climate changes sharks
Sharks are survivors, surviving all 5 of the mass extinctions over the last 400 million years (Rosa, Rui, et al.). They are leaders of their surrounding ecosystems which help to combat any issues, such as too big populations and the degradation of their habitats. Yet, sharks have become collateral damage due to human actions that have caused the ruination of oceans. Climate change’s effects have not been limited to a specific type of shark or type of ocean, but all sharks and all oceans.
The tropical parts of the Atlantic Ocean are seeing drastic changes. “The Atlantic Ocean is warming the fastest, reporting the largest area-averaged warming at 1.42 joule per square meter” (Chacko, Susan). The average sea surface temperature rising due to the greenhouse effect by 1°–3 °C in 2100, along with a decrease in the ocean pH by 0.3–04 units by the end of the century (Pistevos, Jennifer C A, et al.). The South Atlantic ecosystems are being affected to the point of chronic stress. It is a transitional part of the ocean, from the more temperate areas of the north to the tropical areas of the south. It has some of the most extensive reef habitats, the second-largest estuary on the Atlantic seaboard, and a gradually sloping shelf (NOAA). There has been a decrease in upwelling, the process of bringing nutrient-rich waters from the bottom to the surface. Ocean acidification has increased; acidification happens when there is a reduction of pH in the ocean, which is caused by the increase of carbon dioxide coming from the atmosphere.
Sea levels have risen; South Florida and the Cape Hatteras region have the highest projected rates of sea level rise along the South Atlantic coast (NOAA). The South Atlantic continental shelf waters have become much more acidic due to the waters absorbing more carbon dioxide and coastal runoff (NOAA). The lower food chain not having what they need, like calcium carbonate to form skeletons (NOAA), coupled with the apex predators' numbers dwindling is proving disastrous. There have been changes in the variability of the Gulf Stream location in the past 5-7 years, which is one of the main drivers in the South Atlantic system (NOAA). Coral reef ecosystems, common in the Atlantic tropical areas, are in danger due to more carbon dioxide being absorbed by the water; if the pH continues to change and the reefs keep facing more violent storms (American Oceans), then sharks will become endangered, such as the Caribbean reef shark (Carcharhinus perezi). The changing of the Atlantic Ocean will lead to every aspect of sharks being threatened.
Sharks have been around for over 450 million years and have had to go through many changes (American Oceans) but climate change has been affecting the oceans at a rate at which sharks have no experience evolving. One of the main areas being researched that have seen massive change is the tropical area of the Atlantic Ocean. Sharks are the apex predator, a beast known for survival; yet human actions have become an even larger predator than sharks could ever hope to dominate. While sharks in the past have had to accommodate warmer and more acidic waters, the sharks of today have not, nor has either group dealt with change at such an extreme rate. It was once thought that modern-day sharks would not be affected by rising CO2 levels because they evolved in the Devonian era when the CO2 levels were much higher than the present day (Harriet). This is not true. Most sharks are ectothermic, and the rising temperatures are making them more vulnerable (Harriet). Twenty-eight species of sharks have already been reported as having incubation time decreasing due to warmer waters (Harriet). Sharks protect and increase blue carbon, carbon stored in marine and coastal ecosystems, reducing the amount of grazing on kelp forests and seagrass meadows (Harriet). Tiger sharks commonly found hunting prey in seagrass habitats help keep seagrass evenly distributed; this helps seagrass capture carbon 35 times faster than that of tropical rainforests (Harriet). Sharks are made up of 10 to 15 percent of carbon which means through death their bodies bury the carbon (Harriet). To keep the atmosphere healthy, sharks need to function in their natural habitats. Bull sharks have started changing their migration patterns and scientists are confirming it is due to the warming waters (American Oceans). Changing migrations will cause disruption, like becoming a threat to established nursery areas, and food competition in the ecosystems they are joining.
Tiger sharks have shifted north for decades, mainly due to the warming of the US Northeast Continental Shelf Large Marine Ecosystem (NOAA). Their migration stretches from Massachusetts to the Gulf of Mexico. Tiger sharks are migrating towards the northeast shelf waters earlier, moving even further north by around 4 degrees of latitude (NOAA). Tiger sharks appear in the north 14 days earlier for every 1-degree increase in sea surface temperature and strange occurrences (NOAA). High catch density areas have shifted more than 248.548 miles since the 1980s (NOAA). Their new migration behaviors have been proved by satellite telemetry data from the University of Miami, remotely sensed environmental data from NOAA CoastWatch, habitat modeling, and capture data from the NOAA Fisheries’ Cooperative Shark Tagging Program (NOAA).
More than a third of sharks are currently facing extinction; there are 71% less sharks in the open ocean than there were 50 years ago (IFAW). The rate at which sharks can reproduce is little to none compared to the effects global warming has already put in place. Recent studies have suggested that there is a correlation between rising acidification and pups, baby sharks (Rosa, Rui, et al). The causation is thought to be less time maturing and less time as embryos (Rosa, Rui, et al.). Oviparous sharks may be able to have adaptive mechanisms when it comes to tolerating CO2 conditions inside the egg capsules (Rosa, Rui, et al.). According to a 2019 study, warming temperatures and increasing carbon dioxide levels are affecting the brain development of sharks, which could change behavior, and decision-making capabilities, and result in smaller brains (American Oceans).
Increased CO2 levels affect sharks' behaviors by reducing their capacity to engage in their large olfactory structures and ampullary electroreceptor systems (Rosa, Rui, et al.). This causes them to not sense predators or prey around them because their navigation, detection of bioelectric fields, and avoidance have been impacted (Rosa, Rui, et al.). It is thought that their GABA-A receptors become excited and change (Rosa, Rui, et al.) which accounts for their behavioral abnormalities. Sharks took 4 times longer to locate prey in water with higher CO2 levels, 2/9 sharks did not respond at all (Pistevos, Jennifer C A, et al.). They had a much higher failure rate when they did engage in hunting (Pistevos, Jennifer C A, et al.). When the water had higher temperatures, hunting time was down by 1/3, although it did have a larger variance (Pistevos, Jennifer C A, et al.). Sharks in more acidic waters had a harder time finding dead prey when using their olfactory senses. Sharks rely heavily on odor and electroreception (Pistevos, Jennifer C A, et al.), so if they could not find dead prey, this means sensory failure could be caused by higher acidity levels. The higher CO2 waters halt sharks' ability to hunt, which would go well with higher temperatures since sharks showed an increase in a need for food and metabolic rate. Recent empirical studies show that physiological impairments because of CO2 were less clear than behavioral (Rosa, Rui, et al.). When put in water that has the same temperature as forecasted by the end of the century, the embryonic period was 40 days out of 10-12 months on average (Pistevos, Jennifer C A, et al.). This is alarming if they are not developing fully which could them entirely. In water with higher CO2 and temperatures, growth was affected negatively (Pistevos, Jennifer C A, et al.). Lower growth rates and lower hunting skills put sharks at a much higher risk, which would cause a negative cascading effect. When sharks were in water with higher temperatures, they needed much more food; this reflects a correlation between higher temperatures and a higher metabolic rate (Pistevos, Jennifer C A, et al.).
After 7 months of exposure to higher temperature and CO2 waters, the sharks, pups turned juveniles, tested showed no signs of acclimation (Pistevos, Jennifer C A, et al.). This suggests that sharks will also not be able to acclimate when they are in their later stages of life, such as the time to mate and give birth. With lower growth rates, sharks in the tropical Atlantic will not be able to dominate their surroundings as easily. Sharks that tend to be in coastal areas and reefs are already on the smaller side of sharks, this will make ecosystems self-implode without their natural leaders. Combined with 1/3 of sharks already being threatened worldwide, the tropical waters need to be heavily guarded and monitored.
Sharks' locomotion, essentially the mechanics of how animals move, is changing due to warming temperatures and acidification (Vilmar, Di Santo). Acidification and warming affect locomotive efficiency by affecting skeletal mineralization, increasing metabolic rates when swimming, prolonging the time it takes to recover from exercise, and the time it takes to locate prey (Vilmar, Di Santo). Acidification could affect the skeletal density of sharks, making them heavier than normal, which reduces buoyancy (Vilmar, Di Santo). Both factors are leading to reduced swimming efficiency (Vilmar, Di Santo). This could lead to them not being able to do the large-scale migrations that are necessary for survival.
The absence of sharks would bring the end of balanced ecosystems. Without reef sharks eating bigger fish, there will not be enough algae-eating fish which will lead to the smothering and killing of coral, harming millions of organisms (IFAW). Sharks also transport different kinds of nutrients by moving between the deep and shallow waters, such as nitrogen; without sharks, the coral reef systems would struggle due to a lack of nitrogen (IFAW). This would ruin the entirety of ecosystems within the Caribbean and Brazilian coastal waters. Without them, there would be more prey which leads to a higher carbon system being produced from a higher biomass in prey (Harriet). Higher prey numbers would lead to more agitation in the sediment, releasing carbon into the atmosphere (Harriet). Sharks are some of the most helpful creatures in the ocean, and they need to be a priority when saving the oceans.
Scientists agree that sharks are being affected by climate change and that there needs to be more researched. They have underestimated the impacts CO2 and acidification would have on these predators. There needs to be more studies on juvenile and baby sharks, physiology, locomotion, and morphology. There have not been a lot of disagreements, besides to what degree a variable's impact is having. More empirical data is needed to properly assess the vulnerability sharks have and what needs to be done so proper policy is put in place. The sharks within the tropical Atlantic Ocean are facing harsh consequences and are unable to evolve at the necessary rate; more research is needed on this topic overall, and until then, data remains inconclusive.
Works Cited
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Dolce, Chris. “Why the Tropical Atlantic Ocean Is Different from This Time Last Year, and What It Could Mean for Hurricane Season.” The Weather Channel, The Weather Channel, 3 May 2018,
“Ecosystem Responses to Climate Change.” Mid-Atlantic Regional Ocean Assessment,
“The Effects of Climate Change on Sharks.” American Oceans, 2 May 2022,
Fisheries, NOAA. “Climate Change Is Shifting Tiger Shark Populations Northward.” NOAA, 19 Jan. 2022,
Fisheries, NOAA. “The U.S. South Atlantic Marine Ecosystem: An Ecosystem in Transition.” NOAA, 25 Mar. 2022,
https://www.fisheries.noaa.gov/news/us-south-atlantic-marine-ecosystem-ecosystem-transition.
Gallagher, Austin J., et al. “Tiger Sharks Support the Characterization of the World’s Largest Seagrass Ecosystem.” Nature Communications, 1 Nov. 2022,
https://www.nature.com/articles/s41467-022-33926-1.pdf.
Harriet, Harriet. “Sharks and the Climate Crisis.” Sharkguardian, Sharkguardian, 20 Oct. 2022,
“How Sharks Keep Our Oceans Healthy.” IFAW (international fund for animal welfare), 12 July 2022,
Pistevos, Jennifer C A, et al. “Ocean Acidification and Global Warming Impair Shark Hunting Behaviour and Growth.” Scientific Reports, U.S. National Library of Medicine, 12 Nov. 2015,
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4642292/.
Rosa, Rui, et al. “Biological Responses of Sharks to Ocean Acidification.” The Royal Society
Publishing, 29 Mar. 2017
https://royalsocietypublishing.org/doi/10.1098/rsbl.2016.0796.
Vilmar, Matilda, and Valentina Di Santo. “Swimming Performance of Sharks and Rays under Climate Change.” Springer, Stockholm University,
https://link.springer.com/content/pdf/10.1007/s11160-022-09706-x.pdf?pdf=button.
