NOTE Graves et al An evakialion of iatellite tags for estimating postrelease srirvivai of Mnkaim nigiican^ 



135 



hillfish on the liigli seas. Pop-up satellite tags are capable 

 (if recording environmental variables over predefined in- 

 ten-als, of detaching from an animal at a designated time, 

 lioating til the surface, and of transmitting the stored data 

 to a satellite. Until now, these tags have been deployed pri- 

 marily on bluefin tuna for relatively long durations (up to 

 nine months) to determine movement patterns (Block et 

 al.. 1998a; Lutcavage et al., 19991. Recovery of tag data has 

 been very good in most cases, with some reported rates in 

 excess of 90% (Block et al., 1998a; Lutcavage et al., 1999). 

 These results suggest that the technology may be well suit- 

 ed for shorter term studies, including the determination of 

 postrelease sui-vival. In this paper we present the results of 

 a preliminary study to evaluate the feasibihty of applying 

 pop-up satellite tag technology to estimate short-term sur- 

 vival of blue marlin. We also include a brief analysis of the 

 movement and behavior of blue marlin that we inferred 

 from the pop-up tagging results. 



Materials and methods 



Pop-up satellite tags 



The Microwave Telemetry. Inc. PTT-100 pop-up satellite tag 

 was used in this study. The tag can withstand a pressure 

 of 1000 psi (equivalent to a depth of about 650 meters) and 

 is sufficiently small (38 cm by 4 cm diameter) that it would 

 not appear to impose a major drag on a large marine tele- 

 ost. such as blue marlin (Block et al.. 1998a). Tags were 

 progi-amed to measure water temperature every hour and 

 record the mean value for each two-hour period for a total 

 of 61 cycles (122 hours). Inclinometer values were taken 

 every two minutes and summed for the periods before tag 

 detachment (pre-pop-up) and after tag detachment (post- 

 pop-up). For each period the inclinometer started with an 

 initial value of 128. If at the time of measurement (every 

 two minutes) the tag was oriented below 30 degrees above 

 horizontal, a value of one was subtracted from the total. If 

 the tag was above 30 degrees above horizontal at the time 

 of measurement, the inclinometer total was increa.sed by 

 one, but could not exceed 255. Final values below 255 indi- 

 cated sufficient forward propulsion such that the positively 

 buoyant tag was depressed below 30 degrees above horizon- 

 tal for certain periods, demonstrating forward propulsion. 



All nine tags were progi-amed to detach from the fish 122 

 hours after activation, at which time the memory within 

 each tag would contain 61 direct temperature measure- 

 ments and the pre-pop-up inclinometer value. The five-day 

 attachment period of the pop-up tag was chosen, in part, 

 as a result of a review of data from conventional tag-re- 

 captured blue marlin in the Cooperative Tagging Center 

 (CTC) database (E. Prince, unpubl. data). Of the 160 blue 

 marlin tag returns in CTC that have been validated, ten 

 individuals were recaptured within five days of release, 

 suggesting that some blue marlin are able to survive the 

 catching and tagging event and commence feeding again 

 within a few days. In addition, acoustical tagging studies 

 have shown high sui"vival rates of different marlin species 

 in the first 1-2 days following release, demonstrating that 



mortality, when it occurred, generally happened within the 

 first 48 hours of release (Pepperell and Davis, 1999). With 

 these considerations in mind, we assumed that the five- 

 day period of tag attachment was an adequate period for 

 catch and release mortality to be expressed. As indicated 

 by Goodyear (in press), the duration of this type of experi- 

 ment should be the minimum number of days necessary 

 to account for postrelease mortality events. Longer periods 

 would allow for greater influence of tag shedding, tag mal- 

 function, and natural mortality, all of which could compro- 

 mise estimates of postrelease survival. 



Tag deployment 



Pop-up satellite tags were activated and tested at the 

 start of each fishing day. Blue marlin were caught south- 

 west of Bermuda in the vicinity of Challenger and Argus 

 Banks on standard recreational gear for the blue marlin 

 fishery in Bermuda ( 130 lb test line) by using trolled high- 

 speed lures or skirted dead baits (in most cases with two 

 hooks). All hooks employed in this study were "J" hooks 

 (no. 16/0-20/0). We tagged the first nine fish available to 

 us. Six blue marlin were caught on the vessels we were 

 aboard. Three individuals were taken on other vessels 

 and transferred to the tagging vessel after the fish were 

 brought to leader (brought to the boat): one blue marlin 

 was caught and attached to a drifting buoy until the tag- 

 ging vessel, which was several miles away, could gain 

 access to the fish; and two fish were directly transferred 

 after capture from the fishing vessel to the tagging vessel 

 by using a procedure described in Block et al. ( 1998b). 



Once fish were brought to leader (reeled to the side of 

 the boat), quieted and secured, the pop-up satellite tag 

 and a conventional (streamer) tag were deployed. Pop-up 

 satellite tags were attached to one end of a 400-lb ( 182 kg) 

 test monofilament leader about 18.5 cm in length, with an 

 outside diameter of 1.8 mm. The other end of the leader 

 was attached to a double barb nylon anchor (about 33 mm 

 long and 10 mm wide) made of medical-grade nylon. The 

 anchors were implanted by using a stainless steel tag ap- 

 plicator modified to accomplish placement to a depth of 

 about 10 cm into the dorsal musculature, about 10 cm pos- 

 terior and 5 cm below the base of the peak of the first dor- 

 sal fin (Fig. 1). Hook location, as well as observations on 

 foul-hooking (tissue damage, bleeding, etc.), were noted at 

 the time of hook removal. 



Analyses 



After detachment from the animal, the positively buoyant 

 tags floated to the surface and began transmitting data to 

 satellites of the Argos™' system. Position information and 

 sections of the temperature and inclinometer data were 

 captured with each satellite pass and transmitted to a 

 ground station and ultimately to the investigators by the 

 internet. Data were analyzed to determine net movement 

 from the point of detachment to the point when the tag 

 popped-up (usually the first tag transmittal; however, if 

 the first satellite pass was near the horizon, the location 

 of the second transmittal was used to obtain greater accu- 



