So we’ve finally come to the end of our time with the fishing industry and its pollutive nature. To conclude this series, I’d like to talk about an interesting article I came across about the long-lasting impacts of the release of nuclear, radioactive wastewater from a power plant in Fukushima on the fishing industry.
This study is an excellent example of transboundary pollution as it provided insights on the perspective of a neighboring country, China [1]. 10 years after the nuclear disaster in Fukushima, the Japanese government decided on releasing wastewater from the damaged plants into the marine waters [2]. Despite their claims of having treated the wastewater and removed its radioactive components, there was still strong push-back from the local fishing industry and neighboring countries such as China and South Korea [2]. The study cited several ways that the wastewater could harm the environment as seen in Figure 1 below [1].
Figure 1: Exposure pathways of Fukushima nuclear wastewater [1,3].With the aid of oceanic currents, the radioactive wastewater can potentially enter the fishing grounds of other neighboring countries [1]. This can become a prominent issue when these countries are not equipped to handle such pollution. From the perspective of China, their current regulations for their fishing industry has been insufficient to address the problem of transboundary nuclear waste pollution and existing regulations are not strictly upheld by the authorities [1]. Due to this, fisheries in China are not prohibited from fishing in contaminated waters and can continue to sell contaminated fish to their consumers [1].
Li et al. proposed possible solutions to this problem by changing China’s current legislations on transboundary nuclear pollution [1]. Regulations need to be placed on catching contaminated fish, and to enact a strict regulation of jurisdiction limits on fishing activities. Inspection efforts and monitoring technologies should also be ramped up to prevent illegal fishing of contaminated fish.
Overall, it really struck me how even years after such disasters, the negative impact on the environment and society persists despite years of rehabilitation and continues to spread beyond just the place of disaster [2]. Such impacts can become more severe when the affected countries and industries are unable to effectively combat it. In the case of the fishing industry, the lack of proper regulations can harm more than just the fish, but also the consumers who eat the contaminated fish.
References:
[1] Li M. Fishery legislative reform towards Japan’s Fukushima nuclear wastewater discharge into the sea—A Chinese perspective. Frontiers in Marine Science. 2023 Feb 21;10.
[2] BBC. Fukushima: Japan approves releasing wastewater into ocean. BBC News [Internet]. 2021 Apr 13; Available from: https://www.bbc.com/news/world-asia-56728068
[3] The Fukushima Daiichi Accident. Non-serial Publications. IAEA, Vienna. 2015.
In wetland fish farms, fish are not the only important residents – and their indispensable yet underrated cohabitants may just surprise you. Playing an important role in biogeochemical cycling in wetlands, bacterial communities are dynamic players of wetland ecosystem functions [1]. While coexisting with fish in wetland aquacultures, their diversity varies depending on environmental conditions and reared fish species [2]. Extensive research has been thus far carried out on this relationship, but our blog today will be focusing on a study by Tyagi et al. [2] on the less studied fish farms of East Kolkata Wetland (EKW).
Water Quality of East Kolkata Wetland’s Aquaculture Farms
Figure 1: Location of sampling sites and visualization of sewage pathways into fish farms [2]The aquaculture farms of EKW are set apart from others due to the input of treated sewage to propagate fish in channels such as shown in Figure 1 above [2,3]. Treated sewage water was deemed a suitable input for fish farms due to their supply of nutrients that promoted fish productivity [4]. Tyagi et al. used bacteria diversity to assess the water quality of these aquaculture farms, their relation to sewage inputs, and potential health risks [2].
The majority of the reported bacteria phyla and genera were ones that contribute to the ecological functions of ecosystems such as the genera Arcobacter and Pseudomonas for their role in nitrogen cycling and the genus hgcI clade for its role in carbon cycling [2].
However, some of the bacteria detected in the sewage samples were found to be at levels that suggested poor conditions for fish farming that could lead to higher mortality rates and diseases. Some examples included:
Genus C39’s rare appearance in a fish dominated setting and its correlation to mosquito breeding suggested that the sewage samples were ideal for breeding of Aedes koreicus mosquitoes [5].
Genus Cyanobium suggested the occurrence of algal blooms and possible eutrophic conditions [2]. They also suggest possible production of cyanotoxins that have negative repercussions on fish health [6].
Genus Pseudomonas (specifically the strain of Pseudomonas tructae) has been reported to be related to fish mortality due to its pathogenicity [7].
Genus Arcobacter possess species that are pathogenic, causing infections to fish organs [8].
How is bacterial diversity related to water quality?
Based on the correlation between specific bacterial abundance and environmental parameters, the proliferation of several toxigenic and pathogenic bacteria can be attributed to the favorable environmental conditions and poor water quality of the sewage water (despite treatment). The study took into account various water quality parameters such as biochemical oxygen demand (BOD), dissolved oxygen (DO), chemical oxygen demand (COD).
Figure 2: Correlation matrix of environmental parameters and bacteria community at (a) phylum level and (b) at genus level. Positive correlations are shown in blue, while negative correlations are shown in red. [2]Here are some examples of this phenomena:
Abundance of pathogenic genus Pseudomonas is strongly positively correlated to BOD in sewage that was found to be at values (as shown in Figure 2) beyond the healthy limit prescribed by India’s authorities (<=4) [2,9].
Harmful levels of phylum Cyanobacteria can be attributed to high levels of BOD and low levels of DO [2].
Overall, low DO, high BOD and COD led to poor water quality of the sewage samples with water quality index (WQI) values that did not meet the required standards [2]. The low water quality of sewage is hence the driver behind harmful bacterial community structure within the fish farms. This defeats the purpose of using sewage to promote fish production, as the treatment of sewage of water is insufficient and has led to the proliferation of bacteria that increases fish mortality. To prevent such occurrences, the sewage water must be properly managed and treated before use.
References:
[1] Portier RJ, Palmer SJ. Wetlands Microbiology: Form, Function, Processes. In: Hammer DA, editor. Constructed Wetlands for Wastewater Treatment. CRC Press; 2020. p. 89–105.
[2] Tyagi I, Tyagi K, Bhutiani R, Chandra K, Kumar V. Bacterial diversity assessment of world’s largest sewage-fed fish farms with special reference to water quality: a Ramsar site. Environmental Science and Pollution Research. 2021 Apr 4;28(31):42372–86.
[3] Abraham TJ, Qureshi QA, Bardhan A. Enteric Pathogenic and Multiple Antibiotic-Resistant Escherichia coli in Farmed Indian Major Carps and Their Environments in Peri-Urban Kolkata, India. Journal of Aquatic Food Product Technology. 2022 Oct 12;31(10):1092–108.
[4] Mandal R, Das A, Chattopadhyay D, Hussan A, Adhikari S, Paul B, et al. Use of sewage in split doses to enhance water productivity for fish culture. Aquaculture and Fisheries. 2021 Nov;6(6):609–16.
[5] Alfano N, Tagliapietra V, Rosso F, Manica M, Arnoldi D, Pindo M, et al. Changes in Microbiota Across Developmental Stages of Aedes koreicus, an Invasive Mosquito Vector in Europe: Indications for Microbiota-Based Control Strategies. Frontiers in Microbiology. 2019 Dec 10;10.
[6] Yanez-Montalvo A, Aguila B, Gómez-Acata ES, Guerrero-Jacinto M, Oseguera LA, Falcón LI, et al. Shifts in water column microbial composition associated to lakes with different trophic conditions: “Lagunas de Montebello” National Park, Chiapas, México. PeerJ. 2022 Sep 16;10:e13999.
[7] Oh WT, Kim JH, Jun JW, Giri SS, Yun S, Kim HJ, et al. Genetic Characterization and Pathological Analysis of a Novel Bacterial Pathogen, Pseudomonas tructae, in Rainbow Trout (Oncorhynchus mykiss). Microorganisms. 2019 Oct 10;7(10):432.
[8] Cui X, Zhang Q, Zhang Q, Zhang Y, Chen H, Liu G, et al. Research Progress of the Gut Microbiome in Hybrid Fish. Microorganisms [Internet]. 2022 May 1 [cited 2022 Jul 16];10(5):891. Available from: https://www.mdpi.com/2076-2607/10/5/891
[9] Guidelines for Water Quality Management [Internet]. CPCB | Central Pollution Control Board. 2008. Available from: http://www.cpcb.nic.in/
In this week’s blog, let us consider biological pollution in the form of invasive marine species and how it’s linked to the fishing industry. In their blog about marine pollution, Goh and Li addressed the distinction between alien species and invasive species, with invasive species being alien or non-native species that have dominated an ecosystem and brought upon negative effects [1]. When we talk about invasive species in the ocean, one prominent example would be that of the lionfish. In the video linked at the bottom of the post, marine biologist Jason Hall-Spencer succinctly explains how overfishing has led to the domination of lionfish in Mediterranean waters [2].
“There’s an acute biodiversity problem in that all of the big fish pretty much are being hunted and killed by humans. And it’s skewed the whole system towards small organisms [like the lionfish].”[2]
While the lionfish invasion is an interesting topic, I’d like to focus on another invasive marine creature – the jellyfish. Overfishing has frequently been linked to the extensive invasion and blooms of jellyfish [3]. But what about mariculture farms? In a case study of shrimp farms in Acaraú, Brazil, the population and size of Cassiopea spp, an invasive jellyfish species, was studied in relation to the environmental parameters of the farms and nearby mangroves [4].
It was found that the jellyfish population of the shrimp farms saw stable numbers throughout the year, and was not inflicted by the same seasonal variation in population size that was observed in the mangroves [4]. The jellyfish were also found in astonishing sizes, at 49 cm umbrella diameter, almost twice that of the global average [4].
Figure 1: Drone Image of Cassiopea spp blooms along the Brazilian coast [5].The study attributed these findings to the more stable supply of nutrients and organic matter originating from the shrimp farms compared to the mangroves, allowing the jellyfish population to maintain and establish itself in the ecosystem throughout the year [4]. Water effluent from shrimp farms are also significant contributors of organic matter – this was thought to promote vigorous heterotrophic feeding and immense growth of the jellyfish [4]. Such observations of population size and individual jellyfish growth hint that shrimp farms promote the invasion of the Cassiopea populations.
Here are some past events of Cassiopea spp invasions and their impacts on the ecosystem:
The invasion of extensive blooms of Cassiopea spp along the Meirim River estuary in Brazil was accompanied by a lack of seagrass, macroalgae, fish species such as mullet, snapper and flounders [6].
The growing spread of Cassiopea andromeda throughout the Mediterranean Sea with periodic outbreaks in areas such as Lebanon, Turkey and even the Maltese islands [7].
While the jellyfish population of the Acaraú shrimp farms is not a severe case of invasion, it is essential to understand the dynamics between population size and the shrimp farm effluent parameters to take note of what factors need to be monitored. Through this, further expansion and invasion of the jellyfish can be culled before it results in irreversible damage on the ecosystem.
References:
[1] Goh RT, Li HYJ. The Art of War/Invasion [Internet]. OCEAN-US MATTERS! 2020. Available from: https://blog.nus.edu.sg/waterwegoingtodoaboutmarinepollution/2020/07/16/invasion-attack/
[2] euronews. Invasive species: Are they really threatening the Mediterranean Sea and local fisheries? [Internet]. www.youtube.com. 2022 [cited 2023 Apr 12]. Available from: https://www.youtube.com/watch?v=mCEcp7eU7aI
[3] Richardson AJ, Bakun A, Hays GC, Gibbons MJ. The jellyfish joyride: causes, consequences and management responses to a more gelatinous future. Trends in Ecology & Evolution. 2009 Jun;24(6):312–22.
[4] Thé J, Barroso H de S, Mammone M, Viana M, Batista Melo CS, Mies M, et al. Aquaculture facilities promote populational stability throughout seasons and increase medusae size for the invasive jellyfish Cassiopea andromeda. Marine Environmental Research. 2020 Dec;162:105161.
[5] Thé J, Gamero-Mora E, Chagas da Silva MV, Morandini AC, Rossi S, Soares M de O. Non-indigenous upside-down jellyfish Cassiopea andromeda in shrimp farms (Brazil). Aquaculture. 2021 Feb;532:735999.
[6] Stampar SN, Gamero-Mora E, Maronna MM, Fritscher JM, Oliveira BSP, Sampaio CLS, et al. The puzzling occurrence of the upside-down jellyfish Cassiopea (Cnidaria: Scyphozoa) along the Brazilian coast: a result of several invasion events? Zoologia [Internet]. 2020 Sep 12;37:1–10. Available from: https://zoologia.pensoft.net/article/50834/
[7] Mammone M, Ferrier-Pagés C, Lavorano S, Rizzo L, Piraino S, Rossi S. High photosynthetic plasticity may reinforce invasiveness of upside-down zooxanthellate jellyfish in Mediterranean coastal waters. Campbell DA, editor. PLOS ONE. 2021 Mar 19;16(3):e0248814.
So far, we’ve established that the fishing industry has a large carbon footprint, be it from the use of diesel to power vessels, or the remobilization of carbon in disturbed marine sediments. Aquaculture farms are no different as emitters of greenhouse gas, but the current state of their technologies provide immense possibilities of growth and innovations that turn to more energy efficient, and clean technologies [1]. There is an increasing need for the fishing industry to develop such technologies, in order to reduce emissions and achieve a “zero carbon” status [2].
Figure 1: Strategies to achieve “zero carbon” fishery ports [2]A study by Alzahrani et al. suggested a possible pathway and actions to be taken in order to achieve this [2]. They procured a prototype model of a fishery port that possessed their own solar farm, with a micro-grid controlled by a smart decision-making system as shown in Figure 1 above [2]. The system would balance out surplus solar energy throughout the grid based on localized differences in supply and demand [2]. Overall, they stress the importance of an effective management and allocation system to maximize the benefits of locally produced renewable energy [2].
Figure 2: NGP-Taiwan’s solar fishery and electricity symbiosis project
Currently, there exists several aquaculture farms that have put into the play use of solar energy for their operations. One such fishery can be found in Taiwan which installed photovoltaic (PV) devices on top of the fish ponds as seen in Figure 2. This strategy was utilized due to Taiwan’s limited amount of viable non-mountainous land [3]. It was deemed as a win-win solution that consolidated various functions into a single location [3]. They could produce low carbon energy, while farming fish all in one place – what could possibly be bad about that?
Unfortunately, even solutions like this encounter several environmental impacts despite their environmentally-friendly intentions. In solar fishery farms such as the above, sunlight is blocked from entering the water. This can inhibit aquatic plant growth that is essential to maintain healthy levels of dissolved oxygen for the farmed fish [4]. Additionally, the water bodies may become heat sinks resulting in higher than normal water temperatures [4]. With regards to the fish farm operations, the deployment of PV panels can negatively affect fish productivity – excessive shading can reduce appetites, and reductions in primary producers such as phytoplankton can increase toxicity as nitrogen concentrations increase [5].
Overall, for such strategies to reap the maximum benefits (of reduced carbon emissions and increased clean energy production), planners and managers of these solar fisheries must take into account the trade-offs between solar power, fish production and environmental repercussions .
References:
[1] MacLeod MJ, Hasan MR, Robb DHF, Mamun-Ur-Rashid M. Quantifying greenhouse gas emissions from global aquaculture. Scientific Reports [Internet]. 2020 Jul 15;10(1):11679. Available from: https://www.nature.com/articles/s41598-020-68231-8
[2] Alzahrani A, Petri I, Ghoroughi A, Rezgui Y. A proposed roadmap for delivering zero carbon fishery ports. Energy Reports. 2022 Jun;8:82–8.
[3] Hsiung KH. Policy and Legal Issues of the Environmental and Social Inspection in Fishery-Solar Energy. IOP Conference Series: Earth and Environmental Science. 2022 Apr 1;1009(1):012009.
[4] Li P, Gao X, Li Z, Zhou X. Physical analysis of the environmental impacts of fishery complementary photovoltaic power plant. Environmental Science and Pollution Research. 2022 Feb 14;29(30):46108–17.
[5] Château PA, Wunderlich RF, Wang TW, Lai HT, Chen CC, Chang FJ. Mathematical modeling suggests high potential for the deployment of floating photovoltaic on fish ponds. Science of The Total Environment [Internet]. 2019 Oct 15 [cited 2021 Nov 21];687:654–66. Available from: https://www.sciencedirect.com/science/article/abs/pii/S004896971932474X
In a previous post in this blog, we touched on how bottom trawling was able to remobilise carbon stored in marine sediments and their potential role in exacerbating climate change [1]. I would like for us to consider if there are other ways in which the fishing industry has disturbed the ocean’s carbon cycle. Let us look deeper into how fish and marine animals can play a dynamic role in the sequestration of carbon – and consequently, how fisheries undermine that role.
Fish and Biogeochemical Cycles
Although limited, there have been recent research studies made on the relationship between fish biomass and carbon cycles. A study by Bianchi et al. in 2021 had indicated that fish communities were able to cycle biomass (by consuming primary production fixed by phytoplankton and releasing metabolic and organic waste as illustrated in Figure 1 below) at significant rates in areas of high fish abundance [2]. These areas can be found along the coastlines of continental shelves where productivity is highest [3]. It has been found that such organic waste particles from fish can sequester carbon for up to 600 years, especially at depths below 1000 m when the rate of sinking is at its peak [2,4].
Figure 1: Illustration of biomass cycling via respiration, organic waste particle production and diel vertical migrations (DVM) during preindustrial times [2]
Impact of Fishing Industry on Carbon Sequestration
Now that we are aware of the importance of fish in cycling and sequestering carbon, we need to consider how the fishing industry can negatively impact these engines of the oceanic carbon cycle.
Bianchi et al. also investigated how the fishing industry can significantly alter biogeochemical cycles in the ocean due to reduced fish biomass to cycle oxygen and export carbon [2]. As seen from Figure 2 below, fish biomass has reduced to as much as 20% of preindustrial times, especially in areas with high initial biomass, hence indicating heavy exploitation of productive ecosystems.
Figure 1: (A) Preindustrial biomass of fish, (B) fish biomass during global peak catch, and (C) percentage of biomass left relative to preindustrial biomass [2]As biomass is reduced greatly from preindustrial times, fish are less able to carry out their roles in cycling carbon by consuming phytoplankton and producing fecal pellets. Carbon sequestration becomes especially hindered when fish species that live near the seabed as the quickest source of sinking fecal pellets are extensively harvested. Additionally, due to the oceans’ biological pumps that transport carbon through the mesopelagic zone and prevents extensive mixing of carbon-rich waters up the water column, the potential exploitation of mesopelagic fish may lead to greater reductions in carbon sequestration [5,6]. Besides fish, the removal of large marine mammals such as whales through whaling (as a subsection of the fishing industry) have also been noted to reduce export and sequestration of carbon in marine sediments [7].
Figure 3: Referring to relevant points only, fishing directly impacts carbon cycle by removing (3) pellet-producing species, (4) fish near the seabed, and (7) large fish and marine mammals that should produce dead organic matter [7].Overall, more extensive research should be carried out moving forward to fully establish how marine animals act as drivers of the ocean’s biogeochemical cycles. This can be achieved by establishing more robust links between geochemical models and marine ecological studies. In doing so, it will be easier to place fishing activities as a disruptive force of such cycles.
References:
[1] Sala E, Mayorga J, Bradley D, Cabral RB, Atwood TB, Auber A, et al. Protecting the Global Ocean for biodiversity, Food and Climate. Nature. 2021 Mar 17;592:397–402.
[2] Bianchi D, Carozza DA, Galbraith ED, Guiet J, DeVries T. Estimating global biomass and biogeochemical cycling of marine fish with and without fishing. Science Advances. 2021 Oct 8;7(41).
[3] Atwood TB, Witt A, Mayorga J, Hammill E, Sala E. Global Patterns in Marine Sediment Carbon Stocks. Frontiers in Marine Science. 2020 Mar 25;7.
[4] Boyd PW, Claustre H, Levy M, Siegel DA, Weber T. Multi-faceted particle pumps drive carbon sequestration in the ocean. Nature. 2019 Apr;568(7752):327–35.
[5] Cavan EL, Laurenceau-Cornec EC, Bressac M, Boyd PW. Exploring the ecology of the mesopelagic biological pump. Progress in Oceanography. 2019 Sep;176:102125.
[6] Davison PC, Checkley DM, Koslow JA, Barlow J. Carbon export mediated by mesopelagic fishes in the northeast Pacific Ocean. Progress in Oceanography. 2013 Sep;116:14–30.
[7] Cavan EL, Hill SL. Commercial fishery disturbance of the global ocean biological carbon sink. Global Change Biology. 2021 Dec 18;28(4):1212–21.
On a fishing vessel, there is no end to the need for fuel to power its operations. To operate fishing vessels for extended periods of time, large amounts of fuel are needed to power the engines. Fuel is also needed to deploy heavy machinery such as towing machines on trawling vessels. We also cannot ignore the intensive fuel use of industrial refrigerators on board the vessels to store the fish. When we consider all these, it is not a surprise that purchasing fuel oil accounts for up to 60% of operating costs on a fishing vessel [1].
Figure 1: Effect of vessel length and number of days at sea on amount of fuel consumed [2]A study by Chassot et al. investigated the variations in fuel consumption with increasing vessel size and number of days at sea for a fleet of purse seiners in the western Indian Ocean [2]. Their results showed that larger vessels that spend longer periods of time out at sea would consume larger amounts of fuel as shown in Figure 1 [2]. Data was also obtained on greenhouse gas emissions from the fleet, showing increases proportional to fuel consumption as seen in Figure 2 [2]. Considering that the energy efficiency of diesel engines have been found to be only up to 40%, the environmental consequences can be said to be disproportionate to the amount of energy obtained [3].
Figure 2: Variability in (a) fuel consumption, (b) greenhouse gas emissions, and (c) sulfur dioxide emissions from a western Indian Ocean purse seine fishery from 1981 to 2019 [2]
Fuels for Cooling Refrigerator On-board Fishing Vessels
The presence of extensive industrial refrigerators is what sets the fuel consumption of fishing vessels apart from that of other maritime vessels. Due to the perishable nature of fish, these refrigerators are essential to ensure freshness of fish that are safe for consumption [4]. They are traditionally powered by electricity generated by the vessel’s diesel engines to drive ice making and air conditioning systems [3]. It has been found that this method of powering the refrigerators consumes an excessive amount of fuel as the biggest consumers of energy on the fishing vessel [5,6].
Fortunately, there have been recent studies investigating the possibility of replacing fuel with other forms of energy such as Liquefied Petroleum Gas and solar energy [4,7], or recovering energy by using excess exhaust heat for adsorption refrigerators [3]. Continuing such studies is critical to find the optimum powering systems for refrigerators with high energy efficiency and minimal carbon footprints.
Other Forms of Pollution due to Fuel Consumption in the Fishing Industry
On the topic of fuel, like all shipping vessels, it is without a doubt that fishing boats also contribute towards the disposal of oil products into the ocean due to the usage of oil as engine fuel [8]. Waste oils such as lubricating oil and bilge water are also produced from the myriad of machinery and moving parts in a vessel, contributing towards the [8].
If we look further than the fishing vessel, the overall fuel consumption of the fishing industry rises exponentially as fuel is needed to manufacture the vessel and gear, prepare bait, transport the fishery hauls, package the products, and more [9]. Fuel is consumed in every step of the supply chain for fish products, making it hard to effectively curtail consumption in the industry [9].
Overall, it is evident that the fishing industry is one that is extremely fuel intensive, raising concerns on the extent of its emission footprint and impact on air quality and climate change.
References:
[1] Saputra H, Fathallah AZM. Formulation of Fuel Oil Consumption Estimation on The Fishing Vessels Through The Gill Net and Bubu Fishing Gears for Evaluating Fuel Subsidies in Bintan Regency – Indonesia. IOP Conference Series: Earth and Environmental Science. 2023 Mar 1;1148(1):012015.
[2] Chassot E, Antoine S, Guillotreau P, Lucas J, Assan C, Marguerite M, et al. Fuel consumption and air emissions in one of the world’s largest commercial fisheries. Environmental Pollution. 2021 Mar;273:116454.
[3] Xu X, Li Y, Yang S, Chen G. A review of fishing vessel refrigeration systems driven by exhaust heat from engines. Applied Energy. 2017 Oct;203:657–76.
[4] Sunardi, Kadhafi M, Khulwatu M, Rahman MA, Sulkhani E. Technical study on fish cooling refrigerator using Liquefied Petroleum Gas (LPG) fuel generator on fishing vessel. IOP Conference Series: Earth and Environmental Science. 2020 May 1;493(1):012034.
[5] Alzahrani A, Petri I, Rezgui Y, Ghoroghi A. Developing Smart Energy Communities around Fishery Ports: Toward Zero-Carbon Fishery Ports. Energies. 2020 Jun 1;13(11):2779.
[6] Ireland’s Seafood Development Agency. Resource Efficiency Guide for Seafood Processors [Internet]. Dublin, Ireland: Bord lascaigh Mhara; 2016 p. 40. Available from: https://bim.ie/wp-content/uploads/2021/01/BIM-Resource-Efficiency-Guide-for-Seafood-Processors.pdf
[7] Hu B, Bu X, Ma W. Thermodynamic Analysis of a Rankine Cycle Powered Vapor Compression Ice Maker Using Solar Energy. The Scientific World Journal. 2014;2014:1–6.
[8] Lin B, Lin CY, Jong TC. Investigation of strategies to improve the recycling effectiveness of waste oil from fishing vessels. Marine Policy. 2007 Jul;31(4):415–20.
[9] Parker RWR, Blanchard JL, Gardner C, Green BS, Hartmann K, Tyedmers PH, et al. Fuel use and greenhouse gas emissions of world fisheries. Nature Climate Change. 2018 Apr;8(4):333–7.
Pollution from the fishing industry goes beyond just the dumping of nets, lines and microplastics into the ocean. Noise pollution is surprisingly one of the most significant impacts of commercial fishing methods. While there has been considerable research done on noise pollution emitted from vessels in general, studies focusing on fishing vessels specifically have thus far been limited. Fortunately, slow but steady progress has recently been made on investigating the extent of noise pollution and its impacts on different marine species. In this blogpost, we shall be using a 2021 study on bottom trawling noise to evaluate the extent and impact of noise pollution from bottom trawlers.
Bottom Trawling Noise
Noise pollution from bottom trawlers is an example of “anthropogenic noise” – an unwelcome and pervading cacophony of sounds emitted from human activities underwater [1]. These sounds can be emitted from the engine near the water’s surface or from the trawling gear that are dragged across the seabed. Hums can also be generated from trawl lines due to cable tension while in the water.
In their study, Daly and White’s comparison of noise extent from different sources revealed that the trawling activities mentioned above emitted noise levels that were significantly higher than ambient noise and noise from the research vessel [1]. This can be seen from Figure 1 below, Sound Pressure Levels (SPLs) of trawling noise were highest for each sampling site and for each frequency band [1].
Figure 1: Range of Sound Pressure Levels for each frequency band (categorised by noise originating from trawling event, survey vessel and ambient noise for two sites – PANiC and GIST)
When trawling noise was further broken down into surface noise (from the fishing vessel) and seabed noise (from trawling gear lowered onto the seabed), it was revealed that seabed sources of noise contributed to a larger and more effective portion of the noise generated [1]. Figure 2, as seen below, reveals that the (lateral and vertical) transmission loss of noise propagated from the surface was greater compared to noise originating at lower depths [1].
This signifies that noise originating from the seabed would propagate more effectively through the water column – this would include noise from trawling equipment on the seabed. Such results solidify the claims that bottom-trawling vessels could incur greater noise pollution (and its related damage on the environment) compared to regular vessels due to equipment extending to the bottom of the water column.
Figure 2: Modelled Transmission Loss outputs at the trawling site. (a) shows sound speed profile while (b) and (c) shows modelled transmission loss with noise sources located 0m and 224m deep respectively.
Another concern that was brought up in the study was the influence of seafloor topography on the amplification or reduction of noise pollution from trawlers [1]. Further research into the topic could possibly aid in the identification of zones that are more vulnerable to noise pollution.
Significance of Trawling Noise
While we may now be aware of the contribution of bottom-trawling towards noise pollution, it is also important to understand why such an issue can be problematic and require solutions. With noise pollution, the impact on marine animals is significant, with their behaviour and cognition being most notably affected.
Studies on marine animal response to noise pollution have shown evidence of avoidance behaviour and changing migration patterns in marine animals. From the perspective of the fishing industry, such changes in behaviour can reduce trawling productivity as fish density decreases and their movement is disturbed [2,3]. Other impacts include communication impediment for marine mammals (that affects crucial activities and functions such as breeding and socialising) and avoidance of feeding areas, all of which can indirectly affect their survival [4,5].
In Daly and White’s study, focus was placed on physiological damages instead of behavioural changes in different cetacean species. Their estimates showed that during trawling activities, the noise levels close to the source had exceeded the threshold at which most cetacean species can endure without suffering temporary harm [1]. At some instances, noise levels had even been high enough to incur permanent damage to the selected cetaceans [1].
Studies such as this prove that mitigation measures must be implemented to regulate bottom trawling activities directly, by modifying trawl equipment and operations, or indirectly, by banning trawling operations in more vulnerable environments.
References:
[1] Daly E, White M. Bottom trawling noise: Are fishing vessels polluting to deeper acoustic habitats? Marine Pollution Bulletin. 2021 Jan;162:111877.
[2] Ona, E., & Godø, OR. Fish reaction to trawling noise: the significance for trawl sampling. Rapp. P.-V. Réun. Cons. Int. Explor. Mer. 1990; 189:159–166.
[3] Handegard N. Avoidance behaviour in cod (Gadus morhua) to a bottom-trawling vessel. Aquatic Living Resources. 2003 Jul;16(3):265–70.
[4] Erbe C, Marley SA, Schoeman RP, Smith JN, Trigg LE, Embling CB. The Effects of Ship Noise on Marine Mammals—A Review. Frontiers in Marine Science. 2019 Oct 11;6.
[5] Gomez C, Lawson JW, Wright AJ, Buren AD, Tollit D, Lesage V. A systematic review on the behavioural responses of wild marine mammals to noise: the disparity between science and policy. Canadian Journal of Zoology. 2016 Dec;94(12):801–19.
A previous post in this blog explored sediments as sinks for contaminants that get reintroduced into the ecosystem after trawling events [1]. In this case, however, we go further into depth on how marine sediments in particular are prominent carbon sinks, creating a semi-permanent store of carbon preserved from as far as millions of years ago.
Sediments as Carbon Sinks
A study by Atwood et al. in 2020 attempted to map and consolidate the amount of carbon stocks available in marine sediments based on data from various published sources [2]. Their numerical model quantified carbon stocks in marine sediments at 1 m depth globally to be at 2322 Pg, with greater amounts found in deep-sea basins compared to shallower waters near the continental shelf as illustrated in Figure 1A below [2].
Figure 1: (A) Distribution of carbon stored in top 1m of marine sediments globally; (B) Uncertainty in carbon amounts; (C) Marine protected areas in red [3]
Bottom-Trawling Remobilisation of Carbon
While the article does not focus on bottom trawling specifically, it mentions bottom-trawling as a potential anthropogenic activity that could remobilise the stored carbon. This phenomenon was instead investigated by a more recent study in Sala et al (2021). Using the modeled data above and a satellite-inference of bottom-trawling range, they were able to estimate that 1.47 Pg of the stored carbon would be metabolized into aqueous CO2 emissions within a year after a trawling event [3]. The subsequent 9 years of trawling would have seen reduced emissions at around 0.58Pg of CO2 [3].
Such values were found to be comparable to emissions from the global aviation industry, making it a significant contributor to global carbon emissions [4,5]. These quantities of aqueous CO2 emissions can threaten the ocean’s normal functioning of its carbon cycle and potentially release more CO2 into the atmosphere [3]. This can greatly aggravate the extent of climate change and its impact on the environment [5].
Marine Protected Areas to Reduce Emissions
Figure 2: Changes in (b) biodiversity conservation, (d) catchable species due to spillover from marine protected areas (MPAs), and (f) carbon disturbance in response to changes in area of ocean protected (blue bars indicating current MPAs). Proposed MPAs that prioritize (a) biodiversity, (c) food, and (e) carbon [3]
It is also important to note that as trawling technology improves to go further and deeper, there is greater possibility of remobilising carbon stored in deeper basin areas and the estimated values above would see definite increases. To mitigate this, Sala et al. proposed potential locations for MPAs that could effectively curtail the remobilisation of carbon [3]. The allocation of these MPAs were made easy due to geographic concentration of trawling activities. As such, they concluded that:
“At our working resolution of 50 km × 50 km, eliminating 90% of the present risk of carbon disturbance due to bottom trawling would require protecting 3.6% of the ocean (mostly within EEZs)”[3]
The implementation of MPAs in areas of top priority would hence ensure maximum carbon benefits with only a small fraction of the ocean protected as seen in Figure 2f above.
References:
[1] Bradshaw C, Tjensvoll I, Sköld M, Allan IJ, Molvaer J, Magnusson J, et al. Bottom trawling resuspends sediment and releases bioavailable contaminants in a polluted fjord. Environmental Pollution. 2012;170:232–41.
[2] Atwood TB, Witt A, Mayorga J, Hammill E, Sala E. Global Patterns in Marine Sediment Carbon Stocks. Frontiers in Marine Science. 2020 Mar 25;7.
[3] Sala E, Mayorga J, Bradley D, Cabral RB, Atwood TB, Auber A, et al. Protecting the Global Ocean for biodiversity, Food and Climate. Nature. 2021 Mar 17;592:397–402.
[4] Rocliffe S, and Leeney RH, Research briefing: Bottom trawling and the climate crisis. Blue Ventures, London, United Kingdom. 2021.
[5] Einhorn C. Trawling for Fish May Unleash as Much Carbon as Air Travel, Study Says. The New York Times [Internet]. 2021 Mar 17; Available from: https://www.nytimes.com/2021/03/17/climate/climate-change-oceans.html
Long gone are the days of simple fishing lines and traps, as commercial fishing evolved through the technological advancements and the mechanization of fishing methods [1,2]. No longer are their activities limited by depth as is evident from the commonly utilized bottom-trawling methods. However, the evolution of the fishing industry comes at a cost when bottom-trawling ends up triggering a cascade of sediment-based pollution issues on the ocean floor.
Bottom Trawling
Bottom-trawling is a fishing method that involves the use of a weighted meshed net that is kept open while it sinks to the seafloor and towed across the seabed [3]. Fish are trapped in the net as machinery onboard the fishing vessel hauls the net back up to the surface [3]. Depending on the target species of the haul, different features are attached to the nets but no matter the type of equipment, the bottom-trawling method is generally thought to be destructive regardless [3,4].
Its destructive nature lies in the fact that its large nets are indiscriminate with what they hit, collapse and tear out in their goal to capture as many fish as possible along the seafloor. In the process, it is inevitable that sediment on the seabed be stirred up and resuspended in the water.
Resuspension of sediments in Eidangerfjord in Norway
This sediment disturbance phenomenon brought upon by bottom trawling was investigated specifically in a fjord in Norway by Bradshaw et al in a field investigation detailed as in Figure 1 below [5]. While not many fisheries operate there, a small prawn fishery can be found operating within the fjord that utilizes a bottom-trawling method [5]. Although their scale of operations is limited to 4 fishing boats and the use of small trawls, the impact of their bottom-trawling activities were still significant [5].
Figure 1: Path through Eidangerfjord taken by trawler, with details on locations of caged mussels and measurement stations as well as how measurements on turbidity and current were taken [5].Through their research, Bradshaw and his team quantified the vertical and horizontal extent of the sediment plumes created by the trawls to be up to 18 meters in height and 150 meters wide [5]. The sizeable plumes multiplied the amount of total suspended matter in the waters up to 70 times the usual [5]. They concluded the possibility of a lasting blanket of suspended sediment over the seabed due to the several days needed for the small sediments to fall out of suspension [5].
Why does this spell trouble for the environment?
We must first consider the anthropogenic history of the fjord. In the 1950s, a nearby magnesium production plant had released toxic by-products such as dioxins and polycyclic aromatic hydrocarbons (PAHs) into a neighboring fjord which eventually leaked into the Eidangerfjord [5,6]. While the authorities have attempted to reduce the extent of contamination through restrictions and treatments, the contamination persists in the accumulated sediment on the seabed [5]. Secondly, we must also consider the role of sediments as highly effective sinks and sources of contaminants [7]. Studies have shown that sediments take up
Figure 2: Location of Eidangerfjord in relation to Frierfjord (circled) and the source of contaminants (black marker) in southern Norway [6]This had immense repercussions on the environment when you consider the ability of bottom-trawling to resuspend these contaminated sediments. The research carried out by Bradshaw and his team suggested that most of the contaminants found in the water column came from the sediments suspended by bottom-trawling [5].
Their research also revealed that the lasting blanket of suspended sediment paired with the slow sediment transport rate out of the fjord indicates a “minimal net removal and/or degradation of contaminants” [5]. This means that whatever contaminants entered the fjord stayed within the fjord for a long period of time. The settling of contaminated sediments onto the seabed also creates conducive anaerobic conditions for the continued preservation of pollutants [7]. This would have led to the long-term accumulation of toxins within the fjord – a sink of contaminants that threatened to bring massive repercussions due to bottom-trawling [5,7]. Although Eidangerfjord may not have been directly contaminated by the magnesium plants and measured lower pollution levels than Frierfjord, the long residency period of the contaminants exacerbates the impact that the contaminants have on the ecosystem [6].
In this study, blue mussels Mytilus edulis were introduced into the fjord as field-exposed indicators of contaminant uptake by marine organisms in the fjord [5]. The concentration of contaminants such as PAHs and polychlorinated dibenzo-p-dioxins and -furans (PCDD/Fs) in the mussels were used to gauge the bioavailability of the contaminants [5]. The increasing concentrations within mussels nearer to the seabed revealed a definite uptake of contaminants by marine organisms, with sediments being the clear source of contaminants [5,8]. Studies have shown that the uptake of such contaminants are more prominent in filter feeders, but biomagnification through the food web guarantees the persistence of these contaminants in most other aquatic organisms in the ecosystem [5,8]. It is without a doubt that concentrations rise exponentially up the food chain, with humans bearing the highest concentrations [9]. Estimations also revealed that continued consumption of these marine organisms by humans could lead to potentially toxic repercussions [5,8].
Moving forward, environmental risk assessments of contamination in sediment beds should be carried out prior to bottom trawling to evaluate the extent of potential harm to the environment [7]. Factors such as contaminant types, species of marine organisms in the ecosystem, and other external stressors that affect the bioavailability of the contaminants should be monitored. Guidelines on bottom trawling operations need to take into account these assessments to decide on appropriate locations and post-trawling management efforts. The next blog post will evaluate how sediment resuspension by bottom trawling can be exacerbated by climate change and in turn, how it can contribute to it as well.
References:
[1] Brandt, A. R.F.T. von , Borgstrom, . Georg A. , Pike, . Dag , Purrington, . Philip F. and Sainsbury, . John C. (2022, February 1). commercial fishing. Encyclopedia Britannica. https://www.britannica.com/technology/commercial-fishing
[2] Commercial fishing methods. Sustainable Fisheries UW. (2019, August 8). Retrieved March 9, 2023, from https://sustainablefisheries-uw.org/seafood-101/commercial-fishing-methods/
[3] Fisheries, N. O. A. A. (2022, July 6). Fishing gear: Bottom trawls. NOAA. Retrieved March 9, 2023, from https://www.fisheries.noaa.gov/national/bycatch/fishing-gear-bottom-trawls#:~:text=Bycatch%20Reduction-,Bottom%20trawling%20is%20a%20fishing%20practice%20that%20herds%20and%20captures,Bottom%20trawl
[4] L Windom, H., & Stickney, R. R. (1976). Environmental aspects of dredging in the Coastal Zone. C R C Critical Reviews in Environmental Control, 6(2), 91–109. https://doi.org/10.1080/10643387609381635
[5] Bradshaw, C., Tjensvoll, I., Sköld, M., Allan, I. J., Molvaer, J., Magnusson, J., Naes, K., & Nilsson, H. C. (2012). Bottom trawling resuspends sediment and releases bioavailable contaminants in a polluted fjord. Environmental Pollution, 170, 232–241. https://doi.org/10.1016/j.envpol.2012.06.019
[6] Hylland, K., Ø. Aspholm, O., Knutsen, J. A., & Ruus, A. (2006). Biomarkers in fish from dioxin-contaminated fjords. Biomarkers, 11(2), 97–117. https://doi.org/10.1080/13547500600565602
[7] Chiaia-Hernández, A. C., Casado-Martinez, C., Lara-Martin, P., & Bucheli, T. D. (2022). Sediments: Sink, archive, and source of contaminants. Environmental Science and Pollution Research, 29(57), 85761–85765. https://doi.org/10.1007/s11356-022-24041-1
[8] Fletcher, C. L., & McKay, W. A. (1993). Polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (pcdfs) in the aquatic environment — a literature review. Chemosphere, 26(6), 1041–1069. https://doi.org/10.1016/0045-6535(93)90194-a
[9] Davies, O. A., Amachree, D., & Kpikpi, P. B. (2019). Contamination of Dioxins in Nigerian Inland Waters: A Review. Sumerianz Journal of Scientific Research, 2(12), 183–190.
With the abundant usage of plastics in our current lifestyle, microplastics have come to be dispersed throughout the natural environment to the extent where they have reached the far reaches of the Arctic and Antarctic [1]. Oceans, especially, have become the holding ground for large quantities of microplastics, whether they were washed offshore from land or were directly dumped into the sea.
The fishing industry is one such source of sea-based microplastic pollution due to their usage of plastic fishing gear that degrade under rough environmental conditions. Although not well-studied, there has been some research on the matter to investigate microplastic pollution from the fishing industry.
Our previous blogpost touched on one such case study in Norway that proved fishing gear indeed emitted microplastics from wear and tear [2]. Similar research had also been carried out in Weihai, a coastal fishing city in China [3]. This case study, however, was able to quantify the exact contribution of fisheries towards microplastic pollution within that area [3].
Microplastics from the fishing city of Weihai
The coastal waters of Weihai are saturated with fishing grounds for marine aquaculture and commercial fishing of prawn, kelp, oysters and other seafood [3]. Despite its dominant fishing industry, Weihai is also home to several scenic spots and bays, such as Liugong Island and Jingzi Bay, that were demarcated as restricted or prohibited areas for fisheries [3].
Figure 1: Fishing boats docked at Shidao fishing port in Rongcheng, Wehai [4]Seawater samples from a variety of sites in both protected areas and fishing grounds were collected and their microplastic content were compared based on their abundance and characteristics [3]. The results of the study revealed that microplastic concentration was highest in the sites closest to the fishing grounds and most of the microplastics could be traced back to fishing gears based on their polymer type, shape and colour [3]. A total of 73.6% of the microplastics sampled were concluded to be sourced from polyethylene and polypropylene fishing gear [3].
Studies such as this reveal how the fishing industry has become a major contributor to microplastic pollution, especially in coastal fishing cities where fishing activity is highly concentrated. It raises the question of what kind of negative impacts microplastic pollution can bring and if substantial, why has their pollutive nature been allowed to continue at this level?
So why do we care about microplastics?
Surely they’re too small to pose a problem at all? Unfortunately, the phrase “strength in numbers” is immensely relevant to these extremely small plastic fragments. As they travel through the marine environment, microplastics are consumed by marine creatures and slowly bioaccumulate within them [5]. As the concentration of these microplastics increase within their bodies, the impact on the health of marine animals becomes more pronounced and deadly. These impacts include suffocation, diminished metabolism and poisonous effects due to ingestion of toxic chemicals [5]. Many aspects of a marine creature’s normal biological functions are inhibited by significant concentrations of microplastic within their bodies, leading to the overall reduction of growth rate and increased mortality.
Such is the tragic fate of fish exposed to microplastics in the marine environment, especially in coastal areas where concentrations are much more significant [5]. Although the loss of biodiversity is in itself a negative impact of microplastic pollution, the severity becomes larger when we take into consideration the impact on food security, especially for communities dependent on seafood. It is also important to consider how microplastics can be transferred from seafood to humans upon consumption and consequently hand over the negative impacts of the bioaccumulation of microplastics.
References:
[1] Aves, A. R., Revell, L. E., Gaw, S., Ruffell, H., Schuddeboom, A., Wotherspoon, N. E., LaRue, M., & McDonald, A. J. (2022). First evidence of microplastics in Antarctic Snow. The Cryosphere, 16(6), 2127–2145. https://doi.org/10.5194/tc-16-2127-2022
[2] Syversen, T., Lilleng, G., Vollstad, J., Hanssen, B. J., & Sønvisen, S. A. (2022). Oceanic plastic pollution caused by Danish seine fishing in Norway. Marine Pollution Bulletin, 179, 113711. https://doi.org/10.1016/j.marpolbul.2022.113711
[3] Zhang, X., Li, S., Liu, Y., Yu, K., Zhang, H., Yu, H., & Jiang, J. (2021). Neglected microplastics pollution in the nearshore surface waters derived from coastal fishery activities in Weihai, China. Science of The Total Environment, 768, 144484. https://doi.org/10.1016/j.scitotenv.2020.144484
[4] 郭凯. (2021). Fishing boats prepare to sail in Weihai. Chinadaily.com.cn. Retrieved February 16, 2023, from https://global.chinadaily.com.cn/a/202102/23/WS60347502a31024ad0baaa719_1.html
[5] Vázquez-Rowe, I., Ita-Nagy, D., & Kahhat, R. (2021). Microplastics in Fisheries and Aquaculture: Implications to food sustainability and safety. Current Opinion in Green and Sustainable Chemistry, 29, 100464. https://doi.org/10.1016/j.cogsc.2021.100464
So we’ve looked into the matter of fishing nets and gears, and the whole shebang on ghost fishing. These are obviously the more common and most visible pollutive issues with regards to the fishing industry. But what about the micro ones? The issues that are so small you wouldn’t think to worry about them at first glance. With microplastics, it’s possible that they may have been too small to see at all.
Microplastics are most commonly defined as plastics that are <5mm and can come from various sources – one of which would be the fishing industry [1]. Fishing nets don’t have to be discarded into the ocean as a whole for them to wreak havoc on the environment. Even while they are in usable condition and in active operation, fishing gear can still manage to pollute the ocean through the gradual release of microplastics into the ecosystem [2].
When fishing equipment are cast out to sea from the vessels, they encounter harsh natural elements such as strong water currents, rough sea surface features, and aggressive wave formations that apply friction on the fishing gear [2]. Despite their long-hailed durability, plastic nets and lines are not immune to wear and tear, hence are susceptible to these natural elements that slowly chip away at their forms, producing microplastics that escape into the marine environment.
Of course, it goes without saying that Abandoned, Lost and otherwise Discarded Fishing Gear (ALDFG) are also sources of such microplastics as they spend their remaining lifetime floating through the oceans [2].
Microplastics from Danish seine fishing
Previous studies had already reported that Norwegian fisheries as a whole emit around 200,00 kilograms of microplastics annually [3]. A recent study by Syverson et al [3] had attempted to assess the contribution of specifically Danish seine fishing in Norway towards this mass of microplastic pollution in the ocean.
Figure 1: Illustration of Danish seine fishing method and stages [4]Danish seine fishing, also known as anchor seining, involves the use of ropes and a conical net that sweeps through the water for fish before they are slowly hauled back up [3,4]. The report was able to pick out various reasons for the degradation of these plastic seine ropes, and cited exposure to UV radiation as the most common cause [3]. After being weakened by UV radiation, the ropes are more vulnerable to wear and tear due to friction when in contact with the water and seabed.
Figure 2: Worn Danish seine rope after 12 months of use [3]In the end, it was found that Danish seine fishing gear suffered an annual total mass loss of up to 97,000 kilograms due to wear and tear, half of which was contributed by the larger fishing vessels. Although the results suggest significant contribution of microplastics from fishing gear, it is important to note that such studies come with significant amounts of uncertainty due to the difficulty in obtaining large and representative sample sizes, as well as trying to account for the myriad of factors that could affect wear and tear.
References:
[1] US Department of Commerce, N. O. and A. A. (2016, April 13). What are microplastics? NOAA’s National Ocean Service. Retrieved February 10, 2023, from https://oceanservice.noaa.gov/facts/microplastics.html
[2] Montarsolo, A., Mossotti, R., Patrucco, A., Caringella, R., Zoccola, M., Pozzo, P. D., & Tonin, C. (2018). Study on the microplastics release from fishing nets. The European Physical Journal Plus, 133(11). https://doi.org/10.1140/epjp/i2018-12415-1
[3] Syversen, T., Lilleng, G., Vollstad, J., Hanssen, B. J., & Sønvisen, S. A. (2022). Oceanic plastic pollution caused by Danish seine fishing in Norway. Marine Pollution Bulletin, 179, 113711. https://doi.org/10.1016/j.marpolbul.2022.113711
[4] Australian Fisheries Management Authority. (2014, March 22). Danish seine. Australian Fisheries Management Authority. Retrieved February 10, 2023, from https://www.afma.gov.au/fisheries-management/methods-and-gear/danish-seine
Even after the fishing boats have left for land, the fishing industry continues to wreak havoc on the marine ecosystem via ghost fishing – the killing of marine animals by the masses of discarded fishing gear floating around the ocean after disposal [1].
Officially referred to as Abandoned, Lost or otherwise Discarded Fishing Gear (ALDFG), these pollutants may have entered the marine environment due to a myriad of reasons, some of which have been listed in Figure 1 below [2]. They could have been intentionally disposed of into the ocean due to irreparable damage, lack of space or simply for convenience’s sake [2].
Alternatively, some may have been unintentionally introduced into the marine environment due to poor weather conditions or wear and tear of equipment while in the water [2,3]. While this suggests that some extent of fishing gear disposal may be “inevitable”, it does not excuse the negative impacts of these pollutants and the extent to which they have harmed marine ecosystems [2].
Figure 1: Causes of ALDFG (Source: FAO [2])Schools of fish, the curious seal, and the unsuspecting turtle are all victims to these silent killers as marine animals continue to get entangled, strangulated and irreversibly scarred by improperly discarded fishing gear. Ghost fishing targets all marine organisms indiscriminately, killing fish beyond their target group as well as vulnerable and at-risk marine species [2]. Predator and scavenger species are also implicated when they get attracted to concentrations of prey species entangled in the fishing gear [3].
When fish are caught in these derelict nets, the population of fish available for human consumption further drops. It can be inferred that the pollutive nature of the fishing industry has created a positive feedback cycle that only serves to exponentially reduce the population of fish as the fishing industry grows without proper regulations – a situation that does not help our food security in any way.
Attempts have been made to quantify ghost fishing mortality from specific types of gear through models that take into account the number of ghost fishing gear, “number of effective contact”, death rate, and other spatial and temporal parameters [4,5,6]. A specific case study by Matsuaoka [4] in southern Japan revealed a mortality of up to 500,000 octopuses within a year, in a fishing ground covering 2,390,000 square meters. This value was found to be a considerable amount when compared to the yearly yield from the fishing grounds, further cementing the notion that ghost fishing can significantly curtail food availability [4].
Figure 2: Examples of ghost fishing by cage traps and gillnets (Source: Matsuoka [4])Despite the widespread acknowledgement of the destructiveness of ALDFG in the form of ghost fishing, the extent of their disposal and circulation in the oceans remain to be most regretfully, poorly understood. Data regarding their volume and physical concentration are outdated and unrefined, making it hard to convince people with the authority to enact changes of the necessity of their removal.
Perhaps, moving forward, more intensive research on these sea-based pollutants can provide greater insight into target locations or specific problematic sources of ALDFG.
References:
[1] US Department of Commerce, N. O. and A. A. (2011, September 27). What is ghost fishing? NOAA’s National Ocean Service. Retrieved February 1, 2023, from https://oceanservice.noaa.gov/facts/ghostfishing.html
[2] Macfadyen, G., Huntington, T., & Cappell, R. (2009). Abandoned, lost or otherwise discarded fishing gear Vol. 185, Ser. UNEP REGIONAL SEAS REPORTS AND STUDIES. United Nations Environment Programme.
[3] Gilman, E., Musyl, M., Suuronen, P., Chaloupka, M., Gorgin, S., Wilson, J., & Kuczenski, B. (2021). Highest risk abandoned, lost and discarded fishing gear. Scientific Reports, 11(1). https://doi.org/10.1038/s41598-021-86123-3
[4] Matsuoka, T., Nakashima, T., & Nagasawa, N. (2005). A review of Ghost Fishing: Scientific Approaches to evaluation and solutions. Fisheries Science, 71(4), 691–702. https://doi.org/10.1111/j.1444-2906.2005.01019.x
[5] Guillory, V. (1993). Ghost fishing by Blue Crab Traps. North American Journal of Fisheries Management, 13(3), 459–466. https://doi.org/10.1577/1548-8675(1993)013<0459:gfbbct>2.3.co;2
[6] Kaiser, M. J., Bullimore, B., Newman, P., Lock, K., & Gilbert, S. (1996). Catches in ‘ghost fishing’ set nets. Marine Ecology Progress Series, 145, 11–16. https://doi.org/10.3354/meps145011
As of recent years, media coverage of marine pollution has been dominantly focused on plastic, primarily that of single-use plastics that are thrown away by consumers and washed out to sea at the end of their life cycle [1]. And for good reason too – single use plastics make up around 50% of the total amount of plastic being produced annually and more often than not find their way into the ocean due to improper waste disposal [2]. Their devastating effects towards the marine environment are widely researched and acknowledged, befitting of the spotlight they have received.
However, marine pollution goes beyond just single-use plastics. Recent studies are now critiquing the media and government’s narrow focus on the disposal of end-of-life plastics originating from the consumer end of the global supply chains, instead of tackling the larger systems at play [3,1]. While we should not disregard the relevance of single-use plastics, perhaps it is time to broaden our perspectives and venture to uncover other significant yet less publicly condemned sources of marine pollution. And what better way to start than to turn towards the one industry with its operations dependent on the ocean itself and has precariously floated under the radar of public scrutiny for its pollutive nature?
The Fishing Industry
Source: FAO [4]
Think of your weekly grocery runs to the supermarket or the neighborhood fishmonger and being met with a variety of fish and crustaceans for your choosing. Have you ever stopped to consider how this seemingly never-ending (and always replenishing) supply of fish came to existence?
It is definitely no miracle that brought these fish right to your markets for you to purchase whenever you craved it. Instead, it’s this huge fishing industry that sends out countless fishing vessels out to sea every day, and the extensive expanse of fish farms cultivating the fish that we so eagerly consume. It is an industry that we depend so heavily on to meet our food consumption levels such that around 40% of the global population relies on seafood for at least 20% of their intake of animal protein [4]. In higher income countries, the total per capita consumption of seafood can reach more than an astounding 25 kilogrammes per year [4]. These statistics are a testimony to the indispensability of the ocean, and in extension, the fishing industry, towards global food security.
Source: FAO [4]
Despite the necessity of such an industry, we cannot ignore the extremely pollutive nature of its operations that value profit-making and human consumption at the expense of the environment. When it comes to marine pollution, the fishing industry is one of its largest contributors, ticking off almost every form of pollution, be it plastic, chemical, light or noise.
A study of plastic debris picked up by The Ocean Cleanup’s operations revealed that Abandoned, Lost or otherwise Discarded Fishing Gear (ALDFG) from fishing vessels constituted an estimated 80% of the masses of plastic floating at sea in 2019 [5]. Besides fishing gear, the leakage of oil and disposal of general waste from fishing vessels into the ocean has driven the degradation of marine habitats, deterioration of water quality and disturbed the ecological functions of marine ecosystems.
Photo credit: Fedde Poppenk [5]
With a fast-growing global population comes a rapid rise in the demand for seafood, and to cope with the demand, commercial fishing and aquaculture practices have grown extensively in its scale and intensity of operations [6]. For the past 70 years, the total production from global fisheries and aquaculture operations have increased almost tenfold, although growth of wild capture fisheries has somewhat stagnated in recent years.
Despite the stagnation, we cannot ignore the sheer size of the current industry and the potential future growth of aquaculture operations in particular, especially as the fishing industry copes to meet the ever increasing demand for seafood – which has been projected to double by 2050 [7].
What would such a projection eventually mean for the environment if nothing is to be done to curb the amount of pollution from the fishing industry? With more fish farms and fishing vessels out at sea, one can only imagine the even larger mass of pollution being dumped into the ocean.
References:
[1] Keller, E., & Wyles, K. J. (2021). Straws, seals, and supermarkets: Topics in the newspaper coverage of Marine Plastic Pollution. Marine Pollution Bulletin, 166, 112211. https://doi.org/10.1016/j.marpolbul.2021.112211
[2] Schnurr, R. E. J., Alboiu, V., Chaudhary, M., Corbett, R. A., Quanz, M. E., Sankar, K., Srain, H. S., Thavarajah, V., Xanthos, D., & Walker, T. R. (2018). Reducing marine pollution from single-use plastics (SUPS): A Review. Marine Pollution Bulletin, 137, 157–171. https://doi.org/10.1016/j.marpolbul.2018.10.001
[3] Williams, A. T., & Rangel-Buitrago, N. (2022). The past, present, and future of Plastic Pollution. Marine Pollution Bulletin, 176, 113429. https://doi.org/10.1016/j.marpolbul.2022.113429
[4] FAO. 2022. The State of World Fisheries and Aquaculture 2022. Towards Blue Transformation. Rome, FAO. https://doi.org/10.4060/cc0461en
[5] Lebreton, L., Royer, S.-J., Peytavin, A., Strietman, W. J., Smeding-Zuurendonk, I., & Egger, M. (2022). Industrialised fishing nations largely contribute to floating plastic pollution in the North Pacific Subtropical Gyre. Scientific Reports, 12(1). https://doi.org/10.1038/s41598-022-16529-0
[6] Skirtun, M., Sandra, M., Strietman, W. J., van den Burg, S. W. K., De Raedemaecker, F., & Devriese, L. I. (2022). Plastic pollution pathways from marine aquaculture practices and potential solutions for the north-east Atlantic region. Marine Pollution Bulletin, 174, 113178. https://doi.org/10.1016/j.marpolbul.2021.113178
[7] Carlsen, L. (2021, September 15). Global demand for aquatic foods set to nearly double by 2050. BFA. Retrieved January 24, 2023, from https://bluefood.earth/news/demand-press-release/
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