Decadal acoustic monitoring of toothed whales in the Gulf of Mexico post-oil spill

Shortly after the Deepwater Horizon oil spill began in April 2010, a widely spaced passive acoustic monitoring array was deployed in the northeastern Gulf of Mexico to document the impacts of this unprecedentedly large and deep offshore oil spill on oceanic marine mammals. The array was subsequently maintained for over a decade. Here we document decadal density declines for seven of eight monitored species groups, including sperm whales (up to 31%), beaked whales (up to 83%), and small delphinids (up to 43%). Declines were observed both within and outside of the surface oil footprint. Though not conclusively linked to the oil spill, the broad spatial and temporal scale of these declines observed for disparate marine mammal species is consistent with Deepwater Horizon impacts. These declines have exceeded and outlasted post-spill damage assessment predictions, suggesting that the offshore ecosystem impacts of Deepwater Horizon may have been larger than previously thought.

Methods

Passive acoustic recordings were collected using High-frequency Acoustic Recording Packages (HARPs) at five monitoring stations between May 2010 and March 2020 (Table S1). The total recording duration across the five sites amounted to 37 instrument-years of continuous data sampled at 200 kHz. Sites include three deep sites and two shallow shelf sites that monitor primarily shallow water species.

Echolocation clicks and other impulsive signals from odontocete species were detected using an impulse detector and then classified into species groups based on spectral characteristics and inter-click intervals. Automated detection and semi-supervised clustering techniques identified signals from target species, allowing for group-based density estimation of each species across time. Processing steps included high-pass filtering, calibration of hydrophones, and applying a neural network classifier to attribute signal identities. Acoustic presence data were converted into local density estimates, accounting for detection probability, group size, vocal probability, and false detection rates to analyze long-term trends. This approach allowed for robust monitoring of marine mammal density changes in the region​

The dataset was collected using a passive acoustic monitoring array, deployed in the northeastern Gulf of Mexico shortly after the 2010 Deepwater Horizon oil spill and maintained for over a decade. High-frequency Acoustic Recording Packages (HARPs) were placed at five monitoring sites, capturing echolocation clicks and other impulsive signals from odontocete species, which were then classified into species groups based on spectral characteristics and inter-click intervals. Automated detection and semi-supervised clustering techniques identified signals from target species, allowing for group-based density estimation of each species across time. Processing steps included high-pass filtering, calibration of hydrophones, and applying a neural network classifier to attribute signal identities. Please see the associated manuscript for additional details:

Frasier, K.E., Kadifa, M.A., Solsona Berga, A., Hildebrand, J.A., Wiggins, S.M., Garrison, L.P., Frouin-Mouy, H., Gracia, A., Serrano, A., Hodge, L.E.W., Wall, C.C., Le Hénaff, M. & Soldevilla, M.S. (202X) A decade of declines in toothed whale densities following the Deepwater Horizon oil spill. Nature Communications Earth and Environment.

2010年4月“深水地平线”（Deepwater Horizon）原油泄漏事件发生后不久，研究人员便在墨西哥湾东北部布设了间距较大的被动声学监测（passive acoustic monitoring）阵列，以记录这场史无前例的大型深海近海石油泄漏对海洋哺乳动物造成的影响。该阵列后续被维持运行十余年。本文中，我们记录了8个被监测物种类群中7个的十年间种群密度下降情况，包括抹香鲸（降幅最高达31%）、喙鲸（降幅最高达83%）以及小型海豚科动物（降幅最高达43%）。下降趋势在海面油膜覆盖区域内外均有观测到。尽管尚未与此次漏油事件建立确凿的因果关联，但针对不同海洋哺乳动物物种观测到的、覆盖广阔时空尺度的种群密度下降，与“深水地平线”漏油事件的影响特征相符。这些下降幅度已超出并远超漏油后损害评估的预测值，这表明“深水地平线”事件对近海生态系统的影响可能比此前预想的更为严重。

**方法**
2010年5月至2020年3月期间，研究人员在5个监测站点使用高频声学记录包（High-frequency Acoustic Recording Packages, HARPs）采集被动声学录音数据（详见补充表S1）。5个站点的总有效录音时长共计37个仪器年，采样率为200 kHz。监测站点包含3个深海站点与2个浅海陆架站点，主要针对浅海物种开展监测。

研究人员利用脉冲检测器识别齿鲸类（odontocete）的回声定位咔哒声及其他脉冲信号，并基于频谱特征与咔哒声间隔将其分类至不同物种类群。通过自动化检测与半监督聚类技术，研究人员识别出目标物种的信号，进而实现各物种类群的跨时间密度估算。数据处理流程包括高通滤波、水听器（hydrophone）校准，以及应用神经网络分类器归属信号类别。声学存在数据被转换为局地密度估算值，同时考虑了检测概率、种群规模、发声概率与误报率，以分析长期变化趋势。该方法可实现该区域海洋哺乳动物密度变化的可靠监测。

本数据集依托被动声学监测阵列采集，该阵列于2010年“深水地平线”漏油事件后不久部署于墨西哥湾东北部，并持续运行十余年。研究人员在5个监测站点布设高频声学记录包（HARPs），采集齿鲸类的回声定位咔哒声及其他脉冲信号，随后基于频谱特征与咔哒声间隔将信号分类至不同物种类群。研究人员通过自动化检测与半监督聚类技术识别目标物种信号，进而实现各物种类群的跨时间密度估算。数据处理流程包括高通滤波、水听器（hydrophone）校准，以及应用神经网络分类器归属信号类别。更多细节请参见相关论文：
Frasier, K.E., Kadifa, M.A., Solsona Berga, A., Hildebrand, J.A., Wiggins, S.M., Garrison, L.P., Frouin-Mouy, H., Gracia, A., Serrano, A., Hodge, L.E.W., Wall, C.C., Le Hénaff, M. & Soldevilla, M.S. (202X) 《深水地平线漏油事件后齿鲸密度的十年下降趋势》，《自然通讯：地球与环境》（*Nature Communications Earth and Environment*）