LEE's FERRY FISH MANAGEMENT REPORT L994-Lgg7
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COLORADO RIVER LEE'S FERRY FISH MANAGEMENT REPORT L994-Lgg7 Arizona Game and Fish Department 222L W. Greenway Road Phoenix, M 85023 Scott Reger, Fisheries Program Manager, Region II Charles Benedict, Fisheries Specialist Jodi Ni ccum, Fi sheri es Speci al 'ist Yvonne Magnuson, Creel Clerk Bill Persons, Research Branch Andrew Ayers, Research Branch INTRODUCTION Since its "discovery" by the angling public, the blue - ribbon fishery at Lee's Ferry has probably generated more controversy than any other fishery in the state. Since 1978 there has been a virtual continuous argument over flows, management, and especially angling regulations. In the mid 1980's a combination of past stocking, high flows, and a tremendous increase in angling pressure greatly reduced the quality of the fishery. Changes in stocking, more stable flows, more restrictive regulations and reduced pressures resulted in an improvement in the late 1980's. Test flows in 1990 - l99l appear to have reduced the food base, and this stress was concurent with an explosion of parasitic nematodes. The result was poor condition and the eventual mortality of a large percentage of the adult trout (and a subsequent reduced angling pressure). Most recently, the situation has been one of "interim flows" - which greatly reduced flow fluctuations, a rising (55 feet in 1993) Lake Powell, the supplemental stocking of larger trout, and light fishing pressure - mostly from catch-and- release anglers. As a result, natural recruitment is high, growth has improved, fish condition-- is improvinB, and fish numbers and catch rates are increasing. Because of these confounding influences, the effectiveness of the present slot limit in bringing back, let alone maintaining, a blue ribbon fishery is not yet clear. In recent years, despite an apparent increase in growth rate for rainbow trout up to 12 inches, there has been a decline in the number of fish in the slot. The decline has not been caused by harvest since fish in the slot are protected from harvest. Two potential causes for the decline in slot fish could be: l) Not enough large prey items to sustain growth of the larger fish. 2) Too many fish below the slot competing for food . STOCKING Results of oxytetracycline marking of stocked fish (Janisch, 1985), indicated that stocked fish contributed approximately 75Yo to the harvest. The rate reported by Maddux et al (1987) was 27.5%o natural reproduction, or 72.5 Yo due to stocking under steady high flows. An average of 154,000 fish per year were stocked from 1985 - 1989 (Table l). Persons et al (1985) presented a model to calculate stocking rate at Lee's Ferry. Bait fishing was still allowed, so mortality rates may have been higher (release rates were also lower then). The conclusion was to stock 111,000 fish annually to sustain 350,000 angler hours at a harvestnarvest rate ofot u.l)0.15 fishIlsh per hour. ljyBy thisthrs formulalonnula itrt wouldwoulcl requirerequrre u),uuu85,000 fishtlsh to .,rp be stocked annually to sustain 200,000lvvrvvv anglercuttsrer hourstlrr(llD ato. 0.2v,L fishrrJu psrper hourtl\Jtll harvest,tt<uvsJL, *:urs LrsDt l..j] lltY?tV/nr::lri/J , estimate in 1989. has been as low as .05 fish per hour in recent years, and pressure'rgple 'r)l,u y ddwn tq-100 hours. In 1990 the average annual stocking rate was reduced ',i!;l, olr' to 71,000 per year. Natural reproduction represented over 70o/o of the 1991 and 1992 year classes sampled by electrofishing (Persons, B., and M. Muysl, unpublished data). During 1994 more and'larger fish were stocked to make up for the fish lost during the test flows. In 1996 stocking was reduced to 20,000 fish per year because of high rates of natural recruitment. Natural recruitment has been in excess of 80% since Mav 1995 and was 88.8% in April 1997 (Ayers, personal communications). Table l. Stocking Summary for Lee's Ferry 1978-1997 in Thousands of Trout Year Rainbow* Brook Cutthroat Total r978 50 200 60 310 t979 43 43 1980 l5 40 I 56 1981 108 60 168 t982 50 100 1983 99 50 149 1984 128 128 1985 l2l 50 r7l 1986 t28 40 168 1987 l2l 25 t46 1988 lso 150 1989 129 t29 1990 6l 6l t99l 72 72 t992 78 78 1993 73 73 1994 103 103 1995 73 73 t996 20 20 t997 25 25 * including Kamloops 1985 - 60, 1986 - 34, 1987 - 21, 1988 - 66 Distribution of stockings both in time and geographically, as recommended by Gosse (1985) Persons et al. (1985) and Reger (1986), by using tanks mounted on a raft has been accomplished. Shimano assisted by providing the use of their stocking boat from 199l-1993. Since 1993 the department has provided the boat and conducted the stocking. Average size of fingerlings stocked has not quite been the 3" minimum recomme,nded. STRAIN SELECTION Early stockings by AGFD were made largely on the basis of availability of healthy, low cost eggs regardless of strain. It is highly unlikely tributary stockings by NPS, USFS, or USFWS even earlier were selected for strain, or that strain was even a concern at that time. AGFD contracted with Illinois Natural History Survey (Clausen and Philipp, l99l) to assess genetic variability in trout populations in Glen and Grand Canyons. They found a great deal of variation both among tributaries and years. Perhaps their most revealing conclusion was that (there is) "no evidence to support the idea that different stocks inhabit different reaches of the river." When concern over dam operations effects on the trout fishery escalated in the early 1980's, Bel Aire strain rainbow trout were in use at Lee's Ferry. The decision at that time was to continue to use this strain, as baseline data collected by AGFD was based on this strain. The need for a consistent strain to reduce sources of variation also became important to GCES after it began in 1984. Kamloop strain was evaluated in 1985-1988; fingerlings had adipose fin clips by volunteers prior to stocking. Other than Kamloops AGFD has stocked only Bel Aire strain rainbows since 1986. The growth rate of Kamloops was very similar to Bel Aires however, condition factor, especially in the smaller fish, was not as good as Bel Aire rainbow and brook trout (Reger et al, 1988). Return to creel was poor - Kamloops were 38oZ of the rainbow trout stocked in 1985- 1986 but orily 2Yo of the rainbow trout creeled in 1987-1988, Both Kamloops and Brook Trout stockings have been discontinued. There was concern, both from outside and within AGFD, that there might exist a strain better adapted to maintaining a blue - ribbon tailwater fishery. Davis (1992) compiled data on 164 strains and brood stocks for nine performance characteristics. When discussing available data on strains and predictability of future conditions, he states that (the) "ideal matchup of strain and environment is not likely to occur except by chance with the present level of knowledge". He does suggest some strains that show promise, based largely on longevity, glowth rate, and difficulty to catch. The two that stand out in this comparison af,e Kamloops and Eagle Lake. Kamloops had already been stocked at Lee's Ferry and discontinued due to poor performance (see 'above). Information from Davis (1992) data indicates that Bel Aire growth was equal to Eagle Lake and better than Kamloops (so previous growth data @eger et al, 1988) is consistent with the literature). Another strain, Shasta, shows growth better than most strains, although not as good as Eagle Lake. Eagle Lake and Shasta both showed excellent survivability. Davis also suggests that while little data has been collected, Nehring (1991) has reported better riverine survival from a "wild strain" Colorado River rainbow strain (held at Bellevue experimental hatchery in Colorado) when compared to Bel Aire Strain. Bel Aire Strain in captivity reach 9-12 pounds at 5-6 years old, respectively (Sorensen, Personal Communications). It would appear that these three, Eagle Lake, Shasta, and "wild strain" Colorado River represent the three most promising strains in captivity to try to obtain for testing in Lee's Ferry. It *wild might also be worth investigating establishing our own strain" from fish taken in the " wild" at Lee's Ferry. Another approach would be to go to wild spawn only and stop stocking. This would allow the Lee's Ferry strain to develop and allow testing of this strain under various conditions to determine its true potential. CREEL SURVEY METHODS The boat launch at Lee's Ferry provides the only access point for boat anglers, and affords an ideal point at which to interview large numbers of anglers as they complete their trips. An AGFD creel clerk was stationed there an average of 6 days a month from 1985 - 1995. Since 1996 a creel clerk has been stationed there an average of 8 days a month. The number of fish harvested is calculated from the harvest rate (caloulated from AGFD creel census data) and the number of angling hours expended (calculated from NPS use data). Calculations are stratified by boat and shore fishermen. Boat counts (NPS data), parlry size and tnp length (creel data) are used to calculate boat fisherman hours. Shore angler counts are treated as an average number of anglers present each daylight hour. Hanrest is not stratified by weekend-weekday, as count data (NPS) is not. A}IGLING PRESSURE Angler use of Lee's Ferry @ased onNPS use data) peaked in the early 1980's (Table 2). Reductions in pressure occurred in 1978 (four fish bag limit), 1980 (immediate kill regulation), 1985 (reduction in size of creeled fish), 1986 (artificial only regulation) and 1992 (word of skinny fish reached public).