Dr Abdul Aziz al Marzouqi, director of the Marine Science and Fisheries Center, Ministry of Agriculture and Fisheries, said, “On May 11, an Omani fisherman reported about a huge tuna catch in a longline about 40 nautical miles off the Sur coast in Arabian Sea. After analysing its biological and morphological parameters we identified it to be a Pacific bluefin tuna (Thunnus orientalis) .”
Samples were collected from different parts of the body for analysis. “Through Otolith Age reading we found that the fish was ten years old. The average lifespan of this fish species is 15 years and more. It grows to a total length of up to 2.5m and weighs around 237kg.”
He added that the genus Thunnus alone has eight species and found worldwide. “Of these, three species are available in Omani waters. These areThunnus tonggo (longtail tuna), Thunnus albacore (yellowfin tuna) and Thunnus obesus (bigeye tuna). The Pacific bluefin tuna is the second largest species after Atlantic bluefin tuna (Thunnus thynnus) .”
Explaining how the Pacific bluefin tuna could have reached Omani waters, Dr Marzouqi said, “The Pacific bluefin tunas can travel long distances because of their fusiform bodies. The fish variety seasonally inhabits the sub-arctic, temperate, and tropical waters in the North Pacific Ocean as well as temperate waters in the Southern Hemisphere around Australia and New Zealand.”
According to Dr Shama Zaki, a marine science expert this particular species can bear extreme temperatures and it could be one of the reasons for its migration.
However, she said, there could be other reasons as well. “It could be an incidental catch or disorientation of fish. The migration could also be linked to ecological changes that could be attributed either to a rise/decline in water temperatures in its region, or due to unknown biotic and/or anthropogenic factors.
Dr Shama said that another possibility could be that increase in sea surface temperature may have caused a decline in food in its habitat. “So, the fish may have travelled to a more abundant prey region tolerant of warmer waters. This may result in increased competition with other predators and a shift in the structure and trophic flows within. Increased accessibility of trawling in the ecosystem could also be a reason.”
Dr Marzouqi added, “The Sea of Oman is connected to the Arabian Sea which too is linked to the Indian Ocean. Arabian Sea is rich in nutrients which attract more species.
“Now, Omani fishermen have state-of-the-art trawlers which help them to venture far and get closer to the migration path (if this path exists) of migratory species.”
Dr Shama explained that Pacific bluefin tuna is under the red list of International Union for Convention of Nature and the status has been defined as vulnerable. “The USA National Oceanic and Atmospheric Administration is now conducting a status review of Pacific bluefin tuna to be included under the Endangered Species Act.”