Determination of Temporal Spawning Patterns and Hatching Time in Response to Temperature of Atlantic Bluefin Tuna (Thunnus thynnus) in the Western Mediterranean

This study analysed the temporal pattern of Atlantic bluefin tuna (ABFT) spawning in the Balearic spawning ground and examined its reproductive performance after years in captivity. Furthermore, ABFT hatching time at different on-site temperatures was determined for the first time. Spawning surveys carried out in 4 spawning seasons (2009-2012) aboard tuna transport vessels. Three groups of spawners were monitored: a captive group transported to the spawning region and monitored throughout the four spawning seasons and two wild groups caught in 2009 and 2010 which were transferred to a monitoring transport cage immediately after being caught. Surface plankton samples were collected nightly, beginning immediately after the first purse seine catches were made and concluding after spawning was observe have ended. All groups displayed the same spawning hours, restricted between 2:00-5:00 a.m. The captive group, as they got older, shifted towards the earliest hour, suggesting an age influence on reproductive time. The onset of spawning varied annually from the end of May to the at temperatures around 19 degrees C-20 degrees C ending by weak of July. The peak of spawning was consistently around the um er solstice, June negative effect of unstable oceanographic conditions in the spawning process which productive success of ABFT. The influence of temperature on hatching time was higher species, twice as fast at 26 degrees C (23 h) as at 19.5 degrees C (49 h) Overall his study shows the strength of ABFT that controls spawning traits. Spawning in ABFT is cyclical and highly synchronised on diel and annual scales consider that h timing of spawning rather influenced by day length and its adaptive significance is discussed.