Coldwater stream habitats are critical to species like the brook trout, but these environments are vulnerable to warming waters. It is difficult for scientists to measure the actual water temperatures that fish experience in streams. Traditional water temperature loggers can estimate stream and lake temperatures at different locations and depths, but often miss small patches of coldwater habitat like those created by groundwater inputs. Recently, miniaturized temperature recording tags that can be implanted in fish has made this process easier for scientists – so what’s the catch?  

A new study by Northeast CASC-supported researchers demonstrates how fish size could be a major limitation when interpreting data from the miniature temperature recording tags.  

In a laboratory, the researchers tested the miniature tags in brook trout of different sizes and found that the tags implanted in larger fish show a delay, or lag-time, when the fish experienced rapid changes in temperature (for instance, an eight-degree Celsius change in under two seconds). In contrast, slower temperature changes (such as a two-degree Celsius change over an hour) were detected similarly regardless of the size of the fish. Because fish in the wild can move quickly between water of different temperatures, knowing the size of the fish is critical for accurately interpreting data and understanding how temperature really varies in streams. Without accounting for fish size, data may mislead researchers to underestimate temperature variation in some warming streams and cause them to incorrectly determine which streams have enough coldwater input from groundwater to support brook trout. 

These miniaturized tags offer an important way to understand how fish’s habitat and behavior relate to water temperature. However, as demonstrated by this Northeast CASC study, recognizing limitations is essential for accurately interpreting data and for informing management decisions.  

This research was supported by the Northeast CASC Project titled “Understanding Brook Trout Persistence in Warming Streams.”