Did you hear about the evil tuna?

He was rotten to the albacore.

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Figure 1 A school of yellowfin tuna.

Source: http://russgeorge.net/wp-content/uploads/2016/05/yellowfin-tuna.jpg

Okay, so lame jokes aside… This week we had an interesting presentation this week from Brett Falterman. Working with the Louisiana Department of Wildlife and Fisheries (LDWF), he holds two titles: Program Manager of the Fisheries Management Section and the Director of the Grand Isle Fisheries Research Lab. His presentation centered on yellowfin tuna (Thunnus albacares) management.

A large portion of fisheries management is the communication between citizens and scientists. Scientists are often portrayed as the villains when they hand down recommendations. These recommendations usually include reducing harvest limits, changing collection methods, or changes in size minimum for harvest. We also have a difficult time conveying scientific findings in a way which non-scientists can understand the implications and significance of findings and the ‘inability to reject the null hypothesis’.

LDWF has been actively tagging and tracking individual yellowfin tuna using a few different kinds of tags. The number of tags and transmitters which are recovered are incredibly low but through use of connecting and giving incentives to recreational and commercial fishermen, the percentage of tags recovered have increased. Two kinds of tags (Internal Archival Tags and the commonly used anchor tags) need to be physically processed in order to gain any information from them.

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Figure 2: A yellowfin tune with an anchor tag.


Source: http://fishingvideos.com/news/media/2008images/20080501-RS4-08underwater%20tag%20Tuna%20SM.jpg


Brett told us about his experiences with collaboration between commercial fishermen and scientists. Some of these were incentivized, and others came with the allure of aiding in important scientific research and the hope of improved understanding and management of an economically significant species.

The study species, the yellowfin tuna, is currently believed to be managed globally in a sustainable way as compared to the ill-management of bluefin tuna. The belief that a global harvest of 1.2 million metric tons annually is sustainable is a bit hard to swallow. Through age and growth studies and tracking individuals, scientists are better able to understand population dynamics of specific species.

A study conducted by the LDWF used over 2,000 yellowfin tuna carcasses from a commercial fisherman in Venice, LA. Through this cooperation, the stomachs, reproductive organs, tissue samples, and small ear bones were removed and kept for later tests. These ear bones were able to be used for two analyses. You may be asking why tiny ear bones from a fish matter. Well, one thing that they can be used for is to determine age.

Depending on the species of fish, the ear bones can be quiet large in fish which produce and hear sounds. But in the case of tuna and other fast moving fish, they have smaller ear bones. Each year, the fish’s ear bones grow some and create a new ring, much like the rings that trees produce. Yellowfin tuna ear bones grow very slowly over time, this has led to an underestimation of age. Old estimations said that yellowfin tuna only lived to be around 8 years old and data collected from this fishery’s waste has led to the new discovery that yellowfin tuna can live to be 13 years old.

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Figure 3 Each year the ear bones of fish grow and create rings, much like a tree. This Atlantic cod ear bone is from a fish, which was 10 years old.

Source: http;//1.bp.blogspot.com/-pi2naeJlcKQ/T7_YlaquekrNI/AAAAAAAAAA/IDEQldhrdrNw/s1600/otolith+rings.jpg.

The inner portion of these ear bones also had a number of tests performed to measure trace elements like Barium, Strontium, and Magnesium. The ratio of these three elements can determine the waters of which a fish were born in. For yellowfin tuna, this tells us where the fish are coming from originally. It turns out that nearly 66% of the yellowfin tuna in the Gulf of Mexico are actually born in the Eastern Atlantic Ocean.

The information gathered from this study would not have been possible if fishermen and scientists had not cooperated. This information will lead to better management strategies and hopefully further cooperation between commercial fishermen and government scientists.

Interactions and population mixing is important for sustaining a genetically healthy population of yellowfin tuna. Much like fisheries, management practices are dependent upon interactions. Management practices involve the interaction between commercial fishermen, politicians, and the public. Just as scientists were able to gain information from the waste of tuna fishermen, the fishermen and scientists can gain information and understanding from each other and develop better management practices which are both sustainable and scientifically informative.

-Ellie Wallace

Read more with these articles available on Google Scholar:

Hampton, J., Kleiber, P., Langley, A., Takeuchi, Y. and Ichinokawa, M., 2003. Stock assessment of yellowfin tuna in the western and central Pacific Ocean. WP YFT-1, SCTB, 16.

Jepsen, N., Koed, A., Thorstad, E.B. and Baras, E., 2002. Surgical implantation of telemetry transmitters in fish: how much have we learned?. In Aquatic Telemetry (pp. 239-248). Springer Netherlands.

Langley, A., Hoyle, S. and Hampton, J., 2011. Stock assessment of yellowfin tuna in the western and central Pacific Ocean. Westtern and Central Pacifc Fisheries Commission.

Miller, M.L., Kaneko, J., Bartram, P., Marks, J. and Brewer, D.D., 2004. Cultural consensus analysis and environmental anthropology: yellowfin tuna fishery management in Hawaii. Cross-Cultural Research, 38(3), pp.289-314.

Wild, A., 1986. Growth of yellowfin tuna, Thunnus albacares, in the eastern Pacific Ocean based on otolith increments. Inter-American Tropical Tuna Commission Bulletin, 18(6), pp.421-482.

Zhang, Y., Chen, Y., Zhu, J., Tian, S. and Chen, X., 2013. Evaluating harvest control rules for bigeye tuna (Thunnus obesus) and yellowfin tuna (Thunnus albacares) fisheries in the Indian Ocean. Fisheries Research, 137, pp.1-8.