Today my students and I visited the Monterey Bay Salmon and Trout Project hatchery, to learn about local efforts to save the federally endangered coho salmon (Oncorhynchus kisutch). The coho is one of five species of Pacific salmon found on the coast of North America, the other four being the Chinook (O. tshawytscha), the chum (O. keta), the sockeye (O. nerka), and the pink (O. gorbuscha). The coho's range extends in the North Pacific from northern Japan up along Russia, across the Aleutians, and down the coast of North America to the northern bit of Monterey Bay. In our area the coho return to their natal streams (Scott Creek, Big Creek, and occasionally the San Lorenzo River) during the winter rains in January and February.
The local population of coho make up an evolutionarily significant unit (ESU). This means that they are locally adapted to the extent that they are biologically and genetically distinct from other populations. For example, coho from Alaska, where they are much more common, cannot be successfully transplanted into our watershed because they are genetically programmed to spawn in the fall, the time of year when our streams are dry or disconnected from the ocean due to sand bars. So these fish aren't just any old salmon. They have evolved to live in this particular watershed and as such are irreplaceable.
Our first stop of the morning was to the fish trap on Scott Creek. The weir, the structure that extends across the river in the photo below, traps fish that are swimming upstream. Once on the upstream side of the weir, the fish are directed into the cage, from which they can be removed so that fisheries biologists can collect life history data--species, sex, weight, length--before they are released to continue their journey upstream (if they are steelhead) or transported to the hatchery to be spawned (if they are coho).
No fish were in the trap when we got there this morning but our host, a NMFS biologist named Erick, told me that eight coho had been caught yesterday. We did see a pair of steelhead swimming in the water upstream of the weir. Anytime I see a fish out of water, I forget how difficult it is to find them when they're in their natural habitat. The spots on a steelhead's back blend in perfectly with the ripples of the water and the gravel of the stream bed.
Do you see two faintly reddish blurs in the photo above? Those are the fish. They are facing upstream, to the right. The larger fish on the top is the female.
After the visit to the fish trap on Scott creek we drove up to the hatchery, which is located along Big Creek. The hatchery's day-to-day operations are run by a couple of people from MBSTP. During the busy seasons staff and interns from the NMFS lab in Santa Cruz work up there, too, so the little hatchery building gets quite crowded. We were fortunate to get to see pretty much all the steps involved in trying to return an endangered species from the brink of extinction.
Male salmon, called bucks, are held in pens outdoors. They can contribute more than one sperm donation in a season, just as in the wild a male can fertilize the eggs of more than one female. A buck is taken from the pen, sedated, and then is milted for his sperm. The milt is collected into a glass test-tube and kept dry; once the sperm make contact with fresh water they become activated, and there is a 30-second window during which they can fertilize eggs. Sperm can also be damaged by exposure to UV radiation, so the test tubes are always held in a closed hand. Back inside the hatchery building Erick takes a look at the sperm under a microscope to make sure they can swim properly.
Female salmon are called hens. Before eggs are taken the hens are anaesthetized and examined by palpation and ultrasound to confirm that their eggs are mature. A sample of ovarian fluid is taken and sent off to be tested for disease. When a hen passes the ripeness test she is sliced open to release her eggs into four metal basins.
A single female's eggs are fertilized by the sperm of four males. The fisheries biologists keep a detailed matrix of who mates with whom, so that they can avoid additional inbreeding in a population of fish that has already undergone a genetic bottleneck. Milt that has been collected from broodstock males is placed over the eggs. Fertilization occurs once fresh water is added to the basin. The egg-sperm combination is swirled ("just like panning for gold," Erick explained) for two minutes, then the eggs are rinsed and disinfected before being placed into a 100% humidity cold incubator held at 11°C.
The eggs remain in the incubator until the embryos have developed eyes. Then they are transferred into trays through which water flows. When they've absorbed most of their yolk sac they get placed into large indoor trays where they will be fed until they are big enough to go into the outdoor tanks. They'll spend about a year in the outdoor tanks and should then be ready to undergo the process of smoltification, during which their physiology undergoes the alterations necessary for the transition to marine life.
When I took last year's class to the hatchery we didn't get to see much activity because there were so few fish returning due to the prolonged drought and low water in the creek. This year's El Niño, which has brought rain, has also made it possible for the fish to get into the creeks. Coho are a 3-year species, so the fish returning this year were born in 2013. These fish outmigrated as smolts into drought conditions, and fortunately for them they return during a rainy year. Their progeny will outmigrate in 2017, hopefully into a strong upwelling which will produce lots of food. And when they return in 3-4 years, I hope that there is enough rain for their creek to flow.