Are spatial and temporal patterns in Lynn Canal overwintering Pacific herring related to top predator activity?

• Published in: Canadian journal of fisheries and aquatic sciences Vol. 73; no. 9; p. 12
• Main Authors: Boswell, K M, Rieucau, G, Vollenweider, J J, Moran, J R, Heintz, R A, Blackburn, J K, Csepp, D J
• Format: Journal Article
• Language: English
• Published: 01.01.2016
• Subjects: Clupea pallasii; Marine; Megaptera novaeangliae; ISEW, Southeast Asia
• ISSN: 0706-652X; 1205-7533

In Southeast Alaska, overwintering Pacific herring (Clupea pallasii) form large conspicuous schools that are preyed upon by an abundance of mammalian and avian predators, thus leading to the question of why herring adopt a strategy that appears counterproductive to predator avoidance during these periods. We examined the spatial and temporal dynamics of overwintering Pacific herring and associations with predators through monthly hydroacoustic surveys during two consecutive winters. Large variation was observed through the winter season in herring distribution, school morphology, and density. Herring school characteristics and biomass estimates were negatively correlated with humpback whale (Megaptera novaeangliae) abundance patterns during both winters, and as whales departed towards the end of winter, herring distributions shifted from dispersed schools in the water column toward deep, dense schools. We postulate that the schooling patterns observed in Lynn Canal overwintering herring are likely to be mediated by predation threat rather than energetics or feeding activities. An additional consequence of humpback whales dispersing herring in the water column may be an increased threat of predation by other surface-oriented predators.