The minimum landing size (MLS) is the smallest

fish measurement Fish measurement is the measuring of individual fish and various parts of their anatomies, for data used in many areas of ichthyology, including taxonomy and fishery biology. Overall length Standard length (SL) is the length of a fish measured ...

at which it is legal to keep or sell a

fish A fish (: fish or fishes) is an aquatic animal, aquatic, Anamniotes, anamniotic, gill-bearing vertebrate animal with swimming fish fin, fins and craniate, a hard skull, but lacking limb (anatomy), limbs with digit (anatomy), digits. Fish can ...

. The MLS depends on the species of fish. Sizes also vary around the world, as they are legal definitions which are defined by the local regulatory authority. Commercial trawl and

seine The Seine ( , ) is a river in northern France. Its drainage basin is in the Paris Basin (a geological relative lowland) covering most of northern France. It rises at Source-Seine, northwest of Dijon in northeastern France in the Langres plat ...

fisheries can control the size of their catch by adjusting the mesh size of their nets.

Effect of selection on fish sizes

The idea behind this limitation is that only the older, mature fish get taken, leaving juveniles behind to continue breeding and propagating their species. There is some criticism of this legal requirement, however, as it applies selection pressure to the fish: as the larger fish get taken, the genes for larger size are reduced or removed from the gene pool, while fish that mature at a smaller size continue breeding. The average size of fish shrinks over time. This has led to a collapse in the amount of fish being caught in some fisheries.

Aboriginal Australians Aboriginal Australians are the various indigenous peoples of the Mainland Australia, Australian mainland and many of its islands, excluding the ethnically distinct people of the Torres Strait Islands. Humans first migrated to Australia (co ...

around Moreton Bay had a practice based on traditional knowledge which avoided this pitfall. The mullet is a migratory fish, being present around different areas of Moreton Island at different times of the year. Traditional knowledge said that at some points of their migration path, people could only harvest smaller fish, since the larger (and older) fish needed to pass on their knowledge of the migration path. If the older fish were taken at this point, the mullet would swim away from the shore, to the open sea, and this food source would be lost forever. This explanation does not align with scientific knowledge of fish migration, however, the practice did sustain the fishery for several thousand years. Taking only smaller fish applied selection pressure which encouraged the fish to grow to a larger size faster. The area and season at which the traditional knowledge said that fish of all sizes could be taken just so happened to be a point after the mullets' annual spawn, and so did not have a detrimental effect on the future population size.Barker, Tanuja and Ross, Annie (2020
". Exploring cultural constructs: the case of sea mullet management in Moreton Bay, south east Queensland, Australia"
'Putting Fishers’ Knowledge to Work– Conference Proceedings.''

Effect of selection on fish sizes

See also

References

Other Links