Underwater video of lake whitefish Coregonus clupeaformis spawning in lake Michigan

The lake whitefish Coregonus clupeaformis, dikameg in Anishinaabemowin, holds cultural importance, and is a mainstay of commercial, recreational, and subsistence fisheries throughout North America. In the Laurentian Great Lakes, declines in recruitment, since the early 2000s, have raised concerns among stewards and fishery managers. A more detailed understanding of the lake whitefish mating system could help resolve potential recruitment bottlenecks and thus inform appropriate stewardship actions. Herein, we describe, for the first time, a single lake whitefish spawning event captured using high-resolution underwater videography. From 94 h spent on the water, we captured and analyze a 4.5 min video clip that shows pre-mating, mating, and post-mating behaviour of a male and female lake whitefish from Lake Michigan. The clip shows a number of what we interpret as courtship, site-selection, and spawning behaviours culminating in release of about 20 eggs in a single spawning event. Behaviours that included travelling, physical contact, chasing, circling, orienting, and gamete release are described and time-referenced to a video supplement. This single observation is part of a larger project to assess lake whitefish spawning behaviour in the wild but is noteworthy in that it provides new insights into the spawning behaivour of lake whitefish and appears consistent with reproductive behaviours observed in European coregonines.

Methods
During 2022-2023, we used a Boxfish Robotics (https://www.boxfishrobotics.com) “Luna” craft to capture high-resolution underwater footage of spawning lake whitefish in lakes Huron and Michigan. The Luna craft is a next-generation drone that utilizes advanced full-frame imaging from a 4K 10-bit 4:2:2 120p Sony A7SIII camera equipped with either a Sony 16-35 mm f/2.8 or a Sony 24mm f/1.4 Zeiss lens. In shallow water, a 250-mm Nauticam glass dome port was used for the best edge-to-edge image quality, but for deepwater filming, a 200-mm Boxfish acrylic dome rated for 500 m depth was used. High sensitivity up to ISO 409,600 provided exceptional low-light camera performance. Two dimmable 8,500-lumen lights attached via adjustable arm mounts to the front of the craft provided ample illumination under all light conditions encountered. The ROV was tethered to the surface by a 300-m long, 2.7-mm diameter, lightweight, fiber-optic cable which allows recording on the surface in 4k ProRes Raw at 30p and frame stabilizing in post-production. The craft was controlled from the surface via a pilot console equipped with a 17-inch 4K monitor and a 10-inch sunlight readable secondary navigation display. The ROV carried sensors for depth, acceleration, internal humidity, temperature, and pressure and a 3D compass and precision gyroscope. A Subsea USBL transmitter and receiver provided GPS location of the ROV underwater (i.e., georeferenced on a map) and a Doppler Velocity Log sensor allowed the pilot to hold station thereby facilitating precise real-time control and adjustment of the craft and camera.

湖白鲑（lake whitefish, *Coregonus clupeaformis*）在阿尼希纳贝语（Anishinaabemowin）中被称为dikameg，兼具重要的文化价值，同时是北美地区商业、休闲及自给渔业的核心支柱物种。自21世纪初以来，圣劳伦斯五大湖（Laurentian Great Lakes）的湖白鲑种群补充量持续下降，引发了渔业管护者与管理人员的广泛担忧。若能深入解析湖白鲑的交配系统，将有助于破解潜在的种群补充瓶颈，进而为科学的管护行动提供理论支撑。

本研究首次报道了一例通过高分辨率水下摄像技术记录到的湖白鲑产卵事件。本次水下作业总时长94小时，最终采集并分析了一段时长4.5分钟的视频片段，该片段完整记录了密歇根湖（Lake Michigan）中一对湖白鲑雌雄个体的交配前、交配及交配后行为。视频中呈现了多种经我们解读为求偶、场地选择与产卵的行为，最终在单次产卵事件中释放了约20枚鱼卵。本研究详细描述了巡游、身体接触、追逐、环绕、定向及配子释放等行为，并为视频补充材料标注了精确的时间轴。这一单次观测是评估野生湖白鲑产卵行为的大型研究项目的组成部分，但其独特价值在于为湖白鲑的产卵行为提供了全新的认知，且其观测结果与欧洲白鲑亚科（coregonines）物种的繁殖行为报道相一致。

## 研究方法

2022—2023年，本研究使用Boxfish Robotics公司（https://www.boxfishrobotics.com）研发的"Luna"型水下无人机，对休伦湖（Lake Huron）与密歇根湖中的湖白鲑产卵行为开展高分辨率水下影像采集。

"Luna"型水下无人机为新一代遥控水下机器人（Remotely Operated Vehicle, ROV），搭载索尼（Sony）A7SIII全画幅相机，支持4K 10-bit 4:2:2 120p成像规格，可选配索尼16-35 mm f/2.8或索尼24 mm f/1.4蔡司（Zeiss）镜头。在浅水环境作业时，搭配250 mm口径的Nauticam玻璃圆顶端口以实现最优的边缘到边缘成像质量；深水拍摄场景下，则采用额定工作深度500 m的200 mm口径Boxfish亚克力圆顶端口。该相机的感光度最高可达ISO 409600，可在低光照环境下实现优异的成像性能。无人机前部通过可调节臂架安装了两盏可调光8500流明补光灯，可适配各类水下光照条件，提供充足照明。

该遥控水下机器人通过一条长300 m、直径2.7 mm的轻量化光纤缆绳与水面操控平台连接，支持以30p帧率录制4K ProRes Raw格式视频，并可在后期制作中进行画面稳定处理。操作人员通过水面操控控制台完成机器人操控，控制台搭载17英寸4K显示器与10英寸阳光下可读的辅助导航显示屏。该水下无人机搭载了深度、加速度、内部湿度、水温、水压传感器，以及三维罗盘与精密陀螺仪。水下超短基线（Subsea USBL）收发系统可实现水下机器人的GPS定位（即地理配准至地图坐标系），多普勒速度日志（Doppler Velocity Log）传感器则可协助操作人员维持机器人定点悬停，从而实现对机器人与相机的精准实时操控与调整。