A Honeymoon for Fish14.04.2020
Banning fishing in the Mediterranean during breeding season
Spring is the most romantic time in nature. All the flora and fauna are busy with courtship and mating – the flowers are flowering, the birds are chirping, and the fish are breeding. At this time, “their minds are elsewhere” and the fish are more susceptible to fishing. In order to let fish reproduce in peace, we must stop fishing during the breeding season.
Every year, the fishing department determines the dates most suitable for fishing bans based on the timing of breeding seasons. Different habitats are used by fish at different stages of breeding, spawning, and recruitment. In most cases, in rocky habitats, a large number of adult fish gather for courtship and breeding, which results in a large number of new offspring; while in soft sandy substrates we might find large numbers of juvenile fish during certain seasons. However, there are species where the situation is reversed: adult fish in the sand during breeding season, and juvenile fish recruited in the rocky areas.
Along the Israeli coast there are over 80 fish species that form part of the fishing catch. Each species has its own spawning and growing conditions, but most often, environmental conditions such as temperature and food availability create species synchronization during the breeding season and recruitment.
Fish are also “recruited”. What does this actually mean?
After breeding season and egg development, the juvenile fish begin to look for a school to join. The youngest fish (larvae) get swept away with the currents and spread out into the sea. At the end of this stage, when the fish are one to a few-months old, the juvenile fish begin a “recruitment” process: they gather (mainly in sandy substrates) and join adult fish schools. Therefore, during the recruitment season, there are a large number of fish present, but they are predominantly young and of low economic value. The recruitment times of the various species can be estimated mainly by examining and measuring the trawler fishing catch.
Fishing bans at different times:
Gill nets and sport fishing mainly focus on the species that live and reproduce in rocky substrates. During the breeding season their stomachs are filled with sperm and egg cells. To allow the fish to reproduce in peace, coastal and sport fishing have been banned during breeding season. A few months after spawning season, juvenile fish reach the recruitment stage, especially in sandy habitats.
Prohibition on fishing groupers and meagers:
Some fish species cluster for breeding purposes. Therefore, during the breeding season, many individuals of the same species can be found in one area. Such clustering is typical of ‘grouper’ fish. Groupers are usually territorial and do not interact with each other most of the year. Therefore, they need regular meeting places to breed. In addition, during the gathering time, individuals involved in reproduction show a behavioral shift which makes them less aware of their environment. This makes the species much more susceptible to fishing during breeding season; catching them during this season can cause huge damage to the adult reproductive population – a real danger to the continued existence of the next generation. In addition to groupers, the meagres are another fish family that is important to protect.
During the breeding season, the rangers of the INPA’s Marine Unit will enforce the fishing ban in all parts of the country and at all hours of the day.
How do we determine when to ban fishing?
The reproductive fitness of a fish is determined by its size at maturity and by measuring fertility levels. Timing of the breeding season is mainly affected by food availability and various environmental conditions such as tides, day and night, and water temperature.
One of the most important and common metrics for determining the breeding season and fertility levels of each species and/or population is the gonadosomatic index: the weight of the reproductive organs relative to the total weight of the fish. During breeding season, the reproductive organs grow, and the ratio of reproductive organs to fish size increases as the fish approaches its peak breeding season.
Each species of fish has a characteristic gonadosomatic index and a typical rate of change. For example, in species with a short breeding season of just one month, the weight of the reproductive organs peaks quickly. In other species with much longer breeding seasons of up to five months, the reproductive organs develop more slowly or are at peak maturity for a length of time.
In order to decide the best time to ban fishing, the breeding times of most species are examined, and dates are chosen that protect the majority of the breeding fish populations.
Protecting the fish during breeding season is intended to ensure that we have a sea rich in fish, whether we are commercial fishers, sport fishers, or simply people who love the sea.
Translated by Daphna Shapiro Goldberg