9640 - Laserfiche WebLink

Home Browse Search

a b AN, z ¢ GO a" t Col GM zZ2 ass m CIOI ZO G02 Z25 AB1 zz, ABf z,x AB5 Z25 ASS rya A92 ryo A81 Yy5 A83 YV4 A85 M LD, roz - 0.001 0.001 C ,0 13 P R2 0.001 Figure 4. Coalescent genealogies that maximize the likelihood of the DNA data for (u) humpback chub, (b) bonytail, and (c) razorback s Garrigan et al. 2002). Branch lengths are scaled in terms of the nu tions per site. The letters on the tree branches represent the names o and numbers represent individuals with those sequences. The dicta identical sequences represents the time, in generations, since a com three remaining haplotypes are quite divergent; this suggests that present genetic variation still reflects a high degree of an- cestral variation. Variation in the other three species remains even more intact. However, this variation will decay quickly if population sizes that define recovery are small and, more critically, if the population is founded or maintained by small numbers of brood fish. The Fish and Wildlife Service (USFWS 2002a, 2002b, 2002c, 2002d) proposed recovery goals of N_ = 700-5800 wild fish per species or river reach for big-river fishes in the upper Colorado basin. Recovery goals for downlisting and delisting include minimum census population sizes of 2100 adult humpback chub in each of 3 populations, 4400 bonytail in each of 4 populations, 5800 razorback sucker in each of 4 populations, and 700 (upper Col- orado River) or 800 (San Juan River) plus 2600 (Green River) Colorado squawfish (USFWS 2002a, 2002b, 2002c, 2002d). Brood stocks for razorback sucker, on which future stocking toward re- covery is to be based, have been de- veloped from as few as 5 and up to 25 paired matings using 5 males and 5 fe- males (Minckley et al. 1991). Such low initial stocks are utterly inade- quate and cannot be supported by any contemporary science. The goals proposed by USFWS are lower than any historical estimate of population size for bonytail, the species with the smallest estimated long term Ne These low numbers are especially dis- conc:efting for the other taxa because far larger numbers, and thus far more genetic variability, can be readily maintained. We strongly recommend circum- venting the pitfalls of hatchery culture (Ryman et al. 1993, Hindar 1994, Dowling et al. 1996a), as this has al- ready severely restricted the genetic variability of hatchery stocks and their progeny of bonytail (Hedrick et al. 2000) and razorback sucker (Dowling et al. 1996a). However, we recognize there are differences of opinion rela- mitochondrial tive to the role of artificial propagation tuber of substitu- (juvenile or adult) life stages. Re- ueker (from and growth from larvae into larger the haplotype, gnudless of the mating strategy ap nce between plied, the only genetic variation that non ancestor. can be passed to the future from a hatchery setting is that of the original brood fish. Despite uninformed protestations to the contrary, all pos- sible combinations of 5 males and 5 females still provide the genetic variation of only 10 fish and are wholly inadequate for the recovery of lower Colorado River native fishes. If N is re- duced, either naturally or through improper management, ge- netic variation is diminished and less new variation generated, potentially reducing fitness because of fixation of detrimen- tal alleles. Such reductions in fitness when 1q declines appear to be a particularly severe problem in species with large an- cestral populations and high historical genetic loads (Hedrick and Kalinowski 2000). A far higher target for 1\ must be set so all four endangered fishes may continue to evolve in a way resembling that of the 226 BioSdence • March 2003 / Vol. 53 No. 3