Natural floating objects (NLOGs) are a major component of the habitat of pelagic species. Since the 1990s, the number of floating objects in the open ocean has increased greatly as a result of the introduction of drifting fish aggregating devices (DFADs) by the industrial tropical tuna purse seine vessels. These changes, and their potential impacts on the species that associate with floating objects, remain poorly understood. If the habitat modifications induced by DFADs have been recently characterized and quantified, the impact of other human activities on the number of floating objects is poorly studied. Relying on lagrangian simulations at the scale of the whole Indian Ocean, from 2000 to 2019, we assess the potential modifications of the pelagic surface habitat that could originate from forest cover change and climate variations. We develop several scenarios, based on coastal and river forest cover, precipitations and river discharge, to simulate densities of NLOGs. Our results suggest no significant increase in average NLOG densities in the ocean and highlight important regional and seasonal variations of these densities driven by both forest cover change and precipitations. These preliminary findings underscore the limited understanding of this critical element of pelagic species habitat. Therefore, there is pressing need to intensify monitoring efforts for pelagic species habitat and raise awareness about potential impacts of habitat modifications on tuna and other pelagic species.

中文翻译：

---

公海中的漂浮物体：揭示森林覆盖变化和气候变化引起的远洋栖息地的变化


天然漂浮物（NLOG）是远洋物种栖息地的主要组成部分。自20世纪90年代以来，由于工业热带金枪鱼围网船引入了漂流鱼聚集装置（DFAD），公海漂浮物的数量大幅增加。这些变化及其对与漂浮物体相关的物种的潜在影响仍然知之甚少。如果最近已经对 DFAD 引起的栖息地改变进行了表征和量化，那么其他人类活动对漂浮物体数量的影响却很少研究。依靠 2000 年至 2019 年整个印度洋规模的拉格朗日模拟，我们评估了森林覆盖变化和气候变化可能引起的中上层栖息地的潜在变化。我们根据沿海和河流森林覆盖、降水和河流流量开发了几种情景来模拟 NLOG 的密度。我们的结果表明，海洋中的平均 NLOG 密度没有显着增加，并强调了由森林覆盖变化和降水驱动的这些密度的重要区域和季节变化。这些初步发现强调了对中上层物种栖息地这一关键要素的了解有限。因此，迫切需要加强对中上层物种栖息地的监测工作，并提高人们对栖息地改变对金枪鱼和其他中上层物种潜在影响的认识。