Presentation on theme: "Relative vulnerability to avian predation of PIT-tagged Columbia River subyearling Fall Chinook salmon Scott H. Sebring, Melissa C. Carper Pacific States."— Presentation transcript:
Relative vulnerability to avian predation of PIT-tagged Columbia River subyearling Fall Chinook salmon Scott H. Sebring, Melissa C. Carper Pacific States Marine Fisheries Commission Richard D. Ledgerwood, Gene M. Matthews, and Ben Sandford NOAA Fisheries
Washington Oregon East Sand Island The Columbia River estuary hosts large migratory populations of colonial nesting waterbirds 20,000 terns22,000 cormorants
These avian species consume lots of outmigrating Columbia River salmon Combined consumption of outmigrating salmon by terns and cormorants nesting on East Sand Island is estimated at 17.5 million (13.3 – 21.7 million; 95% CI; Roby et al. 2009). Such large consumption is problematic because many salmon species are listed under ESA. Management of avian predation is an element in the NOAA Biological Opinion.
Nesting chronology and foraging ecology of Caspian terns and double-crested cormorants Foraging ecology Caspian terns Plunge-diving Double-crested cormorant Pursuit-diving Nesting Chronology Caspian terns (late March – early September) Double-crested cormorants (late March – late September)
Birds exhibit preference for particular salmon species Predation rates of PIT-tagged salmonids are variable, but generally ~5% upon entering the lower-river; yet there are notable exceptions Predation rates for steelhead regularly exceed 15% because this species is surface-oriented, and thus highly vulnerable to Caspian terns It is unknown whether predation rates are uniform among a similar species across ESUs
Objectives and methods Our objectives were to: -document vulnerability of lower-river hatchery released subyearling Chinook salmon. -evaluate vulnerability of different subyearling Chinook salmon ESUs and stock types (Tule and Upriver bright). We PIT-tagged 3,000 subyearling fall Chinook salmon each year at hatcheries within the lower-river (downstream of Bonneville Dam). We compared predation rates of PIT-tagged subyearlings released from lower-river hatcheries to those detected at Bonneville Dam.
Avian predation rates are estimated by recovering PIT tags from vacated breeding colonies Juvenile salmon are implanted with PIT tags. Avian predators “sample” these fish and deposit PIT tags on colony surface. We electronically detect PIT tags deposited by avian predators on East Sand Island using methods discussed in greater detail by Ryan et al. (2001).
Predation of lower-river PIT-tagged subyearlings by East Sand Island bird species Year 20022003200520062007200820092010Total Tule stock Released (#)5,3155,8472,9993,03112,33012,19012,11612,25153,828 Predation rate (%)32.622.822.233.014.837.523.420.626.6 Release groups2211444422 Upriver bright stock Released (#)3,0042,9935,997 Predation rate (%)22.214.171.124 Release groups112 If predation rates of PIT-tagged fish are similar to those of non-marked fish, consumption of lower-river subyearling fall Chinook salmon is ~6.5 million annually.
Number released Release yearRelease siteStockTOTAL % 2002 Big CreekTule2,92732 Sea ResourcesTule2,38834 Bonneville DamUpriver bright11,2033 2003 Big CreekTule2,97415 Sea ResourcesTule2,87331 Bonneville DamUpriver bright8,0732 2005 Big CreekTule2,99922 Bonneville hatcheryUpriver bright3,0045 Bonneville DamUpriver bright8513 2006 Big CreekTule3,03133 Bonneville hatcheryUpriver bright2,9933 Bonneville DamUpriver bright11,0685 Summary results (2002 – 2006)
Summary results (2009 – 2010) Release yearRelease siteStockNumber releasedTOTAL % 2009 Big CreekTule3,03823 Deep RiverTule3,16226 Kalama FallsTule2,90222 WarrentonTule3,01423 Bonneville DamTule13,3696 Bonneville DamUpriver bright12,7485 2010 Big CreekTule3,05127 Deep RiverTule3,08526 North ToutleTule3,07316 WarrentonTule3,04219 Bonneville DamTule1,24321 Bonneville DamUpriver bright13,3363 If predation rates of PIT-tagged fish are similar to those of non-marked fish, consumption of lower-river subyearling fall Chinook salmon is ~6.5 million annually.
Big Creek and Sea Resources hatcheries (2002 & 2003) Predation rate (%) Number of fish detected or released (N) Date of release or detection Detections (N) Tule (%) URB (%) Bonneville Dam Releases (N) Tule (%) URB (%) Lower-river
Big Creek and Bonneville hatcheries (2005 & 2006) Predation rate (%) Number of fish detected or released (N) Date of release or detection Detections (N) Tule (%) URB (%) Bonneville Dam Releases (N) Tule (%) URB (%) Lower-river
Big Creek, Elochoman, Kalama, North Toutle, Washougal, WHS hatcheries (2007 & 2008) Predation rate (%) Number of fish detected or released (N) Date of release or detection Detections (N) Tule (%) URB (%) Bonneville Dam Releases (N) Tule (%) URB (%) Lower-river
Big Creek, Deep River, Kalama, North Toutle, WHS hatcheries (2009 & 2010) Predation rate (%) Number of fish detected or released (N) Detections (N) Tule (%) URB (%) Bonneville Dam Releases (N) Tule (%) URB (%) Lower-river
Bonneville Dam Year Cormorant (%) Tern (%) Cormorant (%) Tern (%) 2002841650 200375252971 200587133565 200674263070 200779213763 200888127030 200978226931 201077238218 Mean802050 Mean annual proportions of PIT-tagged subyearlings consumed by release location
Why are predation rates so different? Researchers from coastal B.C. to the Sacramento Valley have documented prolonged residency of subyearling Chinook salmon in estuaries and seasonally flooded wetlands. Upriver bright stock (because of their genetics and generally longer migration distance) rear in the estuary for less time than do Tule stock. Tule originate closer to the estuary and juvenile outmigrants need more time to rear prior to ocean entry. This suggests that prolonged residency in locations nearby large breeding colonies may be a disadvantage. It is unknown whether lower-river fish exhibit behavior immediately following release causing exceptional vulnerability.
Summary Subyearling tule fall Chinook salmon are the most vulnerable salmonid ESU known in the Columbia River. Annual consumption of subyearlings released into the lower-river is approximately 6.5 million fish. The majority of subyearling Chinook salmon is consumed by double-crested cormorants. Will management agencies successfully relocate both Caspian terns AND double-crested cormorants outside of the Columbia River Basin?
Funding provided by: U.S. Army Corps of Engineers Walla Walla District Thanks: April Cameron Allen Evans Matt Morris Michael Morrow Beth Phillips Michelle Rub Brad Ryan Nick Zametkin and others who assisted this tagging project over the years Acknowledgments