Behavior of captive herring exposed to naval sonar transmissions (1.0–1.6 kHz) throughout a yearly cycle

Abstract

Atlantic herring, Clupea harengus, is a hearing specialist, and several studies have demonstrated strong responses to man-made noise, for example, from an approaching vessel. To avoid negative impacts from naval sonar operations, a set of studies of reaction patters of herring to low-frequency (1.0-1.5 kHz) naval sonar signals has been undertaken. This paper presents herring reactions to sonar signals and other stimuli when kept in captivity under detailed acoustic and video monitoring. Throughout the experiment, spanning three seasons of a year, the fish did not react significantly to sonar signals from a passing frigate, at received root-mean-square sound-pressure level (SPL) up to 168 dB re 1 μPa. In contrast, the fish did exhibit a significant diving reaction when exposed to other sounds, with a much lower SPL, e.g., from a two-stroke engine. This shows that the experimental setup is sensitive to herring reactions when occurring. The lack of herring reaction to sonar signals is consistent with earlier in situ behavioral studies. The complexity of the behavioral reactions in captivity underline the need for better understanding of the causal relationship between stimuli and reaction patterns of fish.

The reaction of a captive herring school to playbacks of a noise-reduced and a conventional research vessel

“…When disturbed, schooling herring typically perform a coordinated diving response (Vabø et al 2002;Ona et al 2007;Doksaeter et al 2012). However, in this study, the reactions were weaker and the depth distribution of herring backscatter became shallower during the simulated vessel passage.…”

“…The mean score assigned by each panelist across the different observation systems was 0.87 ± 0.04 (mean ± standard error). This response was weaker than expected from previous observations of dramatic herring reactions to the vessels (Vabø et al 2002;Ona et al 2007), as the potential scores ranged from 0 to 5, where 5 represented the dramatic coordinated escape response exhibited by startled herring (e.g., as observed by Doksaeter et al 2012 for exposures to impulsive sound). When comparing the different treatments (Fig.…”

“…Crowding in the pen may have altered the avoidance response reactions, but earlier studies on Norwegian Spring Spawning herring held in pens produced dramatic responses to other types of sounds (Doksaeter et al 2012), in particular those with impulse-like characteristics and broadband noise (which included lower frequency components than in the current work). In addition, the herring used in this study were much more reactive to predator models (Rieucau et al 2014a) than the vessel playbacks, which indicates that the fish were capable of more dramatic reactions and that the vessel playbacks were not highly disturbing to the herring.…”

“…The vertical echo sounder provided data for quantitative observations of the behavioural response. This approach is similar to that of earlier studies (Doksaeter et al 2012;Rieucau et al 2014a) that evaluated the behavioural response of schooling herring exposed to low-frequency military sonars and simulated predator attacks, respectively.…”

“…2). The mean s v in the depth interval between 0.3 and 8.5 m at the time of the playback was compared with mean s v prior to initiation of the playback, using the vessel avoidance coefficient (VA) of Vabø et al (2002), which is the ratio of backscattering coefficients observed during vessel passage and prior to exposure, defined as Herring often dive when disturbed (Vabø et al 2002;Ona et al 2007;Doksaeter et al 2012), and to examine any changes in mean depth of the herring backscatter in response to the playbacks, we defined the depth difference dd as the difference in s v -weighted mean depth prior to the vessel playback and the time interval surrounding the maximum level of vessel noise playback …”