Calculating and Increasing Portfolio Diversity for Native Trout Conservation

Management strategies that increase biological diversity and promote varied

approaches to population protection are more likely to succeed during a future where global

warming drives rapid environmental change and increases uncertainty of future conditions. We

describe how the concept of a diverse management portfolio can be applied to native trout

conservation by increasing Representation (protecting/restoring diversity), Resilience (having

sufficiently large populations and intact habitats to facilitate recovery from rapid environmental

change), and Redundancy (saving enough different populations so that some can be lost without

jeopardizing the species). Saving diversity for native trout requires the conservation of

genetically pure populations, the protection and restoration of life history diversity, and the

protection of populations across the historical range. Protecting larger, stronghold populations is

important because such populations will have a better chance of surviving future disturbances,

including those associated with climate change. The long-term persistence of populations is

likely to require management for larger population sizes and habitat patches than currently exist

for many native trout populations. Redundancy among these elements is important given that

many populations are small, occupy reduced habitat in fragmented stream systems, and therefore

are increasingly vulnerable to extirpation. Application of the concept is further described in case

studies of Yellowstone cutthroat trout Oncorhynchus clarkii bouvieri and Rio Grande cutthroat

trout O. c. virginalis, two subspecies that illustrate many of the management challenges common

to western native trout.