Recovery initiatives under Canada's Species at Risk Act contribute to a better understanding of geographic distribution and diversity within the Endangered Nooksack dace (Rhinichthys cataractae)

The Nooksack dace and the Columbia form of the longnose dace are genetically and morphologically distinct forms of Rhinichthys cataractae (Valenciennes, 1842)) that come into contact in several areas of the lower Fraser River valley, southwestern British Columbia. The Nooksack dace is listed as Endangered under Canada’s Species at Risk Act owing to habitat degradation within its small geographical range. We report on recovery motivated surveys that report new records of Nooksack dace and Columbia form R. cataractae in the Chilliwack River/Lake system draining into the south side of the Fraser River, but only Columbia form dace in the Chehalis River/Lake system or in Harrison Lake which both drain to the north side. In the Chehalis and Chilliwack drainages, dace occupied lake and stream habitats and we found some morphological differences between lake and stream fish. Although lake fish were shallower and more narrowly-bodied with shorter pectoral fins than stream fish, the only significant effect was attributable to differences between watersheds. Our results extend the known distribution of Nooksack dace both in area and number of locations which may necessitate revision of quantitative criteria related to their conservation status. Our results also provide a further example of potentially functionally significant morphological specialization in stream and lake-dwelling fishes.