Ocean ecology of salmon

1
Ocean ecology of salmon

• Distribution
• Mortality
• Food and growth
• Maturation

2
Coastal range of anadromous Pacific salmon and
trout
3
Alaska
Bering Sea
Gulf of Alaska
B.C.
Washington
North Pacific Ocean
Oregon
California
4
Much of what we know about the migrations and
ecology of salmon at sea is based on work by the
International North Pacific Fisheries Commission,
now the North Pacific Anadromous Fish Commission
Various techniques were employed to catch salmon
at sea
Purse seine fishing
5
Longline fishing
Gillnet fishing
6
Extensive tagging programs have been carried out
Sockeye salmon
7
Immature and maturing salmon tagged at sea are
recovered in coastal locations, indicating the
marine waters occupied by those populations
8
Juvenile salmon are tagged before they leave
freshwater
9
Extent of migrations at sea Pacific salmonids
show 4 migration patterns 1. Smolts migrate
rapidly northward along the coast during the
summer, then move offshore until they mature
sockeye, chum and pink salmon
Juvenile sockeye salmon
10
Marine distributions of North American and
Japanese chum salmon
11
Patterns of ocean migrations 2. Smolts migrate
along the coast or move offshore until they
mature coho, chinook and masu salmon
Adult coho salmon
Juvenile sockeye salmon
12
Most coho salmon are caught at sea near their
area of origin but they may move south or north
Catch area
Weitkamp and Neely 2002
13
Patterns of ocean migrations 3. Smolts migrate
directly offshore and remain at sea until they
mature steelhead (sea-run rainbow trout)
Juvenile sockeye salmon
14
Patterns of ocean migrations 4. Marine
distribution largely limited to estuarine or
coastal waters near the natal stream cutthroat
trout, bull trout (charr), Dolly Varden and
Arctic charr
Sea-run bull trout Salvelinus confluentus
15
Anadromous cutthroat trout, Oncorhynchus clarki
Anadromous cutthroat trout, Oncorhynchus clarki
16
Duration of stay at sea (winters) typical ( ),
less typical (), or rare
17
Survival of salmon at sea

• Attributes of the fish (size, migration date)
• Attributes of the environment
• Predators

18
It has been assumed that mortality is most severe
on small salmon, soon after they enter the ocean.
As they grow, survival rates are assumed to
decrease (e.g., Karluk Lake sockeye salmon
Ricker 1976).
19
Estimated mortality rate of Columbia River and
coastal Oregon coho salmon (1982-1985 William
Pearcy)
20
Large size at seawater entry favors survival but
is not the only factor
21
Large size affects smolt survival within but not
among years
Chilko Lake sockeye salmon
Year 1
Year 2
Survival ()
0 5 10 15 20
70 80 90 100
Length (mm)
22
Survival of coho salmon smolts was more strongly
affected by release date than body size
Quinsam River, B.C.
23
Extrinsic factors affecting survival

• Are there features of the ocean that affect (or
  are correlated with) survival?
• Are there trends in these features or periods of
  time when survival rates are high or low?
• Can these periods or trends be predicted?

24
Relationship between upwelling index and
post-smolt survival rate of Oregon hatchery coho
salmon
Upwelling
S. Mathews (1984)
25
Relationship between catches of central and
southeast Alaska pink salmon and coho off
Washington, Oregon and California (Francis and
Sibley 1991, updated).
26
Pink salmon catches in central and southeast
Alaska seem to follow winter temperatures
(November - March air temperatures in Sitka,
southeast Alaska).
27
We now understand that climate and ocean
conditions are linked. There are regimes that
favor salmon in one part of the range but not
others
Weak Aleutian low pressure system, located to the
west, favors southern populations
Strong Aleutian low pressure system, located to
the east, favors northern populations
28
Predation

• It is assumed that most of the mortality of
  salmon at sea results from predation, at least in
  a proximate sense
• Factors such as size or health may pre-dispose
  some fish to being eaten
• How do we determine the importance of a given
  predator to salmon, or the importance of salmon
  to a given predator?

29
Predators Are harbor seals (for example) a
significant predator on salmon?

• How many seals are there? 12,990 prior to
  pupping and 15,810 afterwards.
• How much fish do they eat? 1.9 kg or 4.3 body
  weight per day per seal
• What is the composition of their prey?

(Olesiuk 1993)
Mostly Pacific hake from April to November and
mostly Pacific herring from December to March in
the Strait of Georgia
30
Harbor seal diet in the Strait of Georgia, B. C.
Olesiuk (1993)
31
Marine mortality and the life cycle of salmon

• How does the reproductive output of salmon
  balance the various rates of mortality that they
  experience in freshwater and at sea?

32
Stage-specific mortality and the dynamics of
Fraser River chum salmon
Beacham and Starr. 1982. Fishery Bulletin 80
813-825
33
Feeding and growth of salmon at sea

• Salmon time their seaward migration to take
  advantage of marine prey
• Salmon grow rapidly and achieve gt 99 of their
  total weight at sea
• Salmon diets reflect the size and species of the
  fish, and the prey available to them
• Growing conditions vary among years, owing to
  physical processes and density of salmon

34
Synchronous downstream migration of pink salmon
fry and density of zooplankton in Prince William
Sound, Alaska (Cooney et al. 1995).
35
Annual cycle of average zooplankton density at
Ocean Station P (mean and standard error from
Brodeur et al. 1996).
36
Common salmon prey organisms
Hyperiid Amphipods
Euphausiids
Themisto pacifica
Thysanoessa longipes
15 23 mm
2 8 mm
37
Pteropods
Squid
Limacina helicina
Berryteuthis anonychus
Gonatopsis borealis
2 3 mm
Gonatus kamtschaticus
38
Some fishes eaten by salmon at sea
Northern lampfish (lanternfish)
Northern smoothtongue - Bathylagidae
Leuroglossus schmidti135 mm SL
39
Gelatinous zooplanktonctenophores, medusae,
salps (tunicates)
Beroe spp. 45 mm TL
40
Prey of salmon collected from the Bering Sea
basin 1991 to 2003
Sockeye lots of euphausids, amphipods, squid and
fish
Pink squid, euphausids, fish
Chum gelatinous material, pteropods, euphausids
Nancy Davis, FRI High Seas Salmon Project
41
Salmon prey composition Bering Sea Basin, summer
1991-2003
Coho fish, squid, euphausids
no data
no data
Chinook fish, squid, euphausids
42
Growth

• How does feeding translate into growth?
• Is there any evidence of density-dependence?
• Does temperature affect growth?

43
Density-dependent growth at sea mean length of
Hokkaido chum salmon as a function of the number
of adult chum salmon that year (from Kaeriyama
1998).
44
Mean length (mid-eye to fork of tail, males and
females combined, for fish spending two years at
sea) of adult Bristol Bay sockeye salmon as a
function of the number of adults returning to
spawn that year.
45
Hypothesized effects of ocean temperature and
density on sockeye salmon growth rate
Temperature 1
Body Size at Age
Temperature 2
Abundance
(Peterman 1984)
46
Growth and maturity

• Growth rate and age at maturity are inversely
  related
• Salmon that are large are more likely to mature
  whereas slower growing individuals stay at sea
  for another year
• Thus the largest salmon at maturity are typically
  the slowest growing ones

47
Conclusions

• The ocean is a rich (but not infinite) feeding
  pasture for salmon but it is also dangerous
• Salmon balance the reproductive benefits of large
  size against the risks of mortality at sea
• They stay at sea no longer than they must to get
  big enough to successfully reproduce

48
(No Transcript)
49
Back-calculated lengths of chinook salmon (in mm)
at different ages, as a function of their final
age at maturity (data from Parker and Larkin
1959).
50
Percent volumes of stomach contents for salmon
sampled in Strait of Juan de Fuca
lt 55 cm
gt55 cm
Total
Sockeye
0 40 80
stomach volume
lt 55 cm
lt 55 cm
Pink
0 40 80
Fish
Crustaceans
Miscellaneous
51
Percent volumes of stomach contents for salmon
sampled in Strait of Juan de Fuca
lt 40 cm
40-60 cm
Total
gt 60 cm
Coho
0 40 80
stomach volume
lt 40cm
lt 40-60 cm
gt 60 cm
Chinook
0 40 80
Fish
Crustaceans
Miscellaneous
52
Vancouver Is.
Puget Sound
Washington
Columbia River
Oregon
California
Sacramento River
53
Mean length has little or no bearing on variation
in annual smolt-to-adult survival
Chilko Lake sockeye salmon
Survival ()
0 10 20 30
72 82 92 102
Mean length (mm)
54
Mean fork length of Chilko Lake sockeye salmon
smolts and lengths of those that survived to
adulthood
In general, large smolts were more likely to
survive than smaller smolts in a given year.
(Henderson and Cass)
55
Commercial catches of salmon in Alaska (Rigby et
al. 1991, and unpublished data from the Alaska
Dept. of Fish and Game)
56
Growth of salmon at sea
McGurk 1996, Groot and Margolis 1991, Bigler et
al. 1996, Burgner et al. 1992, Kato 1991.