which are eaten by sharks. You get the picture. The oceans around Hawai‘i are low in important nutrients for life, like iron and phosphorus. As a result, our plankton biomass is low compared to cold-water oceans. Less plankton means less food for fishes.

Pacific Whale Foundation scientists take samples to send to the Hawai‘i Marine Institute of Biology from a humpback whale placenta they found floating in the water near Maui. Operating under Dr. Kristi West’s NOAA Permit # 18786-03

Whales boost the entire food chain by shedding their skin. Like humans, shedding the outer layer of a whale’s skin cells is vital for allowing new, healthy skin cells to replace old ones. When you are 40-feet-long and underwater, how do you exfoliate? The need to maintain healthy skin is one of the main reasons Robert Pitman from Oregon State University’s Marine Mammal Institute and other whale scientists think whales migrate to warmer waters. In warmer waters, a whale’s skin sheds naturally. Not in huge sheets, but more perhaps, like a really bad case of whale dandruff, except all over.

Shedding whale skin is made up of proteins and fats, perfect for zooplankton to eat. What is critically important is to understand is that 80 percent of Hawai‘i’s zooplankton is made of tiny, newly-hatched offspring of species we see every day; all kind of reef fishes, he‘e (octopus), wana (urchins), coral, sea stars, jellyfish and even o‘opu and hihiwai, freshwater gobies and snails that spend part of their early life cycle in the ocean before migrating upstream to grow to adulthood and spawn. So, more zooplankton means more fishes, he‘e, coral, and hihiwai — in other words, our marine and freshwater ecosystems are fed by whales.

An ‘ōpelu (mackerel scad, or Decapterus macarellus) nibbles on the skin of a resting male humpback whale. Screen grab from a Customized Animal Tracking System audio/visual recorder, temporarily attached to the whale with suction cups. Photo by Dr. Marc Lammers/HIHWNMS, NOAA permit #19655

A concrete example of the importance of whale skin was recently caught on camera. Dr. Marc Lammers, Research Ecologist with the Hawaiian Islands Humpback Whale Sanctuary, uses suction cups to temporarily attach movement recording devices on the backs of whales to study their behavior underwater. Last winter, he was able to include a tiny video camera. The camera documented that whenever the whales rested, schools of ‘ōpelu (mackerel scad) would immediately appear and start nibbling their skin. Better nutrition can boost reproduction, so it is not a stretch to say that the annual return of whales is an important part of keeping ‘ōpelu populations thriving. Why do we care if ‘ōpelu thrive? Schools of ‘ōpelu are the favorite prey item for deeper water fishes we humans value, such as mahimahi, tuna, ono and marlin, which is why, of course, they are used as bait. Perhaps more importantly, ‘ōpelu spawn and rear among inshore reefs, so a thriving ‘ōpelu population provides prey for predatory reef fish.

While in Hawai‘i, humpback whales generally do not eat, so whale poop is not a big nutrient contributor to our ocean. However, in 2014, Dr. Trish Lavery from Australia’s Department of the Environment and her team determined that juvenile male blue whales excreted iron in their poop, “which would stimulate primary production equivalent to that required to support prey consumption by the entire Australian population of blue whales.” In other words, whale poop provides iron to phytoplankton, the base of the food chain.

Something rarely observed or photographed: the placenta of a humpback whale. Photo by Jens Currie, Chief Scientist, Pacific Whale Foundation

Whales give birth in Hawai‘i, and because they are mammals like us, that means that each birth has a placenta — the concentrated network of blood vessels and supportive tissue that transfers oxygen and nutrients from the mother to the growing baby. We all know that blood has iron; tiger sharks follow birthing humpback whales, ostensibly waiting to grab that gigantic, easy, iron-rich meal that doesn’t try to swim away. In 2007, Anthony Antonelis (Pacific Islands Fisheries Science Center), Dave Johnson (Duke University), and David Mattila (then, at HIHW) estimated that every year, about eight percent of the returning whales are pregnant. Assuming for math purposes that we have at least 8000 whales returning (we don’t actually know, but estimate 8000-12,000 whales return to Hawaii annually), about 640 would give birth. At an estimate of 50 – 75 pounds per placenta, that’s roughly 16 – 24 tons of food delivered to our ecosystem. Why do we care if tiger sharks have an easy meal? That means that they are eating fewer fishes.

Finally, whales give us the ultimate gift: their entire bodies. Inevitably, some whales die when in Hawai‘i, although we have no idea how many, because most whale carcasses sink to the bottom of the ocean. Based on the Antonelis-Johnson-Mattila ratios, it is estimated that of those 640 babies, 17 would not make it, and approximately 6-7 adults would also die while in Hawai‘i.

In the last decade, whale researchers all over the world, such as Craig Smith from the University of Hawai‘i, Yoshihiro Fujiwara from Japan’s Agency for Marine-Earth Science and Technology, or Paulo Sumida from Brazil’s Instituto Oceanográfico have determined that a deceased whale feeds a whole series of scavengers and decomposers as each consumes part of the whale: first free-ranging animals like octopuses and sharks, followed by animals that remove stored fats from the bones like polychaete worms, clams, and crustaceans (crabs and shrimps) — some of them, like bone-drilling snails, new to western science. Microbes are of course also critical for this decomposition process.

In addition, when a whale’s body falls in the deep ocean, the carbon stored in its bones stays in that deep sea ecosystem, which keeps that carbon out of the atmosphere. The International Monetary Fund suggests that the value of storing carbon in the ocean floor ecosystem is worth millions of dollars per large whale to humanity.

Many of us find the whales a source of delight and awe. We thrill at hearing the males “sing” underwater, and smile watching babies learn how to breach and slap their tails. For some, the whales are a physical manifestation (kino lau) of Kanaloa, one of the four major Hawaiian gods. For those in the whale-watching and tourism industry, the whales pay the bills. And some worry about whales getting entangled in their fishing lines or colliding with their boats. No matter your view of whales, they are ultimately a gift to Hawai‘i Nei. They literally feed us and keep our marine and freshwater systems healthy and functioning.

So, when you see the whales this year, thank them. Māhalo nui o ke koholā!

• Jeannine Rossa is an aquatic ecologist and fisheries biologist. She is the acting State Co-Manager of the Hawaiian Islands Humpback Whale National Marine Sanctuary. She works for the Hawaii Department of Land and Natural Resources, Division of Aquatic Resources and is based on the island of Maui. She can be reached at rossa.researcher@hawaii.gov