284
Marine Mammal Physiology: Requisites for Ocean Living
Alternatively, trails from trail generator and experimental subject need to be recorded
with tracking devices attached to the generator or subject. Generally with these tracking devices, experimenters face the problem that usually these devices only send signals when the subject or trail generator surfaces. Thus, reliable tracking instruments
need to be developed that can operate even when attached to an object fully and constantly submerged.
12.4 Unsolved mysteries
Most experiments reported in this chapter have been conducted with harbor seals as model
organism. Thus, the question arises if other marine mammals possess comparable sensory
abilities. However, the generalization from harbor seals to other marine mammals even
to closely related species is complicated by the fact that all species differ in many aspects
and show specific adaptations to their environment and lifestyle. To give an example, the
vibrissae of harbor seals are undulated in shape whereas otariids and even some phocids
possess smooth vibrissae (see for example, Hanke et al. 2010). Or, even though a number of
studies have analyzed the vibrissal follicles in various species many structures within the
follicle vary interspecifically and often their function is unknown. In conclusion, visual
as well as hydrodynamic experiments comparing the performance of other marine mammals to the documented performance of harbor seals in visual and hydrodynamic flow
perception experiments are required.
The finding of optic flow perception in harbor seals will influence research in the
field of marine mammal science and underwater locomotion and orientation. It forces
researchers to rethink underwater locomotion and orientation in general as optic flow
is, for example, induced by movement through dissolved particles that have previously
been listed in support of the view that underwater visual orientation is often restricted
if not impossible. Current research has focused on optic flow induced by movement
through particles. In the future, it awaits determination if seals are also able to use the
optic flow induced by movement over the ground or underneath the water surface. And,
as the first optic flow experiment was assessing optic flow sensitivity in response to a
simulation, it needs to be determined how and what for optic flow is used in marine
mammals.
Research on underwater optic flow perception will significantly enhance vision science generally since specifics of the underwater situation (Gläser et al. 2014) are likely
to require novel strategies for optic flow analysis. In addition to a pure visual solution
of these problems, an analysis of the integration of information from hydrodynamics and
vision can bring the field forwards. In detail, one challenge is that harbor seals have to
cope with optic flow induced by external water movements such as currents. The question thus is if harbor seals are able to analyze optic flow fields in the presence of drift.
If harbor seals were not able to solve the task using vision alone, they might be able to
sense the external water movement with the help of their vibrissae. By integrating visual
and tactile flow information they might then be able to subtract the optic flow induced
by external water movements from the overall flow pattern. Generally, the vibrissal system faces a comparable problem; a trail generated by a fish is masked by medium movement noise (Dehnhardt and Mauck 2008). This problem will also have to be addressed
in future experiments.
Experimental results from optic flow as well as from hydrodynamic experiments will
and already have an impact on underwater robotics, for example, for controlling movement in three-dimensional flow of remotely operating vehicles (ROVs).
Marine Mammal Physiology: Requisites for Ocean Living
Alternatively, trails from trail generator and experimental subject need to be recorded
with tracking devices attached to the generator or subject. Generally with these tracking devices, experimenters face the problem that usually these devices only send signals when the subject or trail generator surfaces. Thus, reliable tracking instruments
need to be developed that can operate even when attached to an object fully and constantly submerged.
12.4 Unsolved mysteries
Most experiments reported in this chapter have been conducted with harbor seals as model
organism. Thus, the question arises if other marine mammals possess comparable sensory
abilities. However, the generalization from harbor seals to other marine mammals even
to closely related species is complicated by the fact that all species differ in many aspects
and show specific adaptations to their environment and lifestyle. To give an example, the
vibrissae of harbor seals are undulated in shape whereas otariids and even some phocids
possess smooth vibrissae (see for example, Hanke et al. 2010). Or, even though a number of
studies have analyzed the vibrissal follicles in various species many structures within the
follicle vary interspecifically and often their function is unknown. In conclusion, visual
as well as hydrodynamic experiments comparing the performance of other marine mammals to the documented performance of harbor seals in visual and hydrodynamic flow
perception experiments are required.
The finding of optic flow perception in harbor seals will influence research in the
field of marine mammal science and underwater locomotion and orientation. It forces
researchers to rethink underwater locomotion and orientation in general as optic flow
is, for example, induced by movement through dissolved particles that have previously
been listed in support of the view that underwater visual orientation is often restricted
if not impossible. Current research has focused on optic flow induced by movement
through particles. In the future, it awaits determination if seals are also able to use the
optic flow induced by movement over the ground or underneath the water surface. And,
as the first optic flow experiment was assessing optic flow sensitivity in response to a
simulation, it needs to be determined how and what for optic flow is used in marine
mammals.
Research on underwater optic flow perception will significantly enhance vision science generally since specifics of the underwater situation (Gläser et al. 2014) are likely
to require novel strategies for optic flow analysis. In addition to a pure visual solution
of these problems, an analysis of the integration of information from hydrodynamics and
vision can bring the field forwards. In detail, one challenge is that harbor seals have to
cope with optic flow induced by external water movements such as currents. The question thus is if harbor seals are able to analyze optic flow fields in the presence of drift.
If harbor seals were not able to solve the task using vision alone, they might be able to
sense the external water movement with the help of their vibrissae. By integrating visual
and tactile flow information they might then be able to subtract the optic flow induced
by external water movements from the overall flow pattern. Generally, the vibrissal system faces a comparable problem; a trail generated by a fish is masked by medium movement noise (Dehnhardt and Mauck 2008). This problem will also have to be addressed
in future experiments.
Experimental results from optic flow as well as from hydrodynamic experiments will
and already have an impact on underwater robotics, for example, for controlling movement in three-dimensional flow of remotely operating vehicles (ROVs).