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Glossary of Fisheries terms
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
This glossary has been extracted from the Bureau of Rural Sciences publication, Fishery Status Reports 2004. Some items included in the Glossary may relate to use in previous editions of Fishery Status Reports.
1+ year-class—fish that are between one and two years old (similarly, ‘2+’ between two and three years etc).
200-nautical-mile zone—see Australian Fishing Zone.
A
Acoustic survey—a systematic method of gathering information on the abundance of a species in a water body with the help of sophisticated echo sounders and sonar, which use ultrasonic sound to detect the fish. Thepatterns can be interpreted to identify some species.
Aerial survey—a method of gathering information on movements and density of fish near the surface by visual observation and photography from low-flying aircraft.
Age-structured assessment—an assessment of the status of a fish stock, based on therelative abundances of fish of different ages in the stock.
Ageing technique—a method of determining the ages of fish, most often done by counting daily or seasonal rings laid down in hard parts of the fish body, such as otoliths, scales or vertebrae.
Age–length composition (age–length key)—a table of the frequency of fish of each age in each length-group in a catch (or population) of fish. Tables of yearly age–length composition of catches provide the input for cohort analysis (see cohort analysis).
Age–length curve—a curve that shows the relation of length and age; it is a simplification of an age–length key.
Aggregation—a group (usually large) of fish of a single species that comes together to feed or spawn—or for some unknown reasons.
Alginate—a gel substance sourced from the marine alga, kelp (Phylum: Phaeophyta), which is used industrially as a thickening agent for such things as food and paint.
Anoxic sediments—sediments that lack oxygen between the particles.
Aquaculture—the commercial growing of marine (mariculture) or freshwater animals and aquatic plants. Often termed ‘fish farming’ in relation to fish.
Aquifer—an underground layer of rock or soil able to hold large amounts of ground water.
Archival tag—an implanted fish tag that detects and records (‘archives’) several environmental variables (for example, water temperature and pressure) over time. These tags giver a unique record of the movements and behaviour of individual fish. Some tag types can transmit data to satellites.
Area closure—the closure of a fishing ground, or part of one, for a defined period of time; used as a tool in the management of a fishery.
Area swept—in reference to a demersal trawl, it is the area of the sea floor over which the net is dragged during its operation. It is estimated by multiplying the width of the net mouth by the distance the net is dragged. The density of fishes caught in a unit area swept gives an estimate of the biomass in that part of the sea.
Artisanal fishing—fishing for subsistence by coastal or island ethnic groups using traditional methods.
Australian Fishing Zone (AFZ)—Australia has proclaimed a zone 200 nautical miles wide around its mainland and territories coasts, within which it controls domestic and foreign access to fish resources.
B
Bait net—a net used to catch bait fish for activities such as longlining and pole-and-line fishing.
Benthic—associated with the bottom of a water body, such as a sea or lake.
Berried—female crabs, lobsters, etc. that have eggs attached to the appendages on the underside of the abdomen are described as berried or ‘in berry’.
Billfish—marlins, sailfish, spearfish and swordfish; that is, fish where the snout is extended into a bill or ‘spear’.
Bimodal—see length–frequency distribution.
Biodiversity—biological diversity; variety among living organisms—including genetic diversity, diversity within and between species, and diversity within ecosystems (see also ecosystem).
Biological reference points—indicators of the status of a stock; they provide a standard for comparison. Reference points can be either ‘target reference points’ or minimum biologically acceptable limits (‘limit’ reference points). They are often based on fishing mortality rates or on the maintenance of adequate recruitment to the stock.
Biomass—total weight of a stock or of a component of a stock; for example, the spawning biomass is the combined weight of mature animals.
Biota—living things.
Biotoxins—natural toxins produced by organisms, often for defence.
Boat-day—a measure of fishing effort; for example, 10 vessels in a fishery, each fishing for 50 days, would have expended 500 boatdays of effort.
Bobbin gear—a roller or cylindrical shaped object attached to the foot rope of an otter trawl net to allow the footrope and net to travel over uneven or even areas of the seabed.
Brackish water—slightly saline water (between 0.5 and 30 ppm salt), often resulting from saline ocean waters mixing with, and being diluted by, freshwater sources, as in estuaries.
Brood—a group of young produced at the same time; cf. cohort.
Buy-back of fishing units—reducing fishing effort by buying fishing boats and licences back from the fishers.
Bycatch—species taken incidentally in a fishery where other species are the target. Some bycatch species are of lesser value than the target species, so are often discarded (‘trash’ species), but other bycatch species have some commercial value (‘byproduct’) and are retained for sale (see also non-target species).
Bycatch reduction device (BRD)—a modification to fishing gear to reduce the catch or kill of bycatch species.
C
Cage culture—a type of aquaculture in which fish are grown on in enclosures in open water; also referred to as fish farming or sea ranching.
Carapace—the shield covering the part of upper surface of the body of crustaceans (for example, the broad shield of crabs, and of the head and ‘chest’ of prawns and rock lobsters).
Carid prawn—prawns of the infraorder Caridea, which include fresh and brackish water shrimps and prawns and snapping shrimps. Members of Caridea carry fertilised eggs below the abdominal segments of the female, whereas in the infraorder Penaeidea females release their eggs directly into the sea.
Catchability—in a general sense, the extent to which a stock is susceptible to fishing; quantitatively, the proportion of the stock removed by one unit of fishing effort.
Catch-at-age data—data on the number of fish of each age group in the catch of a fishery, usually derived from the lengths of fish in representative samples of the catch.
Catch-at-length data—data on the number of fish of each length group in the catch of a fishery, usually obtained by measuring the lengths of fish in representative samples of the catch but occasionally derived from individual weights of fish.
Catch-at-weight data—data on the number of fish of each weight group in the catch of a fishery, usually obtained by measuring the individual weights of fish in representative samples of the catch.
Catchment—the surrounding region of land from which rain drains into a main waterway.
Catch per unit of effort (CPUE)—the number or weight of fish caught by a unit of fishing effort; for example, 80 kilograms per hour of trawling. CPUE is often used as a measure of fish abundance.
Catch rate—see catch per unit of effort.
Cephalopods—literally ‘head-foot’; animals like squid and octopus in which the tentacles converge at the head.
Codend—the closed end of a trawl net.
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.
Cohort analysis—a technique for estimating the magnitude of fishing mortality and the number of fish at each age in a stock by tracing the history of the cohorts.
Commercial value—the landed value of the catch to the fishers.
Conspecific—individuals that are members of the same species.
Continental shelf—seabed from the shore to the edge of the continental slope.
Continental slope—region of the outer edge of a continent between the generally shallow continental shelf and the deep-ocean floor, usually demarcated from the shelf by the 200 m isobath.
Cottage industry—small, locally owned businesses usually associated with low relative yield and limited technology.
Crab pot fishery—a type of passive fishing method where crabs are lured by bait into stationary traps called ‘pots’.
D
Danish seining—local terminology for the main form of demersal seining in Australia, used on the continental shelf out to its edge. In reality ‘fly dragging’, that is, the gear is set along the sea floor in a pear shape with the net at the base of the pear and the ropes making up the sides; it is retrieved by a combination of the vessel moving forward, and a powered winch hauling, to bring the ropes together, close the net, and bring it up; cf. purse seine.
Decision rules—agreed responses that management must make under pre-defined circumstances regarding stock status.
Demersal—found on or near the bottom of the sea or lake; cf. pelagic.
Demersal trawling—operation of a trawl net designed for use on or near the bottom of the sea or lake, for example, otter trawl.
Depletion (stock depletion)—reducing the biomass of a fish stock through fishing.
Development (of fisheries)—transition from exploratory and experimental fishing to the establishment of commercial activities and markets, with the ultimate goal of sustained long-term fishing; cf. ecologically sustainable development.
Discarding—a less emotive description for the disposal (or ‘dumping’ or ‘trashing’) of unsaleable catch, dead or alive, during or after fishing operations (see also bycatch, non-target species).
Domestic fishery—a fishery within the Australian Fishing Zone operated by Australian-flagged vessels.
Dressed-weight—weight of the carcass after processing (e.g. gills and viscera removed). Driftnet—a gillnet suspended by floats so that it fishes the top few metres of the water column.
Dropline—a fishing line with one or more hooks, held vertically in the water column with weights. It is generally used on the continental shelf and slope. Several droplines may be operated by a vessel, on either manually or mechanically operated reels.
E
Echinoderms—the group of animals that includes seastars, sea urchins and bêche-de-mer (‘sea cucumbers’ or trepang).
Ecologically sustainable development—using, conserving and enhancing the community’s resources so that ecological processes, on which life depends, are maintained, and the total quality of life, now and in the future, can be increased.
Ecosystem—a complex of plant, animal and micro-organism communities that, together with the non-living components, interact to maintain a functional unit.
Effluent—complex waste material, such as industrial waste or sewage discharge, which is often contaminated with damaging dissolved and suspended materials.
Effort—see fishing effort.
Effort restriction—a type of input control used as a management tool, it restricts the amount of fishing effort (for example, trawl hours) expended by fishers in a particular fishery.
Egg survey—a systematic gathering of information on the occurrence and abundance of fish eggs and larvae by collecting them in nets and traps.
Electrophoresis—technique for separating proteins such as enzymes, based on their different mobilities in an electric field. It is used to identify species that may look similar and to distinguish sub-populations or stocks.
El Niño—Southern Oscillation episodes—large-scale, cyclical (3–7 years), warming and cooling episodes across the equatorial Pacific; warm water pools in the east during El Niño conditions and, conversely, in the west during ‘La Niña’ conditions.
Endangered species—under endangered species protection legislation, a species in danger of extinction because of its low numbers or degraded habitat; or a species likely to become so unless there is an improvement in the factors affecting its status (see also vulnerable species).
Endemic, endemism—so called ‘native species’, which are confined to a given region; for example, a species endemic to Australia is not found beyond Australia.
Epibenthos—invertebrate animals living on the surface of the seabed.
Epipelagic—associated with the surface layer of a water body; cf. pelagic.
Exclusive Economic Zone (EEZ)—200-nautical-mile zone declared in Augustv1994 by Australia in line with the provisions of the United Nations Convention on the Law of the Sea. Australia has the right to explore and exploit, and the responsibility to conserve and manage, the living and non-living resources within this area; cf. Australian Fishing Zone.
Exploitation rate—the fraction of total animal (usually fish) deaths caused by fishing, usually expressed as an annual value. Exploitation rate can also be defined as the proportion of a population caught during a year.
F
Fecundity—number of eggs an animal produces each reproductive cycle; the potential reproductive capacity of an organism or population.
Fish (fishes; finfish; scalefish)—literally, a vertebrate (animal with a backbone) that has gills and lives in water, but often used more broadly to include any harvestable animal living in water (‘fishes’ refers to more than one species of fish; ‘finfish’ refers to sharks, some rays, and bony fishes; and ‘scalefish’ refers to
fish with scales).
Fishing-down—a fish stock that has not been heavily fished may have a large number of older fish. When such stocks are fished, catches are highest at first, but the rate cannot be sustained once the abundance of older fish has been reduced. Removing the older fish in this way is termed fishing-down.
Fishery—a term used to describe the collective enterprise of taking fish. A fishery is usually defined by a combination of the species caught (one or several), the gear and/or fishing methods used, and the area of operation.
Fishery-independent survey—a systematic survey carried out by research vessels or contracted commercial fishing vessels for the purpose of gathering information independent of normal commercial fishing operations.
Fishing capacity—the total fishing effort that can be expended by the fleet operating in a fishery.
Fishing effort—amount of fishing taking place, usually described in terms of gear type and frequency or period during which the gear is in use; for example, ‘hook-sets’, ‘trawl-hours’, ‘searching hours’.
Fishing mortality—the rate of deaths of fish due to fishing. The rate indicates the percentage of the population caught in a year; for example, a fishing mortality rate of 0.3 implies that e-0.3 of the population—about 35%—is being removed in a year by fishing (see also mortality, natural mortality).
Fishing power—the effectiveness of a vessel’s fishing effort relative to the effectiveness of other vessels’.
Fishmeal—protein-rich animal feed made of fish or fish waste.
‘Fish-out’ fish—fish that are caught in ‘fishout’ ponds, where anglers can take fish upon payment of a fee.
Flag-of-convenience—the registration of a ship to a country other than the country of ownership.
Fork length (FL; LCF)—the length of a fish measured* as the distance between the tip of the snout and the most anterior point of the fork or ‘V’ of the tail. This is the measure commonly used for the recording length of commercial fish species because it is usually little-affected by damage to the tail fin; c.f. total length. * From point to point—not, for example, by laying a tape along the body surface, which would result in a longer measurement for full-bodied fish like tuna.
Free-diving—diving under water without the assistance of breathing apparatus, to collect pearl oysters, corals, sponges, etc. The gear used may include a snorkel, facemask, a pair of flippers, weight belt and wetsuit.
Front (temperature front; frontal region)—region where a sharp gradient in temperature occurs, often indicating the demarcation between two current systems or water masses; usually associated with intense biological activity.
Fully fished—describes a fish stock for which current catches and fishing pressure are close to optimum (the definition of which may vary between fisheries; for example, catches are close to maximum sustainable yield). Categorising a species as ‘fully fished’ suggests that increasing fishing pressure or catches above optimum (allowing for annual variability) may lead to overfishing (see overfished).
G
Gear restriction—a type of input control used as a management tool to restrict the amount and/or type of fishing gear that can be used by fishers in a particular fishery.
Ghost fishing—where lost gear, usually nets or traps, continues to capture and kill fish.
Gillnet, monofilament gillnet—a type of passive fishing gear consisting of panels of net held vertically in the water column, either in contact with the seabed or suspended from the sea surface, such that fish attempting to swim through the net are entangled. The mesh size of the net determines the size range of fish caught, as smaller fish can swim through the meshes and larger fish are not enmeshed (see also driftnet).
Global positioning system (GPS)—a device that uses satellite signals to determine a vessel’s position and course accurately.
‘Grow-out’ ponds—ponds that are used to hold hatchery-reared or wild-gathered stock until they reach the desired marketable size.
Growth model—mathematical description or representation of the rate at which a species grows at different sizes or ages.
Growth overfishing—occurs when too many small fish are being harvested; a restraint on catching them would result in an overall increase in yield from the fishery.
H
Handline—hand-held lines of various types that are used widely throughout Australia to catch fish.
Harvest strategy—well-managed fisheries have an unambiguous (explicit and quantitative) harvest strategy, robust to the unpredictable biological fluctuations to which the stock may be subject. It states how the catch will be adjusted from year to year depending on: the size of the stock, the economic or social conditions of the fishery, conditions of other interdependent stocks, and the uncertainty regarding biological knowledge of the stock.
Hatchery production—the process of incubating eggs and rearing juveniles for release into streams, rivers or aquaculture systems.
Haul net—a fishing gear similar to a Danish seine, but operated from a small boat in shallow water (less than 5 m) or from the shore. Unlike a Danish seine, it has short ropes and is hand-hauled while the boat is stationary.
Headrope (headline)—the length of rope or wire in a trawl to which the top wings and cover netting are attached.
High Seas—waters outside national jurisdictions.
Hookah—underwater breathing device consisting of an on-board air compressor and an air supply tube to a diver’s mouthpiece or helmet.
Husbandry—management and control of a hatchery to produce fish or wildlife.
I
Impoundment—any enclosure or facility used to restrict the movement of fish stocks, whether in natural or artificial environments.
Incidental catch—see bycatch.
Index of abundance—a relative measure of the abundance of a stock; for example, catch per unit of effort.
Individual transferable quota (ITQ)—a management tool by which portions of the total available catch quota are allocated to individual fishers or companies. These individuals or companies have long-term rights over this quota but can trade quota with others (see also quota).
Input controls—indirect restraints placed by management to reduce the amount of fish caught; for example, gear restrictions, closed seasons; cf. output controls (see also limitedentry fishery).
Inshore waters—waters of the shallower part of the continental shelf; cf. nearshore waters.
Intertidal—the region of land that is submerged at high tide and exposed at low tide.
Introduced species—a species brought into an area where it does not naturally occur, and able to survive and reproduce there; loosely used for species from outside Australia.
Invertebrates—animals without a backbone; for example, shellfish, worms, jellyfish, sponges, seastars and corals; cf. vertebrates.
Isobath—contour line linking regions of the same depth.
Isopods—the group of small crustaceans that includes fish lice.
Isotherm—contour line linking regions of the same temperature.
J
Jig—to fish with lures on a vertical line that is moved up and down, or jigged. Jigging is done with hand-operated spools or automatic machines, as in the southeastern Australia fisheries for arrow squid.
Joint Authority—an Offshore Constitutional Settlement arrangement whereby a fishery is managed jointly by the Commonwealth and one or more States under a single (Commonwealth or State/Territory) jurisdiction.
Joint venture—collaborative fishing operation, usually involving two companies from different countries.
K
Key threatening process—under endangered species protection legislation, a process that threatens the survival, abundance or evolutionary development of a native species or ecological community, requiring the formal development of a threat-abatement plan (see also threat-abatement plan).
L
La Niña—an oceanographic condition involving excessive pooling of cool waters in the equatorial Eastern Pacific Ocean (see also El Nino – Southern Oscillation episodes).
Latent effort—fishing capacity that is authorised for use but not currently being used.
LCF—length to caudal fork (see also fork length).
Length–frequency distribution [modal size]—the number of individuals in a catch or catch sample in each group of lengths (length intervals). The modal size is the length group into which most individuals fall. Some distributions may show several modes, reflecting fish of different ages.
Limited-entry fishery—a fishery where the fishing effort is controlled by restricting the number of operators. It usually requires controlling the number and size of vessels, the transfer of fishing rights, and the replacement of vessels; cf. open-access fishery.
Line fishing—a general term for a variety of fishing methods that use fishing lines in one form or another. It includes handlines, hand reels, powered reels, pole-and-line, droplines, longlines, trotlines and troll lines.
Logbook—an official record of catch and effort data made by fishers. In many fisheries, a licence condition makes the return of logbooks mandatory.
Long-term potential yield—an estimate of the largest annual harvest that could be taken from a fish stock on a sustainable basis, allowing for variable environmental conditions. This may be estimated in various ways, ranging from taking an average of a time-series of historical catches to using sophisticated mathematical models.
Longline—a fishing gear in which short lines (‘droppers’) carrying hooks are attached to a longer main line at regular intervals. Pelagic longlines are suspended horizontally at a predetermined depth with the help of surface floats. The main lines can be as long as 100 km and have several thousand hooks. Droppers on demersal longlines (set at the seabed with weights) are usually more closely spaced.
M
Mariculture—fish farming or aquaculture of marine animals or plants.
Market niche—a small gap in a market, that could be filled by a particular enterprise.
Maximum constant yield (MCY)—a different approach to maximum sustainable yield; the maximum constant catch sustainable for all probable future levels of stock biomass (see also long-term potential yield). In contrast, a larger long-term average catch would be achieved were the catch adjusted each year to take account of stock increases and decreases because of environmental variability.
Maximum sustainable yield (MSY)—can be defined in various ways, but originated from surplus-production models as the maximum catch that can be removed from a stock over an indefinite period without affecting sustainability. MSY defined in this way makes no allowance for environmental variability, and studies have demonstrated that fishing at the level of MSY is often not sustainable (cf. longterm potential yield).
Migration—non-random movement of individuals of a stock from one place to another, often moving in groups.
Minimum size—by law, no individual smaller than the size prescribed for its species is allowed to be retained.
Model (population)—hypothesis of how a population functions; often uses mathematical descriptions of growth, recruitment and mortality.
Mode; modal size—see length–frequency distribution.
Morphology—the study of the form and shape of animals and plants.
Morphometrics—the form and shape of an animal. Differences in morphometrics are often used to distinguish different stocks of the same species.
Mortality—rate of deaths (usually in terms of proportion of the stock dying annually) from various causes (see also natural mortality, fishing mortality).
N
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; for example, a natural mortality rate of 0.2 implies that e-0.2 of the population—about 22%—will die in a year from causes other than fishing.
Nautical mile (n.mile)—unit of distance equivalent to 1 minute of the great circle of earth (= 1.852 km).
Nearshore waters—shallow inshore waters.
Neritic zone—the shallow pelagic zone over the continental shelf.
Non-target species—species that are unintentionally taken by a fishery or not routinely assessed for fisheries management (see also bycatch).
Not overfished—see overfished.
Nutrient upwelling—divergence of water currents or movement of the surface water away from land can lead to a ‘welling-up’ of deeper water that is usually richer in nutrients than the surface water.
O
Observer data—fisheries information collected on fishing vessels by independent observers.
Oceanic—to do with the open-ocean waters beyond the edge of the continental shelf.
Offshore Constitutional Settlement (OCS)—the 1982 package of uniform Commonwealth and State/Territory laws that provided a basis for the Commonwealth and one or more States, depending on the geographical range of the fishery concerned, to enter into agreements for a specified fishery in waters within and beyond territorial limits to be managed by a State alone, by the Commonwealth alone, or by a joint authority comprising Ministers responsible for fisheries in all the polities concerned. Fisheries for which OCS arrangements are not in place may be managed under joint control or continue under current management arrangements.
Offshore waters—usually refers to the more oceanic waters, though can refer to outer continental shelf waters; cf. onshore waters.
Onshore waters—waters abutting the coastline; cf. nearshore waters.
Open-access fishery—fishery in which there is no limit on the number of operators or vessels; cf. limited-entry fishery.
Otoliths—bones formed in the inner ear of fish. The rings or layers can be seen in the entire or sectioned otolith, and counted to determine age.
Otter trawl—demersal trawl operated by a single vessel in which the net is held open horizontally by angle-towed otter boards (large rectangular ‘boards’ of timber or steel) and vertically opening by a combination of floats on the headrope and weights on the ground line. Attached between the head and ground ropes and the towing warps, the otter boards are spread apart by the hydrodynamic forces acting on them when the net is towed.
Output controls—management measures directly limiting fish catch or landings (for example, by quota); cf. input controls.
Overfished—a fish stock with a biomass below a prescribed threshold or limit reference; see pp. 2–4 for additional information. As well as implying that a fish stock is not below a prescribed threshold, the term not overfished is used where status classifications of fully fished or underfished were used in previous editions of Fishery Status Reports.
Overfishing—the amount of fishing exceeds a prescribed level or limit reference; see pp. 2–4 for additional information.
Oxy-tetracycline (OTC)—an antibiotic injected in a fish to leave a mark on skeletal structures, such as otoliths. When the fish is later recaptured, the mark left by the OTC can be used to validate age estimates, as the date of injection is known.
P
Pair-trawling—trawling by two vessels steaming in parallel with the net towed between them. Very large nets can be held open and towed in this manner. The net is generally hauled alternately aboard the two vessels for processing of the catch.
Parameter—characteristic feature or measure of some aspect of a stock, usually expressed as a numerical value; for example, see natural mortality.
Parental biomass—the weight of the adult population of a species; for example, if southern bluefin tuna mature at eight years of age, the weight of all southern bluefin eight years and older (see also spawning biomass).
Pelagic—inhabiting surface waters rather than the sea floor. This term is usually applied to free-swimming species such as tunas and sharks; cf. demersal and epipelagic.
Penaeid prawn—prawns of the infraorder Penaeidea. This infraorder includes the bulk of the prawns taken in commercial quantities in Australia. Female penaeid prawns release their eggs directly into the sea; cf. carid prawn.
Pole-and-line fishing (poling)—also called pole-and-live-bait fishing, involves attracting schools of fish to the vessel with live or dead bait, then getting them into a feeding frenzy with more bait and water sprayed onto the sea surface to simulate the behaviour of small bait fish. Fishers use a pole with a short, fixed line and lure, ‘poling’ the fish aboard.
Population structure—composition of a population in terms of size, stock (genetic or regional), age class, sex, etc.
Potential yield—see long-term potential yield.
Precautionary principle—where there are threats of serious irreversible environmental damage, lack of full scientific certainty should not be used as a reason for postponing measures to prevent environmental degradation. In the application of the precautionary principle, public and private decisions should be guided by: (i) careful evaluation to avoid, wherever practicable, serious or irreversible damage to the environment and; (ii) an assessment of the risk-weighted consequences of various options.
Productivity—when applied to fish stocks the term ‘productivity’ gives an indication of the birth, growth and death rates of a stock. A highly productive stock is characterised by high birth, growth and mortality rates, and can sustain high harvesting rates.
Projection—with the help of a mathematical model as a numerical representation of the population, a prediction of what may happen in the future under a variety of conditions.
Purse seining—a fishing method capable of harvesting large quantities of surface-schooling pelagic fish by surrounding the school with a net. A line that passes through rings on the bottom of the net can be tightened to close the net so that the fish cannot escape; cf. Danish seining.
Q
Quota—amount of catch allocated to a fishery as a whole (total allowable catch) or to an individual fisher or company (see individual transferable quota).
Quota species—species for which catch quotas have been allocated.
R
Recovery plan—a recovery plan is a management process put in place to rebuild a stock when the measure of its status (e.g. its biomass) is below a defined limit (i.e. it is assessed as overfished). Recovery plans should include elements that define stock specific management objectives, harvesting strategies controlled by decision rules, and recovery periods.
Recruit (recruitment)—usually, a fish that has just become susceptible to the fishery; for example, a recruit to the Australian southern bluefin tuna surface fishery is one to two years old, whereas a recruit to the Japanese longline fishery is three to four years old. Sometimes used in relation to population components; for example, a recruit to the spawning stock.
Recruitment overfishing—occurs when excessive fishing effort or catch reduces recruitment to the extent that the stock biomass falls below the pre-defined limit reference point.
Reference point—an indicator of the level of fishing (or stock size), used as a benchmark for assessment (see also biological reference points).
Risk analysis—analysis that evaluates the possible outcomes of various harvesting strategies or management options.
S
Sashimi—Japanese dish of raw sliced fish.
Scampi—small, clawed marine lobsters belonging to the family Nephropsidae.
Seasonal closure—the closure of a fishing ground for a defined period of time, used as a tool by fishery managers, frequently to protect a stock during a spawning season.
Shelf break—region where the continental shelf and continental slope meet; that is, where the more gently sloping region of the seabed adjacent to a landmass rather abruptly slopes steeply down towards the ocean depths; commonly around depths of 200 m.
Shot-by-shot—pertaining to each separate deployment of a fishing gear by a fishing vessel.
Size-frequency—see length–frequency distribution.
Size-at-age—length or weight of fish at a particular age.
Size-at-first-maturity—length or weight of the fish when it attains reproductive maturity.
Slope (mid-slope; upper-slope)—continental slope. The more steeply dipping seafloor beyond the edge of the continental shelf.
Spawning-stock biomass—(also called spawning biomass) the total weight of all adult fish in a population.
Spawning-stock biomass per recruit (SSB/R)—the effective contribution to the stock’s spawning output that a recruit makes throughout its life. Each recruit must be able to replace itself to ensure sustainability. Analyses using the SSB/R approach attempt to determine critical levels of fishing effort above which sustainability is endangered.
Species—members of a species of plants or animals can breed with another member and produce fertile (capable of reproducing) offspring. In this way, a species maintains its ‘separateness’ from other species; for example, yellowfin tuna and bigeye tuna are two distinct tuna species, whereas the general term ‘tuna’
includes all tuna species.
Species group—group of similar species often difficult to differentiate without detailed examination.
Statutory fishing rights (SFR)—rights to participate in a limited-entry fishery.
Stock—a group of individuals of a species occupying a well-defined spatial range independent of other groups of the same species, and so with different gene patterns. Such a group is regarded as an entity for
management or assessment purposes. Some species form a single stock (for example, southern bluefin tuna), while others form several stocks (for example, albacore tuna in the Pacific Ocean belong to separate northern Pacific and southern Pacific stocks). The impact of fishing on a species cannot be determined without knowledge of this stock structure.
Stock-reduction analysis—an assessment method that estimates the biomass of a fish population from its catch history, information on the productivity of the species, and a timeseries of abundance indices such as catch per unit of effort.
Stock–recruitment relationship—the relationship between the size of the parental biomass and the number of recruits it generates. Determination of this relationship is difficult; it involves studying the population’s size–age composition, growth and mortality rates.
Straddling stock—a fishery term used to describe migratory species that spend part of their lifecycle in two or more jurisdictions; especially those that migrate between EEZs and the high seas.
Subantarctic waters—waters adjacent to, but not within, the Antarctic circle (about 66°30´S).
Subtropical waters—waters adjacent to, but not within, the tropics; in the Australian region the waters south of the Tropic of Capricorn (about 23°28´S).
Super seiner—a large purse seiner, usually more than 70 m long and equipped with considerable freezing and storage facilities, capable of undertaking extended transoceanic voyages for harvesting fish.
Surplus production—inherent productivity of a fish stock that can be harvested on a sustainable basis. Based on the theory that, at large stock size, rates of reproduction and stock increase are slowed by self-regulating mechanisms, and that the stock increases faster after removals, because the stock attempts to rebuild. In theory, fishing can be moderated to take advantage of the more productive rates of stock increase, provided it does not exceed the stock’s capacity to recover.
Surplus-production model—mathematical representation of the way a stock of fish responds to the removal of individuals (for example, by fishing).
Sustainable yield—catch that can be removed over an indefinite period without reducing the biomass of the stock. This could be either a constant yield from year to year, or a yield that fluctuates in response to changes in abundance.
Swept area—see area swept.
T
Tagging—marking or attaching a tag to an animal so that it can be identified when recaptured; used to study fish growth, movement, migration, stock structure and size (see also archival tag).
Target fishing (targeting)—fishing selectively for particular species or sizes of fish.
Taxonomic group—an organism’s location in the biological classification system used to identify and group those with similar physical, chemical and/or structural composition.
Threat-abatement plan—a plan formalised under endangered species legislation to counter the effects of a listed key threatening process (see also key threatening process).
Tori line—a line with streamers, towed as a scaring device over the area behind a vessel where sinking baited hooks are within range of diving seabirds; attached to a tori pole (boom) at the vessel’s stern.
Total allowable catch (TAC)—for a fishery, a catch limit set as an output control on fishing;see output control.
Total length (TL)—the overall length of a fish, measured as the distance between the mostforward point of the snout and the mostrearward part of the tail; c.f. fork length.
Trap fishing—fishing by means of traps, often designed to catch a particular species, forexample, rock lobster pots.
Trash fish—discarded catch with no or little commercial value.
Trawl-fishing—a fishing method in which a large bag-like net is drawn along behind a boat to target either demersal or pelagic fish species. There are many variations.
Trigger points, trigger rates—not usually used as a criterion for overfishing, but to indicate the need for review of management.
Trolling—a fishing method in which lines with baits or lures are dragged by a vessel at a speed of 2–10 knots. Trolling is used Australia-wide to catch such fish as Spanish mackerel, yellowtail kingfish and several tuna species.
Trotline—a dropline where hooks are held away from the mainline by rigid spacers.
Turtle excluder device—a modification to prawn trawl nets that, while retaining prawns, allows turtles to escape.
U
Uncertain—a fish stock that might be not overfished, overfished, or subject to overfishing, but for which there is inadequate or inappropriate information to make a reliable assessment of its status.
Underfished—a fish stock that has potential to sustain catches higher than those currently taken. The classification is not applied to stocks where catches have been limited to enable the stock to rebuild (see overfished).
V
Vertebrates—animals with a backbone, including fish (sharks, rays and bony fish), amphibians, reptiles, birds and mammals; cf. invertebrates.
Virgin biomass—the biomass of a stock that has not been fished (also called the unfished or unexploited biomass).
Virtual population analysis—a mathematical modelling technique used in stock assessment, whereby the number of fish in each cohort is estimated from numbers in the next oldest or next youngest age group, adjusted for the changes due to fishing and natural mortality; see also cohort analysis.
Vulnerable species—under endangered species protection legislation, a species that within 25 years will become endangered unless mitigating action is taken; see also endangered species.
Y
Year-class—individuals spawned in the same year (or spawning season, when that spans the end of one year and the beginning of the next).
Yield—total weight of fish harvested from a fishery.
Yield-per-recruit analysis—analysis of how growth and natural mortality interact to determine the best size of animals to harvest; for example, it may be more beneficial economically for fish to be caught when they are young and plentiful, or when older and larger but reduced in numbers by natural causes.