Action 3 : Fish Biology and catching in the vicinity of FADs

Motivation and objectives

Fishing associated with FADS mainly occurs (over 80 % of landings) for 3 species: blue marlin, yellowfin tuna and blackfin tuna. 79 % of the landings are made up of immature fish. The state of the stocks of blue marlin and of blackfin tuna has been badly assessed, or not been assessed, due to insufficient knowledge about their biology and to the lack of statistical data about the catches and the fishing effort

Because of its abundance, at the adult stage, under the devices, the blackfin tuna seems to constitute a potential resource for moored FADs fishing in the Lesser Antilles (Doray, 2006). They could provide an alternative resource in the event of proven abusive catches of various species. The development of selective fishing methods would be then necessary, because currently only a very small of this species aggregated biomass is tapped into. The blackfin tuna reproduction timings, sizes and zones are hardly known.

The structure of the population of this species at a regional level is possible due to its biological characteristics and behaviour. This is crucial for the evaluation and managment of the species since ignoring the structure of a small population or of a large population can generate important diagnogstic errors which lead to over fishing of a species group.

In response to these facts, the work to be carried out will attempt to provide, for each island and/or for the zone of the Lesser Antilles, new information about the following aspects:

This action will be coupled with the one on statistics that must provide reliable information on the landings of this species and the associated fishing effort, by type of equipment. The emphasis will be placed on the identification of the small tunas species and their biological sampling.
Efficiency and selectivity of the fishing techniques used around FADs: frequency of size per species and specific composition of the catches, according to the gears or their implementation. Particular attention will be paid to possible techniques enabling more blackfin tuna and yellowfin adults to be exploited and fewer blue marlins and juvenile tuna.
Biology of the blackfin tuna: knowledge of their migration, relationship with reproduction or prey season, size of first reproduction, period and location of reproduction and assessing whether there is a structuring pattern of this blackfin tuna population at a regional scale.
Experimentation of selective innovative methods targeting in priority adult blackfin tuna and enabling to reduce FADs catches of juveniles and blue marlin.

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Material and methods

To reach these objectives, observations and a collection of data will be organized over a zone accessible to the pollsters. Its size (or the number of sampling days) will be according to the facilities that can be mobilized.

On all the islands, during the biological samplings which will be done at the landing sites, the blackfin tuna gonads will be taken to be weighed and the gender and the stage of maturity will be noted (see table of reference of the stages of maturity). Gonad samples will be taken on this species for microscopic study. A biopsy (i.e. piece of dorsal edge preserved in alcohol) will be carried out on measured individuals. This biopsy will enable the identification of neutral genetic markers on the mitochondrial DNA and the measurement of variability between individuals and sites, which will in fine make it possible to test if these populations are genetically structured at a regional scale or not.

Two experimentation campaigns on fishing techniques will be carried out in Martinique at 2 different periods of the year. The tested techniques are those that avoid the use of juvenile fish as bait. A specific selectivity will be required, supporting the tuna catches rather than marlin and allowing a development of the adult blackfin tuna resource aggregate under the FAD. Only techniques that can be used on the small boats currently used by the West-Indian fishermen will be tested. These experiments could be undertaken in other islands according to the resources available.

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Implementation

During the investigations at the landing spots and the biological samplings, gonads observations and their sexual maturity will be made on blackfin tunas, weekly (even more often, resources allowing). The gonad sampling will be made on this species and will be preserved for microscopic analysis. Each island will insert and process its data. The pooling of all this information for specific surveys will be made at the time of the meetings with all the partners. The microscopic samples for analysis will be centralized by Martinique. A technical assistance will be brought by Ifremer for the definition of the working protocols (sampling plan, …) data input and processing.

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Participants

Ifremer (Palavas)

Support

Ifremer (Martinique)

Coordinating the collection and processing of data in all the islands.
Collecting the data in Martinique.
Participating in the synthesis work.

Countries of the Caribbean

Collecting the data and processing it.
Participating in the synthesis work.

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Work schedule

Work schedule - Action 3 Global work schedule project

Month 7: during the first meeting, clarification of the protocols the samples collection and monitoring of the stages of maturity.
Month 8 to 21: removal of gonads (blackfin tunas) and pieces of fishbone for genetic study (blackfin tuna)
Between months 8 and 21 : 2 experimental fishing surveys in Martinique

The meetings with the partners of the project will be held :

Month 7 : see the objective above.
Month 18 : presentation of the progress of the work and discussion of initial results.
Month 23 : synthesis of the work and recommendations to be made at the outcome of the project.

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