Negative Impact of Climate Change on Great White Shark Migration and Behaviours

Introduction:
Climate change is commonly investigated in the world today and has become an increasingly popular research topic. Many scientists are still trying to understand climate change’s capabilities and how it will affect the future of the planet. One of the most common ways in which scientists have researched climate change has been to explore its effects on the ocean. The ocean is responsible for the overall survival of humans as it absorbs large amounts of solar radiation as well as local heating within the upper layers via phytoplankton. Without the absorption of this solar radiation by the oceans, land surface heat would reach an inhabitable high that would devastate life on Earth [1]. For instance, sea surface temperatures found in tropical regions worldwide have increased up to 0.5-0.6 ºC since the mid-nineteenth century owing to the weakening of tropical atmospheric circulation when compared to earlier circulation [2]. If warming of sea surface air temperatures were to continue on the predicted trends, the model projections also suggest that average surface air temperatures will also increase between 2ºC and 5ºC and a decrease in pH by about 0.4 units by 2100 due to anthropogenic forcing [3]. Anthropogenic changes such as warming of surface air temperatures have greatly altered the abundance of essential oceanic species, especially large predators at high trophic levels such as sharks. Sharks occupy high trophic levels in marine habitats, and play a key role in the structure, function, and health of marine ecosystems [4]. Like other apex predators, great white sharks are vital to the marine ecosystem due to the fragility of the food chain and overall ocean health. Great white sharks maintain the species inferior to this species. They allow for and facilitate the ocean ecosystem to continue to function by also attributing to the removal of weak or sick species on which they feed [5]. Great white sharks are a keystone species within the aquatic ecosystem, and if there were to be an imbalance or complete removal of this species, the ocean ecosystem as a whole would experience devastating consequences that would affect hundreds of other species. With warmer oceans, great white sharks have experienced changes within their behavior including their migration patterns specifically [6]. Due to changes in ocean temperatures, ocean acidifications and other climate change effects, the migration patterns and overall vulnerability of great white sharks has been negatively altered, causing an imbalance within ecosystems and negative effects due to the needed change of these sharks’ patterns. These changes could have great implications to the great white sharks’ role and investigation of the changes in their migration patterns, impacts to breeding and birthing, and the future of this species are essential to undergo. When looking at migration patterns in great white sharks, scientists have already found a shift poleward due to raising temperatures found in tropical and equatorial regions. Many oceanic species are moving poleward, resulting in their predators also moving in this direction as a means of survival [4]. Great white sharks are migrating with their prey, causing a large amount of species to shift away from their normal habitat, causing the balance of ecosystems to crumble. Movement and migration changes such as this cause a domino effect within a given environment and usually result in a downward spiral for many species in the future, one of which could be the great white shark. Not only does climate change affect migration, but many scientists have found a shift within breeding, birthing and mothering patterns in white sharks globally. Since sharks are ectothermic, they are unable to generate and maintain their own body heat, which is essential when breeding, carrying, and birthing offspring. With changing ocean temperatures, great white sharks must alter their once-routine breeding behavior to compensate for the environmental changes that caused nonoptimal conditions for young.

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Researching the future of great white sharks is highly reliant on predictions, models, and theories. With no concrete way to answer or investigate, many scientists and researchers perform experiments and undergo research that can explain certain changes within a species, allowing for a cause and effect answer. Scientists then use this trend to predict the future based on the information found and known. From the given trends of ocean warming and acidification that have been expertly computed, scientists predict what their findings may suggest for the great white shark.
Methods:
 Understanding the future of any species is a complex idea. With the added changes of investigating an aquatic species, there were many different methods of research used by different scientists to predict the future of the great white shark. Migration and future demographics of great white sharks were researched. In one study performed by Dr. Shannon M. O’Brien and Dr. Vincent F. Gallucci, these researchers used nine total shark species, one of which was the white shark, to determine how climate change would affect the species in the future. The scientists were able to do so by compiling and grouping shark data by species with 59 great white shark individuals [6]. They then utilized the universal shark primer for the two regions of the mtDNA (ND2 and CR) which were initially developed from ND2, CR as well as the adjacent tRNA sequencing through NCBI GenBank. The sequences for the individuals were then aligned through the use of ClustalW 2.0 in Geneius 5.1 and the primers found on both sides of the given ND2 and CR regions and were used to amplify the primers. Complete genomic DNA was extracted from muscle tissues using Qiagen DNA easy Tissue Kits, and they followed the manufacturer’s instructions for extraction, amplification, and sequencing. The PCR products that resulted from the muscle tissue sequencing were then sent to the University of Washington’s Department of Genome Sciences for further sequencing. Both reverse and forward sequences for individuals in the mtDNA region were assembled into contigs in Geneius v5.1 then were visually inspected for accuracy. The ND2 sequences for all individuals of each species were aligned and summary statistics were found, including the number of polymorphic sites, number of transitions and transversions, haplotypes amount, haplotype diversity, nucleotide diversity and the mean pairwise difference. The specific dN/ds ratios were found in each species, and models were run in CODEML. Models were then used to investigate the demography of past populations. Using Arlequin v3.5.1.2, each species calculated 10,000 simulated samples to detect any departures from population expansion or neutrality. Haplotype networks were also constructed in order to assess the demographic history qualitatively. Maximum likelihood trees were comprised of the data collected and aligned in DNAML. From all the data collected and detailed above, past changes in effective population size were also investigated using coalescent-based Bayesian skyline plot or BSP. These methods allowed for the construction of gene genealogies [6].
The ND2 and CR of the mtDNA was successfully amplified for the great white shark. The final length of the sequences was used in order to explore past demographic histories. Nucleotide and haplotype diversity for the mtDNA CR of each species was graphed. The symbols within the graph of nucleotide diversity (pi) on the X-axis and haplotype diversity (h) of the Y-axis represented the predictions of how strongly historic climate change affected the demographic history of each shark species. The researchers included factors such as distribution, habitat, nursery requirements, and migratory ability. The researchers determined that white sharks fell in the “moderately” affected region in between slight and severe [6]. These methods were very detailed and relied on the DNA sequencing of individuals to determine how climate change may affect the great white shark. Although this was a very successful and eye-opening experiment, there are some changes that should be made to the better the results. The researchers did not use species-specific reverse primers, which would have eliminated some issues and would allow for more consistency that caused the removal of some individuals, which they later discussed. It would have also been beneficial and more informative to compare the same species in different locations to get a better picture of the animal. For instance, the scientists should have taken 60 individuals of great white sharks located in California, Australia, Hawaii, and various location along the Atlantic coast rather than just in California. This would give more applicable data to the species as a whole population rather than just a sample.
Another study was conducted to investigate the effect that climate change may have in the early-life of sharks. Although the experiment was not performed on great white sharks, the researchers suggested that a similar experiment on ovoviviparous species such as great white sharks would clarify early life exposure to white shark offspring. In the experiment conducted by Dr. Rosa Rui and others, 60 recently spawned bamboo shark embryos were collected, incubated, and acclimated to a change in pH of 0.5 and 0.14% CO2 increase as well as a 4ºC increase in temperature as this is what is predicted to be the conditions of the ocean by 2100. A control group was also present in order to compare at 26ºC and 8.0 pH whereas the experimental group was held at 30ºC and 7.5 pH. Life support systems were replenished daily with new seawater to maintain alkalinity and dissolved inorganic carbon speciation owing to bacterial activity. The age of each individual shark was estimated according to the description of the embryo, and all 60 were tagged. After hatching, juvenile bamboo sharks were removed from their incubation systems in order to be weighed and measured as well as tagged. Fulton’s condition was calculated by using the formula K=(weight/TL3) x 100. Two-way ANOVAs were conducted to detect significant differences in development time, yolk consumption, SGRs, juvenile RMRs, and ventilation rates. Survival of bamboo shark embryos at the present-day thermal scenario (26ºC) was 100%, but the survival rate of sharks under the future ocean warming conditions(30ºC) was only 80% [2].
Although this was not performed on great white sharks, the scientists who performed this experiment made the prediction that all sharks would experience a similar trend in lower survival rates in shark offspring. One way an experiment could be designed for white sharks would be either of the following two options. Scientists could track and investigate great white sharks in different regions based on temperature to investigate the survival rate of offspring in warmer regions versus cooler regions in the field. This would take an almost unrealistic amount of people and resources since white sharks do not lay eggs. Another alternative may be to bring new-born or juvenile white sharks into a research facility that could maintain their swimming habitats for a brief period of time and study how acclimation to the various temperatures may affect their health. It is difficult to research great white sharks as they are unable to be held captive for a large amount of time as many aquariums have tried to do so, resulting in death. Scientists have minimal options for investigating early life of great white sharks.
In a final experiment that was investigated, the researchers assessed the vulnerability and possible implication in the future to different species of sharks, including great white sharks. There were three main steps: defining the assessment context, assessing components of vulnerability and integrating vulnerability components to derive the predicted vulnerability of each species of shark in the Great Barrier Reef to climate change. The researchers used up-to-date regionally down-scaled climate change projection of the GBR for the next 100 years using A1 and B2 emission scenarios from the 2007 IPCC and ranked their certainty. Lineage between climate change factors and the species, habitats, physical and ecological processes of GBR ecosystems were provided. Each species was assigned an ecological group. The whole process was broken down into the following steps: define climate change scenarios, define the entity to be assessed, identify relevant attributes, assess exposure, assess sensitivity and adaptive capacity, integrate vulnerability components, collate ranking and consider interactions, synergies and knowledgeable gaps. In the results, the scientists reveal that the white shark was moderately vulnerable, coinciding with the first experiment, since these species tended to have moderate to high rarity, immobility, and limited latidunal range [8]. This experiment was very broad when compared to the first experiment, which was very specific. In order to adapt these methods, the researchers should use more field data to compare to the document they relied heavily on by Johnson and Marshall. This was a good document used to establish understanding of climate impacts and was easily repeated if needed.
After investigating research on climate change effects on migration, offspring, and overall vulnerability of the great white shark, there was similar reliance on past data, but the processes were much different. There were no experiments that followed similar methodology on databases. The great white sharks are rare and very difficult organisms to study. There are endless limitations due to their inability to survive in captivity and their low numbers in the wild. This caused a large variety of experiments and scholarly articles. However, the information found allowed for interesting insight on the species and their potential future.
Results and Discussion:
After researching and better understanding the effects climate change has on great white sharks, I was shocked to find how much uncertainty there was in the scientific world. I also was surprised by the decline that this species was experiencing. From previous knowledge, I was aware that almost all shark species were in decline, but I was surprised to find that in the past 15 years, great white sharks (along with scalloped hammerhead and thresher sharks) have declined by over 75% in the Northwest Atlantic [4]. Predicting the demographic responses of marine species to contemporary climate change has also proven to be extremely difficult and continues to challenge researchers, as seen in many of the methods provided. Climate fluctuations affect growth, reproduction, and survival and can thus lead to changes in abundance, shifts in distribution, and local extinctions [6]. Despite their ecological diversity, shark species share many similar life history characteristics and may be especially vulnerable to anthropogenic and climate impacts [6]. Through the overlapping data provided, one can see that climate change is attacking the great white shark species in various ways, including their migratory patterns, offspring/birthing rates and survival, as well as their overall vulnerability. One researcher estimated that due to warming waters, the edge of the sharks’ range could shift as much as 40 miles poleward per decade after following prediction trends and running numerous models, pushing the sharks away from the warming oceans near the equator into different habitats [7]. Although sharks have evolved to fill many ecological niches at an extremely impressive range globally within a wide variety of habitats for over 450 million years, they have unfortunately limited capability to rapidly adapt when it comes to human-induced changes within their environments [2]. Due to climate change creating unfavorable conditions for great white sharks, migratory behaviors are shifted poleward to uncharted and unfamiliar territory. This causes the sharks to move out of their previous ecosystem and invade another, which impacts all ecosystems at hand. Comparing patterns of genetic variability, mismatch distributions, and demographic reconstructions from coalescent approaches among temperate and tropical shark species with differing ecological characteristics is important when investigating the effect of the past glaciation cycles on population abundance. This research also allows one to see how truly impactful climate change is and how vulnerable the great white shark is [6]. Great white sharks are apex predators and vital to the ocean as a whole. This research is not only essential to protect the fragility of the great white shark population but the future of the ocean and marine biology. Every species in the ocean is impacted by climate change in one way or another, affecting all marine biology studies and the future of the field. Humans are more reliant on the ocean than the general population may believe. The ocean absorbs copious amounts of solar radiation, preventing humans from enduring unhabitable temperatures [9]. In addition to human dependence on the oceans for life, work, food, travel, and fun, human health is also associated with the oceans [10]. For activities like fishing alone, billions of dollars are generated annually, and many nations are dependent on the ocean for their entire economy and source of income for tourism and food. Many researchers are utilizing organisms from the ocean for cancer research as well. As a whole, the ocean is essential for life as humans know it. Without the ocean, its ecosystems and its organisms would fail, the planet would fail.
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