Soundscapes of Pacific Herring (Clupea pallasii) spawning aggregations

Background/Question/Methods

Pacific herring, Clupea pallasii, are an ecologically and culturally important forage fish. These small pelagic schooling fishes aggregate each spring in coastal embayments to spawn. These spawning events are an important ecological event, aggregating and providing feeding opportunities for predators including birds and marine mammals. They also provide important fisheries opportunities for both coastal First Nations and commercial fishers, and for scientists to monitor herring populations. The remote nature of much of Canada’s Pacific coast represents a challenge for effective monitoring of herring spawning activity, increasing uncertainty for managers. Pacific herring are soniferous, or sound producing fish, generating a fast repetitive tick sound in laboratory conditions. While Atlantic herring sounds have been documented in the wild, Pacific herring sounds have not. In addition to herring-specific calls, many of the other taxa that aggregate in response to herring spawn are also sound producing, suggesting passive acoustic monitoring may be an effective tool to document the occurrence of herring spawning in remote locations. We deployed autonomous hydrophones at 3 suspected spawning sites in the Strait of Georgia, BC, manually identified sounds, and calculated acoustic complexity indices and sound pressure levels for biologically relevant frequency bands.

Results/Conclusions

Herring spawned at two of three locations where we deployed recorders. We were able to detect herring sounds at all sites, regardless of whether or not spawning occurred. These sounds are short, averaging 0.09 seconds typically ranging from 2-4 kHz with a median peak frequency of 2.70 kHz. Across sites herring sounds were more prevalent between dusk and dawn. We also detected bird calls and sea lion vocalizations at both sites where herring spawned. This work represents the first time Pacific herring sounds have been documented in the wild and the first description of the overall soundscape of Pacific herring spawning aggregations. Ultimately, this represents the first step towards developing a passive acoustic monitoring system for herring spawning in the northeast Pacific.