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Fishery Bulletin 102(1) 



2000 in waters with a surface temperature of 21.9°C. The 

 longline set contained 184 hooks set at depths between 

 70 m and 90 m and was made at 06:00 h and retrieved at 

 09:00 h. Circle hooks (L2045 20/0 circle hook, Eagle Claw, 

 Denver, CO) were used to avoid hooking of the gut, and 

 the shark in this study was hooked in the corner of the 

 jaw. Hooks were baited with squid, and chemical light 

 sticks were attached to every other line. The mass of the 

 shark was visually estimated at 170 kg by an experienced 

 commercial longline fisherman, which corresponds to a 

 fork length of 229 cm, and a total length of 377 cm, based 

 on the weight-length relationship of Kohler et al. (1995). 

 According to this size estimation and the published size-at- 

 maturity data (Chen et al., 1997; Liu et al., 1998), the shark 

 was mature. The sex of the shark was not determined. The 

 second shark was captured by hook-and-line gear near 

 Hawaii at 19.5°N, 156.0°W on 13 May 2003 in waters with a 

 surface temperature of 25.5°C. A baited circle hook set at a 

 depth of 40 m was taken by the shark at 02:00 h. The mass 

 of the shark was estimated at 200 kg by an experienced 

 sportfishing captain, which corresponds to a fork length of 

 242 cm, and a total length of 400 cm (after Kohler et al., 

 1995). Given this size, the shark was mature (Chen et al., 

 1997; Liu et al., 1998), but its sex was not determined. 



Each pop-up satellite archival tag was attached to a tita- 

 nium dart (59 mm x 13 mm) with a 17 cm segment of 136- 

 kg monofilament line ( 300-lb test extra-hard Hi-Catch, Mo- 

 moi Fishing Net Mfg. Co. Ltd., Ako City, Hyogo prefecture, 

 Japan). The dart was inserted into the dorsal musculature 

 of the shark at the base of the first dorsal fin, such that the 

 tag trailed behind the fin. Following attachment of each 

 tag, the fishing line was cut near the hook and both sharks 

 swam away vigorously. Tagging locations were recorded by 

 using the vessel's global positioning system. After the Gulf 

 of Mexico shark was tagged, a depth-temperature recorder 

 (ABT-1, Alec Electronics, Kobe, Japan) was used to deter- 

 mine the temperature-depth profile of the upper 200 m of 

 the ocean at the release site, at a resolution of 1 m. 



The pop-up satellite archival tag deployed in the Gulf 

 of Mexico was programmed to collect pressure and tem- 

 perature data at two-minute intervals, which the on-board 

 software (PAT software version 1.06, Wildlife Computers, 

 Redmond, WA) summarized into six-hour bins. This version 

 of PAT software did not permit light-based geolocation. The 

 summary data for each time interval comprised percentage 

 distributions of time-at-depth and time-at-temperature, 

 and profiles of temperature-at-depth. Temperature-depth 

 profiles for this generation of software were recorded at 

 intervals by measuring a single temperature at depths of 

 0, 25, 50, 75, 100, 125, 150, 200, 250, 300, 350, and 400 me- 

 ters for the deepest dive. A mean temperature-depth profile 

 was obtained by calculating the mean temperature at each 

 specified depth for all profiles taken during the track. The 

 endpoint position of the shark's track was obtained from 

 the tag's radio transmissions to the Argos satellites. The 

 six-hour bins were later combined into 12-hour bins repre- 

 senting day (06:00 to 17:59 h local time) and night ( 18:00 to 

 05:59 h local time). At the time and place of tag deployment, 

 sunrise occurred at 05:45 h and sunset at 18:28 h; whereas 

 at the popup time and position, sunrise occurred at 05:02 h 



and sunset at 18:55 h (U.S. Naval Observatory), such that 

 the day and night bin cutoffs were always within one hour 

 of true sunrise and sunset. 



The pop-up satellite archival tag deployed off Hawaii col- 

 lected data at 30-second intervals and summarized them 

 into four-hour bins (PAT software version 2.08e, Wildlife 

 Computers, Redmond, WA). The data were later combined 

 into day and night bins as for the first tag, and the actual 

 sunrise and sunset times were within one hour of 06:00 h 

 and 18:00 h, respectively (U.S. Naval Observatory). The tag 

 measured the minimum and maximum temperature at the 

 surface, maximum depth, and six intermediate depths, for 

 the deepest dive in each time interval. Temperature-depth 

 profiles for each time interval were later constructed by us- 

 ing the maximum temperature at each depth for all profiles 

 taken during the track, and a curve was fitted by using a 

 LOWESS (locally weighted regression smoothing) function 

 (Cleveland, 1992). Version 2.08e PAT software collected 

 light data for geolocation; however the diel dive pattern of 

 the shark prevented the calculation of accurate positions. 



The vascular circulation to the brain and eyes was exam- 

 ined in two bigeye thresher sharks: one common thresher 

 shark and one pelagic thresher shark iAlopias pelagicus). 

 A female bigeye thresher (1.5 m fork length) was captured 

 off Cape Hatteras, North Carolina, and a male (1.4 m fork 

 length) was captured in the Gulf of Mexico. The circula- 

 tory systems of the bigeye threshers were injected with 

 latex to aid in identifying the blood vessels. A male com- 

 mon thresher (1.3 m fork length) was captured off Cape 

 Hatteras, North Carolina, and was examined without 

 being frozen or preserved. An immature female pelagic 

 thresher shark (1.37 m fork length) was captured in the 

 Indian Ocean. The orbital retia mirabilia were prepared 

 from casts of the vascular circulation that were removed 

 from the orbit. 



Results 



One bigeye thresher shark was tracked in the Gulf of 

 Mexico for 60 days, and another in the Hawaiian Archi- 

 pelago for 27 days, by using pop-up satellite archival tags. 

 Both tags released from the sharks as programmed and 

 transmitted summary information to Argos satellites. The 

 tag deployed in the Gulf of Mexico popped up on 10 June 

 2000 at 27.95°N, 89.54°W (Fig. 1A). The shark moved a 

 straight-line distance of 320 km during the track, start- 

 ing from the central Gulf in depths exceeding 3000 m and 

 moving to waters 150 km south of the Mississippi Delta 

 where depths were approximately 1000 m. The second 

 shark was tagged off the Kona coast of Hawaii and the tag 

 released on 9 June 2003 at 24.2°N, 165.6°W. northeast of 

 French Frigate Shoals, a straight-line distance of 1125 km 

 from the deployment position (Fig. IB). 



The depth and temperature distributions of the bigeye 

 thresher sharks showed a strong diel movement pattern 

 (Fig. 2). The Gulf of Mexico shark spent the majority of 

 the daytime (84 f * (±2.39H. mean [±1 SE]) below the ther- 

 mocline between 300 m and 500 m and the majority of 

 nighttime (809? [±4.7%], mean (±1 SE] ) in the mixed layer 



