New technologies in Saint Martin to protect fish
As part of Life BIODIV’OM, the National Natural Reserve of Saint-Martin, in partnership with the French company Ecocéan, has deployed innovative methods on their territory allowing to obtain more knowledge on Nassau grouper and the Atlantic goliath grouper. Follow the guide, here we explain everything to you.
The life cycle of reef fish
This cycle begins with a phase from a few days to several months in the open ocean in the form of a transparent larva (oceanic planktonic phase) which will end with an adult phase to coral reefs. Between these two phases, reef colonization takes place during which the post-larvae present in the ocean undergo a significant morphological transformation and then return to the coasts.
This colonization phase takes place mainly around the new moon or black moon, the post-larvae taking advantage of the absence of light to avoid predation. The post-larva of fish is therefore the last larval stage of their ocean life cycle. In the vast majority of cases (more than 95%) these post-larvae disappear by natural predation or failing to reach an adequate habitat after 10 days.
PCC (Post-Larval Capture and Culture) is an innovative technique for sampling at sea and rearing artificial post-larvae in an artificial environment. The PCC consists in taking post-larvae present in the ocean before they undergo this high mortality and to raise them until more advanced stages in order to release them and to reinforce the populations of fish in the natural environment. This method also makes it possible to know the identity of the species and the period at which they settle in coastal waters.
Concretely, there are two main techniques for capturing the post-larvae of fish: the nets arranged on the reef crest which filter the water masses arriving on the reef and which thus trap the post-larvae and the luminous floating attractors, called CARE, which use the phototrophic nature of the majority of post-larvae to facilitate collection. The choice of method depends on the location and the objective of the project, the cost and its ease of use. In Saint-Martin, the Light trap method is currently used to capture post-larvae.
These collectors are installed at sunset during new moons or black moons over areas 15 to 30 meters deep, then will be raised at sunrise after a full night of fishing. The devices are moored to a ballast and provided with air chambers to ensure flotation, the post-larvae evolving on the surface. The next day, the larvae are collected in a PVC collector.
Once on the ground and after careful sorting, the post-larvae are placed in a breeding aquarium on a farm or in the laboratory. During this stage, the post-larvae are sorted and reared in experimental tanks until the juvenile or adult stage.
BioHut are artificial nurseries: small, highly complex habitats installed to allow young larval stages to hide from predators and grow safely.
These BioHut limit predation by allowing juveniles or post-larvae to hide inside this system composed of barriers blocking passage to large predators. Another benefit of this system is the supply of food within the habitat itself, becoming the support where a diverse fauna and flora develops (grids, empty oyster shells, cords made of coconut fibers, etc.).
Easy to set up (40 BioHut per day) and composed of wood, steel and mollusc shells, these BioHut can be installed on port infrastructures or marinas to restore the ecological function of nursery lost by planarization of the substrate. In Saint-Martin, these artificial nurseries are installed on structures such as artificial habitats, moorings, a pontoon and in the mangrove.
Ultimately, these biodiversity huts may contain more than 150 species of flora and fauna. These innovative devices will make it possible to monitor the arrivals of groupers and other fish species, which have apparently escaped the CARE (light collectors).
Ecocean is a French company (Montpellier) which acts and innovates in favor of aquatic biodiversity. Founded in 2003, the company has developed the collection and breeding of post-larvae (PCC) for the sustainable development of marine resources and the conservation of biodiversity in marine ecosystems. Now a world leader in PCC technique, Ecocean is associated with the LIFE BIODIV’OM program as a partner of the National Natural Reserve of Saint Martin.
Trained by the Ecocéan company in October 2019, the agents of the National Natural Reserve of Saint-Martin have thus deployed the CCP method by light traps and set up BioHut on the island. As part of LIFE BIODIVOM, the Reserve has implemented these protocols in order to study the arrival flows of post-larvae on the shallow coastal bottoms, in particular two species of grouper: the Nassau grouper and the giant grouper , both threatened globally. These innovative techniques will make it possible to acquire new knowledge on post-larvae of groupers, such as the period of colonization and the species concerned.
AGRNSM, as part of LIFE BIODIV’OM, will also be involved in the transfer of know-how related to PCC and BIOHUT, to their local counterparts and more particularly the staff of the Territorial Environment Agency (ATE) from Saint-Barthélemy.
For more information : Ecocean website
Two endangered grouper species
The Nassau Grouper and the Atlanctic goliath grouper are two globally threatened species. On the island of Saint Martin, the Nassau grouper is observed but its population has dropped considerably worldwide. The presence of the Atlantic goliath grouper is now anecdotal in the West Indies. The stocks of the species have collapsed and the species, originally present on the West and East coast of the Atlantic Ocean, is only present in the West zone.
In addition to the lack of regulation, other threats such as human activities contribute to the reduction of their populations such as the destruction of essential grouper habitats by coastal developments, discharges of wastewater, clearing of the coastline and over- frequentation of reef areas. In addition, coral reefs, habitat frequented by the Atlantic goliath grouper and the Nassau grouper, suffer particularly from the consequences of global changes, inducing a reduction in coral cover and episodes of coral bleaching.