Document: ERI-3-69-29

Catastrophic disturbance and population viability of coho salmon (Oncorhynchus kisutch) in central California.

KAPLAN, I.C.* and E.P.BJORKSTEDT

National Marine Fisheries Service, SWFSC, Santa Cruz/Tiburon Laboratory, Tiburon, CA 94920, USA ¹

Abstract:
Coho salmon (Oncorhynchus kisutch) in the Central California Evolutionarily Significant Unit (ESU) exhibit a relatively inflexible, semelparous life history, such that distinct brood-year classes of coho salmon occupying the same watershed exhibit independent dynamics. Anecdotal observations of severe, storm-related disturbance indicate that catastrophic disturbance at the scale of individual watersheds may be an important factor affecting the viability of coho populations in this region, since depletion of individual brood-year class is not rapidly offset by "temporal straying" from other brood-year classes in the same watershed. We analyzed spatial and temporal variation in proxy measures of distubance (e.g., rainfall, storm events and stream flow during spawning periods) to develop a disturbance climatology for the Central California ESU, and coupled this model of catastrophic disturbance to a simulation model for metapopulation dynamics for coho salmon to assess current population viability and explore potential recovery scenarios. Results of this analysis and simulations indicate that high rates of occupancy of coastal watersheds by coho salmon were as important as maintaining large populations in individual watersheds, and that small scale variation in the effects of disturbance contributed to low correlation in the fate of populations at inter-watershed scales. Results from analysis of ESU viability simulations are, not surprisingly, sensitive to rates of dispersal among subpopulations.

Keywords: metapopulation, disturbance, population viability, coho salmon

This abstract is being presented at: 10:30 AM in session:
Poster Session #9: Fish, Lakes, Streams and Wetlands.