Exploring the Contemporary Relationship between Predator and Prey in a Significant, Reintroduced Lahontan Cutthroat Trout Population

Abstract

Lahontan Cutthroat Trout (LCT) Oncorhynchus clarkii henshawi have experienced some of the most marked reductions in abundance and distribution among Cutthroat Trout subspecies. The population of LCT in Pyramid Lake, Nevada has returned from the brink of extirpation, and although it is highly managed via stocking, the population is thriving and has recently started to reproduce naturally. Our objectives were to determine (1) whether predator and prey remain tightly coupled, (2) whether LCT are food limited, and (3) the status of the LCT population with regard to the potential prey-based contemporary carrying capacity. We used a multifaceted approach, including intensive field sampling of fish, bioenergetics modeling, cohort reconstruction, and comparisons of prey availability to consumption. We estimated that the average population of LCT in Pyramid Lake is 1.2 million, average annual stocking is 650,000, and the number of fish angled ranges from 5,000 to 14,000 per year, with a 90% release rate. Driven by seasonal and size variation in consumption, individual annual consumption by LCT varied from 667 to 992 g/year for small LCT (200-400 mm TL) and from 2,388 to 3,057 g/year for large LCT (>400 mm TL). Lahontan Cutthroat Trout are consuming, on average, 14-63% of the standing crop of Tui Chub Siphateles bicolor annually, indicating that LCT are currently not exceeding their prey-based carrying capacity. The LCT in Pyramid Lake remain tightly coupled to their primary native prey, Tui Chub, despite considerable changes to the ecosystem; therefore, managing for a robust population of LCT translates largely to managing for forage fish. This supply-versus-demand issue is of particular concern for Pyramid Lake given that the density of Tui Chub may be declining concordant with declining lake elevation. Given the conservation importance of this LCT population, careful monitoring is critical; however, "predation inertia" indicates that effective short-term management in response to fluctuations in forage fishes is likely possible.

Informing Management of Henrys Lake, Idaho, using an IntegratedCatch‐at‐AgeModel

“…2020; Budy et al. 2021). Estimating recruitment using catch‐at‐age models for populations with natural recruitment can add considerable uncertainty to estimated parameters and predictions (Fournier and Archibald 1982; Maunder and Deriso 2003; Maunder and Piner 2015).…”

“…Moreover, we are unaware of any published integrated assessments for fisheries that are maintained or supplemented through juvenile fish stocking. However, collecting a time series of catch-at-age data from such fisheries is not uncommon (e.g., Parsons and Pereira 2001;Felts et al 2020;McDougall et al 2020;Budy et al 2021). Estimating recruitment using catch-atage models for populations with natural recruitment can add considerable uncertainty to estimated parameters and predictions (Fournier and Archibald 1982;Maunder and Deriso 2003;Maunder and Piner 2015).…”

Pelagic food web interactions in a large invaded ecosystem: Implications for reintroducing a native top predator

“…Studies evaluating potential limiting factors for and the trophic ecology of reintroduced lacustrine LCT emphasise the need to elucidate food web interactions (Al-Chokhachy et al, 2009;Budy et al, 2021;Heredia & Budy, 2018;Meeuwig & Peacock, 2017).…”

“…Studies evaluating potential limiting factors for and the trophic ecology of reintroduced lacustrine LCT emphasise the need to elucidate food web interactions (Al‐Chokhachy et al, 2009; Budy et al, 2021; Heredia & Budy, 2018; Meeuwig & Peacock, 2017). Investigations in Lake Tahoe have only characterised food web structure (Vander Zanden et al, 2003), not function, making it difficult to identify suitable paths forward for reintroduction.…”

Growth of Lahontan cutthroat trout from multiple sources re-introduced into Sagehen Creek, CA

“…These loses have complicated efforts to manage the species. Translocations and reintroductions remain the primary management tool for reversing Cutthroat Trout declines in their native range ( Harig, Fausch & Young, 2000 ; Budy et al, 2021 ). There are three cultivated strains (broodstocks) of Lahontan cutthroat trout available for reintroduction: Pilot Peak, Independence Lake, and a contemporary Pyramid Lake strain which is derived from Summit Lake.…”