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The seafood industry contains many products that are considered an important food commodity, and one of those products that are sought-after and unique to the market is tuna fish. More specifically, the Atlantic Bigeye, Yellowfin, and Bluefin tuna, are some of the most overfished fish in the ocean. Seafood provides livelihood to billions of people all over the world and around 40% of the world’s population consumes seafood. Not only do these tuna fish serve as a main source of food for people around the globe, but they also play a key role in sustaining the ecosystem and keeping balance. Predator-prey relationships can be thrown into disarray creating a ripple effect through the food chain if fisheries alter the relative abundance patterns in stocks (Murawski, S. 2000). Recent human activity in the past few decades has taken a major toll on the tuna fish population due to overfishing, which means that the fish are being caught way faster than they can breed to restock the population. Commercial fishing threatens species to great extents but is rarely ever identified until the species have already suffered an immense population decline (Burgess et al., 2013). Not only does overfishing affect the ecosystem, but it can also affect climate change and increase neurotoxicity in marine predators. According to an article written by Asif Qureshi et al. (2019), they discuss how fish are a paramount source of methylmercury (MeHg) in the diet of humans. It has also been proven through research that overfishing has introduced a larger concentration of MeHg into fish such as the Atlantic cod by more than 20%, between the years of 1970 and 2000. This is because of the seawater temperature increase due to climate change and human involvement in our oceans. Many factors are affected by overfishing all around the globe, and it isn’t until the populations of these important species are affected that we do something about it. Overfishing tuna creates issues in many different categories, such as a large decline of the Atlantic Bigeye, Yellowfin, and Bluefin tuna populations and affecting the ecosystems they live in, pollution due to fishing boats and fishing gear along with adding stress on the species, climate change on land and in the oceans, and an increase of methylmercury in marine predators and the diets of humans. The destruction of marine ecosystems is a large con of overfishing, and it can cause a large domino downfall effect on the species in it.
Over 3 billion people around the world consume seafood and consider it as a main source of protein in their household. The number of fish that need to be caught in order to keep up and maintain that demand is through the roof, and fisheries around the world are having trouble doing so due to the rapid decline of tuna fish populations in the ocean. In fact, the decline of bluefin tuna, in specific, has been so great while the demand has been so high, that a single 202-kilogram tuna was sold in Japan at the Tsukiji market for $862.00 (Escontrela, D. 2012). The reproduction rate of these tunas is nowhere near the amount needed in order to be at or above the number of fish needed to supply the globe. Not only does it affect our food supply, but it also affects the many different species that are eaten by or eat tuna fish. Tuna fish are located in the middle of the food web and are both predators and prey to many different species. Tunas usually hunt and eat small fish such as herring, sardines, and mackerel, and even invertebrates like crustaceans and squid. They are also hunted by predators like killer whales, sharks, other big fish, and of course, humans. With the large social, economic, and ecological importance of these tuna fish and their family, it would be expected for their trajectories and status to be monitored closely and understood well but, surprisingly, the degree of their impacts globally on the fishing market is uncertain (Juan-Jordá, M. et al. 2011). Using the same source mentioned, a model was constructed to view the age-structured stock assessments for over 20 different populations of tuna and their family members. This model portrayed the geographic locations, years, and temporal span of these species. It was found that by observing the total biomass of the largest adult species such as the yellowfin, bigeye, and bluefin tunas, and the smallest species such as mackerels, has declined the most with 62.8% and 58.1% respectively since 1954. This model proves how the decline of tuna fish has become a large ongoing issue since the 20th century, and many other species of tuna have suffered this same trend due to overfishing. With the decline of these 3 important types of tuna, there will be an overabundance of smaller fish and organisms that can eat and basically “infest” the oceans. On the other hand, though, when fisheries catch tuna and farm them to be a good size for selling, they also capture twice as many smaller pelagic fish to feed the tuna and keep them healthy. This change to the ecosystem increases the demand for these smaller fish as well, and a lot of the baitfish come from the borders of the Mediterranean Sea, which allows for a presentation of invasive species and pathogens (Forrestal, et al. 2012). Using that same source, the goal for most aquaculture that captures bluefin tuna is not to expand the levels of biomass but to increase the fat content in a single bluefin tuna. This enlarges the value of that fish in the marketplace and with the model presented in this article, increases the biomass from 0.100 to 0.106 t km^(-2). With the removal of these tuna and smaller fish from their ecosystems, it creates a disruption in the balance. Human activity such as fishing, and boating can create even more of a disruption as well.
Not only does the actual act of overfishing affect the tuna fish and species around them, but so does the equipment that is used to do it. There are almost 5 million fishing boats around the world lurking in the oceans, and the amount of oil needed to fuel these ships is extremely great. Fishing gear such as plastic bait, fishing poles, fishing lines, nets, lost items that fall overboard, oil spills, and many other things create stress on the species in the ecosystem. Fishing boat and gear pollution make up over 80% of trash populated in our oceans, and marine traffic contributes to millions of tons of waste due to oils and burning fuel spilled into the water. Another con is that human activities, such as aquaculture, shipping, and opening the Suez Canal, are introducing around 1000 foreign alien species into the Mediterranean Sea (Coll, M. et al. 2014). Using this same source, these alien species are detrimental to many ecosystems that they come across because they throw off the balance that is permitted in that ecosystem. They can also become invasive and change habitats and the structure of aquaculture communities, affect human health, cause loss in the economy, and even wipe out native genotypes. It was found with this source’s model that out of the 986 species that were reported in the Mediterranean, 114 of those species have been assigned to more than 1 possible pathway, 799 have been identified to 1 pathway, and the other 73 species that remain have been identified as unknown (Coll, M. et al. 2014). This shows how human activities have created chaos without even realizing it, and the side effects of overfishing harm the ecosystems as well. Traffic in the marine also affects climate change since oil spills and pollution change seawater temperature and concentration levels.
Climate change is another factor that is affected by overfishing in our oceans, and that is due to the idea that having more fish in the ocean creates less of climate change. Since overfishing does quite the opposite and creates fewer fish in the ocean, climate change under the sea has been prominent. Many factors have adjusted to the constant change, such as reduced oxygen levels and pH levels underwater and the changes in force of major currents. Along with that, oil spills also contribute to a change in climate in the oceans since the concentrations of the sea are affected when foreign matter enters. It also has been shown that seawater temperatures have risen by 0.3 °C in the upper 300 meters of the ocean and are expected to increase throughout the 21st century (Liu, Y. et al 2011). Using that same source, it has also been projected that water temperatures in the Gulf of Mexico (GOM) will be greatly affected as well, along with recreational and commercial fisheries. Adult bluefin tuna like to reproduce and spawn in warmer waters, usually between 24°C and 27°C, and their larvae are usually collected between water temperatures of 23.5°C and 28°C. Constant shifts in seawater temperature can affect spawning times and areas, the behavior of how the bluefin tunas migrate, and the effects of fisheries and stock size. Overfishing has also introduced a surge of methylmercury levels into the oceans, which is brutal to certain ecosystems.
Fish is the number one source of methylmercury, MeHg, in a human’s diet, and according to many scientists, a link between overfishing and an increased level of mercury in the diet of humans and skin tissue of tuna fish has been found. An introduction of great amounts of methylmercury into the human diet can cause numerous amount of health problems, an important one being central nervous system damage. In the United States alone, 82% of methylmercury exposure in the population is due to eating marine seafood, and 40% is from canned and fresh tuna (Asif Qureshi et al. 2019). Not only is it affecting human diets, but it is also greatly affecting tuna fish and the predators that eat them. Asif Quereshi and his team have found that by analyzing the stomach contents of 2 major marine predators, the spiny dogfish and Atlantic cod, between the year of 1970 to 2000, they were able to determine that cod in the 1970s ate 8% more small clupeids than they did in the 2000s. This is because of the overharvesting and decreased supply of herring, so the cod were forced to consume small clupeids. It was also found that concentrations of methylmercury in spiny dogfish were 33-61% larger in the 2000s when herring was more prominent than clupeids. The results from these findings show that perforations in the trophic structure of marine organisms due to overfishing can greatly affect MeHg concentration levels throughout different species. This is an unexpected side effect of human activity bombarding the oceans, and another reason why regulations should be set in place to control this.
In conclusion, the act of accumulating more fish from the ocean than they are able to spawn and reproduce is very detrimental to our marine ecosystems. More specifically, overfishing to an extent causes a large population of three very important tuna species: Atlantic Bigeye, Yellowfin, and Bluefin tuna. Taking out a key factor in an ecosystem, such as tuna, can greatly impact the peaceful chain that goes on under the sea. Many other factors are affected due to overfishing, such as pollution as a result of fishing boats and fishing gear along with adding stress on the species, climate change on land and in the oceans, and an increase of methylmercury in marine predators and the diets of humans. Overfishing effects will not only be visible in the large depletion of fish stocks but also will shoot consequences that wave through the world that humans live in, along with the economy and ecosystems that fish are an integral part of (Kraemer, E. 2013).
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