Glossary of Fishery Terms - S

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• Salinity gradient - Salinity gradient: Change in salinity with depth, expressed in parts per thousand per metre. See halocline.

• Sample - A relatively small part of a fish stock which is removed for study, and which ideally is representative of the whole. The greater the number and size of the samples, the greater the confidence that the information obtained accurately reflects the status (such as abundance by number or weight, or age composition) of the stock.

• Seamounts - underwater mountains rising at least 1000 metres above the sea floor.

• Sea grass - members of marine seed plants that grow chiefly on sand or sand-mud bottom. They are most abundant in water less than 10 metres deep. Common types are eel grass, turtle grass and manatee grass.

• Selectivity - ability of a type of fishing tackle or gear to catch a certain size or kind of fish, compared with its ability to catch other sizes or kinds.

• Seashore - the coast or that part of the land adjoining or near the ocean. See intertidal zone.

• Shelf break - where the continental shelf and continental slope meet. At the shelf break, the more gently sloping region of the seabed adjacent to a landmass rather abruptly slopes moresteeply down towards the ocean depths, commonly around depths of 200 metres.

• Shellfish - general term for aquatic invertebrates (molluscs, crustaceans and echinoderms).

• Shoal - or sandbar is a somewhat linear landform within or extending into a body of water, typically composed of sand, silt or small pebbles. Bars can appear in the sea, in a lake, or in a river.

• Shoaling - describes the behaviour of fish which aggregate together, including mixed species groups. Fish derive many benefits from shoaling behaviour including defence against predators through better predator detection and by diluting the chance of capture, enhanced foraging success, and higher success in finding a mate. It is also likely that fish benefit from shoal membership through increased hydrodynamic efficiency.

• Shore - A shore or shoreline is the fringe of land at the edge of a large body of water, such as an ocean, sea, or lake. A shore of unconsolidated material is usually called a beach. See intertidal zone.

• Simulation - An analysis that shows the production and harvest of fish using a group of equations to represent the fishery. It can be used to predict events in the fishery if certain factors change. See population dynamics.

• Socioeconomics - A word used to identify the importance of factors other than biology in fishery management decisions. For example, if management results in more fishing income, it is important to know how the income is distributed between small and large boats or part-time and full-time fishermen.

• Spawning - the production or depositing of large quantities of eggs in water.

• Species - a group of organisms capable of interbreeding and producing fertile offspring.

• Species density - the number of species in a sampled area.

• Species group - a group of similar species. Similar species are often difficult to differentiate without detailed examination.

• Sport fishery - See recreational fishery.

• Stakeholder - anyone who has a stake or interest in the outcome of the project, as well as anyone one who is affected by the project.

• Standardization - procedures which maintain methods and equipment as constant as possible. Without standardization one cannot determine whether measurements of yearly differences in relative abundance are caused by actual fluctuations in stock abundance or by differences in the measurement procedure used. Lack of standardization is one reason why surveys using different commercial fishing vessels in different years do not produce comparable information. For example, if two vessels of different horsepower are used in separate years, the results can't be compared unless vessel mensuration experiments are performed. This would involve comparing the two vessels' catches to determine the influence of their fishing power on the size of the catch, and a determination of a correction factor.

• Stock - group of fish of the same species (for example, snapper) that occupy a defined area of the ocean. Fish stocks are the basis of fisheries’ management. Not to be confused with stockfish.

• Straddling stocks - A term defined by the United Nations as "stocks of fish such as pollock, which migrate between, or occur in both, the economic exclusion zone of one or more states and the high seas". They can contrasted with transboundary stocks. A stock can be both transboundary and straddling.

• Subantarctic waters - waters adjacent to, but not within, the Antarctic circle (about 66030'S).

• Subtropical waters - waters adjacent to, but not within, the tropics.

• Super seiner - a large purse seiner, usually over 70 metres long, with freezing and storage facilities, and capable of fishing for an extended period in open oceans.

• Surf - collective term for breakers. Also the wave activity in the area between the shoreline and the outermost limit of breakers.

• Surf zone - As ocean surface waves come closer to shore they break, forming the foamy, bubbly surface called surf. The region of breaking waves defines the surf zone.

• Surface ocean currents - surface currents are generally wind driven and develop typical clockwise spirals in the northern hemisphere and counter-clockwise rotation in the southern hemisphere. In wind driven currents, the Ekman spiral effect results in the currents flowing at an angle to the driving winds. Surface currents make up about ten percent of the water in the ocean, and are generally restricted to the upper 400 meters. They can be contrasted with deep ocean currents, which are driven by density and temperature gradients.

• Surplus production - Surplus production is the inherent productivity of a fish stock that can be harvested on a sustainable basis. Based on the theory that, at large stock size, reproductive rates and rate of stock growth are slowed by self-regulating mechanisms, and that stock growth rates are faster after removals, as the stock attempts to rebuild. In theory, fishing can be moderated to take advantage of the more productive stock growth rates, provided that it does not exceed the stock recovery capacity.

• Sustainable fishing - fishing activities that do not cause or lead to undesirable changes in biological and economic productivity, biological diversity, or ecosystem structure and functioning, from one human generation to the next.

• Sustainable yield - Sustainable yield is the catch that can be removed over an indefinite period without causing the stock to be depleted. This could be either a constant yield from year to year, or a yield which is allowed to fluctuate in response to changes in abundance.