Estimating delayed density-dependent mortality in sockeye salmon (Oncorhynchus nerka): a meta-analytic approach

1997 ◽  
Vol 54 (10) ◽  
pp. 2449-2462 ◽  
Author(s):  
R A Myers ◽  
M J Bradford ◽  
J M Bridson ◽  
G Mertz
Keyword(s):  
Time Series ◽  
Sockeye Salmon ◽  
Analytical Approach ◽  
Oncorhynchus Nerka ◽  
Fishing Mortality ◽  
Density Dependent ◽  
Density Dependent Mortality ◽  
Cyclic Patterns ◽  
Adult Abundance ◽  
Dependent Mortality

Delayed density-dependent mortality can be a cause of the cyclic patterns in abundance observed in many populations of sockeye salmon (Oncorhynchus nerka). We used a meta-analytical approach to test for delayed density dependence using 34 time series of sockeye data. We found no consistent evidence for delayed density-dependent mortality using spawner - spring fry or spawner-recruit data. We did find evidence for delayed density-dependent mortality at a 1 year lag for the spawner - fall fry and the spawner-smolt data; however, effects at lags greater than 1 year were weak and not statistically significant. Between-cohort interactions at a 1-year lag are not sufficient to cause the observed cycles in adult abundance, although they will tend to reinforce patterns established by other mechanisms. Our results imply that reductions in fishing mortality in off-peak years should result in an increase in abundance.

Genetic Models for Cyclic Dominance in Sockeye Salmon (Oncorhynchus nerka)

1992 ◽  
Vol 49 (2) ◽  
pp. 281-292 ◽  
Author(s):  
Carl Walters ◽  
J. C. Woodey
Keyword(s):  
Sockeye Salmon ◽  
Oncorhynchus Nerka ◽  
Large Fraction ◽  
Fishing Mortality ◽  
Age At Maturity ◽  
Dominant Trait ◽  
High Productivity ◽  
Cyclic Patterns ◽  
The Face ◽  
The Stability

A simple genetic mechanism may be partly responsible for maintaining violent cycles in abundance of some Fraser River sockeye salmon (Oncorhynchus nerka) stocks. If age at maturity is highly heritable, spawning runs in low cycle lines may have high percentages of age 5 spawners that tend to produce offspring that will return at age 5, due to production of low percentages of such spawners by preceding high cycle lines. Then even if each low cycle line has a high productivity per spawner, a large fraction of this productivity may be "lost" to the cycle line, in the form of age 5 recruits to other cycle lines. In the face of high fishing mortality, even a small relative loss from any cycle line may cause it to remain small relative to other lines. This model explains several observations, such as high productivity per spawner in low cycle lines, that cannot be explained by previous hypotheses involving depensatory predation or food supply. However, it is unlikely that genetic effects alone are responsible for the stability of cyclic patterns, unless low offcycle runs consist entirely of "temporal colonizer" genotypes that produce a high proportion of age 5 offspring as a dominant trait.

An Experiment On Spacing-Out as a Defence Against Predation

Behaviour ◽  
1967 ◽  
Vol 28 (3-4) ◽  
pp. 307-320 ◽  
Author(s):  
D. Franck ◽  
M. Impekoven ◽  
N. Tinbergen
Keyword(s):  
Selection Pressure ◽  
Standard Sample ◽  
Direct Detection ◽  
Natural Populations ◽  
The Other ◽  
Detection Distance ◽  
Density Dependent ◽  
Density Dependent Mortality ◽  
Scattered Population ◽  
Dependent Mortality

AbstractThe paper is concerned with the tracing of a selection pressure which would account for the fact (believed to be sufficiently well established) that individuals of many well-camouflaged species live further away from other individuals of their species than the distance from which even bird predators are able to detect them. Artificially camouflaged hens' eggs were laid out in plots of different densities. Wild Carrion Crows were attracted to each plot by a standard "sample egg" which, while painted in the same way as the other eggs on the uppermost half, was laid out in a more conspicuous way. In spite of the fact that the Crows spent more time searching in the "scattered" than in the "crowded" plots, the crowded eggs suffered a much higher mortality. It is concluded that even for individuals of a well-camouflaged species it must be of advantage to live further away from others than the Direct Detection Distance of their predators. However, the experiments do not show that a crowded population as a whole suffers higher predation than a scattered population; experiments to test this and other aspects of the problem are in progress. It is argued that the absolute values of the density dependent mortality scores of the experiments cannot be applied to natural populations, because their density will in most cases be determined by other ultimate factors as well.

POPULATION DYNAMICS OF THE CEREAL LEAF BEETLE, OULEMA MELANOPUS (COLEOPTERA: CHRYSOMELIDAE): A MODEL FOR AGE SPECIFIC MORTALITY

1972 ◽  
Vol 104 (6) ◽  
pp. 797-814 ◽  
Author(s):  
Robert G. Helgesen ◽  
Dean L. Haynes
Keyword(s):  
Pupal Stage ◽  
Leaf Beetle ◽  
Fourth Instar ◽  
Egg Survival ◽  
Density Dependent ◽  
Cereal Leaf Beetle ◽  
Density Dependent Mortality ◽  
Oulema Melanopus ◽  
First Instar ◽  
Dependent Mortality

AbstractThe cereal leaf beetle, Oulema melanopus (L.), has rapidly increased its numbers and range since it was discovered in Michigan in 1962. We have shown in this report that intraspecific density-dependent mortality is the major constraint on survivorship. We have attempted to quantify survival within a generation from the egg stage to the adult.Larval mortality varies among populations. Density-dependent mortality, caused by intraspecific competition, accounts for most of the variation of within-generation survival of the cereal leaf beetle in wheat and oats. Mortality in the first instar on oats and the fourth instar on wheat and oats is a linear function of the logarithm of total egg density. Establishment of the first instar on oats appears to become more difficult as density increases because leaf surface disturbance and interference with larger larva increases. Competition for food accounts for the increase in mortality of the fourth instar in both wheat and oats as density increases. Egg survival, survival of the first instar on wheat and in the second, third, and pupal stage in both crops are constants with respect to density. These constants can be expected to change with respect to other environmental parameters however, e.g. host variety, planting date, rainfall, etc.

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