Scientists Say Almost Nothing Is Known About The Tiger Shark In South Atlantic Waters

The tiger shark (Galeocerdo cuvier) is one the most recognizable of the shark species, but even it has a few secrets of its own. Turns out almost nothing is known about the tiger shark in South Atlantic waters!

What we do know of these sharks is extensive in other parts of the world. The largest Carcharhinidae member and one of the largest apex marine predators, it has a circumglobal distribution in both tropical and temperate waters And is famous for its opportunistic feeding habits. These sharks are known to eat both normal shark prey (like fish, turtles, seabirds, marine mammals) and a wide variety of unusual items (to name a few: tires, license plates, TNT, chicken wire, porcupine and echidna parts, a suit of armour, songbirds). Like many elasmobranchs, tiger sharks are an important part of the marine ecosystem, helping structure marine environments by maintaining food web stability and nutrient and energy cycling between trophic levels, as well as contributing to prey population control. And also like many other elasmobranch species, tiger sharks are highly at risk due to several negative marine environment pressures. Currently listed as Near Threatened at a global level based on declines of about 30% in the past three generations (53–68 years), their biggest threat is fisheries exploitation and mortality resulting from shark control programs. This has led to a decreasing population trend with evidence of global fragmented populations.

A regular star of nature documentaries and scientific articles, you would think we knew all we needed to know about tiger sharks. But a recent paper that reviewed currently available tiger shark research papers, led by scientist Samuel Balanin, has reported several knowledge gaps that the scientists say should be the focus of future studies for this species. Not only that, but the 41 published papers examined exhibited a trend: most are about the species in the North Atlantic Ocean than the southern region. “For example, basic tiger shark biology data has been available for the North Atlantic since 1949, and several Northern hemisphere regions have made use of such a high available data volume to direct conservation actions,” the authors state in their paper. “Underdeveloped and developing countries, however, have not matched these research efforts, due to a suite of issues, ranging from scarce or non-existent fishing regulations and fisheries statistics, lack of financial support, government funding cuts, and the still prohibitively high costs of several research methods and technologies in these regions, hindering shark fisheries management. Thus, tiger shark biology and ecology assessments in these areas are still significantly lacking on several fronts, significantly hindering conservation and management efforts.”

“This is a species of great importance for the marine ecosystem, in addition to being a shark with many curious features from a scientific point of view, including feeding habits (they can eat pretty much anything), migratory patterns (that can be extremely random and difficult to categorize and predict), and reproductive aspects (a special mode of embryo nourishment that is only known for this species),” says Natascha Wosnick, co-author of the study and postdoctoral researcher at the Federal University of Paraná in Brazil. “However, even with an expressive amount of data on the tiger shark in North American and Caribbean waters, the lack of data for the South American and African continents raised a red flag, which motivated us to study more deeply what information was or not available for these regions.”

The topics most studied and published about tiger sharks was ‘Feeding Ecology’ (n = 12), followed by ‘Human Interactions’ (n = 8), and ‘Movements and Migration’ (n = 7). While the first study dates from 1977 (from Ceará, Northeastern Brazil), this remained the only article published for tiger sharks in the South Atlantic for two decades. No articles were published in the 1980s and it wasn’t until 2010-2019 that Wosnick and the team saw a peak in studies (71%). Additionally, an increasing number of publications has been reported since the beginning of the 2020 decade. This knowledge gap puts tiger sharks in danger, Wosnick says: “The fact that we do not have a detailed diagnosis of tiger shark commercial fishing in a significant portion of a large ocean prevents us from generating public policies that can protect the species. In addition, the lack of knowledge about migratory patterns and habitat use prevents us from assessing the real effectiveness of protected marine areas and ecological corridors to be proposed as conservation measures in the future. Also, as the species is involved in many cases of attacks on humans, the lack of a monitoring program in most affected regions represents a human safety issue, that needs to be urgently prioritized.”

Brazil is a leader in the South Atlantic area with tiger shark publications, specifically the northeastern part of Brazil (Southwest Atlantic, n = 22). This may be due to the higher coastal abundance of tiger sharks in this area, alongside a high number of attacks recorded in the city of Recife, in the state of Pernambuco. Moreover, a well-known tiger shark incursion hotspot is noted at the Fernando de Noronha Archipelago, clearly attracting further attention to the species. Previous research has highlighted evidence of mating scars in female tiger sharks (Galeocerdo cuvier) here, and that they might use the Brazilian continental shelf as pupping grounds. But with the exception of data from the states of Pernambuco and Paraná (Northeast and Southern Brazil, respectively), nothing is known about tiger sharks in the western South Atlantic. The situation is even worse for the eastern South Atlantic, as only one study, in which the tiger shark was not the focus, has been published so far.

So what can be done? “While it is important for data to be generated for the South Atlantic, it is necessary that this be done by local researchers, preventing all the knowledge generated from now on to be based on parachute science. It must be emphasized that it is very important to have researchers from countries with more resources studying data-poor regions, but this needs to be done through collaboration with native researchers – not just using them as a workforce, but giving them the opportunity to be principal investigators, first or last authors of papers to be published and also as country representatives in international meetings,” says Wosnick. “It is also important that such partnerships bear fruit for the country, not only through scientific papers or tv shows but also in the form of professional training, local community engagement, and most importantly, technical reports that can be directed to local governments on how things can be improved towards species’ conservation.”

The lack of financial investment, a recurring problem in the countries bordering the South Atlantic, can be one of the (many) reasons why tiger shark research here is scarce to non-existent. But this knowledge gap opens the area up to parachute or colonizing science, (explain what this is). Wosnick and her co-authors strongly suggest the governments of the countries bordering the South Atlantic, along with national and international funding agencies, recognize the importance of financing local projects over those from outside the region: “It is vital that more financial support is given to research groups that are interested in working with the species in these regions, as well as partnerships between countries and governments so that quality data (especially on commercial capture) can be collected. Coalitions between research groups and NGOs from South American and African countries are also promising ways to advance knowledge about the species. It is also imperative that partnerships are made with commercial fishers, as most of the data that needs to be generated for the regions can benefit from access to commercial landings – especially from small-scale and artisanal fleets that are prevalent in South American and African countries.”

One of the most iconic shark species still has a lot to teach us, despite gracing the cover of practically every wildlife magazine out there and making cameos on natural history documentaries worldwide. Are we ready to support those who are trying to uncover those lessons and tease apart those mysteries?