Movements, behavior, and habitat selection of bigeye tuna (Thunnus obesus) in the eastern equatorial Pacific, ascertained through archival tags

Ninety-six bigeye tuna (88– 134 cm fork length) were caught and released with implanted archival (electronic data storage) tags near fish-aggregating devices (FADs) in the equatorial eastern Pacific Ocean (EPO) during April 2000. Twenty-nine fish were recaptured, and the data from twenty-seven tags were successfully downloaded and processed. Time at liberty ranged from 8 to 446 days, and data for 23 fish at liberty for 30 days or more are presented. The accuracy in geolocation estimates, derived from the light level data, is about 2 degrees in latitude and 0.5 degrees in longitude in this region. The movement paths derived from the filtered geolocation estimates indicated that none of the fish traveled west of 110°W during the period between release and recapture. The null hypothesis that the movement path is random was rejected in 17 of the 22 statistical tests of the observed movement paths. The estimated mean velocity was 117 km/d. The fish exhibited occasional deep-diving behavior, and some dives exceeded 1000 m where temperatures were less than 3°C. Evaluations of timed depth records, resulted in the discrimination of three distinct behaviors: 54.3% of all days were classified as unassociated (with a floating object) type-1 behavior, 27.7% as unassociated type-2 behavior, and 18.7% as behavior associated with a floating object. The mean residence time at floating objects was 3.1 d. Data sets separated into day and night were used to evaluate diel differences in behavior and habitat selection. When the fish were exhibiting unassociated type-1 behavior (diel vertical migrations), they were mostly at depths of less than 50 m (within the mixed layer) throughout the night, and during the day between 200 and 300 m and 13° and 14°C. They shifted their average depths in conjunction with dawn and dusk events, presumably tracking the deep-scattering layer as a foraging strategy. There were also observed changes in the average nighttime depth distributions of the fish in relation to moon phase.

Morphometric studies in Penaeus merguiensis from Ratnagiri waters for selection of the brood stock in genetic improvement programmes

Studies on genetic improvement of penaeid prawns for the character higher tail weight using methods of selective breeding were undertaken. Prior to the actual breeding experiments it was necessary to find out the quantum of available variability in the character tail weight amongst the natural populations of Penaeus merguiensis from the Indian waters. Thirteen morphometric variables were measured and various statistical analyses were carried out. The tail weight showed almost double values of coefficient of variation in the females than the males (C.V. 20.37 and 11.08 respectively). The combination of the characters viz. sixth segment length (SSL), sixth segment depth (SSD) and posterior abdominal circumference (PAC) gave the highest R super(2) values. These variables were easy to measure and gave maximum variation in the character tail weight without sacrificing the breeders in the brood stock. The quantitative character tail weight was influenced by both genetic and environmental factors was statistically ascertained by applying 2-Factor analysis.