Rays

Range and fishery interactions

• Giant mantas have a broad range, roaming across the Pacific from near-equatorial waters out to subtropical regions. They often frequent productive zones (like upwellings or convergence fronts) where plankton and small forage fish are abundant. In the WCPO, mantas might be encountered by purse seine vessels particularly in areas where they come to the surface to feed. However, given their strong swimming ability and size, they can often evade nets; this makes actual captures infrequent relative to smaller rays.
• Longline interactions with mantas are rare but can occur if a manta becomes snagged or entangled in the fishing line or branchlines. Mantas do not typically bite baited hooks (since they feed on tiny plankton), but a feeding manta could accidentally swim into a line. Most documented fishery interactions with giant mantas in the WCPO have been in purse seine nets or occasionally in coastal gillnet fisheries (the latter being outside WCPFC’s high-seas jurisdiction but contributing to overall mortality).
• Even low levels of bycatch are a concern for mantas. A single death can have outsized effects on the population because each female produces so few offspring over her lifespan. This is why WCPFC management emphasizes preventing mortality entirely – the goal is that any manta that enters a net or is incidentally caught will be released alive and unharmed.

Effective bycatch mitigation for fleets

• Avoid encirclement if possible: Purse seine captains should be vigilant for the presence of mantas when setting a net. If a large dark shape (a manta) is seen in the area, some captains choose to delay or adjust the set to avoid capturing it. This proactive avoidance is the first and best step to mitigate manta bycatch.
• Prepare release equipment in advance: Vessels operating in manta-prone waters often carry a robust sling or stretcher specifically for handling big rays. By having this gear ready, crew can quickly deploy it when a manta is in the net – gently corral the manta into the sling underwater, then lift and release it over the side without ever pulling it onboard. Ensuring the manta stays in water (or is out of water for only a minimal few seconds) greatly increases survival chances.
• Never use sharp implements or excessive force: Crew must not gaff a manta or use hooks/ropes through its body to lift it. Instead, they should use handlines under the manta’s body or the aforementioned net sling. If the manta is tangled, carefully cut away the netting. The manta’s skin and gills are easily damaged, so all actions should be slow and deliberate, prioritizing the animal’s wellbeing over fishing operations.

Monitoring priorities

• Enhanced reporting of sightings and interactions: Given the relative rarity of encounters, WCPFC scientists have requested that even non-capture sightings of mantas by crews be reported when possible (e.g., if a vessel sees mantas aggregating, note the location). This can help map important habitats and times of year for giant mantas in the WCPO.
• Post-release survival tagging: To gauge how well mantas survive after release, researchers are exploring the use of satellite tags that can attach to a manta’s body temporarily after it’s freed. Data from these tags (e.g., dive behavior, travel paths) can indicate whether the manta resumes normal activity. A healthy post-release trajectory suggests current handling methods are effective, whereas a tag that reports a mortality would signal the need for improved practices.
• Coordination with tourism and coastal management: Many Pacific Island nations value mantas as a tourism resource (e.g., well-known manta viewing sites in Palau, Fiji, etc.). WCPFC can collaborate with such local efforts by sharing data on manta movements or threats. If a particular sub-population is identified (say, mantas that breed in one country’s waters but feed in another’s offshore areas), international cooperation will be needed to fully protect that group.

Distribution and interactions

• Spinetail devil rays are found throughout tropical and warm-temperate oceans. In the WCPO, they are encountered from the equatorial zone up to subtropics (e.g., as far north as the waters off Japan in warm seasons). They seem to favor open-water environments where they forage near the surface. Purse seine fisheries in the equatorial Pacific (10°N–10°S band) report most of the spinetail ray bycatch, often during sets on tuna schools associated with FADs. The structure and cover provided by FADs may attract small baitfish and plankton, indirectly drawing in rays.
• Interaction rates in purse seine gear are generally low (on the order of a few rays per hundred sets), but because the tuna fishery effort is very large, those small numbers accumulate. Prior to the 2010s, many of these rays might have been misidentified or not recorded; improved observer training has increased reporting of Mobula japanica specifically. Longline fisheries occasionally snag spinetail rays, typically when a ray becomes entangled rather than hooked. Such events have been recorded, but are uncommon compared to purse seine captures.
• When captured in a purse seine, spinetail rays face risks of injury from net pressure or being hit by other fish. If they are hauled onboard in the brailer along with fish, the ray can be badly hurt or suffocate. That’s why current guidelines stress removing rays separately from the main catch. Data from other oceans (e.g., Eastern Pacific) suggest that following best practices can drastically improve survival – fleets that adopted gentle handling have much higher live-release rates for mobulids.

Effective actions for fleets

• Have a release plan for every set: Crew should be assigned roles in case a ray is in the net. For example, one team readies the “ray release” net or canvas sling while others carefully gather the ray. By planning ahead (as part of the pre-set toolbox talk), the vessel can respond faster and more calmly when a ray is encountered.
• Minimize air exposure and handling time: If a spinetail ray is entangled, stop the net haul as soon as it is safe to do so. Gently disentangle the ray underwater if possible. If the ray must be brought on deck, immediately cover it with a wet cloth (to keep it moist and calm) and carry it to the railing for release. Ideally, two or three crew members can do this swiftly for a medium-sized ray. The entire process from capture to release should be under a few minutes.
• Document the condition on release: Whether an observer is onboard or not, crew should note if the ray swam away strongly or was released in a weakened state. This information (often recorded by observers) is important to evaluate the effectiveness of handling. Over time, patterns like “rays caught by certain vessel practices have higher mortality” can be identified and addressed through improved techniques or gear changes.

Data and monitoring needs

• Species identification and training: Continual emphasis in observer programs on distinguishing Mobula japanica from other rays is needed. Misidentification can lead to underestimating how many spinetail rays are affected. Providing observers with clear ID photos (e.g. spinetail rays often have a distinctive spine at the end of the tail and specific dorsal spot patterns) and possibly genetic ID tools for ambiguous cases will improve data quality.
• Post-release survival studies: Building on initial studies, WCPFC supports efforts to tag released spinetail devil rays with pop-up satellite tags to monitor their fate. A key question is what fraction of “released alive” rays survive long-term. Early research indicates that some do not survive beyond 1–2 days due to internal injuries. Identifying the causes (such as pressure trauma or rough handling) can guide better practices or technological fixes (like gentler net retrieval methods).
• Hotspot analysis: As more data accumulate, scientists plan to analyze whether there are spatial or temporal hotspots for spinetail ray bycatch (for example, a particular area of the WCPO where ray encounters peak, or certain months when rays congregate). If such patterns emerge, management could consider advisories or even time-area closures to avoid high-risk interactions during those periods.

Habitat and fishery interactions

• Sicklefin devil rays are true denizens of the open ocean. They have been recorded around remote islands and seamounts (for example, tagging studies elsewhere have shown them associating with underwater features), but they also undertake long migratory journeys. In the WCPO, their distribution likely overlaps with tuna fishing grounds broadly, but their low encounter rate suggests they are not very abundant or frequently at the surface. When they do come near the surface to feed, they could be inadvertently encircled in a purse seine set targeting tuna or associated species.
• Purse seine interactions are the primary concern, as few (if any) sicklefin devil rays have been reported caught on longlines in this region. Their diet of deepwater fish and plankton means they seldom go after baited hooks. Nevertheless, if a ray does get hooked or entangled on a longline, it often results from the ray’s body snagging a line rather than taking the bait. Such cases are extremely infrequent. Most WCPO records of this species come from purse seine observer reports, and even those are sporadic.
• Given the low number of observations, each interaction is valuable data. WCPFC scientists treat any reported sicklefin ray capture as an important event to study. For example, details like the ray’s size, condition (released alive or dead), and the set circumstances (FAD vs free school, time of day) are analyzed to glean insights. So far, no clear pattern has emerged (no “hotspot” for sicklefin bycatch is known), which suggests that avoiding these rare events is challenging beyond the general mitigation already in place.

Recommended handling

• Use heavy-duty release gear: Because an adult sicklefin ray can weigh several hundred kilograms, a purse seine crew should never attempt to lift it by hand. The recommended approach is to maneuver the ray into a large mesh cargo net or a robust canvas sling while it’s still in the water. Using the vessel’s crane or power block (with the net attached) to slowly raise the ray out of the net and lower it over the side is the safest for both the ray and the crew.
• Keep the ray horizontal and supported: A sicklefin ray’s body needs full support when lifted. Crew should ensure the ray’s pectoral fins (wings) are spread naturally and not bent sharply. If using a sling, center the ray’s body on it so that the head and tail aren’t drooping. The ray should be released by submerging the sling at the surface, letting it swim out on its own if possible.
• Be prepared to cut the net: In some cases, if a ray is extremely large or thrashing in a way that complicates handling, the captain may decide to sacrifice a portion of the net to free the animal (by lowering a section of corkline or cutting the net webbing around the ray). While losing some netting is costly, WCPFC members recognize that saving a critically endangered ray is more important, and the measure expects crews to prioritize the ray’s safe release over gear retention.

Data gaps and research

• Population connectivity: It’s unknown whether the sicklefin devil rays observed in the WCPO are part of a larger Pacific-wide population that also traverses the Eastern Pacific or Indian Ocean. Collecting tissue samples from any individuals encountered (for genetic analysis) could help determine if there are distinct sub-populations. Such information is crucial for assessing the species’ status; a small isolated population would be at greater risk than a large interconnected one.
• Deep habitat use: Researchers are interested in how often and why this species comes shallow (into fishing gear range). Using satellite tags that record depth could reveal the daily habits of sicklefin rays – for instance, do they spend daylight hours at 500 m and only surface at night? If so, certain fishing practices (like setting at particular times) might pose less risk. Understanding their ecology better could lead to refined mitigation (e.g., avoid setting nets at dusk if that’s when rays are near-surface).
• Inter-regional cooperation: The rarity of WCPO sightings means that data from other regions (like Indian or Eastern Pacific Oceans) is valuable to fill the knowledge gap. WCPFC’s Scientific Committee works with other tuna RFMOs to share mobulid bycatch information. If a pattern or effective mitigation is discovered elsewhere for sicklefin rays, the WCPO can adopt similar strategies proactively.

Fishery profile

• Bentfin rays occupy both offshore waters and areas not far from land (especially around productive reefs or shelves where plankton gather). In the Pacific, this means a bentfin ray might be encountered by a range of fisheries, from purse seiners in the high seas to artisanal nets in coastal zones. Within WCPFC’s purview (mainly the purse seine and longline fisheries), bentfin bycatch is relatively uncommon. When it does occur, it’s most likely in purse seine sets in tropical waters. For example, observers have noted occasional captures in the western equatorial Pacific purse seine fishery, perhaps when these rays are aggregating to feed.
• Because bentfin rays are smaller, they could sometimes escape nets by finding gaps or being pushed out with the water flow during net hauling. Those that do get caught in purse seines typically come up with the brail. If unnoticed, they could end up on deck mixed with tuna. This underscores the importance of diligent observation by crew and observers during brailing – spotting a ray in the catch at an early stage allows for quick intervention.
• Longline interactions with bentfin devil rays are extremely rare. As filter feeders, bentfins are unlikely to bite a baited hook. There’s a slim chance one might entangle with a line near the surface, but few if any such cases have been documented. Therefore, mitigation in longline fisheries is more about general best practices (e.g., cutting loose any ray seen tangled on the line) rather than species-specific rules.

Handling best practices

• Swift, gentle release: For a bentfin ray brought aboard in a brail, the crew should act immediately. Using a wet tarp or cloth to cover the ray can calm it if it’s thrashing. Then, two crew members (one holding each wing near the base) can lift the ray and slide it back into the sea, making sure it goes in head-first. This entire process should be done as smoothly as possible to avoid dropping the ray or causing it to hit the side of the vessel.
• Check for entanglement: Often, a ray might come aboard with some netting still wrapped on it. Crew must carefully cut away any mesh or line from the ray’s body before release. Common spots to check are around the wings and tail. Removing all entangling material ensures the ray isn’t hindered or wounded after it swims away.
• Crew safety and ray safety: While bentfin rays are not aggressive, they do have a tail spine that can inflict a wound (similar to a stingray’s barb) if mishandled. Crew should avoid the tail region during handling or use gloves and tools to control it if necessary. By handling the ray by its sides and keeping clear of the tail, they protect themselves and also avoid injuring the ray’s sensitive tail.

Monitoring and research

• Increasing data resolution: One challenge is ensuring that bentfin rays aren’t simply recorded as “unidentified mobula.” The more observers can confidently distinguish M. thurstoni, the better researchers can assess its bycatch frequency. Development of better identification keys (e.g., noting the distinct coloration or fin shapes of bentfins) is underway to assist observers in the field.
• Community and fisher science: In areas where scientific observer coverage is low, WCPFC is considering ways to leverage fishers’ knowledge. For instance, encouraging fishers to report sightings of ray schools or unusual bycatch through logbooks or apps can supplement formal data. Over time, this might highlight previously unknown areas where bentfin rays congregate, allowing for proactive management.
• Life history studies: More research is needed on bentfin devil ray reproductive biology and lifespan, much of which comes from studies outside the WCPO. WCPFC can support collaborations with academic scientists to study any specimens (e.g., if a dead specimen is collected, it could be examined for age, maturity, etc.). Understanding these parameters better will improve risk assessments for bentfin rays and ensure that WCPFC measures continue to align with the species’ conservation needs.