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First Past the POST |
| July 12, 2005 |
Acoustic Tracking System Unravels Ocean Mysteries
By Andy Torr, AquaNews Editor
 | | Click image to watch animation. The Pacific Ocean Shelf Tracking (POST) project, administered by the Vancouver Aquarium, is bringing scientists closer to solving the mysteries of ocean-going salmon. |
From the surface, life in the ocean may appear deceptively simple: swim, eat, reproduce, die. But the life of a Pacific salmon is considerably more complicated, for between the inevitable bookends of birth and death is an epic journey—a lifelong marathon from river to ocean and back again. It is a life in which the only sure thing is a relentless gauntlet of predators and obstacles, and where the odds of surviving to spawn are a thousand to one.
For centuries, salmon have represented one of the ocean's greatest mysteries. Their enigmatic ocean journeys have inspired an entire field of marine science, to which many a researcher has dedicated their entire career. David Welch is one such scientist, and his relentless enthusiasm for unraveling the mysteries of ocean migrants like salmon have put him at the forefront of one of the most ambitious scientific endeavours ever proposed: the Pacific Ocean Shelf Tracking (POST) project.
"POST is about a grand idea," says Welch, the project's Chief Scientist. "We want to be able to follow everything from salmon to whales, anywhere along the West Coast of North America. We want to be able to measure their day-to-day movements and their seasonal migrations from feeding grounds to spawning grounds and back."
To accomplish this mammoth task, Welch proposes building something akin to an underwater telephone system: an array of 'listening lines' that span the continental shelf from Baja to the Bering Sea and detect acoustic signals from tagged fish as they swim past. Each tag, surgically implanted in the fish, transmits a unique code that enables researchers to follow the individual migrations of thousands of fish.
This summer, the POST project enters the second half of its demonstration phase. Last year's trials, in which a small number of listening arrays were tested off the coast of British Columbia, achieved a technical milestone: POST scientists detected 91% of all tagged fish that swam past any given listening line. That's a huge advance from the past, says Welch, when scientists were not able to consistently detect even a single fish.
"This means the world has changed," Welch says. "Now, for the first time, we can really follow these animals with the full knowledge that we can get a complete migration track for every one of them. In 2005, with some of the refinements we have made, we're probably going to be up around a 97-98% detection rate."
 | | Above: A snapshot of the evolution of acoustic technology: Tags 16mm in diameter (top) were used in the 1990s and lasted a few months. The 7mm diameter tags below it are currently used by POST. They last 4-20 months. Click to enlarge. |  | | The new generation of Vemco acoustic tracking receiver (above) has an integral acoustic modem, which allows data to be collected without the need to physically retrieve the unit. Click to enlarge. |
Revolutionary Change
Although POST was originally conceived to focus on salmon, the project has since widened its scope to include larger species. "We have recently developed tags that will continuously track a two-kilogram fish for ten years and a five-kilogram fish for 20 or more years," Welch says. "That's a revolutionary change that will apply to everything from rockfish to blue whales to dogfish to salmon sharks to halibut—and anything else you might want to study. All of these species and stocks have fundamental questions about where they go in the oceans that nobody has ever been able to address in an effective way."
As POST refines its tracking capability, the sensors populating the 20-30 kilometre-long listening lines have also improved. This summer, Welch and colleagues will test an array of sensors that can be submerged for up to seven years. Onboard each sensor is a modem that can remotely connect to a shipboard computer and download months of tracking information in a few minutes. This advance will make a huge difference, Welch says, because it will enable his team to leave the system on the seafloor and obtain data year-round.
"There are a lot of scientists along the West Coast using the same types of general equipment to track fish, but they take their equipment out of the water after a few months and are geographically constrained in what they're trying to do," he notes. "We want to do the same types of tracking studies, but we're more ambitious; we want to measure survival rather than just detect the movements of fish. We want a complete record of everything going past. And we want to make it permanent and cost-effective."
Good News for Salmon
Welch agrees that a project of this scope could contribute significantly to deciphering the 'black box' that is the Pacific Ocean, but he emphasizes that POST is about more than just scratching a scientific itch; it has enormous implications for the responsible conservation of marine species—particularly salmon stocks.
"Salmon survival in the ocean has dropped tremendously in the last 20 years, and that has probably had a far larger impact on stocks than the loss of freshwater habitat," he says. "We still don't understand where it has happened and why it has happened, and if we don't get that critical information we run the risk of repeatedly making the same management mistakes over and over again. And that means more than just dwindling salmon stocks. There are enormous economic costs tied up in running fisheries management systems that are bound to repeat the mistakes of the past because of a lack of new data."
POST is about more than just finding out where Pacific salmon go once they reach saltwater; previous studies have already determined that they travel north along the continental shelf to the Bering Sea. Instead, POST researchers are tracking thousands of individual salmon to study where and when they die in the ocean. By charting survival by area – the West Coast of Vancouver Island, for example, or from the Alaskan panhandle to the Aleutians – researchers hope to identify important foraging or transit areas, particularly those used by endangered salmon populations. Protecting these areas will help to improve ocean survival and promote the recovery of dwindling stocks.
"You don't have to be a salmon fisherman to want to see salmon stocks conserved," Welch insists. "We've seen ocean survival of the young fish drop to one-tenth of what it was. That's like taking 90% of all the fish out of the system, before any of the commercial or sports fisheries get started. These are far larger effects than our sport and commercial harvests combined. We need to find out why that radical change has happened, and if we don't, we can't conserve the stocks.
"Equally importantly, we could be spending a lot of money on trying to fix the wrong things," he adds. "So while POST is useful for people concerned with salmon conservation, it also has a role in good management and the responsible use of tax dollars."
 | | Click image to play animation. Tracking data can be used to determine the migration paths and speeds of tagged animals. This animation is a sample representation as visualised by Baird & Associates. |
Welch cites the example of the Sakinaw and Cultus Lake sockeye stocks, two critically endangered B.C. salmon populations currently at the centre of a heated debate between scientists and fisheries managers. These now-tiny, remnant populations of sockeye return from the ocean through the Strait of Georgia at approximately the same time as other, larger and healthier sockeye populations. The Sakinaw stock dropped from about 40,000 adults two decades ago to only three fish in 2003; the reasons are still unknown. The story is the same for the Cultus sockeye, although the magnitude of the population collapse is not – as yet – quite as extreme.
The concurrent migration of these weak and healthy stocks creates a mixed-stock fishery, making it impossible for fishers to control the origins of the salmon they catch. Under the right conditions, a large commercial fishing effort in southern British Columbia could inadvertently wipe out an entire run of either sockeye stock. But the alternative – shutting down the sockeye fishery to protect a handful of endangered fish – is an economic gamble most fisheries managers are not willing to make when almost 18,000 British Columbians depend on the salmon fishery.
Enter POST: In 2004, POST scientists surgically implanted 97 special "sleeper" tags into the young Sakinaw sockeye before they were released into the ocean. Nineteen survived to leave the Strait of Georgia, migrating north out of Johnstone Strait. The tags in these fish were programmed to turn off in early September, conserving battery power for the all-important adult return in 2006. If all goes well, the tags will turn on their tiny beacons during the return journey to announce the timing and migration path of the surviving adults.
Projects like these give a glimpse of a radically new future for fisheries management and marine science. By monitoring the progress of a handful of tagged adult sockeye as they navigate their return through an array of listening lines, researchers could measure exactly when the returning salmon will enter the mouth of the Fraser River—and how they will get there. Equipped with such scientific clairvoyance, fisheries managers could suspend commercial fishing efforts for just long enough to provide safe passage upstream for the bulk of any endangered population, without incurring the economic repercussions of a prolonged fishery closure.
"There are a lot of valuable and very poorly understood fish resources out there. The slope water at the edge of the continental shelf is where most developing fisheries are occurring because things have been fished down on the shelf. I think it's important for POST to get out there before these resources are depleted, so that we get the sort of information needed to manage them."
- David Welch on the potential applications of POST along North America's West Coast. |
Sea Change
Fisheries management is a precarious balancing act of conservation and economics, and it is a familiar world to David Welch. The defining moment in his career – and, as it turns out, the genesis of POST – came in 1989 when he abandoned a major research effort he was developing that would manage salmon stocks using large-scale computer models to analyze and predict their movements.
"I realized that the computer models by this point had vastly outstripped any knowledge of what was happening in the ocean," he explains. "We were making up assumptions about what the salmon were doing so that we could solve these really complex problems on the computer. Even in 1989, the computer models were complex and powerful but they were built on a fundamentally flawed assumption: that we actually knew what was happening in the oceans.
"So, in 1990 I put my rubber boots back on and went out to sea, because that was where the big questions lay with salmon and no one was really addressing them. Here we are in 2005, fifteen years later, and ironically I'm now developing a system that will give us the fundamental information I felt was critical in 1990 but that we had no hope of ever feeding into our computer models."
The Promise of POST
Welch's career has come full circle, it seems, and his hope is that the scientists of the 21st century will utilize the POST array to make the management of fish stocks far more effective and efficient than ever before. POST is now a key part of the Census of Marine Life (CoML), an unprecedented ten-year, billion-dollar survey of the world's oceans and everything in them. By 2010, when the Census wraps up, Welch is expected to have created an infrastructure around the POST technology that will allow scientists from around the world to use it for their own research.
"For POST to be really successful, it has to be a worldwide effort," Welch says. "We want to tie together all these regional efforts on different continents. We want to develop the synergies between people in different countries and different ocean basins. Imagine discovering that great white sharks from South Africa visit the southern tip of Vancouver Island each August. There's no way you could do that right now, but if we incorporate regional efforts into a much larger whole, we will make big discoveries like this. That's the promise POST holds."
Like all people with big ideas, Welch has his work cut out for him. He is busy gathering politicians, fisheries managers, First Nations, and other scientists under the POST banner, while trying to prove that the naysayers who do not share his vision are wrong.
"The biggest misconception about POST is that we're crazy and we can't do it," Welch laughs. "We are crazy, but we can do it."
| Source: Vancouver Aquarium Marine Science Centre |
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