Tuesday, February 05, 2008

Virus farms or salmon farms? Wild salmon and IPNV

Here in the Valley, many of us love our local Atlantic salmon. We wait patiently watching as thousands of shad, and hundreds of eel pass by the murky fish ladder windows - where thick panes of glass separate us from the roiling Connecticut in spring - hoping to glimpse the rare silvery salmon. We scan the scoreboard, where FirstLight Power Resources, the local dam and fish ladder operators, records numbers of each species passing by the ladders. How many salmon, we wonder, will make it back to Holyoke where the majority of returning fish are captured and transported to the Richard Cronin National Salmon Station in Sunderland, for spawning?

Each winter and spring, school kids tend salmon eggs in their classrooms, watching as the large salmon embryos develop. They squeal with delight as the young salmon squirm from their translucent shells and begin to dart about the tank, their oversized yolk sacs sustaining them for the months to follow. Finally, as the salmon absorb the last of their maternal sustenance, developing into fry, the stage at which they’ll be released into the wild, they name them, and say their farewells, gently tipping cups of fry into local streams. In this valley, to paraphrase Monty Python, “every salmon is sacred.”

So when I awoke one Monday morning this past fall to Laurie Sanders’ familiar voice explain on Field Notes, her weekly show aired on WFCR, why most of this year’s 141 sea run returns – 121 salmon possibly raised and released by some hopeful school kids, fish that had spent the past two or so years at sea, dodging predators, seeking out food, and finding their way back home – were destined not for reproduction but for destruction, I turned to my own resident salmon expert, conveniently lounging in bed beside me: my husband Ben.

For the past ten years as an aquatic ecologist at the Silvio Conte Anadromous Fish Research Center in Turners Falls, Ben has led a team of scientists and resource managers who mix and match salmon mates, using genetic marker-assisted broodstock management techniques to better understand the factors limiting restoration and population growth of Atlantic salmon.

“What does she mean,” I asked, “that they have to destroy all those salmon?”

“Not just the salmon,” he said, regretfully, “but all their eggs too.” He’d just spent over a week at Cronin playing matchmaker for those 121 doomed salmon. Turns out, as Ms. Sanders explained, ovarian samples from two of those returning adult fish were infected with Infectious Pancreatic Necrosis Virus or IPNV, a potentially lethal disease in salmon. And so, as a precaution to prevent the possible spread of the disease, all of the adults, and over seven hundred thousand of their eggs were slated for destruction at the hands of the hatchery managers who had tended and cared for these precious wild fish.

As one who’d killed many a fish for research, but who towards the end of her career could barely kill a minnow, I couldn’t imagine how they must have felt.

“I was devastated,” said Mickey Novak, hatchery manager for the Cronin station, speaking of the drastic measures required to stay the spread of IPNV. “I’ve tested thousands of samples. I’ve never had to do this in my entire career.”

On the other hand, noted Novak, “had we missed those eggs, once they hatched [fertilized salmon eggs from Cronin are transported to the White River National Fish Hatchery in Bethel, VT] they could have contaminated the entire Connecticut River watershed with IPNV – and other susceptible species like bass and trout could easily have been wiped out.” Humans, notes Novak, are not susceptible.

Because of the threat that sea-run fish may bring to not only their own progeny but to the program as a whole, salmon that come into the hatchery are run through a battery of tests for viral, fungal and bacterial diseases. Some tests rely on blood samples, while others like IPNV require different bodily fluids. In this case, ovarian fluid from strip spawned females is collected and sent to the Lamar Fish Health Center, U.S. Fish Wildlife Service, in Lamar, PA, where it is cultured for IPNV.

According to Trish Barbash, assistant fish health biologist at Lamar who tested those samples, “IPNV is endemic to freshwater rivers and streams in the northeast and may actually have originated here in Brook Trout…. This is the first occurrence of IPNV in Northeastern wild Atlantic salmon since many of these restorations began.” That is, in the over 30 years since efforts to restore Atlantic salmon stocks began, this disease has never once been detected in Atlantic salmon returning to natal rivers along the northeast coastal United States. Additionally, as Barbash noted, though the disease is endemic in Pennsylvania and some other Northeastern states, it has not been detected in Massachusetts rivers and streams in any species.

Where did the strain infecting the Cronin salmon come from? Barbash's analysis reveals that the virus infecting the Cronin salmon is not a known North American strain, but is genetically more similar to a Canadian genotype. So, it is unlikely that the salmon were infected with IPN during their life stages in the waters of the U.S., but may have come in contact with Canadian or European fish carrying this virus strain during their migration in the ocean. As Novak explained, back in the dark ages of conservation, the late 1800s, IPNV was likely transported from the U.S.Europe along with native brook trout. Over the past 100 years all sorts of trout and their associated diseases have crossed the Pond, in tanks rather than under their own piscine power, thanks to our incessant meddling, and
over the years, IPNV has diversified into a whole range of different strains. These strains are geographically scattered across the world, but not necessarily out of reach of the Connecticut River Atlantic salmon when one considers their migratory trek.

Ironically, though this is the first appearance of IPNV in wild U.S. salmon stocks, IPNV is well known in Europe, particularly in (or perhaps thanks to) European fish farms in Norway, Scotland and Ireland. Because of its impact in Europe, it is currently considered the most important viral disease for salmon in the European Union. Several years ago, IPNV was estimated to cost Norwegian salmon farms upwards of 100 million krone. In case you haven’t traveled to Norway lately– that’s roughly 20 million dollars. And, IPNV is just one disease of many endemic to salmon farms.

When I’d first heard that the fate of the Cronin fish may have been in some way associated with European salmon farms, I felt that familiar surge of anger towards industrial tinkering with natural systems mixed with guilt as I looked forward to my morning coffee, toasted bagel, cream cheese and, you guessed it – salmon. Salmon that likely traveled from a farm in Norway, Scotland, Chile or maybe Canada to my breakfast plate. As we all know, viruses thrive when their hosts gather in high densities, be it a crowded airport, our kid’s classrooms, or a fish farm. So while scientists estimate the prevalence (or number of existing cases) of IPNV to be very low in wild fish populations – making this year’s finding of IPNV in wild North American stock all the more important – that is not the case in fish farms.

Fish farms may be, according to a recent report by the Norwegian Seafood Federation’s aquaculture division, “the most important reservoir of IPN virus in the aquatic environment,” as infected fish shed virus in feces, urine, dead and dying fish into surrounding waters. And, according to some reports, IPNV can survive up to twenty days in seawater. As wild salmon migrate past infected Norwegian or, say, Scottish fish farms, though they may flip a fin at their captive cousins, they may also swim away host to a deadly disease.

But wait, you say. What’s fish in farming Europe got to do with Connecticut River salmon? It’s a big ocean after all – hard to imagine our small fry out there mingling with the Euro crowd.

Yes there’s lots of wide-open space out there in the North Atlantic. But, in the ocean, as on land, migrating animals tend to follow the beaten path, so to speak, or in this case ocean currents. So after spending two to three years, half their lives, in freshwater rivers and streams around the Valley, the salmon that many of us gently tip from PVC buckets, increase in size and grow into sea-ready salmon smolts, and head on out into the big blue. There, according to Janice Rowen of the U.S. Fish and Wildlife Service Connecticut River coordinator’s office, “They migrate to the North Atlantic following ocean currents. They spend a couple of years off the west coast of Greenland feeding, and sometimes, rarely, they stray further east. European salmon may mix with North American salmon there. But, the majority of European salmon seem to migrate to an area closer to Europe, near the Faroe Islands.” Large quantities of capelin are apparently at least one attraction, as salmon from afar mix, mingle, gorge, and as with any crowd anywhere – share disease before heading back from whence they came.

For years, Mickey Novak has been sampling - looking out for what wasn’t there. Thanks to Mickey, Jan and Trish and others who patiently sample and test, year in, year out, it still isn’t.

This article was first published in the Montague Reporter, Montague, MA

No comments: