Variations in physical and biological oceanography, juvenile salmon and age-0 pollock during fall in the eastern Bering Sea

1
Variations in physical and biological
oceanography, juvenile salmon and age-0 pollock
during fall in the eastern Bering Sea

• L.B. Eisner, K.D. Cieciel, M.D. Courtney, E.V.
  Farley, A. Middleton, J.M. Murphy, J. Pohl and
  J.H. Helle
• National Marine Fisheries Service, Auke Bay
  Laboratory, Juneau, Alaska

2
Objective

• To compare oceanographic characteristics to the
  distribution, abundance and condition of juvenile
  salmon and other pelagic fish in the eastern
  Bering Sea during fall.

3
Survey design and vessel

• 2000-2001 Prior studies 2002-2005 BASIS
• Commercial trawler (39 m)
• Mid-Aug to mid-Oct (Bristol Bay sampled late Aug
  to early Sept)

4
Methods

• Surface Rope Trawl
• Collect juvenile salmon, pelagic fish, jellyfish
• Surface trawl (60m X 15m)
• Stomach content
• Scales for age and growth
• Caloric content
• DNA analysis for stock ID
• Isotope and fatty acid analyses for trophic
  interactions

5

• Zooplankton
• Bongo net oblique tow (335 and 505 µm mesh)
• Juday net vertical tow (160 µm mesh)

• Oceanography
• Thermosalinograph
• CTD
• Chl a
• Beam c
• PAR
• DO

• Water samples (2003-2005)
• Microzooplankton
• Phytoplankton
• Chl a gt 0.7 µm (GF/F), gt 2 µm, gt 5 µm, gt 10 µm
  size fraction
• Nutrients (N, P, Si)

chl a filtration
6
Outline

• Patterns in oceanographic variables
• T, S, density
• Nutrients, chl a
• Patterns in forge fish distribution and condition
• Herring
• Juvenile sockeye salmon
• Age-0 pollock
• Conclusions

7
Results
Surface (5 m) T and S
2000
2001
2002
2003
2004
2005
8
2003
2004
5 m nutrients and chl a (from discrete water
samples)
Nitrate (µM)
Total Chl a (µg L-1)
9
2002
2003
2004
2005
Temp 40 m
10
Pelagic fish biomass (kg m-2), fall 2004
Salmon (all species)
Herring
Pollock
SST
Salinity
Blue Adult Red Juvenile
11
Juvenile sockeye distribution and SST
2001
2002
2003
2004
2000
5 m Temp
Juvenile Sockeye Salmon
12
Biological Indices for Bristol Bay Sockeye Salmon
Abundance
In general, indices of condition were
significantly higher during 2002 and 2003 when
compared to 2000 and 2001.
13
245
Zoo biomass (505 µm)
2001 164W transect
S. vol. (ml)
J. sockeye
CPUE
Age 0 pollock
CPUE
Temp (C)
Chl a
14
Zoo biomass (505 µm)
2003 164W transect
S. vol. (ml)
J. sockeye
CPUE
Age 0 pollock
CPUE
Temp (C)
Chl a
15
Age-0 pollock energy density 2003 and 2004
Central
N. Bering
Bristol Bay

• Central Shelf age-0 pollock energy density
• Lower than other regions
• (plt 0.05).
• Lower in 2003 than in 2004 (plt 0.05).

Angela Middleton (unpubl.)
16
2003 coccolithophore and age-0 pollock
distribution
SeaWiFS coccolithophore mask image
19-Sept-03, Saitoh and Iida (unpubl.)
17
Conclusions

• SST higher in 2002 2005 than 2000 2001.
• High surface nutrients in SE Bristol Bay.
• Low nitrate below pycnocline in Central Shelf.
• J. sockeye salmon in 2000 2001
• distributed further south
• less abundant, smaller, lower marine survival
• Age-0 pollock
• primary prey for J. sockeye (60-75 wet wt. in
  2003-2004)
• lower abundance in 2000-2001
• energy density lower in Central Shelf
• energy density lower in 2003 (related to
  coccolithophore distribution?)

18
Conclusions (cont.)

• Zooplankton, phytoplankton, herring, age-0
  pollock, J. sockeye vary across fronts.