Recent Submissions

  • Spatial and temporal distribution of reef fish spawning aggregations in the Seychelles – an interview-based survey of artisanal fishers

    Öhman, M.C.; Isidore, M.; Payet, R.J.; Robinson, J.; Marguerite, M.A. (WIOMSA, 2004)
    Many coral reef fish species aggregate at specific times and locations for the purpose of spawning. This study examined the spatial and temporal distribution of spawning aggregations in the Seychelles. An interview-based survey of the principal stakeholders, mainly artisanal fishers, yielded 89 reports of aggregation fishing for 26 demersal and semi-pelagic fish species. Grouper aggregations were largely concentrated in the outer coralline islands of the exclusive economic zone, whilst those of snappers and rabbitfishes were mainly reported from locations on the Seychelles Bank. The spatial patterns among fish families were attributed to a combination of differences in species abundance and distribution as well as variation in fishing effort. Spawning periodicity reported by fishers indicated that for snappers and rabbitfishes, the most activity occurred across a protracted period of October to April/May, with peaks in activity at either end of that period. Grouper spawning activity was concentrated in the northeast monsoon months of November to January. The findings of this study suggest that several spawning aggregations are targeted by fishers on a regular basis, a practice that constitutes a primary issue for artisanal fisheries research and management in the Seychelles.
  • Feeding partitioning among tuna taken in surface and mid-water layers: the case of yellowfin (Thunnus albacares) and bigeye (T. obesus) in the Western Tropical Indian Ocean

    Sabatié, R.; Marsac, F.; Hallier, J.P.; Potier, M.; Lucas, V.; Ménard, F. (WIOMSA, 2004)
    The trophic relations of two apex predators, yellowfin and bigeye tuna (Thunnus albacares and T. obesus), and their prey were investigated in the western tropical Indian Ocean. The contents of 173 non-empty stomachs were analysed from specimens caught with longlines and purse seine during scientific and fishing cruises. Diet data were processed by occurrence, by number, and by wet weight and a comparison of diets between surface and deep swimmers made. Crustaceans were the almost exclusive food source of surface-swimming bigeye tuna, with the stomatopod (Natosquilla investigatoris) being the sole prey item recorded in this category. The diet of deep-swimming yellowfin tuna was balanced between epipelagic fish, crustaceans and cephalopods. Bigeye tuna fed predominantly on cephalopods and mesopelagic fish (Scopelarchidae and Paralepididae), for which this predator appeared to be the most active chaser. The diet of the two predators reflects their ability to catch the prey, and their vertical distribution.