9666

• UCREFRP Catalog Number: 9666
• Author: VanHaverbeke, D. R. and Robert L. Simmonds Jr.
• Title: Final Report - The Feasibility of Developing a Program To Augment the Population of Humpback Chub ‎(Gila cypha)‎ In Grand Canyon.
• USFW Year: 2004.
• USFW - Doc Type: Flagstaff, AZ.
• Copyright Material: NO

recruitment rates continue to remain at the mid-1990s level; a factor that mayor may
not be realized in the years to come.

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1990 1995

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;

2000

2005

2010

2015

2020

Year

I-+-age 1 recruits ___Age 4+ spawners I

Figure 3. Provisional estimated and projected humpback chub population (Little
Colorado River [LCR] stock) in Grand Canyon, assuming recruitment remains at mid
1990s level. This example figure of the base Age Structured Mark-Recapture model
depicts the predicted effect of capturing 1,350 age-O humpback chub per year from the
LCR, growing them in captivity to 171 mm, and beginning release in 2005. The model
predicts that by the year 2020, abundance estimates of age-4+ fish would equal the
abundance estimated to be present in the year 2000.

As mentioned above, based on culturing bony tails, mortality in the hatchery system
could easily average 20%, and one might reason that the less time fish spend in the
hatchery, the less chance for mortality to occur. Also, if the low survival rates of other
stocked species are any indication (McNeil 1991, Salvanes 2001), we can only assume
that post-stocking mortality of humpback chub could be high (i.e., >50%, or much higher
than wild survival rates for an equivalent sized fish). This suggests that the numbers of
age-O fish collected may need to be doubled (C. Walters, UBC, pers. com.). It should
also be understood that if positive results are achieved, they may not be self-sustaining
if the original causes for the decline in wild recruitment failure have not been solved. In
addition, about 50 to 60 fish are generally killed for health studies each time fish are
brought from the wild into a hatchery station (J. Thoesen, USFWS, Fish Health, pers.
com.).

The question has been raised as to what proportion of the wild population will be
removed annually for this endeavor. Estimates of 1 year old recruits (-93 mm; Table 1)
in the past few years have been -4,000 to 5,000 fish (C. Walters, UBC, pers. com.).

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