Assessing Estuarine Residence Time in Sockeye and Coho Salmon

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Assessing Estuarine Residence Time in Sockeye and
Coho Salmon

• Mary Anne Bishop,
• Sean P. Powers, And Gordon H. Reeves

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Salmonids
Sockeye
Silver
Pink
Chinook
NMFS
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PWS
Copper River

• 6th largest watershed in Alaska
• 2nd highest average discharge in Alaska
• 69 107 million tons suspended sediment

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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.

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Surface Salinity 2004
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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

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Cordova.
Eyak R.
Scott R.
Sheridan R.
Eyak R.
Copper R.
Alaganik
Alaganik
Watershed
Fyke Net Seine Stations
Trawl station
Screwtrap
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Sockeye Migration Timing
Data are from the Eyak River Screwtrap in 2005
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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
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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
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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
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Otolith Microchemistry
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Typical Adult Profiles
res time 40 days
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Validation of Sr Concentration as a proxy for
salinity
Salinity increase in experiment
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Validation of Sr Concentration as a proxy for
salinity
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Juveniles captured in the estuary
Estimated residence time 56 days
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Adult coho profile
Estimated residence time 19 days
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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.

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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