Influence of Water Temperature on Eastern Brook Trout Growth in the Slide Brook Tributary of the Nash Stream

Chelsea L. Lloyd
Charles Curtin
Department of Environmental Studies
Aging Eastern brook trout or brook trout (Salvelinus fontinalis) using scale-based techniques is a common practice to determine stream or watershed health and productivity. Using water temperature data and brook trout data collected from the Nash Stream Forest Restoration Project headed by the New Hampshire Fish and Game Department (NHFGD) in northern most NH, I determined mean growth between fish of the same age among years 2009-2011, and differences in water temperatures for annual months (May-September) among years 2009-2011. Scale analysis and back-calculation techniques were used to determine an individual’s age and growth history. The Nash Stream Forest is the largest state owned property in New Hampshire and supports a large population of wild brook trout. Slide Brook is one of four research streams to Nash Stream and has the lowest productivity and growth of wild brook trout in the Nash Stream Forest watershed; this makes it a useful comparison to the other tributaries in terms of determining what, if any, environmental factors could be impacting this population. Water temperature data, trout total length and scale samples were collected from Slide Brook from fall 2009 to fall 2012.

My research explores the role of water temperature influencing growth of wild brook trout from pre-existing data. Specifically, my work addressed two questions: 1) What is the mean growth between cohorts of brook trout from one year to the next? 2) Does growth for fish of the same age vary among years, and if so, does water temperature account for this between the years of 2009-2011? My hypothesis was brook trout growths in Slide Brook are correlated to annual (May-Sep.) monthly water temperatures. Using back calculation techniques and a modified Fraser-Lee equation, I back calculated the body length of each individual fish when an annulus 13 was formed. I took the difference between the calculated body lengths of each age group to determine the growth of fish among years. I then compared growth from the same group of aged fish among years and determined there was a significant difference among years 2009-2011 for Age 0-1 fish (P = 0.014). The differences for Age 0-1 fish growth between 2009 and 2011 (P = 0.0238) and between 2010 and 2011 where highly significant (P < 0.0001). However, there was no significant difference in growth among years 2009-2011 for Age 1-2 fish (P = 0.149) and Age 2-3 fish (0.695). I also determined there were significant differences in annual (May-September) water temperatures among years (P = 0.0001). Age 0-1 fish showed the greatest differences in growth among years, therefore I compared only Age 0-1 fish to their corresponding water temperature year. Correlation tests could not be conducted as data between the two variables was insufficient and sample sizes greatly skewed. Therefore a relationship of water temperatures influencing brook trout growth in Slide Brook was hypothesized. Overall my results did not suggest water temperatures influenced brook trout growth for Age 0-1 in Slide Brook.