Researchers in the International Commission for the Conservation of Atlantic Tunas (ICCAT) and Tagging of Pacific Predators (TOPP) have been tracking bluefin tuna on a scale so large it has never been done before in an attempt to determine their migration patterns so as to overcome overfishing affecting this readily declining species.
Using electronic tags and chemical signatures in the form of oxygen isotopes, researchers have discovered distinct bluefin tuna populations in the Gulf of Mexico, Mediterranean Sea, California current large marine ecosystem (CCLME), and North Pacific transition zone (NPTZ) which have explicit migratory routes. By following the annual movements of bluefin tuna in relation to ocean processes such as temperature, their population can be better managed to avoid reduction in their numbers.
Bluefin tunas exhibit natal homing, meaning adults return to their natal birthplace to reproduce. By tracking the tuna using oxygen isotopes in their otholiths, or ear stones, their spawning areas were discovered in both the Gulf of Mexico and Mediterranean Sea, allowing for control of fishing in these areas to be thusly changed to allow reproduction to effectively proceed. Understanding these migratory routes of the bluefin tunas can allow population baselines to be established in both areas so numbers do not drop dangerously low.
The northern slope waters of the Gulf of Mexico are a critical habitat for bluefin tuna when spawning season is in place, thus protection of the tuna at this time is integral so the population can replenish itself. Knowing this, time-area closures could be implemented to reduce the incidental catch of bluefin tuna attempting to spawn by fisheries operating in the Gulf of Mexico.
The CCLME is an area of high productivity, meaning large amounts of vegetation for consumption by prey of the tuna, which the tuna then consume, while the NPTZ serves as an east-west migration corridor, making both areas popular locations for bluefin tuna habitation and migration. During warmer months, bluefin tuna tend to range farther north where the water is cooler. Knowledge of this is useful to fisheries when they plan on fishing in these areas. If the tuna migrate northerly in certain months, fisheries can now utilize this information to change their catch numbers, since constant catch rates are not appropriate if the population of fish in the area is changing at certain times of the year. This can keep overfishing of this species from continuing further.
Long-term observations of the movements of marine predators can provide information on the spatial extent of the migratory populations of many species including bluefin tuna and also the potential rates of exchange among these populations. Comprehending migratory routes can lead to understanding of the harmful effect of industrial fishing on fish populations that may be in steep decline and on the verge of endangerment.
By improving understanding of the three-dimensional distribution of any species, not just bluefin tuna, it could better inform management protocols to reduce the bycatch of species that are either threatened or endangered. This information is beneficial for effective management of resources and zoning of areas that support significant predator populations in order to avoid their decline so that the biodiversity of these locations is not essentially lost.
