With moderate El Nino conditions predicted for this winter, Northern California just might be in for a warm, wet rainy season, good news for drought-parched hills, farms, and cities. But what all that warm water will mean for local marine ecosystems is much more complicated. There’s a lot more going on out there than El Nino, and scientists are closely watching how it all plays out for the region’s marine species.
Last April, PRBO Conservation Science researchers waited in vain for the arrival of Brandt’s cormorants to the Farallon Islands, the largest seabird-nesting colony on the West Coast south of Alaska. During the rest of the year, the cormorants follow their prey up and down the coast from Alaska to Baja. Last spring, the Farallones’ normally thriving “cormorantville” remained deserted until May, when just 1,200 cormorants arrived, a 35-year low. Even worse, the birds’ nesting attempts ended in failure with no fledged chicks.
The news from another important Brandt’s nesting site, Alcatraz Island, was no better. PRBO’s Sara Acosta says that although some birds showed up in April and May (including dozens that were found dead), none nested. In 2007, the scientists counted 1,782 nesting Brandt’s; in 2009, zero. (Double-crested cormorants are faring poorly as well.)
“The nesting failures at the Farallones and Alcatraz appear to be linked, with prey availability the major driving factor,” says PRBO Farallon Program Manager Russell Bradley. Anchovies are a primary food source for the birds, and anchovies have become locally scarce.
“Anchovies and sardines have been shifting south for several years,” says Steve Ralston, a fishery biologist at the National Oceanic and Atmospheric Administration’s Southwest Fisheries Science Center. The California Current, a broad band of cold ocean water that flows south against the West Coast, goes through shifts in temperature; when the waters are cooler they support more rockfish and krill, and when they’re warmer they favor sardines and anchovies. “In 2005, a warmer year, there were low abundances of young-of-the-year rockfish, hake, and lingcod, but elevated catches of sardines and anchovies,” he says. “Since then, there’s been a shift to a cooler ocean environment.”
From Point Sur north to Bodega Bay in May and June 2009, NOAA’s groundfish analysis team found no anchovies, and on the Farallon Islands scientists observed common murres feeding their chicks more juvenile rockfish. “While there are more juvenile rockfish around this year, it was not enough. It takes a lot of juvenile rockfish to equal a big anchovy,” says Bradley. A murre commonly switches to anchovies as its chicks grow, but this year that didn’t happen. The Farallon blog reported in June that, along with a three-week relaxation in upwelling, many murres abandoned their nests and chicks, indicating poor foraging conditions. The murres had their worst breeding year since 1992, says Bradley, and one of the worst recorded in 35 years.
“Although it can’t be ruled out completely, the relaxed upwelling was probably not a direct consequence of El Nino,” says Daniel Palacios, oceanographer at the University of Hawaii. “We’re learning that unusual warming conditions off the West Coast are not always caused by El Nino.”
Scientists are observing more fluctuating conditions overall in recent years. “We are seeing some results [at the Farallones] that have never before been observed, making them difficult to categorize,” says Bradley. “Nothing is normal.” According to the National Climatic Data Center, the world’s oceans were on average warmer last July than at any time in the last 130 years of record keeping.
What will happen when warmer ocean temperatures and El Nino collide? “Human-induced climate change has now become a part of earth’s climate system,” says Palacios. “It’s not cyclical but is going in one direction, which is up. If it keeps going in the same direction, it will amplify the effects of El Nino.”
Ralston says the warming waters of this winter’s El Nino will likely mean poor reproductive success for winter-spawning rockfish in 2010. But perhaps the anchovies will also shift north and the Brandt’s cormorants will return to Alcatraz and the Farallones to breed. At this point, the scientists can only watch and wait, continuing to add data points to their portrait of an ocean in constant and perplexing flux.