Mud Eaters, Big and Small, of Saratoga Passage

This short essay is a reworking of a piece I wrote earlier about our kayak from Langley to Camano Island State Park. -Woody

We were sad to say good-bye to Giovannia’s parents, but the sea was calling and we had several miles to make on a rather cold and foggy morning. After a morning stop at the Bagel Factory, Gio’s dad dropped us and our sizable load of gear off at Langley Marina and we made a bee-line across Saratoga Passage for Camano Island. One of our friends described the geology of Whidbey Island as a “glacial turd,” and Camano must be another, smaller bit of geologic scat as well. Like Whidbey, Camano Island is rimmed with high, loose bluffs. The evidence of past landslides is everywhere, and the fortunate few able to build homes on top of the hill often have long, winding stairs, usually in a semi-state of collapse, that snake their way down to the coast below. The shoreline itself is very beachy, which made for easy landings. All of the eroded sediment forms long, sandy beaches with extensive sand flats that stretch as much as a quarter mile offshore. Cruising along the beaches at low tide, the swell would often break several hundred feet from shore, leaving us a narrow, watery passage of relatively calm water. Our kayaks only drew nine inches of water at most and so we were able to slide between the waves and the beach. Stretching my imagination, I felt like we were cruising along the barrier reef in Belize, inside the safety of the lagoon.

Looking down into the shallows, we could see flatfish – C-O Sole or English Sole – darting along the sandy bottom, spooked by the shadows of our passing kayaks. From time to time, we’d even spy a few sand dollars (Dendraster excentricus), their disc-shaped, brown, fuzzy bodies, stuck askew into the sand. Sand dollars have always fascinated me. They’re echinoderms, related to sea stars and sea urchins, with whom they share a pentagonal, five-part body symmetry (next time you see one, notice the five grooves on both sides.) They looked barely alive, but I’m sure they were hard at work processing what little food they could find in the benthos (aka the bottom of the ocean.) Most sand dollars are “deposit feeders,” meaning they survive by parsing out the minuscule fraction of edible organic material that resides in the sediments. Using minute spines, similar to their echinoderm cousins the sea urchins, sand dollars move their food, particle by particle towards their central mouth, located right in the middle of their bodies. Like both sea urchins and sea stars, echinoderms have a feeding apparatus in their mouths called Aristotle’s Lantern, which looks like a boney version of the claw used in that arcade game where you try to pick upup stuffed animals and other toys. It’s named after the Greek philosopher who first described its structure in his Historia Animalium (The History of Animals). The Aristotle’s Lantern macerates and processes food particles before they move on to digestion in the stomach. Deposit feeding is a rough life; the vast majority of sediments are grains of sand, silt or clay, with no nutritional value. Some deposit feeders, like sea cucumbers (another echinoderm) ingest massive amounts of sediment, only to poop most of it back out, garnering only a small fraction as real nutrition. One study on sea cucumbers on The Great Barrier Reef in Australia estimates that every year, roughly three million sea cucumbers living around a 20 sq km coral reef of Heron Island poop out more than 64,000 metric tons of sediment, the equivalent of five Eiffel Tours. Every year. That’s a lot of poop.

Being such an inefficient method of nutrient acquisition, it appears that our local sand dollar, Dendraster excentricus (eccentric because it’s asymmetrical, not because of its personality) supplements its food intake by also “filter feeding,” or catching floating particles out of the water column. It does this by wedging itself into the sediment so that most of its bottom sticks out at an angle (think of a cookie stuck in a bowl of ice cream.) Then, as tiny plankton and other edible bits float by, it can catch them with its arms and move them to its mouth for digestion. If you ever spot a live sand dollar and notice a little raised pyramid on its surface, that will be where it’s caught one of those food particles and is in the process of moving it – very slowly – to its mouth.

Another animal, much larger (and much more charismatic) also frequents this area of Puget Sound, and it, too, finds its sustenance by processing the sediments, eating the tiny morsels it collects from the ocean’s bottom. Every year, about a dozen Pacific gray whales (Eschrichtius robustus) make a detour during their annual migration from Baja to the Bering Sea to feast on the the nutritious muck of Saratoga Passage. Measuring almost forty feet in length, and weighing as much as 90,000 pounds, the Pacific gray whale makes the longest annual migration of any mammal on earth. Some individuals will travel over 13,000 miles each year between the warm waters off the coast of Mexico and the cold, but food-rich Bering and Chukchi seas. During their migration, whales swim night and day, covering on average about 75 miles in a twenty four hour period. For a 90,000 pound animal, such a journey requires massive energy inputs, and the gray whales get their calories from the critters that live in the mud under the ocean.

Like other baleen whales, such as the humpback whales or blue whales, gray whales open their mouths when feeding to take in large gulps of their surroundings and then filter out the stuff they don’t want, trapping their food particles inside the baleen which they then ingest with their massive tongues. Unlike the other baleen whales, which filter seawater to catch the fish, krill or things floating in it, gray whales take big gulps of mud and filter out the benthic critters that live in the murky bottom. Along their journey, amphipods (think of the sand fleas you find at the beach) make up a huge portion of their diet, but in Saratoga Passage, they’ve discovered a benthic environment full of ghost shrimp (Neotrypaea californiensis) and appear to feast on them like a high school wrestling team at Sizzler after a big tournament.

A recent study by local scientists, John Durban and Holly Fearnbach, and reported by Lynda Mapes in the Seattle Times, has shown that the gray whales, which frequent Saratoga Passage from about March to May, are able to time their feeding with the Salish Sea tides, waiting for hours in deeper water until the tide gets high enough to cover the shrimp beds. They then feed like mad for a couple of hours, returning to the depths in time to escape being stranded. These whales, which are often between 36 and 42 feet, will feed in water that is only seven to nine feet deep, barely enough to cover their massive bodies and keep their immense bulk afloat. When they feed, the whales scoop up mud with one side of their mouth, typically their right (gray whales appear to have a preference for the right side over the left, similar to handedness in humans.) They pulse the mud against their baleen, filtering out the ghost shrimp, other edible bits, and use their tongues to slurp it all down. The whales leave behind thousands of feeding pits, measuring about six feet long and two feet wide, which can be seen along the mudflats after the tide has retreated.

The Pacific gray whale was removed from the endangered species list in 1994, and is now considered to a species of least concern. Still, between 2016 and 2020, the northeastern Pacific population fell from about 27,000 to 21,000 individuals, almost almost a quarter of its animals gone in just four years. However, the gray whales that frequent Saratoga Passage – affectionately known as The Sounders – seem to be doing just fine. Maybe it’s all of those shrimp, or the extra-nutritious mud we have in Puget Sound. I would have thought that years of contamination from nearby Everett, with its massive naval shipyard and a Boeing factory, would have made Saratoga Passage sediments particularly toxic, but a 2013 study, by a group of Salish Sea researchers from both sides of the border, indicated that concentrations of persistent pollutants, such as PCBs and PBDEs, have been declining in the local harbor seal population since the 1980s, indicating that Puget Sound might actually be getting cleaner.

Unfortunately, there’s still plenty of rubbish out there in the Sound, and it doesn’t stay in the water.

On April 14, 2010, a juvenile gray whale, presumably migrating from Baja to Alaska, made a detour into Puget Sound, traveled farther south than its brethren and eventually stranded itself on Arroyo Beach, a private stretch of coastline, in the southern part of Seattle. It died shortly thereafter. My colleague, and fellow marine biology instructor, Rus Higley had been wanting a whale skeleton to hang from the ceiling of Highline College’s Marine Science and Technology (MaST) Center. We all thought he was crazy, but then Rus got a call from someone at the National Marine Fisheries Service saying that if he could tow this whale from Arroyo Beach to McNeil Island, he could have it. Rus called a friend with a thirty foot Bayliner, rallied a group of fifty volunteers who didn’t mind the stench of rotting flesh (I was in that group), and just over a year later, the whale’s thirty-eight foot skeleton was hanging above main foyer of the MaST Center.

Since then, as an instructor at the MaST Center, I have often used the whale in my lessons on cetacean biology and ecology. The baleen plates hanging from the upper jaw bone illustrate the process these animals use to slurp food from the seafloor. The small, floating pelvic bones elucidate cetacean evolution and mark the vestiges of its land-dwelling ancestral anatomy. But the most educational piece of this display isn’t located on the whale’s skeleton, but in a nondescript, thirty gallon aquarium sitting on a small stand down the hall from the leviathan. In this tank, are the remnants of indigestible items found in the gray whale’s stomach during the necropsy. Floating lifelessly in the clear waters of the aquarium one can see several plastic bags (the kind you put produce in), a Capri-Sun drink pouch, a piece of fabric that looks like it came from a pair of sweatpants, and a golf ball.

This gray whale washed ashore with all of these items in its gut. And while it was concluded that they did not directly lead to the whale’s demise (it appeared to have a genetic disorder similar to rheumatoid arthritis that certainly shortened its lifespan,) it’s no mystery how they got there. Feeding on the muddy bottom, the animal slurped up massive amounts of sediment to procure the edible bits living in the mud. This strategy has worked for this species for millions of years. But now there’s an added component the whales never had to deal with: human garbage. It’s estimated that of the more than 300 million tons of plastic we produce every year, more than eight million tons end up in the ocean. And so, while my students are always horrified to learn that these mythically noble animals are ingesting our garbage, they all nod with understanding when they see where our trash eventually ends up.