FISHERY BULLETIN: VOL. 80, NO. 1 



11425). Dolphins were captured by encircling 

 one to nine animals with a 455 m X 4.5 m net 

 dropped from a fast moving boat in shallow 

 water. An inner circle enclosure method (Asper 

 1975) was used to minimize escapes. The inner 

 circle was partitioned so that individual dolphins 

 could be isolated and entangled without 

 collapsing the entire net on remaining animals. 

 Tangled dolphins were removed from the net 

 and placed for tagging in a stretcher, usually 

 held in the water alongside a boat. All animals 

 were sexed, measured, and photographed before 

 tagging. Previously tagged dolphins were 

 examined and retagged as necessary before 

 being released. 



The study area was surveyed as thoroughly as 

 possible at least biweekly in a 7.3 m Wellcraft 

 Fisherman 5 boat equipped with a 3 m tuna 

 tower. All dolphin sightings were recorded 

 during 228 surveys; photographs were taken to 

 facilitate identification of tags and distinctive 

 dorsal fins. 



Radio Tags 



An improvement (Model PT 219) of the radio 

 tag developed for small pelagic cetaceans by 

 Ocean Applied Research Corporation (Martin et 

 al. 1971) had not been tested on T. truneatus. In 

 our first efforts, the transmitter was attached 

 with plastic straps to a foam-lined fiber glass 

 saddle and secured to the dorsal fin with a 

 stainless steel bolt through the fin. Because 

 saddles provided by the manufacturer were too 

 small for most T. truneatus, the transmitters 

 were attached to fiber glass saddles molded by 

 the authors (Fig. 1 A, C). The saddles were lined 

 with open cell foam to protect the animal from 

 abrasion and to allow water circulation for 

 thermoregulation. 



Transmitter saddles were attached using 

 techniques developed by other investigators (see 

 review by Leatherwood and Evans 1979). The 

 first seven saddles were attached with single 

 bolts through the dorsal fin. The last three 

 saddles were attached with bolts fore and aft to 

 provide greater stability against water flow 

 (Fig. 1C). Spring-loaded bolts with dissolving 

 nuts were designed to release the saddle and 

 transmitter from the dolphin sometime after the 

 1-2 mo life of the lithium batteries. 



Reference to trade names does not imply endorsement by 

 the National Marine Fisheries Service, NOAA, or the U.S. 

 Fish and Wildlife Service. 



Ten radio tags (designated RT-1 through RT- 

 10) were attached to dolphins between 29 

 January 1975 and 9 June 1976. The RT-1 

 transmitter consisted of a single 35 cm long X 

 3.7 cm diameter tube with a 63 cm high spring 

 steel antenna on the forward end. Transmissions 

 from RT-1 gradually failed within 2 h, ap- 

 parently due to saltwater leakage into the 

 battery case. Cause of failure could not be 

 confirmed because the transmitter was missing 

 from the saddle when it was sighted 2 d after 

 attachment. Transmitters on subsequent radio 

 tags were attached to the saddle with bolted 

 aluminum plates (Fig. 1A, C) instead of plastic 

 straps. 



The transmitter antenna on RT-2 was ob- 

 served to be broken off at the base 5 d after 

 attachment. Consequently, transmitter pack- 

 ages on RT-3 through RT-10 were modified to 

 two tubes, 19.2 cm long X 3.8 cm diameter, 

 connected by copper tubing at the forward end. 

 A flexible 42.5 cm high whip antenna extended 

 vertically from the rear of the starboard tube. 

 The tubes, with transmitter assembly in one and 

 batteries in the other, were bolted to either side 

 of the saddle, and the connecting tubing was 

 solidly encased in fiber glass (Fig. 1C). 



Visual Tags 



The button tags described by Evans et al. 

 (1972) had proven not to be durable on T. 

 truneatus (Irvine and Wells 1972). Therefore, we 

 elected to try rectangular fiber glass "visual 

 tags" (Fig. 2). These tags were 10 cm X 7.5 cm 

 and made of 0.4 cm thick yellow laminated fiber 

 glass with 5.1 cm high black tape numerals 

 epoxied to the surface. Each tag was held in 

 place by Teflon bolts with stainless steel washers 

 and cotter pins. The bolts were placed near the 

 anterior edge of the tag to produce a streaming 

 effect as the dolphin moved through the water. 

 The bolt hole was bored through the fin and 

 cauterized with a heated rod, and sheathed with 

 Plexiglas tubing in the same manner as for radio 

 tags. 



Double bolt tags, also yellow rectangles with 

 black numerals, were cut from 0.2 cm thick fiber 

 glass and varied in size from 9.0 cm X 12.9 cm to 

 10 cm X 15 cm, depending on the size of the 

 dorsal fin to be tagged. The bolts were located 

 near the anterior and posterior edges of the tag. 

 Numerals were 7.7 cm high. Because cotter pins 

 had sheared some of the Teflon bolts on single 



136 



