The Natural Laboratory Podcast Transcript: Tracking the Coho Salmon
[Intro music]
Kelly Reeves: This is The Natural Laboratory, a podcast exploring science for Bay Area National Parks. Today, I learn how biologists keep an eye on the endangered salmon that live a quiet life in the streams that flow through the parks.
Casey Del Real is standing knee-deep in a narrow creek. He's holding a metal rod into the water and he's about to shoot 175 volts of electric current through it.
Casey Del Real: If you stick your hands in the water, you will be shocked.
KR: Casey is a certified electrofisher. For him, electrofishing is not sitting back shocking the water and then calmly collecting hundreds of belly-up fish.
Unidentified fisheries biologists: There you go, there you go. Oh, a big one! Two big ones! Nice!
KR: It's a bit more vigorous.
[Unintelligible talk in the background.]
KR: When Casey stuns the fish, the shock only slows the fish to, maybe, a fast crawl. A flash of silver on the creek surface is all you see. Netters on either side of him stab the water to scoop up the fish. The netter plunks each fish into a white holding bucket.
Unidentified fisheries biologist: What did we get here?
Second unidentified fisheries biologist: Uh, it looks like one coho and a couple steelhead.
KR: Which one is the coho?
Second unidentified fisheries biologist: It is the smaller one right here.
KR: The coho is silver is big dots on its side. Casey grabs for it in the bucket. The coho's head sticks out from his fist about an inch. Like all newborns, its eyes seem a little too big for the rest of its body.
Unidentified fisheries biologist: Oh, oh, right there!
KR: Coho salmon are endangered in this area of California and steelhead trout are threatened. National Park Service biologists track these two types of fish, coho especially.
Michael Reichmuth: Coho would be a good indicator of the overall health the system. Not only does coho use the creeks, but also uses the estuary and all parts of the system, all the way from the tributaries all the way down to the mouth.
KR: That's Michael Reichmuth. He leads the crew that monitors stream fish in San Francisco Bay Area national parks.
MR: Coho have a three-year life cycle and they are born in the springtime and then they rear in the summertime.
KR: Right now, the fish are hanging out in the creek, gaining weight so that springtime next year they can make a break for the ocean. When they returned 18 months later, they spawn eggs and die. Mike and his crew keep track of all these life stages. They're in the creeks pretty much year-round.
MR: So, it's pretty intense.
KR: Park Service biologists have monitored stream fish since 1997. But, since the coho salmon have a three-year life cycle, biologists have so far only tracked six cohorts from birth to death. From so few cohorts, they can’t really say have the coho are doing. But Mike says they do know that more coho need to survive before they are no longer considered endangered.
MR: Ideally, we’d like to keep monitoring the populations until they get to recovery. To have a viable population you need around 2,000 spawners a year. So, we're actually well below what we would need to actually consider the fish stable. So, we have a lot to work for so I think we're going to be monitoring for quite a long time.
KR: Mike say that, in 2007, more coho one-year-olds survived the winter to swim to the ocean than normal, probably because few storms swept the coast this winter.
[Unintelligible talk in the background.]
KR: Mike measures and weighs all the fish netted today. At the end of the day, he pours the fish swimming the recovery pocket back into their home. Mike, Casey, and their crew will be electrofishing twice a week until October and then they'll start observing adults from the class of 2005 returned to their home creek to spawn. This is Kelly Reeves from the Pacific Coast Science and Learning Center.
[Exit music]
