Research Document - 2009/067
Scientific information in support of a Recovery Potential Assessment for the salish sucker (Catostomus sp.) in Canada
By B. Harvey
Abstract
This Recovery Potential Assessment provides technical advice to the Minister of Fisheries and Oceans concerning the amount of allowable harm to Salish sucker Catostomus sp., which is listed as Endangered (Schedule 1) under the Species at Risk Act (SARA).
The suckers are a large freshwater family of fish that includes the widely distributed longnose sucker Catostomus catostomus. Salish sucker is a divergent form of longnose sucker found in western Washington and the lower Fraser Valley, B.C. It is genetically distinct but not yet recognized as a separate species. Salish sucker have been extirpated from at least one watershed in the Fraser Valley (Little Campbell River), and are presently confined to ten others. In these rivers, its distribution is concentrated within a few reaches. Most home ranges are small.
Small, short-lived and early-maturing, Salish sucker have an opportunistic life history that may facilitate population recovery if disturbances are short-term and confined to small areas. Salish sucker are most commonly found in marshes and beaver ponds where water is deeper than 70 cm. They require deep water with access to spawning riffles and shallower nursery habitat. Potential critical habitat is defined for all reaches currently containing populations of Salish sucker as reaches with more than 50 m of continuous pool that is deeper than 70 cm at low flow. Critical habitat includes riparian reserve strips on both river banks. Most of the potential critical habitat has been mapped and presently includes 141.5 km of surveyed channel (approximately 50% of the total surveyed).
Based on limited data to 2004, estimated mean abundances were well below the minimum viable population sizes commonly accepted as a ‘rule of thumb’ for vertebrates when abundance data are weak. If all potential critical habitat were occupied at a density of .05 fish/m2, the estimated carrying capacity ranges between 800 and 7,000 fish per stream, also below the accepted vertebrate minimum. This is a strong argument for preserving as much critical habitat as possible.
The main cause of human-induced harm is agricultural and urban development in the Fraser Valley. Hypoxia, which can result mainly from pollution by agricultural fertilizers and manure, is the most serious threat. Habitat loss, fragmentation and degradation lead to sedimentation and isolation of sub-populations.
A Nutrient Management Planning Strategy developed by government agencies and agricultural producers identifies strategies whereby farms can achieve an acceptable nutrient balance and reduce the risk of hypoxia in Salish sucker habitat. Reducing habitat destruction and fragmentation can be achieved using existing regulatory mechanisms to develop reach-specific best management practices, as well as through restoration of damaged habitat. Public awareness materials and a participatory approach will be crucial. Minimum instream flow prescriptions should also be developed, and the licensing of groundwater withdrawal considered.
The opportunity exists to eliminate harmful activities in sections of the watersheds where critical habitat is damaged. Portions of actively farmed riparian land could be removed from production. A model is the Conservation Reserve Enhancement Program (CREP), a land retirement program administered by the United States Department of Agriculture. In Canada, similar objectives can be achieved through land trusts, some of which operate in a way analogous to CREP. The BC Environmental Farm Plan initiative also offers some immediate opportunities for protecting fish habitat.
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