7. Role of Lipids in Fish Populations
137
mouth bass, Adams and DeAngelis (1987) demonstrated that late-spawned individuals were too small to ingest their primary prey of young-of-the-year shad.
These fish, therefore, failed to reach the critical size needed to accumulate sufficient lipid stores by the end of their first growing season, resulting in a decreased
probability of overwinter survival. Increased risk of predation may arise because
of the weakened condition of the fish due to insufficient energy (body lipids).
Increased predation risk could also occur due to an increase in foraging activity
after spawning when the lipid reserves are depleted (Roff, 1982). Small fish, by
diverting energy from maintenance into reproduction, which has a higher energy
cost, greatly increase their vulnerability to predation.
For several species living in the temperate and north-temperate zones, their first
winter is considered to be the final survival bottleneck before year-class strength
is set (Thompson et aI., 1991; Henderson et aI., 1988). Overwinter mortality can
cause substantial variability in year-class strength of some species that is independent of adult stock sizes (Post and Evans, 1989). Size-dependent predation and
overwinter mortality, which are influenced by lipid stores, have been implicated
as possible regulators of year-class strength in yellow perch. An abundant youngof-the-year perch population can suppress their own food resources resulting in
utilization of suboptimum prey sizes. This situation in tum causes densitydependent starvation and mortality to increase (Post and Evans, 1989). Winter
starvation mortality, therefore, is maximal at northern latitudes, and at more
southerly latitudes with longer growing seasons and shorter winters, overwinter
mortality is lower and less variable with population sizes being more stable.
Summary and Future Initiatives. Availability of lipid reserves can have major
consequences on the health of individual fish and influence survival and population success. Fish, particularly the smaller individuals in a population, that do not
enter the winter nonfeeding period with sufficient fat reserves not only decrease
their probability of overwinter survival but usually have reduced reproductive
performance the following spring. Impaired osmoregulatory ability, possibly due
to utilization of structural membrane lipids and concomitant changes in membrane permeability, may be a major factor for increased mortality of smaller fish
over the winter. Starvation and depletion oflipids to critically low levels can result
in increased susceptibility of fish to disease, predation, and other environmental
stressors. The dynamics of overwinter survival as dictated by lipid stores can be a
major regulator of year-class strength in many fish populations, particularly those
from north-temperate areas. Species from higher latitudes are more vulnerable to
starvation and overwinter mortality because of shorter time periods for feeding
and energy accumulation and the longer periods over which dependence on stored
lipids is required. Density-dependent controls can also operate in fish populations
to regulate the number of individuals competing for limited food resources, thus
optimizing the amount of energy available to individuals for lipid storage and for
increasing their probability of overwinter survival.
The seasonal availability of lipid stores is critical to the health and future
success of many fish species. It is therefore important to have a better understand-
137
mouth bass, Adams and DeAngelis (1987) demonstrated that late-spawned individuals were too small to ingest their primary prey of young-of-the-year shad.
These fish, therefore, failed to reach the critical size needed to accumulate sufficient lipid stores by the end of their first growing season, resulting in a decreased
probability of overwinter survival. Increased risk of predation may arise because
of the weakened condition of the fish due to insufficient energy (body lipids).
Increased predation risk could also occur due to an increase in foraging activity
after spawning when the lipid reserves are depleted (Roff, 1982). Small fish, by
diverting energy from maintenance into reproduction, which has a higher energy
cost, greatly increase their vulnerability to predation.
For several species living in the temperate and north-temperate zones, their first
winter is considered to be the final survival bottleneck before year-class strength
is set (Thompson et aI., 1991; Henderson et aI., 1988). Overwinter mortality can
cause substantial variability in year-class strength of some species that is independent of adult stock sizes (Post and Evans, 1989). Size-dependent predation and
overwinter mortality, which are influenced by lipid stores, have been implicated
as possible regulators of year-class strength in yellow perch. An abundant youngof-the-year perch population can suppress their own food resources resulting in
utilization of suboptimum prey sizes. This situation in tum causes densitydependent starvation and mortality to increase (Post and Evans, 1989). Winter
starvation mortality, therefore, is maximal at northern latitudes, and at more
southerly latitudes with longer growing seasons and shorter winters, overwinter
mortality is lower and less variable with population sizes being more stable.
Summary and Future Initiatives. Availability of lipid reserves can have major
consequences on the health of individual fish and influence survival and population success. Fish, particularly the smaller individuals in a population, that do not
enter the winter nonfeeding period with sufficient fat reserves not only decrease
their probability of overwinter survival but usually have reduced reproductive
performance the following spring. Impaired osmoregulatory ability, possibly due
to utilization of structural membrane lipids and concomitant changes in membrane permeability, may be a major factor for increased mortality of smaller fish
over the winter. Starvation and depletion oflipids to critically low levels can result
in increased susceptibility of fish to disease, predation, and other environmental
stressors. The dynamics of overwinter survival as dictated by lipid stores can be a
major regulator of year-class strength in many fish populations, particularly those
from north-temperate areas. Species from higher latitudes are more vulnerable to
starvation and overwinter mortality because of shorter time periods for feeding
and energy accumulation and the longer periods over which dependence on stored
lipids is required. Density-dependent controls can also operate in fish populations
to regulate the number of individuals competing for limited food resources, thus
optimizing the amount of energy available to individuals for lipid storage and for
increasing their probability of overwinter survival.
The seasonal availability of lipid stores is critical to the health and future
success of many fish species. It is therefore important to have a better understand-