South Sound Science: Mysterious Pre-spawn Mortality of Coho Salmon in Urbanized Streams

Blake Feist of the NOAA/Northwest Fisheries Science Center on:

New predictive, spatially explicit model of coho pre-spawn mortality rates for the eastern Puget Sound basin.

Notes from his talk:

Over the past 10 years, people have been seeing coho salmon dying before they spawn. Sometimes within hours of returning to the streams.

What is causing the prespawn mortality?

Car exhaust? There are a lot of chemicals (lead, benzine, etc) coming from cars and car exhausts.

In Longfellow Creek, there seems to be a correlation between rain and prespawn mortality. There is something being washed out by the rain that is killing the fish.

The purpose of the study was to create a pre-spawn mortality model to predict the phenomena.

The study focused on largely urbanized creeks, the least urbanized (and reference creek) was Fortson Creek. Forston had a .9 percent pre-spawn mortality.

The study looked at variable such as traffic flow, road types, tree cover.

There is a relationship between heavily used roads and pre-spawn deaths of coho salmon.

Questions and Answers:

Why aren’t all the fish dying in the stream?

Chum and chinook are not impacted. Even coho smolts are not impacted. Don’t know why.

Was there pre-spawn mortality more than 10 years ago?

It was likely that it was going on longer.