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Introduction to stock assessment

Glossary

Here are definitions of some of the technical terms found in the Introduction to stock assessment online course.

Abundance (N)
total number of fish in a stock.
Assumption
a statement introduced into an argument that is accepted as being true.
Availability
the likelihood that a fish will enter fishing gear.
Biomass (B)
the total weight of all fish in a stock.
Bycatch
the unintentional catch of a species when meaning to catch another. The retained portion of bycatch is called incidental catch, whereas the portion returned to the water is called discards.
Carrying capacity (K)
stock size limited by environmental factors and resource availability (for example, food, habitat, mates).
Catch per unit effort
the quantity of fish caught with one standard unit of fishing effort (e.g., the number of fish taken per 1000 hooks per day or the weight of fish taken per hour of trawling). CPUE is often assumed to be a relative abundance index (i.e., proportional to the portion of the stock biomass (or numbers) vulnerable to the gear).
Catchability
a concept that reflects the efficiency of a fishery. It is the combination of availability (the likelihood that a fish will enter fishing gear) and selectivity (the likelihood of retention once a fish enters fishing gear). Gear selectivity is affected by gear design, such as mesh type and size, escape panels, and hook size.
Cohort
(also known as a year-class) fish of a stock born in the same spawning year.
Conflict of interest
an interest held by a participant that may affect or be perceived to affect their objectivity and independence in contributing to the peer review process.
Consensus
an absence of opposition to the peer review meeting conclusions and advice.
Conservation unit (CU)
a group of fish sufficiently isolated from other groups that, if it goes locally extinct, is very unlikely to recolonize naturally.
Decision tables
a simple way to present advice regarding the potential consequences and trade-offs of making different decisions.
Depletion
a measure of the current biomass of a stock relative to the average unfished biomass.
Dredge
a fishing method whereby a dredge is dragged across the sea floor, either scraping or penetrating the sea floor.
Ecosystem approach to fisheries management (EAFM)
a single-stock approach to fisheries management that incorporates ecosystem variables into stock assessments, science advice, management recommendations, integrated fishery management plans or other harvest strategies (i.e., the science-management cycle) to better inform stock and individual fishery-focused decisions.
Ecosystem variables (EVs)
elements, features and/or processes of an ecosystem that are likely to vary or change, such as those related to climate (e.g., large-scale atmospheric forcing, climate change), oceanography (e.g., temperature, salinity, nutrients, pH) and ecology (e.g., predator-prey interactions, habitat), which can affect the productivity (e.g., growth, mortality, recruitment) and/or availability (e.g., distribution, catchability) of the stock.
Electrofishing
an electric field emitted from a pulser to temporarily stun fish that can then be collected via dip net.
Fish
in accordance with the Fisheries Act, the term “fish” includes:
  • fish, shellfish, crustaceans, and marine animals
  • any parts of fish, shellfish, crustaceans, and marine animals
  • eggs, sperm, spawn, larvae, spat, and juvenile stages of fish, shellfish, crustaceans, and marine animals
Fishery
the sum of all fishing activity on a resource.
Fishery-dependent data
data collected directly from commercial, recreational, or Indigenous food, social, and ceremonial (FSC) fisheries.
Fishery-independent data
data collected from outside of fisheries.
Fishing effort
a measure of fishing activity using metrics such as:
  • the number of nets or lines used
  • the number of fishing vessels deployed
  • the number of hours spent fishing
Fishing mortality (F)
measure of deaths in a stock due to all fishing activities, including:
  • targeted fishing
  • bycatch and discards
  • other incidental mortality in other fisheries
Gillnet
a fishing net that is hung vertically so that fish get trapped in it by their gills.
Groundfish
(also known as demersal fish) species that live and feed on or near the seafloor.
Harvest rate
the proportion of the recruited or vulnerable biomass that is caught during a certain period, usually a fishing year (also referred to as exploitation rate).
Hydroacoustic
the study of sound in water.
Hyperdepletion
catch declines faster than fish abundance.
Hyperstability
catch remains high as the fish stock declines.
Indicators
measurements that provide information on the state of a stock attribute of interest. A series of indicators over time creates an index.
Indigenous food, social, and ceremonial (FSC) fishery
the right to fish for food, social and ceremonial purposes is protected under section 35 of the Constitution. It is a collective right, not an individual one. Designated Indigenous harvesters can catch what is needed for themselves and/or their community for FSC purposes. FSC fishing does not provide an opportunity for the sale of catch. It may also occur at various times of the year, which are not always aligned with commercial fishery seasons or areas. Decisions about when a fishery is opened or closed are made through the fish management process.
Indigenous Ways of Knowing
the overarching term is used in this training to convey the multiple forms of knowledge that Indigenous Nations, governments, communities, organizations, experts, Elders, and Knowledge Holders possess and may choose to share with DFO during collaborative research, monitoring, and/or science advisory processes. There is no universal definition of Indigenous Ways of Knowing and its composition is determined by First Nations, Inuit, and Métis using their own terms.
Limit reference point (LRP)
the stock status below which serious harm is occurring to the stock.
Longline
a type of fishing gear consisting of a long main line with shorter lines with baited hooks fastened at intervals.
Maximum sustainable yield (MSY)
the maximum average annual catch that can be removed from a stock over an indefinite period of time under current environmental conditions
  • BMSY
    the stock biomass that produces the maximum sustainable yield.
Models
tools used to simplify a natural system so it can be more easily understood.
Moratorium
a temporary prohibition of an activity.
Natural mortality (M)
measure of deaths in a stock due to everything other than fishing, such as:
  • predation
  • disease
  • prey availability
  • competition for resources
Operating models
computer models that simulate how fish stocks grow, reproduce, and interact with the environment.
Otolith
small structures in the inner ear with growth rings that can be counted, similar to counting tree rings.
Parameter
numbers that summarize a measurable characteristic of a stock.
Pelagic
fish inhabiting the water column of the open ocean between the surface and the seafloor.
Population
a group of the same species that occupies a particular geographical region and interbreed.
Precautionary approach
being cautious when scientific information is uncertain, unreliable, or inadequate and not using the absence of adequate scientific information as a reason to postpone or fail to take action to avoid serious harm to a resource.
Predictions
forecast the most likely scenario.
Probability
the extent to which an event or scenario is likely to occur.
Productivity
the rate at which biomass is generated in a stock.
Projections
explore and compare the outcomes of many scenarios that could happen.
Quota
see definition for Total Allowable Catch (TAC)
Recruitment
occurs when new fish are added to a population. It is commonly measured when small or young fish grow large or old enough to be caught in a fishery (which may be affected by catch limits or gear type) or scientific survey.
Reference point
a benchmark against which the biomass or abundance of the stock or the fishing mortality rate (or exploitation rate) can be measured in order to determine its status. These reference points can be targets, thresholds or limits depending on their intended use.
Removal reference
the maximum removal rate of a fish stock.
Rights-holders
modern successors to the Indigenous collectives that signed treaties, occupied and used land, and engaged in historic practices that support a finding of an Aboriginal right or Aboriginal title. Aboriginal rights are the collective rights of Indigenous Peoples flowing from their status as the original peoples of Canada and can vary from nation to nation and community to community. They refer to practices, traditions, and customs integral to the distinctive culture of an Indigenous collective. These rights are site, community, and fact-specific, and depend on historical facts. Treaty rights are rights of Indigenous Peoples that are either established in or codified in Crown-Indigenous treaties. Aboriginal title is one type of Aboriginal right. It means the right to have control over the use and occupation of specific land.
Seine
a fishing net that hangs vertically in the water with floats at the top and weights at the bottom; the ends are drawn together to encircle the fish.
Selectivity
the likelihood of retention once a fish enters fishing gear. Gear selectivity is affected by gear design, such as mesh type and size, escape panels, and hook size.
Sensitivity analysis
allow scientists to explore the impacts of uncertainty and assumptions by testing different scenarios (e.g., random variation in recruitment or different environmental factors affecting natural mortality). They are sometimes included alongside science advice for context.
Serious harm
a fish stock experiencing serious harm may be depleted to the point where it has impaired productivity or reproductive capacity. As a result, the stock would be less resilient to fishing and could not easily rebuild. Serious harm may be irreversible, or only slowly reversible over the long-term, and can be due to fishing, other human-induced impacts, or natural causes.
Spawning potential ratio
number of eggs produced by a fish stock under specific fishing conditions relative to number of eggs that would be produced if it is not fished.
Spawning stock biomass (SSB)
the total weight of all fish in a stock that have reached reproductive maturity.
Stakeholders
for this training, individuals or organizations with an interest in the science and management of fisheries and the marine environment.
Steepness
(also known as recruitment compensation) measure of juvenile fish survival under conditions where there is little to no competition for resources.
Stock
groups of the same species with a shared characteristic(s) of interest to managers.
Stock assessment
the scientific process of analyzing data to evaluate the abundance and productivity of fish stocks in the past, present, and future.
Stock management unit (SMU)
collections of stocks that are managed together with a joint stock status.
Stock status
refers to a determination made, on the basis of stock assessment results, about the current condition of the stock.
Target reference point (TRP)
the overall stock level target.
Total allowable catch (TAC)
a catch limit set for a particular fishery.
Trap
static fishing gear that work passively to entangle or trap fish that move towards or into it.
Trawling
a method of fishing that involves pulling a fishing net that is heavily weighted to keep it on the seafloor through the water behind 1 or more boats. The net used for trawling is called a trawl.
Uncertainty
the incompleteness of knowledge about a natural system.
Upper stock reference point (USR)
a threshold below which fishing must be reduced to avoid reaching the limit reference point.
Unfished biomass
total weight of fish that would exist in a stock if it is not fished.
Unfished recruitment
expected recruitment if the fish stock is not fished.
Yield per recruit
the expected lifetime catch in weight produced per recruited fish in the stock.
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