Field work in Sri Lanka

Nimna Wickramasingha

University of Leeds

My travels funded by the Challenger Society of Marine Science took me to Valaichchenai, Sri Lanka. The aim of my travels was to scope fisheries landing sites, and trial and refine sampling methodologies for my final year dissertation project titled “Using eDNA for rapid monitoring of elasmobranch landing sites in Sri Lanka”.

Sri Lanka's waters are rich in biodiversity, including endangered and endemic species such as stripenose guitarfish (Acroteriobatus variegatus). These waters are also crucial to the livelihoods of many artisanal fishers, creating the need for sustainable fisheries management. Currently observational surveys are used to inform national management strategies and monitoring elasmobranch populations. The need for trained experts to identify species, among other resource limitations, often hinder routine and accurate monitoring. As eDNA can generate species inventories from residual DNA in water, it offers a convenient and efficient enhancement to visual surveys. It is effective at detecting elusive species, resulting in more comprehensive species inventories and precise identification.

In collaboration with my supervisor Dr. Simon Goodman and Blue Resources Trust (BRT), a non-profit research and conservation organisation that has been actively monitoring chondrichthyan fisheries in Sri Lanka, we have designed a project that supports fisheries management efforts critical for conserving declining chondrichthyan species in Sri Lanka. Our goal is to assess the potential of environmental DNA (eDNA) from wastewater samples at fishing wharfs and boat holds to accurately characterize catch compositions and identify overlooked elasmobranch species. To improve our sampling methodology, I used this opportunity to trial a recently validated eDNA capture method using a ‘metaprobe’ deployed with gillnets. The metaprobe is a hollow perforated spherical probe containing rolls of gauze that capture DNA, removing a time-consuming step of active filtration.

Valaichchenai consists of a main harbour used by artisanal multiday boats and a smaller number of one-day boats. The harbour was active throughout the day, primarily bringing in yellowfin tuna. Additionally, several smaller landing sites were used by fishers operating single-day boats. During my time visiting the harbour and landing sites, I witnessed a diverse array of elasmobranch species in the fishers’ catch, including silky sharks, a snaggletooth shark, several rays (such as blue-spotted stingrays, manta rays, white-spotted whiprays and an electric ray), and a few stripenose guitarfish.

I sourced the metaprobe from a local plastic shop and deployed it with a one-day fisher at the Pethalai landing site. The fisher received the metaprobe in the evening before heading out to sea, and I retrieved it the following morning when they returned. In addition to metaprobe samples, I collected water samples from the boat holds of multiday boats at the Valaichchenai harbour, alongside observation records. Initially, I aimed to collect water from wharf washings as well, but as this water drained into a highly polluted drain, I opted instead to rinse the weighing scale used for the catch from the same boat.


As the sampling progressed, I refined my approach. I decided to focus on collecting samples from only the Pethalai landing site. This allowed me to establish a field control by rinsing the weighing scale before the catch of interest was weighed. This was not feasible at the main harbour due to the presence of multiple weighing scales, making it difficult to determine which one would be used for a particular catch. However, at the smaller landing sites, only two weighing scales were in use. On the following sampling days my routine included deploying the metaprobe in the evening, retrieving it the next morning, along with collecting boat hold samples from the same boat, rinsing the weighing scale before and after the catch was weighed and noting down the caught species. However, I still faced some challenges. On one occasion, the fishers used a different weighing scale than the one from which we had collected the field control. On another day, a different boat weighed its catch before our target catch, introducing potential contamination. Regardless, through the help of the BRT members, I was able to communicate and build good relations with fishers, identify fish species, and collect the samples needed. The fishers were interested in the project and were supportive of sample collection.

All collected samples were transported to the University of Leeds, where I will extract DNA and carry out sequencing over the next few months. This process will provide me with essential laboratory training for my project. As a novice in the field, this experience has been invaluable in preparing me for my main fieldwork. I have gained critical insights into the study site, fisheries operations, potential cross-contamination, optimizing resource use for successful sampling, and refining my overall sample collection strategy. I am beyond grateful for the Challenger Society of Marine Science for making this trial period possible and look forward to carrying out my dissertation project in July 2025.



Profile
I am currently in my penultimate year of my MBiol at the University of Leeds, supervised by Dr. Simon Goodman. As a Sri Lankan national eager to apply my knowledge and skills in marine sciences to improve marine resource management and conservation efforts back home, I collaborated with Blue Resources Trust, whose goals align with mine. Together, we designed my MBiol project to contribute to conserving vulnerable marine species through innovative applied research. The project is set to commence in July 2025 and will run through to March 2026.