Bruce MacFarlane has been studying salmon for 25 years, and he still sounds amazed when he talks about their evolutionary adaptations.
“It’s a brilliant survival strategy,” he says. “They spend most of their lives in the ocean–it’s a nutrient-rich environment. There’s loads of food. But it’s also a predator-rich environment. So where do they go to lay their eggs? To these inland streams, where there aren’t as many predators. But there isn’t as much food, either, so at some point they have to return to the ocean. By the time they hit the ocean in April, May, June, you’ve got a bustling farm out there for them.”
As MacFarlane says this, he’s standing next to a swimming pool-size tank at the NMFS Terrace Point complex where nearly grown coho are flitting among shadows. Some of them will eventually be transported to a hatchery on Big Creek just off Swanton Road where their eggs will be harvested and fertilized.
The Central California coho exist in such low numbers south of San Francisco that without a hatchery program they might not be here at all. Santa Cruz County is at the southernmost end of the coho’s historic range, and populations at the edge of their range are never very stable, says MacFarlane. Add to that the fact that the coho are the hothouse flowers of the salmon world, and it all spells trouble. Coho aren’t able to tolerate fast-moving water. They require deep, shady pools for spawning. Their strict three-year life cycle means they can’t breed with older or younger fish, which makes year lineages vulnerable. Nature did deal them one good card; up to 30 percent of coho migrate to other streams to spawn. Indeed, recently a handful of coho have popped up in Soquel and Aptos creeks–places they’ve never been documented before. It gives the species a little flexibility.
Jonathan Ambrose, a Santa Rosa-based biologist with the NMFS (and the husband of Charlotte Ambrose), says coho have evolved to be able to survive catastrophes like landslides, wildfires and even a spate of poor ocean condition years. But that only works if their habitat is healthy.
“They’re remarkable in the sense that one female can carry 5,000 eggs, and she can re-enter a stream and if the instream conditions are good, she can quickly repopulate it. That’s show these fish have evolved,” he says.”But what we’re realizing is, the instream conditions across the range of the Central California coho are in poor shape. Even if the fish make it back from the ocean, if the instream conditions aren’t there, the fish can’t do what they’ve evolved to do, and that’s quickly recolonize.”
Scientists point to a variety of factors in the destruction of coho habitat. The main one, in Jonathan Ambrose’s view, is urbanization. As an example, he offers up the San Lorenzo River, which had coho until 1982 (and had a few again in 2005).
“The San Lorenzo comes up as probably the watershed in the overall worst condition,” he says. “And why is that? Because you have an incredibly high density of roads. Lots are not properly maintained. Dirt bleeds into the creek. All kinds of people are living on the river because, what a beautiful place.
“But what happens is, this fish needs to have complex instream habitat, and in Santa Cruz County that’s primarily formed by trees falling into the creek, creating deep pools. But in Santa Cruz, the county funds the removal of large woody debris in the stream–and no other county does this–and if you don’t have large woody debris in the water, you won’t have fish.”
Drought and water diversion wreak havoc, too, says MacFarlane, and it could worsen. “If climate change has an adverse impact on the hydrological cycle here, what’s going to happen to the fish?”
via Traci Hukill for Metro Santa Cruz