106 Sharks: The Animal Answer Guide
hard thorns. Southern Thorny Skates (Amblyraja doellojuradoi) do this when
caught in nets.
Divers in Norway have made intriguing observations of the defen-
sive behavior of skates. Divers who bump into or prod juvenile Thorny
Skates have been surprised to see the skates quickly roll up hedgehog-
style with their pectoral fins curled around their bellies, essentially lying
on their backs with their heads up and their thorny tails presented to the
intruder. What makes this behavior intriguing is that the surface presented
to a would-be predator is the part where the electrogenic tissue of skates
is concentrated. One of the nagging questions in elasmobranch anatomy
and behavior is the function of this tissue in skates. Skates emit a relatively
weak electric charge, nothing like that of a torpedo ray. The function(s)
of skate electric discharge remains something of a mystery, although mat-
ing skates discharge electricity, implying some reproductive purpose. The
major predators of Starry Skates are two species of sharks, the Greenland
Shark and Tope. One idea proposed is that a skate that is discharging its
electric organs might somehow jam or overwhelm the extreme electric sen-
sitivity of a predatory shark. It’s an idea worth testing.
Most chimaeras have first dorsal fin spines with a sawtooth back edge,
covered with a venomous toxin. Researchers and fishers unlucky enough
to get stuck by a ratfish report that it is a painful experience, the wound
remaining red and swollen for several days. Presumably, natural predators
have the same experience. The toxic spines of Spiny Dogfish may function
similarly.
By Being Hard to Eat. Anything a prey animal can do to make it-
self harder to swallow works to its advantage. Tough skin and stiff spines,
especially long spines with toxins, deliver a message of inedibility. Stiff
spines also increase an animal’s overall size, assuming the predator must
swallow its prey whole (this works better as a defense against predatory
bony fish that can’t chop up their prey the way that most predatory sharks
can). Bramble sharks (Echinorhinus, Echinorhinidae) live as deep as 900 m
(2,970 ft). Their unique large thornlike denticles might give them physical
protection from deepwater predators such as somniosid sleeper sharks and
sperm whales. The tough skin and spines of Horn Sharks apparently work
to deter predators. A Pacific Angelshark (Squatina californica) was filmed in-
haling a juvenile Horn Shark, only to spit it out shortly afterward, probably
because of the boxlike body and stiff spines that give the shark its name.
The idea that making yourself bigger prevents a predator from swallow-
ing you underlies the anatomy and behavior of several shark species. Puff-
adder shysharks (Haploblepharus spp.) and Pajama Catsharks (Poroderma af-
ricanum) curl into a circle and cover their eyes with their tail when threat-
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