Steelhead spawn timing: Why care?December 10, 2016
Not only does a loss of early timed wild winter steelhead limit our fishing opportunity it can also reduce the resilience of our steelhead populations. Spawning early is risky business as it takes place during the window of peak Northwest winter runoff when redds could be scoured, but let’s not forget that coho make a living doing the same thing – largely by spawning in smaller streams, which is also what early-timed steelhead appear to do. So while it is risky, there are some advantages. First, early freshwater entry allows more time for returning adults to reach portions of the watershed that later timed fish are unable to reach when flows are lower, thereby increasing their spatial distribution within a watershed. Second, fry that emerge from the gravel at an earlier date have more time to grow and essentially have a head start on later emerging fish. More growing time leads to a greater body size and it has been shown that larger smolts survive at higher rates than smaller counterparts. Hence, not only does spawn timing spread steelhead out in space it spreads them out in time. This helps spread risk of negative influences, such as landslides and floods, which in turn, increases the resilience of the population. This is important because models predict warmer summer stream temperatures and an earlier onset of summer for the Northwest over the coming century, in many cases resulting in less hospitable conditions for late emerging fry. As temperature and flow regimes change over the next few decades early spawning fish are likely to become more important as their particular life history strategy is disproportionately favored. Managing our fisheries to protect the breadth of spawn timing and the overall diversity of steelhead should therefore improve the abundance and capacity of wild populations, in turn creating better fishing.