UW Aquatic & Fishery Sciences Quantitative Seminar

Jim Thorson

NOAA Northwest Fisheries Science Center

Demographic variation over time, space, and among individuals: Why care and what to do?

Abstract

Populations and communities exhibit variation in demographic rates over time, space, and among individuals. Theoretical and applied ecologists must account for demographic variability, e.g., to provide an appropriate "null" model when testing new ecological theory, or to simulate realistic data when testing management systems in silico. However, the magnitude and consequences of variability in demographic rates remains has received little systematic or comparative treatment in marine ecology or fisheries management. We therefore use elasticity analysis to illustrate the potential impact of demographic variability on biological reference points (BRPs) used in fisheries management. We compare results with estimates of variability in growth and recruitment rates obtained using publicly available databases. We also summarize a preliminary literature review regarding variation in maturity and natural mortality rates. Finally, we propose three recommendations when dealing with demographic variability: (1) increased application of mixed-effect estimation methods; (2) increased data collection for maturity and mortality estimation; and (3) managing marine systems for variability. We conclude with ongoing and recommended research regarding the magnitude and implications of variability in marine systems.