Because Clark County has the BEST teachers a Salmon in the Classroom program could hope for, we had a couple questions about whether our salmon would survive the high run-off conditions in our streams and rivers. It’s been RAINY. I released some fish yesterday for Illahee Elementary, and the water was chocolate brown from all the rain…
I also recently read an article about spawning Coho dying because of urban stormwater runoff in the Seattle area: (http://www.seattletimes.com/seattle-news/environment/whats-killing-coho-study-points-to-urban-road-runoff/)
Nooooo!!! I can’t release my precious baby salmon into brown, dirty stormwater! I want them to liiiivve! If you had similar thoughts during your fish release this fall, don’t despair just yet!
Here are a few questions I sent to John Allen, Fish Hatchery Specialist 4:
Since Coho spawn in the fall/winter, I imagine the hatchlings often deal with problems caused by heavy rains and runoff. Any idea about how resilient they are to this type of thing?
Fish have been around for a long time. That should answer the question of resiliency! High flows and turbidity are good for juvenile salmon and steelhead to an extent. The increased flows bring more oxygen into the river system and turbidity allows cover from predators. With flows increased, this should allow the juveniles a better opportunity to out migrate to the Col. River estuary.
I’ve heard that Chum salmon will wait to migrate into the rivers if the water temperatures are too warm. Would Coho migrate into the ocean early, if conditions in the river were not great?
I wouldn’t think the Coho would go to the ocean earlier than normal because of high water.
In times of heavy rain, which parameter is the biggest threat to salmon: increased flow, increased turbidity, chemical runoff, or something else?
I’ve not heard of any storm water issues in S.W. Washington before, only in the greater Seattle area with regard to toxin levels. High toxicity levels are usually a problem during the first good flushing rain that washes the heavy metals into the smaller streams (mostly brake dust from vehicles). Increased flow in a small stream is a good thing for fish trying to find their place in the world!
Jim Byrne, Area Fish Biologist, also shared this with me:
Rain and heavy rain volumes typically do not pose problems for juvenile fish that have buttoned up. They will hide in the gravel, or in side channel low- flow areas until the high water passes. However, alevin are totally dependent on stream flows. They can either get buried by high sediments or have the gravel and eggs scour out downstream. Eggs in the gravel are very delicate, and any jarring can negatively affect their development. Also, in very high flow events with erosion high turbidity can irritate fish’s gills. Fish will locate to lower turbidity areas when possible. Chemicals can and will disrupt the fish’s physiology.
All salmonids will wait rather than swim into too warm waters. We have concentrations of mid- and upper Columbia River salmon staying in the cool water pools at the mouth of tributaries; while the mainstem Columbia is warm. They use the tributary mouths as cold water refugia. Eventually as their eggs become fully developed, they will have to spawn somewhere. Coho juveniles in their local stream would migrate early if that stream gets too hot. They have no idea though, of what water temperatures are at the estuary. They will attempt to find cooler water. They cannot move into sea-water until they have smolted and are physiologically able to make the transition to marine waters.
Thanks to genetics and survival of the fittest, fish in streams should have evolved to meet the historical stream hydrology of their natal stream. Rivers that have early high flow events should have fish that return to spawn, in most years, after those flow events have occurred. Their timing is based on the rivers historical flow regime. Fish that spawn too early or too late don’t survive. One shouldn’t take an early spawning fish stock and plant it in a river with late high flow, erosional events. The right stock in the right river are resistant to high flow events. That is why we still have naturally produced fish (progeny of wild or hatchery parents) still residing in our local river systems.