Seasonal presence and potential influence of humpback whales on wintering Pacific herring populations in the Gulf of Alaska Deep Sea Research Part II: Topical Studies in Oceanography

This study addressed the lack of recovery of Pacific herring (Clupea pallasii) in Prince William Sound, Alaska, in relation to humpback whale (Megaptera novaeangliae) predation. As humpback whales rebound from commercial whaling, their ability to influence their prey through top-down forcing increases. We compared the potential influence of foraging humpback whales on three herring populations in the coastal Gulf of Alaska: Prince William Sound, Lynn Canal, and Sitka Sound (133–147°W; 57–61°N) from 2007 to 2009. Information on whale distribution, abundance, diet and the availability of herring as potential prey were used to correlate populations of overwintering herring and humpback whales. In Prince William Sound, the presence of whales coincided with the peak of herring abundance, allowing whales to maximize the consumption of overwintering herring prior to their southern migration. In Lynn Canal and Sitka Sound peak attendance of whales occurred earlier, in the fall, before the herring had completely moved into the areas, hence, there was less opportunity for predation to influence herring populations. North Pacific humpback whales in the Gulf of Alaska may be experiencing nutritional stress from reaching or exceeding carrying capacity, or oceanic conditions may have changed sufficiently to alter the prey base. Intraspecific competition for food may make it harder for humpback whales to meet their annual energetic needs. To meet their energetic demands whales may need to lengthen their time feeding in the northern latitudes or by skipping the annual migration altogether. If humpback whales extended their time feeding in Alaskan waters during the winter months, the result would likely be an increase in herring predation. Grant no. NA17NMF4720027

本研究针对阿拉斯加州威廉王子湾（Prince William Sound）的太平洋鲱（Pacific herring, Clupea pallasii）种群恢复停滞问题，探讨其与座头鲸（humpback whale, Megaptera novaeangliae）捕食活动的关联。随着座头鲸种群从商业捕鲸的破坏中逐步恢复，其通过下行调控作用影响猎物种群的能力也随之增强。本研究于2007至2009年间，比较了阿拉斯加湾沿岸三个鲱鱼种群——威廉王子湾、林恩运河（Lynn Canal）与锡特卡湾（Sitka Sound）（经度范围133°W–147°W，纬度范围57°N–61°N）所面临的觅食座头鲸的潜在影响。研究通过收集鲸类的分布、丰度、食性以及鲱鱼作为潜在猎物的可获得性等数据，分析越冬鲱鱼种群与座头鲸种群之间的相关性。在威廉王子湾，座头鲸的出现时段与鲱鱼种群的丰度峰值恰好重合，使得鲸类能够在向南洄游之前最大化捕食越冬鲱鱼。而在林恩运河与锡特卡湾，座头鲸的峰值到访时段更早，即秋季，此时鲱鱼尚未完全迁入该区域，因此捕食作用对鲱鱼种群的影响程度相对有限。阿拉斯加湾的北太平洋座头鲸种群可能正面临营养胁迫：要么种群数量达到或超过了环境容纳量，要么海洋环境发生了足够显著的变化，导致猎物基础发生改变。种内食物竞争可能进一步加剧座头鲸满足年度能量需求的难度。为满足能量需求，座头鲸可能需要延长在高纬度北部海域的觅食时长，或是完全放弃年度洄游活动。若座头鲸在冬季延长在阿拉斯加海域的觅食时长，鲱鱼被捕食的压力大概率会随之上升。资助编号：NA17NMF4720027