Taylor,
T., 2004. Decay on the Delta: Estimating time-since-death for
marine mammal carcasses in the northern Gulf of California, Mexico. Gulf of
California
Marine
mammal carcasses decay after death.
Their rate and pattern of decay is important to the use of carcasses in
surveys of the living fauna and also to interpretations of fossil
skeletons. I observed nine carcasses of
marine mammals in the northern Gulf of California during survey trips in
December 2001, December 2002, and March 2003.
I found carcasses of four species known from the northern Gulf of
California: Bottlenose Dolphin (Tursiops
truncatus, 4 carcasses), California Sea Lion (Zalophus californianus, 2 carcasses), Balaenoptera spp. (Balaenoptera physalus or edeni, 2 carcasses), and Long-beaked
Common Dolphin (Delphinus capensis, 1
carcass). Two of the Bottlenose Dolphin
carcasses were observed during both the December 2001 and 2002 trips, providing
11 observations of nine carcasses.
My
preliminary results suggest six taphonomic stages: Fresh/Bloat, Intact Mummy,
Skull/Tail Exposure, Body Breach, Disarticulated Bones, and Scattered
Bones. Stage 1: Fresh/Bloat is when the
carcass has not yet degassed, the tongue, eyes, and most teeth are still
present, and body fluids are present in or around the carcass. Stage 2: Intact Mummy is after the carcass
has degassed and becomes dehydrated, tongue, eyes, and most teeth are missing,
and the skin becomes leathery. Stage 3:
Skull/Tail Exposure is when the skin around the rostrum is gone, the caudal
vertebrae are exposed, and the carcass is very dehydrated. Stage 4: Body Breach (i.e. Bag o’ Bones) is
when thoracic and lumbar vertebrae along with ribs are exposed, the skin is
flaking, and the carcass is completely dehydrated. Stage 5: Disarticulated Bones (i.e. Pile o’ Bones) is when
tendons and ligaments holding the bones together dry and become brittle and
bones start to disarticulate, some skin and tendon may still be present, and
bones may be greasy. Stage 6: Scattered
Disarticulated Bones is when very little skin and tendon is present, bones are
scattered over an area larger than the initial carcass, and bones are in some stage
of bleaching.
I
found one carcass in Stage 1, four carcasses in Stage 2, three carcasses in
Stage 3, one carcass in Stage 4, one carcass in Stage 5, and one carcass in
Stage 6. The two Bottlenose Dolphin
carcasses that were observed in subsequent years were initially in Stage 2; the
following year one carcass remained in Stage 2 while the other carcass was
found in Stage 3 of decay. Based on
published description of whale decay in the North Sea, and human decay in humid
and arid environments, I estimate that Stage 1 is a few weeks in duration,
Stage 2 is typically up to three to five years long, Stages 3, 4, and 5 are one
to four years each, and Stage 6 can be as long as five years.