NMML Bering Sea Cetacean Survey 1999

Original provider:
National Marine Mammal Laboratory

Dataset credits:
National Marine Mammal Laboratory

Abstract:
Visual line-transect surveys for cetaceans were conducted in the central-eastern Bering Sea (CEBS) from 5 July to 5 August 1999, in association with a pollock stock assessment survey aboard the NOAA ship Miller Freeman. Observers scanned for cetaceans with 25x (Big Eye) binoculars form the flying bridge (platform height &#61; 12 m) at survey speeds of 18.5-22 km h-1 (10-12 knots). Transect survey effort was 1,761 km, in a study area 196,885 km2. An additional 609 km of trackline was surveyed, while in transit to or from Pollock survey way points. Fin whales (<i>Balaeoptera physalus</i>) were the most common large whale, and Dall&#39;s porpoises (<i>Phocoenoides dalli</i>) were the most common small cetacean. In the CEBS 1999, uncorrected cetacean abundance estimates were: 3,368 (CV &#61; 0.29) fin whales, 810 (CV &#61; 0.36) minke whales (<i>B. acutorostrata</i>), 14,312 (CV &#61; 0.26) Dall&#39;s porpoise, and 693 (CV &#61; 0.53) harbor porpoise (<i>Phocoena phocoena</i>). Non-pollock echosigns observed near cetaceans, some of which may have been cetacean prey, were not routinely identified during trawl sampling because the research focus was on pollock abundance assessment. Clearly, additional surveys and concomitant assessment of cetacean prey are needed to better define their role in the Bering Sea ecosystem. Such surveys, combined with measures of local hydrography and prey field should be the goal of future cetacean assessments.

Purpose:
Cetacean distribution and abundance in the Bering Sea is poorly described, with even recent reviews of cetaceans&#39; role in the ecosystem reliant on data from the commercial whaling era. Commercial harvests of baleen whales (mysticetes) were extensive in the North Pacific and Bering Sea, especially between 1835 and 1850 for North Pacific right whales and between 1965 and 1979 for fin and humpback whales. The effect of these large-scale removals on the marine ecosystem is largely unknown. Similarly, some species of toothed whales (odontocetes) are sometimes killed in the course of commercial fishing operations. Pelagic dolphins and Dall&#39;s porpoise were especially vulnerable during high seas driftnet fishing in the North Pacific in the 1980s, and once again the long-term ramifications of these removals are unknown. One reason for this uncertainty is the lack of data on current cetacean distribution and estimates of abundance in pelagic environments. Surveys to determine distribution and abundance are costly and, therefore, often confined either to coastal waters where the logistics are most practical, or to areas of the ocean where marine mammal mortality associated with commercial fishing is particularly high. The pelagic waters of the Bering Sea have not met either criteria and so are comparatively undersampled for cetaceans.

Cruises were undertaken in association with the Alaska Fisheries Science Center/Resource Assessment and Conservation Engineering (AFSC/RACE) division to conduct visual surveys for cetaceans during the semi-annual acoustic trawl surveys for walleye pollock (<i>Theragra chalcogramma</i>) on the Bering Sea shelf. Biologists from the AFSC/National Marine Mammal Laboratory (NMML) were able to join surveys in the central-eastern Bering Sea (CEBS) in 1999, providing an opportunity to describe cetacean distribution and calculate abundance over a broad area of the Bering Sea shelf.

Provisional results of the 1999 survey in the CEBS were presented, but without clear reference to the three hydrographic domains (coastal, middle shelf, and outer shelf) that delineate oceanographic and productivity patterns in the Bering Sea. Here, we present the first estimates of cetacean abundance that can be compared between two broad pelagic zones, as well as cetacean distribution and sighting rates relative to hydrographic domains and fronts commonly referred in papers describing oceanographic processes in the eastern Bering Sea.

Supplemental information:
12/8/06: Species code 66 was mistakenly assigned to northern right whale (<i>Eubalaena glacialis</i>). It is replaced with North Pacific right whale (<i>Eubalaena japonica</i>).

原始提供方：国家海洋哺乳动物实验室

数据集信用：国家海洋哺乳动物实验室

摘要：1999年7月5日至8月5日，在NOAA船米勒·弗里曼号上进行的鲱鱼种群评估调查期间，对中东部白令海的鲸类进行了视觉线状航迹调查。观察者使用25倍（大眼）双筒望远镜从飞行甲板（平台高度为12米）以18.5-22公里/小时（10-12节）的航速进行观察。横断面调查工作量达1761公里，研究区域为196,885平方公里。此外，在前往或离开鲱鱼调查航点的途中，还调查了609公里的航迹线。座头鲸（Balaeoptera physalus）是最常见的大型鲸类，而达尔克豚（Phocoenoides dalli）是最常见的小型鲸类。在1999年的中东部白令海（CEBS）中，未经校正的鲸类丰度估计为：3,368头座头鲸（CV = 0.29），810头小须鲸（B. acutorostrata）（CV = 0.36），14,312头达尔克豚（CV = 0.26）和693头港湾海豚（Phocoena phocoena）（CV = 0.53）。在调查过程中观察到的非鲱鱼回声信号，其中一些可能是鲸类的猎物，但在拖网采样中并未常规识别，因为研究重点在于鲱鱼丰度评估。显然，为了更好地定义其在白令海生态系统中的作用，需要开展额外的调查和相应的鲸类猎物评估。此类调查应与局部水文测量和猎物场测量相结合，成为未来鲸类评估的目标。

目的：白令海的鲸类分布和丰度描述不佳，即使是近期对鲸类在生态系统中所扮演角色进行的综述，也依赖于商业捕鲸时代的资料。在北太平洋和白令海，须鲸（mysticetes）的商业捕捞量很大，尤其是在1835年至1850年间的北太平洋右鲸和1965年至1979年间的抹香鲸和座头鲸。这些大规模移除对海洋生态系统的影响 largely 未知。同样，一些齿鲸（odontocetes）的物种有时在商业捕鱼过程中被杀死。在20世纪80年代的北太平洋公海流刺网捕鱼期间，远洋海豚和达尔克豚特别脆弱，而这些移除的长期影响同样未知。这种不确定性的一个原因是缺乏关于当前鲸类在远洋环境中的分布和丰度估计的数据。确定分布和丰度的调查成本高昂，因此通常限于沿海水域，那里的后勤工作最为实用，或者限于与商业捕鱼相关的海洋哺乳动物死亡率特别高的海洋区域。白令海的远洋水域尚未满足这些标准，因此在鲸类的样本量上相对较少。

巡航是在阿拉斯加渔业科学中心/资源评估和 conservation engineering（AFSC/RACE）部门的支持下进行的，旨在在白令海大陆架上进行半年度声学拖网调查鲈鱼时对鲸类进行视觉调查。来自AFSC/国家海洋哺乳动物实验室（NMML）的生物学家能够在1999年加入中东部白令海（CEBS）的调查，从而有机会描述鲸类的分布并计算白令海大陆架广阔区域内的丰度。

初步结果于1999年在CEBS中提出，但未明确提及划分白令海海洋学和生产力模式的三个水文域（沿海、中部大陆架和外部大陆架）。在此，我们提出了首次可以比较两个广泛远洋区的鲸类丰度估计，以及与描述东部白令海海洋学过程的文献中常见的海洋水文域和锋面相关的鲸类分布和观测率。

补充信息：2006年12月8日：物种代码66被错误地分配给北大西洋鲸（Eubalaena glacialis）。它被替换为北太平洋鲸（Eubalaena japonica）。