When sea lions go bad: “native invaders” divide loyalties

California sea lion at Bonneville fish ladder. Photo credit :National Oceanic and Atmospheric Administration.

By: Lauren Kuehne, Olden Research Lab, University of Washington

As an early career ecologist, I could easily spend all my time (and even time I don’t have) writing my own “stuff”: grant proposals, manuscripts, blog posts. But taking the time to review and write about the work of other researchers in my field (especially a paper I don’t necessarily agree with or would not have read otherwise), is rewarding in a very different way, forcing me to really get inside a different perspective. So when I was recently asked to blog about a new paper from a colleague on a somewhat controversial topic of “Native Invaders”, I jumped at the chance.

The new review article, which appeared in the September issue of Frontiers of Ecology and the Environment, has the ear-catching title of “Native Invaders – challenges for science, management, policy, and society”. Departing from the more typical line of documenting the ills of invasive species, the article instead describes the challenges and heartbreaks when native species run amok in the sense of having negative ecological impacts we typically associate with non-native species.  Examples in the paper range from unchecked expansions of juniper trees in sagebrush ecosystems with wildfire suppression to overgrazing by elk released from predation by removal of wolves and mountain lion.

Juniper encroachment in sagelands. Photo credit: M.M.Rowland, USDA Forest Service.

I didn’t love this paper at first, thinking that the concept seemed…well, gimmicky. But as I read into it, I saw that the one of major points the authors (ie, my colleagues) make is that these “native invaders” usually rear their ugly heads in response to some kind of human-mediated environmental change. This means that unless the environmental change is addressed or reversed, the problems are likely to persist. Further, their very status as natives means these nuisance species are prone to being a public relations and public education quagmire.

Caspian terns with juvenile salmon. Photo credit: Tom Good, National Oceanic and Atmospheric Administration.

Since the authors call the Pacific Northwest home, the paper illustrates the cycle of environmental change to persistent management dilemma by focusing on four native species which negatively interact with endangered Pacific salmon: Caspian terns, rainbow trout, northern pikeminnow, and marine mammals (i.e., sea lions and seals).  For the terns and pikeminnow, the hydropower corridor of 14 major dams on the Columbia River has created congregations of juvenile salmon prey migrating to sea. As a result, terns have gradually shifted their historically small and scattered colonies to artificial (and largely predator-free) islands near dams, while pikeminnow populations artificially expanded around inflated food supplies. The juvenile salmon that survive their ocean time to adulthood run a return gauntlet of seals and sea lions, which will swim nearly 240 km (150 miles) upriver to take advantage of the buffet the base of fish ladders.

Laugh-out-loud moments

I don’t usually find myself laughing out loud over a journal article, but the ensuing tangle of mitigation, litigation, and public opinion in managing native invaders can border the ridiculous – and that’s leaving out the (spoiler alert!) elk contraception program in use at Rocky Mountain National Park. A favorite section describes attempts over the years to deter sea lions from fish ladders with physical barriers, acoustic deterrents (eg underwater percussion devices), above-water pyrotechnics, harassment (eg boat chasing, rubber bullets), and relocation.” At first read I wondered if this was an attempt to lure teenagers into scientific careers, but alas, comedy is often based on real tragedy – and aside from a good deal of uncertainty as to whether these kinds of measures actually help, they can be confusing for the public at best and wildly unpopular at worst. In the case of the sea lions, an eventual lethal removal decision was challenged and reversed in court, highlighting the particular management challenge of needing to communicate the ecological nuances of native invaders. The public message of “Yes, they are native, but aren’t doing any good here and in these numbers” is complex to convey, and may get garbled after passing through a few news outlets. And yet, the alternative practice of categorizing “native = good” and “non-native = bad”, as opposed to understanding and managing ecological impacts, means we might (literally) be missing the sagebrush forest for the juniper trees.

One thing I really liked about this work is that the paper outlines some tangible strategies to address native invaders. Raising awareness of ecological impacts of native invaders will help, of course. Another strategy includes planning for and managing impacts through endangered species recovery plans (as was successfully done to stop raccoons in the southeastern U.S. from gobbling up loggerhead turtle eggs and babies). Above all, anticipating public reactions, and acknowledging that societal values will not always be aligned with conservation needs will go a long way to developing a more comprehensive view and management approaches for native invaders.

You can link to the Frontiers in Ecology and the Environment article here

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2 thoughts on “When sea lions go bad: “native invaders” divide loyalties

  1. Thank you for this interesting post. Although i don’t necessarily think “invader” is a good term for describing responses from native species to human actions, the problem is actual and “native invader” is a better term than no term at all.

    Then some more technical feedback: it would really help readers from the other side of the Atlantic to follow these posts if the scientific names for species were also mentioned.

  2. This idea of ‘native invaders’ is likely to become an increasing issue as climate change shifts communities around. Attempting to restore a community that was ‘native’ to a certain place may not be feasible as the species that were there can no longer physically tolerate the new climate, rendering restoration efforts a waste of time. You make an important point here, that it is going to take a lot of work to shift public opinion and policy away from managing what we are historically used to towards letting new shifts in ecological relationships guide management. It’s a fine line between knowing when to restore a system that IS salvageable and knowing when to let nature transition to a new steady/dynamic equilibrium state.

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