Glossary of Terms

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95% C.I.
see Confidence Interval.


Adult Abundance
The number of adults in a region. Most values reported here are for wild salmon and steelhead.
Allee Effect
Reduced likelihood of finding a mate when breeding populations are small.
Anadromous fish species spend most of their lives in the ocean and return to freshwater to spawn.
Area-Under-the-Curve (AUC)
To estimate the total number of spawners in a stream segment, the observed numbers of live fish are plotted over time. An additional point with a value of zero is added seven days before or after the first and last observations to close the curve. An integral is used to calculate the area under the curve to estimate fish days. This statistic is then divided by an estimate of the average length of time coho spend on the spawning grounds to estimate the number of fish. (For more information on area-under-the-curve, see Spawner Abundance Analysis Methods.)


Beverton-Holt Model
The Bayesian Salmon Analysis Model uses a Beverton-Holt distribution, and has been referenced by the persistence criterion on this site. It is one of four extinction-risk models used by the coho Technical Recovery Team (TRT) to evaluate persistence. The model combines density-dependent freshwater production with density-independent, environmentally driven marine survival. Recruitment is modeled as a Beverton-Holt compensatory relationship with spawner density modified with an exponential decline in recruits (depensation) at very low spawner densities.
The study of the distribution of biodiversity over space and time. It aims to reveal where organisms live, and at what abundance. Biogeography does more than ask, "Which species?" and "Where?"; it also asks, "Why are these species here" and "Why not?".
Broad Sense Recovery
Goals defined in the recovery planning process, generally by local recovery planning groups, which go beyond the requirements for delisting, to address, for example, other legislative mandates or social, economic, and ecological values.


Confidence Interval (C.I.)
The confidence interval (C.I.) is an interval that is calculated from the data that describes the reliability of an estimate. It gives an estimated range of values which is likely to include the true value of an unknown population parameter. The confidence level describes how frequently we could expect the estimate to fall within the interval. So, for a 95% confidence interval we could expect the interval to contain the estimate 95% of the time, and that in 5% of the cases the true value would fall outside of the interval.
Coriolis Effect
An apparent deflection of moving objects when they are viewed from a rotating reference frame. Perhaps the most commonly encountered rotating reference frame is the Earth. Moving objects on the surface of the Earth experience a Coriolis force, and appear to veer to the right in the northern hemisphere, and to the left in the southern.
Critical Habitat
Under the Endangered Species Act, critical habitat is an area essential to the conservation of a listed species, though the area need not actually be occupied by the species at the time it is designated.


Demographic Variation
Variation in the numbers of individuals in different age classes due to random differences in deaths, births, and migration.
Dependent Population
A collection of one or more local breeding units whose population dynamics or extinction risk over a 100-year time period are substantially altered by exchanges of individuals with other populations. Generally, a population that is so small that it would go extinct if it were isolated, and is dependent on adjacent populations to contribute more individuals or to re-seed it if the population goes extinct. The Cummins Creek coho population is an example of a dependent population.
Reduced survival and production of eggs or offspring when the breeding population is small. This can be due to increased predation per offspring or the reduced likelihood of finding a mate (see Allee Effect).
Distinct Population Segment (DPS)
A distinct population segment is the smallest division of a taxonomic species permitted to be protected under the U.S. Endangered Species Act. Species, as defined in the Act for listing purposes, is a taxonomic species or subspecies of plant or animal, or in the case of vertebrate species, a distinct population segment (DPS).
A measure of where individuals are located and the patterns of their locations.
Within-population diversity is the result of phenotypic differences among individuals. These differences provide the flexibility of the population as a whole to respond successfully to short-term environmental variations. They are also the basis by which populations are able to adapt and evolve as conditions within their home range go through changes that are more permanent.


Ekman Transport
The natural process by which wind causes movement of water near the ocean surface. Each layer of water in the ocean drags with it the layer beneath, thus the movement of each layer of water is affected by the movement of the layer above. In Ekman transport, the force of the wind is balanced by the Coriolis effect, which acts perpendicular to the motion of the water. The ocean's surface current moves to the right of the direction of surface wind in the Northern Hemisphere, and to the left of it in the Southern Hemisphere. The net movement of ocean water due to the wind is perpendicular to the wind (to the right of the wind in the Northern Hemisphere and to the left in the Southern Hemisphere).
Endangered Species Act (ESA)
Federal law designed to protect critically imperiled species from extinction. The ESA's primary goal is to prevent the extinction of imperiled plant and animal life, and secondly, to recover and maintain those populations by removing or lessening threats to their survival. After receiving a petition to list a species, federal agencies take a series of steps, or rulemaking procedures, and make a decision as to whether the species should be listed as threatened or endangered. Once a species is listed, the Fish and Wildlife Service or the National Marine Fisheries Service is required to create a recovery plan outlining the goals, tasks required, likely costs, and estimated timeline to recover the endangered species.
Environmental Protection Agency (EPA)
The Environmental Protection Agency is a federal agency charged with protecting human health and safeguarding the natural environment.
The number of adult salmon or steelhead that escape the fishery and return to the spawning grounds to breed.
Evolutionarily Significant Unit (ESU)
"An ESU is defined as a population that 1) is substantially reproductively isolated from conspecific [same-species] populations, and 2) represents an important component in the evolutionary legacy of the species." (Johnson et al. 1994)
The end of a population, species or group of taxa. The moment of extinction is generally considered to be the death of the last individual of that species (although the capacity to breed and recover may have been lost before this point and the species or population is considered functionally extinct).
Extinction Risk
The probability that a given species or population will go extinct over a specified period of time.


Fishery Regulation Assessment Model (FRAM)
Estimates impacts of proposed ocean and terminal fisheries on chinook and coho salmon stocks for the entire West Coast. (See
The capability of an individual of a certain genotype to reproduce.
Functionally Extinct
A population that is no longer viable; there are no individuals able to reproduce, or the small population of breeding individuals will not be able to sustain itself due to inbreeding depression and genetic drift, which leads to a loss of fitness.


Genetic Drift
The change in the relative frequency in which a gene variant (an allele) occurs in a population due to random sampling and chance. The effect of genetic drift is larger in small populations
Geographic Information System (GIS)
A system that captures, stores, analyzes, manages, and presents data that are linked to location. Technically, a GIS is a system that includes mapping software and tools that can be implemented with GIS software to analyze spatial data.
The Columbia Basin Partnership Task Force, Phase 2 Report defines the geometric mean as the nth root of n product of n numbers. Geometric means are considered to be a better measure of central tendency for data such as fish abundance which is typically highly skewed. The geometric mean smooths the contribution of periodic large run sizes which can inflate simple averages relative to typical population values. The 10-year period was selected to represent an interval of sustained abundance across multiple generational cycles.


Harmonic Mean
The harmonic mean is another way of calculating an average. It is the reciprocal of the arithmetic mean of reciprocals of the data. For n numbers x1, x2, ... , xn, the harmonic mean equals n/(1/x1 + 1/x2 + ... + 1/xn).
Hockey-Stick Viability Model
One of four extinction-risk models used by the coho Technical Recovery Team (TRT) to evaluate persistence. This model is a stochastic viability model developed as part of a suite of models known as SPAZ. The model uses a hockey stick form of the stock recruitment relationship, with a linear increase in recruitment at low stock abundance and constant recruitment when the stock is at or above habitat capacity.


Inbreeding Depression
Reduced fitness in a given population as a result of breeding of related individuals.
Independent Population
A collection of one or more local breeding units whose population dynamics or extinction risk over a 100-year time period are not substantially altered by exchanges of individuals with other populations. Essentially, a population large and robust enough to persist in isolation. The Nehalem River coho population is an example of an independent population.
Interior Columbia Technical Review Team (ICTRT)
Group of salmon scientists convened by the Salmon Recovery Team of the National Marine Fisheries Service (NMFS).


Precocious males which return to spawn a year or two earlier than their counterparts. They can be half the size of an adult.


Life-cycle Monitoring
Studies that aim to separate different portions of the life-cycle to estimate productivity and survival in each life stage. For salmon, it is useful to be able to isolate the freshwater and saltwater portions of the life-cycle. To do this, it is necessary to obtain estimates of the number of returning adults and the number of outmigrating juveniles.
Life History
Age-specific patterns of survivorship probability, migration, age-at-first-reproduction, clutch size, and reproductive frequency.


Major Spawning Area (MaSA)
A system of one or more branches that contain sufficient spawning and rearing habitat to support 500 spawners.  For Interior Columbia salmonid populations: defined using results from intrinsic potential analysis. 
Marine Survival Category
The 2000 revision to Amendment 13 to the Pacific Salmon Plan identifies 4 marine survival categories for coho within the Oreon Production Index (OPI) which includes coastal and Columbia River hatchery coho. Goals for wild Oregon Coast coho abundance and distribution are scaled depending on the marine survival category.
Minimum Abundance Threshold
The minimum number of spawners needed for a population of the given size category to achieve a 95 percent probability of persistence over 100 years (a 5 percent (low) risk of extinction) at a given productivity.  Size categories are Basic (500), Intermediate (750), Large (1,000), and Very large (2,000).  Developed by the Interior Columbia Technical Review Team (ICTRT) to partially serve as a metric to evaluate the changing status of the population, its viability and risk level over time. Minimum abundance thresholds are evaluated against a 10-year geomean to determine viability.
Minimum Productivity Threshold
Minimum threshold of a population’s productivity (the average number of surviving offspring per parent).  Productivity is a measure of the population’s ability to sustain itself and can be represented as spawner-to-spawner ratios (returns per spawner or recruits per spawner).  Often represented together, abundance and productivity are linked; above a certain threshold, higher productivity can compensate for lower abundance and vice versa.  Viable populations should demonstrate sufficient productivity to support a net replacement rate of 1:1 or higher at abundance levels established as long-term targets.  Productivity rates at relatively low numbers of spawners should, on the average, be sufficiently greater than 1.0 to allow the population to rapidly return to abundance target levels.
Minimum Viable Population (MVP)
Lower bound on the population of a species, such that it can survive in the wild. More specifically, MVP is the smallest possible size at which a biological population can exist without facing extinction from natural disasters or demographic, environmental, or genetic stochasticity.
Minor Spawning Area (MiSA)
A system of one or more branches that contains sufficient spawning and rearing habitat to support 50 – 500 spawners.  For Interior Columbia salmonid populations: defined using intrinsic potential analysis. 


National Marine Fisheries Service (NMFS)
The National Marine Fisheries Service (NMFS) is a division of the National Oceanic and Atmospheric Administration (NOAA) dedicated to the stewardship of living marine resources through science-based conservation and management, and the promotion of healthy ecosystems. This agency makes decisions about listings of marine and anadromous species under the Endangered Species Act (ESA).
National Oceanic and Atmospheric Administration (NOAA)
The National Oceanic and Atmospheric Administration (NOAA) is a federal agency focused on the condition of the oceans and the atmosphere. The National Marine Fisheries Service (NMFS) is synonymous with the NOAA Fisheries Service.
Nickelson-Lawson Model
One of four extinction-risk models used by the coho Technical Recovery Team (TRT) to evaluate persistence, this particular model is a stochastic, habitat-based life-cycle model adapted from Nickelson-Lawson 1998. The model steps through the coho life-cycle and includes both compensation and depensation at different life stages, with environmental and demographic stochasticity entering the model at each life stage. The dynamics of each population are driven by the quantity and quality of winter habitat, with habitat quality determining smolt capacity and overwinter survival. Egg to parr survival is density-dependent.


The manner in which adults (spawners) are distributed within the freshwater portion of a population's home range.
Salmon most often found in coastal streams, and which tend to migrate to saltwater at a younger age, (e.g. fall chinook).
Oregon Department of Fish and Wildlife (ODFW)
The state agency charged with conserving and managing fish and wildlife populations. The mission of the Oregon Department of Fish and Wildlife is to protect and enhance Oregon's fish and wildlife and their habitats for use and enjoyment by present and future generations.
Oregon Plan for Salmon and Watersheds (OPSW)
The Oregon Legislature and Governor established the Oregon Plan for Salmon and Watersheds in 1997 with the support and participation of a wide spectrum of stakeholders. The original impetus was a State response to listings of coho salmon and other salmon species under the federal Endangered Species Act. The plan aims to restore native fish populations and the aquatic systems that support them to productive and sustainable levels that will provide substantial environmental, cultural, and economic benefits.


A parr is a juvenile fish that is more mature than a fry, but has not yet started to smolt to adapt to salt water entrance. The markings on the sides of fish at this stage are also called parr.
The probability that a population will persist over a specified period of time.
Population Dynamics
Population dynamics describes the ways in which a given population grows and shrinks over time, as controlled by birth, death, and emigration or immigration.
Population Viability Analysis (PVA)
Population viability analysis (PVA) is a process of identifying the threats faced by a species and evaluating the likelihood that it will persist for a given time into the future. It is used to estimate the likelihood of a population’s extinction and indicate the urgency of recovery efforts, as well as to identify key life stages or processes that should be the focus of recovery efforts. PVA is also used to compare proposed management options and assess existing recovery efforts.
The number of offspring that survive to adulthood and return to spawn within a given group of spawning salmon. For salmon, productivity is often divided into freshwater productivity and saltwater productivity (which is in turn sometimes divided into estuarine productivity and ocean productivity).


Quasi-extinction Threshold (QET)
The capacity to breed and recover may be lost before the last individual of a species or population dies. When a population shrinks to such a small size that it is unlikely to recover, this is sometimes referred to as the quasi-extinction threshold. Where to draw the line on that threshold is open to debate. Models labeled QET-1 use a quasi-extinction threshold of only 1 remaining individual. Models labeled QET-50 use a quasi-extinction threshold of 50 individuals.


Recovery Implementation Science Team (RIST)
Group of salmon scientists convened by the Salmon Recovery Team of the National Marine Fisheries Service (NMFS).
The ratio of the number of offspring of a brood that survive to adulthood divided by the number of parents. For coho, recruitment = (# adults harvested + # spawners) / (# spawners 3 years before)
Nests in the gravel of streams or rivers where salmon lay their eggs.
Ricker Model
One of four extinction-risk models used by the coho Technical Recovery Team (TRT) to evaluate persistence. This model is a density-dependent, count-based population viability analysis (PVA) model that assumes that coho salmon recruitment conforms to a Ricker compensatory recruitment function, modified to remove the descending limb of the recruitment curve at higher spawner abundance levels.
The interface between land and a stream. Plant communities along the river banks are called riparian vegetation. Riparian zones are significant in ecology and environmental management because of their role in soil conservation, their biodiversity, and the influence they have on aquatic ecosystems. They can occur in many forms, including grassland, woodland, wetland or even non-vegetative.
Run Timing
The period of time during which a stock of salmon returns to freshwater to spawn.


Species that are members of the family Salmonidae, which includes salmon, trout, chars, freshwater whitefishes, and graylings.
At the smolt stage, salmonids become physiologically adapted to saltwater and begin migrating to saltwater environments.
To produce or deposit eggs; to produce young, especially in large numbers.
Spawner Abundance
The number of adult salmon or steelhead that return to spawning grounds to breed.
Events that happen by chance; random variation. In stochastic processes there are many possibilities of how a process might evolve over time, but some paths may be more probable than others. Stock market fluctuations are an example of a stochastic process.
Evolutionarily significant units (ESUs) can be divided into biogeographic groups (or strata) that each encompass several independent and dependent populations. For example, the Coastal Coho ESU can be divided into five distinct strata: North Coast, Mid Coast, Umpqua, Lakes and Mid-South Coast.
Salmon that tend to migrate to headwater streams of large river systems. They have a longer freshwater residency and thus are more dependent on freshwater habitats (e.g. spring chinook).


Technical Recovery Team (TRT)
A multi-agency team of salmon scientists convened and chaired by the Salmon Recovery Team of the National Marine Fisheries Service (NMFS).


Wind-driven currents are diverted to the right of the winds in the Northern Hemisphere and to the left in the Southern Hemisphere due to the Coriolis effect. The result is a net movement of surface water at right angles to the direction of the wind, known as the Ekman transport. When Ekman transport is occurring away from the coast, surface waters moving away are replaced by deeper, colder, and denser water.


Viable Population \ Viability
An independent population of any Pacific salmonid (genus Oncorhynchus) that has a negligible risk of extinction due to threats from demographic variation, local environmental variation, and genetic diversity changes over a 100-year time frame