Abstract
We present evidence of predator interactions with 8 juvenile loggerhead sea turtles Caretta caretta equipped with pop-up satellite archival transmitting tags (PSATs) following incidental capture in the Northwest Atlantic. Ingestion of PSATs occurred up to 5 mo after tagging and was identified by an abrupt change in depth distribution, a stabilization and/or increase in ambient temperature and a marked drop in light levels to near zero, with cessation of diel light level cycling. In some cases, following expulsion from the digestive tract of predators, positively buoyant PSATs descended to the sea floor or beyond the programmed release depth threshold (1800 m), indicating that they remained tethered to the indigestible carapaces of turtles and that the entire turtle was originally consumed. PSAT data, combined with the sudden termination of satellite uplinks from 2 loggerheads also equipped with platform transmitting terminals, provided additional evidence of whole-turtle predation. PSAT data indicated that both endothermic and ectothermic sharks ingested tags. Based on PSAT-logged temperature data, dive patterns and geographic distribution, the following shark species were considered as candidate predators: white, porbeagle, shortfin mako, tiger and blue. This study represents the first analysis of data collected by loggerhead turtle PSATs inside predators. The results expand the list of shark species known to prey on large juvenile loggerheads and point to the importance of acknowledging predation as an important source of mortality for loggerhead turtles in the Northwest Atlantic Ocean.
Highlights
Application of electronic tags to wildlife facilitates studying behaviour in situ and is commonly used to remotely monitor movements and collect environmental data
From 2011 to 2018, 62 juvenile loggerhead sea turtles that were incidentally captured in pelagic longline fisheries targeting tunas and swordfish in Canadian waters were boarded with a dip net and tagged with pop-up satellite archival transmitting tags (PSATs) (PAT-Mk10, Mini-PAT, or SPLASH323-B; Wildlife Computers), attached by a ~20 cm tether to the posterior margin of the carapace following the protocol of Epperly et al (2007)
Data from 8 of 62 (0.13) PSATs deployed on juvenile loggerhead turtles were consistent with ingestion of the tag, or tagged turtle predation (Fig. 1)
Summary
Application of electronic tags to wildlife facilitates studying behaviour in situ and is commonly used to remotely monitor movements and collect environmental data. A diverse suite of biologging instruments exist, from archival data recorders equipped with sensors to measure depth, temperature and salinity, to satellite-linked transmitters which facilitate long-term terrestrial and marine animal tracking. Endang Species Res 46: 279–291, 2021 patagonicus tagged with flipper bands which have a significantly higher mortality rate than untagged individuals, linked, in part, to reduced swimming efficiency (Saraux et al 2011). Ross & McCormick (1981) showed that externally radiotagged fish were more vulnerable to predation than controls. There are exceptions: Janak et al (2012) reported no difference in predator avoidance between untagged and externally tagged juvenile chinook salmon Oncorhynchus tshawytscha
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