This is a glossary of terms used in fisheries, fisheries management and fisheries science.
A Abundance – is a measure of how many fish are in a population or a fishing ground. See relative abundance and absolute abundance. Acoustic survey – a systematic gathering of information on fish availability and abundance using underwater sound. Acoustical oceanography – the use of underwater sound to map underwater topography and the contents of the sea. Aerial survey – a method of gathering information on surface fish movement and density by visual observation and photography from low-flying aircraft. Aggregation – any grouping of fish, for whatever reason (or unknown reason) they are concentrating. See shoaling. Agricultural runoff – surplus water from agricultural land, often draining into rivers and then into the sea, and often enriched with nutrients, sediment, and agricultural chemicals. Alginate production – a gel substance extracted from brown algae and used industrially as a thickening agent for food and paint. Algal bloom – a rapid excessive growth of algae, generally caused by high nutrient levels, particularly phosphorus. When the algae die, algal blooms can deplete oxygen to the point where fish cannot survive. Artisan – someone who practices a craft as a livelihood, as opposed to an artist, who practices an art for its own sake. Artisan fishing – a term sometimes used to describe small scale commercial or subsistence fishing practices. The term particularly applies to coastal or island ethnic groups using traditional techniques and traditional fishing boats. Anadromous – fish that live their adult lives in the ocean but migrate up fresh water rivers to spawn. Examples are Pacific salmon. Fish that migrate in the opposite direction are called catadromous. Anoxic sea water – sea water depleted of oxygen. See hypoxia. Anoxic sediments – sediments depleted of oxygen. Antarctic Convergence – a line encircling Antarctica where cold, northward-flowing Antarctic waters meet and sink beneath the sub-Antarctic waters, creating an upwelling zone which is very high in marine productivity, especially in Antarctic krill. Aquaculture – the farming of freshwater and saltwater organisms including molluscs, crustaceans and aquatic plants. See also fish farming and mariculture. Availability – (1) the proportion of a fish population living where it can be fished. (2) catch per unit effort. (3) a term sometimes used to describe whether a given fish of a given size can be caught by a given type of gear in a given fishing area.
B Bait fish – are small fish caught for use as bait to attract large predatory fish. See forage fish. Bathypelagic – the open ocean or pelagic zone that extends from a depth of 1000 to 4000 meters below the ocean surface. Beach – a geological landform along the shoreline of a body of water, consisting of loose particles composed of rock, such as sand, gravel, shingle, pebbles, or cobble, or of shell fragments or coralline algae fragments. Beam trawling – the simplest method of bottom trawling. The mouth of the trawl net is held open by a solid metal beam attached to two solid metal plates, welded to the ends of the beam, which slide over and disturb the seabed. This method is mainly used on smaller vessels, fishing for flatfish or prawns, relatively close inshore. Bed – the bottom of a river, or watercourse, or any body of water, such as the seabed. Benthic zone – the ecological region at the lowest level of a body of water such as an ocean or a lake, including the sediment surface and some sub-surface layers. Organisms living in this zone are called benthos. Benthos – aquatic organisms which live on or in the seabed, also known as the benthic zone. Included are both mobile animals, such as crabs and abalone, and non mobile animals, such as corals and sponges. Billfish – large, predatory fish characterised by their long sword-like bill. Billfish include the sailfish, marlin and swordfish. They are important apex predators feeding on a wide variety of smaller fish and cephalopods. Bioacoustics – in underwater acoustics and fisheries acoustics this term is used to mean the effect of plants and animals on sound propagated underwater, usually in reference to the use of sonar technology for biomass estimation Bimodal – a bimodal distribution is a distribution with two different modes which appear as distinct peaks. An example in fisheries is the length of fish in a fishery, which might show two or more modes or peaks reflecting fish of different ages or species. Biodiversity – is the variation of life forms within an area. In the context of fisheries the number and variety of organisms found within a fishery. Biomass – the total weight of a fish species in a given area. Can be measured as the total weight in tons of a stock in a fishery, or can be measured per square metre or square kilometre. The most successful species worldwide, in terms of biomass, may be the Antarctic krill, with about five times the total biomass of humans. Biotone – a region where a distinctive transition from one set of biota to another occurs. An example is the region where tropical and temperate waters mix. Biotoxins – natural toxins produced by organisms, often for use as a defence mechanism. Bony fish – fish that have a bony skeleton and belong to the class osteichthyes. Basically, this is all fish except for sharks, rays, skates, hagfish and lampreys. Bottom trawling – a fishing method that involves towing trawl nets along the sea floor. Bottom trawling can cause serious damage to sea floor habitats. Brackish water – water that has more salinity than fresh water, but not as much as seawater. It may result from mixing seawater with fresh water, as in estuaries. Breach – a whale's leap out of the water. Breaker zone – the zone where ocean surface waves approaching the shore commence breaking, typically in water depths between five and ten metres. Brood – the collective offspring of a species produced in a particular time span. See also cohort. Buoy – a floating object usually moored to the bottom. Buoys can be used as temporary markers, called dans, during Danish seine fishing to mark the anchor position of a net, or when fishing with lobster pots to mark the position of the pots. Bycatch – bycatch is the harvest of marine life and seabirds during fishing operations when other fish were the target. For example, bycatch might consist of a species which was not the targeted species, such as a shark caught on a tuna longline. Or it might consist of fish of the targeted species, but not of the targeted age or size. Some shrimp fisheries have a bycatch five times the weight of the caught shrimp. See also incidental catch.
C
Carapace – a calcified protective cover on the upper frontal surface of crustaceans. It is particularly well developed in lobsters and crabs. Carrying capacity – the supportable population of a species, given the food, habitat conditions and other resources available within a fishery. Casting – the act of throwing bait or a lure over the water, using a fishing rod. Catadromous – fish that live their adult lives in fresh water lakes or rivers but migrate down rivers to spawn in the sea. An example are freshwater eels of genus Anguilla, whose larvae drift on the open ocean, sometimes for months or years, before travelling thousands of kilometres back to their original rivers (see eel life history). Fish that migrate in the opposite direction are called anadromous. Cephalopods – (from the Greek for "head-feet") animals such as squid and octopus where tentacles converge at the head. Cephalopods are the most intelligent of the invertebrates with well-developed senses and large brains. Cetacean – member of the group of marine mammals that includes whales, dolphins and porpoises. They are the mammals most fully adapted to aquatic life and are noted for their high intelligence. Cetacean bycatch – the incidental capture of non-target cetacean species by fisheries. Bycatch can be caused by entanglement in fishing nets and lines, or direct capture by hooks or in trawl nets. Climate change – variation in the Earth's global climate or in regional climates over time. Climate change involves changes in the variability or average state of the atmosphere over time periods ranging from decades to millions of years. These changes can be caused by natural processes on Earth, external factors including variations in sunlight intensity, and more recently by human activities. cohort – those individuals of a stock born in the same spawning season. For annual spawners, a year's recruitment of new individuals to a stock is a single cohort or year-class. See brood. Commercial fishery – An umbrella term covering fisheries resources and the whole process of catching and marketing fish, molluscs and crustaceans. It includes the fishermen and their boats, and all activities and resources involved in harvesting, processing, and selling. Conspecific – organisms or populations that belong to the same species. Organisms that don't belong to the same species are heterospecific. Continental margin – the zone of the ocean floor that separates the thin oceanic crust from the thick continental crust. Continental margins constitute about 28% of the oceanic area. Continental rise – is below the slope, but landward of the abyssal plains. Extending as far as 500 kilometres from the slope, it consists of thick sediments which have cascaded down the slope and accumulated as a pile at the base of the slope. Continental shelf – the seabed from the shore to the edge of the continental slope, covered by relatively shallow seas (known as shelf seas) and gulfs. Continental slope – the slope which starts, usually abruptly at about a 200-metre depth, at the outer edge of the continent shelf and dips more steeply down to the deep-ocean floor (abyssal plain). Coriolis effect – due to the Earth's rotation, freely moving objects on the surface of the Earth veer right in the northern hemisphere and left in the southern hemisphere. This effect is called the Coriolis effect, and works, in particular, on winds and ocean currents. The effect varies with latitude and is zero at the equator and increases towards the poles. Cottage industry – small, locally owned businesses usually associated in fishing with traditional methods and low relative yield. Crab pot fishery – a fishing technique where crabs are lured by bait into portable traps, sometimes called pots. Crustaceans – A group of freshwater and saltwater animals having no backbone, with jointed legs and a hard shell made of chitin. Includes crabs, lobsters, crayfish, shrimp and krill.
D Danish seine – a widely used commercial fishing technique which uses a small trawl net with long wire warps. The seine boat drags the warps and the net in a circle around the fish. The motion of the warps herds the fish into the central net. Danish seining works best on demersal fish which are either scattered on or close to the bottom of the sea, or are aggregated (schooling). See also purse seine. Dead zone – an area in an ocean or large lake where oxygen levels are extremely low, often due to eutrophication. Dead zones have been increasing since the 1970s. Deep ocean currents – currents in the deep ocean, also known as thermohaline circulation or the "conveyor belt", are driven by density and temperature gradients. They can be contrasted with surface ocean currents, which are driven by the wind. Demersal zone – the zone at or near the bottom of a sea or lake. Inhabitants of the demersal zone feed off the bottom or off other demersal fish. See also pelagic zone. Demersal fish – fish that live in the demersal zone. Examples are cod, flounder and snapper. Compared to pelagic fish, demersal fish contain little oil. See also bottom feeder. Demersal trawling – trawling on or near the bottom of a sea or lake. See also bottom trawling.