2005 November - NOAA Research
More NOAA research at Kingfisher Flat Hatchery
By Susan Sogard
The NOAA Fisheries Santa Cruz laboratory has an extensive ongoing research project in Scott Creek, with chief researchers Sean Hayes, Chad Hanson, and Morgan Bond, who are examining a multitude of ecological factors affecting wild Coho salmon and steelhead and their interactions with hatchery fish. In addition to this field-based study, NOAA Fisheries is also conducting laboratory work, headed by Sue Sogard, at their facility on Terrace Point (adjacent to Long Marine Lab, UCSC).
This study is an effort to determine what factors lead juvenile steelhead to adopt different life history pathways. Steelhead are amazingly complex in their life histories. Some of the earliest studies of the species were conducted on Waddell Creek, where researchers first documented this remarkable diversity. Some fish go to sea after only 1 year in freshwater, whereas others wait an additional year or even 3 or 4 years before migrating. Some fish never leave at all and mature in fresh water, thus becoming a rainbow trout, the nonanadromous form of this species. Some fish (usually males) mature as parr after only a year in freshwater, and attempt to spawn with returning adult females. These fish may still later undergo smoltification and go out to sea and come back again as anadromous males. The time spent in the ocean is also very variable among individuals.
How does a young fish make the initial decision to stay in the creek or head to sea? We think it must happen well before the actual time of downstream migration because of all the physiological changes that accompany the transition from a freshwater to saltwater environment. Studies with Atlantic salmon, which also has a great diversity of life history options, have found that growth rates in their first summer set fish on a particular pathway, with fast growers likely to leave the system in the following spring while slow growers stay behind. Males that grow particularly quickly may mature early - these fish will not start the smoltification process. The pathway selected also influences the fish’s behavior during the winter, with fish destined to stay another summer in freshwater adopting a low risk lifestyle. This group will give up on attempting to grow during the winter and will hide in any available shelter rather than risk being caught by a predator. Our lab studies have two primary goals:
- Determine the influence of growth rates on life history pathways and behavior of steelhead during their first year of life, and
- Determine the role of genetics in life history decisions.Â
Our methods for the first goal involve raising fish through the egg and early juvenile stages at the Kingfisher Flat Hatchery, then transporting the young fish to our lab aquarium in Santa Cruz. They are then assigned to different food levels to manipulate growth rates. We monitor growth from fall through spring and videotape their behavior during the winter. In the spring we use a combination of gill enzyme assays and seawater tests to determine which fish have made the decision to go to sea. The results so far have shown that fast growth does indeed make it more likely that a fish will leave freshwater after only a year. However, our behavior experiments have not shown any evidence of a ‘lay low and avoid all risks’ strategy for fish that have decided to stay in freshwater for another summer. Instead, these fish are highly active and attempting to grow despite the low food levels we are providing. We think the explanation for the difference between Atlantic salmon and California steelhead lies in the very different winter environment. Here on the central coast, winters are relatively benign and the opportunities for growth are actually better in the winter than in the summer, a very different seasonal pattern than what Atlantic salmon face.
For the second goal of our study we are artificially crossing steelhead with rainbow trout to determine the role of genetics in life histories selected by young fish. In March and April of 2004, we mated two anadromous females with a mix of different males, including some that had spent two years at sea, one year at sea (jacks) or rainbow from above the falls that had never been to sea. Fertilization of the eggs was very high except for two of the rainbow males, perhaps suggesting some incompatibility of steelhead eggs with rainbow sperm. But once the eggs had been fertilized, the life history of the male had little effect on survival of the eggs or hatched fry. The young fish were moved to our lab tanks, then fed either an unlimited amount of food or a restricted diet to slow down their growth rates. In the spring we took samples of their gill membranes to test for the levels of enzymes indicating seawater readiness and gave the fish a ‘seawater challenge’ to directly test their tolerance of oceanic salinities. These data are now being analyzed to determine the role of the fathers in determining the life history pathway of their progeny.
We are deeply indebted to Dave Streig and all of the MBSTP volunteers for raising the fish through their early stages at the Kingfisher Flat Hatchery. Our research would not be possible without their invaluable dedication and long hours spent tending to the needs of thousands of baby fish.  We are extremely fortunate to have this amazing resource here in Santa Cruz county and are grateful for the continued benefits of our collaborations.
