Resilience in the Open Oceans: The Case of Overfishing
The open oceans, also known as pelagic ecosystems are the water area that are located away from the coast, beyond the continental shelf’s edge and above the seabed or the benthic zone. The water column is divided into 5 zones, the epipelagic zone (0-200m), the mesopelagic zone (200-1000m), the bathypelagic zone (1000-4000m), the abyssalpelagic zone (4000-6000m) and the hadalpelagic zone (deeper than 6000m).
An ecosystem’s resilience is its capacity to stay in a stable state when it is facing a disturbance or rather to be able to recover, back to this state, after overcoming a shock. The resilience has three to four defining characteristics, depending on the authors, with the main ones being the amount of change the system can undergo before reaching a no-return state, also known as latitude, how the system is able to return to its original state and the adaptation/learning abilities of the system.
In the 50s and 60s, an enormous growth for fisheries’ effort occurred, not only in terms of number of boats, but also in terms of technological advances like the power of the engines, the size and capacity of the boats etc. This led to a formidable increase of fish catches, thus putting a lot of pressure on the pelagic fish communities such as sardines, anchovies or herring (Pauly, 2018).
Nowadays, overfishing causes the fish stocks as well as the surrounding ecosystems to be declining. On top of that, climate change leading to physical, chemical and ecosystemal disruptions empowers this decline. There is currently a lot of focus on climate change but not much is being said about overfishing.
There are some examples throughout history of fish populations crashing to almost reach the non-recovery point. A famous example is the Californian sardines; during the 30s and 40s, it was the most prominent fished caught, composing 25% of the weight of fish landed in the united states, peaking in 1936 at 700,000 metric tons. By the end of the 40s, the sardine population declined and crashed. After that, the population remained at low levels for approximately 40 years. Quite some time after the crash, in 1967, the California Fish and Game Commission established a moratorium to control the number of sardines fished and even halted in 1974 all the commercial fishing targeting those sardines as well as their use as bait. In 1986, the 18-years moratorium was lifted but the fishery was limited to 907 metric tons per year. The population was declared fully recovered by 1999, which means that it was found in its historical range again, in great numbers and with all the age classes present in the population (Protasio, 2011).
To counter these crashes, models have been established in order to determine the numbers in fisheries so that the populations can withstand the pressure of fishing and be resilient. However, even with these models, catastrophes happen. A famous example are the Peruvian anchovies in the 70s. The yield was determined using a fixed based on the maximum sustained yield of 10 million ton per year. Even with these precautions, the population crashed in 1972. Reasons are that the model did not include the environmental factors, notably the influence of El Niño on the population as well as the fact that the reported catch was way higher than the real actual catch (150% more, approximately 18 million ton). It took 25 years for the anchovies’ population to recover (Schwartzlose et al., 2010).
So, one could ask are these limitations really helpful? They are helpful if they are based on strong reliable models. These models take into account a maximum of factors (environmental, natural mortality natural birth rate etc.) or at least uses assumptions that are close to reality. A duality exists for example as to which theory to choose between the constant-rate harvesting and the relative-rate harvesting (Otto & Day, 2007). In the first one, fishers are allowed to take a fixed amount of fish, independent on the population density at the given time. In the second one, fishers remove fish at a rate that is proportional to the density of the population of the targeted fish. As we, as a society, are focused on producing a lot, the numbers for fish removal are usually placed around the maximum rate of harvesting. With the constant-rate harvesting, a small deviation off of this number causes the population to collapse immediately, while with the relative-rate harvesting, there is a reaction time when the population starts declining, to try and improve the situation. Therefore, a healthy limitation for the populations would be based, for example, on the relative-harvesting rate.
There are more consequences to overfishing than the fished populations’ collapse. By removing predator fish, such as tuna or sharks, the whole food chain is impacted so that some species, with a previously repressed growth by the predators, will increase in population size. This will lead to a maybe irreversible upheaval of the whole ecosystem. Several marine environments are also impacted, such as the coral reefs which become even less resilient to changes once the small fishes disappear due to fishing and the algae are allowed to thrive as a consequence of this fishing as well. Another consequence is the socio-economic impact of overfishing on smaller communities, relying on the presence of fish, who will have a harder time finding food resources but also on the industries and their employees, relying, financially, on the presence of industrially fished animals to live a healthy life.
In conclusion, overfishing impacts the resilience not only of the open ocean’s ecosystem but also several other environments as well as the socio-economic resilience in some of society’s sectors. Among the solutions, come education of the retailers and fishers, establishment of strong, long lasting harvesting models, marine protection, governmental engagement or responsible aquaculture/fish farming.
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