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By
Glen Martin, Chronicle Environment
Writer
Tuesday, July 12, 2005
Oceanic plankton have
largely disappeared from the waters off Northern California, Oregon and
Washington, mystifying scientists, stressing fisheries and causing widespread
seabird mortality.
The phenomenon could have long-term implications if it
continues: a general decline in near-shore oceanic life, with far fewer fish,
birds and marine mammals. No one is certain how long the condition will last.
But even a short duration could severely affect seabird populations because of
drastically reduced nesting success, scientists say.
The plankton
disappearance is caused by a slackening of what is known as "upwelling:" the
seasonal movement of cold, nutrient-rich offshore water into areas near
shore.
This cold water sustains vast quantities of phytoplankton and
zooplankton, which are the basis of the marine food web. During periods of
vigorous upwelling and consequent plankton "blooms," everything from salmon to
blue whales fattens and thrives on the continental shelf of the West
Coast.
The larger fish and baleen whales eat mostly krill: free-floating,
shrimp- like crustaceans ranging from one to two inches, the upper size limit of
the zooplankton realm.
When the water is cold, krill swarm off the
Northern California coast by the tens of thousands of tons. Now that they are
largely absent, fisheries and wildlife are feeling the effects.
In
perhaps the most ominous development, seabird nesting has dropped significantly
on the Farallon Islands off San Francisco, the largest Pacific Coast seabird
rookery south of Alaska.
Bill Sydeman, the director of marine ecology for
the Point Reyes Bird Observatory, a science and conservation organization that
maintains a research station on the Farallones, said the collapse of the nesting
season is unprecedented in the three decades the group has monitored the
islands.
Cassin's auklets -- a relatively rare seabird that feeds almost
extensively on krill -- have been particularly hard hit, Sydeman
said.
"Normally they breed in March," Sydeman said. "They got started
late this year, and by May they had virtually disappeared. We expect zero
nesting success for them this year, or close to it. We've never seen anything
like it."
Sydeman said other seabirds are also showing the effects of the
reduced marine productivity.
"We have little or no nesting of pelagic
cormorants (at the Farallones), and Brandt's cormorants are nesting at reduced
numbers," he said. "Double- crested cormorant nesting is down by 50 percent (in
the Bay Area)."
Upwelling cessation is typically caused by El Niņo events
-- warm water intrusions from the equatorial Pacific. But what is happening off
the coast right now is not a true El Niņo, Sydeman said.
"We really don't
have a clear idea of what it is," Sydeman said, noting that standard El Niņos
can be tracked as they progress from the equator to temperate waters, something
that hasn't occurred in the current case.
"Some are calling it an El Niņo
Norte; others think it's some sort of anomalous intrusion of warm offshore blue
water onto the continental shelf," he said.
A recent study indicated the
phenomenon may be long term, and linked to global warming.
Last week,
Fisheries and Oceans Canada -- the federal agency dealing with Canada's marine
and inland waters -- released a report saying 2004's spring and summer ocean
surface temperatures in the Gulf of Alaska and off British Columbia were the
warmest in 50 years.
The study concluded the record high temperatures
were caused by abnormally warm weather in Alaska and western Canada, as well as "general warming of global lands and oceans."
Some pulses of upwelling
occurred off Northern California in June, Sydeman said, but they're unlikely to
significantly increase marine productivity.
"Upwelling has slackened
along all the West Coast, except for a little bit of recent activity off
Northern California," Sydeman said. "At this point, it's too little and too
late. Things aren't going to turn around. For krill predators in this system,
it's a very serious situation."
Juvenile rockfish numbers are also way
down.
"We annually survey (juvenile rockfish) from San Diego to Cape
Mendocino, and this is the lowest catch we've recorded in the 23 years we've
been doing it," said Stephen Ralston, a supervising research biologist at the
Santa Cruz office for the National Marine Fisheries Service, the federal agency
that oversees fisheries in federal waters.
Like krill, young rockfish are
a significant food source for seabirds, large fish and marine mammals; they are
also essential to maintaining healthy stocks of mature rockfish, esteemed by
commercial fishermen and sport anglers.
Off the coast of Oregon,
abnormally warm marine water is continuing unabated, affecting local birds and
salmon.
"Things are pretty grim up here," said Bill Peterson, an
oceanographer with the National Marine Fisheries Service office in Newport,
Ore.
Peterson said a major die-off of double-crested cormorants recently
occurred in Oregon, and juvenile salmon numbers have dropped precipitously. Both
events, he said, are likely due to the warm water.
"We do salmon surveys
every spring and summer," he said. "Normally, we catch several hundred salmon in
the spring. This year we caught eight. And we usually get several thousand fish
in the summer. This year, it was 80."
Peterson said the water temperature
off Oregon in late June is normally 10 degrees Celsius (about 50 Fahrenheit), "and this year it's 16 degrees (about 61 F). Our (upper layer of warm water) is
normally 15 meters thick, and this year it's 30 meters. Krill numbers are down,
and the plankton we are seeing are as unusual as can be -- warm water species
that you'd find off San Diego or Monterey."
Peterson said it is unlikely
Oregon waters will cool significantly this summer.
"It takes an enormous
amount of (offshore wind) energy to push that much warm water offshore, which is
what we would need to see for significant upwelling," he said. "I don't see that
happening anytime soon."
Near San Francisco, salmon have switched from
krill to bait fish, and appear to be holding their own -- at least for
now.
"The fishing is terrific," said Roger Thomas, the president of the
Golden Gate Fishermen's Association and the owner of the recreational angling
boat the Salty Lady.
"It's true there's not much krill, but there're lots
of anchovies and sardines," Thomas said, "and the salmon are filling up on
those."
Thomas acknowledged that the bait fish wouldn't benefit many
coastal and offshore birds.
"Sardines are too big for the auklets, and
even for other species like common murres," he said. "They rely on smaller prey
species."
In fact, say scientists, krill are the keystone forage species
for almost everything that swims off Northern California.
"It's the krill
that drive the food web dynamics off this coast," said Ellie Cohen, the
executive director of the Point Reyes Bird Observatory. "Their absence has
tremendous implications for everything out there, right up to the humpback and
blue whales. We don't know if this is a result of global warming or some natural
cycling, but without the krill, you could be looking at a food web
collapse."
E-mail Glen Martin at glenmartin@sfchronicle.com