Stocked Trout Survival and Camera-based Angler Survey at Selected ACA Stocked Ponds
Kevin Fitzsimmons and Britt Keeling
The Enhanced Fish Stocking (EFS) project creates recreational fisheries in areas of the province where such opportunities do not otherwise exist. Through EFS, we stock approximately 120,000 catchable-sized (i.e., 20 cm) trout into 60 ponds each year, creating “put-and-take fisheries” that allow anglers to harvest up to five fish per day. Most EFS ponds are situated close to urban centres, making them popular family destinations. However, recent evidence suggests some of these ponds may not be capable of supporting trout survival beyond mid-summer. Our data suggest that poor water quality, particularly high temperature and low dissolved oxygen (DO), and avian predation may be key contributing factors. During the summer of 2014, we assessed 12 representative EFS ponds to estimate survival of stocked trout and determine which water quality variables drive fish survival. As well, we conducted camera-based angler surveys to estimate fishing effort and harvest at these ponds. In the summer of 2015, we examined the extent of avian predation at four ponds (Bashaw, Vegreville and Windsor ponds, and Mirror Reservoir) and assessed the effectiveness of various avian deterrents at Mirror Reservoir.
We obtained adequate angler survey data to estimate parameters at four ponds during the summer of 2014. The total number of estimated trips made by anglers to these ponds ranged from 537 at Westlock to 3,212 at Cipperley’s. Angler effort ranged from 7 h/ha (95% CI = 3 – 13) at Mirror to 5,268 h/ha (95% CI = 4,727 – 5,804) at Cipperley’s, and harvest of stocked trout ranged from 3.3% (95% CI = 3.0 – 3.7) at Mound Red to 72.7% (95% CI = 65.5 – 80.5) at Cipperley’s.
Mid-column water temperatures exceeded stress thresholds (19°C) for rainbow trout throughout the summer in most (7 of 12) ponds. Similarly, DO concentrations fell below the 5.0 mg/L limit at 7 of 12 ponds throughout the summer, but there was no clear association between high temperature and low DO. Chlorophyll-a concentrations varied across ponds (1.45 to 110 μg/L), and NH3 concentrations ranged from 0.05 to 0.69 mg/L, well above the Canadian Council of Ministers of the Environment limit (0.019 mg/L) for the protection of aquatic life, as well as above levels (0.04 mg/L) known to have negative impacts on rainbow trout health.
Fish survival varied considerably across the 12 ponds, ranging from 7.5% at Beaumont to 99.7% at Nuggent. At some ponds, low survival could be attributed to high angler harvest (e.g., Cipperley’s 72.7%), indicating a direct benefit to anglers. Conversely, at other ponds, low survival rates more likely resulted from natural mortality, leading to large portions of unaccounted stocked fish (37.4% at Westlock to 79.1% at Mound Red). Trout survival also varied as a function of water quality. Maximum water temperature, minimum DO, NH3 and chlorophyll-a concentrations were key water quality variables that influenced rainbow trout survival.
Avian predation also may have contributed to the high unexplained mortality of stocked fish in some ponds. In particular, we recorded large increases in cormorant presence following trout stocking at Mirror, where cormorant activity increased 14.9 to 39.7 times after stocking than before stocking. Cormorant abundance at Windsor and Bashaw were low compared with Mirror; however, their presence may indicate potential fish predation at these sites as well. No cormorants were documented at Vegreville. Avian deterrents installed at Mirror were not effective in reducing cormorant abundance at the pond.