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First Individual-Based Model of Basking Sharks Replicates Complicated Social and Environmental Drivers of Behaviour

First individual-based model of basking sharks sheds light on what drives their aggregations.

Basking sharks (Cetorhinus maximus) are the second-largest fish in the world, and they’re largely solitary, following highly individual migration routes. Yet off the coast of Ireland, they sometimes gather at the surface in groups of up to 1,000. Researchers are not sure why as to why that is. Food appears to be an obvious explanation, but observations suggest it isn’t the whole story. These gatherings also put the sharks at risk of boat strikes, which makes understanding them a conservation priority.

Previous models have captured long-range migration trends but struggled to reproduce behaviour at finer scales. Chlorophyll a, the usual stand-in for the sharks’ zooplankton prey, has also matched sightings data inconsistently.

A new study in Individual-based Ecology takes a different approach. Dr. Chelsea Gray of George Mason University and the Irish Basking Shark Group, with colleagues, built the first individual-based model of basking sharks. It simulates zooplankton directly, rather than relying on a proxy, and follows sharks around the Inishowen Peninsula in Co. Donegal from 1982 to 2018. The team tested four behavioural versions against three decades of public sightings: sharks seeking food only, sharks seeking other sharks only, sharks seeking both, and random movement as a control.

So what did 36 simulated years reveal, and what could it mean for protecting these animals? We reached out to Dr. Chelsea Gray to ask about her motivation, her biggest surprises from the simulations, and the insights the model could offer for conservation.

Pensoft (P): What motivated you to conduct research on basking sharks?

Chelsea Gray (CG): I am a member of the Irish Basking Shark Group and my previous research was focused on public perceptions of basking sharks as well as interest in basking shark tourism in Ireland. While completing that research, basking sharks were downgraded by the IUCN from ‘vulnerable’ to ‘endangered’. I was also interested in individual-based modelling.

I recognized that basking sharks, with their distinctive migratory and social behavior, were an ideal subject for an individual-based model (IBM), and that this kind of research could directly support conservation.

Ireland and other nations are currently developing or revising their ocean conservation strategies, so this is the right moment to build models and simulations that can inform policy. I have also carried out qualitative research on how to communicate IBM results to policymakers, so that this work can be put to practical use.

P: The model simulated sharks and their zooplankton prey over 36 years. What was the most surprising thing that happened when you ran the simulations, and did the random-movement sharks ever get close to behaving like the real ones?

CG: What surprised me most was how well the model replicated the boom-and-bust cycle of shark aggregations seen in the real world.

This is a complex model, and it took considerable trial and error to get it running and to find settings that produced realistic results. When I finally compared the time series, particularly those of the Food and Food/Social submodels under Test A, the match with real-world sightings data was striking.

The version in which sharks sought both food and each other matched the sightings data most closely, suggesting aggregations emerge from a combination of environmental and social drivers.

A video of the model interface itself. Note: the sharks are not to scale, but are enlarged specifically for the video. Credit to Gray et al., 2026

The random-movement sharks never behaved like real sharks, under any settings. Their aggregations never exceeded two or three individuals, and they formed noticeably fewer aggregations overall. Testing made it clear that the emergent behaviour in the Food and Food/Social submodels resulted from the sharks’ decision-making. This was reassuring, because it shows the model’s results could not have occurred by chance.

P: These gatherings happen at the surface, where boat strikes are a risk. Could this research help keep sharks safe? For example, could the model one day help predict when and where aggregations will form so that boat traffic can be managed?

CG: The model is still at an early stage. As our ability to measure the in-situ preyscape and to remotely sense phytoplankton and zooplankton improve, future iterations of the model will allow for more precise understanding of where the sharks are aggregating. In its current form, it can provide some insight into when (based on zooplankton availability) an aggregation might occur, but not where. It does, however, lay the groundwork for further development. It also serves as a proof of concept, showing that individual-based modelling is a valuable approach to simulating and understanding shark behaviour, even though it demands substantial effort up front.

Head of a basking shark. Credit to Irish Basking Shark Group.

The model also allows us to develop and test future scenarios, which is essential when considering climate change and marine protected areas. Currently, we don’t know much about the impact of climate change on shark migration, however we do have some evidence that their main prey (calanoid copepods) are shifting northwards.

Climate change could therefore impact the timing and location of future shark aggregations, and we will need to account for this when developing voluntary or statutory guidelines to reduce human threats such as ship strikes. Because the model is adaptable, it is particularly well suited to testing multiple scenarios of this kind.

P: Why did you choose Individual-based Ecology to publish this research?

Individual-Based Ecology (IBE) fills a very important niche when it comes to environmental research. When previously looking to publish this article, it was difficult to find a journal that would be interested in a proof-of-concept model, especially one that doesn’t quite have policy application. IBMs also remain underused in environmental research, which makes it hard to find editors equipped to assess both the model design and ecological merits of a study.

The model is freely available in the paper’s supplementary material, and Dr. Gray welcomes questions and ideas from researchers interested in developing or experimenting with individual-based models of basking sharks.

Read the full paper:

Gray C, Rothman DS, Peters-Burton E, Smith C, Parsons ECM, Garretson A (2026) An individual-based model of basking sharks in Ireland. Individual-based Ecology 2: e176474. https://doi.org/10.3897/ibe.2.176474

Why two prehistoric sharks found in Ohio got new names

Research leads to rediscovery of forgotten fossils.

Until recently, Orthacanthus gracilis could have been considered the “John Smith” of prehistoric shark names, given how common it was.

Three different species of sharks from the late Paleozoic Era – about 310 million years ago – were mistakenly given that same name, causing lots of grief to paleontologists who studied and wrote about the sharks through the years and had trouble keeping them apart.

But now Loren Babcock, a professor of earth sciences at The Ohio State University, has finished the arduous task of renaming two of the three sharks – and in the process rediscovered a wealth of fossil fishes that had been stored at an Ohio State museum for years but had been largely forgotten.

Loren Babcock with a collection of Orton Museum’s fossil fishes, including several from John Newberry. Photo by The Ohio State University

In order to change the names, Babcock had to go through a process governed by the International Commission on Zoological Nomenclature (ICZN). He had to document the need to change the names, propose new names and submit them to an ICZN-recognized journal for peer review and then have the ICZN officially accept the names.

Tooth of the shark Orthacanthus lintonensis. The tooth is about 13 mm long.

“It was one of the most complex naming problems we have had in paleontology, which is probably one reason no one attempted to fix it until now,” Babcock said.

“A lot of scientists in the field have written, thanking me for doing this. We are all happy it is finally done,” he said.

One measure of the impact the renaming has had on the field: Babcock’s paper announcing the new names was just published in the journal ZooKeys on Jan. 8, but it has already been referenced on seven different Wikipedia pages.

The original Orthacanthus gracilis fossil was found in Germany and named in 1848. That species gets to keep the name.

The remaining two fossils were found in Ohio and named by the famous American paleontologist John Strong Newberry in 1857 and 1875.

Babcock renamed the Ohio sharks Orthacanthus lintonensis and Orthacanthus adamas, both based on the name of the place where they were originally found.

Why did Newberry give the two Ohio sharks the same name?

“He probably just forgot. It was nearly 20 years between the time the two species were named,” Babcock said.

And as far as giving it the same name as a German species: “In those days, it was really difficult to search for names that were already in existence – they did not have the internet.”

The sharks themselves were fascinating creatures, Babcock said. They were large and creepy, nearly 10 feet long, and looked more like eels than present-day sharks, with long dorsal fins extending the length of their backs and a peculiar spine extending backward from their heads.

They lived in the fresh or brackish water of what are known as “coal swamps” of the late Carboniferous Period (323-299 million years ago) during the late Paleozoic Era. They belong to an extinct group of chondrichthyans (which includes sharks, skates and rays) called the xenacanthiforms.

Dorsal spine of Orthacanthus adamas. The spine is about 71 mm long.

Newberry was for a time the chief geologist at the Geological Survey of Ohio. He played an important role in the early growth of what is now the Orton Geological Museum at Ohio State.

Babcock, who is the current director of the Orton Museum, decided to begin the renaming process after reviewing the museum’s collection. He was surprised to see how many fossils the museum had that had been collected by Newberry, including the two prehistoric sharks.

Babcock wrote about Orton’s Newberry collection in a new article published in the Journal of Vertebrate Paleontology.

Through the years, scientists have written about how various Newberry specimens had been lost. It turns out many had been at the Orton Museum.

“No museum has a larger collection of Newberry’s fossils except for the American Museum of Natural History in New York City,” Babcock said.

“Not a lot of people are aware of that – I did not even know the extent of our collection. If you’re looking for part of the Newberry collection and can’t find it in the American Museum of Natural History, it is probably going to be here.”

Research article:

Babcock LE (2024) Replacement names for two species of Orthacanthus Agassiz, 1843 (Chondrichthyes, Xenacanthiformes), and discussion of Giebelodus Whitley, 1940, replacement name for Chilodus Giebel, 1848 (Chondrichthyes, Xenacanthiformes), preoccupied by Chilodus Müller & Troschel, 1844 (Actinopterygii, Characiformes). ZooKeys 1188: 219-226. https://doi.org/10.3897/zookeys.1188.108571

News piece originally published by the Ohio State University. Republished with permission.

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How many sharks, chimaeras, skates, and rays inhabit Mexico?

Worldwide, Mexico is well-known for a lot of things: its cuisine, tequila, mariachis, pyramids, and beaches, as well as being the country with the most Spanish-speaking residents (more than 120 million people).

In contrast, however, little is known for the country’s chondrichthyan fauna: a class of fishes containing the sharks, chimaeras, rays, and skates.

To fill the gap in the knowledge of the Mexican marine fauna, scientists from the Instituto Politécnico Nacional – Centro Interdisciplinario de Ciencias Marinas (IPN-CICIMAR) conducted a multidisciplinary study on the extant species of the country’s Economic Exclusive Zone (EEZ) and, as a result, reported a total of 217 extant chondrichthyan species. Their findings are published in the open access journal ZooKeys.

In their updated taxonomic list, the team of Dr. José De La Cruz-Agüero, Dr. Jorge Guillermo Chollet-Villalpando, and Venezuelan graduate students Lorem González-González and Nicolás R. Ehemann report eight chimaeras, 111 sharks and 98 ray and skate species. These numbers equate to 18% of the world’s chondrichthyans.

Split between the Mexican coasts there are 92 species recorded from the Mexican Pacific and the Gulf of California, whereas 94 fishes are identified for the Gulf of Mexico and the Caribbean Sea. Additionally, 31 species are known from both coasts.

“The species richness will undoubtedly continue to increase, due to the current investigations in progress, as well as the exploration of deep-water fishing areas in the EEZ,” comment the scientists.

Considered to be primitive fishes, sharks, skates, chimaeras, and rays are believed to have been inhabiting the planet for the last 420-450 million years. To put it in perspective, the earliest evidence of our species – Homo sapiens – is pretty ‘young’ at 315,000 years.

Not only do these species are peculiar with their lack of a bony skeleton when compared to the more recently evolved fishes, but they also have an unusual digestive system, featuring a spiral valve, where the lower intestine is twisted like a corkscrew to increase the surface area. They don’t have a swimming bladder either. Further, there are about 650 extant species, whereas the known bony fishes are estimated to be over 35,000.

Most of the chondrichthyans are considered either ‘Critically Endangered’ (a classification a step below ‘Extinct’) or ‘Endangered’, according to the Red List of the International Union for Conservation of Nature (IUCN). The majority are also featured in the Convention on International Trade in Endangered Species.

As if to make matters worse, these fishes are also particularly susceptible to overfishing and have a low rate of growth and fecundity (females give birth to between 1 and 25 pups a year).

Original source:

Ehemann NR, González-González LV, Chollet-Villalpando JG, Cruz-Agüero JDL (2018) Updated checklist of the extant Chondrichthyes within the Exclusive Economic Zone of Mexico. ZooKeys 774: 17-39. https://doi.org/10.3897/zookeys.774.25028