750 



Evidence of shark predation and scavenging on 

 fishes equipped with pop-up satellite archival tags 



David W. Kerstetter 



School of Marine Science 

 Virginia Institute of Marine Science 

 College of William and Mary 

 Gloucester Point, Virginia 23062 

 E-mail address: bailey@vims.edu 



Jeffery J. Polovina 



Pacific Islands Fisheries Science Center 

 National Marine Fisheries Service 

 Honolulu, Hawaii 96822 



John E. Graves 



School of Marine Science 

 Virginia Institute of Marine Science 

 College of William and Mary 

 Gloucester Point, Virginia 23062 



Over the past few years, pop-up sat- 

 ellite archival tags (PSATs) have 

 been used to investigate the behav- 

 ior, movements, thermal biology, 

 and postrelease mortality of a wide 

 range of large, highly migratory spe- 

 cies including bluefin tuna (Block et 

 al., 2001), swordfish (Sedberry and 

 Loefer, 2001), blue marlin (Graves et 

 al., 2002), striped marlin (Domeier 

 and Dewar, 2003), and white sharks 

 (Boustany et al., 2002). PSAT tag 

 technology has improved rapidly, 

 and current tag models are capable 

 of collecting, processing, and stor- 

 ing large amounts of information on 

 light level, temperature, and pressure 

 (depth) for a predetermined length of 

 time before the release of these tags 

 from animals. After release, the tags 

 float to the surface, and transmit the 

 stored data to passing satellites of the 

 Argos system. 



A problem noted by several au- 

 thors using early PSAT models was 

 the occasional occurrence of tags 

 that did not transmit data. Clearly, 

 a tag attached to a moribund fish 

 that would sink to a depth exceeding 

 the pressure limit of the tag casing 

 would be destroyed. To prevent the 

 loss of tags due to mortality events, 

 tag manufacturers and researchers 



have developed mechanisms that re- 

 lease tags from dead or dying fish 

 before the structural integrity of the 

 tag is compromised at depth. These 

 mechanisms include both mechani- 

 cal devices that sever the monofila- 

 ment tether that attaches the tag to 

 the fish upon reaching a given depth 

 and internal software subroutines 

 that activate the normal electronic 

 release mechanism if the tag either 

 reaches a certain depth or maintains 

 a constant depth for a predetermined 

 length of time. 



Despite the addition of these re- 

 lease mechanisms to PSATs, some 

 tags still fail to transmit data. Such 

 failure could result from any of the 

 following events or conditions: me- 

 chanical failure of a critical tag com- 

 ponent; destruction by fishing crews 

 unaware of or not participating in 

 the present research; excessive epi- 

 faunal growth that makes the tag 

 negatively buoyant or prevents the 

 tag from floating with the antenna 

 in a vertical position; or fouling of 

 the tag on the fish, fishing gear, or 

 flotsam. Another cause of failure is 

 that the tags could be lost as a re- 

 sult of ingestion. For example, a free- 

 swimming white marlin (Tetrapturus 

 albidus) was observed mouthing and 



almost swallowing a free-floating 

 PSAT off the Dominican Republic in 

 May 2002 (Graves, personal observ.). 

 Alternately, the tag could be ingested 

 incidentally with part of the tagged 

 fish, as described by Jolley and Irby 

 (1979) who reported that an acoustic 

 tag on a sailfish (Istiophorus platyp- 

 terus) was eaten along with the fish 

 by an undetermined species of shark. 

 In this note, we present data from 

 PSATs deployed on two white marlin 

 in the western North Atlantic Ocean 

 and on an opah (Lampris guttatus) 

 in the central Pacific; the data from 

 these tags indicate that the tags were 

 consumed by sharks. 



Materials and methods 



White marlin 1 (WM1) 



At approximately 10:00 am local time 

 on 1 September 2002, a white marlin 

 was observed on pelagic longline 

 gear set during the night near the 

 southeastern edge of Georges Bank. 

 The fish, which had been caught 

 on a slightly offset, straight-shank 

 J-style hook (size 9/0), was manu- 

 ally guided with the leader along- 

 side the vessel. A PTT-100 HR model 

 PSAT (Microwave Telemetry, Inc., 

 Columbia, MD) was attached to the 

 dorsal musculature approximately 5 

 cm below the base of the dorsal fin 

 with a large nylon anchor according 

 to the procedure and tether design 

 described in Kerstetter et al. (20031. 

 The tag was activated shortly after 

 the white marlin was first identified, 

 although approximately one hour is 

 required following activation for this 

 tag model to begin collecting data. 

 The tag was programmed to record 

 point measurements of temperature, 

 light, and pressure (depth I in four- 

 minute time intervals and to detach 

 from the animal after 10 days. After 

 release from the fish, the positively 

 buoyant tag was expected to float to 

 the surface and transmit stored and 

 real-time data. For both white marlin 



Manuscript submitted 27 April 2003 

 to the Scientific Editor's Office. 



Manuscript approved for publication 

 7 June 2004 by the Scientific Editor. 



Fish. Bull. 102:750-756120041. 



