Monthly Archives: January 2013

For male humpbacks, trip to isles is all about mating

Published January 21, 2013 in the “Ocean Watch” column, Honolulu Star-Advertiser ©2013 Susan Scott

Humpback Whale in Alaska. ©2013 Scott R. Davis

Several whales I saw from the Lani­kai lookout last week were particularly active, blowing, splashing and flipping their fins. As I watched the peaceful sunrise, I was tempted to imagine that the group was a family consisting of parents and baby, maybe accompanied by an auntie or uncle with a cousin or two.

But that would be wrong. I was almost surely watching male whales fighting.

Male humpbacks migrate from Alaska to Hawaii each winter for one reason, and it’s not for a family vacation. They’re here to mate. Being typical of most mammals, the males want to spread their genes far and wide by mating with as many females as possible. Given the biological drive, it’s the male’s job to fight off other males with the same goal, which is all of them.

To make life even more competitive, there are far more sexually mature males in Hawaii waters than there are receptive females. The male-female numbers in the Alaska feeding grounds are equal, but because females give birth only once every two or three years, not all adult females make the trip south each year. For every female in estrus in Hawaii’s breeding grounds, there are two to three eager males.

From the female perspective, having a
surplus of males is a good thing since female whales go for quality over quantity.
Competition allows a female to pick the biggest, strongest male to father
her offspring.

humpback

Humpback near Juneau, Alaska. ©2013 Scott R. Davis

For males, though, spending the winter among a pack of testosterone-loaded rivals can leave smaller and weaker individuals as bloody messes. Fights can include head butts, body blows and fluke whacks, resulting in head injuries, torn fins and damaged tails.

When not wooing a female or duking it out with challengers, the life of a male humpback is lonely. His interactions with other members of his species usually last only minutes, or maybe an hour or two.

For a male, a long-term commitment is two days, the longest time Hawaii researchers recorded a male staying with a female and her calf. Usually, however, a male’s attention to a female is a few hours — a day, max. The male then moves on to the next encounter.

Or hangs out alone, singing the blues. Or maybe a rock opera with a message. No one knows for sure the meaning of humpback whales’ haunting songs. Researchers do know that the songs occur only during breeding season, that only males sing and that the songs, which the whales learn from each other, do not seem to attract females.

Knowing what we do about male whales, though, you can be sure the always changing songs have something to do with mating.

Most female humpbacks give birth in January, so from now through April it will be common to see calves swimming and frolicking near their mothers.

But when the water is white with fin slaps, tail smacks and body slams, it’s not a family of humpbacks enjoying each other’s company. It’s male whales brawling for their moment of glory. It works. The humpback whale population is growing.


Marine biologist Susan Scott writes the newspaper column, “Ocean
Watch”, for the Honolulu Star-Advertiser, www.staradvertiser.com

©2012 Susan Scott

Curious creatures wash up on shores when winds blow

Published January 14, 2013 in the “Ocean Watch” column, Honolulu Star-Advertiser ©2013 Susan Scott

One windy January day in 1983, shortly after moving to Hawaii, I ran into my University of Hawaii physiology lab partner, born and raised on Oahu. Staring at the mask and snorkel in my hand, he asked where I was going.

The beach, I said.

“The beach?” he said. “It’s winter!”

Thirty years later I’m still going to the beach when it’s windy and raining. That’s when I find the best stuff.

What I look for during my blustery beach walks are any of several marine animals that live on the surface of the open ocean. The scientific name for this remarkable group is pleuston, from the Greek root “pleus,” meaning to float or sail. Pleustonic animals do both, floating passively in currents and, when it’s blowing, sailing with the wind.

The common name for these creatures is the wind drift community, a term that hints at one of the downsides of an offshore existence. When the wind overpowers the currents that usually keep the animals at sea where they belong, and the creatures are positioned upwind of land, the drifters blow ashore to their deaths.

One of these animals is a snail called a violet shell or purple snail, names that describe the creature’s shell colors. The adult snail’s fragile lightweight shell, about thumbnail size, is pale lavender on the narrow pointy side and deep purple on the wide, open side.

Such coloration is good camouflage for the little snail. When a fish predator looks up from the deep, the snail’s light underside is hard to see because it blends in with the sky above. If a hungry seabird looks down, the shell’s purple topside colors match the deep blue-purple of the offshore ocean.

The color distribution tells us the snail’s floating position is foot up or, in our view, upside down. The inversion works because the snail floats on a bubble raft it secretes.

The snails hang onto their mucus floats for all they’re worth because to lose their rafts means to lose their lives. They can’t swim.

A violet snail spends a typical day adrift hoping to run into other species like Portuguese men-of-war, by-the-wind sailors or blue buttons, all jellyfish relatives. This is no social call. Violet snails eat their neighbors.

A nomadic lifestyle would seem to make reproducing difficult, but violet snails have that wired. Males discharge sperm in packets that passing females pick up. Females brood their fertilized eggs until they hatch, releasing bubble-rafting babies directly into the sea.

This method seems pretty hit-and-miss, given that the snail’s habitat is millions of square miles of open ocean. It works because oceanic currents usually herd the snails (and their prey) together. Sailors have reported seeing swarms of violet snails up to 200 miles wide. I’ve not seen this yet, but I live in hope.

When strong tradewinds blow, you’ll find violet snails stranded on windward beaches; during Kona blows, on leeward beaches.

Finding these lavender beauties as I did last week was well worth having salt-sprayed glasses, rain-wet hair and sand-filled ears.

But snorkeling? Please. It’s winter.


Marine biologist Susan Scott writes the newspaper column, “Ocean
Watch”, for the Honolulu Star-Advertiser, www.staradvertiser.com

©2013 Susan Scott

Box crabs hide in the sand and wait to surprise snails

Published January 7, 2013 in the “Ocean Watch” column, Honolulu Star-Advertiser ©2013 Susan Scott

Box crabs hide in the sand and wait to surprise snails. ©2013 Susan Scott

That’s what I wondered last week as I watched a flowery flounder stalk a box crab. I wanted to tell the fantastic flatfish, so colorful that “peacock” is its other name, “Don’t do it! That crab is packing!”

I learned the hard way. Last summer while snorkeling with my young friend Naia, I spotted a cream-colored box crab sitting on a patch of white sand. Box crabs can be hard to find because they look like D-shaped rocks, flat across the back and rounded up front with colors matching their backgrounds. I picked the crab up.

“Naia,” I called. “Look what I found.”

But before Naia could swim my way, the 4-inch-wide crab pinched me. This was no little tweak. The crab’s formidable front claw gouged a piece of flesh from my thumb so deep it hurt for a week and took another week to fill in.

I dropped the crab, of course, and in two seconds the little armored tank had disappeared in the sand, digging in backward with its rear legs. By the time Naia reached my side, all I had to show her was a bleeding digit.

The box crab gets its name from its ability to tuck its heavy curved claws so close to its body that the crab’s shell looks like a solid shield, or box. Because the thick claws cover the mouth, another name for members of this crab family is “shame-faced crab.”

The crab doesn’t looked too ashamed, though, because its eyes stay exposed and alert. You can sometimes see those upright eyes poking out of the sand while the rest of the crab remains hidden.

crab

With its tall eyes, the crab is looking for passing snails, box crabs’ main food.

Box crabs are well equipped to get the snail from inside its hard shell. One of the box crab’s armored front claws is designed to hold the prey while the other chips at the shell. As it chips, the crab’s back legs turn the snail, enabling the claw to cut out another notch. The crab turns and chips until the snail’s soft insides are reachable.

That’s what my box crab did to me. As I lifted it, I felt the back legs working against my hand, but figured all I had to worry about were the claws up front. But like a living can opener, the crab turned itself enough in my palm to grab my thumb and … “Ow!”

When it comes to stalking and eating shelled animals, flounders are no slouches, either. The flowery flounder’s favorite food is crab.

flounder

For at least five minutes I watched the flounder wiggle like a flying carpet behind the strolling crab. But when the crab whirled to face the fish, the flounder wasn’t as foolish as I had been. It knew enough to leave that box alone.


Marine biologist Susan Scott writes the newspaper column, “Ocean
Watch”, for the Honolulu Star-Advertiser, www.staradvertiser.com

©2012 Susan Scott