Monthly Archives: February 2014

Eyesight plays crucial part in keeping fish in schools

Published February 24, 2014 in the “Ocean Watch” column, Honolulu Star-Advertiser ©2014 Susan Scott

One of my most memorable snorkeling experiences occurred several years ago in Tonga. The incident involved only one species, but that was the beauty of it. Thousands of identical, 6-inch-long, silver fish let me swim in their school.

Whichever way I turned, twisted or dived, the fish outlined my arms, legs and body perfectly, maintaining a precise space between each other and me. So many fish surrounded me that at times I couldn’t see the surface above or the seafloor below. For a glorious 20 minutes or so, I was one with the fish.

As I approached the dense school that morning, I expected its members (species unknown) to scatter and flee. However, those fish decided, as one entity, not only to stay together, but also to accept me in their midst.

Such are the mysteries of schooling.

Schooling is a social behavior in fish that has fascinated people for centuries. Aristotle noted it, thinking that this is what human society ought to strive for. Today a wide variety of people, from oceanographers to anglers, engineers to biologists, are interested in fish schools. All want to know how fish do it and why.

About 50 percent of fish spend part or all of their lives shoaling. A shoal is a group of fish hanging together in no particular pattern, whereas a school is a polarized, synchronized shoal.

Fish can move in and out of formation in a heartbeat, going from a classic school, where each fish swims in the same direction at the same speed, to a mass of individuals pointed every which way, to veering off and going it alone.

The shape-shifting depends on whether the fish are traveling, feeding, resting, fleeing or spawning. But when it comes to schooling, whatever their mission and however they communicate, all the fish are on the same page.

Given those bulging eyes on each side of the head, most fish have excellent vision and use sight to orient themselves in schools. Researchers know this because schools break up at night. Also, in lab experiments where workers temporarily blind fish, schools fall apart.

The other fish sense crucial to schooling is the lateral line, a streak of supersensitive cells, visible in some species, running the length of a fish on both sides. The cells detect tiny water turbulence made by neighboring fish and, in this way, help individuals keep their distance.

There are many unknowns about why fish school, but scientists have theories. Maintaining a precise position in a neighbor’s wake may increase swimming efficiency, like riding a bow wave or drafting a bicycle.

Schooling may be also be an advantage in finding food, since many eyes searching an area are better than two. The negative of group foraging is that the fish have to share, a drawback for the ones in back. This might be why schools are constantly changing leaders.

Schools also appear useful for confusing predators, finding mates and perhaps other payoffs known only to the fish.

I don’t know what the fish in Tonga were up to the day they let me in, but swirling inside that flowing mass felt like swimming in a lava lamp. It was the best school I’ve ever attended.


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

©2014 Susan Scott

 

Passed gas from bacteria is what we smell at seashore

Published February 17, 2014 in the “Ocean Watch” column, Honolulu Star-Advertiser ©2014 Susan Scott

To my Midwest-bred nose, the smell of the ocean hints of mystery, travel, adventure and romance. When I go to the beach, I take a deep breath and think, ah, love that salt air.

But that’s not salt I’m smelling.

When tiny marine animals graze on tiny marine plants (the base of the marine food web), some plant cells spill their guts in the water. Naturally occurring plant-eating bacteria view the spillage as a feast and chow down. As the bacteria digest these meals, they, well, pass gas.

The gas is a sulfur-based molecule called dimethyl sulfide, or DMS, and when we’re near the ocean, that’s what we smell.

Seabirds smell it, too. Some species, such as storm petrels, fly toward high concentrations of DMS because this is where the action is. It’s a good place to forage.

Research suggests that some seabirds also use the gas to navigate. Because underwater seamounts and shelf breaks influence currents, and those influence plant growth, variations in DMS density may be like maps for the birds. Navigating by nose may be a way seabirds find their tiny, remote island breeding sites.

The marine world has other distinct smells.

Low tides often give off a strong odor because rocks, reefs, sand and sediment trap dead and decaying fish and invertebrates.

At Molokai’s Papo­haku Beach recently, I spotted a fat sea hare rolling over the reef flat. It landed on the sand, and seeing the animal move, I picked it up to return to the ocean. Bad idea. The wiggle I saw in the creature came from escaping gas that filled its dead body.

Even after several saltwater rinses and sand scrubs, my hand smelled so bad I had to rub wildflowers on it to finish my beach walk.

Of course, anything dead long enough stinks, but dead fish and invertebrates have an aroma all their own due to an abundant, odorless chemical in their cells that they need to live in salt water. (Freshwater fish have it, too, but nearly not as much.) After a fish dies, air, bacteria and the animal’s own enzymes change the chemical to two others called amines. It’s the mixing of the two amines that give off that unmistakable fish smell.

Because amines are alkaline based, an acid-based substance neutralizes the smell. Behold the union of lemons and fish.

Some people tolerate the smell of fish better than others. One study showed that people who grew up near the ocean eating fish were far less repulsed by fish odor than those raised inland with little fish in their diet.

The latter would be me. Since fish was a rare meal in my Wisconsin childhood, I don’t crave it now and don’t like the odor of fish markets. My Seattle-raised husband, on the other hand, gets frequent salmon cravings and has an exceptional tolerance for fish smell. What I perceive as something stinking up the kitchen, he perceives as a mouthwatering meal.

Craig’s fondness of fish amines is nothing, though, compared with our little mutt, Lucy, who adores ocean smells. Her goal is to find a dead fish, roll in it and then scent her many sleeping spots in the house with her grand perfume.

Ah, love that passed-gas, dead-fish air.


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

©2014 Susan Scott

Friendly false killer whales known to share their catch

Published February 10, 2014 in the “Ocean Watch” column, Honolulu Star-Advertiser ©2014 Susan Scott

False killer whales have a knotty name, but don’t let the 19th-century label turn you off. There’s so much to love about these animals that after attending whale researcher Robin Baird’s lecture on them at Hanauma Bay last week, I wished I could throw my arms around the neck of a false killer whale and give it a hug.

I mean, what other marine mammal shares its fish not only with others in its pod, but also with swimming humans and people in boats?

The main Hawaiian Islands host about 150 false killer whales that are genetically distinct from other false killer whales of the world. The 11- to 18-foot-long marine mammals (males are larger) spend their lives foraging between Kauai and the Big Island.

Like killer whales, false killer whales are mammals that live in social groups and cooperate in hunts. False killer whales, however, have the charming behavior of sharing their catch.

Researchers know this because false killer whales bring their fish, often a mahimahi, ono or ahi, to the surface. There, pod members pass the prey to each other before eating it.

“Here, you take the first bite,” one seems to be saying.

“No, no, let Grandma have it,” says another, passing it on.

Spotting a researcher photographing such sharing, one false killer whale offered the diver some tuna, too. And when a false killer whale ended up alone in the Puget Sound area (this is normally a tropical and subtropical species), it offered boaters pieces of salmon.

Also, false killer whales really do swim with their grandmas. This is one of only four species in the world whose females go through menopause and live for decades beyond. The other three are orcas, pilot whales and humans.

After reaching their teens, female false killer whales have one calf every six to seven years, experience menopause at about age 40 and live into their 60s.

The false killer whale name came from skull and teeth similarities to killer whales, but the resemblance is superficial. The two are not closely related.

Speaking of researchers, because of Baird and his Cascadia Research team’s 14 years of study, more is known about false killer whales in Hawaii than anywhere else in the world.

Besides discovering that Hawaii has its own population, they also documented an alarming decline in number, to about 150 from 500 in the 1980s. Photos clearly show fishing line injuries to some false killer whales. Necropsies revealed fishhooks in stomachs.

As a result of Cascadia’s publications, the Hawaiian Islands false killer whale was listed as endangered in 2012. In 2013, Hawaii’s longliners switched to circle hooks to stem injury and death.

I doubt I’ll ever get my arms around a false killer whale, but it’s Baird and his team who deserve the hugs anyway. Their research and education efforts got our sharing, ohana-living, funny-named kama­aina whales the break they needed.

For out-of-this-world photos of Hawaii’s false killer whales, as well as coloring pages for kids, check out www.cascadiaresearch.org/hawaii/falsekillerwhale.htm.


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

©2014 Susan Scott

Anchialine shrimp thrive in a troubled environment

Published February 3, 2014 in the “Ocean Watch” column, Honolulu Star-Advertiser ©2014 Susan Scott

Last week I attended a talk given by a federal biologist who, before her funding was cut, worked with Hawaii’s anchialine shrimp, known as opae ula. Although these shrimp inspire nearly endless questions, I had a specific one in mind: Is it OK for a conservation-minded person to buy anchialine shrimp, sold in jars at Shi­ro­kiya and also online?

“Anchialine” (AN-key-ah-lin) is a Greek term meaning near the sea, and describes pools with indirect connections to the ocean. The coastal pools are found in limestone and lava deposits where fresh water and seawater both percolate through the porous rock.

The salt content of anchialine pools varies from pool to pool and from top to bottom. Most pools fluctuate with the tides, but the water doesn’t always mix. Often the deepest part of a pool contains seawater, the middle is brackish and the top is fresh.

At least seven aquatic species thrive in Hawaii’s anchialine pools. Some found in Hawaii are also found in pools of Egypt and Japan, but Hawaii’s most famous inhabitant is the endemic opae ula, the Methuselah of shrimp. Most live from one to six years. No one knows how long the half-inch opae ula can live, but some are still going strong after 20 years in captivity.

Opae ula can also live in fresh to supersalty water and tolerate a 20-degree water temperature change.

Opae ula are “Field of Dreams” creatures in that if you dig it, they will come. Individuals somehow survive for decades in aquatic underground cracks and crevices. But if someone digs a hole above their caves to the surface and cleans all soil and clay from the pores, up come the shrimp.

Life in the sun is grand, with food growing on rocks. With ample algae and bacteria to graze on, the shrimp thrive and multiply.

Oahu, Maui, Kahoolawe and Hawaii island all have anchialine pools containing opae ula. Most are hard to find or visit, but a couple on Hawaii island are easy. Owners of the Kona sea horse farm, Ocean Rider, dug their own pool, and it’s so loaded with opae ula that managers feed the shrimp to their baby sea horses. The Four Seasons Resort at Hualalai also has attractive pools, black lava speckled in bright red.

So. Should admirers of opae ula buy them?

No, the biologist told me. Although the shrimp aren’t officially listed as endangered, their habitat is in trouble. Alien fish introduced to the few remaining anchialine pools eat the shrimp, and hole-filling for development destroys their homes. Also, she said, the shrimp don’t do as well as advertised in those closed ecosystems.

But the government program that enabled this biologist to study the shrimp and restore several of Oahu’s anchialine pools was eliminated by budget cuts. Perhaps by sharing details about their special pets, informed opae ula owners help inspire support to fund studies and protect pools.

To buy or not to buy is just one more opae ula unknown. But one thing I do know. Whether gazing at these creatures in a glass jar, an open aquarium or an anchialine pool, the tiny red crustaceans give a person a lot to think about.


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

©2014 Susan Scott