Welcome to "On the Line", a NOAA Fisheries podcast.

[Music playing]

Brian Spence: Basically this is the last ditch effort to stave off extinction.

Host: That’s Brian Spence, a fisheries biologist with NOAA and he’s talking about coho salmon in the Santa Cruz Mountains of California.

Brian Spence: The Santa Cruz Mountains historically we believe represented the southern edge of the distribution of coho salmon in North America. Between 2006 and 2008 the bottom dropped completely out of the Santa Cruz Mountain populations.

Host: Although the bottom dropped out, the remnants of that population are hanging on with the help of a hatchery run by the Monterey Bay Salmon and Trout Project. Spence and his NOAA colleague, Joe Kiernan, they’re working with the hatchery folks to improve the chances that population will survive, and that one day coho salmon will run wild in the Santa Cruz Mountains again. Last week I got them "On the Line", and I asked them a few questions about their research.

Brian Spence: The ultimate cause of the big declines in these watersheds is generally habitat degradation on the fresh water end of things.You know there’s been a lot of land use practices and water use practices and urban development that have diminished the quality of the freshwater habitat. What happened between 2006 and 2008 is we had a series of poor ocean years and so it took these populations that were hanging on at low levels and it essentially sent them over the edge.

Host: What constitutes poor ocean conditions to a coho?

Brian Spence: Productivity in the marine environment is driven very much by coastal upwelling. When that happens, nutrients from low in the water column of the ocean get pumped up to the surface and that fuels the whole productive regime, the phytoplankton and the zooplankton, and then the fish beyond that.

What can happen is you can have years of poor upwelling. Or, you can have years where the transition from downwelling to upwelling happens very late in the season, in the spring season. And these fish tend to want to go out to the ocean in April and May. And so if the transition hasn’t happened or if upwelling is particularly weak, you could have low productivity and survival of the smolts when they head out to the ocean can be low.

Host: So it sounds like the freshwater habitat put them in a state where they were vulnerable to some random change and...

Brian Spence: Yes. The variability that happens in the ocean becomes more and more important as populations get smaller and smaller because if you have a severe event—and it can be in the fresh water too. You can have droughts, and such, that cause a lot of mortality. But a bad event when the population is low means that it’s much harder for these populations to rebound.

Host: Now you think the coho in this area have a strategy for dealing with uncertainty in ocean conditions. Tell me a bit about that.

Brian Spence: Some research that I’ve been working on for the last several years has looked at patterns of outmigration in different populations of coho salmon all the way from California up to Alaska. And what we found is that the populations in Oregon and California tend to migrate over a broad window of time each spring.

The migration can start as early as March and it can go on into May and even a few individuals trickling out in June. So it’s a two or three month migration. And that’s a really sharp contrast to Alaska where you can get 50 percent of the fish leaving the stream in a five to 10-day period up there. And the entire migration is done in a month. And what we believe is that protracted migration period is a hedge against that uncertain ocean that we talked about earlier. That when you don’t know when the spring transition is gonna happen, you hedge your bets and some individuals go out early, some individuals go out late, and a lot of individuals go out in between.

So some members of the population are likely to hit the ocean when conditions are reasonably good.

Host: OK, so all that’s background to your research. I understand that you’re releasing hatchery-raised coho salmon each year, and that before you release them you tag them. And in fact, you’re tagging all of them. What are you trying to accomplish by tagging these fish?

Brian Spence: One of the things that happens at a lot of hatcheries is that they rear fish up to the smolt size, and then they essentially dump them into the river all at once, or over a very short window of time. So what we’re doing with this tagging experiment is we’re asking that question of whether we might have greater success if instead of releasing the fish over a very narrow window of time in the early spring which has been the traditional practice here, if we spread them out over sort of their natural range of migration…

Host: Wait...hold on. Let me back up here for just a sec so I can fill you in. Brian Spence and Joe Kiernan plan to release coho smolts from the hatchery over a period of ten weeks instead of all at once in order to mimic the natural migration pattern of coho in this part of the country. And what’s more, they’ve devised an experiment to figure out which week during that period of time results in the highest rate of survival.

This spring they’ll release 40,000 coho salmon smolts in batches, one batch a week for 10 weeks. All of those fish will be tagged with what they call "coded wire tags". Those are tiny slivers of metal with serial numbers stamped on them. When the fish come back two years from now to spawn—which not all of them will make it—these guys will collect the salmon and extract the tags and read them. That will tell them which batch of fish released during which week have the highest rate of survival.

In addition, a quarter of the fish will be tagged with what they call "pit tags". Those tags are like the "E-Z Pass" I have in my car so that when I go through a toll booth I get billed automatically. Spence and Kiernan, they’ve set up a bunch of like fish toll booths at different spots on the river and this will allow them to monitor the progress of each batch of fish as it moves downstream to the ocean and back upstream when they return. And they’ll do all of this each year for each of the next three years. Okay, back to the interview...

Brian Spence: With the coded wire tag, there’s a machine that you hold the fish up to a cone and you stick its nose in the cone, you press a button and it injects this sliver-like piece of metal that has the coded wire information on it. And it’s what, a half millimeter if that, in length. It's tiny.

Host: How do you read it when it comes back?

Brian Spence: You look under a microscope. And so these will be retrieved by crews that are doing spawner surveys in the stream. If we find carcasses of fish, we remove their heads and you excise this tag and it has a number on it that we can tell which batch it came from.

Host: You can find a millimeter size tag stuck in the snout of a...

Brian Spence: Yes, you can. You need a metal detector and...patience.

Joe Kiernan: It’s quite a process but, yes, you can.

Host: What do you have an army of undergraduate interns up there? What’s...

Brian Spence: So far it’s us.

Joe Kiernan: We haven’t reached that point yet, but that’s certainly the plan.

Brian Spence: Yeah, that’s—we will be doing that probably to a limited degree next year because some of these fish will return after just six months at sea. But most of these fish will return two winters from now.

So anyway, yeah, so we have the—so through the batch releases we’re trying to get at marine survival through the coded wire tag information primarily. And then through the pit tags, we can look specifically at the in-stream movement which we need to know—to get at that marine survival estimate, we need to know how many fish actually leave the system and head out to the ocean because if there’s mortality that happens in the stream that we weren’t accounting for, our estimates could be off for the wrong reasons.

Host: Great. So now it seemed that the coho have evolved this—or we’re speculating that the coho have evolved this strategy where they release over a longer period of time. So, why does it make sense for you to figure out which time in a given year was the most successful? Why don’t you just take a note from the coho and just time-average them all out?

Brian Spence: Well, that’s a good question. The main reason is this. Twenty-five or 30 years ago there were a couple people who did studies like this where they—what they thought they were trying to do was find the optimal time of release. What we’re trying to do is provide the evidence that in fact the optimal time likely varies from year to year.

And, if that is the case, then the appropriate release strategy is exactly what we’re doing—you know which is spreading it out. And when there are practices that have been used for along period of time, it’s often difficult to change people’s mind about whether that’s the best thing to do. So we need to have some concrete basis for suggesting those kinds of changes.

Host: So say you do demonstrate that the best way to release these salmon is over time rather than all at once. What does that mean for salmon recovery generally?

Brian Spence: What a lot of salmon recovery, I think is about, is restoring the natural variability in these populations. Not all salmon do the same thing, even within the same population. And it’s the diversity of expression of the life history that provides the buffer against disturbance events that affect one part of the population, but not another.

In fact a lot of what we’re doing with the migration timing is thinking about climate change and how that’s likely to disrupt the natural patterns that have evolved over long periods of time.

Really climate change can squeeze fish from both ends. You know on the fresh water end of things, the types of stimuli that send them on their way are things like changes in stream flow which are connected with rainfall events around here, or changes in water temperature or absolute water temperature. All of these things have some influence. And, so if weather patterns change, it’s likely to cause their migratory behavior to change somewhat, and then on the flip side if you have an ocean environment where the spring transitions get shifted earlier or later, it could affect these populations by producing a mismatch in their timing.

And populations down here that exhibit a little more variability could be a little more flexible in their response because there's members of the populations that do different things, as opposed to a place like Alaska where they’re all going out at the same time and if the favorable ocean window shifts by two weeks, it could have a fairly dramatic effect.

Host: As I was wrapping up my interview with Brian Spence and Joe Kiernan, Brian made the point that it’s not just fish that have to be flexible, but scientists have to be flexible as well.

Brian Spence: Just putting fish out into the environment, if you’re not tracking what they’re doing, you just don’t learn from it. And we view this as part of an adaptive management framework where you’re doing experimentation to sort of get real-time answers as you go along. And then you modify your management to respond to what you learn.

Host: Before I sign off, just let me make one more point about how science works. It’s a collaborative process. Brian Spence and Joe Kiernan aren’t working on this project alone. They’re working alongside colleagues from NOAA’s Southwest Fisheries Science Center, from The California Department of Fish & Game, The Santa Cruz Resource Conservation District, The University of California Santa Cruz, and of course, the Monterey Bay Salmon and Trout Project.

Host: Thanks for listening. Join us again next time for more stories about ocean life and ocean science. I’m Rich Press, and you’re listening to "On the Line".

[Music playing]

You have been listening to NOAA Fisheries’ podcast, "On the Line". Join us next time for another first-hand look at the people and the science behind managing our nation’s fisheries. For more information, visit NOAA Fisheries at www.NOAA.gov.

"On the Line" is a production of the NOAA Fisheries Office of Communications.