Seabirds feed on anchovies near Santa Cruz Wharf, harbor – Santa Cruz Sentinel
SANTA CRUZ — Marine life and seabirds of all kinds, from pelicans and gulls to migrating terns and shearwaters, have gathered off the coast in recent weeks — fluttering, screeching, swirling and diving, feathers flying in a feeding frenzy as each creature fights for its share of the anchovies floating beneath the ocean’s surface.
The spectacle is an anticipated event in summer for those who want to observe and admire the flocking seabirds, such as the long-distance, deep-diving Sooty Shearwaters, that migrate en masse from east to west along the Santa Cruz coast.
“It’s remarkable that we have large numbers of sooty doves in our bay every year,” said Josh Adams, a wildlife biologist at the United States Geological Survey’s Western Ecological Research Center. “Some years it may seem like there are more of them, or they’re here longer, or they disappear sooner, but it’s hard to get a handle on the numbers because they travel in such large flocks.”
Adams noted that tens of thousands of sooty shearwaters can be seen circling and moving off the coast of Santa Cruz. Although the birds are native to New Zealand, they travel to California and Monterey Bay during the summer months to molt and fatten before returning home.
“When they come to this part of the world, their diet is known to change from juvenile rockfish and krill to a diet consisting primarily of anchovies in late summer,” Adams said. “The anchovies are the real fuel at the end of their migration. Their protein needs fluctuate throughout the summer and by the time they get here, they are exhausted from the journey from New Zealand and Chile and need protein to replace their feathers, which are made of protein.”
Anyone on the water in the eye of a seabird storm may notice that sooty divers have great difficulty taking off again after diving to feed on anchovies.
“There are several things at play here,” Adams said. “They eat so much food relative to their body mass that they have to use a lot more force to get out of the water. They’re also in their first molt, so they have less wing area. They’re cool because they’re designed to fly both underwater and long distances over the ocean. The molt affects their ability to get up and fly quickly, especially when they have a belly full of anchovies.”
For years, the actual diving depth and length of time sooty shearwaters can stay underwater were unclear statistics until Scott Shaffer, a professor of ecology and evolution at San Jose State, and other researchers used archival markers to measure the birds’ habits in the 2000s, when Shaffer was a postdoctoral researcher at UC Santa Cruz.
“We knew they could dive to depths of 60 meters because some researchers had used these capillary depth gauges,” said Shaffer. “These only indicate the maximum depth. They do not tell us how long or how often they dived that deep. When we put our time-depth recorders on the animals, we were able to get a lot more information about their diving patterns. Their typical diving depths are somewhere between 9 and 14 meters.”
Shaffer and the researchers used the information they gathered to co-author a paper on the habits of the sooty seabird, which he studied in California and New Zealand. He mentioned that the sooty shearwater’s migratory habits between the Northern and Southern Hemispheres allow it to experience an endless summer.
“It’s pretty extraordinary to watch the migrations of these birds, and the idea that they live in a perpetual summer is really fitting,” Shaffer said. “They can get the best of both worlds by crossing the equator and coming here.”
Shaffer said that before tagging the sooty grebes, it was assumed that they flew in a giant circular pattern because the birds typically appear in California, Alaska and Japan before returning to New Zealand. But researchers found that the pattern they followed was more like a figure eight.
“The prevailing view was that they made this wide berth around the Pacific, but we were able to show that that is not actually the case,” said Shaffer. “The birds usually select an area in the North Pacific and, as far as we know, stay there.”
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In addition to sooty shearwaters, Monterey Bay also attracts other shearwater species in smaller numbers, such as the short-tailed shearwater from Australia, the Buller’s shearwater also native to New Zealand, and the short-billed shearwater from Chile.
“It’s similar in size, but it has a slightly different morphology and doesn’t dive as deep as Sooty Lake,” Adams said. “Our summer is kind of a mix season for a lot of species that come to California from the Southern Hemisphere. We also have a handful of dominant native breeding birds that we see in large numbers off Santa Cruz, like western gulls and guillemots and California brown pelicans and some other gull species. We have a really great diversity of seabirds here.”
Now that summer is coming to an end, Adams says most of the migratory sooty divers will soon begin their journey back to New Zealand.
“We’ll see them disappear now and over the next three weeks or so, and then they’ll all be gone,” Adams said. “The anchovy populations will be somewhat depleted by then because there are a lot of animals eating them, but the anchovy aren’t leaving our system.”
Although the flocks of diving seabirds pose a danger to boaters, Santa Cruz Harbormaster Blake Anderson said their attention is mostly focused on the anchovies and they tend to avoid the boats. He said it is the anchovies, not the birds, that are causing a sense of nervousness among boaters, especially those in the harbor.
“The birds themselves don’t come into the harbor, the anchovies do,” Anderson said. “Whenever we see the shearwaters out there, we pretty much know there are big schools of anchovies nearby. So we watch where those anchovies are going, and when they get close to the harbor, we deploy our ventilation system.”
Anderson said some anchovies have entered the port of Santa Cruz and the aeration system has been turned on, but they still hope the fish will stay at sea.
“We’re running our ventilation system and monitoring oxygen levels,” Anderson said. “Everything is stable right now, but if one of these swarms actually gets here, we could be in trouble.”
A year ago, the port was teeming with anchovies, but the ventilation system prevented a mass mortality. The last major baitfish mortality occurred in late summer 2014, leading to massive cleanup operations in the port and a foul fish smell spreading along the affected coast.
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