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A common type of seine is a purse seine, named such because along the bottom are a number of rings. A line (referred to as a purse-line) passes through all the rings, and when pulled, draws the rings close to one another, preventing the fish from "sounding", or swimming down to escape the net. This operation is similar to a traditional style purse, which has a drawstring. The purse seine is a preferred technique for capturing fish species which school, or aggregate, close to the surface: sardines, mackerel, anchovies, herring, and certain species of tuna (schooling); and salmon soon before they swim up rivers and streams to spawn (aggregation). Boats equipped with purse seines are called purse seiners.
Purse seine fishing can be a relatively sustainable way of fishing, as it can result in smaller amounts of by-catch (unintentionally caught fish), especially when used to catch large species of fish (like herring or mackerel) that shoal tightly together. When used to catch fish that shoal together with other species, or when used in parallel with fish aggregating devices, the percentage of by-catch greatly increases.
Use of purse seines is regulated by many countries. In Sri Lanka, using this type of net within 7 kilometers of the shore is illegal. However, they can be used in the deep sea, after obtaining permission from authorities. Purse seine fishing can have negative impacts on fish stocks because it can involve the bycatch of non-target species and it can put too much pressure on fish stocks.