2-2 Oceanic Nekton

2-2 Oceanic Nekton - Oceanic Nekton • Chapter 3 Oceanic Nekton • Nekton swim against currents by creating turbulence – High Re • Dominated

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Unformatted text preview: Oceanic Nekton • Chapter 3 Oceanic Nekton • Nekton swim against currents by creating turbulence – High Re • Dominated by vertebrates – bony and cartilaginous fishes, reptiles, birds, mammals • Invertebrates include cephalopod molluscs and decapod crustaceans (crabs and shrimp) Types of nekton: • Holo-epipelagic – live in epipelagic throughout life – planktonic eggs and larvae in epipelagic • Tuna, sharks, swordfish • very common in tropics Mero-epipelagic: • Some spawn inshore (herring) or freshwater (salmon) • Some enter epipelagic zone at night • Many spawn in epipelagic but juveniles develop elsewhere (e.g., estuaries) Oceanic nekton characterizations: • Most are carnivores, at or near the top of the pelagic food chain • Well-developed sensory capabilities and excellent swimming, orientation and navigation abilities • Long-distance migrations, horizontally or vertically, to feed and/or reproduce – Sometimes seasonal, mostly variable Tuna migrations common: Bluefin Tuna • May transverse the Atlantic Ocean in less than 90 days • About 30% of the sexually immature individuals live on both sides of the Atlantic and cross it frequently • Mature tuna have breeding grounds on both sides of the Atlantic and segregate into eastern and western populations Locomotion • Cost of Transport (COT) = minimum COT in joules/kg body mass/km traveled- Expressed as a function of body mass • COT suggests that swimming is a relatively cost effective way to move about – Water supports body mass and large animals swim in a cost effective way Swimming speeds • Human best = 4-5 km/h in sprints • Tuna have been measured to swim 75 km/h in sprints (estimated at 110 km/h) • Killer whale = 40-50 km/h • Barracuda = 4-m/h Figure 3.1 How do nekton swim so fast? • Nekton use propulsive force to move through the water, and reduce resistance by streamlining • Propelled by undulating motion of the body or fins – However squids use a jet of water from a siphon • In many fishes, contractions of body wall musculature produce side-to-side motion creating turbulence (move water in opposite direction of swimming) and forward thrust Figure 3.9 • However, some fishes (e.g., tuna) use the caudal fins as an undulating hydrofoil • In air breathers, fins are used as a paddle – flukes in whales generate thrust by an up and down motion rather than a side-to-side motion • Up to 200 strokes/min possible Body shapes in fishes • Bar r acudas ar e a r apidly acceler ating fish with a thin, elongate body – pr obably helps in a sudden attack by making it har der to be seen by the pr ey • Maneuver ing fishes (r eef fish) ar e tall and elliptical in cr oss section with lar ge fins that incr ease dr ag Resistance and body shape: • For fast, cr uising fish (tuna and some shar ks) and mammals, an optimal body shape exists: – length about 4.5 times gr eatest diameter – r oundly blunt at fr ont end with a taper to the r ear (tear -dr op shape) – r ound in cr oss section • Minimizes dr ag fr om fr iction, body for m and tur bulence Figure 3.12 Pressure drag minimized Caudal fins...
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This note was uploaded on 09/13/2010 for the course BIOL 4262 taught by Professor Stickle during the Spring '10 term at LSU.

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2-2 Oceanic Nekton - Oceanic Nekton • Chapter 3 Oceanic Nekton • Nekton swim against currents by creating turbulence – High Re • Dominated

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