T-POD click detectors are used frequently to monitor harbour porpoise (Phocoena phocoena) behaviour and habitat use
Hector’s dolphin (Cephalorhynchus hectori) is one of the smallest marine mammals in the world, measuring 1.2–1.5 m in length, and is endemic to the waters of New Zealand. Hector’s dolphin is the most well-known of the four species in its genus Cephalorhynchus. This small marine mammal, with its distinctive round dorsal fin, is the most easily recognised species of dolphin in New Zealand. There are two subspecies of Hector’s dolphin, the more numerous Cephalorhynchus hectori, with a patchy distribution around the South Island, and the Maui’s dolphin (Cephalorhynchus hectori maui), an endangered species with an estimate of only 55 individuals remaining off the northwest coast of the North Island (www.doc.govt.nz). Hector’s dolphin is found normally in relatively shallow, coastal waters in small groups of 2–10 individuals (Slooten et al. 2011).
The population of Hector’s dolphin has declined over the last few decades, with a population estimate of around 7,270 individuals remaining (Slooten et al. 2004). They are therefore listed as Endangered by the International Union for the Conservation of Nature (IUCN) and New Zealand’s Department of Conservation (DOC; www.doc.govt.nz). Hector’s dolphin is a coastal species, and due to its close proximity to human activities, it faces several threats, in particular from fisheries. To date the largest threat to Hector’s dolphin has been entanglement in gillnets (Stone et al. 2000).
The establishment of Marine Protected Areas (MPAs) can be an effective method to protect marine mammals threatened with bycatch mortality. Created in 1988, the Banks Peninsula Marine Mammal Sanctuary (www.doc.govt.nz) was the first protected area for dolphins in New Zealand. The establishment of this protected area prohibited the use of gillnets inside most of the sanctuary (Slooten 2013). A recent study on the Sanctuary’s effectiveness carried out over a 21 year period found that, between pre- and post-sanctuary periods, estimates of mean survival probability increased by 5.4% (Gormley et al. 2012). This result corresponds to a 6% increase in mean annual population growth (Gormley et al. 2012).
The IUCN has recommended that protection for Hector’s and Maui’s dolphin should extend throughout their entire range, by banning gillnet and trawl fisheries in waters up to 100 m deep (IUCN 2012). This recommendation would provide protection to dolphins throughout their range, and would allow the population to recover; however, lower-level human impacts such as pollution, marine mining, boat strikes, and tidal energy generation could continue to be responsible for a certain degree of mortality (Slooten 2013), as can the effect of tourism.
Essential monitoring tools have been developed for assessing impacts on endangered cetaceans. Passive Acoustic Monitoring (www.passiveacousticmonitoring.co.uk) surveys using T-POD click detectors (www.t-pod.co.uk) are proven to have several advantages in terms of research studies on marine mammal habitat use and behaviour. Studies using these acoustic monitoring systems are relatively low cost, static (www.staticacousticmonitoringsystem.com), and fully-automated, providing 24 hour monitoring, while also gathering large datasets over long periods of time.
T-POD click detectors are used frequently to monitor harbour porpoise (Phocoena phocoena) behaviour and habitat use (www.porpoisedetectors.co.uk). Similar to harbour porpoise, Hector’s dolphin also produce High Frequency Narrow-Band (HFNB) clicks; making them suitable for passive acoustic monitoring studies using T-PODs (www.t-podporpoiseclickdetector.co.uk).
In one study, three T-PODs were deployed in the Banks Peninsula Marine Mammal Sanctuary over a two year period to evaluate the effectiveness of the T-POD for addressing habitat use by Hector’s dolphins (Rayment et al. 2009b). The results from the study indicated that season had an effect on detection rate, with more than three times as many minutes with dolphin detections in summer compared to winter. This study has provided an insight into habitat use, distribution, and echolocation behaviour of these animals, demonstrating effectiveness of the T-POD click detector as an acoustic monitoring method.
A study carried out in Flea Bay marine reserve, New Zealand (an area with frequent Hector’s dolphin sightings), found that acoustic detections were made consistently on T-PODs in the presence of dolphins. Results also revealed that, the maximum distance an acoustic detection was recorded on the T-POD was 431 m. Acoustic detection rate and detection probability decreased with increasing distance from the T-POD, with no acoustic detections beyond 500 m (Rayment et al. 2009a).
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