The ocean’s largest inhabitants under the radar…until now

(originally posted in two parts on Conservation International’s blog May 20 and May 22, 2009)

(Part 1)

Multitudes of animal species continue to evade detection by science, mainly because they are really hard to find. Many are tiny, or well-hidden, or live in places that people have a hard time getting to (or escaping from). While roughly a couple of million species have been officially catalogued, perhaps tens (hundreds?) of millions of species remain undiscovered.

So you would figure that we know just about all there is to know about the planet’s biggest species – the ones that rival monster trucks and ocean liners in size…but you’d be wrong. In fact, scientists are still uncovering secrets as to the whereabouts and wanderings of two of the largest animals that have ever lived.

The basking shark (Cetorhinus maximus) is the world’s second largest fish; only the appropriately named whale shark (Rhincodon typus) is larger.

Basking sharks can reach lengths of 10-12 meters (33-40 feet), and are known for swimming with their cavernous mouths – big enough to swallow a person whole (theoretically speaking) – wide open to take in and sieve tiny plankton from the water.

They inhabit mostly temperate (higher-latitude) waters around the world where oceanographic conditions are right for feeding, but they seem to disappear from these areas in the winter.

Where do they go? Do they hibernate? Do they ‘fly south’ like migratory birds and elderly Americans from northern states?

To solve this mystery, marine biologists from Massachusetts and Maine deployed sophisticated satellite-linked archival tags on two dozen basking sharks from off the coast of Cape Cod. To the scientists’ surprise, the sharks crossed 2000 km (more than 1,200 miles) of ocean to previously unknown locations throughout the sub-tropical and tropical western Atlantic. This is also the first ever use of this type of technology to record a fish species crossing the equator.

This expanded knowledge of basking shark geographic range shines new light on many aspects of this species’ biology, particularly reproduction, but also demonstrates the importance of tropical as well as temperate waters to these far-ranging behemoths.

(Part 2)

It’s hard to believe that an animal could dwarf the basking shark, but try to imagine an animal whose heart is the size of a car, whose tongue weighs as much as an elephant, and who has blood vessels wide enough that a grown man could swim through. Can you picture it? If so, you’re imagining the mighty blue whale (Balaenoptera musculus), the largest animal that has ever lived on Planet Ocean. (Planet ‘Earth’ for all you land-lubbers; I am a marine biologist after all.)

Like the basking shark, however, we know shockingly little about how many are left, about its migrations, and even about where it goes to breed and birth its calves.

Most populations of the “great whales,” including blue whales, suffered massive declines due to commercial whaling during the first half of the 20th Century. Historically, blue whales in the North Pacific Ocean were frequent visitors to British Colombia, Canada, and the Gulf of Alaska, but by the 1960s, had virtually disappeared. Meanwhile, large concentrations of blue whales off California and Baja California, Mexico, have been documented since the 1970s, but the relationships between these observations – and the whale populations themselves – had been unknown.

In a recent study, researchers from British Colombia, Washington and California reported numerous sightings in the last decade of blue whales in their former northeastern Pacific stomping grounds, suggesting that the elimination of whaling has allowed blue whales to reclaim old territory. Most interestingly, the scientists used photo identification to confirm that the whales venturing north belonged to the California feeding population.

Whale biologists had feared that ‘memory’ of historical feeding areas like B.C. and the Gulf of Alaska might have been lost by area-specific intensive whaling activities, but these new findings show that tragedy might have been averted in this case. However, the true causes of this re-expansion in blue whale ranges are unclear; the study’s co-authors suggest that fluctuations in favorable environmental conditions could be driving the perceived changes in blue whale movements.

Nonetheless, although there is still cause for concern about the future of blue whales in the North Pacific, we can be happy to see that they are finding their way back to places they once called home.

As impressed and intrigued as I am with the things that we scientists have learned, it’s what we don’t know that continues to capture my interest and imagination.

The fact that colossal creatures like the basking shark and the blue whale could be in any way mysterious to curious scientists and awestruck observers speaks to nature’s complexity and to our meager understanding of it. These cases show that if we stay in pursuit of the answers we need to know and to protect nature’s wonders, they will reveal themselves to us in time. What we do with this newfound knowledge is up to us.

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