PARENT SESSION
Oral Session 9: Marine Ecology I: Management.
Presiding: D Policansky
Monday, August 2, 8:00 AM to 11:30 AM, Meeting Room C 120.
Fishing-induced community shifts on the U.S. Pacific continental shelf: Implications for recovery of imperiled rockfish.
Harvey, Chris*,1, Levin, Phillip1, Tolimieri, Nick1, 1 Northwest Fisheries Science Center, Seattle, WA, USA
ABSTRACT- Rockfish (Sebastes spp.) in the north Pacific are typically long-lived and slow-growing, and are targeted heavily by fishing. We examined the consequences of harvesting 16 rockfish species on the continental shelf of the U.S. Pacific coast over the past two decades at multiple spatial scales. Coast-wide, several species declined by more than 80% in the last quarter century, while others increased sharply in abundance. Despite variability in temporal abundance trends, mean individual body size of most species declined by nearly 50%. At a regional scale (5 major biogeographic zones on the West Coast), dynamics were more complex: most species experienced strong temporal changes, while some showed spatial changes and others had spatiotemporal interactions. These dramatic changes likely impact trophic structure in continental shelf communities. To illustrate the magnitude of these impacts, we examined the effect of size and abundance changes on energetic demands of two co-occurring species, bocaccio (S. paucispinis) and chilipepper (S. goodei). Using bioenergetics models, we estimated that predatory demands of chilipepper increased by 5- to 10-fold relative to bocaccio in 2 of the 4 zones where both fish occur, and by up to three orders of magnitude in a third zone. This enormous change in the energy pathways of rockfish communities may constrain recovery of bocaccio, which are considered critically endangered by the IUCN. Similar scenarios may be occurring in other rockfish assemblages. Our findings suggest that many rockfish community changes have been spatially discrete and require appropriately scaled management responses. This supports a growing consensus that community-based approaches are necessary for sustainable fisheries management.
Key words: food web structure, energy flow, rockfish, fishing