One of the reasons for concern about the consumption of  yellowfin tuna  is the presence of so-called heavy metals. Heavy metals are contaminants of great environmental concern because of their multiple origins (natural and anthropogenic), their ability to accumulate in organs and tissues, and the deleterious effects they can cause in organisms. Studies on the accumulation of metals in marine populations, such as fish, have increased in importance because of the risk to human health when metal-contaminated fish are consumed. The present work aimed to verify the concentrations of cadmium (Cd), mercury (Hg) and lead (Pb) in muscle tissue and liver of yellowfin tuna (Thunnus albacares) and dolphinfish (Coryphaena hippurus) from the eastern Pacific (1).

A comprehensive review of literature and studies on mercury concentrations in 36 fish species showed that (2) fish such as tuna and swordfish have the highest concentrations of CH₃Hg or Methylmercury and mackerel and sardines from the Mediterranean Sea contain more CH₃Hg than other harvesting areas (3). All these and other data are detailed in this study (4).

References________________________________________________________________________

(1) Araújo CVM, Cedeño-Macias LA. Heavy metals in yellowfin tuna (Thunnus albacares) and common dolphinfish (Coryphaena hippurus) landed on the Ecuadorian coast. Sci Total Environ. 2016 Jan 15;541:149-154. doi: 10.1016/j.scitotenv.2015.09.090. 

(2) Pirrone N.; Mahaffey K. R. Dynamics of Mercury Pollution on Regional and Global Scales; Springer Publishers: New York, 2005; p 744.

(3) Pirrone N.; Mason R. Mercury Fate and Transport in the Global Atmosphere: Emissions, Measurements and Models; Springer: New York; p 637.

(4) Driscoll CT, Mason RP, Chan HM, Jacob DJ, Pirrone N. Mercury as a global pollutant: sources, pathways, and effects. Environ Sci Technol. 2013 May 21;47(10):4967-83. doi: 10.1021/es305071v. 

The genus Thunnus , which belongs to the family Scombridae, includes eight species that are commonly known as tuna (1).

• Bluefin tuna (Thunnus thynnus)
• Pacific bluefin tuna (Thunnus orientalis)
• Southern bluefin tuna (Thunnus maccoyii)
• Bigeye tuna (Thunnus obesus)
• Yellowfin tuna (Thunnus albacares)
• Albacore (Thunnus alalunga)
• Skipjack tuna (Katsuwonus pelamis)
• Atlantic bonito (Sarda sarda)

Thunnus albacares (Thunnus albacares, Bonnaterre 1788), also known as Yellowfin tuna,  is an active pelagic migratory predator living in temperate and subtropical waters, but its global genetic structure is still poorly understood despite its importance to the tuna fishing industry (2). It lives in the Pacific, Atlantic and Indian Oceans.

There are several populations of tuna: the Eastern and Western Atlantic and Mediterranean bluefin tuna, the Southern bluefin tuna and the North Atlantic albacore are the most numerous.

Albacares tuna is distributed in a continuous pan-tropical belt of 45 degrees north and south of the equator, from the Gulf of Mexico in the western Atlantic eastwards to the coast of the American continent in the Pacific. It is now recognised as a single species, although it was initially classified into seven sub-species based primarily on morphological variation. Despite its demonstrated capacity for single large-scale movements, tagging studies on this species in the Pacific suggest dispersal on the order of hundreds rather than thousands of kilometres (3).

The global tuna population has declined by an average of 60 per cent over the last half century and fishing mortality has steadily increased to the point where approximately 12.5 per cent of tuna and their neighbouring species (mackerel, Spanish mackerel and bonitos) are caught globally each year (4).

Tuna studies

References_______________________________________________________________________

(1) Collette BB, Nauen C. FAO species catalogue, Vol. 2. Scombrids of the world: an annotated and illustrated catalogue of tunas, mackerels, bonitos, and related species known to date. FAO Fish Synop. 1983;125:1–137

(2) Pecoraro C, Babbucci M, Villamor A, Franch R, Papetti C, Leroy B, Ortega-Garcia S, Muir J, Rooker J, Arocha F, Murua H, Zudaire I, Chassot E, Bodin N, Tinti F, Bargelloni L, Cariani A. Methodological assessment of 2b-RAD genotyping technique for population structure inferences in yellowfin tuna (Thunnus albacares). Mar Genomics. 2016 Feb;25:43-48. doi: 10.1016/j.margen.2015.12.002. 

(3) Grewe PM, Feutry P, Hill PL, Gunasekera RM, Schaefer KM, Itano DG, Fuller DW, Foster SD, Davies CR. Evidence of discrete yellowfin tuna (Thunnus albacares) populations demands rethink of management for this globally important resource. Sci Rep. 2015 Nov 23;5:16916. doi: 10.1038/srep16916.

(4) Juan-Jordá MJ, Mosqueira I, Cooper AB, Freire J, Dulvy NK. Global population trajectories of tunas and their relatives. Proc Natl Acad Sci U S A. 2011 Dec 20;108(51):20650-5. doi: 10.1073/pnas.1107743108.