Net and hook gears have been used throughout history and, before the industrial revolution, were the main methods of fish capture. In modern fisheries, their importance is overshadowed by various ‘bag’ type gears such as towed gears (trawls and seines) or encircling gears (purse seines). However, gillnets and longlines have some advantages and are therefore still popular in a number of fisheries; for example, they are cheap to purchase and use. They are also technologically simple, easy to mend and require little in the way of the equipment on board the vessels used for the fisheries. The gears may be set in areas with difficult bottom conditions, as are often found around coral reefs, in coastal rocky areas or in fresh water bodies where towed gears cannot be used. For these reasons, gillnets and longlines are commonly used in a number of artisanal fisheries from the tropics to the arctic. Gillnets and longlines are also found to be economically advantageous in those fisheries targeting large and expensive fish species that are relatively thinly distributed, e.g. tuna, salmon and halibut. These fisheries are capital intensive ventures applying sophisticated handling systems that allow large amounts of gear to be deployed.
Being passive gears, the energy consumption is generally low implying an environmental advantage compared to the more energy consuming fisheries using towed gears. However, significant environmental problems are found in some fisheries due to by-catches of marine birds (mainly longlines) or marine mammals (gillnets).
From a fisheries research perspective there are good reasons to treat gillnets and longlines together despite the apparent differences regarding both the gear encounter process and the way that the fish are caught. The selective properties of both gear types are typically estimated by the same indirect estimation methods. These methods are conceptually more complicated than the direct estimates used for towed gears. Many selection studies are still carried out by simple non-parametric procedures developed for gillnets in the 1960s (e.g. McCombie and Fry 1960, Gulland and Harding 1961, Holt 1963) despite the existence of a number of parametric methods that have been introduced in the last decade.
For stock monitoring purposes, gillnets and longlines share the virtue of being deployable in areas with a difficult bottom, which cannot be covered by trawl surveys. Gillnets are typically used as a survey gear in fresh water bodies, but both gears may also be useful for covering various marine areas, e.g. coastal habitats and very deep waters. Both gear types suffer from being potentially saturated as the number of available catching sites (meshes or hooks) may decline during the fishing operation. Being passive gears deployed for several hours also implies that fishing station allocations will typically differ from those used in trawl surveys.