External Radio Transmitters Research Articles

Influence of Transmitter Attachment Procedures on Swimming Performance of Wild and Hatchery-Reared Atlantic Salmon Smolts

Effects of transmitter attachment procedures on smolts of Atlantic salmon Salmo salar have primarily been examined in the laboratory with hatchery-reared fish. Biotelemetry researchers must extrapolate findings of tagging studies to wild, migrating smolts. Because hatchery rearing can affect salmonid development and because field tagging procedures and environmental conditions can differ from those in the laboratory, we measured critical swimming speed of hatchery-reared Atlantic salmon smolts equipped with internal, external, or gastric dummy radio transmitters in the laboratory. We then repeated the experiment with wild, migrating fish in ambient environmental conditions. Swimming ability of hatchery smolts was not significantly affected by any attachment procedure, and no significant differences were found between fish tested 1 or 16 h after tagging. Similarly, wild smolts were not impaired by gastric transmitters; however, performance of wild fish tested 1 or 16 h after internal or external attachment was significantly lower than that of wild controls. Thus, reaction of hatchery-reared Atlantic salmon smolts to attachment procedures can differ from that of wild migrants. Biotelemetry researchers should exercise caution in interpreting data obtained from wild Atlantic salmon smolts equipped with internal or external radio transmitters during the first 16 h after tagging.

Can External Radiotransmitters Be Used to Assess Body Temperature and Torpor in Bats?

We tested externally applied, temperature-sensitive, radiotransmitters for determining the body temperature of big brown bats ( Eptesicus fuscus ) in various ambient temperatures (2- 260C). There was a slight, but significant, effect of ambient temperature on skin temperature (measured by the transmitters), but skin temperature accurately reflected rectal temperature in torpid and active bats, and it was never >3.30C below rectal temperature. External radiotransmitters are, thus, useful in studies of torpor in bats, even when only small decreases in body temperature occur.

Evaluation of the accuracy of body temperature measurement using external radio transmitters

The facultative depression of body temperature represents an important energy strategy for small homeotherms. However, measuring body temperature under field conditions by means other than externally attached temperature-sensitive radio transmitters is problematical. We show that skin temperatures measured by external radio transmitters can accurately reflect core temperature for the bat Carollia perspicillata. We compared body and skin temperatures at three ambient temperatures (Ta; 21, 26, and 31 °C). The difference between skin and body temperature (ΔT) was linearly correlated with Ta and can be predicted by ΔT = 4.396 − 0.118Ta. We argue that external temperature-sensitive radio transmitters can provide a reliable index of core temperature and so permit the study of torpor or facultative hypothermia under field conditions.

The application of radiotelemetry for locating and controlling concentrations of red‐billed quelea in Africa

Abstract Radio transmitters weighing 1.8 g were attached to red‐billed quelea (Quelea quelea (L.)) in southwestern Ethiopia during May and June 1981 to determine the feasibility of this technique for rapidly locating nesting colonies and following local movements. Queleas are probably the smallest birds to which external radio transmitters have been successfully attached. Radio‐equipped birds were tracked to four nesting colonies, three of which were in the nest construction stage which occurs during the first three days of colony establishment. This early stage is not normally found using conventional survey methods. Adults usually foraged within 3 km of the colony at the nestling and fledgling stages, indicating that surveys must pass within this distance if the colony is to be located by conventional techniques. The study showed that quelea nesting colonies could be more easily and inexpensively located in remote areas using radiotelemetry than by using only ground or aerial surveys. The early detectio...

Effects of External Radio Transmitters on Fish

Abstract Yellow perch (Perca flavescens) and largemouth bass (Micropterus salmoides) were studied to determine the effects of externally attached radio transmitter tags. Perch that had been tagged with dummy radio tags were more susceptible to predation and more sensitive to environmental stress than were controls. Feeding and respiration rates were similar among dummy tagged and control groups of perch over a 6-week period. The feeding rate of dummy tagged largemouth bass was lower than that of untagged fish over a 3.5-week period. On the basis of these studies, we conclude that weights of external transmitters in water should be less than 1.5% of the fish weight. Design considerations should include streamlining components and an anterior attachment wire at the extreme leading edge of an external transmitter to prevent entanglement of the tag in surrounding vegetation.

Spawning Migration of Adult Chinook Salmon (Oncorhynchus tshawytscha) Carrying External and Internal Radio Transmitters

Upstream movements of radio-tagged and control adult chinook salmon (Oncorhynchus tshawytscha) were monitored during spring and fall 1976 and spring 1977 in the lower Snake River, southeastern Washington. Travel time from point of fish release and percent return to upstream trapping facilities were compared for experimental and control fish. Experimental fish carried anchor tags, and either external or internal radio transmitters. Control fish carried anchor tags only. Chinook salmon that lost external transmitters moved upriver more slowly than control fish although percent returns to upriver trapping facilities were similar. Travel times and percent returns of chinook salmon that retained external transmitters did not differ significantly from those of control fish. Although some salmon tagged with internal transmitters moved upriver, all failed to cross Little Goose Dam 6.5 km from the release site. Most internally tagged salmon eventually swam downstream. Key words: chinook salmon, biotelemetry, behavior, migration, radiotelemetry, bioengineering