Swan River Arctic Grayling and Watercourse Assessment
Brad Hurkett and Logan Redman
The Swan River Arctic grayling population has decreased drastically because of habitat fragmentation and degradation from extensive road networks and high densities of stream crossings associated with industrial development in the watershed. In 2002, Alberta Conservation Association conducted a stream-crossing inventory that identified 195 culvert crossings, of which approximately 70% were fish barriers. In 2015, we reassessed the status of Arctic grayling and stream crossings in the watershed to generate data to support the development of the provincial Arctic grayling Fish Sustainability Index (FSI) and regulatory plans to remediate the effects of industrial activities on Arctic grayling in the watershed. We collected data on the distribution, relative abundance and population structure of Arctic grayling (≥150 mm fork length; FL) and on the level of
fragmentation in the watershed associated with stream crossings.
Stream crossings were assessed using the Alberta government’s Watercourse Crossing Inspection Protocol, focusing on three main fish passage and habitat components, including erosion and sedimentation, culvert placement and condition, and outlet gap height and outfall pool depth. We sampled fish by angling, which aligns with the Arctic grayling FSI sampling protocol. The information collected from crossing assessments permitted us to identify fish barriers and consequently determine the degree of fragmented habitat in the Swan River watershed.
From June 28 to July 31, 2015, we assessed 218 stream crossings in the Swan River watershed, of which 195 crossings were previously assessed in 2002. A total of 66 (30%) crossings were dry, likely due to the historically low stream flows that occurred in 2015; 10 additional sites were ephemeral and non-fluvial. Of the remaining 142 fluvial sites, 131 crossings were impassable to fish; only 11 (8%) stream crossings permitted fish passage. Approximately 737 km of stream (25% of the total stream length in the Swan River watershed) have been fragmented due to damage or poorly installed crossing structures, predominantly in low-order streams.
We completed fish sampling (angling) at 62 sites and sampled a total of 31 km of stream between July and August 2016. We did not observe grayling at 17 sites, 5 of which were located upstream of fish barriers. Most grayling were captured in order-4 streams; most sites where grayling were not observed were in order-3 streams. We captured a total of 431 Arctic grayling, ranging in length between 67 and 315 mm FL, only 6 of which were adult fish (≥283 mm FL). Catch rates for immature grayling (150 – 282 mm FL) ranged between 0 and 13.5 fish/h and averaged (± SE) 1.48 ± 0.31 fish/h (n = 274); catch rates for adult grayling ranged between 0 and 1 fish and averaged 0.03 ± 0.02 fish/h (n = 6). Catches of immature grayling were highest in order-4 and -5 streams and lowest in order-3 and -6 streams; the few adults were only captured in order-5 and -6 streams.