Swimming Slab of Gold: Migration of Atlantic Bluefin Tuna
If sushi were the best representation of Japanese cuisine, then bluefin tuna would be the crown jewel of sushi. With extensive marbling and a perfect balance of scent and flavor, food enthusiasts around the world crave for bluefin tuna. In fact, a 612-pound bluefin tuna was sold at an auction in Tokyo fish market in 2019 for more than 3,000,000 US dollars, setting a record at 5,000 dollars per pound. However, people’s craving is not the only factor in driving up prices. The scarcity of bluefin tuna triggers the law of supply and demand. While people’s demand is increasing, the population of bluefin tuna has been drastically declining since the 1950s.
Population Distribution and Fishing Practices
Bluefin tuna and yellowfin tuna are two subgroups of tunas. Although both fall into the bluefin category, albacore tuna, which is commonly found in canned tuna, has a much smaller size than Atlantic bluefin tuna, which can grow up to 15 feet in length and 1500 pounds. The huge price difference between the two species is mainly attributed to the fact that Atlantic bluefin tuna cannot be artificially cultured and grown for sale. The high tropic property of the species requires an enormous amount of feed and the low survival rate makes it difficult to generate commercial value for aquaculture. Additionally, because of the declining population, the Atlantic bluefin tuna has been listed by IUCN as endangered.
Within the Atlantic bluefin tuna populations, Gulf of Mexico bluefin tuna and Mediterranean bluefin tuna are the two major subgroups. Historically, scientists believe that the two groups do not interact with each other extensively. Each population has its own spawning site and their areas of activities are limited within their respective bodies of water. This has driven fishing companies to measure the health of Atlantic bluefin tuna only based on the tuna in their own fishing zone. Yet, this practice has been challenged by recent findings.
Migration of Atlantic Bluefin Tuna
Scientists from Texas A&M University and University of Maryland found that the two subgroups of Atlantic bluefin tuna, the Gulf of Mexico population and the Mediterranean population, do exhibit cross migration. More specifically, there is a net migration to the Northern Atlantic from the Mediterranean during non-spawning season. These findings generate significant implications for the current fishing practices. Because some Mediterranean bluefin tuna migrate to the North Atlantic, fishing companies that fish in the North Atlantic would overestimate the size of bluefin tuna populations, which leads to overharvesting and overfishing.
Factors Shaping Migration and Future Research
Therefore, scientists have been trying to investigate the characteristics of the group of Atlantic bluefin tuna that migrate. Preliminary studies show that younger Mediterranean bluefin tuna have a higher tendency to leave for the Atlantic Ocean. However, this relationship has not been fully understood and quantified. In a research proposal by Shangqing Cao, the author attempts to quantify this relationship by deploying tagging devices on bluefin tuna and taking otoliths to measure the age of selected tuna. This research can potentially help fishing companies as well as environmental advocacy groups to better estimate the size of the migratory population and the correct size of population for both the Mediterranean and Atlantic bluefin tuna. This would be helpful when it comes to determining quotas as well as seasons of fishing in both the Atlantic and the Mediterranean.
The consumption of bluefin tuna has a rich history and is an important component of many cultures, especially Japan’s. It is unrealistic and impossible to simply ban the consumption of bluefin tuna for protecting the species. However, we can develop systematic infrastructure on fishing quota allocation, encourage sustainable practices, and protect the Atlantic bluefin tuna population.
References:
Rooker, J. R., D. H. Secor, G. De Metrio, R. Schloesser, B. A. Block, and J. D. Neilson. “Natal Homing and Connectivity in Atlantic Bluefin Tuna Populations.” Science322, no. 5902 (2008): 742–44. https://doi.org/10.1126/science.1161473.
