With the arrival of Fall, we often think of everything winding down and getting ready for the winter. We're putting our gardens to bed, the trees are turning, and leaves are falling, many animals are packing on the pounds and preparing to hibernate or at least hunker down. Freshwater mussels are moving deeper and digging in for the winter, and it would be natural to assume that the rest of the river residents are doing similar activities.
In contrast, we often herald Spring as the season of awakening and rebirth, filled with spawning runs, egg laying, and the start of the next generation. But it turns out that there's a lot of action in the fall, too. Fall is when our beautiful native brook trout (Salvelinus fontinalis) begin their spawning runs. Brook trout need cold water (preferably <60°F) year-round, but when the water temperatures hit 40-50°F, they start heading upstream to breed. This usually takes place in late September and October (right now!). Female brook trout excavate a small redd, which gets covered back up with gravel after eggs have been laid and fertilized, then they go on to build another nest. The eggs overwinter in the gravel and the fry hatch out usually around February/March.
Water temperatures affect the timing and success of spawning runs, as well as how long it takes the eggs to develop and hatch. You might be wondering how those little eggs don't freeze in the substrate of cold, shallow, headwater streams that are often home to brook trout. Well, it turns out that the ideal places to construct redds are gravel banks where there is a spring or consistent localized groundwater discharge. That upwelling groundwater helps maintain an appropriate temperature for the eggs to develop, even when the air temperature is well below freezing.
The brook trout's sensitivity to water temperature and oxygen levels, and reliance on the exchange between ground and surface waters for certain life stages, underscores for me yet again how critical it is to consider ecological connectivity when talking about river health and species needs, and to think about how human activities can either enhance or degrade habitat for species like the brook trout, even if those activities are taking place on land. CRC does just that when taking on various projects, including our restoration work. We have undertaken projects in the past specifically to enhance brook trout habitat, and likely will do so in the future as well.
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