Breakthroughs in acoustic tracking shine new light on the lives of fish

02/10/04

Findings could aid design of marine reserves for salmon, cod, sharks and other mobile fish

Acoustic tracking is revealing that movements of potentially far–ranging species such as cod, salmon and sharks may be more predictable than scientists previously believed. The good news is that even small marine reserves could have big benefits for some species.

While the long-term conservation benefits of marine reserves are widely recognized, particularly for species that are "homebodies," a lack of information about how reserves will affect more mobile fish species like Pacific salmon, cod, rockfishes, sharks, and flounders, has fueled the debate over marine reserves. Fishermen, managers, and scientists alike are asking whether place-based measures will truly protect these economically important species.

Scientists speaking at the American Association for the Advancement of Science (AAAS) meeting on February 13th at 9am, revealed how new acoustic tags and underwater listening devices are allowing scientists to continuously peer into the daily lives of fish, providing the detailed knowledge needed to design effective conservation measures. New data on fish movement and habitat use are allowing managers, fishermen, environmentalists and others to evaluate trade-offs of different reserve sizes and locations.

"On land, scientists know where elk or bears roam, what their daily habits are, how far they go from home, but until recently we haven't had the tools to study daily movements of marine fishes," says Richard Starr of the University of California Sea Grant Program. "You have to have this information to understand the value of a marine reserve – it would do no good to block off a section of the ocean and then have all the fish swim out of the area."

"Until recently, scientists have pieced together the movements of marine fish from isolated data points – playing a 'connect the dots' game as fishermen reported recovered tags," said James Lindholm of the Pfleger Institute of Environmental Research. "We could tell that a cod ended up 400 miles from where we tagged it, but there was no way to tell what it did in between – how long it spent in specific habitats, how often it returned to the same site - we had no way to tell whether that 400 mile trip was a regular commute or an annual vacation."

Now, using small, surgically attached tags and underwater listening stations, scientists can track where an individual fish spends it life, and can monitor the trends of an entire population. This new, real-time information is helping scientists answer critical management questions: Is a given marine reserve big enough to protect a species throughout its life cycle? Where should you put a new reserve? What types of undersea real estate must be protected to increase egg production? How many fish will stay in the reserve and how many will "spillover" into adjacent areas where fishermen can catch them? Answers to these questions are beginning to come clear.

"Everyone is tired of saying there isn't enough information," says Lindholm. "We're finally able to address these issues with empirical data."

Protecting small areas of high quality habitat help California gamefish

Tracking of kelp bass and California sheephead, two highly prized nearshore gamefishes, in the Catalina Island Marine Science Center Marine Life Refuge (CMLR) indicates that even small reserves – if strategically placed to contain high quality habitats - can effectively protect adult populations of these fish. Acoustic tracking of these gamefish identified the scope of their daily movements over two years – showing that the home range of these fish is within the reserve boundaries. This "site fidelity" to the reserve is likely due to natural habitat breaks bordered by the reserve boundary.

"At first glance it almost looked as if the fish knew the location of the reserve boundary, but the telemetry data indicated that the fish did not like to cross the habitat break too often," explained Chris Lowe of California State University at Long Beach. "Changes in habitat may function like underwater fences for some fishes, and knowledge of fish habitat affinity gained through studies such as these may enable managers to design reserves with "tight" or "leaky" boundaries, depending on the reserve goals."

Many resource managers would argue that larger reserves are better for protecting overall marine biodiversity and fishery resources, but political realities and concessions with fishermen often result in small reserves –until 2002, the CMLR was the largest no-take reserve in southern California, despite covering only .05 square miles. In addition, managers must weigh the trade-offs between reserves that keep and protect species within their boundaries with long term pay-offs for the fishery versus "leaky" reserves that allow more fish to be caught in surrounding areas.

While a single small reserve will not adequately protect an entire population of fish, these new results show that a network of small reserves may be just as effective in protecting adult fish as a single large reserve. Fishermen might benefit too, as smaller reserves provide more boundary areas where fish will periodically wander out of the reserve and increase catches.

Surprises with Cod, Reef Fish

Scientists used to think that Atlantic cod - an economically, culturally and ecologically important species in New England – moved great distances during their life cycles and would therefore receive little benefit from reserves. But new tracking data from two major off-shore areas show that cod tend to congregate in habitats with lots of places to hide, such as piled boulder reefs and gravel covered seafloors. They return to the same places frequently, using these high quality habitats as home base.

"We're finding that, just like humans, cod have favorite stopping places. It's like life on a freeway system – people are going to aggregate in the rest stops, especially if they have good food or clean bathrooms – if there's no rest stop, or if the surroundings aren't safe, you might not stop," says Lindholm. "Protecting these high-use habitats could provide meaningful protection for these fish."

Similarly, tracking the fine scale movements of commercially important reef fish in the Florida Keys demonstrates that small reserves may help protect these species too. Tagging of yellowtail snapper and black grouper inside the Conch Reef Research Only Area (a small marine reserve off Key Largo) revealed that a majority of the tagged fish tended to stay in the reserve, while others "spilled over" to fishing areas, indicating that these small reserves could potentially serve both conservation and fishery yield goals.

Lingcod Recovery in the Pacific Northwest

Lingcod is one of the most important commercial and recreational species that has experienced dramatic population declines in British Columbia, Washington, Oregon and Northern California. Tracking of individual fish has allowed scientists to quantify the trade-offs of different reserve designs. Tagged fish didn't stay in the reserve for long periods, but also were not gone for long periods, suggesting that lingcod use the reserve as a home base and make frequent forays out of the reserve.

"Marine reserves bring potential positive benefits, but it also removes some areas in the ocean from fishing," says Starr. "Now, with these new tracking systems, we can predict the spillover from a reserve and the fraction of the population that is protected. If a fishery is over-fished, a reserve won't help the lingcod fishery right away, but it will help the population return. It's only when the population is recovered that you see the spillover to help the fishery. Our work shows that you can achieve this win-win situation – you can increase benefits to the fishery and conservation."

Their results show how these benefits change as populations rebound: when the fish population is small, a system of marine reserves can increase egg production with only a small loss of fishery catches. As the population increases to moderate size, marine reserves can be used to increase egg production and maintain fishery catch. With robust populations a system of marine reserves can increase egg production and fishery yield by allowing higher fishing rates outside the reserve than would be advisable without reserves.

Safety for Sharks

On Florida's Gulf of Mexico coast, researchers are using acoustic tags to track several shark species, uncovering trends in the movements of these over-fished populations. "Many of these targeted species use coastal bays as nursery grounds, and protecting these areas may be critical to population recovery," says Michelle Heupel of Mote Marine Laboratory. "We have to understand how the environment affects shark movements in order to define effective protected areas."

Tracking results show that as young sharks grow – even just a few inches – over the course of a few months, they can triple the amount of habitat they use on a daily basis. Young sharks also change location in response to storms and human activities – moving into deeper waters with pre-storm changes in barometric pressure or up and down rivers with changes in salinity. These new data may help design reserves that are of a size and location that could protect young sharks throughout their early years of life, allowing some population recovery.

Predicting Natural Fluctuations and Movements to Inform Reserve Design

Breakthroughs in acoustic technology are also revealing basic information about how fish change their behavior under different environmental conditions. This information is critical to understanding the cause of fluctuations and declines in fisheries catches, as well as designing conservation zones that will effectively ensure the long-term survival of these species and allow for resilience of populations under ever changing conditions.

Pacific salmon, a historical staple in the Pacific Northwest, are a prime example. Scientist know that these fish migrate many thousands of miles in their lifetimes, but until recently had little detailed understanding of how the thousands of individual populations of salmon differ in their marine migrations. New technologies allow researchers to monitor these populations in much greater detail, tracking fish in their early stages of development and making new discoveries about when and where their populations are most vulnerable.

Through the Census of Marine Life program, researchers plan to install a permanent acoustic tracking system along the coast of the entire Pacific Northwest – eventually stretching as a single seamless system from Baja to the Bering Sea. This new Pacific Ocean Shelf Tracking (POST) system will potentially track up to 256,000 fish at once, providing information on their direction, speed, depth and exact position at sea for fish as small as 11 cm.

"Imagine being able to describe the movements of vast numbers of fish as they migrate up and down the west coats of North America, tell where endangered stocks of salmon move, or predict the fishery benefits of alternate marine reserve designs for a multitude of species," says David Welch, Chief Scientist for the POST project. " With continued advances in acoustic telemetry, our technical ability to answer these questions is poised to make quantum leaps in the next few years."

Source: Eurekalert & others

Last reviewed: By John M. Grohol, Psy.D. on 21 Feb 2009
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