Over the past week we have been conducting daily surveys and tagging trips to quantify shark species composition, abundance, and distribution around Clipperton atoll.
We have been using stereo baited remote video stations (BRUVs), where a small amount of bait inside a PVC canister is used to attract sharks and other predatory fishes towards the cameras. Because the video cameras are filming in 3-D, we can use special software to measure each animal’s total length. Marine biologists use total length to estimate maturity stages and the total biomass of fish in the area.
Our preliminary results reveal that Clipperton atoll is a kindergarten for baby sharks! Juvenile and even newborn Galapagos (Carcharhinus galapagensis) and silvertip (C. albimarginatus) sharks are the reef masters around Clipperton coral reefs. On the two-hour camera drops, we have recorded up to 15 individual sharks in an individual video frame and many sharks have given their best pose for the cameras!
In addition to video surveys, we have conducted night fishing trips to catch and tag baby sharks with individually coded radio transmitters. My colleague, Dr. Mauricio Hoyos, has three acoustic receivers located around Clipperton atoll and every time a tagged shark swims past one of these receivers, its presence is recorded.
With this information scientists can determine species-specific habitat use patterns and regional migratory routes. Mauricio is not alone on this quest: a network of scientists involved in the Eastern Tropical Pacific Marine Corridor initiative have additional receivers in Mexico, Panama, Costa Rica, Colombia, and Ecuador. We now know sharks are not ruled by human boundaries and they frequently take long migrations across this region.
For example, few years back in Clipperton Mauricio detected silky shark #55955 (C. falciformes), an individual tagged in the Galápagos Islands, which are located over 1200 miles (2000 km) away! A few months later, this same shark somehow completed a ‘miraculous’ return trip back to the Galápagos Marine Reserve, where sharks are totally protected from fishing.
I say ‘miraculous’ because during this 2500-mile (4000-km) odyssey, sharks need to swim past a curtain of millions of fishing hooks placed by industrial fishing vessels to catch sharks for their fins. Fins are highly valued in Chinese markets as they are used to make shark fin soup, a delicacy in Chinese cuisine. The global hunt for shark fins has resulted in an estimated 90-percent global loss of sharks and large predatory fishes, with more than 100 million sharks killed annually.
While Clipperton is teaming with juvenile sharks, we have hardly encountered any adults in our camera surveys, submersible dives, or tagging trips. In contrast to the Galápagos islands, sharks are not protected here, and discarded fishing lines are a common discovery around Clipperton reefs. Most sharks are likely not as lucky as silky #55955 and never make it past this curtain of hooks after giving birth around the Clipperton kindergarten.
Fortunately, there is still hope for Clipperton sharks: in other areas of the world when fishing is banned, sharks and other fish species quickly bounce back to rule over reefs again.