In the age of conservation technology, scientists are finding new ways to track marine species, without catching or even seeing them. One of the most promising tools is environmental DNA, or eDNA, which allows researchers to detect animals from the microscopic traces they leave behind in water.
A new study out of Southern California has tested the power, and the limits, of eDNA metabarcoding to detect juvenile white sharks (JWS) and their prey in coastal waters. The verdict? It’s not perfect, but it’s powerful, and it’s already changing how we monitor our oceans.
What is eDNA Metabarcoding?
Fish and other marine animals shed DNA into the environment through skin cells, waste, and mucus. Scientists can now filter water samples, extract this DNA, and sequence it to figure out what species were recently in the area.
This study used a method called metabarcoding, which detects a wide range of species at once using universal primers, and compared it to species-specific qPCR, drone surveys, acoustic tags, beach seines (nets), and BRUVs (underwater video systems with bait).
Why Focus on Juvenile White Sharks?
Southern California is a known nursery for JWS, with seasonal hotspots where dozens may congregate. These juveniles are notoriously difficult to detect, they’re few in number, highly mobile, and blend into the blue. Being able to detect them through water samples alone would be a game-changer for research and beach safety.
Key Findings
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eDNA Metabarcoding Detected the Most Species: It outperformed traditional methods like beach seines and BRUVs in total species richness, even with fewer samples.
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But It Struggled with Sharks: Metabarcoding was only half as effective as qPCR at detecting white shark DNA. In fact, it picked up JWS presence in only 29% of cases where sharks were confirmed to be present.
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Species-Specific Tools Work Better for Rare or Elusive Sharks: The qPCR technique, which targets only white shark DNA, doubled the detection rate compared to metabarcoding and is likely a better fit for rare, low-density elasmobranchs.
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Abundance Matters More Than Size: Fish caught in greater numbers were more likely to show up in eDNA, regardless of their total biomass. This may explain why elasmobranchs, which are big but low in number and have slower metabolisms, are underrepresented in the results.
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Environmental Factors Influence Detection: Turbidity (cloudiness) was linked to missed detections, and some unexpected DNA, like from deep-sea fish, was detected close to shore, possibly carried in by tides or currents.
What This Means for Shark Monitoring
This study reinforces that no single method is foolproof. Drones can miss sharks in murky water. Acoustic tags only work on tagged individuals. Netting can harm the animals we’re trying to protect. And eDNA, while incredibly useful, has detection blind spots, especially for cartilaginous species like sharks and rays.
However, eDNA offers huge advantages: it’s non-invasive, scalable, and capable of detecting dozens of species from a single litre of water.
Implications for Shark Safety and Conservation
From a conservation and safety perspective, this research offers two major takeaways:
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We need multiple monitoring methods working together. For example, combining eDNA with BRUVs captured the most complete picture of coastal fish communities.
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eDNA can improve early detection of white shark aggregations, but only when used with targeted primers or alongside other tools like drones and acoustic tracking.
For products like our Shark Stop wetsuits, which are designed to protect in the rare event of an encounter, better detection tools help identify areas of higher shark presence and can guide proactive safety measures for ocean users.
This isn’t just science for science’s sake. Tools like eDNA are reshaping how we monitor marine biodiversity, design shark-safe swimming zones, and conserve vulnerable species. With further refinement, especially in accounting for different shedding rates and improving primer specificity, eDNA could become an even more powerful ally in shark research.
As always, the more we understand shark behaviour and presence, the better we can coexist safely in their environment.