IMIS - Marine Onderzoeksgroepen

The international program BETYP on the bigeye tuna (Thunnus obesus) allowed us to board the Japanese research vessel Shoyo Maru. During this mission, the longline vessel was rigged to carry out four crossings of the Atlantic Ocean. The mission conducted from September 28 to October 26, 2000 corresponds to the first that crosses the Atlantic from west to east. The first operation of project THETIS (UR No. 109 of the IRD) is focused on the study of predator-prey relationships. The program will study the food and trophic relationships of tunas and associated species in four regions of the Indian Ocean and three of the Atlantic. The platform of the Shoyo Maru in the Atlantic was a good opportunity to collect stomach contents of fish caught by longline. Mission Objectives:

• Recovery of water samples at different depths to measure concentrations of nitrite.
• Recovery of stomachs of tunas caught by longline and species associated.
• Study of potential prey for tuna trawling by day and night in the diffusing layer or deep scattering layer (DSL). Particular attention was paid to Vinciguerria nimbaria. The PICOLO program has highlighted the important role of this prey species for tunas in the equatorial Atlantic.
• Collection of otoliths of bigeye tuna (Thunnus obesus) and yellowfin (Thunnus albacares) caught during fishing operations.
• For this mission, tissue samples for the study of genetic populations of some species have been collected.
• Observations of cetaceans and seabirds were also conducted.

An additional sea turtle, Caretta caretta was captured on a longline set for tuna, but the exact time and coordinates of that observation were not available. Records that had an estimated count of "plusieurs" were given a conservative count of "2". When an estimated range of animals was sighted, the median value (rounded down) was used as the observed count; when a minimum number of animals was recorded, the minimum number was used as the observed count (i.e., >100 = 100 animals). This dataset on OBIS Seamap only contains observation data of sea mammals, seabirds and sea turtles.