Photo by John McMillan Spawning habitat Winter rearing Summer rearing Smolt Carrying Capacity

Definition Carrying Capacity = Number of individuals (K) the resources of a given area can support usually through the most unfavorable period of the year. –Tied to Limiting Factors 2

Population Regulation Density Independent Regulation = Population growth is not affected by population density; population persistence is explained by unpredictable environmental variability (Andrewartha and Birch). Density Dependent Regulation = Population growth is affected by mechanisms whose effectiveness increases as population size increases (Nicholson, Lack, and Elton). 3

Evidence of Density Dependence Plot of population size and population growth rate (or surrogates such as mortality, natality, productivity, recruits, individual growth rates, movement). There is a negative relationship between population size and growth rate, which means that carrying capacity may be estimated. 4

Methods for Estimating Carrying Capacity Time series of population growth over time (logistic function) Habitat modeling (maximum number of fish within each habitat type; PHS) Stock-recruitment modeling (Ricker, Beverton-Holt, or Smooth Hockey Stick) 5

Assumptions Assume we can define a population unambiguously. Assume that we can measure population size accurately. Assume that we have a biologically relevant time-step over which to measure the population growth rate. Assume a uniformity of nature. 6

Habitat Models 7

Stock-Recruitment Modeling 8

Chiwawa Spring Chinook Habitat Model No habitat modeling has been completed in the Chiwawa River basin. No estimates of PHS have been calculated. Maximum parr and yearling smolt production likely occurred in 2002 when 1,725 spawners escaped in One can also select the maximum number of parr and smolts. 9

Chiwawa Spring Chinook Stock-Recruitment Model Stock-recruitment functions were fit successfully to parr and yearling smolt data. 10

Chiwawa Spring Chinook Stock-Recruitment Model Parr: Smolt: 11 Model Parameter Carrying capacity Productivity Maximum stock AB Ricker , ,500,000 Hockey Stick , ,455,000 Beverton-Holt 155, , , ∞ Model Parameter Carrying capacity Productivity Maximum stock AB Ricker , ,500,000 Hockey Stick , ,825,000 Beverton-Holt 63, , , ∞

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