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The terms in this glossary have the following meaning in the context of the Australian Stock Status (SAFS) Reports 2020. This is not intended to be an exhaustive list of all fisheries assessment and management related terms.

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Abalone viral ganglioneuritis (AVG). A highly virulent herpes-like virus, which affects the nervous tissue of abalone and rapidly causes death. Can be spread through direct contact, through the water column without contact, and in mucus that infected abalone produce before dying.

Acceptable biological catch. See Recommended biological catch.

Age-length (age-length key or curve). Relationship between age and length describing the growth of a species. Growth curves are derived from age-length data. Age-length keys are tables of estimated ages of fish of increasing length, usually derived from otolith age readings (see Otoliths). Age-length keys are used to translate length composition data into conditional age at length data, which can be used when fitting age-structured stock assessment models.

Age-frequency/Age-Composition. Numbers of fish in each age class from samples of the fish captured during a fishing season. Sometimes sampled separately for retained and discarded catch. An important data input for age structured fisheries stock assessments. Usually derived from length-frequency data and age-length keys.

Age-structured assessment. Assessment of the status of a fish stock incorporating length- and age-composition data, as well as indices of relative abundance (such as CPUE), whereby the production (recruitment and growth) and mortality (natural mortality and fishing mortality) of each age class in the population are assessed to estimate the number of fish of each age each year.

Aggregation. A group of fish that come together, often to feed or spawn.

Aquaculture. Commercial growing of marine or freshwater animals and aquatic plants. Often called ‘fish farming’.

Area closure. Closure of a defined area/fishing ground, often for a defined period. Used as a tool in the management of a fishery, to reduce fishing mortality in a chosen area at a chosen time. See also Temporal closure.

Artisanal fishing. Fishing for subsistence using traditional methods. Also called traditional fishing.

Australian Fishing Zone (AFZ). The area extending seaward of coastal waters (that is, from three nautical miles from the territorial sea baseline) to the outer limits of the Exclusive Economic Zone (EEZ). In the case of external territories, such as Christmas Island, the AFZ extends from the territorial sea baseline to the outer limit of the EEZ. The AFZ is defined in the Fisheries Management Act 1991 (Cth), which also specifies a number of ‘excepted waters’, notably in Antarctica and the Torres Strait, that are excluded from the AFZ.

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B0 (mean equilibrium unfished biomass). The average biomass level if fishing had not occurred. Usually refers to the historical biomass estimated to have existed before fishing commenced.

Bag limit. The number of fish that one person can legally take and keep in a day’s fishing. Most often applied to recreational fisheries. May be associated with a trip limit.

Benthic. Associated with the seabed underlying a water body.

Berried female. Female crustacean carrying eggs.

Biodiversity. Biological diversity: variety among living organisms, including genetic diversity, diversity within and between species, and diversity within ecosystems.

Bioeconomic model. Method of fisheries stock assessment that models the interaction between the biology of harvested species and the human behaviour of fishers as shaped by economic factors. Seeks to evaluate how economic factors influence fishery performance and economic productivity of a fishery.

Biological reference point. The value of a biological indicator (usually biomass or fishing mortality, but can include surrogate (proxy) indicators, such as length or catch per unit effort) that is used to guide management decisions. Can be either a ‘target reference point’ that management actions seek to attain, or a minimum biologically acceptable limit (‘limit reference point’) that management actions seek to avoid. Proxies can be defined and used for hypothetical biological reference points that are difficult to estimate. 

Biological stock. Genetically or functionally discrete population that is largely distinct from other populations of the same species and can be regarded as a separate homogeneous group for management or assessment purposes.

Biomass (B). Total weight of a stock or a component of a stock.

Biomass limit reference point (BLIM). Stock biomass below which the risk to the stock is regarded as unacceptably high. Usually expressed as a fraction of B0, the average adult biomass before the commencement of fishing.

Biomass at maximum economic yield (BMEY). Average biomass corresponding to maximum economic yield. A target reference point that may be estimated using a bioeconomic model.

Biomass at maximum sustainable yield (BMSY). Average biomass corresponding to maximum sustainable yield. A target reference point estimated using a stock assessment model.

Biomass proxy. A relative biomass level used in place of a quantitatively estimated biological reference point when the latter cannot easily be estimated, usually expressed as a fraction of unfished biomass B0. For example, 0.48 B0 is used as a proxy for the biomass that sustains maximum economic yield (BMEY) in Commonwealth fisheries.

Bioregion. A region defined by common oceanographic characteristics in its marine environment, and by climate/rainfall characteristics in its inland river systems.

Bird baffler. A type of mitigation device that deters seabirds from the area around trawl warps and reduces the risk of warp strikes (see Warp strike). It consists of a curtain of ropes hanging from a line deployed above the warps, from the stern of the vessel to where they enter the water. 

Bird sprayer: A type of mitigation device that deters seabirds from the area around trawl warps and reduces the risk of warp strikes (see Warp strike). High pressure seawater sprayers are deployed above the warps where they extend from the stern of the vessels into the water. 

Boat-days. A measure of fishing effort. Refers to the number of ‘days’ that a fishing licence holder is permitted to fish or has fished.

Boat-nights. A measure of fishing effort. Refers to the number of ‘nights’ that a fishing licence holder is permitted to fish or has fished. Generally used in prawn trawl fisheries.

Boom-and-bust cycle. Repeated and sometimes cyclical increases and decreases in the size of a population, or in the economic productivity of a fishery.

Bycatch. A species that is (a) returned to the sea either because it has no commercial value or because regulations preclude it being retained, or (b) is affected by interaction with the fishing gear but does not reach the deck of the fishing vessel.

Bycatch reduction device (BRD). A device intended to reduce bycatch that allows fish and other animals to escape immediately after being taken in or with fishing gear.

Byproduct. A species taken incidentally in a fishery while fishing for another species. The species is retained for sale because it has some commercial value, but usually does not contribute significantly to economic yield.

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Carapace. The exoskeleton covering the outer surface of the body of a crustacean.

Carapace length (CL). In prawns, the distance from the posterior margin of the orbit to the mid-caudo-dorsal margin of the carapace; in lobster, the distance from the tip of the rostrum to the mid-caudo-dorsal margin of the carapace.

Catch per unit effort (CPUE). The number or weight of fish caught by a unit of fishing effort, such as tonnes caught per day or per fishing operation. Often used as an index of relative fish abundance through time in stock assessments and management decision rules.

Catch prediction. Forecasts undertaken in Western Australian prawn fisheries, based on surveys of recruitment and spawning stocks1.

Catch projection. Forecasts of estimated future yields (catches) from a fishery, produced using the results of stock assessments.

Catch rate. See Catch per unit effort.

Clade. An ancestor (organism, population or species) and all of its descendants, constituting a group of genetically related organisms.

Coastal waters. The waters extending seaward from the territorial sea baseline to a distance of three nautical miles. The states and the Northern Territory have jurisdiction over the coastal waters adjacent to them.

Codend. The closed end of a trawl net, within which fish are retained.

Cohort. Individuals of a stock born in the same spawning season.

Conservation dependent species. The Environment Protection and Biodiversity Conservation Act 1999 (Cth) dictates that a native species is eligible to be included in the conservation dependent category at a particular time if, at that time, (a) the species is the focus of a specific conservation program, the cessation of which would result in the species becoming vulnerable, endangered or critically endangered; or (b) the following subparagraphs are satisfied: (i) the species is a species of fish; (ii) the species is the focus of a plan of management that provides for management actions necessary to stop the decline of, and support the recovery of, the species so that its chances of long-term survival in nature are maximised; (iii) the plan of management is in force under a law of the Commonwealth or of a state or territory; and (iv) cessation of the plan of management would adversely affect the conservation status of the species.

Continental shelf. The continental shelf has been defined in a number of ways. It can mean the area of relatively shallow water that fringes a continent from the shoreline to the top of the continental slope. The top of the continental slope is often defined by the 200 m isobath. Continental shelf may also be defined as the maritime zone to include the continental shelf where it extends beyond the limit of the Exclusive Economic Zone to the limit of the continental margin. This area is also sometimes referred to as the ‘extended continental shelf’, and its limit is determined by the United Nations Commission on the Limits of the Continental Shelf.

Continental slope. Region of the outer edge of a continent between the relatively shallow continental shelf and the abyssal depths. Often characterised by a relatively steep slope compared to the continental shelf.

Coral bleaching. The loss of colour from corals under stressful environmental conditions. Bleached corals have the ability to recover as conditions return to normal; however, if the conditions remain unfavourable for an extended time, they will die.

Cryptic mortality. Unobserved mortality of a fish stock, occurring in part of the fishery, that cannot be detected in fishery data. This may include unobserved mortality of fish that are damaged as they pass through fishing gear, but are not retained by the gear.

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Daily egg production method (DEPM). A method of estimating the spawning biomass of a fish population from detailed sampling of the abundance and distribution of eggs and/or larvae during the spawning season.

Decision rules. Rules that determine agreed management recommendations under predefined circumstances regarding stock status. Also called ‘control rules’ or ‘harvest control rules’. Usually a key component of a Harvest Strategy.

Demersal. Found on or near the benthic habitat (cf. Pelagic).

Depletion (stock depletion). A measure of how close or far the biomass of a fish stock is from a reference condition, usually the average unfished spawning biomass; the smaller the number the more depleted a stock is said to be.

Depletion estimation methods. Stock assessment methods that estimate both the spawning biomass of a stock before exploitation began and that remaining after a period of exploitation.

Developmental fishery. A fishery managed under developmental fishery permits. Developmental fishing involves fishing in an area of Australian jurisdiction as specified in the permit. Activities include (a) assessing the commercial viability of a fishery, and (b) assessing the commercial viability of kinds of fishing activities, vessels or equipment specified in the permit.

Discards. Any part of the catch that is returned to the sea, whether dead or alive.

Domestic fishery. Fishery within the Australian Fishing Zone operated by Australian-flagged vessels.

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East Australian Current. A large-scale ocean current that runs southwards along the east coast of Australia, taking warm tropical waters from the Coral Sea southwards into the temperate waters of the Tasman Sea.

Ecologically sustainable. ‘Use of natural resources within their capacity to sustain natural processes while maintaining the life-support systems of nature and ensuring that the benefit of the use to the present generation does not diminish the potential to meet the needs and aspirations of future generations’ 2.

Ecologically viable stock. ‘Ecologically viable stock refers to the maintenance of an exploited population at high levels of abundance, to maintain biological productivity above target levels, provide margins of safety for uncertainty, and conserve the stocks’ role and function in the ecosystem’2.

Ecological risk assessment. A process of estimating the effects of human actions on a natural resource.

Ecologically sustainable development (ESD). ESD principles require that:

  • decision-making processes should effectively integrate both long-term and short-term economic, environmental, social and equity considerations
  • if there are threats of serious or irreversible environmental damage, lack of full scientific certainty should not be used as a reason for postponing measures to prevent environmental degradation
  • the present generation should ensure that the health, diversity and productivity of the environment is maintained or enhanced for the benefit of future generations (the principle of inter-generational equity)
  • the conservation of biological diversity and ecological integrity should be a fundamental consideration in decision-making; and
  • improved valuation, pricing and incentive mechanisms should be promoted.

Ecosystem. A complex system of plant, animal and microorganism communities that, together with the non-living components, interact to maintain a functional ecological unit.

Effort. A measure of the level of fishing activity used to harvest a fishery’s stocks. The measure of effort appropriate for a fishery depends on the methods used and the management arrangements. Common measures include the number of vessels, the number of hooks set, number of trawl tows, the duration of trawl tows and the number of fishing days or nights.

Effort restriction. Restriction of the permitted amount of fishing effort (for example, the number of vessels or total number of hooks) in a particular fishery; used as a management tool. One of the input controls that can be used to limit impacts of a fishery (see Input controls).

Egg survey. Systematic gathering of information on the spatial distribution and abundance of fish eggs and larvae by collecting them in nets and traps. A key component of DEPM surveys.

El Niño. The extensive warming of the central and eastern Pacific Ocean with northward and southward expansion of equatorial warm waters that leads to a major shift in weather patterns across the Pacific region (cf. La Niña). In Australia (particularly eastern Australia), El Niño events are associated with an increased probability of drier conditions.

Endangered species. A species in danger of extinction because of its low numbers or degraded habitat, or likely to become so unless the factors affecting its status improve. The Environment Protection and Biodiversity Conservation Act 1999 (Cth) dictates that a native species is eligible to be included in the endangered category at a particular time if, at that time, (a) it is not critically endangered, and (b) it is facing a very high risk of extinction in the wild in the near future, as determined in accordance with the prescribed criteria.

Endemic species. Species that occurs naturally and exclusively in a given place.

Environment Protection and Biodiversity Conservation Act 1999 (Cth) (EPBC Act). Australia’s national environment law. The EPBC Act focuses on protecting matters of national importance, such as World Heritage sites, national heritage places, wetlands of international importance (Ramsar wetlands), nationally threatened species and ecological communities, migratory species, Commonwealth marine areas, and nuclear actions.

Escapement. In a fisheries context, escapement is the number or proportion of fish allowed to escape a fishery and go on to spawn.

Eutrophication. The natural or human-induced process by which a body of water becomes enriched in dissolved mineral nutrients (particularly phosphorus and nitrogen) above normal levels, stimulating the growth of aquatic plants and increasing organic production of the water body. Excessive enrichment may result in the depletion of dissolved oxygen and ensuing mortality of organisms that live in the water. See Hypoxia.

Exclusive Economic Zone (EEZ). The area that extends from the limit of the territorial sea, which is 12 nautical miles offshore from the territorial sea baseline, to a maximum of 200 nautical miles, measured from the territorial sea baseline. The EEZ is less than 200 nautical miles in extent, where it coincides with the EEZ of another country. In this case, the boundaries between the two countries are defined by treaty. Australia has sovereign rights and responsibilities over the water column and the seabed in its EEZ, including the exploration and exploitation of natural resources.

Exploitation rate. The proportion of an exploited fish population caught; usually expressed as an annual rate.

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Fishing mortality limit reference point (FLIM). The fishing mortality rate above which overfishing is said to be occurring and the stock biomass would be declining (-depleting). If applied for long enough, this can lead to a stock declining below the biomass limit reference point.

Fishing mortality maximum sustainable yield (FMSY). The fishing mortality rate that, at equilibrium, is expected to produce the maximum sustainable yield.

Fecundity. Number of eggs an animal produces each reproductive cycle, determining the potential reproductive capacity of an organism or population.

Fish-aggregating device (FAD). Buoys or platforms used to attract and aggregate pelagic fishes to increase fishing harvest rates. Can be as simple as a floating log or bamboo raft, but tuna fishers setting purse-seine nets around tuna schools now deploy sophisticated FADs that incorporate satellite tracking and interrogation of information (such as sea surface temperature). Modern FADs may include acoustic devices indicating the quantity of fish around the FAD.

Fishery-dependent data (survey). Data collected directly from a fishery, from commercial fishers, processors and retailers. Common methods include logbooks, fishery observers and port sampling (cf. Fishery-independent data [survey]). May be more prone to bias than fishery-independent data because the fishery-dependent data are influenced by fishers’ attempts to maximise economic returns.

Fishery-independent data (survey). Data collected by scientifically planned surveys, carried out by research vessels or contracted commercial fishing vessels, to gather information independently of normal commercial fishing operations, using standard gear and methods (cf. Fishery-dependent data [survey]).

Fishing down (fish-down). Fishing on a stock that is above the biomass target with the intention of reducing the biomass to the target level, such as the biomass giving MSY. The fishing mortality may be greater than FMSY during a fish-down phase. 

Fishing effort. Amount of fishing taking place, usually described in terms of gear type and the frequency or duration of operations (for example, number of hooks, trawl hours, net length).

Fishing mortality (F). The instantaneous rate of fish deaths due to fishing a component of the fish stock. F reference points may be applied to entire stocks or segments of the stocks.  Instantaneous fishing mortality rates of 0.1, 0.5, 1.0, and 2.0 are equivalent to annual exploitation rates of 9.5 per cent, 39.3 per cent, 63.2 per cent and 86.5 per cent respectively. See also Mortality, Natural mortality.

Fishing power. Effectiveness of a vessel’s fishing effort relative to that of other vessels or in other periods of time. Also used to describe the average fishing mortality per unit of effort of a fishing fleet—this often tends to increase with time as a result of improvements in technology and fisher knowledge.

Fishing season. The period during which a fishery can be accessed by fishers. Sometimes referred to as ‘fishing year’.

Fishing year. See Fishing season.

Fork length (FL). Length of a fish measured as the distance between the tip of the snout and the centre of the fork or ‘V’ of the tail. Commonly used to record the length of commercial fish because it is little affected by damage to the tail fin (cf. Total length). Fork length is measured flat, from point to point, usually on a measuring board, not by stretching a tape along the body surface, which would result in a longer measurement for full-bodied fish like tuna. See also Lower-jaw fork length.

Fully fished. Generally describes a fish stock for which current catches and fishing pressure are close to optimal. In the Status of fisheries resources in NSW 2008–09 

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Gear restriction. Restriction on the amount and/or type of fishing gear that can be used by fishers in a particular fishery; used as a management tool. This is one of the input controls that can be used to limit impacts of a fishery.

Generalist feeders. Species that feed on a variety of food types and are not restricted to a particular food source.

Generation time. Average time taken for an individual animal to replace itself in a population.

Ghost fishing. Ongoing capture of fish in gear—usually nets or traps—that has been lost at sea.

Gross value of production (GVP). A value obtained by multiplying the volume of catch (whole weight equivalent) by the average per unit beach price. In the case of a multispecies fishery, the fishery’s GVP is the sum of the GVP of each species.

Growth overfishing. Occurs when fish are harvested at an average size that is smaller than the size that would produce the maximum yield per recruit. When a fish stock is growth overfished, increases in fishing effort and fishing mortality produce decreasing yields, even though more individuals are harvested, because of the reduced average size of harvested individuals. In the Status of fisheries resources in NSW 2008–093, growth overfished has the specific meaning: ‘Yield per recruit would increase if length at first capture was increased or fishing mortality decreased’.

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Harvest control rules. See Decision rules.

Harvest strategy. An agreed combination of data collection, assessment, decisions rules and management actions intended to achieve defined biological and economic objectives in a given fishery.

High seas. Waters outside national jurisdictions (that is, outside Exclusive Economic Zones).

Hyperstability. A relationship between catch per unit effort (CPUE) and abundance in which, initially, CPUE declines more slowly than true abundance as a stock declines. Hyperstable CPUE provides a positively biased index of abundance.

Hypoxia. A phenomenon that occurs in aquatic environments as dissolved oxygen becomes reduced in concentration to a point at which its level becomes detrimental to aquatic organisms living in the system. Also called ‘oxygen depletion’.

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Incidental catch. See Bycatch.

Index of abundance. Relative measure of the abundance of a stock (for example, catch per unit of effort).

Index of annual recruitment. Estimate of the relative number of individuals entering the fishery each year, usually based on a data source dedicated to the purpose, such as a recruit survey.

Indicator. A quantity that can be measured and used to track changes with respect to an objective. The measurement is not necessarily restricted to numerical values, and categorical values may be used.

Individual transferable effort (ITE). Shares of a total allowable effort that are allocated to individuals. They can be traded permanently or temporarily. Analogous to individual transferable quotas in a fishery managed with a total allowable catch [TAC]. Usually issued at the start of a fishing season. One of the input controls that may be used to limit the impacts of a fishery.

Individual transferable quota (ITQ). Management tool by which portions of the total allowable catch quota are allocated to fishers (individuals or companies). The fishers have long-term rights over the quota, but can trade quota with others (see also Quota). One of the output controls that may be used to limit fishing mortality.

Input controls. Management measures that place restraints on who fishes (licence limitations), where they fish (closed areas), when they fish (closed seasons) or how they fish (gear restrictions).

Inshore waters. Waters of the shallower part of the continental shelf, usually less than three nautical miles from the coast.

Intrinsic productivity. The natural rate of growth of a population, measured as births minus natural deaths per capita in the absence of fishing mortality or environmental constraints on population increase.

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Joint authority. An Offshore Constitutional Settlement arrangement whereby a fishery is managed jointly by the Australian Government and one or more states or territories under a single (Commonwealth, or state or territory) jurisdiction.

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Key commercial species. A species that is, or has been, specifically targeted and is, or has been, a significant component of a fishery. Key commercial species provide most of the economic yield of a fishery and may be managed to a MEY bioeconomic target.

Key threatening process. The Environment Protection and Biodiversity Conservation Act 1999 (Cth) defines a key threatening process as 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. A threatening process is eligible to be treated as a key threatening process if (a) it could cause a native species or an ecological community to become eligible for listing in any category, other than conservation dependent, or (b) it could cause a listed threatened species or a listed threatened ecological community to become eligible to be listed in another category representing a higher degree of endangerment, or (c) it adversely affects two or more listed threatened species (other than conservation dependent species) or two or more listed threatened ecological communities.

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La Niña. The extensive cooling of the central and eastern Pacific Ocean. In Australia (particularly eastern Australia), La Niña events are associated with an increased probability of wetter conditions (cf. El Niño).

Latency (latent effort, latent capacity, latent catch). Fishing capacity that is authorised for use but not currently being used. Depending on how a fishery is managed, latency might appear in effort (for example, unused vessel statutory fishing rights [SFRs], gear SFRs, quota SFRs, permits or nights fishing) or in quota (for example, where total allowable catches [TACs] are not fully caught in a quota-managed fishery). It can be an indicator of fishers’ views about the profitability of a fishery, with high levels of latency suggesting that low expected profits in the fishery do not justify fishing.

Leeuwin Current. A warm ocean current that transports warm tropical water southwards along the Western Australian coast and east around southern Australia.

Length and age frequency. See Age-length frequency.

Length-frequency distribution; modal size. The number or proportion of individuals in a catch or catch sample in each length group (length interval). The modal size is the length group into which most individuals fall. Some distributions may show several modes, reflecting cohorts of fish of different ages.

Limited-entry fishery. Fishery in which the fishing effort is controlled by restricting the number of operators. Usually requires controlling the number and size or fishing power of vessels, the transfer of fishing rights and the replacement of vessels (cf. Open-access fishery).

Logbook. Official record of catch-and-effort and other relevant data completed by fishers. In many fisheries, a licence condition makes the return of logbooks mandatory.

Lower-jaw fork length. Length of a fish measured as the distance between the tip of the lower jaw and the point of the fork or ‘V’ of the tail. Commonly used to record the length of commercial fish with bills (for example, Swordfish) because it is little affected by damage to the tail fin (cf. Total length) and bill. Fork length is measured flat, from point to point, using a measuring board or callipers, not by stretching a tape along the body surface, which would result in a longer measurement for full-bodied fish like tuna.

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Management strategy evaluation (MSE). A structured procedure to test whether a proposed harvest strategy will achieve the required objectives in the context of, and despite, identified uncertainties in monitoring/observations, stock/fishery dynamics and management implementation. Testing is usually conducted by mathematical simulation modelling, but it can also be applied using qualitative expert judgement.

Mantle length. The standard measure of length in coleoid cephalopods (for example, squid, cuttlefish and octopus). Usually measured along the dorsal midline from the mantle margin to the posterior tip of the body, excluding long tails; or from a line joining the midpoint of the eyes, rather than the mantle margin.

Mark-recapture. A method for estimating population size and other parameters by tagging and releasing fish, and comparing the ratios of marked (tagged) to unmarked (untagged) individuals in future catches. Also referred to as tag-recapture or tagging.

Maximum economic yield (MEY). The sustainable catch level for a commercial fishery that allows net economic returns to be maximised. For most practical discount rates and fishing costs, MEY is achieved at an equilibrium stock size larger than that associated with maximum sustainable yield (MSY). In this sense, MEY is more environmentally conservative than MSY and should, in principle, help protect the fishery in the event of decreased biological productivity that results from unfavourable environmental impacts.

Maximum sustainable yield (MSY). The maximum average annual catch that can be removed from a stock over an indefinite period under prevailing environmental conditions. MSY defined in this way assumes that fish stocks reach equilibrium and makes no allowance for productivity changes and environmental variability. Studies have demonstrated that fishing at the level of MSY is often not sustainable in such cases.

Maximum sustainable yield rate (MSYR). The ratio of MSY to the biomass at which MSY is obtained (that is, MSY / BMSY).

Meristics. The counting of body structures occurring in series, such as the number of fin rays or vertebrae. Meristics can be used to describe or identify a species of fish.

Migration. Non-random movement of individuals of a stock from one place to another, often in groups, and often for the purposes of feeding or spawning.

Minimum size (minimum legal size). Size below which a captured animal may not legally be retained. Usually specified by species to protect immature fish and avoid growth overfishing. Management variations include use of a maximum legal size limit to protect large mature fish, and combination of both maximum and minimum legal size limits (that is, ‘slot’ size limits).

Mitigation device. In the context of reducing fishing impacts on vulnerable species, it is a device incorporated into, or deployed in association with, fishing gear, and designed to reduce the risk or rate of interaction with the gear, or to reduce the likelihood of injury or mortality of animals that do encounter the gear. Mitigation devices are most often used to reduce interaction with, or injury to, seabirds, marine mammals and turtles. Mitigation devices may be designed to reduce actual interaction with the gear (such as trawl warps and longlines at the stern of a vessel), or to facilitate escape by animals that do enter the gear (such as trawl nets underwater). See also Bird baffler, Bird sprayer, Warp deflector.

Model (population). Hypothesis of how a population functions using mathematical descriptions of determinants of fish stock productivity, such as growth, recruitment and mortality.

Mortality. Deaths from all causes, usually expressed as a rate or as the proportion of the stock dying each year.

Multispecies fishery. A fishery using non-selective gear(s) that unavoidably catches a variety of species (for example, trawl nets), or in which fishers’ profits depend on the catch of more than one species. Fishery data from multispecies fisheries are more difficult to interpret because of uncertainty around the relative targeting of individual species, and therefore of the extent to which CPUE for the fishery might index the relative abundance of individual species in the mixed catch. Also, the non-selective gear(s) may make it difficult to simultaneously control the catch of each species at intended and/or individually optimal levels. 

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Natural mortality (M). Deaths of fish from all natural causes, excluding fishing. Usually expressed as an instantaneous rate or as a percentage of fish dying in a year. See also Fishing mortality, Mortality.

Nautical mile (nm). A unit of distance derived from the angular measurement of one minute of arc of latitude at the earth's surface, but standardised by international agreement as 1852 metres.

Negligible stock. Stock for which catches have been historically low to negligible and the stock has generally not been subject to targeted fishing. The stock has not been overfished in the past and it is likely that the stock can sustain a higher catch than is currently taken. Fishing is unlikely to be having a negative impact on the stock. There is little information available and a stock assessment is not justifiable.

Nominal catch. The sum of the catches that are landed (expressed as live weight equivalent), as reported, and not scaled up or down by any factor. Nominal catches do not include unreported discards.

Non-fishing effects. Influences on fish stock productivity and abundance that are not related to fishing activities. In the context of SAFS stock status reporting, this particularly refers to substantial impacts that lie outside the normal or expected range of these effects, and which result in substantial and unexpected declines in stock biomass. Examples include, but are not limited to, climatic and oceanographic extremes (cyclones, oceanic heat waves, coral bleaching, floods), disease outbreaks, introduction of exotic species, land-based effects (sedimentation, pollution, eutrophication) and habitat destruction or degradation. To be used as justification that observed declines in biomass are not attributable to fishing, there must be clear defendable evidence that anomalous non-fishing effects have occurred, and have caused substantial and unexpected biomass declines.

Non-target species. Species that is unintentionally taken by a fishery while fishing for other species; may not be routinely assessed for fisheries management. See also Bycatch, Byproduct.

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Observer. A certified person on board fishing vessels who collects scientific and technical information for the management authority on the fishing operations and the catch. Observer programs can be used for monitoring fishing operations (for example, areas fished, fishing effort, gear characteristics, catches and species caught, discards, collecting tag returns). Observers usually have some degree of independence from the fishing operator and may or may not have legal coercion powers, and their data may or may not be used for non-scientific purposes (for example, enforcement).

Oceanic. Open-ocean waters beyond the edge of the continental shelf.

Offshore Constitutional Settlement (OCS). The 1982 package of national, state and territory laws that forms the basis for Australian governments (national, state and territory) to enter into agreements for specified fisheries to be managed by a particular government or group of governments. A fishery might be managed by the Australian Government, one or more state or territory governments, or any combination of these acting through a joint authority. Fisheries for which OCS arrangements are not in place may be managed under joint control or continue under separate management arrangements in each jurisdiction.

Oligotrophic. Refers to water bodies that are poor in nutrients and have low primary productivity. Low nutrient content reduces plankton blooms, which reduces the likelihood of depletion of dissolved oxygen.

Open-access fishery. Fishery in which there is no limit on the number of operators or vessels allowed to operate in the fishery (cf. Limited-entry fishery). In the absence of economic constraints or other controls or incentives to reduce catches (see Output controls), such a fishery is liable to suffer the ‘tragedy of the commons’, where a ‘race to fish’ generally leaves a fish stock below its maximum sustainable yield and unable to support an economically profitable fishery. Under open access, a fishery operates with a harvest and effort that result in total revenue equalling costs, with no economic profits being generated (that is, the open-access equilibrium). The fishing effort employed at this point exceeds the level that would achieve maximum economic yield, and both profitability and stock biomass would be improved by reducing fishing effort.

Otoliths. Bone-like structures formed in the inner ear of fish. Seasonal variation in appearance of annual rings or layers deposited as otoliths grow can be counted to determine age, similar to growth rings in trees.

Otolith microchemistry. A technique used to delineate fish stocks and characterise movements and natal origin of fish from analysis of the microscopic chemical composition of otoliths, which changes as otoliths grow over time, depending on the chemical composition of the water in which the fish are at the time.

Output controls. Management measures that place restraints on what is caught, such as total allowable catch limits (TACs) and quotas, rather than on the fishing effort put into the fishery (cf. Input controls). These usually species-specific, but may include limits for mixed catches.

Depleted stock. Spawning stock biomass that has been reduced through catch and/or non-fishing effects, so that average recruitment levels are significantly reduced (recruitment is impaired). Current management is not adequate to recover the stock, or adequate management measures have been put in place but have not yet resulted in measurable improvements. (Referred to as 'Overfished stock' in Status of Australian fish stocks reports 2012 - 2016)

Ovigerous. Carrying or bearing eggs.

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Panmictic. The population is considered to be capable of mixing across its entire range. A panmictic population is one where all mature individuals have equal opportunity of mating. This assumes that there are no mating restrictions, either genetic or behavioural, on the population.

Pelagic. Inhabiting waters at or near the ocean surface, rather than in midwater or near the sea floor. Usually applied to free-swimming species, such as tunas and sharks (cf. Demersal).

Performance indicator (performance measure). Measurable parameter used to assess the performance of a fishery against predetermined sustainability objectives (such as current biomass compared to some reference biomass level).

Perkinsus species. Protistan parasites that infect many species of marine molluscs throughout the world, and can cause mass mortality.

Pinkie. See Warp deflector.

Planktonic larval stage. An early life stage of many marine organisms, when larvae are dispersed in the water column before settling on suitable habitat and developing into their adult form.

Population modelling. Mathematical description of a population that is designed to simulate the life cycle of animals in that population. Population models form the underlying basis of most stock assessments, and can be used to project the effects on the population of various catch levels, or of environmental factors or biological characteristics of these animals.

Possession limit. The maximum number of fish or other harvested organism that a person is allowed to have in their possession at any time. It discourages the accumulation of large quantities of fish by recreational fishers (see Bag limit).

Precautionary approach. Approach to fisheries management where the absence of adequate scientific information, or uncertainty in scientific information, should not be used as a reason for postponing or failing to take measures to conserve target species, associated or dependent species and non-target species and their environment. 

Pre-recruits. The proportion of a population that has not yet entered a fishery (that is, not yet able to be caught or retained by the fishing gear).

Productivity (biological). A measure of the rate at which a fish stock is capable of producing biomass, as a result of the birth, growth and death rates of the stock. A highly productive stock is characterised by high birth, growth and mortality rates, shorter life span and early maturation, and can usually sustain high harvesting rates.

Productivity (economic). The ability of firms or an industry to convert inputs (labour, capital, fuel, etc.) into output. Economic productivity is often measured using productivity indexes, which show whether more or less output is being produced over time with a unit of input. The index is calculated by comparing changes in total output (fish catch) to changes in total inputs (such as fuel, labour and capital).

Protected species. As per the meaning used in the Environment Protection and Biodiversity Conservation Act 1999 (Cth).

Protogynous hermaphrodites. Organisms that change sex from female to male during their life cycle.

Puerulus. The last stage of rock lobster larvae, when lobster larvae change from the floating planktonic distribution stages to the stage that settles onto the seabed. Surveys to estimate the density of rock lobster pueruli that settle on the seabed are sometimes used to provide indices of future recruitment strength in rock lobster fisheries.

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Quota. Amount of catch allocated to a fishery as a whole (total allowable catch) or to an individual fisher or company (individual transferable quota).

Quota species. Species for which allowable catches are limited by allocation of catch quotas.

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Real-time management. Method of fisheries management that allows fishing activities (for example, vessel movements, fishing effort, catch) to be monitored and controlled or adjusted in real time.

Recommended biological catch (RBC). The estimated total annual catch that can be taken by fishing, while achieving the management objectives for that fishery. Under a harvest strategy, the RBC is calculated from the best estimate of current biomass by application of the harvest control rule.

Recruit. Usually, a fish that has just become susceptible to the fishery. Sometimes used in relation to population components (for example, a recruit to the spawning stock).

Recruitment failure. A situation in which a population is not able to naturally produce sufficient viable offspring to maintain itself as a consequence of physical factors (for example, damaged spawning areas or unsuitable water temperatures) or biological factors (for example, inadequate numbers of fish).

Recruitment impaired. The point at which a stock is considered to be recruitment impaired is the point at which biomass has been reduced through catch so that average recruitment levels are significantly reduced. This can occur due to a number of factors, including fishing, environmental effects or other non-fishing effects.

Recruitment overfishing. A level of exploitation that, if maintained, would result in the stock falling to levels at which there is a significant risk of recruitment and stock collapse. The corresponding term for the state of the stock is ‘recruitment overfished’, in which the average annual recruitment to the stock is significantly reduced as a result of fishing. Where reduction in recruitment has resulted from both fishing and/or other non-fishing effects, the equivalent term is 'recruitment impaired'. Both terms define a limit reference point (for exploitation rate or stock size) beyond which urgent management action should be taken to reduce exploitation and recover the stock.

The following uses of the term provide some guidance to how it should be interpreted and applied.

The FAO fisheries glossary ( defines recruitment overfished as ‘a situation in which … annual recruitment … has become significantly reduced. The situation is characterized by a greatly reduced spawning stock, a decreasing proportion of older fish in the catch, and generally very low recruitment year after year’.

Cook4 defines recruitment overfished as a situation in which ‘a reduction in the proportion of fish caught would be more than compensated for by the increased number of recruits to the fishery as a result of increased escapement of mature fish’.

The EPBC Guidelines for the ecologically sustainable management of fisheries5 define recruitment overfishing as occurring ‘where fishing activities are causing a reduction in recruitment in succeeding years and cause the mortality of too many fish in total, too many pre-productive fish, or too many fish that have only spawned a few times. The end result is that the stock can no longer replenish itself adequately’.

Various jurisdictions have defined a biomass limit reference point (BLIM) that is considered to correspond to this state of recruitment overfishing. These limit reference points (LRPs) are often specified in terms of some fraction of the biomass at which maximum sustainable yield (MSY) occurs. Examples of LRPs include:

  • BLIM = 0.5BMSY (Commonwealth of Australia)
  • BLIM = 0.5BMSY (or greater) (United States)
  • BLIM is usually defined relative to fishing mortality rates rather than biomass (European Union)
  • BLIM = 0.5BMSY (or greater—for example, for forage fish) (Marine Stewardship Council).

New Zealand explicitly uses the concept of recruitment overfishing, which is defined as occurring ‘when excessive fishing effort or catch reduces the spawning stock biomass to a level below which future recruitment levels may be jeopardised; this spawning biomass level should correspond closely to the biomass limit reference point’.

No jurisdictions have explicitly defined by how much recruitment would need to be reduced to constitute recruitment overfishing or impairment. Recruitment is usually difficult to measure directly, and so proxies expected to avoid recruitment impairment (such as maintaining stocks above 0.5BMSY) are more usually used.

Reference point. An indicator, typically of the level of stock biomass or fishing mortality rate, used as a benchmark for assessment and as the basis for management objectives set within harvest strategies (see also Biological reference point).

Relative abundance. The number of living individuals at a point in time, expressed as a fraction of the average number of living individuals at some other point in time (such as before the beginning of fishing, or some chosen reference year) or under other conditions (such as if no fishing was currently occurring).

Risk analysis. Analysis that evaluates the likelihood (risk) of not achieving chosen objectives under various harvesting strategies or management options.

Rotational closure. Closure of an area to allow stocks to rebuild, while another area that has been previously closed and allowed to rebuild is opened to fishing.

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Sacrificial panel. Part of a trap designed to rust out after a short period to allow fish to escape if the trap is lost at sea; reduces the impacts of ghost fishing.

Seasonal closure. Closure of a fishing ground for a defined period. Used as a management tool, often to protect a particular component of the stock at a particular time, such as a spawning aggregation.

Semelparous. Species that reproduce only once and then die, such as some arrow squid species.

Settlement. Transition from a floating pelagic larval stage to a substrate-associated juvenile or adult existence.

Shared biological stock. A biological stock that spans the waters of more than one jurisdiction.

Shark finning. The removal and retention of shark fins. The remainder of the body is discarded, often still alive. The process of finning and discarding sharks has been banned in Australian waters, and management measures are in place to reduce or restrict targeting of sharks for fin markets by illegal, unreported and unregulated fishing.

Shell height. In bivalve mollusc species, a straight-line measurement from the hinge to the part of the shell that is furthest away from the hinge.

Shell length. A straight-line measurement of molluscs, often at the widest point of the shell.

Size frequency. See Length-frequency distribution.

Spatial closure. A method of fisheries management that prevents fishing in a defined area.

Spawning biomass (SB). The total weight of all adult (reproductively mature) fish in a population.

Spawning stock biomass. See Spawning biomass.

Species complex. A group of similar species that are often difficult to differentiate without detailed examination.

Species group. A number of species that are grouped together for the purposes of fisheries management, either because they are difficult to differentiate (see Species complex), or to show similar biological and productivity characteristics, or because they are caught in association and it has been decided to manage them as a group.

Standardised data. Data that have been adjusted to be directly comparable to a unit that is defined as the ‘standard’ one, usually by correcting for the effects of other parameters that might affect the data, other than the parameter of interest. Standardisation might, for example, involve the correction for effects of different vessels to provide indices where inter-annual changes in catch rate are more directly comparable. Standardised catch per unit effort data are often used as an indicator of relative fish abundance.

Standard length (SL). The length of a fish measured from the tip of the snout to the posterior end of the last vertebra or to the posterior end of the mid-lateral portion of the hypural plate.

Statoliths. Bone-like structures found in cephalopods that can be used to record life history events. Similar to otoliths found in fish (see Otoliths), and may also be used for age determination of some squid species.

Statolith microchemistry. A technique to characterise life history, natal origin and movements of cephalopods by analysis of the microscopic chemical composition of statolith areas deposited at different ages (see also Otolith microchemistry).

Statutory fishing right (SFR). Right to participate in a limited-entry fishery. An SFR can take many forms, including the right to access a particular fishery or area of a fishery, the right to take a particular quantity of a particular type of fish, or the right to use a particular type or quantity of fishing equipment.

Stochastic demographic modelling. A form of stock assessment method used to estimate the intrinsic productivity and response to fishing of fish stocks, using age composition and providing for time-varying annual recruitment.

Stock. Within the Status of key Australian fish stocks reports, the term ‘stock’ is used generically in reference to three levels of stock status assessment—biological stocks, management units and populations assessed at the jurisdictional level. See also Biological stock.

Stock-recruitment (S-R) relationship. Relationship between the size of the parental (mature or spawning) biomass and the number of recruits it generates. This is often a key determinant of stock productivity, but is difficult to estimate. In the absence of direct estimates of biomass and recruitment (such as might be obtained from fishery independent surveys), these are usually estimated within stock assessments. S-R relationships can be highly variable, particularly at intermediate to larger stock sizes, with a wide range of recruitment possible for a given stock size. Climate induced changes in S-R productivity can result in substantial changes in estimates of sustainable harvest rates.

Stock reduction analysis. A group of methods for inferring the extent to which a fish stock is likely to have been reduced by fishing over time, assuming constant recruitment. Requires only a time series of total catch data and some assumptions regarding biology, but can also incorporate other information. These methods form the basis of a number of data-poor methods of stock assessment.

Stock synthesis model. A statistical framework for fitting of a population dynamics model to a range of fishery and survey data. It is designed to accommodate both age and size composition samples from a fishery, and multiple stock subareas. Selectivity can be modelled as age specific only, size specific in the observations only, or size specific with the ability to capture the major effect of size-specific survivorship. The overall model contains sub-components that simulate the dynamics of the stock and fisheries, derive expected values for the various observed data, and quantify the magnitude of difference between observed and expected data to allow a ‘best fit’ model to be selected as the basis for management advice.

Sustainable stock. The agreed national reporting framework for the Status of key Australian fish stocks reports defines the term ‘sustainable stock’ as follows: Stock for which biomass (or biomass proxy) is at a level sufficient to ensure that, on average, future levels of recruitment are adequate (that is, not recruitment overfished) and for which fishing pressure is adequately controlled to avoid the stock becoming recruitment overfished.

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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 Mark-Recapture).

Target biomass (BTARG). The desired biomass of the stock, chosen to be the management target within a harvest strategy.

Target catch range. The range of annual catches, taking into account natural variations in recruitment to the fished stock, that may be expected under a fishing effort-based management plan.

Target fishing (targeting). Fishing selectively for particular species or sizes of fish.

Target species. See Key commercial species.

Temporal closure. Closure that is implemented to protect fish stocks during specific stages of their life cycle (for example, while spawning).

Territorial sea (12 nautical mile limit). ‘The Territorial Sea is a belt of water not exceeding 12 nautical miles in width measured from the territorial sea baseline. Australia’s sovereignty extends to the territorial sea, its seabed and subsoil, and to the air space above it. This sovereignty is exercised in accordance with international law as reflected in the Convention on the Law of the Sea. The main limitation on Australia’s exercise of sovereignty in the territorial sea is the right of innocent passage for foreign ships. The territorial sea around certain islands in the Torres Strait is 3 nautical miles6.

Territorial sea baseline. The baseline from which all the zones (for example, the Exclusive Economic Zone) of Australia’s maritime jurisdiction are measured. The baseline is defined as the level of lowest astronomical tide, but straight baselines and bay or river closing lines may be drawn further out from the low-water mark to encompass areas such as the mouths of rivers, bays, ports, roadsteads and fringing reefs.

Threatened species. As per the meaning used in the Environment Protection and Biodiversity Conservation Act 1999 (Cth).

Torres Strait Protected Zone. An area defined under an agreement between Australia and Papua New Guinea that describes the boundaries between the two countries and how the sea area may be used. A key purpose of the protected zone is so that Torres Strait Islanders and the coastal people of Papua New Guinea can carry on their traditional way of life. For example, traditional people from both countries may move freely (without passports or visas) for the purpose of traditional activities in the protected zone.

Total allowable catch (TAC. An overall catch limit set as an output control on catches (see also Output controls). Where resource-sharing arrangements are in place between commercial and recreational fishers, the term total allowable commercial catch (TACC) can be applied to the commercial catch component. The term ‘global’ is applied to TACs that cover fishing mortality from all fleets, including Commonwealth, state and territory fleets.

Total allowable catch (TAC)—actual. The agreed TAC for the species with amendments applied, such as carryover or debits from the previous year.

Total allowable commercial catch (TACC). The commercial catch component of a Total allowable catch.

Total allowable effort (TAE). An upper limit on the amount of effort (such as number of vessels, days fished, number of hooks or fishing operations) that can be applied in the fishery.

Total length (TL). The length from the tip of the snout to the tip of the longer lobe of the caudal fin, usually measured with the lobes compressed along the midline. It is a straight-line measure, not measured over the curve of the body (cf. Fork length).

Depleting stock. Biomass is not yet depleted and recruitent is not yet impaired, but fishing pressure is too high (overfishing is occurring) and moving the stock in the direction of becoming recruitment impaired. (Referred to as 'Transitional-depleting stock' in Status of Australian fish stocks reports 2012 - 2016)

Recovering stock. Biomass is depleted and recruitment is impaired, but management measures are in place to promote stock recovery, and there is evidence that recovery is occurring. (Referred to as 'Transitional-recovering stock' in Status of Australian fish stocks reports 2012 - 2016)

Trigger points. Pre-specified levels (total catch, spawning biomass, etc.) that, if breached, indicate the need for some action, such as implementation of pre-determined measures or a more general review of fishery management.

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Undefined stock. Not enough information exists to determine stock status.

Unfished biomass. Biomass that existed, or that would exist, for a stock that has not yet been fished, or if it had not been fished (also called the ‘unfished’ or ‘unexploited’ biomass or unfished level). This may refer to an estimated historical biomass level before fishing commenced, or the current biomass that would have existed had no fishing occurred.

Upwelling. An oceanic process whereby cold, nutrient-rich water is brought to the surface as a result of winds moving surface waters offshore, away from continental shelves, or seabed currents interacting with land masses. Typically results in increased productivity of fisheries where it occurs, as a result of the increased nutrients being brought into sunlit surface waters.

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Vessel monitoring system (VMS). Electronic device that transmits the identity and location of a vessel.

Virgin biomass. See Unfished biomass.

Vulnerable species. Species that will become endangered within 25 years unless mitigating action is taken (see also Endangered species). The Environment Protection and Biodiversity Conservation Act 1999 (Cth) dictates that a native species is eligible to be included in the vulnerable category at a particular time if, at that time (a) it is not critically endangered or endangered, and (b) it is facing a high risk of extinction in the wild in the medium-term future, as determined in accordance with the prescribed criteria.

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Warp deflector. A type of seabird mitigation device that uses an inflatable plastic buoy (referred to by fishermen as a ‘pinkie’) clipped to a trawl warp where it enters the water, to deter seabirds from the area around the warps and reduce the risk or warp strikes (see Warp strike).

Warp strike. Incident of seabirds striking the trawl warps (towlines) while trawl nets are being towed, potentially resulting in injury or mortality.

Weight-of-evidence approach. The systematic consideration of a range of biological and fisheries information, each used to provide a measure or proxy for biomass status and levels of fishing mortality, to support a status determination. Lines of evidence used in the weight-of-evidence approach may include empirical indicators (catch, effort, catch rate, size- or age-based indicators, spatial and temporal distribution of the fishery), risk assessments, fishery-independent surveys, quantitative stock assessment models and harvest strategies.

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Yield. Total weight of fish harvested from a fishery.

Yield-per-recruit (YPR) analysis. Analysis of how growth and natural mortality interact to determine the optimal size of animals to harvest to achieve maximum sustainable yields. YPR analysis assumes that yield and productivity will reach equilibrium at some optimal level, and biological reference points based on yield-per-recruit analysis will be expected to lack precaution because of natural variability in stock productivity, particularly if the potential for reduced future recruitment resulting from decreased parental biomass is not considered. YPR analysis does not take economic factors into consideration, and it may be more economically beneficial to catch fish at some other preferred market size (such as when they are young and plentiful, or when they are older and larger but fewer). Alternatives such as dollar-per-recruit and spawner-per-recruit exist, which attempt to address some of the limitations of YPR.

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  1. Fletcher, WJ and Santoro, K (eds) 2011, State of the fisheries and aquatic resources report 2010–11, Western Australian Department of Fisheries, Perth.
  2. Australian Government Department of the Environment and Water Resources 2007, Guidelines for the ecologically sustainable management of fisheries, 2nd edn, DEWR, Canberra.
  3. Rowling, K, Hegarty, A & Ives, M (eds) 2010, Status of fisheries resources in NSW 2008–09, Industry and Investment NSW, Cronulla.
  4. Cook, JG 1984, Glossary of technical terms, in RM May (ed.), Exploitation of marine communities, Springer- Verlag, Berlin, 341–348.
  5. Australian Government Department of the Environment and Water Resources 2007, Guidelines for the ecologically sustainable management of fisheries, 2nd edn, DEWR, Canberra.
  6. Geoscience Australia 2012, Maritime boundary definitions, Geoscience Australia, Canberra,