Weighing the Facts for Lake Trout

 

Williston Lake TroutThrough partnership with Duz Cho Logging and others, the Williston Lake Trout Project and local anglers at the annual Duz Cho fishing derby are helping to collect monitoring data on Williston Reservoir lake trout. Over the last 2 years we have weighed, measured, and sampled 66 lake trout to determine age, growth patterns, fecundity, and food habits, and we are at it again this year. Tracking changes in fish age-length-weight relationships provides clues for sustainable fisheries management and is a simple and effective way to keep tabs on population health.

Lake trout have a remarkable diversity of growth patterns. In populations where adult fish feed primarily on insects and plankton – for example, in Carbon Lake near Hudson’s Hope – body sizes remain small. By contrast, populations with ideal habitat and abundant prey fish can grow rapidly to large sizes. In BC, lake trout typically range 45 – 65 cm in length and 2 – 6 lbs weight. In rare cases “trophy” fisheries emerge, with adult lake trout reaching lengths greater than 70 cm.

Big fish have advantages over smaller fish, including higher survival rates and more reproductive capacity. Larger fish produce disproportionately more eggs, but also larger eggs, which in turn results in offspring that are more resilient. Most lake trout measuring at least 50 – 60 cm in length are sexually mature and capable of spawning, but variation in growth rates means northern BC lake trout can take 5 to 15 years or more to reach that size. The effects of late maturity are compounded for lake trout because each female typically only spawns every 2 – 3 years.

Despite the reservoir’s low productivity, Williston lake trout are likely benefitting from the nutrient influx that government-stocked kokanee and native whitefish are providing. When it comes to size and growth rates, the Williston lake trout population is unlike any other in BC. In fact, Williston lake trout growth patterns are most similar to a reservoir in Colorado, where lake trout growth is faster than any other population in North America.

The 66 Williston lake trout (35 females, 31 males) submitted for sampling ranged from 60 – 95 cm in length. The largest fish were not necessarily the oldest, with ages ranging from 12 – 29 years. Two fish had exceptional growth: one large female (82 cm long, 15 lbs) was only 12 years old and one large male (90 cm, 19 lbs) was only 14 years old. For 12 females (age 12 – 23 years) weighed in late August, egg weight was 6 – 13 % of their total body weight, indicating that all would be spawning that fall.

If you catch and keep Williston lake trout as part of your daily allowable quota, consider donating your fish heads to the Williston Lake Trout Project for population age-length-weight monitoring. Weigh and measure (nose to fork-in-tail) your fish before cleaning, contact us for pickup, and we’ll tell you how old your fish is.

[Published in the August 20 issue of the Mackenzie Times, 2014]

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