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Gaps in our knowledge of basic fish ecology have provided impetus for development of novel "ecology tags" to detect and quantify hard to observe behaviors such as spawning, schooling and feeding. The acoustic envi- ronment is one source of potentially useful information about these behaviors. We implanted an acoustic recording tag (Bioacoustic Probe) into the gut cavity of a blacktip reef shark to determine whether an implanted tag could success- fully record external and internal sounds. The tag successfully recorded reef fish vocalizations, boat engine noise, the sound of the shark feeding and unidentified rhythmic sounds that may derive from shark tail beats. Technical challenges remain, but sound recording tags have the potential to provide novel insights into shark and fish ecology.

Traditional telemetry methods have been used to quantify the horizontal and vertical displacement of marine species, but are unable to identify specific physical activities such as swimming or gliding, resting, foraging, or spawning. We tested the utility of an acceleration data logger to quantify activity patterns of three captive whitetip reef sharks (Triaenodon obesus ) in an enclosed lagoon using internal and external attachment methods. Data obtained using both attachment methods allowed swimming and resting behavior to be differentiated. All sharks showed constant swimming for 5–14 hours post-tagging before adopting a pattern of daytime rest and nocturnal activity throughout the 6–16 day deployments. Sharks showed a diel activity pattern, spending 10–24% of their time swimming during the day, and 42–67% swimming at night. Overall, sharks spent an average of 35 ± 11% (mean ± SD) of their time swimming. Mean tailbeat frequency was found to be 0.89 ± 0.03 beats s−1 in one shark for which it was measured. Respirometry experiments that measured the metabolic rate of two neonate whitetips showed significantly higher metabolic rates at night compared to the day. When taken in conjunction with the acceleration data, these results suggest that whitetips are nocturnally active and show diel circadian rhythms shortly after birth. Our study demonstrates that acceleration data loggers can be used to quantify activity patterns and offer promise for quantifying energy budgets of various reef sharks both in captivity and in the field.

Little is known about the feeding habits of large free ranging fish, due in large part to lack of an appropriate technique for quantifying feeding variables. A previous study demonstrated that changes in gastric pH can be used as a proxy for feeding events in free-ranging sharks. Here we describe the development of a new acoustic pH transmitter to remotely measure gastric pH in sharks in the field. The transmitter consists of a dual sensor (pH and temperature) continuous pinger, and was tested in captive adult blacktip reef sharks (Carcharhinus melanopterus). The transmitter was retained in the shark's stomach for between 5-12 days. The empty stomach had a low pH (1.6 ± 0.2) and feeding induced a rapid increase in gastric pH, which was clearly distinguishable from baseline levels. Meal size showed a significant linear relationship with the magnitude of the pH changes. Measurement accuracy of the pH transmitter ranged from 0.05-0.9, although resolution of the VR100 receiver that decoded the transmitter signal was 0.1 units. The pH transmitter can be used to determine when free-ranging sharks in the field are feeding and hence quantify feeding chronology, frequency and daily ration.

Yellowfin tuna (Thunnus albacares) are known to preferentially occupy the Surface mixed layer above the thermocline and it has been Suggested that they are physiologically restricted to water lerriperatt.11-CS no more than 8 degrees C colder than Surface waters. However, we here report for dive data acquired from a large yellowfin tuna which demonstrate for the first time that this species is indeed capable of making prolonged dives into deep cold waters. A yellowfin tuna (134 cm fork length) caught near ail anchored fish aggregating device (FAD) in the Seychelles (Western Indian Ocean) was equipped with all internally implanted archival tag and released. The fish was recaptured 98 days later. As predicted for this species, this fish spent 85% of its time shallower than 75 in (maximum thermocline depth experienced by the fish) but, over the Course of the track, it performed three deep dives to 578 in, 982 In and 1160 In. Minimum ambient water temperatures recorded Lit these depths were 8.6 degrees C, 7.4 degrees C and 5.9 degrees C respectively and varied by up to 23.3 degrees C from surface temperatures. The fish spent 8.3% of its time in waters more than 8 degrees C colder than the surface layer and daily experienced a wide range of sea temperatures (mode at 15- 16 degrees C) and of temperatures of the gut cavity (mode at 6 degrees C). The reason for these dives call not be known. These depths and temperatures significantly exceed those reported ill the literature so far and clearly demonstrate that this species has the physiological and behavioral ability to penetrate deep cold sections of the ocean.