Earl F. Prentice

Morphological indices of developmental progress in the parr-smolt coho salmon, Oncorhynchus kisutch

Abstract By common usage rather than by strict definition a parr is understood to be a young salmonid with vertical dark stripes, and a smolt is a slightly older and larger fish in which the dark stripes are obscured by a deposition of guanine in the scales and the skin, giving a silvery color. Although parr and smolt remain satisfactory terms for general usage, they are not sufficiently precise to describe the normal genetically based developmental variants in salmon, and certainly they cannot specify or describe the non-synchronous development of young salmon subjected to experimentally altered environments (e.g., special diets, hormonal manipulation, photoperiod, temperature, salinity). To aid in more detailed description of developmental variants in the parr-smolt transformation a study was made of externally measurable features that change significantly during this period. In addition to pigmentation and length, the following items proved to be useful indices of differentiation: emergence and growth of teeth on the maxilla, mandible and tongue; growth and changes in shape of integumentary folds adjacent to the cloacal opening; growth and change in shape of the auxillary appendage of the pelvic fin; and growth in the scales with respect to radius and number of circuli. These additional features appear to reflect chronological age more faithfully than does integumentary pigmentation. In further studies of experimentally altered parr and smolt, and in normal genetic variants, these features, when related (or not) to differentiating physiological and biochemical properties, should greatly amplify and improve the precision of descriptions of developing salmonids.

Effects of UV-B Radiation on Near-surface Zooplankton of Puget Sound*

SummaryAn increase in incident solar ultraviolet irradiation, resulting from possible deterioration of the stratospheric ozone layer, would have important biological effects. Though the oceans are relatively opaque to UV radiation, compared to visible light, increases in incident UV may affect organisms living within the first few meters of the sea surface.Shrimp larvae, crab larvae, and euphausids were exposed to various low levels of simulated solar UV radiation (UV-B, 290–315 nm) under laboratory conditions. Comparisons between solar and artificial spectra were based on spectroradiometric measurements converted to erythemally effective irradiance. These zooplankton tolerated UV-B irradiance levels up to threshold levels with no significant reduction in survival or developmental rates compared to control organisms. Beyond the threshold levels, activity, development, and survival rapidly declined. The apparent UV thresholds are near present incident UV levels.Observed survival threshold levels for each experimental group were superimposed on seasonal solar incident UV levels at the experimental site. These threshold levels appeared to be exceeded by median ambient UV levels late in the season of surface occurrence of each species. UV increases resulting from ozone depletion may significantly shorten this season. Although the apparent impact would be lessened by the decrease in UV with depth, irreversible detrimental effects would probably occur before reported survival thresholds were exceeded.

Use of the Passive Integrated Transponder (PIT) in a Fish Identification and Monitoring System for Fish Behavioral Studies

Abstract Use of the passive integrated transponder (PIT) as a fish identification and monitoring system for behavioral study of Arctic char Salvelinus alpinus was evaluated. The system was developed in order to track individual differences, mainly in rheotactic behavior. In a preliminary experimental setup, Arctic char (N = 20, 9–140 g each) were PIT-tagged and their movements were recorded at regular intervals in a circular stream channel. Two PIT tag loop detectors, placed on a narrow part of the channel, automatically recorded identity and swimming direction of tagged fish. We demonstrate some of the applications in behavioral research, such as individual, general, and diel locomotor activity patterns, rheotactic behavior, and sociograms showing activity relationships among individuals within a group.

Measuring the Performance of Two Stationary Interrogation Systems for Detecting Downstream and Upstream Movement of PIT-Tagged Salmonids

We tested the performance of two stationary interrogation systems designed for detecting the movement of fish with passive integrated transponder (PIT) tags. These systems allowed us to determine the direction of fish movement with high detection efficiency and high precision in a dynamic stream environment. We describe an indirect method for deriving an estimate for detection efficiency and the associated variance that does not rely on a known number of fish passing the system. By using six antennas arranged in a longitudinal series of three arrays, we attained detection efficiencies for downstream- and upstream-moving fish exceeding 96% during high-flow periods and approached 100% during low-flow periods for the two interrogation systems we tested. Because these systems did not rely on structural components, such as bridges or culverts, they were readily adaptable to remote, natural stream sites. Because of built-in redundancy, these systems were able to perform even with a loss of one or more antennas owing to dislodgement or electrical failure. However, the reduction in redundancy resulted in decreased efficiency and precision and the potential loss of ability to determine the direction of fish movement. What we learned about these systems should be applicable to a wide variety of other antenna configurations and to other types of PIT tags and transceivers.

Comparison of Sequential Coded Wire and Passive Integrated Transponder Tags for Assessing Overwinter Growth and Survival of Juvenile Coho Salmon

Abstract Wild juvenile coho salmon Oncorhynchus kisutch in a natural stream were marked with either sequential coded wire (s-CW) tags or passive integrated transponder (PIT) tags to assess possible differences in growth and survival from fall to spring between fish tagged with the two types of tags. Survival, estimated from recovery of out-migrants, varied between years (25.4% in 1990–1991 and 42.1% in 1991–1992), but there was no difference in apparent survival between fish of the two tag groups in either year. Weight gain from fall until emigration from the stream the following spring also varied between years (0.021 and 0.028 g/d in 1990–1991 and 1991–1992, respectively; final weights: 4.55 g in 1990–1991 and 6.01 g in 1991–1992), but growth did not differ between tag groups. Differences in survival and growth were not detected in even the smallest size-class tagged (53–70 mm). We conclude that overwinter growth and survival estimates of coho salmon as small as about 2.8 g and 65 mm fork length would n...

Technology developed for diverting passive integrated transponder (PIT) tagged fish at hydroelectric dams in the Columbia River Basin

Data collected on juvenile salmonids tagged with passive integrated transponder (PIT) tags as they migrate seaward through the Columbia River Basin provide fisheries managers and resource agencies with valuable information to evaluate the effectiveness of current management actions and restoration strategies. The development of new technology to route PIT-tagged fish through multiple alternative pathways as they pass through the interrogation systems at the fish bypass/monitoring facilities at hydroelectric dams provides another valuable real-time tool to monitor and evaluate the migration, passage, and survival of PIT-tagged juvenile salmonids in the basin. The authors describe the current computer program and gate-control technology for routing fish, and provide detailed descriptions of three new types of fish-diversion gates. The comparative advantages and disadvantages of each gate are discussed. The prototype of a fourth diversion gate, with only one moving part, is also described.

Evaluation of a flat-plate PIT tag interrogation system at Bonneville Dam

Abstract In the spring of 1996 and 1997, a prototype 400 kHz flat-plate (pass-by) passive integrated transponder tag interrogation (PIT tag) system was installed at the terminus of the downstream migrant (DSM) channel of the Bonneville Dam First Powerhouse, located on the Columbia River. The system was designed to interrogate previously PIT tagged juvenile salmonids migrating down the Columbia River without interfering with the traditional subsampling of fish passing through the facility. In addition, the design enables fish of virtually any size, and debris, to pass over the systems antennas without the port restrictions imposed by traditional pass-through PIT tag interrogation systems. We describe the fish facility in addition to the flat-plate system and its operation. The system tag reading efficiency was evaluated during 1996 and 1997 using a direct method based on the release of known numbers of tagged test fish and an indirect statistical procedure based on tagged run-at-large fish. The results showed that PIT tag reading efficiency during both years using the direct method averaged 97%, while that using the statistical procedure averaged 99% for the dual multiplexed antenna array. During the 1996 and 1997 field seasons 4371 and 14 733 fish, respectively, were recorded. Daily system functionality was monitored using stick tests (i.e., the passing of PIT tagged sticks across the antenna array).

Passive Monitoring of Migrating Adult Steelhead with PIT Tags

Abstract In 1985, two independent passive integrated transponder (PIT) tag monitoring systems were installed at the exit area of the weir leading into a fish trap on the north-shore fish ladder at Bonneville Dam, Columbia River. One hundred PIT-tagged adult steelhead Oncorhynchus mykiss were released in groups of 10 into an enclosed area of the ladder downstream from the detectors. The tagged fish were detected after they volitionally swam through the weir and slid through the detection system at velocities of 0.6 m/s or greater. Overall PIT tag reading efficiency was 98% and no tag-reading errors were recorded. Individual tag code, date, and time of the passage of each tagged fish were automatically recorded into a computer file and simultaneously printed onto a paper copy. These results suggest that PIT tag monitors of this design could be deployed at select adult passage facilities presently operating in the Columbia River Basin to interrogate returning PIT-tagged adult salmonids.

Vulnerability of Marked Age-0 Steelhead to a Visual Predator

Abstract The assumption that marking does not alter the vulnerability of fish to a visual predator was examined. Similar numbers of age-0 steelhead Oncorhynchus mykiss were tagged with binary-coded-wires, tagged with passive integrated transponders, freeze branded, marked with fingerling tags, or left unmarked. All were subjected to age-1 steelhead predators for 24 h in 2.4-m-diameter circular tanks filled with clear well water. Twice as many marked as unmarked age-0 steelhead prey were eaten. There was no significant survival difference among the four marked treatment groups, which suggested that in the laboratory the trauma associated with marking is more important than mark type. We conclude that marking may effect postrelease survival and recommend that mark–recapture experiments be used to empirically determine and correct for differences in survival of marked and unmarked fish.

A Study to Determine the Biological Feasibility of a New Fish Tagging System; Annual Report 1994-1996.

This report covers work done during 1997 and 1998 (FY98) on a project to expand and improve technology for Passive-Integrated-Transponder tags (PIT tags) throughout the Columbia River Basin (CRB).