204
Marine Mammal Physiology: Requisites for Ocean Living
against potential body damage as they work through the heavy Arctic ice. George working with Alaska native hunters was able to obtain deep body temperature profiles from
bowheads and found that they were cooler than expected (33°C–34°C) (George 2009). They
are so heavily insulated (perhaps over insulated) that one intriguing model suggested that
they could swim through liquid oxygen at −183°C and still remain at 33°C–34°C in their
core (Hokkanen 1990), and others estimated that the animals were “100× over insulated”
(Kanwisher and Ridgway 1983). Elsner et al. (2004) has looked at the circulatory system in
the flukes of bowheads and found a suite of blood vessels that could be utilized to conserve
or dump heat as discussed previously. How these interesting animals balance their thermal
needs will be questions for many investigators yet to come.
9.6 Toolbox
Because of the many different types of studies involved in the field of thermoregulation,
there are a wide range of technical and scientific tools that are used by scientists to investigate questions about body temperature, heat loss, insulation, and more. From relatively
simple remote thermometers to complex heat flow devices, the field is one where technical
advancement draws heavily on medical and engineering approaches to make a rapidly
changing toolbox for data collection and theoretical models.
9.6.1 Measuring blubber
Much of the early knowledge about blubber was limited in scope and was collected from
harvested animals. Because blubber depth on the body can vary from site to site on the
body, it was standard to measure the blubber thickness on a seal at the midline on the ventral side (xiphosternal), if only one measurement could be taken (Pitcher 1986; Fadely 1997).
However, advances in non-imaging ultrasound technology in the 1980s changed how
we could measure blubber. Ultrasound functions on the principle that sound travels at
different speeds through different types of tissues. In some cases, such as bone, the sound
does not travel through at all, but instead is refracted. Ultrasound allowed for the estimation of blubber depth in phocids, in particular, given their relatively uniform blubber layer
and clear signal at the blubber–muscle interface (Gales and Burton 1987; Slip et al. 1992).
This led to the ability to perform time-series studies in individuals, and the important
finding that not only does blubber depth vary by body site, it can vary seasonally and is
quite species-specific, for example, Rosen and Renouf (1997) and Mellish et al. (2007).
These first portable ultrasound devices provided a simple LED scale of blubber depth,
but not long after, “advanced graphic display imaging” ultrasound revolutionized the ability to detect blubber depth both rapidly and effectively (Mellish et al. 2004). As these units
have shrunk from the size of a wheeled cart to the size of a backpack, and now to the size
of a smartphone, they have become a part of regular health examinations for cetaceans
and pinnipeds at aquaria around the world, and are found in the gear complement of most
field physiologists (Noren et al. 2008; Mellish et al. 2011; Hoopes et al. 2014).
In its simplest form, one can model the body shape of a marine mammal as a core
of muscle, surrounded by a ring of blubber and build a series of volume cones to estimate body mass, blubber content, and so on (Castellini et al. 2009). However, blubber is
almost non-existent in the flippers and tails, usually thin around the head, and so forth. As
described in Chapter 10, it is most accurate to obtain a suite of blubber thickness measurements around the body and then build a model of total blubber content, as defined for your
particular species (Shero et al. 2014; Shuert et al. 2015).
Marine Mammal Physiology: Requisites for Ocean Living
against potential body damage as they work through the heavy Arctic ice. George working with Alaska native hunters was able to obtain deep body temperature profiles from
bowheads and found that they were cooler than expected (33°C–34°C) (George 2009). They
are so heavily insulated (perhaps over insulated) that one intriguing model suggested that
they could swim through liquid oxygen at −183°C and still remain at 33°C–34°C in their
core (Hokkanen 1990), and others estimated that the animals were “100× over insulated”
(Kanwisher and Ridgway 1983). Elsner et al. (2004) has looked at the circulatory system in
the flukes of bowheads and found a suite of blood vessels that could be utilized to conserve
or dump heat as discussed previously. How these interesting animals balance their thermal
needs will be questions for many investigators yet to come.
9.6 Toolbox
Because of the many different types of studies involved in the field of thermoregulation,
there are a wide range of technical and scientific tools that are used by scientists to investigate questions about body temperature, heat loss, insulation, and more. From relatively
simple remote thermometers to complex heat flow devices, the field is one where technical
advancement draws heavily on medical and engineering approaches to make a rapidly
changing toolbox for data collection and theoretical models.
9.6.1 Measuring blubber
Much of the early knowledge about blubber was limited in scope and was collected from
harvested animals. Because blubber depth on the body can vary from site to site on the
body, it was standard to measure the blubber thickness on a seal at the midline on the ventral side (xiphosternal), if only one measurement could be taken (Pitcher 1986; Fadely 1997).
However, advances in non-imaging ultrasound technology in the 1980s changed how
we could measure blubber. Ultrasound functions on the principle that sound travels at
different speeds through different types of tissues. In some cases, such as bone, the sound
does not travel through at all, but instead is refracted. Ultrasound allowed for the estimation of blubber depth in phocids, in particular, given their relatively uniform blubber layer
and clear signal at the blubber–muscle interface (Gales and Burton 1987; Slip et al. 1992).
This led to the ability to perform time-series studies in individuals, and the important
finding that not only does blubber depth vary by body site, it can vary seasonally and is
quite species-specific, for example, Rosen and Renouf (1997) and Mellish et al. (2007).
These first portable ultrasound devices provided a simple LED scale of blubber depth,
but not long after, “advanced graphic display imaging” ultrasound revolutionized the ability to detect blubber depth both rapidly and effectively (Mellish et al. 2004). As these units
have shrunk from the size of a wheeled cart to the size of a backpack, and now to the size
of a smartphone, they have become a part of regular health examinations for cetaceans
and pinnipeds at aquaria around the world, and are found in the gear complement of most
field physiologists (Noren et al. 2008; Mellish et al. 2011; Hoopes et al. 2014).
In its simplest form, one can model the body shape of a marine mammal as a core
of muscle, surrounded by a ring of blubber and build a series of volume cones to estimate body mass, blubber content, and so on (Castellini et al. 2009). However, blubber is
almost non-existent in the flippers and tails, usually thin around the head, and so forth. As
described in Chapter 10, it is most accurate to obtain a suite of blubber thickness measurements around the body and then build a model of total blubber content, as defined for your
particular species (Shero et al. 2014; Shuert et al. 2015).