A labour of love: Using photo-identification to track Pacific white-sided dolphins

“What are they doing and why are they here and what’s their story?”

Pacific white-sided dolphins are known for their distinct colouring and are a highly playful and social marine mammal.
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Dr. Erin Ashe discovered her fascination for Pacific white-sided dolphins more than 10 years ago when a daunting white wall of rushing water along the horizon gradually advanced on her small boat. She didn’t know what it was at first, thinking it might be a squall.

And even as her now-husband and co-researcher Rob Williams pointed to the charging water, exclaiming, “Look, Lags!” Ashe still didn’t quite understand what she was seeing. It wasn’t until she peered through her binoculars that she realized the “wave” was actually hundreds of Pacific white-sided dolphins (Lagenorhynchus obliquidens, or Lags) crashing through the water, stirring up foam and whitewash, stampeding like an army into battle. Immediately, Ashe wanted to know their story.

Dr. Erin Ashe is the co-founder and executive director of the research and conservation non-profit Oceans Initiative.
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Since then, the scientist and executive director of Oceans Initiative, a non-profit marine life conservation centre, has dedicated her career to these animals. Her research involves using photo-identification methodology to track the dolphin population off the northeastern coast of Vancouver Island in the Broughton Archipelago. The goal is to photograph each of the dolphins as they breach the water, ideally capturing photos of them from both sides. These photos can then be used by the researcher to identify individual dolphins based on the notches, scars, scratches and markings on their dorsal fins.

“Photo-identification is a great way to monitor a particular population year upon year,” Ashe explains. “You can look at the demographic component in relation to different environmental factors, like how the prey is doing or whether they’re affected by predation.”

Monitoring a concentrated population also allows Ashe to gather a detailed assessment of injury rates, how often females are calving, and whether they develop long-term, sociological relationships with others in their pod.

But while each dolphin is unique, just as each human is, it is very difficult to collect a high-quality, usable photograph of each animal when it’s part of a pod of several hundred. “That’s where we rely on statistics and different mathematical approaches to estimate things like abundance and survival and fidelity,” Ashe explains.

Although orcas are members of the dolphin family, they are still natural predators of the Pacific white-sided dolphins.
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Orcas are found in all three of Canada's oceans, but are most common off the southern coast of British Columbia.
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This photo-identification is hugely time-consuming and researchers are always conscious that human error is a challenge with a large group of similar-looking animals and photos that aren’t always razor sharp. If Ashe and her team are too cautious with their identification, avoiding pairing up certain photographs because they aren’t 100 per cent certain they’re the same dolphin, they risk concluding a larger-than-reality population. But if they’re too generous with their identification, their research risks erring on the side of a smaller-than-reality population estimate.

It can take hundreds of hours for Ashe to scour countless photographs to match dorsal fin images. This, in turn, helps her to determine accurate population counts.
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To reduce the possibility of inaccurate readings, Ashe has used a “certainty score” to better estimate various population abundances. Her 2022 study published in Mammalian Biology explained it succinctly: ‘Identified individuals within an encounter were matched and a certainty score of “Certain” (100% confident), “Likely” (< 100% but ≥ 90% confident), or “Possible” (< 90% but ≥ 50% confident) was assigned to putative matches between pairs of photographs based on the degree of confidence in each match.’ The researcher then took those certainty scores and used them to determine three different population estimates with minimal human bias.

Photo-identification is just as painstaking and labour intensive as it sounds — Ashe spends hundreds of hours scouring countless photographs to match dorsal fin to dorsal fin. It can take up to a year to go through a season’s worth of photos, with the resulting data then used to come up with population estimates. Until the 1990s, this photo-identification work was done with film cameras, with renowned American-Canadian marine biologist Alexandra Morton a major contributor.

“She was shooting on film at this remote base, and so she would shoot on film, then put the film on a float plane,” Ashe explains. The film would then go to a photo lab, which would send back contact sheets compiling all of Morton’s photos. The researcher would then have to look through a loupe (a special type of magnifying glass), picking out and circling which photos she wanted to get printed. Then she’d send her choices back on the float plane and wait for the photos to be printed and returned to her. “So that was a whole other level of love!” says Ashe.

Although the orca pictured here is a female, male orcas have the largest dorsal fin of any marine mammal, up to 1.8 metres in height.
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Algorithms can often be used to help match nicks and scars on the dolphins' fins to help cut down the time it takes for researchers to analyze images and identify individuals.
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Ashe, who works in the age of digital photography, has seen photo-identification advance quickly with more sophisticated technology — she’s carrying on that evolution with artificial intelligence.

Using algorithms that can match nick to nick and scar to scar on individual dolphin fins, this process significantly cuts down the time researchers spend bending over images, and also allows for collaboration between researchers and citizen scientists, who are encouraged to submit their own photos to researchers. While this program is still in its infancy, Ashe is hopeful that AI will be a valuable tool for researchers and help boost conservation efforts.

If Ashe can determine more accurate population numbers based on her photo-identification research, she can use this as a backbone for further study on how they thrive and reproduce even while sharing the seas with predators such as orcas.
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It all adds up to helping Ashe and other researchers keep ever-more-accurate tabs on a species that, while not currently endangered, is facing constant population shifts. Whether that’s due to predation, bycatch or changes in habitat distribution, Ashe is determined to avoid a “conservation by crisis” approach where extreme methods of preservation are only enacted at the crisis point when a species is facing extinction. “You don’t want to get into that position and it can happen really quickly,” she says.

Even after more than a decade, Ashe says she still has much to learn about Pacific white-sided dolphins. “As the world is changing, the environment’s changing, what I’ve learned … is that long-term datasets are worth their weight in gold.”

She wants to dive deeper into her unanswered questions about this species, like how they thrive and reproduce even while sharing the seas with predators such as orcas — and she believes photo-identification is the backbone to discovering those answers.

“The dolphin project represents this wonderful scientific curiosity and connection with nature. They have this ability to draw people in and really appreciate and connect with nature — and I think that’s something we all need right now more than ever.”


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