In the Bay of Biscay
PELGAS which means monitoring of small PELagic fish in the Bay of Biscay is an Ifremer programme.
It is designed to find out about the constitution of stocks of exploited fish as well as the functioning of their ecosystem in the French Atlantic zone.
Within the framework of MEGASCOPE, the PELAGIS observatory collects data each year by placing experienced observers on these programmes. This enables us to obtain more information on the use of these areas by top predators (cetaceans and seabirds) as well as their place in the pelagic ecosystems. The advantage of these study platforms is that they are intended for the collection of scientific data, and once these have been gathered, a coherent picture of the environment in question is obtained .
The MEGASCOPE methodology is based on 2 active observers on the deck, recording a certain number of parameters in the sampling area covered by the vessel.
Firstly, they note the observation conditions, i.e. whether or not they are beneficial for the detection of cetaceans.
Then, they will note all the observations made, which requires identifying and counting the megafauna present (cetaceans, seabirds, turtles, large pelagic fish…) and also any object encountered (waste, ship…).
Illustration: Mapping of cetacean sightings in the Bay of Biscay during the PELGAS 2016 campaign.
With several years of monitoring and sufficient data collected, densities can be calculated and modelled in space (example for some flagship species of this campaign).
These campaigns are primarily aimed at quantifying fish stocks. This is reflected in the scientific fishing activity on these stocks and the search for their larvae and eggs. Acoustic prospecting is also a decisive tool in trying to locate areas with or without concentrations of pelagic fish. In addition to this, other activities such as studies of water masses and small marine organisms used as prey by fish are also carried out.
These studies target key links in the oceanic food chain where top predators are located. The results obtained make it possible to compare the distribution of cetaceans with that of pelagic fish in order to learn more about the relationships between these predators and their potential prey.
These missions are of major importance for understanding this marine environment. They constitute the first series of data on the distribution and composition of the population of marine top predators for spring in the Bay of Biscay. In addition to this, other campaigns of this type have been carried out, such as EVHOE in the autumn or IBTS or CGFS in the Channel.
Today, these results are the source of long term monitoring which allow us to have clear answers to characterise preferential habitats, notably for some indicator species such as the common dolphin or the Northern Gannet.