Forest Fish Project

Basics of Brook Trout Ecology

Adult brook trout seek out groundwater seepage for spawning in the autumn of each year. There are relatively few spawning areas in lakes and streams, and these areas are stable in location for decades and likely for much longer periods of time. The terrestrial recharge areas associated with these spawning areas have been estimated at several hectares. The shoreline length associated with spawning areas can range from a few metres to over 40 metres, indicating that the lenses of coarse overburden material associated with seepage areas at the lake shore and used for spawning can be quite extensive in some lakes. The number of spawning sites (redds) within the spawning areas can be variable from lake-to-lake and from year-to-year within a lake, but only sites with high annual flow are used every year for spawning. The use of redds within a spawning area is not evenly distributed, largely because of micro-scale variations in seepage rate.

Stream resident brook trout populations are also common across the boreal and Great Lakes-St. Lawrence forest regions of Ontario. Groundwater inputs are critical to the maintenance of these brook trout habitats by providing sufficient base flow levels and maintaining low water temperatures. Brook trout is the only fish species to occupy the headwater areas of stream system in some areas, and the upper tributaries of these systems often provide critical nursery habitats that are not occupied by the adults during summer. The distribution of brook trout through stream systems is often discontinuous, and areas with potentially reproductive sub-populations are often associated with very small tributary streams used exclusively by young-of-year, a situation quite similar to the pattern observed in lakes. Many of these small streams do not appear on Ontario Base Maps (OBMs), and therefore may not be protected under the current guidelines. The development of topographic models to predict the location of habitat suitable for spawning and the location of small streams is a critical step in improving our ability to plan forest management activities to protect brook trout.

Young-Of-Year

Young-of-year (YOY) brook trout emerge from gravel spawning areas in early spring and live in shallow nearshore habitat in streams and lakes.  In stream populations, YOY brook trout form stationary feeding territories and defend these territories against other YOY brook trout.  Formation of territories and limited space in streams combine to determine the upper limit on brook trout abundance in stream ecosystems.  In lakes, YOY brook trout do not form territories but spread out from the spawning area along the lakeshore.  The spread is a simple diffusion process to locations that have seeps or streams at the lake edge.  Seeps and streams found along the stream or lake edge provide thermal habitat for the YOY brook trout.  Many of these locations are not found on current base maps for Ontario and we suspect for any other jurisdiction.