Download Effects on Marine Mammals and Sea Turtles

Ecological Features
• Sharks originated 423 mya
• They comprise half of all Chondricthyes
• Over time, selection favored larger bodies and
they fit the niche for the top marine predator
• Found everywhere in the ocean but mostly on
continental shelves
• Range from filter feeders to suction feeding to
carnivorous
• Feed on a variety of prey (including humans!)
• Can eat things that are larger than their mouth
• Life history = determines level of mortality
sharks can sustain
– Adapted very slowly
• Low growth rate
• Late sexual maturity
• Vulnerable to life history, habitat loss, and
catchability
• Ability to recover from depletion is low
• Respond strongly to changes in fishing
Cody, Nolan, Kyle, Morgan
Effects on Mesopredators
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Elasmobranch: Subclass of cartilaginous fish
Mesopredator: Predator not on top of the food chain
Generally, when large sharks species decline, mesopredators
increase
o Unclear if true in pelagic ecosystems as well
Mesopredator populations may decline quickly due to serial
depletion
Dogfish
Source: Elasmodivers.com
Effects on Marine Mammals and Sea Turtles
• Sharks increase in abundance in the warmer months
– Most marine mammals move away from these areas to avoid predations; however, sea
turtles do not like to move and therefore are more subject to predation
• There are increases in marine mammal populations in
response to decreases in predatory shark population
– Ex. sharks tend to prey on seal pups
• A study removed 10 Galapagos sharks from a Monk seal pupping beach area: this
reduced the pup mortality from 28 mortalities to 3 mortalities annually
• Trophic cascade effects:
Decrease in shark population  increase in prey population  primary producers
• Sharks play an important role in sea population dynamics
ex. 50% of harbor seal population decline due to sharks
• Temperature of water controls which predatory shark species
is present and dominant
Group 6: (possible trophic cascades) Eric Crees, Madisen Egan, Sophia
Mickman
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As the percentage of larger sharks caught in nets are decreasing, on average, the percentage of
smaller sharks and rays caught in nets is increasing.
The netting is directly affecting the large and small sharks, while the rays and bony fish are
mostly being indirectly affected.
During the first time period, the number of small sharks caught in nets increases due to
increased populations. Once angeling is introduced during the second time period, the numbers
caught in nets decreased due to lowered populations.
There is an inverse relationship between the predatory small sharks and their prey, the bony
fish, that can clearly be seen in these graphs.
• Coastal Ecosystems
– Ecosystem in coastal zone, where interaction of sea
and land processes occur
– Shark nesting programs
– No human activity of fishing
• Demersal Ecosystems
– Continental shelves and slopes
– Vulnerable to trawl fishing
• Pelagic Ecosystems
– The “open ocean”
– Industrial fisheries to catch tuna and swordfish
Coastal Ecosystem
Demersal Ecosystem
Pelagic Ecosystem