The Bone Zone

The purpose of this paper was to simulate various scenarios based on population data and predict the fate of Atlantic bluefin tuna populations. 

Keywords: 

• Biomass: The total mass of organisms in an area or volume. 
• Spawning Stock Biomass: The combined total of all individuals within a fish stock that are capable of reproduction. 
• Temporal: of, or relating to, time. 
• Recruitment: The production rate. 
• Individual relative fecundity: The personal ability to reproduce and create offspring in large numbers. 
•  Stochastic modeling: A model type that predicts outcomes while taking into account a degree of randomness or unpredictability. 
•  Parameterize: To describe or represent in terms of parameters. 
• Hockey stick model: A model that starts flat but will then diagonally go up or down, and resembles a hockey stick. 

Hypothesis: The adult population of bluefin tuna will decrease 75% in 2011 compared to 2005, and the quotas for fisheries would allow for this to occur. 

This experiment utilized data on fishery assessments, population trends, and  from International Commission for Conservation of Atlantic Tuna (ICCAT). This data was then placed within an age-structured stochastic model and applied to five scenarios that would bring accurate predictions towards bluefin tuna populations.  These simulations had dire results; for example, scenario 2 had a 50% chance of recovery before the 2022 recovery plan goals. The overall biomass trend is that they would decline rapidly and at a dangerous rate. 

The prediction for the biomass trend is that the population would fall 90% by 2022. Thus, making an ecological and fishery collapse. Even if a ban was put in place in 2008, the population would still hit record lows. Knowing that the hockey stick model follows more closely than the Ricker model is not any more promising given that it shows rapid decline. This trend is largely due to the over-fishing of the Atlantic bluefin tuna population that goes beyond the recommended quotas needed for recovery. They end up catching all of the adult tuna, which decreases the ability to recruit more into the population. Other indications of this happening can be seen in how the demographics for the fish have changed in terms of age and reproduction-ability (more young, premature fish are left).  They call for a new recovery plan that is much more strict with the fishing quotas and enforceability, so that the population of tuna can recover over the years to avoid the three generation collapse. 

These results are interesting because we can now compare the findings in 2009 to present day bluefin tuna populations to see if the prediction was accurate. Given that Atlantic bluefin tuna are still endangered and we still face over-fishing issues, the prediction seems to be accurate so far. These findings have a point when it comes to more than just this species of fish. It further points out how not enforcing strict quotas to encourage recovery, and over-fishing, is destroying many species. This model-based prediction of the bluefin tuna populations is just a piece of the puzzle, a consequence for these actions and for the lack of. 

Citation: 

Mackenzie, B. R., Mosegaard, H., & Rosenberg, A. A. (2009). Impending collapse of bluefin tuna in the northeast Atlantic and Mediterranean. Conservation Letters, 2(1), 26–35. doi: 10.1111/j.1755-263x.2008.00039.

https://conbio.onlinelibrary.wiley.com/doi/full/10.1111/j.1755-263X.2008.00039.x

Dickson, K. A., and J. B. Graham. “Evolution and Consequences of Endothermy in Fishes.” Physiol Biochem Zool 77 6 (2004): 998-1018. Print. 

figure 1:figure 2: figure 3:

Viñas, J., & Tudela, S. (2009). A validated methodology for genetic identification of tuna species (genus Thunnus). PloS one, 4(10), e7606. doi:10.1371/journal.pone.0007606. 

The Thunnus genus is a monophyletic group based on mitochondrial and nuclear DNA sampling and comparisons. There are eight recognized species within this genus, but the exact connections between them could still be debated due to molecular similarities of the species. This genus is incredibly similar morphologically, down to the fin location, number, and shape. All Thunnus species have the teardrop shape which allows for thunniform swimming. It is quite useful for their open ocean habitats and predatory lifestyles as it decreases water friction yet increases ability to go long-distance. 

Thunnus thynnus (Atlantic bluefin tuna) have Thunnus alalunga (Albacore) as their closest relative. The main difference, because they are so morphologically similar, is the muscular nature of the fish. Albacore has much more lighter colored, white muscles (good for short, quick distances), while bluefin tuna have much more darker colored, red muscles in comparison (better for long distance cruising).

In terms of overall phylogeny, connections and exact ancestry could still be debated. With the three figures above, even within one study, depending on the methods you utilize it can produce diverging phylogenetic trees. Figure 1 is based on mitochondrial DNA control region, figure 2 on mitochondrial DNA cytochrome oxidase 1, and figure 3 on nuclear rDNA (ITS1).  These figures do switch around basically when the speciation event would have occurred on the tree, but overall closely related species (ex. T. thynnus and T. alalunga) stay the same.  As for the simplified phylogenetic tree, it relies on two clades: the bluefin group and the yellowfin group (T. atlanticus and up). That’s based on separate experiments on Thunnus DNA comparisons. 

Citations: 

Myers, P., R. Espinosa, C. S. Parr, T. Jones, G. S. Hammond, and T. A. Dewey. (2019). The Animal Diversity Web (online). Retrieved from https://animaldiversity.org.

Genus Thunnus. FishIDER. Retrieved from https://www.fishider.org/osteichthyes/scombridae/thunnus-spp/. 

Viñas, J., & Tudela, S. (2009). A validated methodology for genetic identification of tuna species (genus Thunnus). PloS one, 4(10), e7606. doi:10.1371/journal.pone.0007606.