fish report header

Salmon Navigate Home by Earth's Magnetic Map

The epic migrations of salmon have long been a subject of mystery and amazement. What directs these animals' journeys across great stretches of ocean, pulling them back to the very stream where they were born? Chemical cues help fish pinpoint their stream of origin (Johnsen and Hasler 2006), but what steers the salmon's course when it is still thousands of kilometers away? A group of fisheries scientists recently offered the first empirical evidence that salmon navigate using the Earth's magnetic field. The study's findings, published in the journal Current Biology last month, suggest that salmon form an imprint of the magnetic field in their natal streams, and find their way back as adults via a route that matches the magnetic memory of their birthplace.

 

Scientists have hypothesized that migrating animals travel by the magnetic field (Lohmann 2008), but this is difficult to test directly. The authors of the new study devised a natural experiment using 56 years of fisheries records of sockeye salmon (Oncorhynchus nerka) returning to British Columbia's Fraser River. Fish from the Fraser River typically migrate to Alaska's Aleutian Islands, spend two years foraging, then embark on the long trek back to the river to spawn. Along the way, they encounter a major roadblock: Vancouver Island obstructs direct entrance to the Fraser River, forcing salmon to detour to the north or south. The scientists predicted that natural shifts in the Earth's magnetic field from year to year would lead salmon to adjust their route accordingly, choosing the passage with a magnetic field more closely aligned with the magnetic field of the Fraser River two years previously. The team modeled variations in the Earth's magnetic field based on its intensity and inclination, or the angle of intersection with the Earth's surface. They matched this up with a long history of fisheries records that documented how many salmon travelled via the northern route each year, which lies solely in Canadian waters, or via the southern route, which is shared by Canadian and U.S. fisheries.

 

The scientists found that whether the fish turn right or left is far from an arbitrary decision: their selection largely depends on how closely the magnetic field at the route's entryway resembles the magnetic field they experienced at birth. Sea surface temperature also played a big role: in warmer years, more fish followed the northern, cooler route. Results indicated that 68% of the variation in the salmon's choice of direction was explained by variation in the magnetic field, sea surface temperature, or some combination of the two. This study suggests that salmon may follow a magnetic "map" to direct their long-distance migrations, then switch to using chemical cues to home in on a specific stream--similar to the way we may use a GPS system to navigate on long road trips, then switch to following visual landmarks as we get closer to home. The authors say this study could explain why hatchery fish sometimes have trouble finding their way back to spawn: imprinting on a hatchery's human-created magnetic field of electrical wires and iron-reinforced fish tanks could render the fish directionally challenged. 

Follow Us! Like us on Facebook Follow us on Twitter View our photos on flickr View our videos on YouTube
email list
Recent Blog Post
Mekong Environmental Symposium   

FISHBIO recently attended the Mekong Environmental Symposium, held March 5-7

in Ho Chi Minh City,

Vietnam, which gathered governmental decision-makers, scientists, and organizations active in the Mekong Basin region. The German Aerospace Center (DLR) and the WISDOM Project hosted the event, which brought together researchers studying river ecology, environmental monitoring, hydrology, socio-economics, energy, and climate change. The goal of WISDOM, a collaboration between Vietnamese and German scientists, was to design and implement an online data platform for the Mekong Delta, which contains information from the fields of hydrology, sociology, information technology, and earth observation. The first day of the symposium included the handover of WISDOM to the Vietnamese Government, as well as speeches by representatives from each of the six riparian nations: China, Myanmar, Lao PDR, Thailand, Cambodia, and Vietnam. The second and third days of the symposium included many presentations in sessions that broadly covered everything from hydropower development and impacts on river ecology, to capacity building, education, and outreach. Many coffee breaks and long lunches... Read more>

IN THE NEWS: Recent stories you might have missed...
Showdown over salmon: River plan would require more water for fish

Merced Sun-Star 

While environmentalists say newly proposed regulations for the San Joaquin River and its major salmon-bearing tributaries don't go far enough, irrigation officials decry predicted negative economic impacts. The Bay-Delta Water Quality Control Plan in its draft form would require the irrigation districts to leave significantly more springtime runoff in the Merced, Tuolumne and Stanislaus rivers. Specifically, the proposed regulations would restrict the... Read more>  

California officials unveil Delta tunnel plan

Sacramento Bee

A massive plan to build new plumbing in the Sacramento-San Joaquin Delta, California's most important water supply, began trickling out Thursday as state officials released hundreds of pages of draft documents. Known as the Bay Delta Conservation Plan, the major features of the proposal are two giant tunnels to divert the Sacramento River underneath the estuary, and three new intakes along the river in Sacramento County. In addition, 145,000 acres of habitat would be restored to benefit 57 imperiled wildlife species... Read more>

Threatened ocean species get protection
San Francisco Chronicle

A major international meeting on wildlife trade ended Thursday with final decisions to extend protections for dozens of animal and plant species - including five types of sharks - that have come under severe pressure from soaring demand and overfishing. Conservationists welcomed the decisions by the Convention on International Trade in Endangered Species, or CITES, to regulate trade in the threatened species, including for the first time trade in mantas and five shark species: the oceanic whitetip...Read more >

Plan eyes new way to manage fisheries
The Columbian

A draft ecological plan now under review could mark a subtle but significant shift in the way policymakers manage West Coast fisheries.The Fisheries Ecosystem Plan also highlights an often overlooked path to boosting the populations of salmon and other marine wildlife: protecting the small forage fish they eat The initiative reflects a move toward more broad ecosystem-based management, rather than the species-by-species approach... Read more > 

Fish migrate to escape predators
Science Daily

By individually tagging fish in a lake and following their movements, a research team has shown that migration is a very effective defence against being eaten.

Each year billions of animals make annual migrations to escape adverse environmental conditions. Migration is a spectacular and important biological phenomenon, but studying what drives animals to make these arduous journeys is extremely difficult. Food and climate are classic explanations for animal migration, but the idea that animals migrate to escape predators is less well...Read more >  

fishbio.com     info@fishbio.com