The great hammerhead (Sphyrna mokarran) is Critically Endangered and difficult to study. Every encounter with a free-swimming animal is valuable, yet tags and tissue samples are normally obtained in separate procedures. A new study in Marine Biology presents a probe that can perform both tasks in a single deployment.
The research team designed the probe for a modified underwater spear. On contact it attaches a tag to the shark and removes a small tissue sample. The approach is intended to obtain as much information as possible without capturing the animal or pursuing it through several procedures. That shorter interaction can be crucial for rare and sensitive species.
Three field campaigns at Rangiroa and Tikehau
The system was tested on great hammerheads at Rangiroa and Tikehau atolls in French Polynesia. Three campaigns ran from February to March 2023, December 2023 to March 2024, and December 2024 to March 2025. The design was progressively adjusted and improved.
Researchers documented twelve deployments. With the final version, tag attachment succeeded in 83 percent of attempts and biopsy collection in 67 percent. Eight biopsies were obtained across all campaigns; four contained enough muscle tissue, in addition to skin and subcutaneous tissue, for further analyses.
One small sample can answer several questions
Skin and underlying tissue can be used for genetic studies, providing clues about population structure and relatedness. Muscle tissue additionally supports stable-isotope and fatty-acid analyses, which help reveal food sources and the ecological role of sharks.
The four adequate muscle samples weighed an average of 0.11 grams, with a standard error of 0.06 grams. Although small, the study reports that this is sufficient for both stable-isotope and fatty-acid analyses. Combined with movement data from the tag, it creates a much fuller picture of the same animal.
Camera and lasers complement the probe
The probe can be combined with a camera and a laser plate. The camera records the deployment and distinctive features for individual recognition. Laser points provide a scale in the image, allowing body size to be estimated. Tagging, biopsy, photo-identification and size measurement can therefore be brought together in one encounter.
The value lies not only in a new technical design. The probe connects information about movement, diet, genetics, size and individual features. Such combined datasets can show which habitats animals use, how populations are connected and which protected areas matter at different life stages.
Shark research without capture continues to advance
The work is part of a wider change in shark research: attaching a tag does not always require capture and restraint. Another example is the Canadian project described in Canada tags great white sharks by satellite without capture. The new hammerhead probe extends that approach by collecting a biopsy at the same time.
The methods are not identical, but they share the same aim: obtain robust data while keeping the intervention as brief as possible. This is particularly important for great hammerheads, which are sensitive to capture stress and encountered only rarely.
A tool for protecting rare marine giants
The authors see potential uses not only for hammerhead sharks, but also for other sharks, rays and hard-to-access marine megafauna. Adaptation to body shape, skin and behaviour will be required for each species, but the trials show that several important samples and measurements can be collected in one contact.
For conservation, the key question is whether the data improve decisions. Migration routes, residence areas, diet and population structure determine where protective measures need to work. A method that supplies this information with less intervention can make research on rare species more efficient and less intrusive.