Lecture 11 Flashcards
What are the two zones within the pelagic zone?
Neritic zone = over continental shelf
Oceanic zone = beyond the shelf break
Features of pelagic zone
Heterogenous environment
Vertical and horizontal heterogeneity of light, temperature, oxygen, wind-driven currents, mixing of water masses
Leads to differences in spatial distributions of organisms
Dominant pelagic macrofauna
Large zooplankton (jellyfish) Oceanic nekton
Adaptations of pelagic macrofauna
- Buoyancy: swim bladders of slow moving fish, seals have accessory air sacs, sharks and mackerel have lipids to aid buoyancy
- Locomotjon: body shapes to create propulsive force and streamlining to reduce resistance
- Adaptations for defence (e.g. shoaling)
- Camouflage (cryptic colours)
- Sensory systems (echolocation)
- Reproduction (spawning migrations)
Humpback whale migration
26 days average (4-90)
1.7km/hr mean speed
Whales from multiple feeding grounds congregate around the Antilles islands
Leatherback turtles
Spend most of their lives at sea but return to land to lay eggs -
“natal homing”
Feed on zooplankton (jellyfish)
Mature at 8-15 years, females mate every 2-3 years but breed annually
Results of tracking 8 Atlantic leatherbacks
- Extensive movement after egg-laying in Caribbean
- Very little consistency in movement
- Prevention of turtle by-catch from longlines needs to take place across Atlantic basin
Results of tracking 46 Eastern Pacific leatherbacks
More directional movement
Movement consistent - from Costa Rica, last Galapagos into South Pacific gyre
Migration corridor
Seasonally enforced Marine Protected Areas?
How do turtles navigate?
Potentially using geomagnetic cues
Luschi et al. 2007
Turtles displaced and satellite tracked
Those with magnets on their heads had longer homing paths than those without
Atlantic bluefin tuna migration
Thunnus thynnus - large marine predator
Basis for highly profitable fishery - caught using longlines and purse seines
Can live for 30 years, matures at 4-8 years
Downing grounds in Mediterranean and Gulf of Mexico
Western population breed in Gulf of Mexico, forage towards eastern-Atlantic
Eastern population breed in Mediterranean, forage towards western-Atlantic
Populations overlap but generally distinct
Rooker et al. 2008
Movement ecology - finding prey
Marine predators must make foraging movements without knowing distribution of prey
An optimal search strategy may be “Lévy flight”
Describe Lévy flight strategy
Many small movements when you have found a food source, but fewer larger movements when searching for areas with food
Ideally, the Lévy exponent is 2, basking sharks reached 2.3
Lévy-like movements observed in sharks, teleosts, sea turtles and penguins
What are most movements in the ocean?
Straight ballistic trajectories
Less of these movements in coastal waters
