Formal comment to Gong et al.: Ecosystem scale acoustic sensing reveals humpback whale behavior synchronous with herring spawning processes and re-evaluation finds no effect of sonar on humpback song occurrence in the Gulf of Maine in fall 2006.

William T Ellison,Peter J Corkeron,Sofie M Van Parijs,Z Daniel Deng,Denise Risch

doi:10.1371/journal.pone.0109225

Abstract

In their paper: “Ecosystem scale acoustic sensing reveals humpback whale behavior synchronous with herring spawning processes and re-evaluation finds no effect of sonar on humpback song occurrence in the Gulf of Maine in Fall 2006” Gong et al. [1] used acoustic monitoring to detect synchronous herring spawning and humpback whale presence in the Gulf of Maine, presenting novel and interesting data on predator-prey relationships on a major humpback whale feeding ground in the western North Atlantic. In addition, their finding that singing humpback whales recorded on Georges Bank and in the vicinity to their active Ocean Acoustic Waveguide Remote Sensing (OAWRS) source array did not seem to respond acoustically to OAWRS transmissions during a Fall 2006 experiment is also new. Gong et al. [1] argue that it is different from our observations in the Stellwagen Bank National Marine Sanctuary (SBNMS), 200 km distant from the OAWRS source array during the same experiment [2]. However, in contrast to the conclusions of Gong et al. [1], we argue that their results do not contradict, nor necessarily conflict with, our findings. Variable behavioral responses to noise have been shown in a range of marine mammals. For example blue whales have been shown both to increase and decrease calling rates in response to different noise sources [3], [4]. Responses to noise are complex in nature and may depend on factors such as behavioral context, prey availability, distance from source, received level (RL), signal structure and novelty, as well as individual differences [5], [6]. We argue that the finding that humpback whales reacted differently towards the OAWRS signal depending on range to the source, RL above background noise and (likely) differences in behavioral state is an interesting result that should be highlighted rather than discounted. Here we will (1) outline some of the problems in the Gong et al. [1] analysis of humpback whale vocal behavior on Georges Bank, (2) respond to their critique of our findings reported in [2], and (3) discuss Gong et al.'s [1] presentation of the effects of the OAWRS signal source, a low-frequency sound source with source levels (SL) which may be in excess of 210 dB re 1 µPa @ 1 m [7].

Highlights

In their paper: ‘‘Ecosystem scale acoustic sensing reveals humpback whale behavior synchronous with herring spawning processes and re-evaluation finds no effect of sonar on humpback song occurrence in the Gulf of Maine in Fall 2006’’ Gong et al [1] used acoustic monitoring to detect synchronous herring spawning and humpback whale presence in the Gulf of Maine, presenting novel and interesting data on predator-prey relationships on a major humpback whale feeding ground in the western North Atlantic
For the reasons outlined above and as we did not observe large changes in ambient noise levels over the entire time period [2], we are confident in our inference that the changes in humpback whale song we reported were due to changes in occurrence of song originating on Stellwagen Bank
Several humpback whales were observed in the Stellwagen Bank National Marine Sanctuary (SBNMS) area before and during the 2006 Ocean Acoustic Waveguide Remote Sensing (OAWRS) experiment (Figure 2, Table 1)

Summary

Introduction

In their paper: ‘‘Ecosystem scale acoustic sensing reveals humpback whale behavior synchronous with herring spawning processes and re-evaluation finds no effect of sonar on humpback song occurrence in the Gulf of Maine in Fall 2006’’ Gong et al [1] used acoustic monitoring to detect synchronous herring spawning and humpback whale presence in the Gulf of Maine, presenting novel and interesting data on predator-prey relationships on a major humpback whale feeding ground in the western North Atlantic Their finding that singing humpback whales recorded on Georges Bank and in the vicinity to their active Ocean Acoustic Waveguide Remote Sensing (OAWRS) source array did not seem to respond acoustically to OAWRS transmissions during a Fall 2006 experiment is new.

Identification of humpback whale non-song vocalizations

Suggestion of feeding related vocalizations and echolocation