Will harbor porpoises (Phocoena phocoena) be deterred by a pinger that cannot be used as a “dinner bell” by seals?

Abstract

A measure proven successful in mitigating harbor porpoise bycatch, is the use of acoustic deterrents, i.e., pingers. However, most pingers are audible to seals. This may lead to seals associating pinger sounds with easily accessible food, leading to increased depredation, damage, and bycatch. In this study we tested if an experimental pinger, emitting sounds over 30 hr ON/OFF cycles, with low frequency components potentially audible to seals only at close distances, would effectively deter harbor porpoises. The porpoise response was measured by logging echolocation clicks, using C‐POD click detectors, moored at different distances from the pinger. In addition, we calculated the theoretical pinger detection range for seals. Results showed that the pinger had a significant negative effect on the porpoise click activity logged at 0 m and 100 m distance but not at 400 m from the pinger. During pinger ON periods, we found no significant increase in echolocation over consecutive days of the study, suggesting no habituation to pinger sounds. Our theoretical detection distances indicate that seals can only detect the pinger at close distances, preventing seals from using this pinger as a “dinner bell.”

Assessing effectiveness and side effects of likely “seal safe” pinger sounds to ward off endangered franciscana dolphins (Pontoporia blainvillei)

“…Promising results of deterrence by the same pinger model as tested here were also reported for the harbor porpoise, Phocoena phocoena (Omeyer et al, 2020; Königson et al, 2021). In our study, however, the reduction in the click train detection probability of franciscanas in the immediate vicinity of the active pinger was almost half of that observed in harbor porpoises in the study by Omeyer et al (2020), 19.4% and 37%, respectively, but it was higher at 100 m from the pinger (15.4% and 8%, respectively), demonstrating that the same pinger can influence species differently.…”

“…Considering the duration of the experiment (65 days), we believe this result very promising. Habituation was also not observed in P. phocoena during a 64‐day experiment (Königson et al, 2021) and during eight months of experiments with the same pinger (Omeyer et al, 2020). In contrast, Cox et al (2003), using a theodolite to record bottlenose dolphin surfacing in the vicinity of a Netmark 1000 pinger (Dukane Seacom, Sarasota, FL), observed no significant deterrent effect after only 11 days of study, strongly suggesting that habituation occurred.…”

“…Assuming that O. byronia and A. australis have a similar hearing range as the species mentioned above, the lowest frequency components (ca. 58 kHz) of the experimental Banana Pinger should be audible to these species only at very short distances (50–80 m; see Königson et al, 2021), and thus would not provide useful acoustic cues allowing the pinger to act as a dinner bell.…”

A systematic review of sensory deterrents for bycatch mitigation of marine megafauna

“…'Seal safe' banana pingers (50-120 kHz) increase avoidance responses in vulnerable Franciscana dolphins, although this effect is fairly small, with 19.4% reductions in surfacing frequency close to the pinger and 15% at 100 m (Paitach et al 2022). Significant reductions of bycatch and increased avoidance behaviour in harbour porpoises continue, adding to the evidence base that pingers are effective for at least some small odontocetes in gillnet fisheries globally (Chladek et al 2020;Omeyer et al 2020;Königson et al 2021).…”

“…Habituation and habitat exclusion are important factors when using sensory technologies. Habituation to sensory deterrents has been recorded in empirical studies (Amano et al 2017), and where it is not observed, this is perhaps due to the long time periods over which it could occur and difficulties in detecting it during short field studies which focus on immediate results (Königson et al 2021). Habitat exclusion has been found in studies and derived in models when investigating some technologies, although evidence of the effects on populations are not clear (van Beest et al 2017).…”