Effect of Global warming on sharks
Current State of the Ocean
The statistics of the current state of the ocean were presented by the European Union’s Copernicus Marine Service. It showed a global rise in sea level of 3.2 mm per year, a 0.63% increase in chlorophyll per year, which is an indicator of phytoplankton density. It shows a rise in ocean heat content by 0.9 watts m^2 per year, and an increase of sea ice in km^2 in the Southern hemisphere and a decrease in the northern hemisphere....[1].
Predicted State of the Ocean
By 2100, global warming is predicted to warm the climate and raise sea level. Melting glaciers and ice sheets are contributing to the rise in sea level, as well as the expansion of the ocean water as it warms. This increases its volume and is raising sea level. Models predict it to rise between 30-100 cm by 2100.
The ocean is expected to act as a buffer by absorbing excess heat and CO2 from the atmosphere. Long term, this combination is predicted to produce a weak form of carbonic acid within the ocean and increase the acidity by 0.14-0.35 pH by 2100. The warming and acidification of the ocean results in it being able to hold less oxygen, directly impacting organisms.[1]
Microplastic consumption by zooplankton is also influencing global deoxygenation as they are ingesting microplastics instead of organic matter, which interrupts the nutrient cycle, causing more phytoplankton to settle as detritus, increasing carbon dioxide concentrations.[2].
We can predict these ocean parameters using space-based satellite altimetry. This technique is able to determine the height of the sea surface.
By using altimetry we are able to deduce patterns to create models to predict future trends such as changes in sea level.[3]. This technology can also be used to provide real-time observations and predictions for fast-changing fishing grounds.
As an example, by identifying specific parameters that favor specific species, this technology is able to predict where concentrations of fish may be. Tuna catch is higher in sea surface temperatures of 26-28 degrees Celsius and a chlorophyll concentration of 0.2 mg/m3 and a higher sea surface height. Knowing this, altimetry data can aid fishermen in real time.[3]
Physiology of Sharks in a Changing Environment
Changes in ocean parameters would first of all affect the primary physiology of sharks. For example, at higher temperatures, embryonic development is faster.[4]. The rise in temperature and increase of CO2 concentration have detrimental effects on sharks, such as increased energetic demands, which decrease metabolic efficiency. More energy is required to accomplish basic processes such as foraging, growth, and reproduction, that are therefore less efficient. This has as a consequence a reduction of growth rate.[5]. The ability to locate food through olfaction is also reduced, making it even harder to provide the needed amount of nutrients.[6]
This is due to the superior olfactory sensitivity of elasmobranchs. Olfaction is one of the key elements to food localization, predator detection, homing, and navigation. Odor being a chemical stimulus, if the chemical composition of the ocean is modified as a result of an increase in CO2 levels and its consequences, it disturbs the shark’s olfactory sense. Attraction to chemical signals is reduced as those signals are being interfered with.[6]. Therefore, ocean acidification would have a negative effect on sharks’ response to prey odor and impair their food tracking.
Shark Distribution
Species distribution and habitat requirements can be determined from modeling information on occurrence and environmental correlates.
Physical limits are caused by environmental and physiological constraints. Sharks generally follow latitudinal and bathymetric gradients.
Factors that manipulate the richness of an environment for sharks include abiotic variables such as bathymetry, chlorophyll, sea surface temperature (SST), photosynthetically available radiation, pH, cloud cover, the concentrations of calcite, silicate, phosphate, and nitrate, salinity, particulate organic carbon, and dissolved oxygen.[7]
Distribution increases towards the Equator and peaks in shallow continental shelf waters, as 41% of all species are distributed in this area.[8]. Most sharks tend to migrate along the shelf and vary their habitat based on the transfer of nutrients from one site to another.
Predicted Changes in Distribution
As a consequence of overfishing and global warming, oceans are under ecological pressure, such as defaunation, phenological shifts, interactions among species, and distribution shifts. Globally, many shark populations are declining, especially large species that are targeted by fisheries.[9]. To respond to the climatic threat, species must adapt. Poleward migration of subtropical species has been observed[10] because of the increase in SST; species must shift to colder water.
A significant relationship has also been found between the surface-swimming duration of sharks and zooplankton density.[11]. The decrease of zooplankton would imply a decrease and relocation of the species feeding on it. Thus, sharks must follow their prey, and predatory activities increase in these areas. Studies have found that shark occurrence gradually increases towards higher latitudes.[10]
Pelagic species are expected to spread faster than demersal species because of their higher motility and a higher difference in ocean conditions in the surface layer. We expect a strong poleward shift for pelagic species in the years to come.[9] The introduction of these predators into new ocean areas would also impair the balance of pre-existing ecosystems.
Food Webs & Ecosystems
Sharks play a key role in the structure and functioning of marine communities. They exert a top-down predation on their trophic chain. Top consumers affect lower trophic levels by regulating the intermediate levels. It is a cascade effect on all the food webs.[4]
Sharks have a direct impact on their environment. In coral reef ecosystems, they are responsible for the health of the reef by foraging in it.
If a shark species leaves an ecosystem, the top-down regulation won’t happen anymore, and intermediate species might proliferate and become invasive. Therefore, it will have consequences on the entire ecosystem, affecting the lower trophic levels, all the way to the primary producers. It has been observed on sites where sharks left that carnivorous species (mesopredators) that feed on herbivorous fish were proliferating. Therefore, the number of herbivorous fish decreases, and algae overgrow the coral reef, depleting the oxygen from the water and bringing in unwanted microbes and pathogens.[12]. Sharks are, in consequence, vital to the balance of ecosystems such as reefs, and their presence is affecting way more than just the lower trophic levels.
In contrast, the introduction of a new apex predator to a site would disturb the pre-existing food web by decreasing the number of higher trophic levels and letting lower ones grow, which would be expected to deplete the zooplankton and primary producer resources.
Impact on Fisheries
The tracking of sharks showed a correlation between high productivity and physiological thermal tolerances, either by the shark itself or its prey. These parameters are in alignment with Areas of Ecological Significance, which are characterized by their nutrient abundance, biodiversity with multiple trophic levels, and colder water temperatures resulting in higher oxygen concentrations. Areas such as the Southern Ocean have been recognized as places that can be sustainable habitats and require protection since they are critical in the face of climate change as they become high in demand.[13].
Current Areas of Ecological Significance are located on the Antarctic ecological shelf and around the sub-Antarctic islands. 29% of AES are under formal protection, called marine protected areas (MPAs),[13] which affect fishing practices. If species are migrating to protected regions, this can affect fishing in two ways. Once fish mature in MPAs, they often leave to replenish nearby fishing grounds, which is a benefit to fishing communities. In contrast, MPAs can prevent fishing communities from using areas of the ocean that they have always used, making government and local fisherman communication critical when deciding upon the location and enforcement of MPAs.[14][8].
The aggregation of sharks in these cooler areas poses a threat to fishing as the fish are their prey. The sharks are causing a depreciation of catch for fisheries, which in turn poses a threat to the animals themselves. They are at an increased risk of ruining fishing gear, being caught as bycatch, or being subject to lethal retaliation.[15]
A study found a higher incidence of catching sharks in fishing grounds where the catch of blue shark was found to be higher in places above the oxygen minimum zone. This becomes more frequent as there are more sharks aggregating in a smaller volume of water in order to stay within a boundary of a habitat suitable for their physiological needs.[16]
Knowing that certain zones within the ocean have higher concentrations of oxygen could potentially affect where fishermen fish, along with how plentiful their catch is; if fish are aggregating within a specific area, it is easier to fish them in abundance, and the same goes for the shark. Studies suggest that blue sharks could become more vulnerable to fishing. By knowing this information, it gives us the opportunity to recognize the changing distribution patterns of sharks and allows us to manage it by looking for ways to slow and reduce the impact of climate change while implementing MPAs. Doing so is beneficial for both sharks and the economic impact. [citation needed]
References
- ↑ 1.0 1.1 "Ocean Prediction - modelling for the future". public.wmo.int. 2021-03-23. Retrieved 2021-12-18.
- ↑ Kvale, K.; Prowe, A. E. F.; Chien, C.-T.; Landolfi, A.; Oschlies, A. (2021-04-21). "Zooplankton grazing of microplastic can accelerate global loss of ocean oxygen". Nature Communications. 12 (1): 2358. Bibcode:2021NatCo..12.2358K. doi:10.1038/s41467-021-22554-w. ISSN 2041-1723. PMC 8060285 Check
|pmc=value (help). PMID 33883554 Check|pmid=value (help). - ↑ 3.0 3.1 Liu, Cho-Teng; Nan, Ching-Hsi; Ho, Chung-Ru; Kuo, Nan-Jung; Hsu, Ming-Kuang; Tseng, Ruo-Shan (2003), "Application of Satellite Remote Sensing on the Tuna Fishery of Eastern Tropical Pacific", International Association of Geodesy Symposia, Berlin, Heidelberg: Springer Berlin Heidelberg, pp. 175–182, doi:10.1007/978-3-642-18861-9_21, ISBN 978-3-642-62329-5, retrieved 2021-12-18
- ↑ 4.0 4.1 Pistevos, Jennifer C. A.; Nagelkerken, Ivan; Rossi, Tullio; Olmos, Maxime; Connell, Sean D. (December 2015). "Ocean acidification and global warming impair shark hunting behaviour and growth". Scientific Reports. 5 (1): 16293. Bibcode:2015NatSR...516293P. doi:10.1038/srep16293. ISSN 2045-2322. PMC 4642292. PMID 26559327.
- ↑ Osgood, Geoffrey J.; White, Easton R.; Baum, Julia K. (2021-07-06). "Effects of climate‐change‐driven gradual and acute temperature changes on shark and ray species". Journal of Animal Ecology. 90 (11): 2547–2559. doi:10.1111/1365-2656.13560. ISSN 0021-8790. PMID 34145907 Check
|pmid=value (help). Unknown parameter|s2cid=ignored (help) - ↑ 6.0 6.1 Dixson, Danielle L.; Jennings, Ashley R.; Atema, Jelle; Munday, Philip L. (2014-08-11). "Odor tracking in sharks is reduced under future ocean acidification conditions". Global Change Biology. 21 (4): 1454–1462. doi:10.1111/gcb.12678. ISSN 1354-1013. PMID 25111824.
- ↑ Guisande, Cástor; Patti, Bernardo; Vaamonde, Antonio; Manjarrés-Hernández, Ana; Pelayo-Villamil, Patricia; García-Roselló, Emilio; González-Dacosta, Jacinto; Heine, Jürgen; Granado-Lorencio, Carlos (2013-06-15). "Factors affecting species richness of marine elasmobranchs". Biodiversity and Conservation. 22 (8): 1703–1714. doi:10.1007/s10531-013-0507-3. ISSN 0960-3115. Unknown parameter
|s2cid=ignored (help) - ↑ Bird, Christopher S.; Veríssimo, Ana; Magozzi, Sarah; Abrantes, Kátya G.; Aguilar, Alex; Al-Reasi, Hassan; Barnett, Adam; Bethea, Dana M.; Biais, Gérard; Borrell, Asuncion; Bouchoucha, Marc (February 2018). "A global perspective on the trophic geography of sharks". Nature Ecology & Evolution. 2 (2): 299–305. doi:10.1038/s41559-017-0432-z. ISSN 2397-334X. PMID 29348645. Unknown parameter
|s2cid=ignored (help) - ↑ 9.0 9.1 Pereira, Henrique M.; Leadley, Paul W.; Proença, Vânia; Alkemade, Rob; Scharlemann, Jörn P. W.; Fernandez-Manjarrés, Juan F.; Araújo, Miguel B.; Balvanera, Patricia; Biggs, Reinette; Cheung, William W. L.; Chini, Louise (2010-12-10). "Scenarios for Global Biodiversity in the 21st Century". Science. 330 (6010): 1496–1501. Bibcode:2010Sci...330.1496P. doi:10.1126/science.1196624. ISSN 0036-8075. PMID 20978282. Unknown parameter
|s2cid=ignored (help) - ↑ 10.0 10.1 Niella, Y; Smoothey, Af; Peddemors, V; Harcourt, R (2020-05-28). "Predicting changes in distribution of a large coastal shark in the face of the strengthening East Australian Current". Marine Ecology Progress Series. 642: 163–177. Bibcode:2020MEPS..642..163N. doi:10.3354/meps13322. ISSN 0171-8630. Unknown parameter
|s2cid=ignored (help) - ↑ Sims, D.W.; Southall, E.J.; Merrett, D.A.; Sanders, J. (2003-04-09). "Effects of zooplankton density and diel period on surface-swimming duration of basking sharks". Journal of the Marine Biological Association of the United Kingdom. 83 (3): 643–646. doi:10.1017/s0025315403007598h. ISSN 0025-3154. Unknown parameter
|s2cid=ignored (help) - ↑ Ferretti, Francesco; Worm, Boris; Britten, Gregory L.; Heithaus, Michael R.; Lotze, Heike K. (May 2010). "Patterns and ecosystem consequences of shark declines in the ocean". Ecology Letters. 13 (8): 1055–1071. doi:10.1111/j.1461-0248.2010.01489.x. ISSN 1461-023X. PMID 20528897.
- ↑ 13.0 13.1 "Antarctic marine predators tracked to Areas of Ecological Significance". www.antarctica.gov.au. Retrieved 2021-12-18.
- ↑ (PDF) https://www.tigurl.org/images/tiged/docs/activities/511.pdf. Unknown parameter
|url-status=ignored (help); Missing or empty|title=(help) - ↑ Tixier, Paul; Lea, Mary‐Anne; Hindell, Mark A.; Welsford, Dirk; Mazé, Camille; Gourguet, Sophie; Arnould, John P. Y. (2021). "When large marine predators feed on fisheries catches: Global patterns of the depredation conflict and directions for coexistence". Fish and Fisheries. 22: 31–53. doi:10.1111/faf.12504. Unknown parameter
|s2cid=ignored (help) - ↑ "Climate Change Could Drive Sharks to Fishing Grounds: Study". The Scientist Magazine®. Retrieved 2021-12-18.
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