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Glossary of Fish Terminology

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Abdominal pelvics — Pelvic fins located on the abdomen far behind the pectoral fins; pelvic bones do not attach to pectoral girdle.

Absolute Recruitment  — The number of fish which grow into the catchable size range in a unit of time (usually a year).

Abundance Index  — Information obtained from samples or observations and used as a measure of the weight or number of fish which make up a stock.

Accessory pelvic appendage  — A tapered fleshy lobe above the base of the pelvic fin.

Acclimate  — The adaptation of an organism to environmental changes.

Acclimation pond  — Concrete or earthen pond or a temporary structure used for rearing and imprinting juvenile fish in the water of a particular stream before their release into that stream.

Adaptation  — Changes in an organism's structure or habits that allow it to adjust to its surroundings.

Adfluvial  — Possessing a life history trait of migrating between lakes or rivers and streams.

Adipose fin  — A small fleshy fin with no rays, located between the dorsal and caudal fins.

Aeration Tank  — A chamber used to inject air into water.

Affluent (Stream)  — A stream or river that flows into a larger one; a Tributary.

Age  — The number of years of life completed, here indicated by an arabic numeral, followed by a plus sign if there is any possibility of ambiguity (age 5, age 5+)1.

Age-class  — A group of individuals of a certain species that have the same age.

Alevin  — The developmental life stage of young salmonids and trout that are between the egg and fry stage. The alevin has not absorbed its yolk sac and has not emerged from the spawning gravels.

Anadromous  — Fish that hatch rear in fresh water, migrate to the ocean (salt water) to grow and mature, and migrate back to fresh water to spawn and reproduce.

Anal fin  — The fin located on the ventral median line and behind the anus.

Annelid -- Term used for an aquatic worm which is a common food for trout and other fish.

Annual (or seasonal) Total Mortality Rate  — The number of fish which die during a year (or season), divided by the initial number. Also called; actual mortality rate, *coefficient of mortality .

Annulus  — A mark or ring that forms annually on the otoliths, scales, and other bones of fish, that correspond to the annual period of slow growth that fish go through. Annuli are used by fish managers to determine age and growth of fish.

Antron A synthetic yarn material made of long sparkly fibers used for many aspects of fly tying including wrapped bodies, spent wings, and trailing shucks. Is also used for dubbing material.

Aquaculture  — The controlled cultivation and harvest of aquatic plants or animals (e.g., edible marine algae, clams, oysters, and salmon).

Assessment level  — Categories of the level of complexity of and data available for each assessment included in this document; index of abundance (INDEX), yield-per-recruit analysis (YIELD), analysis of the age structure of the catch (AGE STRUCTURE), analysis including the relationship between recruitment and spawning stock size (SPAWNING STOCK) and assessment that allows prediction of future (one or two years ahead) stock sizes and catches (predictive). These levels are detailed in the subsection titled Kinds of Assessments.

Availability  — 1. The fraction of a fish population which lives in regions where it is susceptible to fishing during a given fishing season . This fraction receives recruits from or becomes mingled with the non-available part of the stock at other seasons, or in other years. (Any more or less completely isolated segment of the population is best treated as a separate stock.) 2. Catch per unit of effort.

Barbel  — A slender tactile process or fleshy projection located around the head.

Basiobranchial  — The small bones behind the tongue on which the gill arches articulate.

Biological reference points  — Fishing mortality rates that may provide acceptable protection against growth overfishing and/or recruitment overfishing for a particular stock. They are usually calculated from equilibrium yield-per-recruit curves, spawning stock biomass-per-recruit curves and stock recruitment data. Examples are F0.1, Fmax and Fmed.

Brood stock  — Adult fish used to propagate the subsequent generation of hatchery fish.

Buccal  — Pertaining to the cheeks or the cavity of the mouth.

Buoyancy  — The tendency of a body to float or rise when submerged in a fluid.

Button-up fry  — A salmonid fry that has not completely absorbed its yolk sac and has emerged from its spawning gravel.

Captive brood stock  — Fish raised and spawned in captivity.

Carnivorous  — Feeding on animal tissues.

Cartilaginous fishes  — A major group of fishes including sharks and rays.

Catadromous  — Refers to fishes that migrate from fresh water to salt water to spawn or reproduce such as the American eel.

Catch Curve  — A graph of the logarithm of number of fish taken at successive ages or sizes.

Catch Per Unit Of Effort  — The catch of fish, in numbers or in weight, taken by a defined unit of fishing effort. Also called; catch per effort, fishing success, availability.

Catchability  — "The fraction of a fish stock which is caught by a defined unit of the fishing effort. When the unit is small enough that it catches only a small part of the stock -- 0.01 or less--it can be used as an instantaneous rate in computing population change. (For fractions taken of various portions of the stock, see ""vulnerability."") Also called; catchability coeificient, *force of fishing mortality"

Caudal  — Pertaining to the tail.

Caudal fin  — The tail fin.

Caudal peduncle  — The tapering portion of a fish's body between the posterior edge of the anal fin base and the base of the caudal fin.

Coded-wire tag (CWT)  — A small (0.25mm diameter x 1 mm length) wire etched with a distinctive binary code and implanted in the snout of s salmon or steelhead, which, when retrieved, allows for the identification of the origin of the fish bearing the tag.

Conditional Fishing Mortality Rate  — The fraction of an initial stock which would be caught during the year (or season) if no other causes of mortality operated. (Also called fishing mortality rate).

Conditional Natural Mortality Rate  — The fraction of an initial stock that would die from causes other than fishing during a year (or season), if there were no fishing mortality. Also called; annual natural mortality rate, seasonal natural mortality rate.

Critical Size  — The average size of the fish in a year-class at the time when the instantaneous rate of natural mortality equals the instantaneous rate of growth in weight for the year-class as a whole. Also called; *optimum size.

Ctenoid  — Having a comb-like margin.

Ctenoid scales  — A type of fish scale that has spines or ctenii on the posterior or exposed portion, found on bass, walleye, and other fish.

Cycloid scales  — Smooth, flat, round scales that have concentric lines called circuli, found on trout, herring, and other fish.

Descaling — A condition in which a fish has lost a certain percentage of scales.

Distal  — Away from the point of attachment or origin.

Dorsal  — Pertaining to the back, or situated near to or on the back.

Dorsal fin  — The fin located on the back of fishes, and in front of the adipose fin, if it is present.

Dorsal fin ray  — Refers to one of the cartilaginous rays (stiff rods) located in the membrane of a dorsal fin.

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Effeciveness Of Fishing — A general term referring to the percentage removal of fish from a stock, but not as specifically either rate of exploitation or instantaneous rate of fishing.

Egg take  — The number of eggs taken at hatcheries when adult salmon and steelhead are spawned.

Egg-to-smolt survival  — The numerical difference between the number of fertilized eggs produced by a groups of fish and the number of smolts resulting from those eggs.

Emarginate  — Having the margin notched.

Embeddedness  — The degree to which dirt is mixed in with spawning gravel.

Embryo  — The early stages of development before an organism becomes self supporting.

Emergence  — The process during which fry leave their gravel spawning nest and enter the water column.

Emigration  — Referring to the movement of organisms out of an area. See immigration and migrating.

Equlibrium Catch  — The catch (in numbers) taken from a fish stock when it is in equilibrium with fishing of a given intensity, and (apart from the effects of environmental variation) its abundance is not changing from one year to the next.

Equlibrium Yield  — The yield in weight taken from a fish stock when it is in equilibrium with fishing of a given intensity, and (apart from effects of environmental variation) its biomass is not changing from one year to the next. Also called; sustainable yield, equivalent sustainable yield.

Euryhaline  — Having a wide tolerance to salinity.

Even-year run  — A population of fish that returns to its natural spawning grounds in even numbered years.

Exploitation pattern  — The distribution of fishing mortality over the age composition of the fish population, determined by the type of fishing gear, area and seasonal distribution of fishing, and the growth and migration of the fish. The pattern can be changed by modifications to fishing gear, for example, increasing mesh or hook size, or by changing the ratio of harvest by gears exploiting the fish (e.g., gill net, trawl, hook and line, etc.).

Exploitation rate  — 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). For example, if 720,000 fish were caught during the year from a population of 1 million fish alive at the beginning of the year, the annual exploitation rate would be 0.72.

Eyed egg  — A fish egg containing an embryo that has developed enough so the eyes are visible through the egg membrane.

F0.1 — The fishing mortality rate at which the increase in yield-per-recruit in weight for an increase in a unit-of-effort is only 10 percent of the yield-per-recruit produced by the first unit of effort on the unexploited stock (i.e., the slope of the yield-per-recruit curve for the F0.1 rate is only one-tenth the slope of the curve at its origin).

Falcate  — Hooked or curved like a sickle.

Fall-run fish  — Anadromous fish that return to spawn in the fall.

Fecundity  — The total number of eggs produced by a female fish.

Fin Ray  — A soft or hard cartilaginous rod in fins.

Fingerling  — Refers to a young fish in its first or second year of life.

Fishing Effort  — 1. The total fishing gear in use for a specified period of time. When two or more kinds of gear are used, they must be adjusted to some standard type. 2. Effective fishing effort.

Fishing Intensity  — 1. Effective fishing effort. 2. Fishing effort per unit area. 3. Effectiveness of fishing.

Fishing Mortality  — Deaths in a fish stock caused by fishing.

Fishing Power  — The catch which a particular gear or vessel takes from a given density of fish during a certain time interval. For example, larger vessels (horsepower) have a greater ability to catch more fish, thus the greater their fishing power. Also, improvements in a vessel or gear, such as electronic fish finders, can increase fishing power.

Fishway  — A device made up of a series of stepped pools, similar to a staircase, that enables adult fish to migrate up the river past dams.

Fluvial  — Migrating between main rivers and tributaries. Of or pertaining to streams or rivers.

Fmax  — The rate of fishing mortality for a given exploitation pattern rate of growth and natural mortality, that results in the maximum level of yield-per-recruit. This is the point that defines growth overfishing.

Fontanelle  — Unossified gap between cranial bones.

Forage Fish  — Small fish which breed prolifically and serve as food for predatory fish.

Frenum  — Referring to the membrane that binds the lip to the snout or lower jaw.

Fry  — A stage of development in young salmon or trout. During this stage the fry is usually less than one year old, has absorbed its yolk sac, is rearing in the stream, and is between the alevin and parr stage of development.

Game fish  — A fish that is regulated by law for recreational harvest.

Gape  — To open the mouth wide. In Zoological terms, it means the measurement of the widest possible opening of a mouth.

Gill rakers  — A series of projections located along the front edge of the gill arch.

Gills  — The fleshy, and highly vascular organs comparable to lungs used in aquatic respiration.

Grilse  — Salmon less than 22 inches (56cm) Fork Length (FL).

Growth overfishing  — The rate of fishing, as indicated by an equilibrium yield-per-recruit curve, greater than which the losses in weight from total mortality exceed the gain in weight due to growth. This point is defined as Fmax.

Hatch box -- A device used to incubate relatively small numbers of fish eggs. The hatch box is usually located adjacent to a stream, which supplies the box with water.

Healthy stock  — A stock of fish experiencing production levels consistent with its available habitat and within the natural variations in survival for the stock.

Heterocercal  — Said of the tail when the vertebrae curve upward into the upper lobe of the caudal fin.

Home range  — The area that an animal traverses in the scope of normal activities. This is not to be confused with territory, which is the area an animal defends.

Homing  — The ability of a salmon or steelhead to correctly identify and return to their natal stream, following maturation at sea.

Husbandry  — The scientific management and control of the hatchery environment for the production of fish or wildlife.

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Ichthyology  — The scientific study of fishes.

Imbricated  — Lying lapped over each other in regular order (like scales of a fish or shingles on a roof).

Immigration  — Referring to the movement of organisms into an area. See emigration and migrating.

Imprinting  — The physiological and behavioral process by which migratory fish assimilate environmental cues to aid their return to their stream of origin as adults.

Inbreeding  — Mating or crossing of individuals more closely related that average pairs in the population.

Incubation  — The period of time from egg fertilization until hatching.

Inferior mouth  — The type of mouth that opens on the ventral surface (like sturgeon).

Instantaneous Rate Of Fishing Mortality  — When fishing and natural mortality act concurrently, F is equal to the instantaneous total mortality rate, multiplied by the ratio of fishing deaths to all deaths. Also called; rate of fishing; instan- taneous rate of fishing, force of fishing mortality .

Instantaneous Rate Of Growth  — The natural logarithm of the ratio of final weigl1t to initial weight of a fish in a unit of time, usually a year. When applied collectively to all fish of a given age in a stock, the possibility of selective morta lity must be considered .

Instantaneous Rate Of Mortality  — The natural logarithm (with sign changed) of the survival rate. The ratio of number of deaths per unit of time to population abundance during that time, if all deceased fish were to be immediately replaced so that population does not change. Also called; “coefficient of decrease.”

Instantaneous Rate Of Natural Mortality  — When natural and fishing mortality operate concurrently it is equal to the instantaneous total mortality rate, multiplied by the ratio of natural deaths to all deaths. Also called; “force of natural mortality.”

Instantaneous Rate Of Recruitment  — "Number of fish that grow to catchable size per short interval of time, divided by the number of catchable fish already present at that time. Usually given on a yearly basis; that is, the figure just described is divided by the fraction of a year represented by the “short interval” in question. This concept is used principally when the size of the vulnerable stock is not changing or is changing only slowly, since among fishes recruitment is not usually associated with stock size in the direct way in which mortality and growth are."

Instantaneous Rate Of Surplus Production  —  Equal to rate of growth plus rate of recruitment less rate of natural mortality--all in terms of weight and on an instantaneous basis. In a “balanced” or equilibrium fishery, this increment replaces what is removed by fishing, and rate of surplus production is numerically equal to rate of fishing. Also called, “instantaneous rate of natural increase.”

Interorbital  — The space between the eyes.

Invertebrate drift  — Stream and terrestrial invertebrates that float with the current.

Iteroparous  — Species that reproduce repeatedly during their lifetime.

Jack salmon — A young male salmon that matures precociously (earlier than other fish in its age-class).

Jennie salmon  — A young female salmon that matures precociously (earlier than other fish in its age-class).

Jugular pelvics  — Pelvic fins in front of the pectoral fins.

Juvenile  — Fish from one year of age until sexual maturity.

Kelt — A spent or spawned out steelhead salmon.

Krill  — Small abundant crustaceans that form an important part of the food chain in Antarctic waters.

Kype  — The distinctive hooked jaw that male salmon develop during spawning.

Lateral line — A series of sensory pores opening to the exterior along the side of fish.

Length Frequency  — An arrangement of recorded lengths which indicates the number of times each length or length interval occurs.

Lentic  — Characterizing aquatic communities found in standing water.

Limnetic  — Referring to a standing water Ecosystem (ponds or lakes).

Limnology  — The study of lakes, ponds and streams.

Littoral zone  — The region of land bordering a body of water.

Live box  — A container filled with water and often equipped with accessories such as aeration equipment that is used to hold and transport live fish.

Long-term potential catch  — The largest annual harvest in weight that could be removed from a fish stock year after year, under existing environmental conditions. This can be estimated in various ways, from maximum values from production models to average observed catches over a suitable period of years.

Lotic  — Meaning or regarding things in running water.

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Macroinvertebrate — Invertebrates visible to the naked eye, such as insect larvae and crayfish.

Maintainable Yield --The largest catch that can be maintained from the population, at whatever level of stock size, over an indefinite period. It will be identical to the sustainable yield for populations below the level giving the MSY, and equal to the MSY for populations at or above this level.

Mandibular  — Pertaining to the lower jaw.

Maxillae or maxillaries  — The upper jaw, the upper jaw bones.

Maximum Sustainable Yield  — The largest average catch or yield that can continuously be taken from a stock under existing environmental conditions. (For species with fluctuating recruitment, the maximum might be obtained by taking fewer fish in some years than in others.) Also called, maximum equilibrium catch ; maximum sustained yield; sustainable catch.

Mental  — Pertaining to the chin or mentum.

Migrant  — Life stage of anadromous and resident fish species which moves from one locale, habitat or system (river or ocean) to another.

Migrating  — Moving from one area of residence to another.

Milt  — The sperm of fishes.

Mixed stock  — A stock whose individuals originated from commingled native and non-native parents; or a previously native stock that has undergone substantial genetic alteration.

Mortality  — The number of fish lost or the rate of loss.

Myomeres  — The muscle segments.

Natal — Birth place.

Natal stream  — Stream of birth.

Natural Mortality  — Deaths in a fish stock caused by predation, pollution, senility, etc., but not fishing.

Naturally spawning populations  — Populations of fish that have completed their entire life cycle in the natural environment without human intervention.

Net Increase (or decrease)  — New body substance elaborated in a stock, less the loss from all forms of mortality.

Nominal catch  — The sum of the catches that are landed (expressed as live weight or equivalents). Nominal catches do not include unreported discards.

Odd-year run — A population of fish that returns to its natural spawning grounds in odd numbered years, such as the pink salmon.

Opercle  — Refers to the largest bone in the operculum.

Operculum  — The gill cover.

Optimum Yield  — (OY) The yield from a fishery which provides the greatest overall benefit to the nation with particular reference to food production and recreational opportunities; it is based on MSY as modified by economic, social or ecological factors. Precision and Accuracy Precision is the closeness to each other of repeated measurements of the same quantity or object, while accuracy is closeness of a measured or computed value to its true value.

Outmigration  — The migration of fish down the river system to the ocean.

Outplanting  — Hatchery reared fish released into streams for rearing and maturing away from the hatchery sites.

Palatines -- Paired bones in the roof of the mouth, lateral to vomer; may bear teeth.

Papilla  — A small fleshy projection.

Papillose  — Covered with papilla.

Parameter  — "A ""constant"" or numerical description of some property of a population (which may be real or imaginary). Cf. statistic."

Parietals  — Pared bones on posterior roof of skull, lateral to supraoccipital.

Parr  — The developmental life stage of salmon and trout between alevin and smolt, when the young have developed parr marks and are actively feeding in fresh water.

Parr marks  — Distinctive vertical bars on the sides of young salmonids.

Passive Integrated Transponder (PIT) tags  —  Passive Integrated Transponder tags are used for identifying individual salmon for monitoring and research purposes. This miniaturized tag consists of an integrated microchip that is programmed to include specific fish information. The tag is inserted into the body cavity of the fish and decoded at selected monitoring sites.

Pectoral fins  — The anterior(front) paired fins, attached to pectoral (shoulder) girdle.

Pelagic  — Of or in the open ocean or open water.

Pelvic fins  — Posterior paired fins, located in the abdominal position or towards the rear.

Peritoneum  — Membrane lining the body cavity.

Pharyngeal teeth  — Teeth located behind the gills and before the esophagus, and anchored in bone.

Phytoplankton  — Microscopic floating plants, mainly algae, that live suspended in bodies of water and that drift about because they cannot move by themselves or because they are too small or too weak to swim effectively against a current.

Placoid scale  — Small plate-like scales that have a rough exterior edge found on sharks and related species.

Plankton  — Minute floating forms of microscopic plants and animals in water which cannot get about to any extent under their own power. They form the important beginnings of food chains for larger animals.

Pond  — A body of water smaller than a lake, often artificially formed.

Pre-smolt  — A juvenile salmon or steelhead that has not yet reached the physiological state known as a smolt.

Pre-spawning mortality  — Generally refers to non-fishery mortality of adult salmon and steelhead between the time the fish enter the Columbia River and the completion of spawning.

Precocious  — Fish that have matured quickly, or faster than the remaining fish of its age-class.

Predation  — Hunting and killing another animal for food.

Premaxilla  — The paired bones forming the front of the upper jaw.

Preopercle  — The large membrane bone lying in front of and parallel to the opercle.

Preorbital  — The membrane bone lying in front of and below the eye.

Production  — 1. The total elaboration of new body substance in a stock in a unit of time, irrespective of whether or not it survives to the end of that time. Also called, net production, total production. 2.Yield.

Pteryhoids  — Bones of the roof of the mouth lying behind and articulating with the palatines.

Pyloric  — Pertaining to that part of the stomach from which the intestine leads.

Pyloric caecum  — A projection in the form of a blind sac attached to the intestine near the posterior end of the stomach.

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Radio-telemetry —  Automatic measurement and transmission of data from remote sources via radio to a receiving station for recording and analysis.

Ramus  — A branch; a projecting part.

Rate Of Exploitation  — The fraction, by number, of the fish in a population at a given time, which is caught and killed by man during the year immediately following . The term may also be applied to separate parts of the stock distinguished by size, sex, etc. Also called, “fishing coefficient.”

Rate Of Removal  — An inexactly-defined term that can mean either rate of exploitation or rate of fishing--depending on the context .

Rate Of Utilization  — Similar to rate of exploitation, except that only the fish landed are considered. The distinction between catch and landings is important when considerable quantities of fish are discarded at sea.

Ray  — One of the supports of a fin.

Rear  — To feed and grow in a natural or artificial environment.

Rearing  — Refers to the amount of time that juvenile fish spend feeding in nursery areas of rivers, lakes, streams and estuaries before migration.

Recruitment overfishing  — The rate of fishing above which the recruitment to the exploitable stock becomes significantly reduced. This 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.

Recruits  — The total numbers of fish of a specific stock available at a particular stage of their life history.

Redd  — A nest of fish eggs covered with gravel.

Relative Abundance  — An estimate of actual or absolute abundance; usually stated as some kind of index; for example, as bottom trawl survey stratified mean catch per tow.

Reproduce  — To produce offspring.

Resident species  — Species of fish which spend their entire lives in freshwater.

Roe  — The eggs of fishes.

Rough Fish  — Those species of fish considered to be of either poor fighting quality when taken on tackle or of poor eating quality, such as carp, gar, suckers, etc. Most species in this group are more tolerant of widely fluctuating environmental conditions than Game Fish.

Run (of fish)  — A group of fish of the same species that migrate together up a stream to spawn, usually associated with the seasons, e.g., fall, spring, summer, and winter runs. Members of a run interbreed, and may be genetically distinguishable from other individuals of the same species.

Salmonid -- Fish of the family Salmonidae, that includs salmon and steelhead.

Sand  — Small substrate particles, generally referring to particles less than 2 mm in diameter. Sand is larger than silt and smaller than cobble or rubble.

Scute  — An extendal bony plate, usually keeled.

Sediment  — The organic material that is transported and deposited by wind and water.

Semelparous  — Species that reproduce only once during their lifetime.

Silt  — Substrate particles smaller than sand and larger than clay.

Smolt  — Refers to the salmonid or trout developmental life stage between parr and adult, when the juvenile is at least one year old and has adapted to the marine environment.

Smoltification  — Refers to the physiological changes anadromous salmonids and trout undergo in freshwater while migrating toward saltwater that allow them to live in the ocean.

Spawn  — The act of reproduction of fishes. The mixing of the sperm of a male fish and the eggs of a female fish.

Spawning stock biomass (SSB)  — The total weight of all sexually mature fish in the population. This quantity depends on year class abundance, the exploitation pattern, the rate of growth, fishing and natural mortality rates, the onset of sexual maturity and environmental conditions.

Spine  — A single, median supporting element of a fin, usually stiff. Distinguished from a ray in that it is single, median, never branched or jointed.

Standard length  — The straight distance between the tip of the snout and the base of the caudal fin rays.

Standardization  — The procedure of maintaining methods and equipment as constant as possible.

Status of exploitation  — An appraisal of exploitation is given for each stock discussed in the Species Synopsis section using the terms unknown, protected, not exploited, underexploited, moderately exploited, fully exploited, and over-exploited. These terms describe the effect of current fishing effort on each stock, and is based on current data and the knowledge of the stocks over time.

Stock  — A specific population of fish spawning in a particular stream during a particular season.

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 which are old enough to reproduce.

Stone  — Rock fragments larger than 25.4 cm (10 inches) but less than 60.4 cm (24 inches).

Straying  — A natural phenomena of adult spawners not returning to their natal stream, but entering and spawning in some other stream.

Subabdominal pelvic fin  — Said of pelvic fins when placed forward on abdomen but not attached internally to pectoral girdle.

Subadult  — A developmental life stage when fish exhibit most but not all traits of an adult fish.

Subpopulation  — A well-defined set of interacting individuals that compose a proportion of a larger, interbreeding population.

Subspecies  — A population of a species occupying a particular geographic area, or less commonly, a distinct habitat, capable of interbreeding with other populations of the same species.

Subyearling  — A developmental life stage of fish that are less than one year old.

Success (of fishing)  — Catch per unit of effort.

Supramaxilla  — A small bone attached to the posterior end of the maxilla, dorsally.

Surplus Production  — Production of new weight by a fishable stock, plus recruits added to it, less what is removed by natural mortality. This is usually estimated as the catch in a given year plus the increase in stock size (or less the decrease). Also called; natural increase, sustainable yield, equilibrium catch .

Survival Rate  — Number of fish alive after a specified time interval, divided by the initial number. Usually on a yearly basis.

Sustainable yield  — The number or weight of fish in a stock that can be taken by fishing without reducing the stock biomass from year to year, assuming that environmental conditions remain the same.

Swim-up fry  — A salmonid fry that is swimming in the water column in search for food.

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TAC — Total Allowable Catch is the total regulated catch from a stock in a given time period, usually a year.

Terminal mouth  — Said of the location of the mouth when it opens at the end of the head, as in trout.

Territory  — The area that an animal defends, usually during breeding season, against intruders of its own species.

Thoracic pelvics  — Said of the pelvic fins when attached immediately below the pectorals and connected internally with the pectoral girdle.

Truncate caudal  — Said of the margin of the caudal fin when it is squared off as in some catfish.

Trunk myomeres of lampreys  — The number of body segments between the last gill opening and the cloacal slit.

Undulating — To move in waves. Referring to the movement of a female fish's tail in a waving motion used to move gravel for the construction of a redd.

Upriver Bright stock (URB)  — A stock of fall chinook destined for the Columbia River and several tributaries upstream from The Dalles Dam. These fish enter the Columbia from early August with the peak of the run at Bonneville Dam in early September.

Upwelling  — The movement of nutrient rich waters from the bottom of the ocean to the surface.

Usable Stock  — The number or weight of all fish in a stock that lie within the range of sizes customarily considered usable (or designated so by law). Also called, standing crop.

Utilized Stock, Utilized Population  — The part, by number, of the fish alive at a given time, which will be caught in future.

Ventral fins — See pelvic fins.

Vermiculations  — Irregular lines or impressions like worm tracks.

Virtual Population  — Utilized stock.

Virtual population analysis (or cohort analysis)  — An analysis of the catches from a given year class over its life in the fishery. If 10 fish from the 1968 year class were caught each year for 10 successive years from 1970 to 1979 (age 2 to age 11), then 100 fish would have been caught from the 1968 year class during its life in the fishery. Since 10 fish were caught during 1979, then 10 fish must have been alive at the beginning of that year. At the beginning of 1978, there must have been at least 20 fish alive because 10 were caught in 1978 and 10 more were caught in 1979. By working backward year by year, one can be virtually certain that at least 100 fish were alive at the beginning of 1970. A virtual population analysis goes a step further and calculates the number of fish that must have been alive if some fish also died from causes other than fishing.

Vomer — The most anterior bone of the roof of the mouth; may bear teeth.

Warmwater fish — A broad classification on non-salmonid fish that generally have at least one spiny ray, have pelvic and pectoral fins located behind the gills, and are usually suited for water that consistently exceeds 70 degrees F.

Weak stock  — Listed in the Integrated System Plan's list of stocks of high or highest concern; listed in the American Fisheries Society report as at high or moderate risk of extinction; or stocks the National Marine Fisheries Service - National Oceanic and Atmospheric Administration (NOAA) has listed. “Weak stock” is an evolving concept; the Council does not purport to establish a fixed definition. Nor does the Council imply that any particular change in management is required because of this definition.

Weir (fish trap)  — Usually a barrier constructed to catch upstream migrating adult fish.

Wild populations  — Fish that have maintained successful natural reproduction with little or no supplementation from hatcheries.

Wild stock  — A stock that is sustained by natural spawning and rearing in the natural habitat, regardless of parentage (includes native).

Year class (or cohort)  — Fish in a stock born in the same year. For example, the 1987 year class of cod includes all cod born in 1987, which would be age 1 in 1988. Occasionally, a stock produces a very small or very large year class which can be pivotal in determining stock abundance in later years.

Yearling — A one year old fish.

Yield-per-recruit  — The expected lifetime yield-per-fish of a specific age (e.g., per age 2 individual). For a given exploitation pattern, rate of growth, and natural mortality, an expected equilibrium value of Y/R can be calculated for each level of F.

Yolk  — The food part of an egg.

Zooplankton — Small aquatic animals that are suspended or swimming in water.

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