Warmer ocean spurs feasting along coast

05/01/2014

Large schools of baitfish off the coast of Point Reyes, presenting a feast for birds and sea mammals and a strange sight for locals last month, may have been lured north and inland because of warmer ocean temperatures this year.

A fisheries scientist at the National Oceanic and Atmospheric Administration said it was too early to tell if the oceanographic conditions might indicate a coming El Niño, since those conditions can be highly variable from year to year; however, last month NOAA reported that the chances of an El Niño event kicking off by this summer exceed 50 percent.

An avian ecologist with Petaluma-based Point Blue said that “off the charts” numbers of pelicans in the area last month might also point to abnormal ocean conditions and a coming El Niño event.

El Niño is a weather event that occurs roughly every three to seven years, when sea surface temperatures in the middle or western Pacific warm by about 1 degree Fahrenheit; it can spur severe weather events around the world, including storms, floods and droughts. And not all El Niños are the same; some can be stronger, others weaker. The event can last from about nine months to two years. Although they are not caused by climate change, there is evidence that modern climate change is increasing their frequency and ferocity. 

On April 19, countless big sardines laid trapped in tiny channels amid the mudflats of Bolinas Lagoon at low tide, drawing the attention of a local birder who watched pelicans gorge en masse for an hour or so. Bolinas resident Burr Heneman wrote to a North Bay birding listserv that he had only seen such a massive baitfish event in Bolinas a few times in the past 40 years, and never in the spring—only in July or August, and only with anchovies. He told the Light that the sardines have been in and around the lagoon for roughly a week before his sighting, and noted that others have seen sardines in Drakes Bay.

“Brown Pelicans swarmed the shallow channels, awkwardly using their bills and pouches as dip nets,” Mr. Heneman wrote. “The pelicans were so thick that the cormorants had trouble maneuvering among them. More dead or still-flopping sardines were on the mud flats than the gulls and terns could eat, though they kept trying. And the sardines I saw were so large (10”-12”?) that even the gulls were having trouble getting outside of them. Or else the gulls were just too full to get another fish down… A great show. An hour later, water covered the flats, and the action was over.”

Mary Jane Schramm, a spokeswoman for the Gulf of the Farallones National Marine Sanctuary, which has jurisdiction over the Bolinas Lagoon, said last week that she has received reports of whales, dolphins and seabirds taking advantage of the unusually abundant baitfish in Bolinas Bay and off Duxbury Reef. 

Large sardines typically spawn in southern California in spring and migrate up the California coast starting in April, but might not typically reach this area until June, said Russ Vetter, a senior scientist at NOAA’s Southwest Fisheries Science Center. But the ocean as recently as two weeks ago was roughly two degrees warmer than is considered normal. Although within the past week he said waters have cooled down, the warmer waters could have both dissuaded the fish from traveling too far south over the winter and spurred the sardines to spawn earlier.

Reports early this year described a decline of the sardine fishery off the southern California coast, likely due to large-scale oceanographic cycles that switch every 20 or 30 years between favoring sardines or anchovies. Fishing crews reportedly struggled to find sardines and typically picked up larger and more mature ones when they caught any at all (so the presence of larger sardines in recent sightings here isn’t surprising).

Sardines don’t typically come so close to the coast when they pass through the area because of the inhospitable cold waters brought to the surface by upwelling. That’s the process by which winds from the northwest—combined with the south-flowing California current and the earth’s rotation—push surface water west and pull nutrient-rich cold water to the top. The nutrients and sunlight fuel the growth of algae, creating food for baitfish, which are then eaten by other sea life and birds. 

In some areas along California’s coast, upwelling occurs in thinner bands. But off the coast of Point Reyes and a few other spots, such as Point Arena and Big Sur, it can extend out a few hundred miles, which accounts for the diversity of sea life around two nearby marine sanctuaries, Cordell Bank and the Farallones.

Although measurements by the Bodega Marine Lab in Bodega Bay show that upwelling began in March—within the normal range—there were fits and starts. There was a relaxation at the end of March, and water temperatures at Point Reyes were warm in the first half of April. But they cooled down by the end of the month, with recent nearshore winds, according to NOAA data provided by Ben Becker, a marine ecologist at the Point Reyes National Seashore.

Mr. Vetter said that upwelling had generally begun late across the state, but it was too early to know whether California’s upwelling would be weak or normal this year, and that more will be known in another month or so. He added that weaker upwelling generally accompanies El Niño events.

Some of the birds that feasted on the sardines, such as gulls, are typically in the area at this time of year and took advantage of an easy meal. But an avian ecologist with Point Blue, Dave Shuford, wrote to the Light that the number of pelicans seen at Bolinas Lagoon was highly unusual for this time of year. That could reflect breeding failures elsewhere, he said, or it could be a harbinger for El Niño. 

“Although occurrence of pelicans in the [hundreds] is not unprecedented in the Point Reyes area in April, the numbers seen the other day appear to be: [a friend] counted about 2,600 pelicans at Bolinas Lagoon on Sunday, which is off charts, I think, for April. Usually the early occurrence of pelicans in this area reflects warm water conditions like El Niño,” he wrote.

A professor of wildlife ecology at the University of California, Davis, Daniel Anderson, said he has heard of other unusual influxes of pelicans along the southern California coast.

A forthcoming scientific paper actually links the mild winter and drought on the West Coast and the frigid winter endured by those in the East both to climate change and a coming El Niño, the Associated Press reported Tuesday, although many scientists hesitate to link singular or very recent weather events to broad shifts like climate change.