Research Document - 2009/056

Identification of Critical Habitat for Sympatric Stickleback Species Pairs and the Misty Lake Parapatric Stickleback Species Pair

By Todd Hatfield

Abstract

In this paper recommendations are provided for defining critical habitat for stickleback species pairs in British Columbia, based on a weight of evidence approach. Recommendations are made for the proportion of existing habitat that can be considered critical, but no effort has yet gone into delineating specific areas in the wild. Critical habitat recommendations were developed using the framework suggested in Rosenfeld and Hatfield (2006). Population targets are explored and supported using multiple approaches, including simple population viability analyses, rules of thumb, and genetic considerations. Simple population viability analyses indicate that stickleback are resilient to environmental stochasticity even when populations are at low abundance. I used two quasi-extinction thresholds, based on environmental and genetic considerations.  Population models could be improved considerably with additional information on stickleback vital rates, but population-specific data are unlikely to be available soon. Habitat required to meet proposed population targets varied from 5% to 100% of existing habitat depending on the modeling approach.

There are two key components of habitat for benthic-limnetic and lake-stream species pairs: 1) habitat features that control the abundance of limnetics and benthics (i.e., population size), and 2) features of the environment that ensure proper mate recognition and assortative mating. Therefore, habitat needs for species pairs include features whose alteration or loss will lead to reduction in abundance to an unviable population level, or breakdown of reproductive barriers sufficient to cause collapse into a hybrid swarm. These habitat features are reviewed briefly here.

Most defensible approaches indicate that a considerable portion of existing habitat is critical, and the dependence of species pair co-existence on reproductive isolation indicates that the habitat attributes required for persistence must be maintained at the ecosystem scale, i.e. that in each case the entire lake plus a riparian buffer should be designated as critical habitat. Recommended critical habitat for benthic-limnetic pairs includes the entire lake for each pair and a riparian buffer of 15 to 30 m width surrounding the wetted perimeter of each species pair lake and all ephemeral and perennial streams flowing into the lakes.

Recommended critical habitat for the Misty Lake pair includes the entire lake, the wetted area of the entire inlet stream, and the wetted area of the outlet stream as far downstream as the lower limit of currently occupied habitat (presently estimated at 2.3 km downstream of the lake). Also included as critical for the Misty Pair is a riparian buffer of 15 to 30 m width on the lake and both inlet and outlet streams, plus any perennial or ephemeral tributaries.

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