Lake Trout Biochronologies as Long-term Climate and Productivity Indicators in Alaska Lake Ecosystems

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High latitude ecosystems are among the most vulnerable to long-term climate change, yet continuous, multidecadal indicators by which to gauge effects on biology are scarce, especially in freshwater environments.

A cross-section of a lake trout otolith (ear bone) under the microscope

A transverse cross-section of a sagittal otolith from a lake trout collected in April, 1989, from Chandler Lake, Alaska, USA. Decadal growth increments (1980, 1970, and 1960) are dotted.
(Credit: Bryan A. Black, University of Texas. Public domain.)

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To address this issue we have applied dendrochronology (tree-ring analysis) techniques to growth-increment widths in otoliths from lake trout (Salvelinus namaycush). We have developed a growth record for lake trout from the Chandler Lake system in Gates of the Arctic National Park and Preserve and are currently working on a similar effort in Lake Clark National Park. Sockeye salmon are a keystone species within Lake Clark National Park and Preserve, which was established “ protect the watershed necessary for the perpetuation of the red [sockeye] salmon fishery in Bristol Bay.” Numerous lakes in Lake Clark National Park are important salmon nurseries that are sensitive to climate change, and increasing temperatures may lead to profound changes in productivity by altering the timing of ice break-up, the timing and duration of thermal stratification, and the timing and intensity of nutrient upwelling. Given that these high-latitude landscapes are among the most likely to experience rapid climate change in the coming decades, the relationships between lake biology and climate variability must be better quantified to forecast impacts on the productivity of sockeye salmon and resident fishes. To address the implications of climate variability in lakes for fish, we borrow from the tree-ring sciences to develop multidecadal chronologies from lake trout otoliths. Just as tree-ring data capture histories of climate and productivity in terrestrial systems, we propose that lake trout otolith data will provide analogous information for lake ecosystems. A particular strength of this study is that final trout chronologies will be exactly dated, allowing us to make high quality comparisons with direct observations of climate (instrumental records) and biology (salmon escapement). Thus, we are developing lake trout otolith chronologies in lake ecosystems of Lake Clark National Park and Preserve to i) quantify long-term effects of climate on growth, ii) evaluate the influence of marine-derived nutrient input from sockeye salmon returns, and iii) compare long-term rates of change in freshwater and terrestrial ecosystems using lake trout and tree-ring chronologies.

Two graphics illustrating the correlation between lake trout growth and air temperature

Spearman correlations between the lake trout master chronology and monthly mean air temperature and degree days from Bettles, AK. Degree days were calculated only for the months of April through October. Asterisk denotes significance at the p \ 0.01 level. Inset The relationship between the lake trout master chronology and mean August air temperature at Bettles, AK. r 2 = 0.32 (p = 0.005). There was no significant autocorrelation in the residuals; DW = 2.39 (p = 0.19). b Lake trout master chronology and August air temperature. Both time series are normalized to a mean of 0 and standard deviation of 1.
(Credit: Bryan A. Black, University of Texas. Graphic used in publication)