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78
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J Anim Ecol. 2023;92:78–96.wileyonlinelibrary.com/journal/jane
Received: 26 May 2022
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Accepted: 24 September 2022
DOI : 10.1111/136 5-265 6.13 83 3
RESEARCH ARTICLE
Identifying mechanisms underlying individual body size
increases in a changing, highly seasonal environment: The
growing trout of West brook
Benjamin H. Letcher1 | Keith H. Nislow2 | Matthew J. O'Donnell1 | Andrew R. Whiteley3 |
Jason A. Coombs4 | Todd L. Dubreuil1 | Daniel B. Turek5
1U. S. Geological Survey, Eastern
Ecological Science Center, Silvio O. Conte
Research Laboratory, Turners Falls,
Massachusetts, USA
2US Forest Service, Nor thern Research
Station, Amherst, Massachusetts, USA
3Wildlife Biolog y Program, Department
of Ecosystem and Conservation
Sciences, Franke College of Forestry and
Conser vation, University of Montana,
Missoula, Montana, USA
4Department of Environmental
Conser vation, University of
Massachusetts, Amherst, Massachusetts,
USA
5Department of Mathematics and
Statistics, Williams College, Williamstown,
Massachusetts, USA
Correspondence
Benjamin H. Letcher
Email: bletcher@usgs.gov
Funding information
U.S. Fish and Wildlife Service; U.S. Forest
Service
Handling Editor: Marlène Gamelon
Abstract
1. As air temperature increases, it has been suggested that smaller individual body
size may be a general response to climate warming. However, for ectotherms
inhabiting cold, highly seasonal environments, warming temperatures may in-
crease the scope for growth and result in larger body size.
2. In a long- term study of individual brook trout Salvelinus fontinalis and brow n tr o u t
Salmo trutta inhabiting a small stream network, individual lengths increased over
the course of 15 years. As size- selective gains and losses to the population acted
to reduce body sizes and mean body size at first tagging in the autumn (<60 mm)
were not observed to change substantially over time, the increase in body size
was best explained by higher individual growth rates.
3. For brook trout, increasing water temperatures during the spring (when both
trout species accomplish most of their total annual growth) was the primary
driver of growth rate for juvenile fish and the environmental factor which best
explained increases in individual body size over time.
4. For brown trout, by contrast, reduction in and subsequent elimination of ju-
venile Atlantic salmon Salmo salar midway through the study period explained
most of the increases in juvenile growth and body size.
5. In addition to these major trends, a considerable amount of interannual variation
in trout growth and body size was explained by other abiotic (stream flow) and
biotic (population density) factors with the direction and magnitude of these ef-
fects differing by season, age- class and species. For example, stream flow was
the dominant growth rate driver for adult fish with strong positive effects in the
summer and autumn, but flow variation could not explain increases in body size
as we observed no trend in flow.
6. Overall, our work supports the general contention that for high- latitude ec-
totherms, increasing spring temperatures associated with a warming climate
can result in increased growth and individual body size (up to a point), but
© 2022 The Authors. Journal of Animal Ecology © 2022 British Ecological Society. This article has been contributed to by U.S. Government employees and
their work is in the public domain in the USA.
[Correc tion added on 17 November 2022, after first Online publication: In affiliation 5, the city name “Williamsburg” has been changed to “Williamstown”.]