A Revolution In Fish Tracking
by Bill Rudolph
The Corps of Engineers hosted its annual research review last week in Portland, where scientists reported on the latest results in their fish survival studies in the Columbia Basin and discussed innovations in fish tracking methods that promise a revolution in fish research with the use of ever-smaller acoustic tags.
Now weighing only about six-tenths of a gram, the tags are surgically implanted in fish, and send out acoustic 'pings' that are picked up by receiver arrays placed just about anywhere researchers want. The ability to track fish over wide areas is their major benefit over PIT tags, which require fish to pass through a relatively confined space, such as a fish ladder, to be detected at all.
However, while the acoustic tags use tiny batteries lasting only 30 to 60 days, the PIT tags are 'passive,' and only respond when detected, so they can work indefinitely and identify individual fish through the adult stage and even longer. Other research groups are still finding thousands of PIT tags at bird colonies where terns and cormorants have feasted on the annual migration, especially steelhead.
So far, much of the acoustic tag research has focused on whether the tags themselves have adverse effects on fish, since they are much bigger than PIT tags. They are also a lot more expensive, costing around $250 a pop.
The results seem pretty positive on all counts, though, and Corps researchers think the improved precision will be worth it. They plan to tag 25,000 fish with them next year.
The increase in precision has already impressed researchers, such as Lynn McComas from NOAA Fisheries, who led a group that used the new tags in a pilot study of fish survival in the Columbia estuary. Until now, survival estimates there have been fraught with uncertainty.
With a string of receivers spread on the river bottom across the mouth of the Columbia, the new work has generated enough data for some preliminary survival data for Snake River spring chinook traveling from Idaho all the way to the ocean. Initial findings for the four release groups in the study show that about 80 percent make it from Lower Granite Dam to the mouth of the Snake and, around 40 percent make it all the way downriver to the ocean, while estuary survival from Bonneville to the ocean ranged between 60 and 85 percent.
For fall chinook moving through the estuary, the researchers found that 85 to 99 percent of earlier release groups made it through the estuary, but survival deteriorated for later groups, ranging from 67 percent to only 17 percent for the last group in the study.
There is still plenty of work going on with PIT-tags, which only cost about two bucks apiece. Other researchers have used them since the early 1990s to estimate inriver survivals of spring chinook from Lower Granite to Bonneville. In 2006, survivals were the highest they have seen since they started keeping track, averaging around 60 percent.
Survival through individual reaches averaged 93 percent. For steelhead, inriver survival averaged 38 percent, with 88 percent survival through individual reaches.
But better inriver survivals don't mean more fish will come back in the future. NOAA Fisheries scientist Bill Muir said the dramatic increase in adult return rates since 1999, is "largely independent" of hydro system survival.
Muir also pointed to an analysis by fellow federal scientist John Williams that suggests the PIT-tagged wild returns actually underestimate the run at large. The same holds for hatchery chinook, though questions were raised about just how robust the estimates of wild untagged smolts really were, since they are not counted. Using data from the Fish Passage Center's own CSS study, the feds said the same results were evident there, too.
Canadian scientist David Welch also reported on his initial findings on near-ocean survival of some Snake and Yakima River spring chinook. (See NW Fishletter 222).
Using acoustic tags that are larger than the Corps' version and longer-lasting, Welch has followed small groups of both barged and inriver migrating fish past the mouth of the Columbia to detection arrays off the Washington coast and the northern tip of Vancouver island. His initial findings showed about 20 percent of both the Snake and Yakima inriver migrating fish made it to the first ocean array off Willapa Bay. About 5 percent of the Snake fish and 2.5 percent of the Yakima fish were detected off Vancouver Island.
Welch said the results show no evidence of any delayed mortality for the Snake fish, which deal with four more dams in their downstream migration.
His research also found that survival of barged Snake River spring chinook (from Dworshak hatchery) was about double that of the inriver-migrating Snake fish, about 38 percent, but their ocean survival to Vancouver Island was half that of the inriver fish.
Welch's 2006 data show that each group of Snake fish, whether inriver or barged, exhibited "substantially less" survival in the 560-km stretch between Willapa Bay (southern Washington coast) and Vancouver Island than in the entire 960-km distance between the Snake and the Willapa receiver array. His study also showed that there was significantly higher survival for Snake River barged fish than for inriver migrating Snake smolts.
Survival of the two Yakima groups (199 fish each) to the north end of Vancouver Island was miniscule--two fish were detected from one group, and none from the other.
That result was similar to the detections for Snake inriver migrants. Of two 198-fish groups released in early May, only one smolt was detected from the first group, and three from the second.
Barged fish from the Snake fared better, with eight detections in one group that was barged downriver June 7, adding up to an 8 percent overall survival rate to Vancouver Island, with a 3 percent survival rate from the second group, barged June 15.
A closer look at barged fish came from NOAA Fisheries scientist Doug Marsh, who announced findings from ongoing survival studies of barged and inriver wild spring chinook from the Snake. Though adult returns to Lower Granite Dam were small--only two dozen in the case of the barged spring chinook--they outperformed inriver migrating (non-detected) chinook by 2.64 to 1.00. Barging from Little Goose showed benefits as well, doing 60 percent better than inriver fish.
For barged steelhead, the results were nothing less than spectacular. They outperformed non-detected inriver migrators by 800 percent. Other new research that may shed light on the vagaries of barging fish reported that overall, barged fish were in better shape than their inriver brethren, based on lab tests that assessed their ability to ward off marine bacteria.
More evidence of the overall benefits of barging came from an analysis by staffers at the University of Washington's Columbia Basin Research group. By analyzing PIT-tag data from hatchery releases from 1996 to 2004, they found ocean survival of the different groups was the most influential factor in determining smolt-to-adult returns. They said transport-to-inriver return ratios and SARs varied broadly with annual flow levels, and that in most cases, barged fish from Lower Granite and Little Goose did better than inriver fish.
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