Release of hatchery adult steelhead for angler opportunity increases potential for interactions with endemic steelhead

Abstract

Translocation is often used to increase local abundance of fish and wildlife populations for conservation or harvest purposes, and effects of releases on recipient populations are context dependent. Release of non-local animals intended for harvest can have negative demographic, genetic, and ecological risks to endemic populations when not harvested. In 2012-2014, we used radiotelemetry to monitor the fate and potential for interactions between non-local hatchery-origin adult summer-run steelhead Oncorhynchus mykiss (n = 423) and Endangered Species Act (ESA)-listed native winter-run steelhead (WRS) in two tributaries of the Willamette River, Oregon, USA. Summer steelhead were recycled-collected, translocated downstream, and released-to provide additional angler opportunity as a part of a regional mitigation program. Overall, reported harvest rate of recycled steelhead was low (15%) and a majority of individuals (62%) were last recorded in the release tributary. Furthermore, 14% of radio-tagged recycled steelhead were last detected outside the release tributary (i.e., strayed after release). Expanded estimates indicate the number of recycled summer-run steelhead remaining in the South Santiam River exceeded the WRS spawning population size. Low reported harvest and straying and demographic estimates indicate the recycling program may have negative effects on endemic WRS. Translocation and hatchery supplementation are likely to remain important conservation and mitigation tools in the future, though these results highlight the importance of post-release monitoring and considering both the risks and benefits of translocations to endemic populations and communities.

Introgressive hybridization between native and non‐local steelhead (Oncorhynchus mykiss) of hatchery origin

“…The continued and frequent introduction of non‐native or non‐local populations results in high propagule pressure that artificially increases the abundance and density of the non‐local, hatchery individuals (Lockwood et al, ; Simberloff, ), and counters the effects of reduced fitness of the hatchery fish in natural environments. In the upper Willamette Basin, the hatchery summer steelhead in the basin outnumber the native winter steelhead preceding reproduction (Erdman, Caudill, Naughton, & Jepson, ). Introgression was detected in 26.4%, and F 1 hybrids were detected in 4.9–10.1%, of the natural‐origin samples.…”

“…In addition, fisheries management in the local basin has included the practice of ‘re‐cycling’ hatchery, summer steelhead to maximize angler opportunity (trapping, transporting, and re‐releasing adult hatchery steelhead downstream). However, although this programme boosts angler harvest by an estimated 15%, it is also likely to increase the reproductive interactions between hatchery and wild steelhead, by leaving many mature, hatchery steelhead in the river (Erdman et al, ).…”