Restoring habitat would seem like a simple process; dump some gravel, add a little water, and watch the salmon populations rebound.
Restoration of degraded habitat is generally considered to be a no-brainer. But, what if by “restoring” the habitat, you inadvertently create a habitat that causes either the target species or other important non-target species to spiral towards extinction—that is, a place that looks good on the surface, but actually leads to poor outcomes for the population? In riverine ecosystems, habitats are generally created through physical processes such as flooding and sediment transport. Over time, fish have evolved the ability to adapt and thrive in the habitat that these processes create. Human changes to river systems often disrupt underlying processes that created natural habitat, and can result in the elimination or degradation of such habitat. When we try to mimic these habitats on the surface with restoration, but without the associated underlying processes, we can create an ecological trap that worsens the problem.
The California Water Blog describes a very real trap on the Shast Valley’s Scott River, where coho salmon — whose smolts spend upwards of 1.5 years in freshwater before migrating to the ocean — are lured to spawn in the canyon section of the river, which (apparently) contains good spawning habitat.
Later in the summer and fall, the coho smolts have no place to go as flows decline (often diverted upstream by irrigators) and water temperatures rise; upstream access is blocked and migrating to the Klamath River isn’t an option due to water that has been warmed and degraded by the Klamath River dams.
The solution? One-dimensional fixes aren’t effective; you have to address all the issues, including water quality, quantity and habitat — across all seasons.
To read more about ecological traps, read the California Water Blog post here.