6013

• UCREFRP Catalog Number: 6013
• Author: U.S. Fish and Wildlife Service, C. R. F. R. T.
• Title: Humpback Chup Recovery Plan.
• USFW Year: 1979.
• USFW - Doc Type: \
• Copyright Material: NO

and roundtail (wide), S) the loss of squamatian, especially on the nuehal
hump (closely approximated in the bonytail chub), and 6) expansive
.falcate fins. Gila
Characters distinguishing young humpbacks from othet youn8
are less definitive. The hump shows signs of forming at aPPrOK~ately 50 mm,
but detectin8 these
as does the flattened head and subterminal mouth,
features is difficult. The dorsal and anal fie ray counts of 9-10, and
subterminal of inferior mouth are probably the best distinguishing
character for young specimens (approx. 70 nom total length).
A considerable number of specimens of Gila have been collected
since the early 195as that do not fit the descriptivn~of either the
bonytail, roundtail, or humpback chub. Most of these fish are inter-
mediate in mosphology between the humpback chub and the other two species.
tail; but lateral creases,
3'he hump is usually similar to that of the bony
characteristic of the humpback chub, are also found on these intermediate
specimens. The intermediates show development of a. flat head, fleshy
snout and small eye, but not as extreme as Gila ~ (Aolden~andeeaathe er
170). These specimens tend to bridge the morphological gap ~~
ail and roundtail, and make it difficult
humpback chub and both the bonyt
to determine the intraspecific limits•of the humpback chub.
A manuscript is press (1978) by Smith, Miller, and Sable (University
of the specimens referred to by floldea and
of Michigan) suggests that many
Stalnaker (1970) and others as intergrades or Yrybrids are actually pure
Although their data are
Gila.cypba (see also Suttkus and Clem~ner 1977).
-sot available yet, it appears that the intraspecific variation of the
~pback chub includes all, or nearly all, abruptly humped specimens.
?his study, whey completed, is expected to clarify the taxonomic Problems.
surrounding the Gila ro, baste complex.
Recently researchers have generally referred to all Gila specimens
lden and Stalnaker 1975;
Frith a hump and lateral creases as Gila cS+yha (S°
Seethaler.et al. 1976; Kidd 1977;~golden 1977). Studies are underway to
zlarify the systemic status of the h~pback chub and to determine tb:relatioa-
ships of the intermediate forms. The humpback chub is defined in this report
ra include these intermediate forma.
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