Stickleback species pairs final recovery strategy: chapter 1

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Executive Summary

The fish known collectively as "stickleback species pairs" are small, freshwater fish descended from the marine threespine stickleback (Gasterosteus aculeatus). Their recent and unique evolutionary history has been of considerable scientific interest and value. Stickleback species pairs were known to exist in four watersheds in the Georgia Basin, British Columbia: two watersheds on Texada Island, and one each on Lasqueti and Vancouver Islands. Within the last decade the species pair on Lasqueti Island has been declared extinct, and the species pair in Enos Lake has collapsed into a single hybrid swarm. The present global range is therefore restricted to four small lakes in two watersheds on northern Texada Island.

The stickleback species pairs each consist of a separate benthic and limnetic form. The species pairs spawn in littoral areas in the spring, rear in littoral and pelagic areas in spring and summer, and overwinter in deep water habitats during the fall and winter. The lakes in which stickleback species pairs developed have abundant and productive littoral and pelagic habitat, and a simple fish community comprised only of stickleback and cutthroat trout. Specific environmental conditions required to maintain abundance and reproductive isolation of limnetic and benthic species include water quality, light transmission, nutrients, littoral habitat, and macrophytes.

The greatest known threats to stickleback species pairs are introductions of exotic species, and impacts from water management and land use. Immediate recovery efforts should focus on controlling and minimizing risks from these threats.

Defining critical habitat of stickleback species pairs is an important action required to meet the recovery objectives, and to help place acceptable bounds on activities that impact the species. Critical habitat will be a collection of environmental 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. Some proposed features of critical habitat are described in this recovery strategy.  A series of research tasks to help identify critical habitat are also laid out in the strategy.

The goal of the recovery strategy is to secure the long-term persistence of all remaining populations of stickleback species pairs. Recovery objectives include the maintenance of species pairs in Paxton Lake and the Vananda Creek watershed, recovery of the Enos Lake species pair, and re-establishment of a species pair in Hadley Lake. Strategies to achieve the recovery goal and objectives fall into three broad, complementary categories: stewardship, protection, and research. These strategies along with their associated actions, performance measures, and relative priority are outlined in detail in this recovery strategy.

Recovery of stickleback species pairs is deemed to be technically and biologically feasible, although they are likely to always be at some risk due to their naturally restricted distribution. Information gaps to be filled are related to species pairs biology, threats, recovery techniques, and the effectiveness of stewardship.