Written by Sofia Perez

Edited by Matthew Tietbohl

Mark the Shark is much like a citizen of Miami, Florida, constantly looking for the coldest (or most air-conditioned) place to be. He is an apex predator, at the top of the food chain with a reputation for a toothy grin and menacing bite. Little do they know, he thinks smugly, I’m sensitive [to temperature]. Like all complex heroes, Mark the Shark, who is just one example of the many tiger sharks in the ocean, has a soft side: heat. 

In response to a changing climate, animals and people all over the world are making adjustments to their daily, weekly, and annual rhythm, including  tiger sharks. Recently, a team of researchers from the University of Miami Rosenstiel School of Marine & Atmospheric Science studied this very phenomenon. Their work is important for a variety of reasons. Importantly though, it must also be noted that while I will discuss the threat of climate change to tiger shark populations, there are other threats as well. 

Now that it’s clear why this kind of study is necessary, let’s dive into the information that has already been established. Firstly, it is clear that climate variability has been changing seasonality in the ocean. This means that the annual cycle of surface temperatures are shifting toward earlier seasons. With changing temperatures comes the vast relocation of animals who prefer a certain temperature in their surroundings. 

Considering the value of this research, we also know that knowledge about changes in migratory timing in the ocean is relatively limited and there are many research gaps to be filled. Nevertheless, a few studies have found seasonal migrations of highly mobile fish to the north are occurring earlier in the year. 

For this study however, conducted by Neil Hammerschlag and his team at the University of Miami, a combined analysis of 9 years of satellite tracking data of tiger shark movements, remotely sensed environmental data, habitat modeling, and nearly 40 years of capture data from conventional tagging were used to study and evaluate the changes in migration patterns of tiger sharks in recent years. These methods primarily served to shed some light on the ‘conservation implications of ocean warming’ in regard to tiger sharks. This will help to create systems that can protect them from extinction. 

In order to achieve this, the study claims to assess five main questions, namely:

1. What is the preferred temperature range of the studied tiger shark population?
2. What is the influence of temperature on tiger shark space use relative to other environmental factors known to affect their movements? 
3. Does the distributional range of tiger sharks extend farther poleward in response to warming seas? 
4. Do seasonal migrations of tiger sharks into their northerly range occur earlier in the year in response to ocean warming?
5. Have climate-driven shifts in tiger shark space use altered their spatial overlap with management zones that afford them protection from capture in longline fisheries as target and/or bycatch? 

After completing the study, Hammerschlag and the team divided up their findings into four main categories: temperature at depth preference, space use and movement of tracked sharks, space use and movement based on shark captures, and overlap with protected areas. In the table below, I have summarized the key findings in each of these areas. 

	Findings
Temperature at depth preferences	Satellite tags measured ambient temperature and depth experienced by 10 female tiger sharks . The data also showed general tiger shark preferences for relatively shallow (<15 m), warm waters above 22°C (78% and 91% of all depth and temperature records, respectively).
Space use and movement of tracked sharks	Tiger sharks satellite tracking data generated 5,227 locations across 9 years from 47 sharks (6 males and 41 females). Models indicated that cold temperatures significantly influenced the probability of tiger shark occurrences in a location.
Space use and movement based on shark captures	Between 1980 and 2018, a total of 8,764 tiger sharks were captured and tagged and/or recaptured as part of the Cooperative Shark Tagging Program. After analyzing the data, a dependency on temperature was also revealed.
Overlap with protected areas	The probability of a shark being positioned within a marine protected area decreased.

Going forward, Hammerschlag’s study claims that key priorities in climate change ecology should be to determine and predict the rate, direction, and timing of the shift in space use and the movements of species as a result of climate change. This has implications for the functioning of key biodiversity hotspots and ecosystems which are vital to the economy. 

Nonetheless, climate change still brings a daunting range of risks. To list only a few examples, it could increase sharks’ vulnerability to fishing, change encounter rates with humans, and have implications for fisheries management and ecosystem functioning. Apex predators, including various but not all species of sharks, also exhibit a relatively high extinction risk, which could threaten the predator-prey interactions that are necessary to maintain balance in their ecosystem, leading to drastic changes in the ecosystem’s structure.

So putting this all together, what steps must be taken? Firstly, it is important that more research be dedicated to the change in migrational patterns among various marine species in response to climate change. Secondly, it is important as a member of the public to become more educated about the impacts of a changing climate on sea life. More specifically, it is also necessary not to proliferate the idea that sharks are the evil villains of the ocean. Like all other creatures, they have a role to play and deserve protection from illegal fishing practices, biodiversity loss, and extinction. Portraying sharks as creatures with negative human qualities only contributes to anti-shark sentiments for factually-dubious reasons. 

It is for this reason that such a study is so crucial and why more research is needed in the field to better understand the right approach to shark conservation. I think we can all agree that it’s some-fin to think about. After all…shark extinction is a fishy business. 

Bibliography

Hammerschlag, Neil, Laura H. McDonnell, Mitchell J. Rider, Garrett M. Street, Elliott L. Hazen, Lisa J. Natanson, Camilla T. McCandless, et al. 2022. “Ocean Warming Alters the Distributional Range, Migratory Timing, and Spatial Protections of an Apex Predator, the Tiger Shark ( Galeocerdo Cuvier ).” Global Change Biology, January. https://doi.org/10.1111/gcb.16045.

“Tiger Shark Migrations Altered by Climate Change: New Migration Patterns Leave Sharks More Vulnerable to Fishing.” 2022. ScienceDaily. January 13, 2022. https://www.sciencedaily.com/releases/2022/01/220113092131.htm.

Udel, Diana. 2022. “Tiger Shark Migrations Altered by Climate Change, New Study Finds.” News.miami.edu. January 13, 2022. https://news.miami.edu/rsmas/stories/2022/01/tiger-shark-migrations-altered-by-climate-change-new-study-finds.html.

Cover photo: https://sitn.hms.harvard.edu/flash/2020/the-shark-movement-fresh-insight-into-tiger-sharks-in-gulf-of-mexico/