The original food web above serves as a more in-depth look at the title of the collection, “APEX.” Bluefin tuna are one of the species at the top of the food chain – an apex species – meaning that the removal or decline of this species could have a significant impact on the rest of the food chain in areas where bluefin tuna exist.
Currently, there are two methods of capturing bluefin tuna for the fish market: farming and fattening (Forrestal et al., 2012). Bluefin tuna farming involves keeping juvenile fish in pens for up to two years before capturing whereas fattening only takes three to seven months and can generate more high-value, fatty fish.
Both methods, however, are problematic for the sustainability of bluefin tuna populations as they fail to address the fish’s life cycle. Atlantic bluefin tuna, for example, reach maturity between 3-5 years of age depending on the location of rearing (Boustany, 2011). Southern bluefin tuna, however, are believed to reach maturity at the age of 8, but other studies estimate that sexual maturity is not acheived until 11 to 15 years of age. Meanwhile, all varieties of bluefin tuna species can live up to a minimum of 26 years (Boustany, 2011). Thus, the process of both farming and fattening prevents bluefin tuna from reaching sexual maturity before they are taken out of the wild, resulting in fewer potential wild bluefin tuna that could be produced.
Aside from the concerns of maturation and overfishing, bluefin tuna are especially important within their ecosystems because they are considered to be a keystone species (Galland & McKinney, 2021). Physiologically, bluefin tuna are well adapted to be top predators within their food chain. Bluefin tuna possess more red muscle fiber than any other species of fish, allowing them to carry out long-term muscle activity (Jeong, 2019). Bluefin tuna also have regional endothermy – the ability to alter its body temperature to inhabit other bodies of water. Bluefin tuna evolved to have a countercurrent exchange system that prevents heat from escaping to the surrounding environment (Jeong, 2019). Not only does this capability allow bluefin tuna to survive in different areas, but it also enables bluefin tuna to swim faster and have sharper reflexes for preying on other fish species.
Being at the top of the food chain with a limited number of predators, overfishing and potential extinction of bluefin tuna could have extreme consequences for both bluefin tuna ecosystems and fisheries management. Overfishing of bluefin tuna could result in increases of crustacean and jellyfish populations (Forrestal et al., 2012). This, however, could result in low-trophic level food webs where energy and biomass is concentrated lower on the food chain. Furthermore, extinction of bluefin tuna could increase squid populations, which would then lead to a decrease in sardine stocks – one species that squid prey upon (Why Is the Atlantic Bluefin Tuna Being Overfished?, 2021). The demise of both bluefin tuna and sardine populations would be detrimental to the fishing industry as it is heavily dependent on both heavily-consumed species.
Art and writing by Ashley Kenney.
References
Boustany, A. (2011). Bluefin tunas: The state of the science. Pew Environment Group.
Forrestal, F., Coll, M., Die, D., & Christensen, V. (2012). Ecosystem effects of bluefin tuna Thunnus thynnus thynnus aquaculture in the NW Mediterranean Sea. Marine Ecology Progress Series, 456, 215–231. https://doi.org/10.3354/meps09700
Galland, G., & McKinney, R. (2021, May 4). Into the Deep With the Atlantic Bluefin Tuna. PEW Charitable Trusts. https://pew.org/3b1ihbz
Jeong, B. (2019). Atlantic bluefin tuna: the forgotten superpredator. Blue Planet Society.
Why is the Atlantic Bluefin Tuna being Overfished? - American Oceans. (2021, February 3). https://www.americanoceans.org/blog/atlantic-bluefin-tuna-overfishing/