Staff of the California Department of Fish and Game's Trinity Fisheries Investigations Project conducted a steelhead, Oncorhynchus mykiss, marking program at Trinity River Hatchery from 5 January through 2 April 1993. Unique combinations of fin clips were given to each group of fish to permit identification of brood year upon recapture. This season we marked 15,665 steelhead held over from the 1991 brood year with an adipose and right ventral fin-clip, 13,582 of which were effectively marked and released as two-year-olds. We also marked 324,875 steelhead from the 1992 brood year with an adipose and left ventral fin-clip, 323,583 of which were effectively marked and released as yearlings.
We checked 1,000 steelhead from the 1991 brood year and 6,470 from the 1992 brood year for fin-clip accuracy prior to release. We found 0.5% from brood year 1991, and 0.11% from brood year 1992, with poor fin clips.
We monitored adult steelhead returning to Trinity River Hatchery from 14 September 1992 through 28 March 1993, when we determined migration to be completed. During that time 586 steelhead returned to Trinity River Hatchery, of which 96.9% (568/586) were fin-clipped.
Steelhead were also checked for fin clips as they entered through the Willow Creek and Junction City weirs. One hundred-ninety steelhead were observed at the Willow Creek Weir, of which 44.7% (85/190) were fin-clipped. Twenty-nine steelhead were observed at the Junction City Weir, of which 58.6% (17/29) were fin-clipped.
To determine relative return rates and contributions to spawning escapements and the fisheries made by steelhead produced at Trinity River Hatchery, and to evaluate experimental hatchery management practices aimed at increasing adult returns.
The completion of the Trinity River Division of the Central Valley Project (15 May 1963) blocked access to a significant part of the historic steelhead spawning and rearing habitat in the Trinity River basin, and resulted in significant downstream flow reductions. Project-induced reduction in fishery habitat and flow are among the factors contributing to the decline of annual runs of steelhead.
In October 1984, U.S. Public Law 98-541 was passed to mitigate for fish and wildlife losses. This act, commonly referred to as the Trinity River Basin Fish and Wildlife Restoration Act, authorized the expenditure of $57 million over a 10-year period to implement restoration of fish and wildlife populations to pre-dam conditions.
Knowledge of hatchery- and naturally produced steelhead escapements into the Trinity River is a necessary component both for management recommendations and determining the effectiveness of those recommendations. To differentiate between naturally produced and hatchery-produced steelhead, all steelhead reared at Trinity River Hatchery from 1978 through 1981 were systematically fin-clipped before being released. Run size and escapement estimates of hatchery-produced and naturally produced steelhead were made during the 1978-79, 1980-81, and 1982-83 seasons. (Heubach and Hubbell 1980; Heubach 1984; Zuspan et al. 1985).
This year, staff of the California Department of Fish and Game's (CDFG) Trinity Fisheries Investigations Project (TFIP) marked steelhead produced at Trinity River Hatchery (TRH) as part of the first phase in meeting the Job Objectives. The second phase included the monitoring of adults returning to TRH.
Steelhead from the 1991 and 1992 TRH brood years (BY) were available for marking this season. Fish of each BY were monitored throughout the season to ensure that groups being marked would meet the hatchery minimum release-size requirement of six inches. Growth was monitored and recorded by hatchery staff during weekly standard weight counts (number of fish per pound), an operating procedure used to determine the amount of food given to fish following feed manufacturers' recommendations (Gary Ramsden, Manager, Trinity River Hatchery, CDFG, pers. comm.). The average weights of individual fish reported in this Chapter were based on these weight count data from TRH feeding schedules. Project personnel also culled fish while marking, placing smaller fish into holding tanks until they could be moved into hatchery ponds for further growth.
A crew of four markers from CDFG's TFIP marked steelhead at TRH inside a 3-m X 3-m wooden shed , positioned directly over the hatchery ponds. The shed contained a four-station marking table and a circulating fresh-water holding tank of approximately 284 liters. Fish were netted directly from the hatchery ponds, and placed into the holding tank. Another smaller holding tank with circulating fresh water was located in the center of the marking table and was used to hold fish immediately before marking. Each station was equipped with a manual counter to count each fish marked.
The marking shed was equipped with a recirculating tricaine methanesulfonate (MS-222/) system (approximately 76 liters), which was changed at least once per day with fresh MS-222 solution. This system used 12 cups of MS-222 per week, and was was installed to minimize fish mortality caused by overdosage of anaesthetic. Carbon dioxide (CO2) was used to anaesthetize the last group of steelhead marked (approximately 4,600 fish) on 2 April 1993, since they were to be released before the 21-day holding period required by MS-222 use. Fresh-water and MS-222 solution temperatures were monitored regularly throughout the day.
Marking of steelhead involved anaesthetizing them with MS-222, removing one or more of their fins by clipping, and releasing them into a pond reserved for marked fish. A combination of right ventral (RV) or left ventral (LV), and adipose (Ad) fin clips were used to differentiate fish from each BY and age-group-at-release. Fish marked this year from the 1991 BY were given an Ad+RV fin clip to be released as two-year-olds, and those from the 1992 BY, an Ad+LV fin clip to be released as yearlings. We randomly checked steelhead one to four times per day throughout marking to see how well the fins were being removed. A sample of fish was netted as they exited the marking shed and checked before they entered the hatchery ponds.
We also examined a larger sample of marked steelhead immediately prior to release to determine fin-clip quality and fish size. Fish were anaesthetized with MS-222, measured to the nearest mm fork length (FL), and fin-clips were inspected. These fish were placed in a separate holding pond, and released after the 21-day holding period required by MS-222 use. Fin clipping is considered a permanent mark if the fin rays are removed to the point of attachment to the bone (Stuart 1958; Eipper and Forney 1965; Jones 1979). Fins which are less than one-half-removed are likely to regenerate, and may appear distorted at the location of the clip. Unless persons checking for fin clips specifically look for distorted rays, fish that were actually marked may be unrecognizable. We determined the number of effectively marked fish by multiplying the percentage of fish with poor fin clips by the total number of fish released, and subtracting this product from the release total. Numbers of fish released from TRH were estimated by TRH personnel using standard weight counts on a subsample of each marked group.
A sample of marked fish was checked for health and general condition through an autopsy conducted by a CDFG Fisheries Pathologist. A complete organosomatic analysis was done and results are on file with the CDFG Region-I pathologist. Results in this report are confined only to general remarks made by the pathologist. Fish were also inspected for general condition during the hatchery mark-evaluation process by Project personnel.
Recoveries of returning marked steelhead were conducted at TRH, river kilometer (RKM) 179.8, and downstream at two trapping locations; Junction City Weir (42.7 km downstream from TRH), and Willow Creek Weir (131.4 km downstream from TRH). Project personnel examined fish for fin clips, measured each to the nearest cm FL, and recorded its sex. Trinity River Project (TRP) personnel operated the Junction City and Willow Creek weirs, where they examined steelhead for fin clips, measured each to the nearest cm FL, recorded its sex, spaghetti-tagged each, then released them back into the mainstem Trinity River. Scale samples were taken from steelhead at all three recovery locations.
