Cycles, stochasticity and density dependence in pink salmon population dynamics

Area of Science:

• Ecology
• Population Dynamics
• Fisheries Science

Background:

• Animal population dynamics often exhibit complex behaviors influenced by both deterministic and stochastic factors.
• Pink salmon (Oncorhynchus gorbuscha) display a unique 2-year life cycle with reproductively isolated odd- and even-year lineages.
• Variations in the abundance of these lineages and phase switches in dominance are observed across North Pacific stocks.

Purpose of the Study:

• To investigate the underlying mechanisms driving the cyclical dynamics and abundance variations in pink salmon stocks.
• To provide empirical estimates of lagged density-dependent mortality in salmon populations.
• To understand the interplay between stochasticity and density dependence in shaping pink salmon population dynamics.

Main Methods:

• Analysis of abundance data from 33 pink salmon stocks along the North Pacific rim.
• Modeling of population dynamics incorporating density-dependent mortality and stochastic perturbations.
• Examination of potential lineage interactions, such as cannibalism, disease, and resource competition.

Main Results:

• Observed patterns suggest stochastic perturbations of damped oscillations are a primary driver.
• Density-dependent mortality, resulting from interactions between odd- and even-year lineages, significantly influences population cycles.
• Lagged density-dependent mortality estimates were comprehensively quantified across multiple stocks.

Conclusions:

• A combination of stochasticity and density dependence, mediated by inter-lineage interactions, drives the cyclical dynamics of pink salmon.
• While mechanisms like cannibalism and disease are plausible, they require further in-depth study.
• The findings offer critical insights into the population regulation of a key commercial fish species.