El Niño-Southern Oscillation can affect tuna fish in the Indian Ocean, says FAO report

El Niño-Southern Oscillation can affect tuna fish in the Indian Ocean, says FAO report

Subject: Environment

Section: Climatology

Context- Along the same lines, the international food agency has published a report titled El Niño Southern Oscillation (ENSO) Effects on Fisheries and Aquaculture, which captures the impacts of ENSO events on global fisheries.

Concept-

Impact on fisheries in the Pacific:

• El Niño, described as an unusual and warm ocean current off the coast of Peru.
• In the Pacific Ocean, during the warm (El Niño) phase, the thickness of the top layer of the eastern Pacific Ocean classically increases, thus preventing cold and nutrient-rich deep waters from reaching the surface, dampening primary production, on which fish depend for food.
• In the eastern Pacific, small pelagic fish such as anchovy can be dramatically impacted while more tropical pelagic fish, like tuna or dolphin fish, are favoured and become more accessible to fishers close to the coast.
• Strong El Niño events has differential impacts on benthic and demersal species, which results in those that survive (for example scallops, octopus, shrimp and lobsters) as well as those that don’t (for instance crabs, clam and some hake species).

Impact on tuna in the Indian Ocean:

• El Niño events usually reduce monsoonal precipitation and alter the probability of extreme events, which may affect inland fisheries and aquaculture in India.
• The ENSO events affect tuna fish in the Indian Ocean. However, globally tuna catches are not impacted by ENSO.
• Tuna have the capability to cope with ENSO events by migrating to other areas.
• The Pacific and the Indian oceans are connected via the Indonesian Archipelago. But the main impact of El Niño on the Indian Ocean is mediated by the atmosphere.
  • An El Niño usually induces warming over the Indian Ocean, as it reduces the cloud cover over this ocean by modifying the atmospheric circulation.
  • El Niño is also responsible for the generation of the Indian Ocean Dipole in the Indian Ocean (though it is not the only generating mechanism), which is known to shift the tuna population.
• The impact of ENSO on tuna fisheries occurs indirectly mainly via the Indian Ocean Dipole, which results in a shift of the tuna population in the Indian Ocean rather than an overall decrease or increase over the entire basin.
• Tunas have a preferred temperature range.
• Tropical tunas (yellowfin, skipjack and bigeye) prefer higher temperatures than temperate tunas like albacore. Neritic tunas (found in shallow seas) have a variety of temperature ranges depending on the species.
• Warming water tends to change the distribution of the species.
• They move to areas where they can find their preferred water temperature. This may affect migrations, feeding and spawning (reproduction), and so may have a profound effect on the long-term viability of the populations.

About Tuna Fish:

• A tuna is a saltwater fish that belongs to the tribe Thunnini, a subgrouping of the Scombridae (mackerel) family.
• Tuna, opah and mackerel sharks are the only species of fish that can maintain a body temperature higher than that of the surrounding water.
• Found in warm seas, the tuna is commercially fished extensively as a food fish, and is popular as a blue water game fish.