Surviving Puget Sound:
One of the best parts of my job is sharing scientific research with anglers, who seem to have an almost insatiable appetite for understanding steelhead. Sharing information is important not only to help anglers understand steelhead, but also because more informed anglers make better advocates. Wild steelhead will need as many advocates as possible if we are to sustain them and their fisheries over the coming decades.
So here is the first of two blog posts I’m writing on recent steelhead studies that illuminate significant management challenges.
Juvenile Steelhead Mortality and its Likely Causes in Puget Sound
Megan Moore, a NOAA scientist, and several co-authors published a study last October that examined steelhead smolt survival and migration in Puget Sound. Marine survival has been a big problem for wild and hatchery steelhead migrating through the Sound, particularly for fish coming out of the South Sound. They tagged wild and hatchery smolts from 2006-2009 from a number of rivers across Puget Sound.
They found three major results. First, only a relatively small proportion of smolts made it out of Puget Sound, and as expected, wild smolts (16%) survived at higher rates than hatchery smolts (11.4%). Second, survival between populations was highly variable, with the lowest survival being 0.8% for the Skokomish hatchery in 2009 while the highest was 39.3% for Big Beef Creek wild fish in 2006
Last, but certainly not least, survival rates for wild fish dropped drastically when large-scale hatchery releases occurred in early-May. The author’s posit that the large releases of hatchery smolts may cause increased mortality because of the predator’s they attract. This phenomenon has also been observed with coho salmon on the Oregon Coast.
See the paper at: http://www.int-res.com/articles/meps_oa/m537p217.pdf
Implications for Steelhead Management
The primary management-relevant messages to take away from the Moore et al paper are: (1) because predation appears to be a major problem for juvenile steelhead soon after they hit the salt – and particularly in the Skagit and Green rivers — strategies are needed to reduce predation levels; and (2) because large releases of hatchery steelhead (and coho) smolts in short periods of time coincide with substantially lower wild steelhead smolt survival in Puget Sound, changes to hatchery operations that could reduce this harmful effect should be tested.
Based on my observations over the past decades, I am not surprised that the lowest survival of wild smolts coincides with the release of large numbers of hatchery fish. River mouths are transitional areas where predators can maximize their feeding opportunity because all migrating fish must travel through a relatively small area. But, each species has evolved slightly different behaviors to help make it through those gauntlets. For example, pink and chum – which produce very small sized smolts — rely heavily on abundance to swamp predators. Out of those millions of smolts, many die, but enough make it to ensure the next generation
Wild steelhead fall on the other end of the spectrum. They are large in size and strong swimmers, and having survived years in freshwater, they are skilled at avoiding predators. As a result, they are less reliant upon mass schooling behavior. Compared to salmon, they essentially sneak out using the same type of diversity that they are famous for. For instance, smolt ages are highly variable and entry into the salt is spread over a broader period, including some fish that smolt in fall. Their diversity in smolt age and ocean entry is a function of the freshwater habitats they reared in.
In contrast, hatchery steelhead are often raised in much the same way as salmon – produced in large numbers and released at the same time. In addition, hatchery steelhead are not skilled at avoiding predators. So, to a predator, capturing a wild fish is analogous to hitting a 90 mph fastball; capturing hatchery smolts is more akin to a slow-pitched softball over the heart of the plate.
It should be no surprise, then, that large releases of hatchery steelhead and coho correlate with low wild steelhead smolt survival. In effect, the hatchery fish “blow the cover” of wild smolts and disrupt their avoidance strategy. In other words, they turn wild fish into slow-pitched softballs, too.
So we need to experiment with strategies to address this problem, and there really are just three. First, eliminate or substantially reduce the size of hatchery releases. Second, use a “trickle out” approach to hatchery releases that more closely mimics the outmigration of wild fish. Third, attempt to reduce the abundance of predators in the estuaries. The first two are likely much easier to implement than the third.
Steelhead Scientist Director