Brook Trout Conservation & Management in a Changing Climate
Collaborators - Dan Josephson, Tom Daniel, Kurt Jirka, Mariah Meek, Matt Hare (Cornell), Dana Warren (Oregon State University)
For more than a decade we have been evaluating how summer thermal conditions influence brook trout populations in four Adirondack lakes. Two of these lakes are shallow and unstratified; the other two are deeper, stratified lakes. The hypolimnion of stratified lake ecosystems provides thermal refuge for coldwater fish during warm summer conditions. By contrast, thermal refuges in the unstratified lakes are restricted in extent. In one unstratified lake, we have identified a metric - the cumulative degree days of bottom water temperatures above 20°C - useful for predicting summer brook trout survival. In this lake total mortality of age 1+ and 2+ fish occurred during two years in which we observed 156 and 210 cumulative degree-days of bottom water temperatures warmer than 20°C, and the cumulative degree day metric accounted for 85% of the variation in fall spawning activity (i.e. redd construction) by brook trout.
In addition, strong differences have been observed in the amount and timing of brook trout spawning and gonad development between stratified and unstratified lakes in hot years (e.g. 2012), but not in years with cooler summer temperatures (e.g. 2013, 2014). In the hot summer of 2012, egg development and spawning by female brook trout in the unstratified lakes with no coldwater refuge was almost completely eliminated, which contrasted with normal egg development and spawning in the two stratified lakes. By contrast, egg development and the timing of spawning by brook trout was similar in the stratified lakes in both the hot year (2012) and following two cool years (2013 & 2014).
These observations highlight the importance for lake-dwelling brook trout of a coldwater refuge below the thermocline in stratifed lakes during years with hot summer conditions. We have observed that populations of brook trout have decreased substantially in unstratified lakes during hot summers, while remaining stable in stratified lakes. Mortality during warm temperature conditions in unstratified lakes exerts a strong selective force upon brook trout in these systems.
An opportunity to expand our understanding of whether and how brook trout populations can adapt to these types of warm temperature conditions has become available through funding from the David H. Smith Conservation Research Fellowship program to Mariah Meek, a post-doctoral associate who started work at Cornell in March 2015 with Cliff Kraft and conservation geneticist Matt Hare. During the next two years Mariah will be investigating local adaptation by brook trout to variable thermal environments in these study lakes. Her work is based on the expectation that brook trout populations in unstratified lakes will demonstrate an increased adaptive capacity to withstand heat stress, as shown by differences in molecular function, physiological capacity, and phenotypic response.
Mariah will use genomic approaches to accomplish two objectives:
1. Experimentally identify the genes and molecular pathways associated with adaptation to thermal stress in brook trout, as evidenced by gene expression in different temperature conditions;
2. Locate the regions of the brook trout genome associated with differences in response to thermal stress and develop an approach for assessing genetic diversity associated with thermal adaptation in other populations.
For further information:
Warren, D.R, J.M. Robinson, D.C. Josephson, D.R. Sheldon and C.E. Kraft. 2012. Elevated summer temperatures delay spawning and reduce redd construction for resident brook trout (Salvelinus fontinalis). Global Change Biology 18:1804–1811. [Link to Full article]
Robinson, J.M., D.C. Josephson, B.C. Weidel and C.E. Kraft. 2010. Influence of variable summer water temperatures on brook trout growth, consumption, reproduction and mortality in an unstratified Adirondack lake. Transactions of the American Fisheries Society 139:685–699. [Link to Full article]