Conservation News
"300 Fish Days" in Santa Cruz County!
By Dougald Scott
"300 Fish Days" in Santa Cruz County!
By Dougald Scott
Ever dream of a "300 fish day" of wild steelhead? Well, I had four of them this summer, right here in Santa Cruz County! The largest fish was a hog, maybe 7 inches long. Most were in the 3-4 inch range, and quite a few were less than 2 inches. For fish of this size, you're probably thinking a 1-weight rod and microscopic size 36 flies. Not on these trips; here is what was going on.
I went out with a team of National Marine Fisheries Service (NMFS) biologists who are studying the life history patterns of steelhead in Soquel and Scott Creeks. The team consisted of seven biologists from the Southwest Fisheries Science Center of NMFS, located at UCSC's Long Marine Lab complex near Natural Bridges. The purpose of this ongoing study is to determine what factors predict which juveniles will migrate to the sea and become steelhead, or not to migrate, and remain in the stream as resident rainbow trout.
Steelhead exhibit a remarkable flexibility in their life histories. They can remain in their natal stream as immature juveniles for 1-4 years, and can migrate to the ocean during any of those years. They may stay in the ocean 1-4 years before returning to spawn as mature adults. Unlike most Pacific salmon species, steelhead often survive after spawning and may spawn again after another year or two of ocean residence. On the other hand, some juveniles may remain in fresh water for life, in which case they are referred to as rainbow trout.
Steelhead and rainbow trout belong to the same species, Oncorhynchus mykiss or O. mykiss, for short. Even using the most sophisticated DNA tests available, biologists cannot detect a genetic difference between steelhead and rainbow trout within the same stream system. This doesn't mean there aren't genetic differences, just that they can't presently be identified. If you encounter a 3-inch juvenile O. mykiss in Soquel Creek, you cannot tell if it is a steelhead or rainbow trout. To find out, you would have to watch it over time and see if it migrates to the sea. This is what the NMFS team is doing: watching the juveniles over time to see if they become a steelhead or rainbow trout. In the course of the study, they hope to determine what factors trigger the choice.
To watch thousands of individual fish over time would be next to impossible without a careful plan and sophisticated equipment. The NMFS team has established a number of sampling sites on Soquel and Scott Creeks, which are representative of the different habitats in each watershed. Each sampling site consists of a 100 meter section of stream. Their strategy is to capture every O. mykiss within the 100 meter reach, unharmed. The captured fish are measured and marked, have scale and DNA samples taken, and then are returned to the same reach in the creek. Each site is sampled in the spring, summer and fall.
To capture the fish, a net is stretched across each end of the reach to prevent fish from escaping. Then a team of 4 or 5 begins "electrofishing," working their way upstream from the bottom of the reach. One person carries an electroshocking backpack and underwater probe that delivers a powerful electric shock and stuns any fish in the vicinity. The remaining team members carry dip nets and buckets. Stunned fish are quickly netted and added to a bucket where they recover within a minute or so. Team members avoid being shocked by wearing waders and rubber gloves (tip: avoid leaky waders when electrofishing). To ensure that virtually all of the fish are captured, the team makes three electroshocking passes through the entire 100 meter reach.
Captured fish are delivered to a second team where they are processed. Each fish is anesthetized, then measured, weighed and marked. For fish over about 2 inches, a PIT (passive integrated transponder) tag is injected under the skin with a hypodermic syringe. The PIT tag is a small piece of wire that has a unique code number programmed into it; the number is read by passing a special instrument over it. The PIT tag serves as a permanent ID for each fish. When recaptured, the biologists will know how much each fish has grown and if it has traveled from where it was first marked. For fish under 2 inches, a color coded fluorescing tag is injected under the skin. In addition, each captured fish has scale and DNA samples taken. Under a microscope, the scales reveal the age and migratory history of the fish.
After several seasons of sampling and data analysis, the biologists hope to discover identifiable factors that predict which life history pathway an O. mykiss will take. This question is of immediate concern because steelhead in California are listed as threatened, and thus protected under the Endangered Species Act. However, similar protection for resident rainbow trout is unclear and being questioned by irrigators and developers. This could mean loss of ESA protection for O. mykiss populations where ocean migration is prevented by drought or man-made barriers.
A future Catchy Releases column will be devoted to the steelhead/resident rainbow controversy and the long-term implications for O. mykiss.
If you are interested in getting on the volunteer list for the NMFS project, send me an email at doscott@cruzio.com.