Use of the Global Positioning System for Locating Radio-Tagged Fish ...

North American Journal of Fisheries Management 17:457-460, 1997 American Fisheries Society 1997

Use of the Global Positioning System for Locating Radio-Tagged Fish from Aircraft ERIC E. HOCKERSMITH AND BRADLEY W. PETERSON Coastal Zone and Estuarine Studies Division, Northwest Fisheries Science Center National Marine Fisheries Sen'ice 2725 Montlake Boulevard East, Seattle, Washington 98II2-2097, USA Abstract.—Tracking from aircraft is a method commonly used to locate radio-tagged animals, and it typically involves observers who assign locations of detected animals in relation to physical landmarks. A technique that uses a Global Positioning System (OPS) receiver instead of observers was developed and tested during 1993 to identify locations of radio-tagged adult rainbow trout Oncorhynchus mykiss during aerial tracking in the Yakima River drainage in Washington. The technique was effective under both ideal and adverse weather conditions. Tracking flights that used the GPS receiver were more efficient, more accurate, safer, and less expensive than traditional tracking flights that require observers to estimate locations by using visual landmarks. Tracking from an aircraft is the most efficient method of locating wide-ranging radio-tagged animals and the method is used frequently to supplement fixed-site monitoring or ground-based mobile tracking. Large or inaccessible areas can be surveyed rapidly, and the detection range is double to triple the range of monitoring from the ground (Winter 1983). Traditional aerial tracking techniques use observers to assign locations of radio-tagged animals based on the locations of physical landmarks viewed from the air. Gilmer et al. (1981) recommended limiting tracking flights to less than 2 h because observer fatigue reduces the accuracy and efficiency of tracking operations. Despite observers skills and familiarity with the study area, they frequently become disoriented when the aircraft makes a series of turns or when weather conditions are adverse, particularly in areas where there are few landmarks. In addition, motion sickness frequently affects observers and can severely impair their ability to make location determinations. During 1993, we developed, tested, and compared a technique that used a global positioning system (GPS) receiver instead of observers to assign locations to radio-tagged fish in the Yakima River drainage, Washington. Aerial tracking was conducted once per week to supplement locations detected from fixed-site telemetry monitors and ground-based mobile tracking.

The GPS was developed in the early 1970s to provide a 24-h system of three-dimensional positioning for military applications (Musser 1992). A GPS receiver determines position in latitude, longitude, and altitude by receiving information from at least 3 of the 24 Block II satellites orbiting the earth. Study Area The Yakima River flows 349 km southeast from its headwaters in the Cascade Mountain Range (elevation, 746 m) to its confluence with the Columbia River (elevation, 91 m) near Richland, Washington, and drains an area of 15,941 km 2 (Figure 1). Its major tributaries include Satus, Toppenish, Manastash, Taneum, and Swauk creeks and the Naches, Teanaway, and Cle Elum rivers. Topographies of the study area include high-gradient, mountainous terrain in the headwaters, moderate gradient though canyons in the midsection, and relatively low-gradient, level terrain in the lower section. Methods Capture and handling.—In 1993, we used DC electrofishing to collect 52 adult rainbow trout Oncorhynchus mykiss between Roza Dam and the confluence of Manastash Creek. Rainbow trout were radio-tagged by surgical implantation techniques similar to those described by Mellas and Haynes (1985). All fish were released near collection locations after recovering from tagging. Radio transmitters.—Radio transmitters (Advanced Telemetry Systems, Inc., Isanti, Minnesota1) were powered by a 3.7-V lithium battery and pulsed once per second on one of nine frequencies spaced 10 kHz apart (30.17 MHz to 30.25 MHz). The electronic character of each pulse provided individual identification codes for each tag. Receivers.—A 12-V DC telemetry receiver, developed and fabricated by the National Marine 1

Reference to trade names does not imply endorsement by National Marine Fisheries Service.

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Keechelus Kachess Reservoir Reservoir cie Elum

Washington

I. Little Naches River

Taneum Creek * ^^-*> Town Diversion Dam -» Manastash Creek

American River

Rlmrock Reservoir

Wapato Dam

Columbia River

-' Sunnyslde Dam Toppenlsh Creek

A N

Snake River

A 0

10

20

30

40

50

Kilometers

FIGURE I.—Map of the Yakima River drainage, Washington, showing major tributaries, irrigation diversion dams, and reservoirs.

Fisheries Service, was used for detecting radiotagged fish during the study. The receiver system consisted of a radio receiver, data processor, internal clock, and data logger. The receiver scanned all nine frequencies every second. Information recorded by the radiotelemetry data logger included tag code and time of detection to the nearest minute. We used a Garmin (model 100 AVD) GPS receiver with an RS-232 output cable and a low-drag blade antenna to determine the locations of tagged fish. The data output format for the GPS receiver was National Marine Electronics Association standard 0183 (NMEA 0183). An Aspect Script program written for PC Plus software was used to communicate between the GPS receiver and a 286 laptop computer. Data were generated at 4,800 baud with each character containing eight data bits, one stop bit, and no parity. The GPS output recorded by the laptop computer included GPS time, computer time, and the latitude and longitude position of the aircraft every minute.

Tracking.—Aerial tracking was conducted from a fixed-wing aircraft fitted with dual-tuned loop antennae mounted on the wing struts and facing down. Detections of radio-tagged fish were made at an altitude of 300 m above ground level at speeds averaging 130 km/h. Flight speed and altitude were based on safety considerations and the ability to detect radio transmitters from the air. Because the telemetry receiver system recorded

the time of contact of radio-tagged fish to the nearest minute, expected accuracy of locations from the air was 2.2 km. The river corridor was flown in both upstream and downstream directions to maximize detection probability. Before takeoff, the telemetry receiver system was tested to ensure proper operation, and clocks on the radiotelemetry data logger and laptop computer were synchronized. Observers on board aerial tracking flights recorded the time and locations of the airplane in relationship to physical landmarks in order to compare locations determined by traditional aerial

MANAGEMENT BRIEFS

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TABLE I.—Test flight conditions, number of radio-tagged fish contacted, and absolute distance of assigned locations in relation to actual locations detennined on the ground for the GPS receiver and observer assigned locations. The asterisk denotes significantly greater mean distance than the other mean measurements (P < 0.0001). Absolute distance of GPS location from ground location (km)

Right weather condition

Number of fish contacted

Mean (SD)

Range

Calm Windy

71 17

1.8(1.4) 1.3(1.2)

0.0-8.0 0.2-3.4

tracking techniques with locations determined by the GPS receiver. After completion of the flight, the locations of fish in latitude and longitude coordinates were determined from GPS output during their time of detection. Latitude and longitude coordinates of individual fish were converted to the nearest river kilometer (distance from the confluence of the Yakima and Columbia rivers) by use of topographic maps of the study area. Observers assigned locations to radio-tagged fish to the nearest river kilometer by interpolating the location of the airplane during the time of detection. For both methods, locations of individual fish recorded during both the upstream and downstream portions of a flight were averaged for a final assigned location. Assigning locations generally took less than 1 h per 50 fish detected for each method. In addition, simultaneous with the tracking flights, radio-tagged fish were located on the ground in order to compare actual locations of the fish to locations determined from the GPS receiver and those assigned by observers. Locations of fish from ground tracking were determined to the nearest 0.1 river kilometer by use of topographic maps.

Results and Discussion A total of four test flights were conducted during May and June 1993. Two flights occurred during good weather conditions with no wind or turbulence, and two flights were conducted during adverse weather conditions with strong winds and frequent turbulence. Both flights conducted during adverse weather conditions were terminated before completion because observers suffered from motion sickness; therefore, fewer fish were contacted on those flights. For analysis, the data from individual flights were pooled by weather condition to increase the number of observations during adverse weather conditions (Table 1). The absolute distance of locations assigned by observers compared with verified ground locations ranged from 0 to 16.3 km. The absolute distance of GPS-determined locations compared with verified ground

Absolute distance of observer location from ground location (km)

Mean (SD) 2.1 (1.4) 8.9(4.3)*

Range 0.0-6.4 3.7-16.3

locations ranged from 0 to 8.0 km. The mean accuracy of the locations determined by use of the GPS receiver were similar during both good and adverse weather conditions and were also similar to the mean accuracy of locations assigned by observers during good weather conditions. However, the mean accuracy of locations assigned by observers during adverse weather conditions were significantly poorer (analysis of variance, P < 0.0001) than the mean accuracy of locations assigned by observers during good weather conditions and the mean accuracy of locations determined from the GPS receiver during both good and poor weather conditions. We identified four advantages of using the GPS receiver compared with using observers who located physical landmarks during aerial tracking flights: safety2 (planes have less cargo weight, fewer people are in the air, and pilots are not distracted by passengers), cost-effectiveness (field personnel can work on other tasks during aerial tracking), improved accuracy (positions are not dependent upon an observer's skill, familiarity with area, ability to identify landmarks, or weather conditions), and utility (flights can take place in other than daylight or good weather conditions). A disadvantage of the GPS approach is that radio-tracking flights without observers will continue without recording data in the event of equipment failure. However, thorough testing of radiotelemetry equipment on the ground before each flight reduces the likelihood of poorly functioning equipment. Although telemetry receivers with integrated GPS receivers are not commercially available, this technique will work well until GPS technology is incorporated into telemetry receivers.

Acknowledgments This paper is dedicated to two of our colleagues, Lester E. Eberhardt and Richard E. Fitzner, and 2

See acknowledgments.

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our pilot, Raymond L. Gilkerson, who were lost in a plane accident near Yakima, Washington, on June 3, 1992, during a radio-tracking study of sage grouse. Mark Kaminski, Byron Iverson, and John Vella of the National Marine Fisheries Service assisted in the field.

References Gilmer, D. S M and five coauthors. 1981. Procedures for the use of aircraft in wildlife biotelemetry studies.

U.S. Fish and Wildlife Service, Resource Publication 140. Mellas, E. J., and J. M. Haynes. 1985. Swimming performance and behavior of rainbow trout (Salmo gairdneri) and white perch (Morone americana): effects of attaching telemetry transmitters. Canadian Journal of Fisheries and Aquatic Sciences 42:488-493. Musser, D. D. 1992. GPS/DGPS in offshore navigation, positioning. Sea Technology 33:61-66. Winter J. D. 1983. Underwater biotelemetry. Pages 371-395 in L. A. Nielsen and D. L. Johnson, editors.

Fisheries techniques, American Fisheries Society, Bethesda, Maryland.