8155

• UCREFRP Catalog Number: 8155
• Author: Minckley, W. L.
• Title: Executive Summary
• USFW Year: 1985.
• USFW - Doc Type: Native Fishes and Natural Aquatic Habitats in U.S. Fish and Wildlife Service Region II West of the Continental Divide.
• Copyright Material: NO

seems to have resembled that of Colorado squawfish (citations above) except
it did not penetrate as far into tributaries of the Gila River. The most
upstream records were Salt River at Tempe (Gilbert and Scofield 1898) and
Gila River at Ft. Thomas (Kirsch 1889); it ~lIas not definitely recorded
in the San Pedro mainstream.

This is 1 iKely the most endangered species in the Region. Onl'l a fel,1I
adul ts and no recognized young have been taKen in the intensive Colorado
River Fisheries Project in the upper basin (Miller et ~. 1982; Keading !1
ll. 1986) and the last 10calit;1 of occurrence in the lmller basin is Lake
Nohave, Arizona-Nevada, where only 24 large adul ts (all greater than 40 cm
TL) have been taKen in extensive trammel-netting operations since 1975 (in
part MincKley 1983).

Reasons for dec 1 i ne of th i s spec i es are as obscure and specu 1 at i ve as
for Colorado squawfish. As already demonstrated for razorbacK sucKer
(H i ncK 1 ey 1983; HcCar thy 1986) bonyta i 1 in that reservo i r seem to be
persisting without successful recruitment. Three specimens from LaKe
Nohave aged by otol ith examination ranged from 34 to 49 years of age.
There may have been little if any reproductive success since at least the
early 1950s, which may have resulted from habitat modifications,
interactions with introduced species, or both. No sol id data have been
accumulated, and the fish is now so rare that no natural populations remain
for study and evaluation. Requirements for maintaining natural stocKs of
this species in Category I or II habitats are as yet unKnown.

A brood stocK of hatchery produced first generation fish derived fram
11 wild-caught adults from Lake Hohave is currently at Dexter NFH. The
species has been artificially propagated and reared to adulthood both in
concrete raceways and earthen ponds (Hamman 1981, 1982a, b). Bony tail also
surprisingly produce substantial year classes under pond conditions at
Dexter NFH (unpubl. data). Furthermore, young placed in a small urban lake
in Blythe, Cal ifornia, and allowed to grow to advanced fingerl ing stages in
isolation, later grew to average more than 25 cm TL despite an expanding
population of non-native mosquitofish and African cichl ids (Oreochromis
spp.) (Linda Ulm~r, Cal ifornia Department of Fish and Gam~ [CDFGJ, pers.
camm.) This provides supporting data for possible maintenanc~ of the
species and perhaps other big-river forms in semi-natural habitats
(Category VI) of USFWS Refuges or other protected lands along the Colorado
River (MincKley 1986) (pp. 102-103).

The only reintroduction attempts have been to augment existing stocks
in LaKe Nohave and a single stocking in an isolated backwater, which
failed. Those placed in the main body of the laKe were later recorded as
an individual gill-n~tted a few weeKs aft~r stocKing (Arizona Game and Fish
Department [AGFDJ, unpubl. data). Loss of the backwater fish was assumed
to result from predation by introduc~d species that survived an attempted
r~novation (unpubl. data). Howe'J~r, no direct elJidence of predation was
collected ev~n in this s~mi-natural situation.

As l,lJith Colorado squal,lIfish, projected reintroductions of bony tail into
the lmver Colorado Ri'.,oer basin ha'Je been delayed by pol itical disputes, but
are anticipated in the near future on an experimental basis. StocKing of
this form in the upper basin may be ill advised because of already-apparent
problem~ ot hybridization in the genu:. Gil3., I,.lIhich in'.'olIJes bony tail,

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