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Population outbreaks of zoantharians in shallow water reefs have been observed globally, including intertidal and subtidal sites in the Canary Islands. This study investigated how zoantharians might be integrating into the local trophic network. For that purpose, we assessed the feeding patterns of common species in zoantharian-dominated habitats, focusing on finding consumers of Zoanthus pulchellus and Palythoa caribaeorum. Through DNA-barcoding and metabarcoding, the gut contents of 11 predatory species were analysed, aiming to characterize their diets and explore local species feeding on zoantharians. Analyses of diet revealed a diverse range of food items and trophic positions of some of the most common and frequent marine species in the archipelago. Furthermore, based on previous observations on the different impacts of Z. pulchellus and P. caribaeorum on shallow benthic ecosystems of the Canary Islands, a preliminary approach to identify their potential influence on feeding patterns of associated species was made. Even though DNA-metabarcoding did not detect zoantharians in the gut contents of any studied species, Sanger sequencing with zoantharian-specific primers indicated their consumption by subject species may be limited to only the crab Platypodiella picta. In addition, by focusing on some of the most common species, this study enhances our understanding of the local trophic network and provides an insight into trophic dynamics in zoantharian-dominated habitats. [ABSTRACT FROM AUTHOR]

Passive acoustic monitoring (PAM) offers considerable potential for density estimation of cryptic cetaceans, such as beaked whales. However, comparative studies on the accuracy of PAM density estimates from these species are lacking. Concurrent, low-cost drifting PAM, with SoundTraps suspended at 200 m depth, and land-based sightings, were conducted off the Canary Islands. Beaked whale density was estimated using a cue-count method, with click production rate and the probability of click detection derived from digital acoustic recording tags (DTags), and distance sampling techniques, adapted to fixed-point visual surveys. Of 32 870 detections obtained throughout 206 h of PAM recordings, 68% were classified as "certain" beaked whale clicks. Acoustic detection probability was 0.15 [coefficient variation (CV) 0.24] and click production rate was 0.46 clicks s − 1 (CV 0.05). PAM density estimates were in the range of 21.5 or 48.6 whales per 1000 km2 [CV 0.50 or 0.44, 95% confidence interval (CI) 20.7–22.4 or 47–50.9), depending on whether "uncertain" clicks were considered. Density estimates from concurrent sightings resulted in 33.7 whales per 1000 km2 (CV 0.77, 95% CI 8.9–50.5). Cue-count PAM methods under application provide reliable estimates of beaked whale density, over relatively long time periods and in realistic scenarios, as these match the concurrent density estimates obtained from visual observations. [ABSTRACT FROM AUTHOR]

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The number and size of whale-watching and swim-with-cetacean vessels are increasing worldwide, but the noise impact on targeted species depends on vessel source characteristics, which remain largely unquantified. Here, we report the acoustic characteristics from 13 whale-watching vessels from Australia and Canary Islands. Acoustic recorders were deployed to measure the frequency-weighted sound levels (for low [LF], mid [MF] and high frequency [HF] cetacean hearing types) of motor sailing, catamarans, and motor vessels operating at 4–8 kn representing the slow speed of whale-watch scenarios. The highest estimated source levels (SLs) were recorded from large catamarans with inboard engines (LF = 160 ± 3, MF = 148 ± 2, HF = 146 ± 2 dB re 1 µPa m). The lowest SLs were from smaller motor vessels and particularly by a hybrid vessel powered by electrical outboard engines (LF = 140 ± 3, MF = 136 ± 2, HF = 134 ± 2 dB re 1 µPa m). We demonstrate that at the same speed and distance, different vessels may produce very different received levels to the animals. To reduce disturbance to cetaceans we recommend tourism vessels meet a broadband (0.2–10 kHz) SL limit of <150 dB re 1 µPa (RMS) when within 500 m of cetaceans. [Display omitted] • Whale-watch vessels spend targeted and potentially large time close to whales. • Noise from whale watch-vessels is the primary driver of disturbance. • Vessel source third octave level below 120 dB re 1 µPa will ensure a low noise induced impact. • Development of an international low noise certification of whale-watching vessels is needed. [ABSTRACT FROM AUTHOR]