DECEMBER 22, 2008
Spawning trout and salmon may be lost due to magnetic interference, soil erosion, and water use. Can they be found?
Researchers now postulate that fish can take magnetic imprints of the streams in which they are born, and are thus able to find their way home to spawn. The findings bolster a report published by a local nonprofit-it shows the fish that fed the famous outdoor tourist industry now face extinction, and are in need of critical support.
The San Francisco-based California Trout, Inc. published a comprehensive review of the state’s native fish species in late November. After reviewing 32 independent, unaffiliated studies, they found that 65 percent of steelhead, salmon and trout will likely become extinct within the next 50 to 100 years, including three species found in the Central Coast. Known for its classic maroon sides and dark green heads, the Central California coast coho salmon is nearly extinct today, and is rarely spotted in local waters.
To help prevent future calamity, the organization recommends more stringent environmental laws and local protection efforts. “The report is a message of hope because there is still time left for people to wake up and rally around these fish,” says Scott Feierabend, interim executive director at CalTrout.
The problem is that reintroducing fish species may be more difficult than previously imagined. CalTrout’s report follows a wave of new studies on fish navigation-while many fish return to their home streams to spawn, hatchery fish often don’t fare as well. New findings suggest this may be due to magnetic imprints the fish use to navigate through the water.
“We propose that salmon and sea turtles form imprints of the unique magnetic signature in their area, and this is how they find their way back to their home,” says Kenneth Lohmann, a biologist at the University of North Carolina, Chapel Hill. “We found that some fish and turtles have the biologic equivalent of a GPS system that helps them with navigation.”
While past research has shown that fish can read magnetic signatures like humans read a compass, Lohmann recently demonstrated that a stream’s magnetic field remains consistent enough over time to serve as a reliable source of information for the fish. The findings were published this month in the academic journal Proceedings of the National Academy of Sciences.
When Fish Get Lost at Sea
While chemical signals help salmon find their way back to specific stretches of river, they don’t diffuse into the ocean. This has long raised questions about the way fish find their original rivers and streams after straying miles up shore.
If magnetic sensing helps fish swim in the right direction along the coastline, and magnetic imprints help fish identify their starting points, this may help explain some of the problems fisheries face when repopulating empty rivers, says Lohmann. Fish introduced to a stream after birth might not ever learn to call it home, and fish born in hatcheries might be confused by the unique magnetic characteristic of the hatchery.
He speculates that rebar, the poles of metal that provide cement walls with structure, might interrupt the magnetic field that surrounds a growing fish. Pumps and other electrical devices used in hatcheries might also play a role. “It’s something that hasn’t been considered very much,” says Lohmann.
While more research needs to be done to test the impacts of hatchery electric fields on spawning fish, the growing body of evidence indicates that animals like turtles and fish are responsive to subtle electromagnetic changes. If returning fish search for the magnetic field associated with an upstream hatchery, they might pass by the river mouth-at least if it has a different magnetic signature.
Historically, even fish of the same species often don’t fare well when raised in hatcheries. While local nonprofits are trying their best to reintroduce coho salmon into the San Lorenzo River, the fish sometimes don’t return to the same area. Even fish that are caught from the wild and then bred in a hatchery don’t take hold.
“It’s hard when the native species goes into a threatened status,” says Bill Kocher, director of the Santa Cruz City Water Department. “You try to fool Mother Nature by raising fish, but even when we trap them and hatch the eggs, we don’t see returns of the hatchery fish.”
Declining local fish populations
While CalTrout’s new report doesn’t emphasize the problems faced by hatchery fish, there is a general agreement that preventing local fish extinctions is better than repopulating rivers after a species has died off. “We will do much better if we can prevent extinctions and local extirpations in the first place,” says Feierabend.
Two fish found along the Central Coast face extinction, says the report. The South-central California coast steelhead, which is found in the Pajaro River and other more southern watersheds, is primarily losing out due to alterations of natural stream flow patterns. Historic runs totaled more than 27,000 adults, but today there are fewer than 5,000 of the fish in California’s waters-during dry seasons this drops below 2,000.
A fish that shares a similar name, the Central California Coast steelhead, has also declined by as much as 90 percent in local streams. Fifty years ago, the San Lorenzo River supported 19,000 fish each year, and coastal tributaries were home to 24,000. The fish were listed as a federally endangered species in 1997, a finding that was reaffirmed in 2006. Due to water diversions, populations continue to dwindle. “Because these species are at the southernmost end of their range, they will also be impacted as water temperatures increase due to global warming,” says Feierabend.
Sedimentation is also named as a critical problem-as winter rains pour down in the Santa Cruz Mountains, soil loosened by development and road construction flows into rivers and streams. “Over time sediment has come down and filled in rocky places where fish used to rear,” says Kocher. “The pools in the rivers are becoming to shallow, and this impacts the water temperature.” Most fish need cool, deep pools in order to spawn and grow, and sedimentation changes both conditions.
Along with wells that detract from the base flow into rivers, and homes that use too much water from local streams, Kocher blames sedimentation and deforestation for the loss of local coho salmon runs over the last 30 years. Spawners typically grow to 30 inches long and weigh as much as 13 pounds, and the fish were a cornerstone of the Santa Cruz fishing industry. Tourists came from across the nation to catch local coho during fishing season.
“Sometimes there would be lines of fishermen three people deep-some fished in waders, some fished from shore and some would be scattered in between,” says John Ricker, the director of the Santa Cruz County Water Resources Division.
Today there are not enough local fish of any species to support a sporting industry, and according to CalTrout, the Central California coast coho salmon is nearly extinct. The southernmost population of remaining coho are in Scott and Waddell Creeks in Santa Cruz County, with the largest remaining population in Lagunitas Creek in Marin. A few scant populations can also be found in Mendocino.
Because the young rear for one to two years in cold-water streams, they need protective cover provided by falling trees, and as dense coastal rainforests have been logged, the fish have dwindled away. Although populations were partially revitalized in the early 20th century, modern efforts have been unsuccessful-likely due to sedimentation, and ongoing development of forested land, says Kocher.
The role played by magnetic fields in salmon reintroduction and migration is just beginning to gain attention, and while redesigning hatcheries might prove helpful, Lohmann says “there is no single approach that will solve the problem.”
To address water diversion and sedimentation problems, roads must be brought up to standard, pipes must be built to carry water under roadways, and native ground cover must be planted to prevent bare dirt from eroding. Adopting low flush toilets, planting native, drought-tolerant plants, and generally conserving water is also critical, says Feierabend.
While this won’t restore local waterways to their historic glory-the San Lorenzo used to be full enough that residents commuted into town from the Boardwalk by boat, after all-it might return enough water for the fish to make their runs.
Until this happens, Feierabend says the status of California’s native fish will serve as an emblem of the water problems of the Pacific coast. The report verified that without interventions taken, two-thirds of our native fish species will go extinct over the next 100 years. “The issue is not only about fish; it’s also about the health of California’s aquatic ecosystems,” says Lohmann. “The reports certainly seem to provide a thorough and careful analysis of the state of California’s native fish, and the outlook is alarming.” Fish Bailout
In the spirit of bailout packages, congress has set aside $170 million in aid for businesses impacted by the 2008 salmon season closure.
Salmon fishing on Central Valley rivers was entirely closed on July 3 in response to an unprecedented decline in the Sacramento River Fall Run Chinook population, which makes up the bulk of salmon caught off California’s coast.
A minimum of 122,000 to 180,000 salmon must return each year to spawn in order to maintain ocean and river fishing seasons. Otherwise there are not enough eggs left for hatcheries. Only 54,000 adults were projected to return this fall due to poor ocean conditions like high surface water temperature, and due to drought.
The California Salmon Council has been conducting outreach efforts to identify businesses eligible for relief. The collapse of the Sacramento River Fall Run Chinook salmon population has negatively impacted commercial fishermen and charter boat operators, as well as river guides and fish processors. Salmon-related enterprises that require a Department of Fish & Game license to operate have been sent disaster forms. Other eligible businesses need to file an application for relief before the Dec. 31 deadline. Disaster relief forms may be obtained online from the California Salmon Council website at calkingsalmon.org or the Pacific States Marine Fisheries Commission website at psmfc.org. Eligible businesses must demonstrate that salmon is at least 30 percent of their normal business. They must also provide documentation indicating their loss up to a maximum of $225,000.