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Title: 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

4
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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
Age of juvenile salmon collected in estuary
2005
2004
Coho
Sockeye
Coho
Sockeye
0
1
2
0
1
2
0
1
2
0
1
2
0
1
2
0
1
2
Upper
Mid
Upper
Mid
n 716 n 309 n 232 n 509
n 97
n 101
n 129
n 93
15
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
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