Preliminary Report: Stream Crossings and Arctic Grayling Conservation in the Athabasca River Basin
Laura MacPherson and Troy Furukawa
The ability to accurately estimate fish abundance allows fishery biologists and managers to monitor fish populations and formulate management strategies. Reliable fish population estimates are particularly important for species at risk, such as Arctic Grayling (Thymallus arcticus), where a lack of population information could result in inappropriately assigned management decisions. Given severe declines in Alberta Arctic Grayling populations, accurate population information is critical for fisheries managers.
In our study of the wadeable tributary streams of the Athabasca River, we evaluated the overall field efficiency of egg kick surveys, angling and electrofishing methods in estimating Arctic Grayling populations. We assessed how stream characteristics and temporal variability influenced Arctic Grayling catch rates, and compared population estimates derived from mark-recapture and three-pass removal methods. In turn, this allowed us to estimate capture probability (q) for small young-of-year (≤110 mm) and large (>110 mm) Arctic Grayling using angling and electrofishing. Lastly, we evaluated habitat fragmentation at stream crossing sites (road bridges and culverts), and at a larger sub-basin scale. Geographic Information System (GIS) analysis was used to assess sub-basin characteristics.
Our results indicate that angling and electrofishing should be used together in order to capture all Arctic Grayling size classes. In addition, unless water conductivities exceed 300 μS/cm, electrofishing should occur later in the summer (July 16 - August 31) when catch rates are highest. Similarly, angling catch rates were highest in the late summer. A small sample size and low recapture of Arctic Grayling precluded us from drawing any definite conclusions about the accuracy of mark-recapture and three-pass removal abundance estimates. We were however, able to determine capture probability (q) by gear type and fish size class.
Given our findings, we created a sampling flow diagram for common fisheries management objectives. We found no evidence that Arctic Grayling populations were fragmented at stream crossing sites or at a sub-basin scale. Despite this, we believe Arctic Grayling populations are likely already too severely impacted by cumulative anthropogenic impacts, including road culverts, such that these relationships were no longer easily discernible.