Indo‐Pacific humpback dolphins (Sousa chinensis) in the Moyang River Estuary: The western part of the world's largest population of humpback dolphins

1. Information gaps from uninvestigated habitats can hinder population assessments and the efficacy of conservation actions for marine mammals, particularly for populations of widely distributed species. The full extent of occurrence of the world's largest (putative) population of Indo‐Pacific humpback dolphins (Sousa chinensis) in the Pearl River estuary (PRE) is not known due to a poor understanding of the western boundary of the population's range. This information gap is the basis of the most critical obstacle for assessing the population's status.
2. To determine the distribution and abundance of the PRE humpback dolphins in the far western portion of its range, systematic line‐transect vessel surveys were conducted in the Moyang River estuary (MRE) during 2013–2015. Photo identification of dolphins and cross‐matching of individual dolphins between different regions were also undertaken to examine individual movement patterns.
3. The abundance of humpback dolphins in the MRE was estimated to be 528 individuals (coefficient of variation: 28.7–50.2%).
4. Cross‐matching of individually identified dolphins from the MRE (present survey area) with those from other survey areas of the PRE showed that dolphins moved frequently across different regions of the PRE, indicating dolphins from both PRE and MRE comprise a single population (which is renamed to be the PRE–MRE population). The western boundary of this population appears to be in the waters on the eastern side of Hailing Island, as dolphins were never observed further west.
5. Supporting around one‐fifth of the PRE–MRE population and providing a quarter of the habitat of the entire PRE–MRE population, the MRE clearly also deserves consideration for greater conservation measures. Strengthening the management with stringent controls over fishing activities in the MRE and establishing a marine protected area in the core habitat are recommended to facilitate better conservation for the entire PRE–MRE humpback dolphin population.

     

Changing distribution of the east coast of Scotland bottlenose dolphin population and the challenges of area‐based management

1. The efficacy of marine protected areas (MPAs) depends on clear conservation objectives and ecologically meaningful boundaries. The east coast of Scotland bottlenose dolphin population expanded its distributional range during the 1990s beyond the boundaries of the Moray Firth Special Area of Conservation (SAC), originally proposed to contain their core area of distribution. Two decades on, this study assesses the importance for this population of St Andrews Bay and the Tay estuary, 300 km south of the SAC.
2. Photoidentification data from 2009 to 2015 were analysed using mark–recapture models to investigate the proportion of the population that uses St Andrews Bay and the Tay estuary. Habitat models were fitted to bottlenose dolphin presence–absence data to identify areas of high use.
3. The estimated number of dolphins using St Andrews Bay and the Tay estuary during the summer increased from 91 (95% confidence interval 78–106) in 2009 to 114 (95% confidence interval 95–137) in 2015, representing, on average, 52.5% of the total estimated east‐coast population for that period. Spatial mixing of individuals during the summer between St Andrews Bay and the Tay estuary and the Moray Firth SAC was estimated to be a minimum of ~6% per year and ~30% over the study period. The entrance to the Firth of Tay and waters around Montrose were identified as areas of consistent high use.
4. The importance of St Andrews Bay and the Tay estuary reconfirms that effective monitoring of the population requires dedicated effort in both this area and the SAC. The results lead to consideration of the wider context of area‐based management for the conservation/management of highly mobile wide‐ranging species and human activities that might impact them.

     

Habitat use of a coastal delphinid population investigated using passive acoustic monitoring

1. The population of bottlenose dolphins in eastern Scotland has undergone significant range expansion since the 1990s, when a Special Area of Conservation was established for the population.
2. Distribution of this population is well described within areas of its range where intensive work has been carried out, such as the inner Moray Firth, St Andrews Bay and the Tay estuary area. However, elsewhere in their range, habitat use is less well understood.
3. In this study, a large‐scale and long‐term passive acoustic array was used to gain a better understanding of bottlenose dolphin habitat use in eastern Scottish waters, complementing and augmenting existing visual surveys.
4. Data from the array were analysed using a three‐stage approach. First, acoustic occupancy results were reported; second, temporal trends were modelled; and third, a spatial–temporal‐habitat model of acoustic occupancy was created.
5. Results from the acoustic occupancy are in agreement with visual studies that found that areas near known foraging locations were consistently occupied. Results from the temporal trend analysis were inconclusive. Habitat modelling showed that, throughout their range, bottlenose dolphins are most likely to be detected closer to shore, and at a constant distance from shore, in deeper water.

     

Changes in habitat use patterns by bottlenose dolphins over a 10‐year period render static management boundaries ineffective

1. Bottlenose dolphins (Tursiops truncatus) in northern New Zealand range widely and their coastal distribution increases their risk of exposure to a variety of threats.
2. Marine protected areas (MPAs) are increasingly used to protect species but there is a paucity of studies examining their efficacy.
3. In the Bay of Islands, New Zealand (35°14'S, 174°06'E), dolphin distribution and habitat use patterns were examined between two time periods: 1996–2000 and 2007–2010. In addition, dolphin use of tourism exclusion zones designed to protect the dolphins were assessed.
4. Spatial distribution was analysed using kernel densities and Mantel tests.
5. Broad‐scale distribution patterns remained constant between the two periods but fine‐scale dolphin distribution patterns shifted considerably.
6. The exclusion zones that were established based on results from the 1996–2000 study were rarely used in 2007–2010, and therefore no longer provided dolphins protection from tourism.
7. This research demonstrates the plasticity in dolphin habitat use patterns through time and the importance of re‐evaluating the efficacy of static protected areas, especially for wide‐ranging species.

Copyright © 2014 John Wiley & Sons, Ltd.     

The abundance of common bottlenose dolphins (Tursiops truncatus) in the former special marine reserve of the Cres‐Lošinj Archipelago,Croatia

1. There is a resident common bottlenose dolphin population inhabiting the Kvarneri? area of the northern Adriatic Sea, Croatia. The observed decline in population size between 1995 and 2003 led to the declaration of a part of the Kvarneri? as the Cres‐Lo?inj Special Marine Reserve (CLSMR) in 2006. Protection lasted 3 years, before lapsing.
2. A boat based photo‐identification study was conducted between 2004 and 2011 with the aim to estimate the number of bottlenose dolphins inhabiting the CLSMR area, investigate the factors influencing their habitat use and explore the possibility that this area is representative of the population for the whole Kvarneri?.
3. Standard mark–recapture methods and the M_th estimator of Chao for closed populations were applied. The lowest value was estimated in 2008 (N = 112; 95% CI = 94–150) and the highest in 2006 (N = 310; 95% CI = 265–392). The statistically significant inter‐annual variability is likely to reflect natural and anthropogenic driven shifts in habitat use rather than real changes in population size.
4. The average monthly sighting rate was lower in the tourist season (Jun–Aug) than in the pre‐ and post tourist‐season, suggesting that developed nautical tourism may influence shifts in habitat use. Other potential causes are distribution of prey and fishing effort.
5. Inclusion of data from the rest of the Kvarneri? for the years of 2005 and 2011 did not reveal a significant increase in estimated abundance (2005: z = ?0.413, P = 0.3398; 2011: z = ?1.749, P = 0.0401). This indicates that the CLSMR area is representative of the whole Kvarneri?.
6. The number of bottlenose dolphins using the CLSMR area seems to have increased compared with the previous study (1995–2003). This could be due to a shift in habitat use or an increase in population size. However, yearly variations indicate processes causing displacements within the dolphin population home range. Conservation measures aiming at reducing the displacements are proposed.

Copyright © 2013 John Wiley & Sons, Ltd.     

Habitat use by a freshwater dolphin in the low‐water season

1. Many river dolphin populations are most vulnerable during the low‐water season when habitat is limited. Indus River dolphin habitat selection in the dry season was investigated using Generalized Linear Models of dolphin distribution and abundance in relation to physical features of river geomorphology and channel geometry in cross‐section.
2. Dolphins selected locations in the river with significantly greater mean depth, maximum depth, cross‐sectional area, and hydraulic radius, and significantly narrower river width and a lower degree of braiding than areas where dolphins were absent. They were also recorded with higher frequency at river constrictions and at confluences.
3. Channel cross‐sectional area was the most important factor affecting dolphin presence and abundance, with the area of water below 1 m in depth exerting the greatest influence. Indus dolphins avoided channels with small cross‐sectional area (<700 m²), presumably owing to the risk of entrapment and reduced foraging opportunities.
4. Channel geometry had a greater ability to explain dolphin distribution than river geomorphology; however, both analyses indicated similar types of habitat selection. The dolphin–habitat relationships identified in the river geomorphology analysis were scale‐dependent, indicating that dolphin distribution is driven by the occurrence of discrete small‐scale features, such as confluences and constrictions, as well as by broader‐scale habitat complexes.
5. There are numerous plans to impound or extract more water from the Indus River system. If low‐water season flows are allowed to decrease further, the amount of deeper habitat will decline, there may be insufficient patches of suitable habitat to support the dolphin population through the low‐water season, and dolphins may become isolated within deeper river sections, unable or unwilling to traverse through shallows between favourable patches of habitat.

Copyright © 2012 John Wiley & Sons, Ltd.     

Demography of southern Australian bottlenose dolphins living in a protected inverse estuary

1. Assessments of demographic parameters are essential to understand the dynamics of wild populations, and for their efficient conservation and management. Here, sex‐specific abundance, apparent survival and temporary emigration of southern Australian bottlenose dolphins (Tursiops cf. australis ) in Coffin Bay (CB), South Australia, is investigated.
2. Results are based on capture–recapture modelling of photo‐identification data and molecular analyses of biopsy samples collected during boat‐based surveys between September 2013 and October 2015 in the inner and outer areas of CB.
3. The total super‐population of dolphins (including calves) using the entire study area (263 km²) was estimated with POPAN models at 306 (95% CI: 291–323), which included 71 (68–73) marked females and 57 (55–60) marked males.
4. Seasonal estimates of abundance for the inner area of CB (123 km²) obtained with Pollock's Closed Robust Design models remained relatively constant over the two years (marked females: 52–60, marked males: 46–52, and total: 193–209).
5. The high density of dolphins inhabiting the inner area (seasonal range: 1.57–1.70 individuals km^?2), high apparent survival rates estimated for both sexes (females: 0.99; 95% CI: 0.96–1.0; males: 0.95; 0.82–0.99), and low temporary emigration rates (0.02; 95% CI: 0.01–0.11) indicate that the inner area of CB offers highly favourable habitat for these dolphins.
6. High biological productivity and low predation risk may promote these demographic patterns in the inner area of CB.
7. This study provides a robust baseline of sex‐specific population demographics of southern Australian bottlenose dolphins with important implications for future research and their management and conservation in South Australia.

     

Dusky dolphin foraging habitat: overlap with aquaculture in New Zealand

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Distribution,abundance, and movements of the bottlenose dolphin (Tursiops truncatus) in the Pelagos Sanctuary MPA (north‐west Mediterranean Sea)

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Determining spatial use of the world's second largest humpback dolphin population: Implications for place‐based conservation and management

1. Place‐based management can be an effective conservation tool to protect cetaceans from anthropogenic pressures. The spatial use of the world's second largest population of the threatened Indo‐Pacific humpback dolphins (Sousa chinensis) is not well‐documented, which makes it challenging to designate protected areas for this population.
2. To address this knowledge gap and to test the efficacy of an existing dolphin protected area (Zhanjiang Leizhou Bay Municipal Humpback Dolphin Nature Reserve, ZLBMHDNR), boat‐based surveys were conducted to document dolphin occurrence from 2015 to 2018, covering an area of 1221 km² in the eastern waters off Zhanjiang, China. In total, 253 dolphin group sightings were obtained during 174 survey days.
3. Spatial analysis showed that humpback dolphins aggregated in three core‐use areas with higher sighting density within the survey area. Furthermore, intermediate‐use and broad‐use areas were identified that could be essential for the movements of humpback dolphins among these core‐use areas.
4. The spatial usage of humpback dolphins was compared inside and outside the ZLBMHDNR. Results suggest that the ZLBMHDNR is insufficient to encompass a significant portion of dolphin habitat. The ZLBMHDNR (21 km²) is not large enough, and thus it should be expanded for effective place‐based conservation management in this region.
5. For developing a protected area network, important dolphin habitats identified in this study should be protected as a single management unit. Additionally, mitigation of anthropogenic pressures is needed to be taken into consideration as conservation initiatives in the study area.
6. This study provides support for a more science‐informed protected area network, and highlights the necessity of implementing place‐based conservation and management for the world's second largest humpback dolphin population.