The Nekton - Swimmers

• Locomotion = swimming
– Capturing prey, avoiding predators
• Patchy distribution
– Determined by primary productivity
– Migratory species
• Over 5000 species
– Invertebrates, fish, reptiles, birds, and mammals

Squid
• Mollusks - cephalopods - squid
• Eight short arms and two long tentacles
• Active predators - common prey
• Many are adapted for life at great depth
• 2 cm to 20 m (Architeuthus)
• No chambers in active swimmers
• Siphons - jet propulsion
• Commercially important

Fish
• Dominant nektonic group
• Complex modifications for locomotion
• Fins and lateral muscle segments (myomeres)
– Wave of body curvature
• Fins
– Maneuvering and stabilizers - pectoral, pelvic, dorsal, & anal
– Locomotion - caudal

Fish
• Shapes - environment and behavior
• Adaptations for Seeking Prey
• Mobility - musculature
– Lungers - white muscle tissue
– Cruisers - red muscle tissue (smaller diameter & myoglobin)
• Speed
– Body length and shape
• Metabolism and Circulatory System

Fish
• Group Behavior
– Schooling
• Why schooling?
• Enhances species survival

Fish
• 2 major groups of nektonic fish
• Chondrichthyes
– Jawed fish with cartilagenous skeletons
• Osteichthyes
– Ray-finned (bony) fish

Sharks and Rays
• Chondrichthyes = one of the oldest orders of fish
• Dentine in scales
• Teeth = modified scales
• Oviporous and viviparous

Sharks
• Over 350 known species
• Found in all pelagic zones
• Very acute sensory organs
– Vision
– Smell
– Electrical
– Hearing, vibration, pressure
• 15 m to less than 1 m
• Predators, scavengers, plankton
• Commercially important
• Shark attacks

Skates and Rays
• Over 500 species
• Flattened bodies
• Locomotion = undulating side fins
• Plankton feeders and predators
• Perfect body plan for feeding and hiding on the bottom
• Protection = venomous barb, electricity

Bony Fish
• Osteichthyes
• Most bizare and least known = deep sea species
• Mesopelagic and below
• Small bodies and large mouths
• Slow metabolisms
• Designed to make do with very little
• Bioluminescence
• Some of the most abundant fish

Bony Fish
• Osteichthyes = most commercially exploited fish
• Most are epipelagic
• Large cruisers
• Schooling herring- types
• Demersal fish
• Rock fish

Marine Reptiles
• Few species
• Tropical and subtropical
• Sea turtles - small, streamlined shell
• 8 species - all endangered
• Herbivorous and carnivorous
• Few predators
• Lay eggs on beaches
• Migration - navigation

Marine Reptiles
• Sea Snakes
• Most highly evolved snakes
• Pacific and Indian oceans
• Small heads, flattened tails
• No fangs - highly venomous saliva
• Why are they so venomous?

Marine Birds
• Tubenoses - the most oceanic bird
– Largest = albatrosses (3.6 meter wing span)
– Southern oceans
– Speed & distance
• Penguins
– Flightless birds
– Southern hemisphere
– Gregarious
– Fatty insulation

Marine Mammals
• Cetaceans
– 79 species
– 1.8 - 33 meters
– Paddle-shaped forelimbs, horizontal tail flukes
– Blubber
– 1 or 2 nostrils
– Large brains
• 2 major groups
– Odontocetes - toothed whales
– Mysticetes - baleen whales

Marine Mammals
• Toothed whales
• Active predators
• Large brains
• Advanced social behavior
• vocalization
• Echolocation

Marine Mammals
• Baleen whales
• Filter feeders
– Water or mud
– krill
• Social groups
• Vocalization
• migration

Marine Mammals
• Whaling
– Industrialized in the 1880’s
– Meat, oil, bone, baleen
– 1986 - IWC
– Japan and Norway
– Minke
– California greys

Marine Mammals
• Carnivora
• Pinnipedia
– Seals, sea lions, walruses
– Leave the ocean periodically
– Coarse hair with soft underfur
• Fissipedia
– Sea otters
– Dense, warm fur
– Molluscks and crustaceans
– Kelp forests

Commercial Fisheries
• Discuss the following with the person next to you
• What are the requirements of a productive fishery?
• What degrades a fishery?
Commercial Fisheries
• Where do developing countries get most of their protein?
• More than 50% from the oceans
• 1995 - 70 billion dollars
• Rising demand
• Mismanagement
– Maximum sustainable yield
• Overfishing - 44%
– Commercial extinction
– Bykill
• Madhouse Economics