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Density-dependent reinforcing mechanisms of anadromy in partially migratory salmonid populations. Matt Sloat Department of Fisheries and Wildlife Oregon State University. Partial migration- populations in which only a portion of individuals adopts a migratory life history.

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slide1

Density-dependent reinforcing mechanisms of anadromy in partially migratory salmonid populations

Matt Sloat

Department of Fisheries and Wildlife

Oregon State University

slide2

Partial migration- populations in which only a portion of individuals adopts a migratory life history.

slide3

Salmonid species exhibiting partial migration:

steelhead/rainbow trout (Oncorhynchus mykiss)

coastal cutthroat trout (O. clarki)

masu salmon (O. masuo)

brown trout (Salmon trutta)

brook charr (Salvelinus fontinalis)

slide4

Partial migration- populations in which only a portion of individuals adopts a migratory life history.

What are proximate mechanisms causing individuals to adopt alternative life histories?

What is the importance of the critical period?

slide5

Stream salmonids actively defend

territories used for feeding on

drifting invertebrates.

Within a given environment

growth depends on access to food

which is driven by social dominance.

Hartman 1965

slide7

Fish with higher relative metabolic rates tend to become dominant (Metcalfe 1995).

Similar results for:

rainbow trout (McCarty 2001)

masu salmon (Yamamoto et al. 1998)

brown trout (Titus and Mosegaard 1991)

slide9

Migrants

Residents

Somatic growth

Waste

Metabolic costs

Fish with higher metabolic costs tend to become migratory.

Brook charr (Morineville and Rasmussen 2003)

Similar results for brown trout (Forseth et al. 1995)

slide10

Hypothesis

  • Standard metabolic rate is a good predictor of competitive dominance in stream salmonids.
  • If intraspecific competition favors individuals with higher SMR, then increases in competitive intensity should increase strength of selection for fish with higher SMR.
  • If having higher metabolic costs increases the probability of becoming anadromous, increasing competition may increase the propensity for anadromy.
slide11

Experimental test of density effects on selection for relative metabolic rate in

O. mykiss

slide13

Experimental channels

inflow

flow direction

0.3 m

2.5 m

bricks

emigration

trap

slide16

Preliminary results

  • Patterns of emigration
  • Final density
  • Otolith size of territorial fish under
  • different treatments
slide17

p1

p3

p2

slide18

Final density

Final channel densities

Stocking density

slide19

CC

B

A

Probability density

Otolith size

slide20

Discussion:

  • If there is selection for SMR with increasing intensity of intraspecific competition what are the implications for life history expression?
slide21

Shift in mean MR to higher

values. Less variance in

individual physiologies.

More variance in

individual physiologies

Metabolic rate

Metabolic rate

Recruits (parr)

Stock (eggs or alevins)

Weak selection on MR. Wider range of realized growth because of wider range of physiologies and decreased energy expenditure defending territories.

Selective emigration or mortality

of low MR individuals. Greater proportion of individuals prone to

migration.

Modified from Titus (1990)

slide22

Summary

  • Standard metabolic rate is a good predictor of competitive dominance in stream salmonids.
  • If intraspecific competition favors individuals with higher SMR , then increases in competitive intensity should increase strength of selection for fish with higher SMR.
  • Since migrants have higher relative metabolic costs, increasing competition may increase the propensity for anadromy.
slide23

Future work (an incomplete list):

  • Refinement of analyses.
  • Respirometry of offspring from resident
  • and anadromous parents.
  • 3) Measurement of other traits correlated
  • with life history expression.
slide24

Acknowledgments:

Funding provided by USFS PNWRS and USGS FRESC, Corvallis.

ORAFS Carl Bond Memorial Scholarship

Thanks to Gordie Reeves, Jason Dunham, Brian Neilson, India Sloat, Don Stevens,

Don Ratliff, Rich Madden, Jack Palmer, Michael Reeves.