Fisheries Behavioral Ecology - Abstracts
Hurst, T.P. 2007. Causes and consequences of winter mortality in fishes. Journal of Fish Biology 71:315-345.
Abstract
Winter mortality has been documented in a large number of freshwater fish populations, and
a smaller, but increasing, number of marine and estuarine fishes. The impacted populations
include a number of important North American and European resource species, yet the sources
of winter mortality remain unidentified in most populations where it has been documented.
Among the potential sources, thermal stress and starvation have received the most research
attention. Other sources including predation and pathogens have significant impacts but have
received insufficient attention to date. Designs of more recent laboratory experiments have
reflected recognition of the potential for interactions among these co-occurring stressors.
Geographic patterns in winter mortality are, in some cases, linked to latitudinal clines in
winter severity and variability. However, for many freshwater species in particular, the effects of
local community structure (predators and prey) may overwhelm latitudinal patterns. Marine
(and estuarine) systems differ from freshwater systems in several aspects important to
overwintering fishes, the most important being the lack of isolating barriers in the ocean.
While open population boundaries allow fish to adopt migration strategies minimizing exposure
to thermal stresses, they may retard rates of evolution to local environments. Geographic
patterns in the occurrence and causes of winter mortality are ultimately determined by the
interaction of regional and local factors.
Winter mortality impacts population dynamics through episodic depressions in stock size and
regulation of annual cohort strength. While the former tends to act in a density-independent
manner, the latter can be density dependent, as most sources of mortality tend to select against
the smallest members of the cohort and population. Most stock assessment and management
regimes have yet to explicitly incorporate the variability in winter mortality. Potential
management responses include postponement of cohort evaluation (to after first winter of life),
harvest restrictions following mortality events and habitat enhancement.
Future research should place more emphasis on the ecological aspects of winter mortality
including the influences of food-web structure on starvation and predation. Beyond illuminating
an understudied life-history phase, studies of overwintering ecology are integral to contemporary
issues in fisheries ecology including ecosystem management, habitat evaluation, and
impacts of climate change.
Last updated
11 October, 2007
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