MEPS 600:239-244 (2018)  -  DOI: https://doi.org/10.3354/meps12655

ABSTRACT: An in situ method was applied to monitor the responses of adult Pacific herring Clupea pallasi to predators. An autonomous, upward-facing echosounder was deployed on the seabed at 40 m just prior to the peak of the herring spawning season in Port Gravina, Prince William Sound, Alaska, USA. Monitoring took place over a continuous 4 d period (9-12 April 2016), during which herring and predators (seabirds and Steller sea lions Eumetopias jubatus) were tracked. Herring speeds varied (mean = 33.1 cm s^-1, range = 0.02-127.1 cm s^-1) and were significantly lower than predator speeds (mean = 56.3 cm s^-1, range = 13.7-144.6 cm s^-1). Swim speeds of herring and predators were positively correlated when regressions were lagged to 2.5 min and indicate a link between activity states of prey and predator. Changes in depth of herring were correlated positively with predator depths over a period of up to 5 min, which corresponds with seabird dive durations. This monitoring method can increase our understanding of sub-lethal effects of predators on Pacific herring and provide a direct method to quantify predation intensity on this critical life history stage.

KEY WORDS: Adult Clupea pallasi · Predation · Swim speeds · Depth · Prince William Sound · Alaska