Over-fishing is possibly humankind’s greatest threat to the marine environment, the ‘Unnatural History of the Sea’ by Callum Roberts tells us that much. The seas have always provided food for human civilisations, and the sustainability of marine ecosystems now depends on the functioning relationship between the economy, environment and society¹.

Over-fishing has been an issue for generations and now the big focus is on Atlantic Bluefin Tuna stocks. There is still scepticism pertaining to the environmental consequences of over-fished populations in society, however even more noticeable is the lack of understanding of the social and economic drivers. A recent report written by Alex Tidd, Julia Blanchard, Laurence Kell & Reg Watson in Scientific Reports titled ‘Predicting global tuna vulnerabilities with spatial, economic, biological and climatic considerations’ aims to define these drivers¹.

World Wild Life picture of Bluefin Tuna Entanglement⁵

Life of the Atlantic Bluefin Tuna

Atlantic Bluefin Tuna play an important ecological role, being one of the open oceans strongest and fastest predators. They go through many stages throughout their lifetime, beginning as extremely tiny larvae, which feed on zooplankton. They reach sexual maturity at approximately 3 – 5 years, when they eat primarily pelagic fishes and invertebrates². They also make long migrations every year, which correspond with spawning events and feeding (Figure 2)⁴. They then separate into two main populations; the first, which reproduces in the Gulf of Mexico and the second which reproduces in the Mediterranean Sea. Whilst both populations of Atlantic Bluefin Tuna experience the pressures of over-fishing, the latter is of a higher conservation concern².

 

Tuna’s Importance to the Global Economy

Bluefin Tuna constitutes a large part of the global seafood economy. Most prominently in Japan, where it is a luxury fish and enjoyed from preparation to meal by consumers³. Bluefin Tuna is a major contributor to the global seafood market with an annual value of over $42 billion. With demand increasing by 4% each year, parallel with the increase of the human population at 1.18% per annum, global fisheries are unlikely to slow down¹. Around 30% of large commercial fish stocks are already over-exploited. Among them is the Atlantic Bluefin Tuna, along with others species from the mackerel family¹. One single Atlantic Bluefin Tuna reportedly sold for $1.75 million. The sheer value placed on the fish is a key driver of non-compliance with internationally agreed quotas. It also drives the development of more refined fishing methods, which are designed to increase catch, leading to illegal ‘pirate’ fishing of tuna⁵.

 

Maximum Sustainable Yields

Maximum Sustainable Yield (MSY) is the common management practice adopted for Bluefin Tuna, and most of the world’s fisheries management¹. MSY refers to the largest possible catch over a period of time to ensure sustainability of the resource. This is extremely difficult to predict with the popular equilibrium model assumptions, which assumes the interaction of predators and grazers in an eco-space. It is also difficult to predict the MSY through analysis of historical fisheries data or a combination of both methods¹. Tuna stocks are generally regulated through recording mortality rate and spawning events, over time¹. Although there has been a goal set to reach sustainability by United Nations, global fisheries, including the Bluefin Tuna industry, still exceed this annually.

 

The Business End: Social and Economic Drivers

The goal of the Tridd et al. report was to analyse and model multiple variables in an attempt to improve management of Atlantic Bluefin Tuna stocks. These variables focused on social and economic drivers of Bluefin tuna catch, along with other over-fished species of mackerel for comparison¹. The work utilised data on how stocks change with respect to income, fuel prices, climate stressors and other changes. The idea is that this can aid in the development of more ergonomic approaches to the future of marine conservation of this species¹.

Findings of the scientific report discovered interesting trends where, countries in the indo- pacific, where many populations suffer from poverty, low literacy and low living standards, are of increasing vulnerability of over-exploitation of fish stocks¹. These populations, being developing areas, rely on tuna for their diet and poverty reduction¹. Comparatively, countries with ‘higher socio-economic status’, which have adopted management methods as a result of over-fishing, are decreasing their risk of exploitation¹.

Model results identified varied relationships between tuna catch and economic drivers. Economically, there was a correlation between fish mortality, MSY and fuel prices¹. This suggests that an increase in fuel price represents decreased mortality rates due to the cost of operation being too high. Although the opposite effect could suddenly occur if fuel prices were to drop significantly, increasing catch and mortality rates  if not regulated properly, threatening the fish population. This would potentially lead to harmful and wasteful fishing practices¹. Tuna prices generally decrease when a moderate catch event occurs, meaning there is a lot of fluctuation driving fishers to catch more fish when they have the opportunity to¹.

The global climate oscillation events El Niño and La Niña were found to carry significant effects on the mortality relative to MSY¹. During events of increased sea surface temperature, there are less Atlantic Bluefin Tuna resulting in a lower mortality rate however, other members of the mackerel family such as Skipjack and Yellowfin Tunas increase in biomass during warmer water body events¹. This led to tens of thousands of tons of catch increase of these species. During La Niña events, Atlantic Bluefin Tuna stocks are more available due to cooler sea surface temperatures. The cooler water brings more food availability and survival of their larvae. This leads to a noticeably large increase in exploitation during these years¹.

 

Conclusions

Atlantic Bluefin Tuna are an important species to many aquatic ecosystems, as well as a resource used by many coastal populations¹. This species has historical significance as a food source to civilisations all around the world making tuna a highly sought after resource, which threatens the existence of this species³. Ultimately, Atlantic Bluefin Tuna contribute to the open ocean ecosystem as a predator with impacts throughout the food chain, their extinction therefore would have devastating effects on the ocean². This fact makes conservation management of the resource our responsibility in order to achieve sustainability. Both anthropogenic and natural forces threaten the balance of sustainability, and the process of better understanding these will in turn improve management practices¹.

 

References

 

1. Tidd, A., Blanchard, J.L., Kell, L. and Watson, R.A., 2018. Predicting global tuna vulnerabilities with spatial, economic, biological and climatic considerations. Scientific reports, 8(1), p.10572.
2. (2014). Overfishing of the Atlantic Bluefin Tuna. Available: https://blogs.umass.edu/natsci397a-eross/overfishing-of-the-atlantic-bluefin-tuna-3/. Last accessed 20th Sep 2018.
3. Fisheries and Aquaculture Department. (2018). Thunnus thynnus (Linnaeus, 1758) . Available: http://www.fao.org/fishery/culturedspecies/Thunnus_thynnus/en. Last accessed 20th Sep
4. Fromentin, J.M. and Powers, J.E., 2005. Atlantic bluefin tuna: population dynamics, ecology, fisheries and management. Fish and Fisheries, 6(4), 281-306.
5. (2018). Bluefin Tuna. Available: https://www.worldwildlife.org/species/bluefin-tuna. Last accessed 20th Sep 2018.