9727

• UCREFRP Catalog Number: 9727
• Author: Marsh, P.C., B.R. Kesner and C.A. Pacey.
• Title: Repatriation as a management strategy to conserve a critically imperilled fish species.
• USFW Year: 2005.
• USFW - Doc Type: North American Journal of Fisheries Management
• Copyright Material: YES

aptured during March
to perform log-linear
-e not caught, and the
:sents the total number
50
i
:ed 4
72 is
sears
nber
the end is swiftly
strophic to success
catching wild lar-
;uccess in reintro-
3 species ultimate-
)n of at least 500
Ig without human
he razorback suck-
Mohave has been
ation of more than
I established, and
c diversity of the
al. 2005). Razor-
obtain survival and
tda, 1999-2002. The
ameters in the model
3
3
3
7
4
i
s
REPATRIATION TO CONSERVE IMPERILED FISH
Lu
0.9
0.8
0.7
2 0.6
0.5
" 0.4
0.3
02
0.1
0.0
0 100 200 300 400 500 600 700
TL (mm)
FIGURE 1.-First-year survival estimates as a function
of total length (TL) at release for repatriated razorbacks
that were later recaptured as adults during annual March
censuses in Lake Mohave, Arizona and Nevada, 1992-
2002. These estimates are derived from Program MARK,
which approximates the intercept and slope of a line-
arized function. The function is a logit-transformed lin-
earization with the original TL multiplied by 0.001, so
that all values lie between 0 and 1, which theoretically
improves chances of optimization. Values are calculated
from the linearized function and back-transformed to
represent actual TL versus survival. Parameter estimates
from the best-fit mark-recapture model in Table 4 were
used to calculate first-year survivorship.
back sucker is a long-lived species, and these in-
dividuals are expected to persist into the middle
of this century (McCarthy and Minckley 1987;
Marsh et al. 2003). However, the population can-
not persist in the long-term without human in-
volvement because nonnative species preclude re-
cruitment.
Successful recovery of razorback sucker is con-
tingent upon establishment of self-sustaining pop-
ulations established through augmentation (USFWS
2002). The Lake Mohave repatriation program dem-
onstrates that stocking has the capability to found
new adult populations, but overwhelming evidence
argues that self-sustenance is not possible in mixed
communities with nonnative fishes (Minckley and
Deacon 1991; Tyus and Saunders 1996; Pacey and
Marsh 1998; Marsh and Pacey 2005 and references
therein) and that perpetuation of razorback suckers
will require human intervention into the foreseeable
future. Survivorship could be increased by actively
managing the rearing habitat wherever razorback
suckers, or other threatened native species of the
lower Colorado River, exist with nonnative fish.
These threatened species could be captured and
transferred to isolated, off-channel habitats free of
nonnative species where they could breed and grow
to adulthood and then be transferred back into the
river (Minckley et al. 2003). Other plans to further
the species persistence have also been proposed
553
700
600 0 80 ° ° °
a
500 '
E 400 Females
(N= 180)
300
200 L(t) = 597*[ I-ezp [-0.84*(t-0.91) ]]
100
0
700
600 s e0 B e°
500 e
E 400 0
Males
F 300 (N = 365)
200 L(t) = 553*[1exp[-0.85*(1-0.98)1]
100
0
0 1 2 3 4 5 6 7 8 9
Years post-release
FIGURE 2.-Von-Bertalanffy growth (VBG) curve of
female and male razorback suckers repatriated as ju-
veniles and later captured as adults in Lake Mohave,
Arizona and Nevada, 1999-2002. Filled triangles rep-
resent total length (TL) at release and open diamonds
represent TL at first capture after release. Actual age at
release was unknown because cohorts were mixed at
rearing sites; thus, age-0 denotes age at release into the
lake whereas capture age was the number of years at
large after release. Data were not limited to only March
censuses and therefore included all unique captures (N
= 545); records with missing TL data and fish with
undetermined sex or documented as juveniles were not
included. Growth parameters are L- (asymptotic length
of the growth curve), K (growth coefficient describing
rate at which the asymptotic length is approached), and
to (theoretical age at length 0).
(e.g., USFWS 1987). However, none of these steps
could be considered recovery in the traditional
sense, and a managed recovery effort may be the
only feasible option.
. Monitoring of the repatriated population has
yielded estimates of population size, and provided
information on size-based mortality rates and in-
sights on how to improve the program. If average
size at release was increased from 300 mm to 350
mm, we predict that survivorship would more than
double, and the economic efficiency of the pro-
gram would increase greatly because the added
costs to rear larger fish would be relatively small,
perhaps as little as 20% (Chester Figiel, USFWS,
personal communication). Size-based mortality es-
timates also are valuable to a managed recovery
plan so that long-term effort and cost can be min-
imized. The prospect for an endangered species