Success of
hatchery-reared juvenile white sturgeon (Acipenser transmontanus)
following release in the Kootenai River, Idaho, USA
S.C. Ireland, R.C.P. Beamesderfer, V.L.
Paragamian, V.D. Wakkinen, J.T. Siple-2002
Journal of
Applied Ichthyology, 18(4-6): 642-650
Abstract:
In 1990 a conservation program began to
evaluate the feasibility of using aquaculture to aid recovery of the white
sturgeon population in the Kootenai River. Because of a virtual lack of
recruitment during the past two decades, the population was formally listed
in 1994 as endangered under the U.S. Endangered Species Act of 1973.
Recovery program goals are to preserve the genetic variability of the
population, rebuild natural age class structure, prevent extinction, and
restore natural recruitment. Mature wild fish are captured prior to spawning
and bred to produce four to 12 separate families per year of four to 10
adults per family at breeding age. We released 2630 age 1-4 juvenile white
sturgeon from 1992 to 1999. Subsequent catches of 39 wild and 620 hatchery
juveniles in an annual monitoring program confirm that wild recruitment of
Kootenai River white sturgeon is very low. Subsequent recaptures of hatchery
fish indicate that significant numbers survived introduction and grew.
Release-recapture and catch curve analyses suggest that average annual
survival rates for hatchery-reared juveniles may approach 60% for the first
year following release and 90% in subsequent years. Growth rates and
condition factors within 3 years after release were often poor as many
hatchery fish adapted to natural conditions. Growth rates increased after
the initial adjustment period. Average growth increments for all recaptured
hatchery fish were 6.4 cm year-1 and 0.206 kg year-1.
These rates are slightly less than the median rate reported for other white
sturgeon populations. Growth varied substantially among individuals. Some
fish grew little even after 3 years but others grew up to 60 cm
after 8 years at large. Relative weight decreased between release and
recapture for 77% of recaptured hatchery sturgeon. Relative weights were 88%
of optimum at release, 78% of optimum at recapture, and increased with
period at large. Relative weight at recapture was inversely correlated with
growth in length and opposite to our initial expectations that higher
condition would accompany faster growth. No obvious patterns in survival or
growth of juveniles could be related to size, time, or condition of release.
These initial results provide a basis for adjusting releases of hatchery
fish consistent with the conservation goal of the hatchery program and also
provide a baseline for comparison with the results of future monitoring to
determine carrying capacity of the Kootenai River system for juvenile
sturgeon.
(Kootenai Tribe of Idaho, P.O. Box 1269,
Bonners Ferry, ID 83805, USA. E-mail: Ireland@kootenai.org)