Fishing Tips
By Brian Chan
Fishing Advisor, Freshwater Fisheries Society of BC
I’m sure I’m not the only angler who, the night before every trip, dreams about catching fish. Mother Nature, local weather, and climatic conditions always work together, though, to ensure that there is a mix of good days and … not so good days.
I’ve heard a similar story from many stillwater anglers over the years. It begins with an early-spring fishing trip in which conditions were ideal: just a day after ice-off, with clear water, and lots of fish moving and feeding in shallow water. The anglers have a great time catching nice-sized trout. Accompanied by more friends, they return a few days later for a repeat performance, but are greeted by murky, stained water with lots of organic matter suspended throughout the depths, and very few fish seen moving or feeding. They leave the lake without catching a thing, and wonder what happened to their favourite fishery.
When it comes to stillwaters, there are two very prominent limnological (in-lake physical and chemical) events that override even the day-to-day influences of weather and Mother Nature. These are spring and fall turnovers, both of which are necessary ecological processes that ensure the stability of the entire aquatic ecosystem. Turnover events occur on small, relatively shallow stillwaters that are found throughout the temperate and northern temperate zones of North America. This includes those waters in at least the mid-latitude and northern United States, as well as in Canada.
What is Spring Turnover?
Lakes that experience turnover, or mixing events, are characterized by small size (typically less than about 200 surface hectares, or 500 acres), maximum depths less than 15 metres (50 feet), and extensive littoral or shallow areas (which provide ideal habitat for the healthy growth of submergent and emergent aquatic vegetation). Many of these lakes support only small inlet/outlet creek systems, or no tributaries at all. The vast majority of these lakes also freeze over for several months a year. The end result is water bodies that are nutrient-rich due to limited (or non-existent) flushing or recharge of water. It is these lakes that undergo the seasonal changes associated with spring, summer, fall and winter.
The typical trout-fishing lake in the interior of B.C. withstands four to six months of ice cover. During that time, there is minimal or no oxygenation of the water. As the ice leaves the lake in spring, the water is often quite clear, with trout concentrated in shallows where there are adequate oxygen levels (in many situations, there is insufficient oxygen in the deeper parts of the lake to support them) and food. This scenario, termed ice-off fishing, can be quite productive.
At ice-off, the upper layers of water are colder than the deeper layers. Heat, produced as a by-product of green plant decomposition that has occurred during the winter months, contributes to warmer bottom layers of water. Since water is most dense when it is at 4°C, and doesn’t mix well when at different temperatures or densities, it can take up to a couple of weeks for the upper layers to warm up to temperatures similar to those on the bottom.
Once the lake water is isothermal (or the same temperature), it will mix. The surface waters will sink to the bottom, and the addition of a blustery springtime wind will contribute energy to stir the entire water column. Murky or coloured water is the result of the mixing event sweeping detritus off the lake bottom, and distributing it throughout the water column. Spring turnover supercharges the entire lake with oxygen, which in turn allows the fish to re-populate all depths.
Unfortunately, during a spring turnover, fishing success is typically very poor since the water quality of the lake has been abruptly changed, and turbidity levels are high. It takes a few days for the water chemistry to stabilize, and the water to clear as the particulate matter settles out.
The good news? Since continually warming water also initiates the first of many abundant aquatic insect emergences, the completion of the spring turnover signals the start of a period of really exceptional trout fishing.