Status and Distribution of Arctic Grayling in the Pembina River, Alberta
Mike Blackburn and Craig F. Johnson
The Pembina River sub-basin, found in the Athabasca River Drainage, supports the most southern, naturally occurring population of Arctic grayling in Alberta. Prior to the 1970's, Arctic grayling were considered common throughout the mid to upper reaches of the Pembina River mainstem. However, since that time, surveys on the Pembina River mainstem suggest low numbers of this species. Consequently, the Alberta Conservation Association, in collaboration with the Alberta Sustainable Resource Development, conducted a study during the open water seasons of 2002 and 2003 to assess the present status and distribution of Arctic grayling in the Pembina River.
The proposed study area included the Pembina River mainstem from the Lovett River confluence downstream to the Paddle River. After preliminary sampling in 2002, the study area was redefined in 2003 to include the Pembina River mainstem from the mouth of the Lovett River downstream to the Highway 16 river crossing at Evansburg.
Species distribution, relative abundance, and population structure data were collected using float electrofishing, angling, and snorkelling. Quantitative habitat data were also collected including: wetted river widths, rooted river widths, and water temperature data collected continuously through time from several locations in the study area. All fish and habitat data were entered into Alberta Sustainable Resource Development’s provincial fisheries database: the Fisheries Management Information System.
Over the two years, a total (combined float electrofishing, angling, and snorkelling) of 2817 fish were captured or observed in the Pembina River. Arctic grayling were rare, accounting for less than 2.5% of the recorded total. Forty-six Arctic grayling were captured in 52.8 km and 591.7 minutes of electrofishing and 22.7 km and 56.5 hours of angling. An additional 22 Arctic grayling were observed during four snorkelling events for a total of 68 grayling. Arctic grayling float electrofishing and angling catch rates from the Pembina River were considerably lower than reported for other Alberta rivers. Angling accounted for 42 of the 46 Arctic grayling which were caught near a road access; 33 of the 42 angling captures were from one pool immediately downstream of a bridge crossing.
The mean fork length of Arctic grayling captured was 213 mm (range = 115 - 339 mm). Ninety-five percent of the captured Arctic grayling were juveniles of either 1 or 2 years of age.
Sampling was initiated during the spring and summer of 2002. Extremely low water conditions during both 2002 and 2003 prevented spring, summer, and fall re-sampling of the float electrofishing sites. Although grayling were captured upstream from the confluence with Paddy Creek only, we were unable to describe Arctic grayling seasonal distribution.
Low numbers of Arctic grayling captured or observed in two years of sampling, low electrofishing and angling catch rates, and a limited river distribution, suggests that Arctic grayling stocks in the Pembina River are probably collapsed.