PORTLAND – Salmon are known as terrific travelers, but a young steelhead left a Washington state hatchery in 2005 on a far more incredible journey than most.
Late in April a tiny electronic tag implanted in the 2.9-inch fish at the hatchery on the Columbia River turned up some 7,700 miles away – inside a young bird killed by a native hunter on an island off southern New Zealand.
Nearly 2 million fish leave the Columbia system with such tags each year, most heading north and west on a more mundane circuit toward Alaska.
The tag’s travels fascinated scientists an ocean apart, who in the past few months set about learning how it got into the stomach of a sooty shearwater chick born on a remote chunk of land called Big Moggy Island.
The likely answer reveals ecological connections stretching across the Pacific and illuminates the value Northwest salmon carry even thousands of miles away.
“It is amazing it made it all that way,” said Jen Zamon, a research fisheries biologist with the NOAA Fisheries in Hammond, Ore. “It’s even more sort of miraculous that someone noticed it.”
Before the tag appeared in New Zealand, the last anyone heard of it was on May 4, 2005, when the steelhead that carried it swam through a channel at Bonneville Dam toward the sea.
Scientists have two theories about what happened next. Both involve the fish getting eaten by an adult sooty shearwater, a globetrotting seabird roughly the size of a pigeon that nests in the South Pacific.
Thousands of shearwaters migrate each year from nesting grounds in New Zealand to forage off the Oregon coast. They are marathon travelers – flying some 40,000 miles a year, and more than 500 miles a day, in figure-eight patterns around the Pacific, according to tracking studies.
Each fall about this time of year, shearwaters gather off the mouth of the Columbia River before beginning their return trip south.
The masses of birds, which are related to the albatross, “carpet the surface of the ocean,” said Zamon, who is studying the birds and the salmon they eat.
One theory is that a shearwater off Oregon ate the young steelhead as it headed to sea in the summer of 2005, and the electronic tag from the fish lodged in the bird’s stomach. There it remained for more than a year, until the bird, back in New Zealand, regurgitated its stomach contents to feed its chick early this year.
Then a Maori hunter named Dale Whaitiri killed the chick and noticed the tag, which is slightly larger than a grain of rice and similar to tags that Whaitiri knew of from fish in New Zealand.
Never before has one of the tags shown up so far away.
The tags are known as PIT tags, which is short for passive integrated transponder, and are similar to identification chips implanted in dogs and cats. Each tag carries an individual code that can be read by an electronic scanner.
Shearwaters have folds in their stomach, and perhaps the tag got caught in one of those folds until it came time to feed the chick, at which time shearwaters “very vigorously empty their stomachs,” Zamon said. Other indigestible items such as bits of plastic and squid beaks are known to collect in birds, she said.
One catch, though, is that shearwaters nest each year, so the tag would have had to hide out in the bird through an entire season of repeated stomach emptying as the bird fed its chick a year earlier, said Dave Marvin, who tracks Columbia River passive integrated transponder – or PIT – tags for the Pacific States Marine Fisheries Commission in Portland.
“When they’re doing that, pretty much everything they’ve got in their stomach comes out,” he said.
He helped piece together the tag’s travels after scientists in New Zealand traced the tag to the Minnesota company that manufactured it, which determined that the tag was shipped west for use in the Columbia system.
Marvin thinks it’s possible the steelhead with the tag was inadvertently caught in a fishing net somewhere in the Pacific, perhaps near Japan or Russia. Northwest steelhead swim in a broad arc across the Pacific, and some have turned up there.
If that theory is correct, the fish might have been cut up on a factory ship or another fishing boat and its remains tossed overboard.
Masses of shearwaters are known to follow fishing vessels and feed on remains dumped into the sea, Marvin said. Shearwaters are too small to eat an adult steelhead but could have swallowed the tag while swallowing smaller remains.
It’s unclear how often Northwest steelhead turn up on factory ships, because there’s little information about their catch or “bycatch” – the unintended catch pulled in with nets. “There’s lots of factory ships out there,” Marvin said. “What their bycatch data is, we don’t know.” If Marvin’s scenario is right, the bird might have picked up the tag much more recently. That way, it wouldn’t have had to stay in the bird’s stomach as long. But all the researchers admit they will never know for sure where the steelhead met up with the shearwater, also known in New Zealand as a muttonbird, or by its native Maori name, titi. The islands where the birds nest in tunnels among the roots of trees are called the Titi Islands.
“We know it went into the ocean, and we know it ended up in New Zealand,” Marvin said, “but what happened in between is speculation.”
Zamon’s team is looking at the relationship between shearwaters and Northwest salmon populations. She said the New Zealand connection underscores the relationship between the two and may lead to more PIT tags getting noticed somewhere on their journey.
“However it happened, we have incredible numbers of these birds that spend time here,” she said. “It shows how interconnected the oceans are.”
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