Spatial and Temporal Occurrence of Blue Whales off the U.S. West Coast, with Implications for Management

Mortality and injuries caused by ship strikes in U.S. waters are a cause of concern for the endangered population of blue whales (Balaenoptera musculus) occupying the eastern North Pacific. We sought to determine which areas along the U.S. West Coast are most important to blue whales and whether those areas change inter-annually. Argos-monitored satellite tags were attached to 171 blue whales off California during summer/early fall from 1993 to 2008. We analyzed portions of the tracks that occurred within U.S. Exclusive Economic Zone waters and defined the ‘home range’ (HR) and ‘core areas’ (CAU) as the 90% and 50% fixed kernel density distributions, respectively, for each whale. We used the number of overlapping individual HRs and CAUs to identify areas of highest use. Individual HR and CAU sizes varied dramatically, but without significant inter-annual variation despite covering years with El Niño and La Niña conditions. Observed within-year differences in HR size may represent different foraging strategies for individuals. The main areas of HR and CAU overlap among whales were near highly productive, strong upwelling centers that were crossed by commercial shipping lanes. Tagged whales generally departed U.S. Exclusive Economic Zone waters from mid-October to mid-November, with high variability among individuals. One 504-d track allowed HR and CAU comparisons for the same individual across two years, showing similar seasonal timing, and strong site fidelity. Our analysis showed how satellite-tagged blue whales seasonally used waters off the U.S. West Coast, including high-risk areas. We suggest possible modifications to existing shipping lanes to reduce the likelihood of collisions with vessels.

美国海域内船舶撞击导致的死亡与损伤，对栖息于北太平洋东部的濒危蓝鲸（Balaenoptera musculus）种群构成了亟待关注的威胁。本研究旨在明确美国西海岸沿线哪些区域对蓝鲸而言最为关键，同时探究这些关键区域是否存在年际变化。
1993年至2008年的夏季及初秋期间，研究人员为加利福尼亚州外海的171头蓝鲸佩戴了经阿尔戈斯（Argos）系统监测的卫星标签。本研究对发生于美国专属经济区（Exclusive Economic Zone, EEZ）海域内的部分追踪轨迹进行了分析，并将每头蓝鲸的家域（Home Range, HR）与核心活动区（Core Areas, CAU）分别定义为90%与50%的固定核密度分布范围。研究通过统计个体家域与核心活动区的重叠数量，识别出蓝鲸使用频率最高的区域。
单头蓝鲸的家域与核心活动区范围存在显著差异，但即便研究涵盖了厄尔尼诺（El Niño）与拉尼娜（La Niña）现象发生的年份，这些范围也未出现显著的年际变化。观测到的年度内家域范围差异，可能反映了不同个体的觅食策略差异。
蓝鲸家域与核心活动区重叠的主要区域，位于商业航运航线穿越的高生产力强上升流中心附近。佩戴卫星标签的蓝鲸通常于10月中旬至11月中旬离开美国专属经济区海域，不同个体的离开时间存在较高变异性。有一条时长504天的追踪轨迹，可用于对比同一头蓝鲸两年间的家域与核心活动区，结果显示其季节活动节律高度相似，且表现出极强的栖息地忠实性。
本研究分析揭示了佩戴卫星标签的蓝鲸如何季节性利用美国西海岸外海海域，其中包括船舶撞击高风险区域。研究建议对现有航运航线进行适当调整，以降低蓝鲸与船舶发生碰撞的概率。