Skip to main content
U.S. flag

An official website of the United States government

Aloha! Message in a Niskin Bottle by Dani Bartz

Aloha! My name is Dani Bartz. I am a Ph.D. student in the Hawai’i Cooperative Fishery Research Unit, located in Hilo, Hawai’i. Field notebook photography and notes: September 2022, it’s a beautiful sunny day for some environmental DNA (eDNA) sampling in Hilo Bay, Hawai’i.

Earlier in the year, after having to drop the acoustic telemetry portion of my project, I dove deep into the world of environmental DNA (eDNA), in hopes to extract and amplify scalloped hammerhead shark DNA from seawater samples throughout Hilo Bay. I was new to the field and doing a lot of learning through trial and error. Thankfully, I had a wonderful mentor, an eDNA expert on the other side of the world in Australia that graciously took me under her wing and helped me design a sound survey. I was taking seawater samples from the surface, but soon realized that I needed to be collecting water from depth if I wanted to increase my chances of capturing hammerhead DNA, because if these sharks were within this coastal embayment, they would likely be juveniles near the bottom.

Hilo Bay is shallow, so I decided to try using a Niskin bottle to grab water from around 50 ft. of depth. I asked one of the professors in my department if I could borrow his Niskin bottle, and began monthly sampling trips with that in the summer of 2022.

black tape cap and clear bottle
Black tape is stretched across the stopper of the 'Niskin' bottle and secured to form a positive pressure seal.

Come September, I was feeling pretty confident with the janky old contraption, and brought two volunteers out on the boat with me for a full day of sampling. We arrived at the first and deepest site, about 50-60 ft deep, and sent the Niskin down on the rusty wire cord. The first two hauls went well, and I sent the collected seawater through my filters using a battery-operated diaphragm pump on the boat. This was when the real fun began. I prepared to send the Niskin bottle down for the third and final drop, hovering over the starboard gunwale. I lowered it to just above the seafloor, and then sent down the weight that traveled down the wire line to hit a button on the top of the bottle and trigger a mechanism to close both ends and hence capture the water inside of the bottle. The only problem was, this time, as soon as I sent the weight down, I felt the line go slack. Yep, that’s right. The wire cord, that I had put my blind faith in to hold, had snapped clear-off.

Now this nearly $1500 piece of borrowed equipment was sitting on the bottom of the seafloor in murky Hilo Bay. The “uh oh” set in and a million anxious thoughts ran through my mind. How do I tell my advisor, and the professor that I borrowed the Niskin from, that I royally messed up? Now we must buy him a new one. Or could I retrieve this one from the bottom of the ocean? It was a longshot. I was a little panicked but trying to keep my cool for the sake of the volunteers that I was mentoring. I had to make a new plan for the remaining sample sites on the fly.

Since we already went through all the trouble to load up the boat with my many waterproof bins full of field gear, I decided that the show must go on and we will sample the three remaining sites from the surface, knowing that there was a slim chance that those samples would successfully capture shark DNA and bias our results. I was feeling defeated as we motored to the next site. One of the volunteers had recently completed her Motorboat Operator course, so I let her drive the boat while I sat there with a blank stare and a racing mind. Then the boat jolts and I hear the engines go “VROOOOOOSH”. Oh no!!

An engine failure was the last thing I had the capacity to deal with. This was a brand-new boat (thanks USGS) so we were still getting a feel for it, and knew it was due for its first oil change after a certain number of engine hours so it could potentially be related to that. We assessed the situation and then I made the daunting call to my researcher to break the bad news to him…not only had I lost the borrowed Niskin bottle to the brown abyss, but now the boat may be acting up. He assured us that everything would be ok, and we would get it figured out, and to just make it back to land safely. The boat appeared to be working again, but we took it nice and slow as we finished up and made our way back to the harbor.

Over the next few days, I obtained quotes for a new Niskin bottle to replace the one I had lost, when I decided to go out on a limb and ask some fellow scientific divers if they would be willing to accompany me on a longshot search and recovery dive the following week. The weather was in our favor, and I didn’t want to wait too long because here in East Hawai’i, that can change on the drop of a dime.

We managed to throw together a dive plan and get out the water again exactly one week after the Niskin had broken loose. We descended into a very murky and desolate part of the bay, with visibility being 5-10 ft at best. We broke up into two teams of two divers each, my buddy and I started a circular search pattern, and the other team ran transects towards the nearest buoy. Thankfully, as soon as the Niskin broke off the week prior, we took a global positioning system (GPS) coordinate and mapped the seafloor using our side-scan sonar to see if there were any distinguishable features that could be the bottle.

Miraculously, about 10 minutes into the dive, I saw the other buddy group swimming towards me, carrying…you guessed it, the Niskin bottle!! I let out a scream of relief into my regulator and did an underwater happy dance. We surfaced, boarded the boat, and all reveled in our good fortune. Aside from some minor biofouling, the Niskin was perfectly intact and the wire cord and weight had been sitting right next to it, so they were also recovered. The longshot dive turned out to be a successful search and recovery mission!

After giving the bottle a good scrub down, I was able to return the Niskin bottle to its rightful owner and avoid having to devote lab resources to replacing it. Although all was made right again, I couldn’t help but think that there had to be a better way to take seawater samples from depth after that stressful experience. Fast forward a few months, and this notion led to the conceptualization, construction, many trials, and eventual field use of a water filtration system designed and built by my lab mate, advisor, and I, that can do just that. It just goes to show that every time one door closes (or sinks to the bottom of the ocean), another door opens!

What is your research focus?

My research is focused on how we can utilize interdisciplinary approaches to improve fisheries management and conservation. I am working to answer a priority question of local fishers and resource managers by analyzing the local ecological knowledge of community members, strategic fishing efforts, and eDNA to assess if there has been a population decline of juvenile scalloped hammerheads in a coastal embayment and recreational fishery in Hawai’i. Additionally, I am using these data streams to piece together historical ecological baseline of how this estuarine habitat has been used as a shark nursery from the 1950s-present. It is my goal to present the results of this study to resource managers in a usable format so that best management practices may be established for this species.

diver with black wetsuit snorkeling in blue clear ocean water
Aloha! The Hawai’i Cooperative Fishery Research Unit (HCFRU) was established in the spirit of cooperation and collaboration, with a shared vision of developing the scientific knowledge and natural resource professionals necessary to ensure the sustainability of Hawaiian natural resources for future generations. The HCFRU is based at the University of Hawai’i at Hilo and is part of the National Cooperative Research Units Program within the U.S. Geological Survey. 

What are your personal hobbies?

In my free time, I absolutely love fishing. I always have, ever since I was a little girl catching tiny fish in ponds with my dad. Now I am enamored by the open ocean, and love getting offshore in the search of tasty pelagic species. I am a big believer in catch and release, unless the animal will be sacrificed as food. I have become increasingly passionate about sustainability since living in Hawai’i and nowadays I only eat animal protein if either myself or someone I am close with has harvested it. I don’t want to support the supply chain that is using such environmentally-taxing resources to ship in unsustainably raised meat.

One of my favorite ways to harvest a healthy meal is through kayak fishing. Any chance we get, my partner and I load up our one-person fishing kayak and launch from a nearby beach or harbor, kick ourselves out 4-8 miles offshore, and fish for things like ahi (yellowfin tuna), mahi mahi (dolphinfish) or ono (wahoo). Last time we went out we came back with four 20-30 lb. mahi mahi, and we could’ve stayed out longer and caught a couple more if the loaded down fish bag hadn’t caused one of the kayaks to start taking on water. We gave one fish to a local elderly friend and veteran, sold the two biggest to a local fish purveyor, and fileted he last one and shared bags of fresh fish with a handful of neighbors and family.

women kayaking spear fishing a green and and yellow mahi mahi
Aloha! My name is Dani Bartz. I am a Ph.D. student in the Hawai’i Cooperative Fishery Research Unit, located in Hilo, Hawai’i. Photographer: Devin Hallingstad, copyright dedication agreement on file.