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Fishery Bulletin 1 12(4) 
temperature drops recorded by the 2 implanted tags. 
No such differences were recorded in this study. Rapid, 
catastrophic extrusions (i.e., endogastric) are almost 
certainly lethal and would result in lower survival 
rates compared with the rates of control groups. We, 
therefore, deem direct extrusion as extremely unlikely. 
It is also possible that rapid temperature drops re- 
sulted from tags liberated by scavengers that fed on 
a carcass within 30-60 min post mortem. Scavenging 
after a longer time would have revealed at least ini- 
tial changes of cooling conforming to a type-II scenario 
(Fig. 2). Many processes that lead to death are associ- 
ated with the reduced ability of marine mammals to 
thermoregulate (Dierauf and Gulland, 2001; Rosen et 
al., 2007; Stoskopf, 2005). Inflammation and infection 
often lead to pyrexia (fever). In extreme cases of sep- 
ticemia, temperatures may even continue to rise post 
mortem. Hypoglycemia, starvation and emaciation, 
congestive cardiac failure, hemorrhage, and shock are 
all associated with a reduced body-core temperature. 
Furthermore, many injured or diseased pinnipeds have 
a tendency to come ashore and die there (Dierauf and 
Gulland, 2001), although this behavior may not apply 
to highly pelagic species, such as elephant seals. None 
of the observed events were associated with any signs 
of compromised health, such as pyrexia or hypother- 
mia, and all events occurred at sea. Death from drown- 
ing (following entanglement) should lead to a type-III 
scenario that involves slightly accelerated, internal 
cooling by inhaled cold water, although not to the level 
exhibited in Figure 3 (in marine mammals, total lung 
capacity [in liters] is typically <10% of body mass [in 
kilograms]; Kooyman [1989]). 
This evaluation of various possible cooling rates and 
antemortem temperatures indicates that, at onset of 
the rapid temperature drops shown in Figure 4 and 
5, the animals were alive and healthy and that death 
likely coincided with rather than preceded releases of 
LHX tags. Therefore, although scavenging shortly after 
death could not be categorically excluded at this point, 
we found no evidence of nontraumatic death at sea and 
deem such an event unlikely. Predation is the most 
likely and consistent interpretation for all 15 events, 
which fit type-I, -III, or -IV scenarios, discussed here. 
Tags from 11 type-I events quickly sensed light or 
air and did not have delayed transmissions. These tags 
reported postmortem temperatures that corresponded 
with regional SST estimates. These events may have 
happened at or near the sea surface, where tags were 
exposed quickly to ambient light while their antennas 
floated above water. Free-floating LHX tags ascended 
at a mean rate of 1.3 m s _1 (standard error of mean 
[SE] 0.05) during runs (n=10) simulated in laboratory 
trials (senior author, unpubl. data). Even tags liberated 
at a depth of 500 m, beyond the 300 m reported as the 
deepest dive depth for juvenile Steller sea lions (Mel- 
lish et al., 2007), still would reach the surface within 
10 min, and, once there, they would record tempera- 
tures corresponding to the SST and the air surround- 
ing their floating antennas, and ambient light levels 
would trigger transmissions. Therefore, no inferences 
can be made from these 11 type-I events on the species 
of the predator. 
One type-III event yielded a gradual temperature 
decline from 1 tag with delayed sensing of light and 
air. The tag cooled to a temperature of 4.51°C, a level 
above the regional SST estimate of 3.7°C but similar to 
values for temperatures at a depth of approximately 50 
m. This temperature pattern could be the result of the 
sinking of the LHX tag after dismemberment of the an- 
imal, with a portion of sea lion tissue surrounding the 
tag, to a depth where the slightly warmer water tem- 
perature was recorded. However, LHX tags are coated 
with a material designed to prevent connective tissue 
growth and encapsulation or adhesion to the omentum 
in the abdominal gut cavity (Horning and Hill, 2005). 
Temperature drops from all other tags indicated imme- 
diate and complete separation from all tissue, and all 9 
tags that were physically recovered — including the tag 
from this type-III event — had no signs of connective 
tissue or adhesion. It is difficult to imagine that a 24- 
kg portion of abdominal tissue could remain after dis- 
memberment and could contain a tag for an extended 
period of time without the tag being released. It seems 
more plausible that this LHX tag and some sea lion 
tissue were ingested together by a cold-bodied predator, 
resulting in gradual cooling in darkness. 
In the 3 remaining events, 4 tags with precipitous 
drops and delayed onset of transmissions recorded 
temperatures different from SSTs but similar to esti- 
mates for temperatures at depths between 50 m (TJ63, 
TJ64) and 200 m (TJ52) for 24 h post mortem (Table 
1; Fig. 5). These tags detected light or air only 5-11 d 
post mortem, at which time uplink temperatures corre- 
sponded with regional SST estimates. The combination 
of the absence of light or air and of extended record- 
ings of deepwater temperatures indicates that these 
tags remained in the dark while surrounded by a cold, 
wet medium after their abrupt removal from the bod- 
ies of their hosts. In 1 event, only 1 of 2 tags recorded 
deepwater temperatures while remaining in the dark, 
but the other tag recorded postmortem temperatures 
that matched regional SST estimates and uplinked 
data immediately after sensing light and air (Fig. 2). 
The postmortem temperatures recorded by each of the 
4 tags with delayed uplinks essentially were constant, 
in comparison with data from tags that floated at the 
surface and recorded temperature fluctuations between 
0.82°C and 2.40°C over a 24-h period. 
The most parsimonious explanation for our data is 
that the 4 tags with precipitous temperature drops and 
delayed onset of transmissions were ingested after an 
attack by a cold-bodied predator. Tag ingestion simulta- 
neously explains absence of air and light, delayed onset 
of transmissions, and constant postmortem tempera- 
tures distinct from SSTs. Three poikilotherm species 
have been reported as potential predators of Steller sea 
lions (Loughlin and York, 2000): the white shark, the 
