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Products on Location: Researchers Filter for Sharks Piece by Piece

Danielle Bartz, a PhD researcher at the University of Hawai'i at Mānoa, spends a lot of time on boats to determine whether scalloped hammerhead sharks still call Hilo Bay home.

Hammerhead shark swimming in Hilo Bay

May 3 , 2023 | 6 min read

Rain and sea spray are key adversaries of Bartz. As someone who works on a boat, she encounters them often. It’s not a rogue splash near a laptop or a finicky instrument that worries her but, instead, a thin filter with a diameter smaller than a soda can. It is designed to get wet — it’s a filter after all — but how it gets wet matters to Bartz.

She uses the paper-thin tool to filter through ocean water in pursuit of sharks – but not in their entirety. Instead, she’s after tiny fragments. Humans shed hair and skin cells and other organisms, like sharks, do too. Biologists now use these small fragments of DNA, known as environmental DNA — or eDNA — to find evidence of elusive species. After they collect scraps of eDNA on the filter, researchers amplify the samples, ultimately working to see whether specific shark species are present in an area.

If Bartz gets the nylon net filter  wet by accident, she introduces eDNA from other sources and contaminates the sample. Given this, she spends more time than the average biologist thinking about how she can keep filters dry.

Through the Products on Location series, we explore how customers — like Bartz — use products in unique places and for unique purposes. We recently caught up with her to learn about research involving sharks, boats and filters.

Note: This interview was edited for clarity and brevity.

Where do you work?

I’m a PhD student in the Marine Biology Graduate Program at the University of Hawai'i at Mānoa, USA. I work in Hilo Bay, which sits on the eastern side of the Island of Hawai'i, also known as the Big Island. I spend a fair amount of my time on a boat cruising in and around the bay, collecting samples for my research.

What do you study?

I study how populations of sharks fluctuate over time. In the 1950s and 1960s, some fishers reported catching 10-12 juvenile hammerhead sharks a day in Hilo Bay, Hawai'i. Now, they are listed as critically endangered and locals rarely see them. Fishers also noticed a massive increase in blacktip sharks, which are a more common, more generalist shark species than hammerheads.

Scalloped hammerheads are so elusive that they're hard to catch on camera, but Bartz is no stranger to swimming with sharks. Here, oceanic whitetips head right towards the camera. Video courtesy of Danielle Bartz.

Why is this work important?

Scalloped hammerheads are critically endangered throughout the globe but are not deemed to be at risk of extinction here in Hawai'i. In the case of Hilo Bay, it appears that we have a near disappearance of scalloped hammerheads from a once-thriving nursery habitat. I’m working to document this and hope to better inform the management of the species across the state.

How do you estimate shark populations?

When I first started my PhD, I planned to estimate the population by catching, tagging and tracking juvenile hammerheads. Despite all the plans, permits and work, this approach didn’t pan out. I couldn’t catch a juvenile hammerhead to save my life. And it wasn’t just me. Nobody was catching them. So, this took me back to the drawing board. My complete failure led me to delve into the world of eDNA, which was completely new to me.

How did you learn this new method?

I was intrigued by eDNA for a few years but was really intimidated to delve into genomics. When I was trying to identify a different approach to estimate population dynamics, I read a paper where researchers detected scalloped hammerheads in a harbor in Guam for the first time in over 50 years using eDNA. Their harbor looked a lot like Hilo Bay, so I thought, why not reach out? I sent Dr. Alyssa Budd a cold email asking if she would chat with me about the research. Honestly, I didn’t really expect much because I was just a random grad student in Hawai'i. But, to my delight, she replied, took me under her wing and became my “eDNA fairy godmother,” as I like to call her. I am so grateful for her continued mentorship and guidance throughout my project.

Two images of Danielle Bartz wearing a pink hat and plastic glove processing samples on a boat. In the left image, Bartz carefully holds tweezers and rolls a filter. In the right image, Bartz stuffs the filters into small tubes.

After Bartz finishes pumping water, she must carefully roll filters and then fit them inside small vials. Photos courtesy of Danielle Bartz.

How do these filters fit into your methods?

Trying to find shark eDNA in the ocean is like trying to find a needle in a haystack. I filter through a decent amount of water to even have a chance of getting a positive read. When I finish, I carefully remove the filter with tweezers. I often put a towel over my head to lower the risk of contamination, since a stray raindrop, splash or fingerprint compromises the sample. I then roll the filter – kind of like a burrito – cut it into pieces and stuff these into tubes, so I can start the process of amplifying eDNA.

What makes for a memorable day in the field?

Days that are both windy and rainy are always interesting. If the filters get hit with rain or sea spray, I throw them out and start again. If the filters get blown away and hit the bottom of the boat, I throw them out and start again. Sometimes this happens when I’m loading the filter and it’s not a huge deal. But if it happens after I filter through ocean water, that’s a total bummer. Rainy and windy days require a lot of carefully planned movements.

Long days in the field are taxing. What motivates you?

I have loved sharks since I was two years old. For me, working in this system is a dream come true. It’s exciting to think that this work could better inform management for scalloped hammerheads across the state — and maybe even more broadly.


About the Series

With 300,000 products, some are bound to end up in interesting places. Through the Products on Location series, we highlight people using our products in unique settings and for unique purposes. On a boat? Absolutely! For an outside-the-box method? Yes! At three in the morning while you sleep at home? For sure.

We are always looking for more stories. If you use some of our products in a location or for a purpose you’d consider unique, send us an email with your idea.

About Nylon Net Filters

We offer an exhaustive portfolio of membrane filters that has helped generations of scientists reach new milestones and use membrane materials for unique applications, as highlighted in this story. Millipore® nylon net filters possess uniform, large pore structure and mesh openings ranging from 10 to 180 µm. With their broad compatibility, strength, flexibility and hydrophilicity, nylon filters are routinely used for particle removal and clarification, as well as solvent filtration. Learn more about nylon net filters.

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