Sharks and Humans 163
yet to discover. But killing massive numbers of sharks for their cartilage as a
source of chondroitin is avoidable, and as a cancer cure is foolish. Such un-
proven and unnecessary uses just promote the overexploitation of sharks.
Do sharks feel pain?
Our understanding of pain is highly colored by our own experience and
reactions. When we talk about pain in other organisms, we must distin-
guish between whether they feel pain versus whether they feel pain they
way we do.
Pain has a technical definition established by a scientific organization
called the International Association for the Study of Pain (IASP). The IASP
defines pain as “an unpleasant sensory or emotional experience associated
with actual or potential tissue damage.” The IASP goes on to list the ele-
ments of a sense of pain, including (1) appropriate anatomical, nervous, and
physiological components; (2) behaviors that are more complicated than
simple reflexes (such as pulling your hand away from the stove when you
burn yourself); and (3) an ability to learn and therefore avoid future painful
events.
If you want to know if sharks feel pain the same way that we do, the
answer is probably no. Our sense of pain involves a part of our brain (the
neocortex) that is lacking in sharks. This would suggest that sharks lack
the first element in the IASP’s list, namely, the appropriate structures.
However, sharks do have pain receptors, called nociceptors, in their skin
just like all vertebrates, so they can certainly sense painful stimuli. They
also show internal stress responses similar to other vertebrates when
caught on a hook and line—specifically, changes in blood chemistry (low-
ered blood pH, elevated cortisol levels). A number of studies show that
sharks can learn as well as bony fishes, including learning to avoid nets after
having been captured in one, which is certainly a stressful situation that
could include painful stimuli. A growing body of experimental evidence
strongly suggests that bony fishes feel pain by all the requirements of the
IASP definition and criteria. Similar studies have yet to be performed on
sharks, leaving the question ultimately up in the air.
The issue is additionally complicated by differences in the ability to ig-
nore pain between different persons, and between people and sharks. Pain
thresholds vary tremendously among people; women have a higher pain
tolerance than men (confirmed in MythBusters episode 142, “No Pain, No
Gain,” which also confirmed that cursing out loud helps a person tolerate
more pain). Sharks feed on stingrays, lionfish, and a variety of other spiny
fishes that inject venom as part of their defensive adaptations. It may hurt
to chomp down on a stingray—and some hammerhead sharks feed heavily