9666 - Laserfiche WebLink

Home Browse Search

portion of fish could be released into eddies and backchannels of the mainstem, with equal numbers of fish released above and below the LCR. Mark-recapture efforts might reveal which is the optimal strategy. Another option may be to stock fish in the left hand channel of the LCR at the confluence region. This is a fairly large pool (probably> 2 acres); generally with very slow currents and some shoreline ledges and vegetation for cover. Here, it may be possible to re-acquaint the fish to LCR waters without potentially overburdening the LCR. From here, the fish would have limited access to the LCR, or full access to the mainstem Colorado River. An important factor determining release sites should be the ability (or lack thereof) to set up soft-release protocols (i.e., short- term holding pens). Efforts should be made to avoid releasing fish under harsh environmental extremes. For example, fish should not be released under flooding conditions in the LCR (although mild-flowing turbid conditions may be acceptable). Likewise, fish should probably be released in the mainstem under periods of minimal fluctuating flows, or periodS of low flows with decreased velocities. To do otherwise may invite undue mortality. An adaptive approach should be taken (i.e., release times should be flexible and dictated by riverine conditions and flows, rather than by inflexible schedules). Paying attention to current and expected hydrographs, both in the LCR and in the mainstem will be important. In summary, because of concerns about potential unanticipated secondary effects related to carrying capacity, density dependence, and disease, and in an effort to increase recruitment to the main LCR population, it is suggested that the first attempts to release supplemental stocked fish are done in the mainstem Colorado River between river mile 58.8 and 64.5 (i.e., in the backchannels and eddies between Kwagunt and Lava/Chuar Rapids). Should these attempts prove unproductive, less conservative measures may need to be taken (i.e., release near the confluence region, or higher up in the LCR watershed). Where could the supplemental fish be grown? It is not the purpose of this document to specifically identify a hatchery where supplemental fish could be grown. Attributes that a facility should possess include all those listed under the previous section for captive brood stock (e.g., experienced personnel, committed long term funding, ability to keep fish unquestionably isolated from other Gila spp., appropriate water flow and temperatures, quarantine facility, etc.). Raceways, circulating tanks, or even outdoor ponds may be useful for grow-out of age-O fish, and the process should be adaptive in nature. It is strongly recommended that the facility have the capabilities for naturalistic rearing (e.g., exposing fish to moving water currents, natural substrates, cover types, periodic elevated levels of turbidity, etc.). For example, marl, sands, gravels and substrate rocks could be obtained from the LCR. This could be accomplished by transporting them via boat. In addition, natural food types and some exposure to predators would be desirable (see Brown and Laland 2001 for review). 33