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Glossary of fishery terms

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Title: Glossary of fishery terms  
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Subject: Alexander Neil McLean, Fishing, Chasse-marée, History of fishing, Fisheries
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Glossary of fishery terms

This is a glossary of terms used in fisheries, fisheries management and fisheries science.


  • A 1
  • B 2
  • C 3
  • D 4
  • E 5
  • F 6
  • G 7
  • H 8


  • 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.
  • Aerial survey - a method of gathering information on surface fish movement and density by visual observation and photography from low-flying aircraft.
  • Aggregation - is a term which can be applied to 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.
  • 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 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.
  • 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.


  • 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.
  • benthos.
  • 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.
  • 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.


  • 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.
  • 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.


  • 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.
  • Depletion - reducing the abundance of a fish stock through fishing.
  • Delisted - a species which is no longer listed under the ESA. See also recovered species.
  • Diatoms - minute planktonic unicellular or colonial algae.
  • Downwelling - A downward movement (sinking) of surface water caused by onshore Ekman transport, converging currents or when a water mass becomes more dense than the surrounding water.
  • dorsal - relating to or situated near or on the back.
  • Dredging - dredge designed to catch scallops, oysters or sea cucumbers are towed along the bottom of the sea by specially designed dredge boats.
  • Driftnet - a gillnet suspended by floats so that it fishes the top few metres of the water column. Drift nets can be many kilometres long. Because drift nets are not anchored to the sea bottom or connected to a boat, they are sometimes lost in storms and become ghost nets.
  • Dropline - a fishing line with one or more hooks, held vertically in the water column with weights and generally used on the continental shelf and slope. Several droplines may be operated by a vessel, either on manually or mechanically operated reels.


  • Echinoderms - a group of marine animals that includes seastars, sea urchins and sea cucumbers, abundant on the floor of the deep sea, as well as in shallower seas.
  • Ecologically sustainable development - in the context of fisheries, using, conserving and enhancing fishery resources so that the ecological processes, on which the fish depend, are not degraded.
  • Economic rent - the profit that could be earned from a fishery owned by an individual. Individual ownership maximizes profit, but an open entry policy usually results in so many fishermen that profit barely matches opportunity cost. See maximum economic yield.
  • Ectothermic - animals that control body temperature through external means, using the sun, or flowing air or water.
  • Ekman transport - resultant flow at right angles to and to the right of the wind direction in the northern hemisphere, to the left in the southern hemisphere.
  • Electrophoresis - A technique used by fisheries scientists. Tissue samples are taken from fish, and electrophoresis is used to separate proteins such as enzymes, based on their different mobilities in an electric field. This information is used to differentiate between morphologically similar species and to distinguish sub-populations or stocks.
  • El Niño - large scale, cyclical (generally three to seven years), ocean warming and cooling episodes across the equatorial Pacific. Warm water pools in the east in El Niño conditions and in the west during La Niña conditions. It begins around Christmas (El Niño means Christ child). These changes disrupt weather patterns and the migration habits of fish.
  • IUCN has calculated the percentage of endangered species as 40 percent of all organisms based on the sample of species that have been evaluated through to 2006.
  • Endemic - native to a certain region, often a fairly small local area.
  • Endothermic - animals which maintain a body temperature which is above ambient temperature. See Ectothermic.
  • Epipelagic - The top layer of the ocean from the surface down to about 200 metres. This is the illuminated zone where there is enough light for photosynthesis. Nearly all primary production in the ocean occurs here. See photic zone.
  • Escapement - the percentage of a spawning anadromous fish population that survives all obstacles during their migration, including fishing pressure and predation, and successfully reach their spawning grounds.
  • Estuary - a semi-enclosed coastal body of water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Healthy estuaries can have high rates of biological productivity.
  • Euryhaline - fish that are tolerant to a wide range of salinities.
  • Eutrophication - an increase in chemical nutrients – typically compounds containing nitrogen or phosphorus – in an ecosystem. Eutrophication in water often results in an increase in algae growth and decay, which can lead to decreased levels of oxygen and fish populations.
  • Exclusive Economic Zone (EEZ) - a seazone under the law of the sea over which a state has special rights to the exploration and use of marine resources. Generally a state's EEZ extends to a distance of 200 nautical miles (370 km) out from its coast.


  • Fecundity - the number of eggs a fish produces each reproductive cycle; the potential reproductive capacity of an organism or population. Fecundity changes with the age and size of the fish.
  • the term "shellfish" refers to molluscs
  • the term "finfish" refers to bony fishes, sharks and some rays
  • the term "scalefish" refers to fish bearing scales
  • the term "fish" can refer to more than one fish, particularly when the fish are from the same species
  • the term "fishes" refers to more than one species of fish
  • Fishery - the activities leading to and resulting in the harvesting of fish. It may involve capture of wild fish or raising of fish through aquaculture. A fishery is characterised by the species caught, the fishing gear used, and the area of operation.
  • Fishmeal - protein-rich animal feed product based on fish.
  • Fishing vessel - any vessel normally used for the harvesting of living aquatic resources or in support of such activity. This includes vessels which provide assistance to other fishing vessels such as supply, storage, refrigeration, transportation or processing (mother ships).
  • Fishing fleet - an aggregation of fishing vessels of a particular country, such as the Russian fishing fleet, or using a particular gear, such as purse seine fleet.
  • Fork length - in fishes with forked tails, this measures from the tip of the snout to the fork of the tail. It is used in fishes when is difficult to tell where the vertebral column ends.
  • Founder effect - the loss of genetic variation when a new colony is established by some individuals moving to a new area that is unoccupied. As a result the new population may be distinctively different from its parent population.
  • Free-diving - diving under water without the assistance of breathing apparatus to collect oysters, abalone, corals, sponges, crayfish etc. The gear usually includes a snorkel, face mask, flippers, weight belt and wet suit.
  • Front - region of sharp gradient in temperature or salinity, indicating a transition between two current systems or water masses. Fronts are usually associated with high biological activity and high abundance of highly migratory resources such as tuna. They are actively sought as fishing areas and can be monitored by satellite remote sensing.


  • Gear - the equipment used by fishermen when fishing. Some examples are hooks, lines, sinkers, floats, rods, reels, baits, lures, spears, nets, gaffs, traps, waders and tackle boxes.
  • Gene flow - The movement of genes from one population to another by individuals moving between the populations.
  • Ghost nets - fishing nets and other gear that has been left or lost in the ocean and continues to capture and kill fish.
  • Gillnet - fishing nets constructed so that fish are entangled or enmeshed, usually in the gills, by the netting. According to their design, ballasting and buoyancy, these nets can be used to fish on the surface, in midwater or on the bottom. The mesh size of the net determines the size of fish caught, since smaller fish can swim through the mesh. See also drift net.
  • Global positioning system - a device which uses satellite signals to accurately determine a fishing vessel's position and course.
  • Global warming - the increase in the average temperature of the Earth's near-surface air and oceans in recent decades, as well as the projected continuation of this trend.
  • Groundfish - fish that lives most of its life on or near the sea bottom, such as cod, haddock, or flounder.
  • Gulf - a large area of water bordered by land on three sides.


  • Habitat - the place where an organism lives.
  • Halocline - a zone in which salinity changes rapidly.
  • Harmful algal bloom (HAB) - an algal bloom that produces toxins detrimental to plants and animals. Scientists prefer this term to red tide, since not all algal blooms are harmful, nor do all algal blooms cause discoloration, and the blooms are not associated with tides.
  • Harvest - the number or weight of fish caught and retained from a given area over a given period of time. Note that landings, catch, and harvest are different.
  • Hatchery - the process of cultivating and breeding a large number of juveniles in an enclosed environment. The juveniles are then released into lakes, rivers or fish farm enclosures.
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