Northwest Fisheries Science Center


Age Class
Age at maturity, which may differ among fish of the same year class.  For example, among wild Snake River spring Chinook born in 2003, 8% may mature as jacks, 73% after 2 years in the ocean, and 19% after 3 years. 
Aleutian Low
A semi–permanent, subpolar area of low pressure located in the Gulf of Alaska near the Aleutian Islands.  It is a generating area for storms, and migratory lows often reach maximum intensity in this area.  It is most active from late fall to late spring.  During summer, it is weaker, retreating toward the North Pole and becoming almost nonexistent.   During this time, the North Pacific High pressure system dominates (NOAA National Weather Service).  Courtesy of NOAA National Weather Service
California Current
The California Current System (CCS) is a southward–flowing ocean current found along the west coast of North America, beginning at the northern tip of Vancouver Island, Canada, and ending near the southern tip of Baja California/Mexico.  It is one of four elements of the anticyclonic North Pacific Gyre.  The North Pacific Gyre includes the southward–flowing California Current, the westward–flowing North Pacific Equatorial Current (which flows toward Japan), the Kuroshio Current (which flows north along Japan) and the North Pacific Current (which flows eastwards towards North America). 
We define catch per unit effort (CPUE) as the number of a particular species caught per kilometer traveled with the trawl under tow.  However, CPUE is a relative and indirect measure of fishing effectiveness or species abundance.  "Catch" can mean weight or numbers of total catch or of a particular species.  "Units of effort" can be measured as individual cruises, the number of sets of a fishing net (or casts of a line), or as units of time or distance. 
Geostrophic Wind
A wind that is affected by Coriolis force, blows parallel to isobars and whose strength is related to the pressure gradient (i.e., spacing of the isobars).  Courtesy of NOAA National Weather Service
For salmon, the proportion of a population that returns as an adult to spawn in the natal stream (having "escaped" the catch in ocean fisheries).
Ichthyoplankton are the eggs and larvae of fish. They are usually found in the sunlit zone of the water column, less than 200 meters deep, which is sometimes called the epipelagic or photic zone. Ichthyoplankton are planktonic, meaning they cannot swim effectively under their own power, but must drift with the ocean currents.
A "Jack" is a male Chinook or coho salmon that returns to spawn prematurely, before growing to the size of a normal adult.  Jacks stay in the ocean from a few months to a year, returning to the natal stream 1–2 years before normal adults of their age class.  Thus numbers of returning jacks are sometimes used as a basis to predict run size the following year. 
NH 05
A sampling station located 5 miles offshore along the Newport Hydrographic Line, a transect of established stations used in oceanographic sampling by NWFSC research teams since the mid-1970s (Figure 1).  Findings at this station are often used as a reference point for ocean ecosystem indicator data. 
Northern California Current
The Northern California Current (NCC) is generally taken to be that part of the California Current that lies between the northern tip of Vancouver Island and the Oregon–California border, between Cape Blanco OR/Cape Mendocino CA.  This portion of the CC shows a generally weak meandering flow year–round, which more–or–less flows parallel to the coast.  It is characterized by strong seasonality in winds, upwelling, and biological productivity.  Winter winds in the NCC are usually from the south or west, whereas summer winds are from the north and cause coastal upwelling. 
North Pacific High
The North Pacific High pressure system is a region of high sea-level pressure that occurs over the sub-tropical eastern North Pacific Ocean (Kenyon 1999). It is the dominant atmospheric pressure system influencing the northern California Current during the summer months, whereas the Aleutian Low is dominant from late fall to late spring.
Oblique Tow
A tow made by pulling the net at a slow tow speed from the sea floor to the surface.  Under this configuration, the angle between the net and sea floor is maintained at 45 degrees. 
Oceanic Nino Index (ONI)
The temperature anomaly within the Niño 3.4 region, averaged over a 3-month period. Values, and additional information, can be found at The next link/button will exit from NWFSC web site
OPIH (Oregon Production Index, Hatchery)
For coho, an estimate of total freshwater escapement, adjusted for ocean and freshwater catch, for public hatchery fish throughout the Oregon Production Index Area.  Private hatchery production is removed from this estimate, so it reflects only public hatchery fish.  Used as the numerator in calculating SARs for the OPIH.
The factors influencing salmon marine survival or adult return numbers are numerous. We recognize that the primary drivers of mortality may vary from year to year. Although any given indicator may be correlated with survival, there may be years where the correlation does not hold (ie, years when the primary driver of mortality is a set of conditions unrelated to this indicator). Therefore, we expect many of the indicators to have outlier years, where the value of thee indicator does not reflect the mechanisms of mortality. Because we do not know the exact mechanism driving mortality each year, we chose a statistical measure to identify and remove outlier years from many of our analyses. Specifically, we calculated Cook's Distance (Cook 1979) and used a cutoff of 4/N (Bollen and Jackman 1990) to identify outlier years. Although we show these years in our plots, we excluded them from analyses when creating out outlooks.
Number or proportion of biomass added to a fish population as a result of growth or reproduction, especially for a given year class. 
Secchi Disk
A device to measure the turbidity (transparency) of the upper water column.  A 30–cm diameter white disc is lowered slowly through the upper water column to the point at which the pattern is no longer visible.  The depth of the disk is then taken as a measure of transparency or turbidity. 
SAR (smolt–to–adult ratio)
For a population of salmon, the number from a given year class that survived to the smolt stage (i.e., migrated as juveniles) divided by the total number of returning adults from that year class (all age classes combined). 
The term "teleconnection pattern" refers to a recurring and persistent, large–scale pattern of pressure and circulation anomalies that spans vast geographical areas. Teleconnection patterns are also referred to as preferred modes of low–frequency (or long time–scale) variability.  Courtesy of the NOAA National Weather Service Climate Prediction Center
A device for measuring beam attenuation, which can be used as a measure of turbidity in water.  A beam of light is cast through the water and the transmissometer records the measure of light at a given point past the source of the beam. 
Year Class
Fish of the same species and stock that are born in the same year.