Transcript Bat Ray Presentation

Bat Ray
Myliobatis californica
By Bridger Tillotson
Topics of Discussion:
• Ecosystem/Role in Ecosystem
• Feeding Behavior
• Reproduction
• Human Impact
Ecosystem
• Bat rays are euryhaline;
able to tolerate and live in
environments with
varying salinity levels.
• Live at depths ranging
from 1 to 46 meters
either solitarily or in large
schools with members of
their own species or
other species of eagle
rays.
• Bat rays can be found in
muddy and sandy bottom
bays, rocky bottom
shorelines, kelp beds,
estuaries and close to
coral reefs.
• Distribution of the species
is limited to the eastern
Pacific Ocean from
Oregon to the Gulf of
California and also near
the Galápagos Islands.
World Distribution
Role in Ecosystem
• Bat rays feed on many
buried organisms;
including mollusks,
crustaceans,
polychaetes and small
bony fish.
• Clams are the dominant
prey item of the
species.
• Bat rays may help
smaller fish to feed on
buried organisms by
uncovering them.
• Preyed upon by white
sharks, seven gill sharks
and killer whales.
Young, immature bat
rays are consumed by
sea lions.
Bat Ray Feeding On Squid
Feeding Behavior
• Bat rays use their snout
to dig up covered prey.
• The species also
captures food by waving
its pectoral fins rapidly
up and down to expose
their prey, creating
suction in the sand and
digging trenches up to
20 cm deep and 4 m
long.
Feeding Behavior
• Dentition of the species consists of a single elongated
medial file and three lateral files of teeth on either
side. The lower tooth plate is flat while the upper
plate is convex in shape. The teeth are hexagonal,
arranged in non-termino-lateral positions. These
plates are used for crushing and grinding prey.
Bat Ray Jaws
Reproduction
• Bat rays mate annually in the
spring or summer.
• After a male bat ray finds a
suitable mate, they swim close
behind the female with his back
touching her underside.
• The male may make repeated
attempts at inserting a clasper
into the female’s cloaca until
successful.
• During copulation, the pair swims
together, moving their pectoral
fins in unison.
• Females may be pursued by more
than one male, resulting in fights
among the males.
• Female bat rays form large
mating aggregations, blocking
other females that are immature
or that have already mated.
Bat Rays Mating
Reproduction
• Ovoviviparous; eggs are
fertilized internally and
litters of up to 12 pups
are born live following a
gestation period of 9 to
12 months.
• At birth, the pups are 30
to 36 cm wide and each
weigh about 1 kg.
• Pups are born tail-first
with their pectoral fins
rolled over the body. The
spines of the pup are
pliable and encased in
tough sheaths, preventing
injury to the female
during birth. The spines
harden and the natal
sheath is discarded soon
after birth.
Human Impact
• Bat rays are not currently
threatened or endangered. The
species is listed as "Least
Concern" with the World
Conservation Union (IUCN).
• The species is non-aggressive and
poses little threat to humans.
However, bat rays possess 1 to 3
venomous spines located at the
base of the tail.
• Bat rays are not fished
commercially in the United
States, but are fished
commercially in Mexico for food.
The species is also targeted for
sport fishing.
• For many years, commercial
oyster growers trapped bat rays
because they thought bat rays ate
large numbers of oysters. But
recently researchers have
discovered that bay rays rarely
eat oysters, and that crabs were
responsible for destroying the
oyster beds. The oyster growers
were actually causing the
destruction of their own oyster
beds by trapping bat rays, which
prey on crabs.
Human Impact
• Bat rays are often
caught in trawling and
gill nets as unwanted
by-catch.
• Bat rays can readily
adapt to captivity and
are commonly displayed
at public aquarium
facilities; including
SeaWorld, Aquarium of
the Pacific and
Monterey Bay
Aquarium.
Review
Topics Discussed:
• Ecosystem/Role in Ecosystem
• Feeding Behavior
• Reproduction
• Human Impact
Main Research Sources
• Florida Museum of Natural History
http://www.flmnh.ufl.edu/
• Aquarium of the Pacific
http://www.aquariumofpacific.org/
• Monterey Bay Aquarium
http://www.montereybayaquarium.org/
Scientific Article
• Food habits, occurrence, and population
structure of the bat ray, Myliobatis
californica, in Humboldt Bay, California
By Ann E. Gray, Timothy J. Mulligan & Robert
W. Hannah