Assessing Estuarine Residence Time in Sockeye and Coho Salmon

1. Assessing Estuarine Residence Time in Sockeye and Coho Salmon Mary Anne Bishop, Sean P. Powers, And Gordon H. Reeves

2. Salmonids Sockeye Silver Pink Chinook NMFS

3. PWS Copper River • 6th largest watershed in Alaska • 2nd highest average discharge in Alaska • 69 – 107 million tons suspended sediment

7. Objectives • (1) determine the age of freshwater outmigration and the length of residency in freshwater, estuarine and marine habitats for a representative sample of coho and sockeyes on the Copper River Delta, Alaska • (2) document habitat use, prey items, and growth of juvenile coho and sockeye during the estuarine phase of migration; and • (3) assess the predation risk of outmigrating juveniles and returning adults in estuarine habitats.

8. Surface Salinity 2004

9. Determining estuarine residence time: Traditional approach: Field Sampling (May – Oct, 2004 & 2005) • Screw trap to document timing of outmigration by life stage • Fyke net and seine collection to examine upper estuary sites. • Mid-water trawls to document, mid and lower estuarine occurrence

10. Cordova. Eyak R. Scott R. Sheridan R. Eyak R. Copper R. Alaganik Alaganik Watershed Fyke Net & Seine Stations Trawl station Screwtrap

11. Sockeye Migration Timing Data are from the Eyak River Screwtrap in 2005

12. Estuary • Sockeye parr and smolt can be found throughout the estuary from May to August • Peak abundance of sockeye smolt and parr occur from late May until early July. • Based on CPUE over time, the max residence time appears to be no more than 30-45 days for parr and smolt. * Data from mid-water trawl samples

13. Estuary • Coho parr and smolt can be found through-out the estuary in the summer • Peak abundance of coho smolt and parr occur from mid-May until mid-June. • Based on CPUE over time, the max residence time appears to be no more than 20-30 days for coho parr and smolt. * Data from mid-water trawl samples

14. 100% 80% 60% 40% 20% 100% 80% 0% 60% 40% 20% 0% Upper Mid Upper Mid Age of juvenile salmon collected in estuary 2004 2005 Coho Sockeye Coho Sockeye 0+ 0+ 0+ 1+ 1+ 1+ 2+ 2+ 2+ 0+ 0+ 0+ 1+ 1+ 1+ 2+ 2+ 2+ Upper Mid Upper Mid n = 716 n = 309 n = 232 n = 509 n = 97 n = 93 n = 101 n = 129

15. res time 40 days Otolith Microchemistry

16. Typical Adult Profiles res time 40 days

17. Validation of Sr Concentration as a proxy for salinity Salinity increase in experiment

18. Validation of Sr Concentration as a proxy for salinity

19. Juveniles captured in the estuary Estimated residence time 56 days

20. Adult coho profile Estimated residence time 19 days

21. Summary • Overall, there was general agreement between results of the intensive field collections and otolith chemical signatures with respect to estuarine residence time. Both techniques indicated a relatively brief period in estuarine waters (10-45 day, average 30 days) for both species. • Because estuarine habitats are critical for osmoregulatory adjustment to marine waters and offer rich foraging opportunities for smolt, estuarine habitats represent essential habitat for salmonid fisheries.

22. Acknowledgments Field Logistics Dan Bilderback, Sage Charters Field & Lab Assistance Brad Reynolds, Ben Hermanns, Margarite Leeds, Sara Ecolano, Signe Fritsch, Nate Geraldi, Monica Powers, Kevan Gregalis Funding sources North Pacific Research Board Prince William Sound Oil Spill Recovery Institute