A low-cost solution for documenting distribution and abundance of endangered marine fauna and impacts from fisheries.

Fisheries bycatch is a widespread and serious issue that leads to declines of many important and threatened marine species. However, documenting the distribution, abundance, population trends and threats to sparse populations of marine species is often beyond the capacity of developing countries because such work is complex, time consuming and often extremely expensive. We have developed a flexible tool to document spatial distribution and population trends for dugongs and other marine species in the form of an interview questionnaire supported by a structured data upload sheet and a comprehensive project manual. Recognising the effort invested in getting interviewers to remote locations, the questionnaire is comprehensive, but low cost. The questionnaire has already been deployed in 18 countries across the Indo-Pacific region. Project teams spent an average of USD 5,000 per country and obtained large data sets on dugong distribution, trends, catch and bycatch, and threat overlaps. Findings indicated that >50% of respondents had never seen dugongs and that 20% had seen a single dugong in their lifetimes despite living and fishing in areas of known or suspected dugong habitat, suggesting that dugongs occurred in low numbers. Only 3% of respondents had seen mother and calf pairs, indicative of low reproductive output. Dugong hunting was still common in several countries. Gillnets and hook and line were the most common fishing gears, with the greatest mortality caused by gillnets. The questionnaire has also been used to study manatees in the Caribbean, coastal cetaceans along the eastern Gulf of Thailand and western Peninsular Malaysia, and river dolphins in Peru. This questionnaire is a powerful tool for studying distribution and relative abundance for marine species and fishery pressures, and determining potential conservation hotspot areas. We provide the questionnaire and supporting documents for open-access use by the scientific and conservation communities.

Tread-water feeding of Bryde's whales.

Many previous studies have shown that rorqual whales (Balaenopteridae), including the blue whale (Balaenoptera musculus), fin whale (B. physalus), sei whale (B. borealis), Bryde's whale (B. edeni), minke whale (B. acutorostrata), and humpback whale (Megaptera novaeangliae), employ a strategy called lunge feeding to capture a large amount of krill and/or fish for nourishment [1]. Lunge feeding entails a high energetic cost due to the drag created by an open mouth at high speeds [1,2]. In the upper Gulf of Thailand, Bryde's whales, which feed on small fish species [3], predominantly anchovies, demonstrated a range of feeding behaviors such as oblique, vertical, and lateral lunging. Moreover, they displayed a novel head-lifting feeding behavior characterized by holding the vertical posture for several seconds with an open mouth at the water surface. This study describes the head-lifting feeding by Bryde's whales, which is distinct from the typical lunge feeding of rorqual whales. Whales showing this behavior were observed on 58 occasions, involving 31 whales and including eight adult-calf pairs. Whales caught their prey using a series of coordinated movements: (i) lifting the head above the water with a closed mouth, (ii) opening the mouth until the lower jaw contacted the sea surface, which created a current of water flowing into the mouth, (iii) holding their position for several seconds, (iv) waiting for the prey to enter the mouth, and (v) closing the mouth and engulfing the prey underwater (Figure 1A-F, Movie S1 in Supplemental Information published with this article online). When a whale kept its upper jaw above the sea surface, many anchovies in the targeted shoal appeared to lose orientation and flowed passively into the mouth of the whale by the current created by the lower mandible breaking the surface of the water. We measured the duration of feeding events when the whales had a wide-open mouth mostly above the sea surface. The mean and maximum feeding durations were 14.5 ± 5.4 (SD; n = 58 events) and 32 s, respectively. Deployment of animal-borne data loggers yielded approximately 44 minutes of recordings from a single whale. The acceleration data showed that stroke rates, including tail beat and whole-body movements during feeding, were faster (approximately 0.7 s cycle) than during a cruising swim (approximately 3 s cycle) (Figure 1G). The swimming speed was lower than that in the stall speed (0.2 m s-1) of the device during the feeding phase, suggesting that thrust force was used to hold the head up and to stabilize body posture (Figure 1G). Stable positioning using the fluke and flipper was confirmed by video data for both the downward and upward direction of the whale (Figure S1). According to the visual and behavioral data, we named the head-lifting feeding as 'tread-water feeding'. Generally, all species of baleen whale, including rorqual whales, show active chasing and feeding, i.e., skimming, suction, and engulfing with lunging [1]. Tread-water feeding is considered passive feeding as compared with other feeding behaviors because the whales do not swim forward in pursuit of prey during the period from mouth opening to closing, and although they need thrust force to stabilize their posture, the head does not actively move. To the best of our knowledge, this discovery of tread-water feeding in Bryde's whales represents the first report of passive feeding in baleen whales, which indicates their flexible capacity to modify their foraging strategy in relation to variable environments.

Callback response of dugongs to conspecific chirp playbacks.

Dugongs (Dugong dugon) produce bird-like calls such as chirps and trills. The vocal responses of dugongs to playbacks of several acoustic stimuli were investigated. Animals were exposed to four different playback stimuli: a recorded chirp from a wild dugong, a synthesized down-sweep sound, a synthesized constant-frequency sound, and silence. Wild dugongs vocalized more frequently after playback of broadcast chirps than that after constant-frequency sounds or silence. The down-sweep sound also elicited more vocal responses than did silence. No significant difference was found between the broadcast chirps and the down-sweep sound. The ratio of wild dugong chirps to all calls and the dominant frequencies of the wild dugong calls were significantly higher during playbacks of broadcast chirps, down-sweep sounds, and constant-frequency sounds than during those of silence. The source level and duration of dugong chirps increased significantly as signaling distance increased. No significant correlation was found between signaling distance and the source level of trills. These results show that dugongs vocalize to playbacks of frequency-modulated signals and suggest that the source level of dugong chirps may be manipulated to compensate for transmission loss between the source and receiver. This study provides the first behavioral observations revealing the function of dugong chirps.

Detection probability of vocalizing dugongs during playback of conspecific calls.

Dugongs (Dugong dugon) were monitored using simultaneous passive acoustic methods and visual observations in Thai waters during January 2008. Chirp and trill calls were detected by a towed stereo hydrophone array system. Two teams of experienced observers conducted standard visual observations on the same boat. Comparisons of detection probabilities of acoustic and visual monitoring between two independent observers were calculated. Acoustic and visual detection probabilities were 15.1% and 15.7%, respectively, employing a 300 s matching time interval. When conspecific chirp calls were broadcast from an underwater speaker deployed on the side of the observation boat, the detection probability of acoustic monitoring rose to 19.2%. The visual detection probability was 12.5%. Vocal hot spots characterized by frequent acoustic detection of calls were suggested by dispersion analysis, while dugongs were visually observed constantly throughout the focal area (p<0.001). Passive acoustic monitoring assisted the survey since detection performance similar to that of experienced visual observers was shown. Playback of conspecific chirps appeared to increase the detection probability, which could be beneficial for future field surveys using passive acoustics in order to ensure the attendance of dugongs in the focal area.

Concentrations of organotin compounds in tissues and organs of dugongs from Thai coastal waters.

Concentrations of butyltin (BT) and phenyltin (PT) compounds were measured in organs and tissues of dugongs (Dugong dugon) from the coastal waters of Thailand. Concentrations of BTs and PTs were in the range of 14-14,468 and <1-30 microg kg(-1)(detection frequency: 79%), respectively. Although concentrations of BTs in dugongs were higher then reported concentrations in cetaceans and pinnipeds, PTs were lower in dugongs. In half of the dugongs in which measurements were made, the concentration of BTs in the liver was the highest among the all the tissues and organs tested. Dibutyltin (DBT) or monobutyltin (MBT) was found to be the dominant compounds among the BTs. The distribution in the body of PTs was not clear because of the lower levels of this compound. TPT was the dominant compound among PTs. The coastal area of Thailand is located off the Gulf of Thailand and the Andaman Sea. Concentrations of organotin (OT) compounds in dugongs collected from the Gulf of Thailand were compared to those from the Andaman Sea. No significant differences in BT or PT concentrations were observed between the two areas (p < 0.05). The concentrations of BTs and PTs in the livers of dugongs were decreased between 1998 and 2002, suggesting a decrease in OT concentrations in the surrounding environment.

Feeding behavior of wild dugongs monitored by a passive acoustical method.

Little is known about feeding behavior of wild dugongs (Dugong dugon) because direct measurements of feeding events in the water were scarcely feasible. In this study, the authors achieved the first successful feeding sound monitoring in a seagrass area using a full-band underwater recording system (called automatic underwater sound monitoring system for dugong: AUSOMS-D). In total, 175 feeding sounds were identified in 205 h of recording. Feeding sounds were only detected at night, implying diurnal differences in the feeding behavior of the studied dugong population. Differences in periodicity of feeding sounds suggested that two or more individuals were in the acoustically observable area. Furthermore, a feeding position monitored by two AUSOMS-Ds was used to calculate source levels of dugong feeding sounds. Assuming spherical_propagation, source levels were measured between 70.6 and 79.0 dB rms re 1 microPa/square root of Hz.

Dugong (Dugong dugon) vocalization patterns recorded by automatic underwater sound monitoring systems.

To quantitatively examine the diurnal, or tidal, effects on dugong behavior, we employed passive acoustic observation techniques to monitor the animals. Automatic underwater sound monitoring systems for dugongs (AUSOMS-D) were deployed on the sea floor at depths of about 5 m south of Talibong Island, Thailand. The AUSOMS-D recorded underwater sound in stereo at a sampling frequency of 44.1 kHz for more than 116 consecutive hours. Dugong calls were automatically detected by newly developed software with a detection rate of 36.1% and a false alarm rate of 2.9%. In total, 3453 calls were detected during the 164 h of recording. The autocorrelation of the call rate indicated an attendance cycle of about 24 or 25 h, and the most frequent vocalizations were observed from 0300 to 0500 h. The calculated bearings of the sound sources, i.e., dugongs, were used as an indicator to track the relative numbers of dugongs during the monitoring periods.

Community perspectives and conservation needs for Dugongs (Dugong dugon) along the Andaman coast of Thailand.

The dugong is classified as vulnerable to extinction by the World Conservation Union on the basis of declines in area or extent of occupancy, habitat quality, and actual or potential levels of exploitation. In Thailand, the largest groups of dugongs are found near islands off the Andaman coast. The authors conducted a 2-year project that included dugong population and habitat assessment as well as interviews with local fishers. The results indicate declining populations of dugongs. The largest threat to dugongs is incidental catch in fishing nets. The numbers of deaths reported place the dugong population along the Andaman Sea in danger of extirpation. Other threats include seagrass destruction both from fishing and coastal development and the use of dugong parts for medicinal purposes. Villagers still show strong ties with dugongs, and the majority favor establishing more large protected areas for the species. These should arise from an integrated national dugong and seagrass conservation strategy formulated by concerned stakeholders from government, non-governmental organizations, scientists, and local communities. The strategy needs to be both top down and bottom up in its formation to balance existing and potential uses as well as conflicts between artisanal and commercial fishers. The strategy should include the development of educational materials and enforceable regulations, as well as the designation of community-protected seagrass beds and a system of dugong sanctuaries along the Andaman coast. An integrated management plan is needed urgently, with the continued input of concerned scientists, to monitor and increase knowledge of dugong behavior and distribution.