Feasibility of Fish Passage at Alameda Creek Diversion Dam
Feasibility of Fish Passage at Alameda Creek Diversion Dam
Feasibility of Fish Passage at Alameda Creek Diversion Dam
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Appendix CTechnical Inform<strong>at</strong>ion on Minimum Viable Popul<strong>at</strong>ion SizeAppendix CTechnical Inform<strong>at</strong>ion on Minimum Viable Popul<strong>at</strong>ion SizeEcologists have developed several models to determine minimum viable popul<strong>at</strong>ion sizes. Thesemodels have been characterized as popul<strong>at</strong>ion viability analyses. The basic model used tocharacterize popul<strong>at</strong>ion growth iswhere,Nt+1 = λN t(1)N t+1 is the estim<strong>at</strong>ed popul<strong>at</strong>ion size in the next gener<strong>at</strong>ion; λ is the r<strong>at</strong>e <strong>of</strong> popul<strong>at</strong>ion growth; and N tis the number <strong>of</strong> breeding pairs currently in the popul<strong>at</strong>ion (i.e., initial popul<strong>at</strong>ion size). If λ=1 thepopul<strong>at</strong>ion is stable, if λ1 the popul<strong>at</strong>ion is growing (Taylor,1995).For salmonids, the growth r<strong>at</strong>e <strong>of</strong> the popul<strong>at</strong>ion, λ, is dependent upon the proportion <strong>of</strong> individualssurviving from one life stage to the next, and can be expressed aswhere,λ = E ⋅ S(2)1⋅ S2⋅ Sy 3⋅ S4E = Eggs produced from previous gener<strong>at</strong>ionS 1 = Egg to fry survivalS 2 = Fry to smolt survivalS 3 = Annual ocean survivaly = Years in ocean (since steelhead will spend <strong>at</strong> least 2 years <strong>at</strong> sea, y = 2)S 4 = migr<strong>at</strong>ion to spawning ground survivalLife stage survival r<strong>at</strong>es reported in the liter<strong>at</strong>ure can be used to estim<strong>at</strong>e λ; however, they are highlyvariable due to differences in inherited traits between popul<strong>at</strong>ions as well as n<strong>at</strong>ural andanthropogenic environmental disturbances. For example, Moyle (1976) reports numbers <strong>of</strong> eggsranging from 200 to 12,000 per adult female, but the number is generally found to be around 2,000eggs per kilogram <strong>of</strong> adult body weight.If conserv<strong>at</strong>ive assumptions are made for values <strong>of</strong> variables used to estim<strong>at</strong>e the growth r<strong>at</strong>e <strong>of</strong> thepopul<strong>at</strong>ion, λ, it is possible to estim<strong>at</strong>e the number <strong>of</strong> adults th<strong>at</strong> could potentially return if there wasenough spawning habit<strong>at</strong> to support 100 breeding females, N t , in the upstream tributaries <strong>of</strong> CalaverasReservoir. One hundred female steelhead producing <strong>at</strong> least 2,000 eggs per kilogram <strong>of</strong> body weight(weighing a minimum <strong>of</strong> 2.5 kilograms) could reportedly produce a total <strong>of</strong> 5,000 fertilized eggs, E.Estim<strong>at</strong>es for egg to fry survival r<strong>at</strong>es reported by Healey (1991) range from 14 to 94 percent inChinook salmon. Bradford (1995) reviewed the liter<strong>at</strong>ure on Pacific salmon survival and reports anaverage egg to smolt survival <strong>of</strong> 7 percent. Healey (1991) reports average ocean survival r<strong>at</strong>es <strong>of</strong>20 to 36 percent annually.ACDD <strong>Passage</strong> June 2009 Page C-1
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