Glossary of Fish Terminology
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
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
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
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
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
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
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
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
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
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
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
Effeciveness Of Fishing — A general term referring to the percentage removal of
fish from a stock, but not as specifically defined.as 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
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
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
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
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 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
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
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
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
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
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
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
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
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
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
Juvenile — Fish from one year of age until
Kelt — A spent or spawned out
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
Length Frequency — An arrangement of recorded
lengths which indicates the number of times each length or length
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
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
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
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
Mortality — The number of fish lost or the rate
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 — 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
Pectoral fins — The anterior(front) paired
fins, attached to pectoral (shoulder) girdle.
Pelagic — Of or in the open ocean or open
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
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
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
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
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
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
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,
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
Subyearling — A developmental life stage of
fish that are less than one year old.
Success (of fishing) — Catch per unit of
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
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.
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
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
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
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
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
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
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
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.