Research Document - 2007/039
Recovery potential assessment of the Cultus Pygmy Sculpin (Cottus sp.)
By Harvey, B.
Abstract
Cultus pygmy sculpin is a landlocked form of the coast-range sculpin Cottus aleuticus. The coast-range sculpin is common in lakes and rivers along most of the Pacific coast of North America; within Cultus Lake, however, the species is mostly represented by the pygmy form. That unique population is listed as Threatened in Schedule 1 of SARA, mainly because it is an extreme endemic; that is, it occurs in only one location that is not connected to other suitable locations. A Proposed Recovery Strategy for Cultus Pygmy Sculpin, prepared prior to the present Recovery Potential Assessment (RPA), details recovery objectives and approaches to meeting them.
We know almost nothing about the natural history of the Cultus pygmy sculpin, the habitat requirements of its different life stages (and which habitats may be limiting), causes of mortality, or environmental factors that affect abundance. For this reason, the present RPA can only provide the ’best advice with the information available,’ while noting the many information gaps. An absolute risk analysis is currently impossible.
The Cultus pygmy sculpin is believed to occupy the greater part of Cultus Lake from surface to bottom, excluding only a poorly defined littoral (shoreline) fringe where it has not so far been observed. Critical habitat for Cultus pygmy sculpin is provisionally described as synonymous with its known distribution (which may change as we learn more). Listing of the Cultus pygmy sculpin is not based on any significant trend in the number of individuals because there are not enough data to show whether there is such a trend, nor are there enough data to estimate the current population size. Until a directed enumeration program for Cultus pygmy sculpin is mounted, the recovery target must remain ’a healthy, self-sustaining population;’ the distribution target should be ’to maintain its current distribution in limnetic, and possibly benthic, areas of the lake and inlet streams.’
Because the designation of critical habitat for the Cultus pygmy sculpin as “synonymous with the known distribution” is a provisional one, it is presently impossible to say whether critical habitat or ecosystem relationships in the lake limit the population’s long term viability. The primary human-caused threat to Cultus pygmy sculpin is the potential introduction of exotic fish species, which could increase predation, introduce diseases, or cause changes in habitat and food supply that are detrimental to survival. The precautionary way to reduce this risk is to mount and continue an awareness campaign including signage, brochures, advertisements, insertions in school curricula and spot inspections. Incidental capture of sculpin in midwater trawls for juvenile sockeye enumeration is an allowable harm.
For a species like Cultus pygmy sculpin, where so little is known of basic biology, habitat use and abundance, identifying alternatives to human activities that cause harm to it or to its critical habitat is an exercise in common sense. No quantitative predictions can be made; these have to await mathematical models based on real-life abundance data. A population viability analysis for Cultus pygmy sculpin is presently impossible because of the lack of data on abundance, habitat use and recruitment. Midwater trawls and hydroacoustic surveys presently used to enumerate juvenile sockeye could be modified to count Cultus pygmy sculpin and thus provide some quantitative basis for a model.
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