The minimum landing size (MLS) is the smallest

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

at which it is legal to keep or sell a

fish Fish are Aquatic animal, aquatic, craniate, gill-bearing animals that lack Limb (anatomy), limbs with Digit (anatomy), digits. Included in this definition are the living hagfish, lampreys, and Chondrichthyes, cartilaginous and bony fish as we ...

. 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 Trawling is a method of fishing that involves pulling a fishing net through the water behind one or more boats. The net used for trawling is called a trawl. This principle requires netting bags which are towed through water to catch different spec ...

and

seine ) , mouth_location = Le Havre/ Honfleur , mouth_coordinates = , mouth_elevation = , progression = , river_system = Seine basin , basin_size = , tributaries_left = Yonne, Loing, Eure, Risle , tributa ...

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 Any cause that reduces or increases reproductive success in a portion of a population potentially exerts evolutionary pressure, selective pressure or selection pressure, driving natural selection. It is a quantitative description of the amount of ...

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 Australian mainland and many of its islands, such as Tasmania, Fraser Island, Hinchinbrook Island, the Tiwi Islands, and Groote Eylandt, but excluding the Torres Strait ...

around

Moreton Bay Moreton Bay is a bay located on the eastern coast of Australia from central Brisbane, Queensland. It is one of Queensland's most important coastal resources. The waters of Moreton Bay are a popular destination for recreational anglers and are ...

had a practice based on

traditional knowledge Traditional knowledge (TK), indigenous knowledge (IK) and local knowledge generally refer to knowledge systems embedded in the cultural traditions of regional, indigenous, or local communities. According to the World Intellectual Property Or ...

which avoided this pitfall. The mullet is a migratory fish, being present around different areas of

Moreton Island Moreton Island (Mulgumpin) is an island on the eastern side of Moreton Bay on the coast of South East Queensland, Australia. The Coral Sea lies on the east coast of the island. Moreton Island lies northeast of the Queensland capital, Brisban ...

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

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