Barracuda Koh Tao
Fish species that live in the water column away from the reef are known as pelagic fish. Pelagic species have several adaptations for streamlining and speed. These adaptations are particularly useful to species that engage in high speed pursuits and so many pelagic species are apex predators that are found at the top of food webs.

Apex predators play an essential role in controlling populations of other organisms within an ecosystem. Predation from apex predators often prevents any mid-trophic organism (found in the middle of a food web) from dominating an environment and outcompeting other mid trophic organisms that complete for similar resources. In doing so, apex predators are significantly important in allowing co-existence of multiple species that fulfil similar ecological roles, and therefore maintain biodiversity across the reef.
Pelagic fish are often high in value and are therefore heavily targeted by the fishing industry. As pelagic fish spend most of their lives in the open ocean, they are also an easy catch for trawling and long line fishing. As a result, fishing of pelagic fish commonly yields extremely high catches.

Communities living in these areas lack extensive data on population trends of pelagic fish that are commonly targeted. This creates difficulties when deciding on total allowable catches (TACs) for these pelagic fish, used to maintain sustainable fishing practices. If the removal of apex predators and other pelagic species exceeds the recruitment of new individuals to their adult stocks, this will result in a decline in their populations and would have serious consequences on the health and biodiversity of nearby isolated pinnacles.

The Roctopus ecoTrust conduct ongoing monitoring of pelagic fish communities around deep submerged pinnacles. A number of fish included in this programme are essential apex predators as well as commonly fished species. This project aims to identify and monitor populations trends for a number of pelagic species in order to help inform relevant authorities of any declining fish populations.

This project also aims to examine the potential effects that overfishing of apex predators and other important pelagic species may have on reef fish communities living near isolated pinnacle reefsSince the COVID lockdown, the team have now begun to analyse trends that may have emerged as a result of reduced activity (e.g. diving, fishing, tourism etc.) around reefs and isolated pinnacles of Koh Tao. This research may reveal essential information on the potential impacts that different resource users and stakeholders may have on marine ecosystems.

Pelagic Fish Monitoring Koh Tao
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