Download Shark Biology and Conservation

8/28/2008
Shark Biology and
Conservation
12 April 2008
J. B. Graham
with presentations by SIO Doctoral students Dan
Cartamil and Andy Nosal
Classification and Terminology
Vertebrates
ƒ The four higher vertebrate groups : amphibians
amphibians, reptiles
reptiles,
mammals, and birds.. total about 20,000 species
ƒ The fourth groupgroup- the fishes over 28,000 species.
– Two groups of fishes those with a bony skeleton, Osteichthyes;
– Those with a cartilaginous skeleton, Chondrichthyes (Cartilaginous
Fishes)
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Chondrichthyes
About 1100 species
57%
40%
rays
sharks
4%.
Elasmobranchs = sharks and rays
chimaeras
Chondrichthyes
Aquatic,
q
g
gill breathing,
g finned vertebrates having
g a simplified
p
internal cartilage
g
and lacking true bone.
Fins lack bony rays, true upper and lower jaw, nostrils underside of head.
Teeth not conspicuous in all species, form transverse rows or fused tooth plates,
and they are replaced continuously from within the jaw.
No bony plates on head, scales are small toothlike dermal denticles-placoid scales,
Have internal fertilization, male intromittent organs…claspers or myxipterygia.
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Chondrichthyes – 2 subclasses
Elasmobranchii - strapped or plated gills. – sharks and rays
Holocephali - chimeras.
What is a chimera?
Compressed body form, four pairs of gill openings covered by a fleshy operculum,
no dermal denticles, teeth fused into three tooth plates… rat or rabbit fish.
Spine on 1st dorsal fin, males have pair of claspers on pelvic fins, a pair in front of
pelvics… prepelvic tenacula… and a single clasper on the forehead ..frontal tenaculum.
Propel by flapping large, fan-shaped pectoral fins.
One order, three families, six genera, over 35 species
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What is a shark?
Cylindrical or flat body, five to seven gill pairs on each side of head, large caudal fin,
one or two dorsal fins that may have spines, pectoral fins not fused to head, anal fin
may be present.
Eight orders, 34 families about 100 genera.
About 410 species,
species
ground or requiem sharks.. O. Carchariniformes
24% of all elasmobranchs
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Propeller
Even More Diverse
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Shortfin Mako
(Isurus Oxyrinchus)
Basking Shark (Cetorhinus maximus)
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The basking shark uses gill rakers to
siphon food out of the water.
Pacific Angel Shark (Squatina californica)
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Carcharocles megalodon
About 55 ft long, 45 tons, lived 18 to 1.5
Mya.
Rays
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What is a ray?
Also known as batoids, or winged sharks…
pectoral fins expand forward and fused to sides
of head over gills.
Short, flat body, five or six paired gill openings
tail morphology varies from whip like to shark like
like.
Skates have caudal fins. One or two dorsal fins,
never a spine, no anal fin. Tail spine present in
stingrays.
One order, 22 families, 71 genera, 650 species:
Skates 44%, whiptail rays 34%,
guitar fishes 11%,
electric rays
y 9%,, and sawfishes…<1%.
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Figure 3.7 Transverse section through the body of a ray showing the paired
spiracle (S) connection to the pharynx
pharynx. Stippled areas are cartilage
cartilage, solid areas
muscle. (Based on Ref. 27 and Wegner and Graham, unpublished)
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What about sharks and rays that bury themselves in
the sand? How do they breath?
Many benthic (bottom
dwelling) sharks and
rays have spiracles.
Bat Rat (Myliobatis californica)
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Spiny Dogfish (Squalus acanthias)
Do sharks need to keep swimming to stay alive?
Leopard
p
Shark - Active Ventilation
Mako - Ram Ventilation
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Elasmobranch Gills
Using magnetic resonance imaging
(MRI) to study shark gills.
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Using Scanning Electron Microscopy (SEM)
Outer Marginal
Channel
Red Blood
Cells
Blood
Flow
Pillar
Cells
Lamella
Water
Flow
Pillar Cells
Lamellar Blood
Channel
Blood-Water
Filament
Barrier
Base
Sensory Biology
The five senses + 1
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Squatinomorphs and
Squalimorphs 2- 6x smaller
Than most galeomorph sharks
1989 J. Exp. Zool. Supplement 2:83-100
squalomorph, Squalus
cerebrum
cerebellum
galeomorph, Mustelus
Northcutt,
1989 J. Exp. Zool.
Supplement 2:83-100
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Hoffman in Hamlett, 1999
Northcutt
Increased cerebellum related to rapid
and fast rate of mobility in 3 dimensions
For mammals, large brain not correlated
with metabolic rate….
Small brained species have short
gestations large litters
gestations,
litters, early maturation
and short life spans… r selection
Large brained mammals…
long gestation, small litters, slow maturation,
long life spans
Large brained elasmobranchs..
shorter gestations, no appreciable
differences in growth, some have early maturity,
Thus data are incomplete regarding life history.
Ampullae of Lorenzini and
Lateral Line
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Bioelectric Field Detection Sensitivity
5 billionths of a volt cm-1
Start with a 1.5 v battery in Denver
Put one lead in Washington DC, other in San Francisco
Distance of poles is about 5000 km = 5 hundred million cm
1.5/500, 000,000 = 3 x 10-9 V cm-1
Scyliorhinus
Flounder in the sand
Covered by agar (no
scent) but bioelectric
field detectable
Flounder scent and
field both shielded
Simulating electrodes
A. Kalmijn, 1971 JEB 55:371-383
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Bioelectric detection as an antipredator
device.
Raja eglanteria late term embryo ventilates
egg case by moving tail.
Effects of three sinusoidal uniform electric
fields…..0.2, 1, and 10 Hz. (o05 uV cm-1)
Are to shut down tail oscillations.. Peak
Response is in the 0.1-2 Hz range, which
corresponds to the phasic electric stimuli
Of potential predators.
Vision
Range 10s of m
Image forming eye
Structure similar to
other verts
Focus mechanism
Is different:
MammalsBony fishesElasmobranchs(= Lens protractor muscle
= contractile papilla )
Historical view that vision was …. Hyperopic finding this was stress related
And that vision was emmetropic, and that accomodation was possible.
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Correlations with body form, behavior, and habitat:
Size and position
Visual field
Protection
lids (occular adnexia)
nictating membrane
rolling eyes back under skin.. 6 eye muscles…4 rectus, 2 obliques
Contrasting scotopic and photopic vision
Protection against too much light
Slits and other shapes in a dynamic
iris
Yellow pigments in lens as a UV light filter
Tapetum lucidum (gold, green eye
shine)
Part of the choroid layer
A means of specular reflection
Light adaptation.. Tapetal curtain
Is drawn in photopic vision
Open in scotopic.
Deep living elasmobranchs have
little or no tapetum.
Deep (dark) water adaptations include
larger eye
less tapetal occlusion
shift to chrysopsin..a retinal pigment
that is more effective (than rhodopsin)
in dim light.
Retina… pigments needed to absorb light
And activate ganglion cells.
Rods and cones… cones onlyy known about
40 years. Skates have rod only
eyes... But show ability for light dark adaptation.
Springer and Gold, Sharks in Question 1989
Sharks likely have color vision… and have rapid
Ability to adapt to changing light conditions.
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Change in Figure the result of D. C. Abel’s and N.C. Lai’s
PhD work in the Graham Laboratory
Eckert Animal Physiology,
Physiology 1978
Eckert Animal Physiology, 2002
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HIGH UREA LEVELS OF SHARKS
ARE INIMICAL TO MAMMALIAN
CELL LIFE
Human Blood Urea Level 2020-30 mg/dl
Severe Uremic poisoning 300 mg/dl
Shark blood has about 400 mmol/liter urea which
is the equivalent of 2400 mg/dl
Nearly 10x the level that causes fatal uremic
poisoning in humans.
Sharks don’t get cancer?
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The shark skeleton is cartilage
Reproduction and Growth
Chondrichthyes
•Fertilization is internal.
* Produce only a few large eggs each time.
* Young look just like parents, only smaller.
* Gestation period is long, up to two years in
some species, such as the spiny dogfish.
* 43% of sharks hatch from fertilized egg cases.
* Sharks can store sperm.
Bony fish
• Most sharks have 2 uteri.
•Most fertilize externally.
* Produce several hundred small eggs
many times each year
* Young are not fully developed after
hatching and are called larva
(sharks are called pups).
* Most lay eggs.
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Internal Fertilization
Alternative Reproductive Styles
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Extended Oviparity
ƒ Large egg fertilized
within oviducts
ƒ Enclosed in an egg case
ƒ Deposited on the
substrate
ƒ After developmental
period, emerges
p
g
miniature shark
ƒ 42% of Chondrichthyans
have extended oviparity
Yolksac Viviparity
ƒ 27% of
chondrichthyan
species
p
including
g
squalomorph and
squatinoid sharks,
some
orectoloboid and
carcharhinoid
sharks,
rhinobatoid,
pristoid, and
torpedinoid
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Cannibal and Placental Viviparity
ƒ Placental Viviparity
– Yolksac p
placenta forms
between mother and fetus
ƒ 9% of species –
Carcharhinoid sharks
ƒ Cannibal Viviparity
– Young absorb yolk early
and feed on siblings and
fertilized eggs produce by
the mother
ƒ 2% of living species –
Lamnoid sharks
Uterine Viviparity
ƒ Uterus of mother
secretes nutritive fluid
((uterine milk)) which is
ingested by the fetus
ƒ 19% of species
ƒ Myliobatid Rays
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Precocial Offspring
ƒ Young are born as
miniature versions of
adults, ready to fend for
themselves
ƒ Some evidence of
habitat selective
behavior to avoid
conspecific
ifi predators
d t
ƒ Parental care of eggs
or young is unknown
Low Fecundity
ƒ Between 1 to 135
eggs produced,
majority produce less
than 50
50, with many of
those producing fewer
than 20 eggs/young
per year
ƒ Very long gestation
periods six months to
t
two
years (live
(li
bearing), while egg
cases take between 2
months to over a year
to hatch
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Slow Growing
ƒ 3 to more than 20
yyears to reach
sexual maturity, and
long lived
Biological Evolution
in 24 hours
Homo habilis 47-94 sec b4 midnight
H. sapiens
1.4 sec
“
“
agriculture
g
0.25 sec
“
“
Industrial Rev. 0.007 sec “
“
Shark and human
collision course
Also talk about the
Role of Homo sapiens
In life on Earth.
Earth
Very recent arrival on
The scene, however,
Having a greater effect
Than any other species
Has ever had.
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Human effect is largely through population growth but also due to resource
consumption.
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Primitive humans
were just parts of food
Webs and subject to the
Same biological factors
Affecting all other
Populations.
But civilization and
Technology changed
Human dependence
Upon nature.
What does the future
Have in store for
The human dominated
Earth?
Both population and technology impact the Biosphere
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Contrast reproductive biology
ƒ Blue Shark
(Prionace glauca)
glauca)
– Slow growth and low
fecundity
ƒ Yellowfin Tuna
(Thunnus albacares)
albacares)
– Fast growth and high
fecundity
Blue shark
Mom is several years old before sexually mature
Lives long time
Each year mom can produce 100 or so
Mother holds eggs full term
Pups born as functional fish that are ready to go … precocial
Because of mom, pups have good chance of survival no risk
in early life stages.
As long as mom survives!!
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Yellowfin tuna
External fertilization of a million eggs per female per year (high fecundity)
Millions of eggs … but only a few survive each of a series of critical steps in
maturation.
maturation
Eggs drift, hatchÆ
hatchÆ larva,
Larva must survive in plankton for a period Æ metamorphosis to juveniles,
Juveniles must find size appropriate food supply in open ocean…
Predation, sinking, nutrition, drifting to an area where
they cannot survive….all are risks
In a good year millions of eggs become a few adults…
Each year the female repeats its reproductive effort.
Overfishing of sharks
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Sharks on the Line
Jeffrey B. Graham, Chugey A. Sepulveda, Nicholas C. Wegner
Scripps Institution of Oceanography, University of California, San Diego.
Shark Reproduction and Biology:
Implications for over-fishing
World Demands and Shark Fisheries
Population Increase
• Slow growth
Conservation: What Have We Done? Where
Are We Going?
• Parental Investment
• Late sexual maturity
• Low fecundity
World Population Growth vs. Ocean Output
Shark products
Shark
vs.
Cod
Less Developed nations
Sharks vs. Cod Fecundity
• Sharks susceptible to all
forms of fishing (purseseine, long line, etc)
• High bycatch rates
Opening of the bamboo curtain has increased
world wide demand for shark fins… for soup.
Total Offspring
Shark Fecundity
Blue Shark (25-50)
100
90
80
70
60
50
40
30
20
10
0
200 mil
150 mil
Mako Shark (8-10)
Cod
•
Cod reproduce annually
•
Number of eggs increases with female size
•
Cod egg and larval success is independent of female survival.
Developed nations
100 mil
Sandbar Shark(8-13)
50 mil
1 mil
Black Tip Shark(4-6)
400
Dusky Shark(14)
0
5
10
15
Age
20
25
30
20
10
30
Age
With the collapse of the cod fishery, fishers now target the spiny dogfish
(shark). Given its long gestation period (22-24 months) and late sexual
maturity (12+ years), how long before this resource is depleted?
Shark Population Declines
• The world’s population continues to increase.
• Demand for shark products rises.
• The max output of the oceans has be reached.
Existing Management
Few countries have shark fishing regulations
U.S., Australia, South Africa
Finning Prohibited
Certain Species Protected
Time and Area Closures
Control Over Market
Declines in relative abundance of sharks in the Northwest Atlantic: (A)
hammerhead, (B) white, (C) tiger, and (D) coastal shark species; (E)
thresher, (F) blue, (G) mako, and (H) oceanic whitetip (Baum 2003).
Collapsed Shark Fisheries
Keys to Shark Conservation
Northwest Atlantic Porbeagle Fishery (1968-1972)
California Soupfin Shark Fishery (1930-1944)
•
•
•
•
Australian School Shark Fishery (1927-1956)
Scottish-Norwegian Spiny Dogfish Fishery (19461986)
British Columbia Spiny Dogfish Fishery (1907-1949)
California Angel Shark Fishery
Basking Shark Fisheries of Northeastern Atlantic
• All shark populations are declining.
• Relative to cod, sharks are much less resilient to over-fishing.
Multi-National Agreements
Ban Finning
Strict Catch Quotas
Understanding Movement Patterns
Large Scale – Knowing migration
Fine Scale - Knowing how sharks
partition their ecosystem
ENFORCEMENT
The Consumer Drives the Market!
Future Projections
and
Eastern and Western Pacific
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There have been many and diverse human impacts on the ocean
Dumping of waste materials
Pollution of coastal areas
Addition of fertilizers
Overfishingg
Bycatch
ƒ Annual global bycatch
estimated at 27 million
metric tonnes, more than
30% of world annual marine
fishery catch (NRC 1998)
ƒ Blue shark byby-catch
estimated at 44-18 sharks
per 1000 hooks
ƒ Yellowfin catch rates range
between 22-20 per 1000
hooks
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Shark By
By--catch
ƒ Global shark byby-catch
exceeds 8 million sharks
per year = 1/3 of world
catch of elasmobranchs
(Bonfil
(B fil 1994)
ƒ Yellowfin longline fishery
in central Pacific
– 2 million blue sharks
incidentally captured in
1988 (Bonfil 1994)
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Sharks on the Line
Jeffrey B. Graham, Chugey A. Sepulveda, Nicholas C. Wegner
Scripps Institution of Oceanography, University of California, San Diego.
Shark Reproduction and Biology:
Implications for over-fishing
World Demands and Shark Fisheries
Population Increase
• Slow growth
Conservation: What Have We Done? Where
Are We Going?
• Parental Investment
• Late sexual maturity
• Low fecundity
World Population Growth vs. Ocean Output
Shark products
Shark
vs.
Cod
Less Developed nations
Sharks vs. Cod Fecundity
• Sharks susceptible to all
forms of fishing (purseseine, long line, etc)
• High bycatch rates
Opening of the bamboo curtain has increased
world wide demand for shark fins… for soup.
Total Offspring
Shark Fecundity
Blue Shark (25-50)
100
90
80
70
60
50
40
30
20
10
0
200 mil
150 mil
Mako Shark (8-10)
Cod
•
Cod reproduce annually
•
Number of eggs increases with female size
•
Cod egg and larval success is independent of female survival.
Developed nations
100 mil
Sandbar Shark(8-13)
50 mil
1 mil
Black Tip Shark(4-6)
400
Dusky Shark(14)
0
5
10
15
Age
20
25
30
20
10
30
Age
With the collapse of the cod fishery, fishers now target the spiny dogfish
(shark). Given its long gestation period (22-24 months) and late sexual
maturity (12+ years), how long before this resource is depleted?
Shark Population Declines
• The world’s population continues to increase.
• Demand for shark products rises.
• The max output of the oceans has be reached.
Existing Management
Few countries have shark fishing regulations
U.S., Australia, South Africa
Finning Prohibited
Certain Species Protected
Time and Area Closures
Control Over Market
Declines in relative abundance of sharks in the Northwest Atlantic: (A)
hammerhead, (B) white, (C) tiger, and (D) coastal shark species; (E)
thresher, (F) blue, (G) mako, and (H) oceanic whitetip (Baum 2003).
Collapsed Shark Fisheries
Keys to Shark Conservation
Northwest Atlantic Porbeagle Fishery (1968-1972)
California Soupfin Shark Fishery (1930-1944)
•
•
•
•
Australian School Shark Fishery (1927-1956)
Scottish-Norwegian Spiny Dogfish Fishery (19461986)
British Columbia Spiny Dogfish Fishery (1907-1949)
California Angel Shark Fishery
Basking Shark Fisheries of Northeastern Atlantic
• All shark populations are declining.
• Relative to cod, sharks are much less resilient to over-fishing.
Multi-National Agreements
Ban Finning
Strict Catch Quotas
Understanding Movement Patterns
Large Scale – Knowing migration
Fine Scale - Knowing how sharks
partition their ecosystem
ENFORCEMENT
The Consumer Drives the Market!
Future Projections
and
Eastern and Western Pacific
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Fishing down the food chain
Top-down effects of human predation on marine ecosystems
Gulf of Alaska
Kelpp forest ecosystem
y
kept
p in balance byy sea otters.
Over extraction of fishes in the Gulf of Alaska leads to
reductions in food supply for harbor seals and Stellar sea
lions.
Killer whales normally each harbor seals and Stellar sea
lions. Killer whales switch to sea otters.
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Otter is a keystone species
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Over Fishing = Overextraction
Changes like these in the Gulf of Maine have occurred
world wide.
Fish down the food chain…large….less large…etc.,
toward the primary producers.
The result of this over fishing is ecosystem dysfunction
Over Extraction and Ecosystem Dysfunction:
Other Examples
Caribbean Sea
Over extraction of green and hawksbill turtles
and manatees. Also, chronic over fishing
Loss of algae eating fishes on coral reefs resulted in rise of
the spiny sea urchin Diadema as main herbivore in this habitat.
Early 1980’s disease wipes out over 90% of the Diadema in
the Caribbean.
Macroalgae without herbivores
Macroalgae,
herbivores, grows over the reefs and
destroy them.
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