Age at first maturityThis is the average age at which fish of a given population mature for the first time.  Ideally it is estimated by sampling a large number of fish from a population, determining their ages, determining whether they are capable of reproduction or not, and then calculating the average age of all the fish that show the first signs of being capable of reproduction.  It can also be estimated from lengths, if the relationship between length and age is known.  It is calculated from the length at first maturity using the inverse of the von Bertalanffy growth function.

Age at maturityThe age when 50% of the fish of a given sex are considered to be reproductively mature (Restrepo 1999).

Age-length data – Data comparing the length of an individual fish with its age.

Assessment tools (syns.: Assessment methods) – Protocols for analyzing data related to the status of a fish population in order to estimate parameters of importance to fisheries management, including population size, productivity, fishing mortality, reproductive capacity, and others.   

At-sea monitoring – The collection of information on fishing activities taking place at sea, including harvesting, catch handling, biological sampling, fishing methods and interactions with protected species. At-sea monitoring is conducted with onboard observers or an electronic monitoring system.

Breeding strategy – The way in which an organism reproduces (and where applicable, rears young).  Provides an indication of the level of natural mortality that may be expected for offspring in the first stages of life. Includes placement of larvae, level of parental protection and length of gestational period (Patrick et al., 2009).

Bycatch (syns.: Incidental catch, Non-target catch/species) – Organisms other than the primary target species that are caught incidental to the harvest of the those species. Bycatch may be retained or discarded. Discards may occur for regulatory or economic reasons (NRC, 1999).

Catch (syn.: Harvest) – The total number (or weight) of fish caught by fishing operations. Catch includes all fish killed by the act of fishing, not just those landed (FAO, n.d.).

Catch accounting – The tracking of fishermen’s catch, including landings and discards, against their share holdings.

Catch at Age The estimated number of fish caught, tabulated by fish age and year of capture (and by other strata such as gear or nation). Catch-at-age may be estimated on the basis of catch-at-size, using age-length keys or cohort slicing (Restrepo 1999).

Catch at Size The estimated number of fish caught, tabulated by size class and by other strata such as gear, nation and quarter. For any given species, catch-at-size should include all fish killed by the act of fishing, not just those fish that are landed (Restrepo 1999).

Catch curve 1. A graph showing the logarithm of the number of fish taken by fishing at successive ages or sizes. 2. Assuming equilibrium conditions, the descending limb of a catch curve can be used to estimate total mortality (Restrepo 1999).

Catch limit (syn.: Total Allowable Catch or TAC) – The scientifically determined, acceptable level of fishing mortality.

Catch-at-age Data on the number of fish of each age group or class in the catch taken from one stock by a fishery, obtained from age-readings (or deduced from the lengths) of fish in representative samples of the catch (FAO, n.d.).

Catch-at-length 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 (FAO, n.d.).

Catch-at-weight Data on the number of fish of each weight group in the catch of a fishery, usually obtained by measuring the weights of fish in representative samples of the catch (FAO, n.d.).

Catch-based data(syn.: fishery dependent data) – Data obtained for fishery catches, such as total catch, catch-at-age, catch-at-length, catch-at-weight, etc.  

Catch-MSY assessment Uses a time series of removals (catch plus discards), estimated ranges of stock size in the first and final years of the catch data, and life history information to calculate Maximum Sustainable Yield (MSY).

Catch-per-unit-effort (CPUE) – The weight or number of fish caught with a specific unit of fishing effort (e.g., time and/or gear used).

Catchability (syns.: Vulnerability, Susceptibility, Sensitivity) – 1. The extent to which a stock is susceptible to fishing. Catchability depends on fish behavior, size, and abundance and on the type and deployment of fishing gear (Blackhart et al., 2006). 2. The fraction of a fish stock which is caught by a defined unit of the fishing effort (FAO, n.d.).

Co-management – A process of management in which government shares power with resource users, with each holding specific rights and responsibilities relating to decision making (FAO, n.d.).

Commercial Fishing – Fishing in which the fish harvested, either in whole or in part, are intended to enter commerce or enter commerce through sale, barter or trade (NOAA 1997).

Community – The populations that live and interact physically and temporally in the same area (Blackhart et al., 2006). Can be applied to humans (e.g. a “fishing community”) or to marine organisms (e.g. “ecological community”).

Controls on fishing mortality  Management measures such as catch limits, gear restrictions and seasonal and spatial closures that limit the total amount harvested each year.  When set at appropriate levels and coupled with effective fishery governance, they can ensure long-term sustainability of stocks.

Data Collection – The gathering of measurements or observations from fishery independent or fishery dependent monitoring activities.

Data-Poor fishery (syn.: Data-Limited fishery) – A fishery with little to no existing scientific information on the fishery characteristics relevant for management decisions (e.g. baseline biological data such as size at maturity, fishing mortality and growth rates, stock assessments, fishing effort assessments, and baseline habitat quality assessments) (adapted from Honey et al. 2010).

Data-Rich fishery – A fishery with large amounts of scientific information on the fishery characteristics relevant for management decisions (e.g. baseline biological data such as size at maturity, fishing mortality and growth rates, stock assessments, fishing effort assessments, and baseline habitat quality assessments), usually sufficient to conduct a stock assessment that results in estimates of stock biomass, productivity, and fishing mortality relative to reference values such as the biomass and fishing mortality associated with maximum sustainable yield (adapted from Honey et al. 2010).

Derby-style fishing (syns.: Olympic-style fishing, Race for fish) – Fishing conditions characterized by short seasons and severe competition for fish, often resulting in low profits and harvests that exceed sustainable levels.

Depletion-based stock reduction analysis (DB-SRA)Combines DCAC with a probability analysis to more closely link stock production with biomass and evaluate potential changes in abundance over time.

Depletion-corrected average catch (DCAC) An extension of potential-yield models, DCAC is based on the theory that average catch is sustainable if stock abundance has not changed substantially. The method differs from simple extrapolation of average catch to estimate sustainable yield by correcting for the initial depletion in fish abundance typical of many fisheries.

(Stock) Depletion levels – A stock driven by fishing at very low level of abundance compared to historical levels, with dramatically reduced spawning biomass and reproductive capacity. It requires robust rebuilding strategies and its recovery time will depend on the present condition, life history traits (e.g., growth rate and reproductive capacity), the level of protection and environmental conditions.

Discard (syns.: Regulatory discard, Economic discard) – To release or return a portion of the catch, dead or alive, before offloading, often due to regulatory constraints or a lack of economic value (FAO, n.d.).

Dockside monitoring – The monitoring of activities taking place upon a vessel’s landing, including weighing or counting offloaded catch, biological sampling and identifying species composition.

DriverA force of change. Stressors or pressures have associated drivers that indicate the mechanism(s) involved in initiating a course of events. According to ecological usage, any force associated with any natural or anthropogenic process, event or activity that causes a change in an ecosystem process, component, function, property or service (Ocean Tipping Points Project 2013).

Economic discard (syn.: Commercial discard) – Fish that are not retained because they are of an undesirable size, sex or quality, or for other economic reasons (16 U.S.C. 1802); i.e., they do not command a high enough price to justify retention and landing.

EcosystemA spatio-temporal system of the biosphere, including its living components (plants, animals, micro-organisms) and the non-living components of their environment, with their relationships, as determined by past and present environmental forcing functions and interactions amongst biota (Garcia 2009).

Ecosystem assessmentA social process through which the findings of science concerning the causes of ecosystem change, their consequences for human well-being, and management and policy options are brought to bear on the needs of decision-makers (Alcamp et a. 2003).

Ecosystem-based management – An approach that takes major ecosystem components and services—both structural and functional—into account in managing fisheries. Goals include rebuilding and sustaining populations, species, biological communities and marine ecosystems at high levels of productivity and biological diversity (FAO, n.d.).  Ecosystem-based management can be operationalized by adjusting fishing mortality to levels that achieve ecosystem state or service goals, taking ecological factors into account when assessing stock status and setting catch limits.

Ecosystem services  The benefits people obtain from ecosystems. These include provisioning services, such as food and water; regulating services, such as flood and disease control; cultural services, such as spiritual and cultural benefits; and supporting services, such as nutrient cycling, that maintain the conditions for producing all of the benefits (FAO, n.d.).

Ecosystem state – A description and characterization of an ecosystem based on key attributes at a particular time.  The attributes can be components, functions, processes or properties that aid in defining the ecosystem state and contrasting it to other possible states (Ocean Tipping Points Project 2013, as adapted from Walker et al. 2002; Suding & Hobbs 2009).

Ecosystem threshold (syn.: Ecological threshold) – A relatively rapid change from one ecological condition to another. When a system is close to an ecological threshold, a large ecological response results from a relatively small change in a driver (Bennett and Radford 2003, Groffman et al. 2006, Suding & Hobbs 2009, Huggett 2005). Ecological thresholds exist at all levels of organization, including single populations and species, species interactions, ecosystem functions/processes, and wholesale ecosystems (Ocean Tipping Points project 2013).

Figure 1. Here an ecological threshold marks the transition from a coral dominated system to an algae dominated system, two regimes that are distinguished by key ecosystem attributes: coral cover, algae cover, and fish species diversity. Figure from:; photos taken by Brian Nielson.

Effort (syn.: Fishing effort) – The amount of time and fishing power used to harvest fish; effort units include the amount of time spent fishing, the number of fishing trips, gear size, boat size and horsepower (Blackhart et al., 2006).

Effort accounting – The tracking of fishermen’s use of effort units against their share holdings.

Effort cap (syn.: Total allowable effort) – The scientifically determined acceptable level of fishing effort, defined as the number of effort units allowed in a given fishery. Effort caps are often based on target levels of fishing mortality.

Electronic monitoring – A technique employed to monitor at-sea fishing activities, often consisting of cameras, sensors and Global Positioning System (GPS) units that record vessel and fishing location, fishing activity, catch (retained and discarded) and compliance with fishing rules.

Endangered species – A species in danger of extinction within the foreseeable future throughout all or a significant portion of its range (USFWS 2014).

Enforcement – Measures to ensure compliance with fishery regulations, including catch limits, gear use and fishing behavior.

Equilibrium –  All the factors affecting stock biomass and productivity are balanced and do not change over time; recruitment, growth and mortality (both F and M) are assumed to be constant over time.

Equilibrium egg production – The level of egg production needed to balance fishery mortality.

Ex-vessel value (syns.: Dockside value, Landed value, Gross landed value) – A measure of the monetary worth of commercial landings, usually calculated as the price per pound for the first sale of landed fish multiplied by the total pounds landed.

Exploitation biomass Refers to that portion of a stock’s biomass that is available to the fishing gear (Restrepo 1999).

Exploitation pattern 1. The proportion of a population at the beginning of a given time period that is caught during that time period (usually expressed on a yearly basis). 2. The ratio of fish caught (fishing mortality, F) to total mortality (Z).

Exploitation rate The fraction of an age class that is caught during the life span of a population exposed to fishing pressure, i.e., the number caught versus the total number of individuals dying due to fishing and other reasons (e.g., Pauly 1984).

Exposure As used in ecosystem risk assessment, exposure is defined as the degree to which an ecosystem or species is exposed to a threat or activity, usually a function of the degree to which the target overlaps in space and time with the threat.

Fecundity ­­– The reproductive capacity of a fish species, usually represented by the number of eggs produced in a reproductive cycle.  Fecundity often increases with age and size (Blackhart et al., 2006).

Fish – Often used to denote finfish, mollusks, crustaceans and any aquatic plant or animal that is harvested even though not all of these are really fish.

Fish density Number or pounds of fish surveyed divided by area surveyed.

Fish stock – The living resources in the community or population from which catches are taken in a fishery. Use of the term fish stock usually implies that the particular population is more or less isolated from other stocks of the same species and hence self-sustaining. In a particular fishery, the fish stock may be one or several species of fish but here is also intended to include commercial invertebrates and plants (FAO, n.d.).

Fish tag – A physical tag or marking placed upon a harvested fish, often used to monitor catch, ensure compliance, reduce illegal fishing and assist in traceability.

Fishery – The combination of fish and fishermen in a region, the latter fishing for similar or the same species with similar or the same gear types (Blackhart et al., 2006).

Fishery information – The information needed in a fishery for science and compliance, which can be collected through various forms of monitoring and self-reporting.

Fishery-dependent data – Data derived from the fishery, usually describing the catch (e.g., weight, species, length-frequency) from commercial and recreational sources. There are a variety of methods for obtaining fishery-dependent data. The most common approach is to use recorded landings. Landings are a record of the amount of fish sold and the numbers are typically reported in total weight. Another common mode for acquiring fishery-dependent data is through portside sampling of the catch of both recreational and commercial fisherman to obtain age and length information on the stock. Other less common methods for obtaining data is through the use of onboard observers, self-reporting, telephone surveys, and vessel-monitoring surveys.

Fishery-independent data – Data collected in ways that are independent of the fishery, such as random scientific fishing surveys or visual census surveys. Intended to avoid the biases inherent to fishery-related data (modified from FAO 1988).

Fishery Management Plan (FMP) – A document that includes data, analyses, and management measures (FAO, n.d).

Fishing community – A community that is substantially dependent on or engaged in the harvest or processing of fishery resources to meet social and economic needs. Includes fishing vessel owners, operators, crew and processors that are based in such a community (16 U.S.C. 1802).

Fishing effort (syn.: Effort) – The amount of fishing gear of a specific type used on the fishing grounds over a given unit of time (e.g., hours trawled per day, number of hooks set per day or number of hauls of a beach seine per day) (FAO, n.d.).

Fishing inputs – The resources used to catch a species or group of species, often including fishing vessels, vessel type and power, gears used, fuel and more.

Fishing mortality – A measurement of the rate of fish removal from a population by fishing. Fishing mortality can be reported as either annual or instantaneous. Annual mortality is the percentage of fish dying in one year. Instantaneous mortality is the percentage of fish dying at any given point in time (Blackhart et al., 2006).

Fishing right A right to catch a specified quantity of fish, or proportion of the total allowable fish catch or a right to use a boat (or any other specified fishing equipment) in a manner specified in a management plan or in the fishery regulations.  Can also denote the right to fish in a certain area.

Fishing zone 1. A zone of variable width (up to 200-nautical-miles) proclaimed by a coastal State around its coast, within which it controls domestic and foreign access to fish resources. 2. A zone of variable width proclaimed by a local government or managing unit of natural resources, within which it controls access to fish resources.

Food web The network of primary producers, grazers, and consumers (predators) within an ecosystem or a community i.e. the predator-prey relationships.

Food security A situation that exists when all people, at all times, have physical, social and economic access to sufficient, safe and nutritious food that meets their dietary needs and food preferences for an active and healthy life (Garcia 2009).

Fork length A measurement used frequently for fish length when the tail has a fork shape. Projected straight distance between the tip of the fish and the fork of the tail. Also see standard length, total length, and head length (Figure 2).

Figure 2: Diagram showing relationship of Total Length, Fork Length, Standard Length, and Head Length for measuring a fish. Figure from:

Fractional change in lifetime egg production (FLEP)An alternative to more data-intensive per-recruit models such as spawning stock biomass per recruit. Length-frequency data from an unfished (or early exploited) population and the current population, along with information on growth and maturity, are used to determine a limit reference point that represents the persistence of a population. The fractional change is calculated as the ratio of LEP between the unfished and current populations.

FrequencyNumber of observations (e.g. fish-at-length, of a repeating event per unit time (e.g. fishing trip).

Generation time Average age (tg) of parents at the time their young are born.

Growth overfishing – When high rates of fishing on juveniles result in low recruitment to a fishery; may result in stock collapse. Restricts fisheries from producing their maximum poundage (Blackhart et al., 2006).

Growth rate The increase in weight of a fish per year (or season), divided by the initial weight (Ricker 1975).

Habitat types The environment in which the fish live, including everything that surrounds and affects its life: e.g., water quality; bottom; vegetation; associated species (including food supplies).

Harvest – The total number or poundage of fish caught and kept from an area over a period of time (Blackhart et al., 2006).

Harvest control rules (syn.: harvests control law, harvest strategy) – 1. A rule that describes how harvest is intended to be controlled by management in relation to the state of some indicator of stock status. For example, a harvest control rule can describe the various values of fishing mortality which will be aimed at for various values of the stock abundance. It formalizes and summarizes a management strategy. Constant catch and constant fishing mortality are two types of simple harvest control rules. (Restrepo 1999). 2. A set of well-defined rules for determining management action (e.g. in the form of a TAC or allowable fishing effort) given input from an estimator or directly from data.

Head length Projected straight distance between the tip of the snout to the end of gill cover. Also see standard length, fork length, and total length (Figure 2, above).

High-grading (syn.: Economic discards) – Selectively sorting fish so that higher value, more marketable fish are retained and fish that could be legally retained, but are less marketable, are discarded (NRC, 1999).

Important or valued stocks Fish or invertebrate stocks that a fishery depends on to achieve goals such as food security, export revenue, profits, livelihoods, etc.

Index of abundance – A relative measure of the abundance of a stock; e.g. a time series of catch per unit of effort data, or the number of marked fish that are recaptured, or the number of fish that are observed in a visual census per unit time or area.

Indicator (of a threshold) – 1. A specific, well-defined, and measurable variable tracked through time that tracks changes in ecosystem condition and provides an estimate of the location of an ecosystem in state space relative to a threshold (Heinz Foundation 2008). Indicators simplify information about complex phenomena to improve understanding (King 1997) (Ocean Tipping Points Project 2013). 2. Signals - of processes, inputs, outputs, effects, results, outcomes, impacts, etc. - that enable such phenomena to be judged or measured. Both qualitative and quantitative indicators are needed for management learning, policy review, monitoring and evaluation (Choudhury and Jansen 1999).

  • Leading (syn.: Early warning sign) – Measurements of a system that provide early warning of an event (in this case, threshold). Leading indicators may focus on drivers and pressures that are expected to shift a system toward a threshold, rather than the internal components of the ecosystem (Herrera & Hovden 2008). Leading indicators are not necessarily good proxies for the changes taking place, but can provide clues about the future (King 1997). In the context of regime shifts, suggested leading indicators that warn of an impending ecosystem shift include increased autocorrelation, rising and variability, and ‘flickering’ between alternate ecosystem states.
  • LaggingMeasurements of a system that are taken after events, which that indicate outcomes, results, and occurrences. Lagging indicators should attempt to provide a signal of the key changes in system interactions after crossing a threshold (Herrera & Hovden 2008). For example, when measuring management performance, a lagging indicator would measure the number of times a threshold was crossed.

Landings – The number or weight of fish offloaded at a dock by fishermen. Landings are reported at the locations where fish are brought to shore (Blackhart et al., 2006).

Length at maturity (syn.: Size at maturity) Lm, average length at which fish of a given population mature for the first time.

Length at optimal yield Length class (Lopt) with the highest biomass in an unfished population, where the number of survivors multiplied with their average weight reaches a maximum (Beverton 1992).

Length-based data (syn.: Length information) – Data based on the length of fish (e.g., length at maturity and maximum length).

Length-based reference point The status of a population can be monitored with three simple metrics based on catch length compositions (i.e., that reflect exclusive take of mature individuals, Pmat; that consist primarily of fish of optimal size, the size at which the highest yield from a cohort occurs, Popt; and that demonstrate the conservation of large, mature individuals, Pmega) relative to exploitation (Cope 2009).

Length-based SPR The LBSPR uses fishery-dependent length frequency data to estimate the current spawning potential ratio (SPR) of the fishery (Hordyk et al. 2014).

Length-based sustainability indicatorThe use of size and/ or length information to evaluate the current status of the population relative to exploitation.

Length classes The distinction between life stages in a fish species, based on length (i.e., juvenile, adult, megaspawner).

Length composition (syn.: Size composition) – The number of individual fish in each size category.

Length frequency data Information on the distribution of recorded lengths (in a total catch, a stock, or a sample) which indicates the number of individuals encountered in each length interval.

Length structure (syn.: length-frequency distribution) – The number of individuals of a catch or catch sample in each length interval. The modal size is the length group with the higher number of individuals. Distributions may be uni- or bi-modal but are more generally multi-modal, reflecting multiple age-groups.

Life-history parameters – Basic biological information such as size and age at maturity, natural mortality and fecundity for a specific species.

Lifetime egg production (LEP) (syn.: egg production per recruit) – The amount of eggs a female can produce in her lifetime. Fisheries are sometimes managed to obtain a certain percentage (e.g., 10%) of the egg production per recruit compared to an unfished population.

Limited access (syns.: Controlled access, License limitation, Limited entry) – A fishery management approach that limits the number of fishermen participating in a fishery, usually by issuing a limited number of licenses.

Limit Reference Point (LRP) – is a numerical value that specifies a level at which the fishery is operating beyond a measure of acceptable risk (e.g., severe overfishing); management should be aimed to improve fishery performance or population levels.

Logbook (syn.: Logsheet) – A detailed, usually official, record of a vessel’s fishing activity registered systematically onboard the fishing vessel. It usually includes information on catch and species composition, the corresponding fishing effort and location (FAO, n.d.).

Macroalgae – Large, multi-celled, photosynthetic algae. Commonly called seaweed.

Marine Protected Area-Based Decision tree Uses spatially explicit, easy to gather catch and age-length data to set and further refine total allowable catch. Additionally, data gathered from inside no-take marine protected areas (MPAs) are used as a baseline for an unfished population.

Marine reserve (syn.: Marine protected area) – A geographically defined space in the marine environment where special restrictions are applied to protect some aspect of the marine ecosystem including plants, animals and natural habitats (Blackhart et al., 2006). No-take reserves are a type of marine reserve.

Market priceThe current trade and price in fish and fishery products.

Maximum Economic Yield (MEY) – The catch level that corresponds to the highest amount of profit that could be earned from a fishery (Blackhart et al., 2006).

Maximum length – The biggest fish, length-wise, in a sample or catch, or the biggest fish recorded for a specific species.

Maximum economic yield –When relating total revenues from fishing to total fishing effort in a surplus production model, the fishery yield associated with the maximum profit (largest positive difference between revenues and fishing costs).

Maximum Sustainable Yield (MSY) (syn.: Maximum equilibrium catch) – 1. The largest average catch that can be taken continuously (sustained) from a stock under average environmental conditions. This is often used as a management goal (Blackhart et al., 2006). 2. The highest theoretical equilibrium yield that can be continuously taken (on average) from a stock under existing (average) environmental conditions without affecting significantly the reproduction process. Also referred to sometimes as Potential yield.

Mean Length (Lbar) Fishing Mortality Estimator The Lbar uses fishery-dependent or fishery-independent length frequency data to estimate fishing pressure using the method described in Ault et al. (2005), assumes that fishing mortality has been constant over the life span of the fish being assessed.

Metadata – The collection of information related to the type and characteristics of data sets and their location in a data archive (Alcamo et al. 2003).

Metapopulation – A set of populations that can effectively be separate, weakly coupled, or globally interacting, through strongly coupled patches (Frank et al. 1994).

Megaspawner – A highly fecund, older female fish (Froese, 2004).

Migratory species Species that move between distinct geographical areas.

Mobile species Species that move; in the context of spatial management, mobile species are usually defined as those species that move too much to be significantly influenced by the management measure (e.g., a spatial closure or marine reserve).

Monitoring (syn.: Catch control) – The collection of fishery information for the purposes of managing the fishery, including setting catch limits and assessing stocks, and ensuring accountability, including catch accounting and enforcing fishery regulations.

Monte Carlo simulations An approach whereby the inputs that are used for a calculation are re-sampled many times assuming that the inputs follow known statistical distributions. The Monte Carlo method is used in many applications such as Bayesian analyses, parametric bootstraps and stochastic projections (Manly 1991).

(Total) Mortality – A measurement of the rate of death of fish, resulting from several factors but mainly (in the context of fishery management) natural mortality (M) and mortality from fishing (F).

MPA density ratioThe ratio (e.g. abundance, size, richness) of the density or abundance of a fishery resource outside to density or abundance inside of a well-enforced and design no-take reserve (Babcock and McCall 2011).  Measurements should be taken in similar habitats inside and outside of the reserve.

Multi-species fishery – A fishery in which more than one species is caught at the same time. Because of the imperfect selectivity of most fishing gear, most fisheries are “multi-species.” The term is often used to refer to fisheries where more than one species is intentionally sought and retained (NRC, 1999).

Natural mortality In the context of fishery management, natural mortality refers to deaths of fish from all causes except fishing (e.g. ageing, predation, cannibalism, disease and perhaps increasingly pollution). 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 approximately 20% of the population will die in a year from causes other than fishing.

No-take reserve (syns.: No-take zone, MPA or marine protected area; ants.: general use zone, fishing zone) – A defined marine area in which fishing and other extractive activities are prohibited.

Non-Equilibrium  All the factors affecting stock biomass and productivity are not balanced and change over time; recruitment, growth and mortality (both F and M) as fish grow and recruit into a fishery.

Non-target species (syns.: Bycatch, Incidental catch) – Species not specifically targeted as a component of the catch but which may be incidentally captured (Blackhart et al., 2006).

Onboard observers (syn.: Observers) – A certified person onboard fishing vessels who collects scientific and technical information on the fishing operations and the catch. Observer programs can be used for monitoring fishing operations (e.g., areas fished, fishing effort deployed, gear characteristics, catches and species caught, discards, collecting tag returns, etc.) (FAO, n.d.).

Open access  Condition in which access to a fishery is not restricted (i.e., no license limitation, quotas or other measures that would limit the amount of fish that an individual fisher can harvest) (NRC, 1999).

Optimum Yield (OY) (syn.: Optimal fishing mortality) – The harvest level for a species that achieves the greatest overall benefits, including economic, social and biological considerations. Optimum yield is different from Maximum Sustainable Yield (MSY) in that MSY considers only the biology of the species (Blackhart et al., 2006).

(Geographic) Overlap The extent to which two spatial entities (usually species and fishery ranges) coincide or potentially coincide. Geographic overlap usually includes aerial and vertical metrics, and sometimes also temporal and seasonal metrics.

Overcapacity  A level of fishing capacity (i.e., fishermen, vessels, gear) that results in fishing costs that are so high that they preclude the generation of desired profits from the fishery given the amount of fish available to catch.

Overcapitalization (syn.: Excess capacity) – In the short term, fishing capacity that exceeds the level required to capture and handle the allowable catch, while generating the desired profit margin. In the long term, fishing capacity that exceeds the level required to ensure the sustainability of the stock and the fishery at the desired level (FAO, n.d.).

Overfished  A state in which a fish stock is below a scientifically determined target biomass (e.g., one half of the biomass that produces Maximum Sustainable Yield).

Overfishing – A rate of fishing mortality that, unchanged, will result in an overfished state.

Potential yield modelA formula that relates the potential maximum yield of a species to its instantaneous annual natural mortality rate. A very simple model was first suggested in Gulland (1971), and subsequently refined in Beddington & Cooke (1983) and in Kirkwood et al. (1994).

Precautionary management (syn.: Precautionary action) – Involves the application of prudent foresight, taking account of the uncertainties in fisheries systems and the need to take action with incomplete knowledge. It requires, inter alia: (i) consideration of the needs of future generations and avoidance of changes that are not potentially reversible; (ii) prior identification of undesirable outcomes and of measures that will avoid them or correct them promptly; (iii) that any necessary corrective measures are initiated without delay, and that they should achieve their purpose promptly, on a timescale not exceeding two or three decades; (iv) that where the likely impact of resource use is uncertain, priority should be given to conserving the productive capacity of the resource; (v) that harvesting and processing capacity should be commensurate with estimated sustainable levels of resource, and that increases in capacity should be further contained when resource productivity is highly uncertain; (vi) all fishing activities must have prior management authorization and be subject to periodic review; (viii) an established legal and institutional framework for fishery management, within which management plans that implement the above points are instituted for each fishery, and (ix) appropriate placement of the burden of proof by adhering to the requirements above (FAO, 1996, para 6).

(Biological) Productivity Generation of biomass.

Qualitative data Data that approximate or characterize but do not measure or quantify the attributes, characteristics, properties of a variable.

Qualitative assessmentAn assessment that relies on qualitative data.

Quota – The maximum number of fish that can be legally landed in a time period. Quota can apply to the total fishery (aggregate quota) or an individual fisherman’s share (individual quota) under a catch share program (Blackhart et al., 2006).

Race for fish (syns.: Derby-style fishing, Olympic fishing) – A pattern of fishing characterized by an increasing number of highly efficient vessels fishing at an increasing pace, with season length becoming shorter and shorter (FAO, n.d.).

Recovery (time) – The time needed to rebuild the stock to a specified level.

Recreational Fishing – (syn.: sport fishing) Fishing for pleasure or competition.

Recruit  An individual fish entering the fishable stage of its life cycle.

Recruitment (rate) – The number of fish added to a fishable stock each year due to growth and/or migration into the stock.

Recruitment overfishing – When high rates of fishing mortality result in low annual recruitment, a reduced spawning stock and decreased proportion of older fish in the catch. May result in stock collapse (Blackhart et al., 2006).

Reference point – The value of an indicator associated with a particular ecosystem state or condition that is associated with a management objective. A related term is a reference direction: the directional trend of an indicator relative to the focal state (Ocean Tipping Points Project 2013).

  • Target reference point – The value of an indicator that management aims to achieve (i.e., a socially desired ecosystem state, zone or point) based on management goals. A target expresses a goal in quantitative, measurable terms that can be practically evaluated; e.g., if the goal is sustainable fisheries, the target is fishing mortality = natural mortality.
  • Limit reference point – A value management aims to avoid. E.g., if the goal is sustainable fisheries, the limit might be a maximum fishing mortality or minimum fish biomass values.
  • Baseline reference point – A value associated with “initial” conditions, which needs context-specific definition. E.g. pre-industrial level biomass.

Resilience – The capacity of an ecosystem to absorb perturbations while retaining its essential structure, function and feedbacks (i.e., stay in the same state, not cross a threshold) (Suding & Hobbs 2009, Folke et al. 2004).  Speed of recovery following perturbation is a common empirical metric of resilience (Ocean Tipping Points Project 2013).

Resistance The ease or difficulty of changing the system.

Rights-based management (RBM) Fisheries management tool that creates rules which define both the right to use and the allocation of fisheries resources. Thus, fishermen, fishing vessels, fishing communities and so forth can be awarded a license, quota or fishing right to stocks or fishing areas.

Sedentary Species Species that don’t move very much or at all during the fishable stages of their life cycles. 

Selectivity Ability to target and capture fish by size and species during harvesting operations, allowing bycatch of juvenile fish and non-target species to escape unharmed. In stock assessment, conventionally expressed as a relationship between retention and size (or age) by the fishery, with no reference to survival after escapement (Garcia 2009).

Sensitivityanalysis An analytical technique to deal with uncertainty about future events and values. It consists of varying one element (e.g. rainfall, market price), or a combination of elements, and determining the effect of those changes on the outcome of a project. In economic analysis, the effect of the changes on a measure of project value is calculated (FAO 1993).

Single-species fishery – A type of fishery in which fishers target only one species of fish, although it is usually impossible not to catch others incidentally (Blackhart et al., 2006).

Size composition (syn.: Length composition) – The numbers of fish that are in each size (length) category.

Size at maturity – The weight or length at which 50% of fish of a given sex reach reproductive maturity.

Spawning potential ratio – The number of eggs that could be produced by an average recruit in a fished stock divided by the number of eggs that could be produced by an average recruit in an unfished stock (Blackhart et al., 2006).

Spawning stock biomass (SSB) (syn.: Spawning stock biomass-per-recruit) – 1. The total weight of all fish (both males and females) in the population which contribute to reproduction. Often conventionally defined as the biomass of all individuals beyond “age at first maturity” or “size at first maturity” i.e. beyond the age or size class in which 50% of the individuals are mature. 2. The total biomass of fish of reproductive age during the breeding season of a stock (Cooke 1984).

Spawning stock biomass-per-recruit (syn.: Spawning Stock Biomass) – The expected lifetime contribution to the spawning stock biomass for the average recruit to the fishery. For a given exploitation pattern, rate of growth, maturity schedule and natural mortality, an equilibrium value of SSB/R can be calculated for any level of F. SSB/R decreases monotonically with increasing fishing mortality F.

Species – A group of living organisms consisting of similar individuals capable of exchanging genes or interbreeding.

Standard length 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 midlateral portion of the hypural plate. Simply put, this measurement excludes the length of the caudal fin. Also see total length, fork length, and head length (Figure 2, above).

Stakeholders The individuals and groups of individuals (including governmental and non-governmental institutions, traditional communities, universities, research institutions, development agencies and banks, donors, etc.) with an interest or claim (whether stated or implied) in a given project.  These individuals and groups are those which can be impacted by or can have an impact on a given project and its objectives. Stakeholder groups that have a direct or indirect "stake" can be at the household, community, local, regional, national, or international level (FAO 1997).

State change (syn.: Regime shift) – Rapid reorganization of a system from one relatively unchanging state to another (Carpenter & Folke 2006) (Ocean Tipping Points Project 2013).

Stewardship – Responsible management of resources for future generations, such as maintaining populations of target and non-target species, protecting wildlife, conserving key habitats and strengthening ecosystem resilience.

Stock – A part of a fish population usually with a particular migration pattern, specific spawning grounds, and subject to a distinct fishery. A fish stock may be treated as a total or a spawning stock. Total stock refers to both juveniles and adults, either in numbers or by weight, while spawning stock refers to the numbers or weight of individuals that are old enough to reproduce (Blackhart et al., 2006).

Stock assessment (syn.: Fishery Assessment) – Assessment that provides fisheries managers with the information that is used in the regulation of a fish stock. Data used in stock assessments can be classified as fishery-dependent data or fishery-independent data. Biological status indicators and reference points are the primary outputs of stock assessments and fishing regulations are set to meet these biological benchmarks.

Stock (or system) collapse – Reduction of a stock abundance by fishing and/ or other causes to levels at which the production is negligible compared to historical levels. The word is normally used when the (reduction) process is sudden compared with the likely time scale of recovery, if any, but is sometimes used melodramatically for any case of overfishing (Cooke 1984).

Stock recovery – The process of a species returning to normal or healthy levels/ numbers.

Stock/ fishery status An appreciation of the situation of a stock, usually expressed as: protected, under-exploited, intensively exploited, fully exploited, over-exploited, depleted, extinct or commercially extinct (FAO 1998).

Susceptibility (syn.: Catchability, Sensitivity) – In the context of fishery management, this denotes the degree to which a stock can be impacted by fishing.

Sustainable fishing – Fishing activities that do not cause or lead to undesirable changes in the biological and economic productivity, biological diversity, or ecosystem structure and functioning from one human generation to the next (FAO, n.d.).

Sustainable harvest (syns.: Sustainable catch, Sustainable yield) – The biomass or number of fish that can be harvested from year to year without depleting the stock biomass to undesirable levels, assuming that environmental conditions remain the same (Blackhart et al., 2006).

Target Reference Point (TRP) – is a numerical value (or range of values) that indicates that the performance of the fishery is at a desirable level; management should be aimed at achieving or maintaining this target.

Target species (syn.: Target stocks) – Those species primarily sought by fishermen in a particular fishery. There may be primary as well as secondary target species (FAO, n.d.).

Threatened species Species which are vulnerable to endangerment in the near future (See “endangered species”).

Total allowable catch (TAC) (syn.: Catch limit) – The annual recommended or specified regulated catch for a species or species group (Blackhart et al., 2006).

Total allowable effort (TAE) (syn.: Effort cap) – The annual recommended or specified effort level applied to catch a species or group of species.

Total catch – The landed catch plus discard mortality (Blackhart et al., 2006).

Total length Refers to the length of a fish measured 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. Also see standard length, fork length, and head length (Figure 2, above).

Unassessed stocks Fish stocks that are not scientifically assessed.  In most cases this results in little or no management.

Visual survey dataData derived from direct observations, often by SCUBA divers or snorkelers swimming transects.  Visual survey data often include habitat types encountered, fish species, fish abundance, and sometimes fish length.

von Bertalanffy growth function – A differential equation which relates the length (l) or weight (w) of a fish to time (t): where are, respectively, the asymptotic maximum length and weight of the fish, and K is a growth rate parameter measuring the rate at which the asymptote is approached (Beddington and Kirkwood 2005).

Vulnerability (syns.: Catchability, Susceptibility, Sensitivity) – Equivalent to catchability, but usually applied to a specific part of the fish stock, such as individuals of a specific size or length (Blackhart et al., 2006). Can also be applied to an entire ecosystem in reference to system susceptibility to fishing or other impacts. In this context, vulnerability is a function of the productivity or resilience of a system or species and its susceptibility to a threat (Turner et al. 2003, Chapin et al. 2009).  Conceptually similar to resilience in that it characterizes the system’s adaptive capacity, sensitivity to change, and ability to cope and recover, but unlike resilience, also includes consideration of the degree of exposure to specific threats (Ocean Tipping Points Project 2013). It is often calculated as the Euclidean distance between a productivity and susceptibility score, and sometimes as the product of these scores.

Yield-per-recruit – The expected lifetime yield per fish recruited in the stock at a specific age. Depends on the exploitation pattern (fishing mortality at age) or fishing regime (effort, size at first capture) and natural mortality (Restrepo 1999).