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Nacre
Smooth, shining, iridescent substance forming inner layer of the pearl oyster.
Native
The natural occurrence of a species in a particular region or ecosystem.
Natural
Existing in or formed by nature.
Natural mortality
Deaths of fish from all causes except fishing. It is often expressed as a rate that indicates the percentage of fish dying in a year, e.g. a natural mortality rate of 0.2 implies that approximately 20 per cent of the population will die in a year from causes other than fishing.
Natural Pearl
A pearl is formed naturally when an irritant, (e.g. a tiny grain of sand, shell or even a parasite) becomes trapped in the soft body of the oyster. The irritant is surrounded by cells (called a ‘pearl sac’) which build up pearl material around it.
Nautical mile
A unit of distance equivalent to one minute of the great circle of the Earth (= 1852 metres).
Nauplius (pl. nauplii)
A planktonic larva of many crustaceans.
NCP
National Competition Policy
NDS
National Docketing System
Neap tides
Occur when the earth, sun and moon are not in alignment and a small range in tides are experienced.
Nearshore
The marine environment from the beach to a depth of 20 metres.
Nekton
Organisms which expertly swim in the pelagic zone.
Nematocyst
A stinging organelle in cnidarians that contains a long filament attached to a barbed tip that can be used in defence or to capture prey.
Neuromasts
Clusters of hair-like cells that act as receptors.
Neutral buoyancy
The state where an object neither sinks nor floats but maintains the same position.
New Moon
A phase of the lunar cycle where the moon is only visible as a narrow cresent, occurring when the moon and sun are on opposite sides of the earth.
Niche
Role an organism plays within the structure and function of an ecosystem, and the way it interacts with other living things and with its physical environment.
Nictitating eyelid
Is a transparent or translucent third eyelid present in some animals that can be drawn across the eye for protection and to moisten the eye while also keeping visibility.
Ningaloo Reef
A fringing coral reef system along the west coast of Western Australia, approximately 300 km long (from Exmouth to just north of Carnarvon).
Non-endemic
Not native.
Northern Hemisphere
The half of the earth between the North Pole and the equator.
Notochord
A flexible rod that lies below the nerve cord of chordates.
Novice
An inexperienced or first time fisher.
NPOA
National Plan of Action for the Conservation and Management of Sharks.
Nucleus
A membrane-bound structure whose interior communicates with the cytoplasm by small pores.
Nursery ground
Area in which fish breed and where juvenile fish grow.
Nutrient
A substance that provides nourishment.