Ecology of stream-rearing salmon and trout Part II

Transcription

1 Ecology of stream-rearing salmon and trout Part II Individual Feeding territory Habitat use Growth Movement Survival Population Population Abundance Density Variation Movement Individual

2 Relationship between stream size and shifts in the structure and function of communities Vannote et al. 1980

3 From the ridge-top to the ocean: Elevation decreases Gradient decreases Air temperature regime changes Stream widens and deepens (slower response to air temperature) Canopy closure is reduced; sunlight increases Primary production shifts from allochthonous (leaves, needles) to autochthonous (algae on rocks) Insect community shifts Non-salmonid and salmonid communities change

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5 Species-specific fry distributions may reflect adult as well as juvenile ecology Cumulative proportion chinook salmon coho salmon cutthroat trout steelhead trout Upstream distance (km) Sitkum River, Quileute River basin: John McMillan & James Starr

6 Species composition and density of juvenile salmonids are affected by stream gradient, reflecting juvenile and adult ecology Gradient (m/km) 0+ coho Fish density (fish/m ) 0+ trout 2 1+ steelhead 1+ cutthroat High (24.1) Low (10.9) Averages of 5 high and 5 low gradient streams in Oregon; Hicks and Hall 2003

7 7 The number of smolts leaving a given stream can vary among years Number of years Number of coho salmon smolts leaving Big Beef Creek

8 What explains the variation in number of smolts produced from a given stream among years? 1) The number of parents that spawned in the previous generation 2) Physical habitat limitation 1) floods during the incubation period 2) low flow during the summer 3) high flow during the following winter

9 When streams reach their carrying capacity, more spawning adults do not produce more smolts Number of smolts 60,000 45,000 30,000 15,000 0 Big Beef Snow Number of parents Lestelle et al. (1993), Thom Johnson WDFW, and Seiler et al. (2002)

10 Relationship between a runoff index and catch of coho salmon Coho salmon catch 2 years later (millions) R 2 = Smoker 1955 Average annual runoff (cm)

11 Given adequate escapement, smolt production may be limited by low flow in some streams Number of smolts 50,000 45,000 40,000 35,000 30,000 25,000 20,000 15,000 10,000 5,000 0 Big Beef Creek, Washington Seiler 2002; USGS records Summer low flow (m 3 /sec)

12 What controls the number of coho salmon smolts produced among different streams? coho salmon smolts All other things being equal, bigger streams produce more smolts than smaller streams Bradford et al stream length (km)

13 Other than size, what determines the capacity of different streams to produce salmon smolts?

14 More coho salmon smolts are produced from streams with a higher density of pools (western Washington streams) 5000 smolts/km Pool area/km Sharma and Hilborn 2001

15 Pool volume is associated with large woody debris (= large organic debris, coarse woody debris) 35 Pool Volume (m 3 /100m 2 ) Murphy et al CJFAS Buffered Old-growth Clear-cut Debris Volume (m 3 /100m 2 )

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17 Abundance of woody debris is positively related to the density of juvenile coho salmon 0.25 Coho density (number/m 2) Hicks et al In: Meehan (Ed) Total Large Organic Debris (m 3 )

18 Is habitat complexity important for salmonids? Dolloff (1996) manipulated the density of woody debris in two Alaska streams and observed reduced summer density of coho salmon and Dolly Varden, especially older fish Tye Creek Cleaned Control Difference Coho Age % Coho Age % D.V. Age % D.V. Age % Toad Creek Coho Age % Coho Age % D.V. Age % D.V. Age %

19 Is habitat complexity important for juvenile salmonids? Lateral habitat (backwaters, eddies) were experimentally manipulated in small Oregon streams prior to emergence of cutthroat trout fry in the spring Response habitat No change habitat % lateral habitat Fish/100 m Fish/100 m 2 lateral habitat Moore and Gregory TAFS 117:

20 Winter survival of coho salmon in Big Beef Creek was positively related to large woody debris density parr - smolt survival (%) Quinn and Peterson 1996 LWD (m 3 per 100 m)

21 Juvenile salmonids use available habitat selectively. Depth (cm) Coho salmon tend to occupy slow, deep water (pools). Healy and Lonzarich 2000 Velocity (cm/sec)

22 Habitat utilization by coho salmon 80 Velocity (cm/s) Tolerance Avoidance Bisson et al. coho conference Preference Depth (cm)

23 Many species show ontogenetic shifts in habitat use: Issaquah Creek cutthroat trout % of the sample Mean = 22.5 Mean = 34.1 Mean = Water depth (cm) age 0 age 1 age 2

24 Salmonid species also segregate to some extent in streams Atlantic salmon (foreground) and coho salmon Roger Tabor

25 Habitat use patterns vary among salmonids (and other fishes), reflecting choice and competition 5 Roni 2002 individuals per 10 m pools riffles 0 coho salmon trout salamanders larval lampreys reticulate sculpins torrent sculpins

26 Competition and segregation among species Trout spawn in spring and have smaller eggs than coho salmon, so the trout fry emerge later and are smaller than the salmon Do the trout tend to occupy shallower, faster water than coho because they are dominated by the larger coho, or because they prefer different habitat? Is the expansion of habitat use by allopatric populations evidence of competitive exclusion? Sabo and Pauley 1997 CJFAS

27 The perspective of salmonid populations in streams Variation among sites Variation among years Stream length (smolts/creek) Density (smolts/year) Fixed attributes (smolts/km) Physical conditions (smolts/female) Within- and between-species effects

28 World-wide, the distribution of stream productivity for salmonids is very skewed. % of estimates High productivity results more from growth than density, and more from chemistry and temperature than habitat and substrate. Coastal NW streams are not highly productive > 20 Bisson and Bilby 1998 Annual production (g/m 2 /year)

29 number of estimates number of estimates median = > 10 Biomass (grams/m 2 ) median = > 1.0 Density (fish/m 2 ) Estimates of biomass and density of trout and charr in western Washington, Oregon and California are generally low. Platts and McHenry 1988

30 Roger Tabor

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