Multispecies aggregations at floating objects are a common feature throughout the world's tropical and subtropical oceans. The evolutionary benefits driving this associative behaviour of pelagic fish remains unclear and information on the associative behaviour of non-tuna species remains scarce. This study investigated the associative behaviour of oceanic triggerfish (Canthidermis maculata) and rainbow runner (Elagatis bipinnulata), two major bycatch species in the tropical tuna purse seine fishery, at floating objects in the western Indian Ocean. A total of 24 rainbow runner and 46 oceanic triggerfish were tagged with acoustic transmitters at nine drifting FADs equipped with satellite linked receivers. Both species remained associated with the same floating object for extended periods; Kaplan-Meier survival estimates (considering the censored residence time due to equipment failure and fishing) suggested that mean residence time by rainbow runner and oceanic triggerfish was of 94 and 65 days, respectively. During daytime, the two species increased their home range as they typically performed short excursions (<2 h) away from the floating objects. Rainbow runner performed more excursions per unit time than oceanic triggerfish; the mean excursion index was 0.86 (±0.8 SD) for oceanic triggerfish and 1.31 (±1.1 SD) for rainbow runner. Ambient light intensity appears to be the stimulus triggering the onset and end of the associative modes. The observed prolonged residency of these two major bycatch species suggests that they are more vulnerable to the tropical tuna purse seine gear than the targeted tuna species.

漂浮物体上的多物种聚集是全世界热带和亚热带海洋的共同特征。推动远洋鱼类这种结合行为的进化优势仍然不清楚，关于非金枪鱼物种的结合行为的信息仍然很少。本研究调查了海洋触发鱼（Canthidermis maculata）和彩虹runner（Elagatis bipinnulata）的关联行为。）是印度洋西部漂浮金枪鱼围网渔业中的两种主要兼捕种类。在配备卫星链接接收器的9个漂移FAD上，总共用声音发射器标记了24个彩虹转轮和46个海洋引金鱼。两种物种长时间都与同一个漂浮物相关联。Kaplan-Meier生存估计（考虑到由于设备故障和捕鱼导致的审查滞留时间）表明，彩虹赛跑者和海洋引金鱼的平均滞留时间分别为94天和65天。在白天，这两个物种的居所范围扩大了，因为它们通常会在短时间内（<2小时）远离漂浮物。彩虹赛跑者每单位时间的游览次数要比海洋引金鱼多。平均偏移指数为0.86（±0。对于海洋引金鱼来说是8 SD），对于彩虹转轮来说是1.31（±1.1 SD）。环境光强度似乎是触发关联模式开始和结束的刺激。观察到的这两种主要兼捕种类的长期居住表明，与目标金枪鱼种类相比，它们更容易受到热带金枪鱼围网渔具的攻击。