Re-assessment of the Conservation Status of the Atlantic Humpback Dolphin, Sousa teuszii (), Using the IUCN Red List Criteria

The biogeography of group sizes in humpback dolphins (Sousa spp.)

Humpback dolphins (Sousa spp.) are obligate shallow-water and resident species, and they typically live in fission-fusion societies composed of small-sized groups with changeable membership. However, we have scant knowledge of their behavioral ecology, starting with potential factors influencing inter-population variability of their group sizes. Here, we compiled a new global dataset of humpback dolphin group sizes based on 150 published records. Our data indicated an inter-specific consistency of group-living strategy among the 4 species in the Sousa genus, as these species preferred living in small-sized groups with a mean size of mostly no more than 10, a minimum size of single individual or small pairs, and a maximum size of several tens or ≈100. In addition, we clearly showed the geographic variations in group sizes of humpback dolphins at a global scale. We found that the geographic variations in humpback dolphin group sizes were primarily associated with the latitude, sea surface temperature, and abundance. To conclude, our findings provide insights into social dynamics and socioecological trade-offs of humpback dolphins, and help better understand how these resident animals adapted to their shallow-water habitats from the perspectives of biogeography and socioecology.

The complete mitochondrial genome of the critically endangered Atlantic humpback dolphin, Sousa teuszii (Kükenthal, 1892)

The Atlantic humpback dolphin remains an understudied, critically endangered cetacean species. Here, we describe the first complete mitogenome of Sousa teuszii, derived from an animal stranded on Île des Oiseaux, Sine Saloum, Senegal. The S. teuszii mitogenome is composed of 16,384 base pairs and is 98.1% identical to its closest relative with a mitogenome, Sousa chinensis. Phylogenetic analysis confirms its placement with S. chinensis, as well as the placement of the genus Sousa within subfamily Delphininae.

Threshold of long-term survival of a coastal delphinid in anthropogenically degraded environment: Indo-Pacific humpback dolphins in Pearl River Delta

Defining demographic and ecological threshold of population persistence can assist in informing conservation management. We undertook such analyses for the Indo-Pacific humpback dolphin (Sousa chinensis) in the Pearl River Delta (PRD) region, southeast China. We use adult survival estimates for assessments of population status and annual rate of change. Our estimates indicate that, given a stationary population structure and minimal risk scenario, ~2000 individuals (minimum viable population in carrying capacity, MVP_k) can maintain the population persistence across 40 generations. However, under the current population trend (~2.5% decline/annum), the population is fast approaching its viability threshold and may soon face effects of demographic stochasticity. The population demographic trajectory and the minimum area of critical habitat (MACH) that could prevent stochastic extinction are both highly sensitive to fluctuations in adult survival. For a hypothetical stationary population, MACH should approximate 3000-km². However, this estimate increases four-fold with a 5% increase of adult mortality and exceeds the size of PRD when calculated for the current population status. On the other hand, cumulatively all current MPAs within PRD fail to secure the minimum habitat requirement to accommodate sufficiently viable population size. Our findings indicate that the PRD population is deemed to become extinct unless effective conservation measures can rapidly reverse the current population trend.

A Review of the Status of the Indian Ocean Humpback Dolphin (Sousa plumbea) in Pakistan

Limited historical and new information on Indian Ocean humpback dolphins, Sousa plumbea, in Pakistan are reviewed. Although present along most of the coast, S. plumbea concentrates in the mangrove-lined creek system of the Indus Delta (Sindh), Miani Hor (Sonmiani Bay), Kalmat Lagoon, Gwadar and the Dasht River estuary (Gwater Bay, Jiwani). Other areas of distribution comprise the Karachi coast, Kund Malir, Ormara and Pasni. In the Indus Delta, 46 small-boat surveys conducted monthly (minus July and October) in 2005-2009, documented 112 sightings (439 individuals) in major creeks, smaller channels and nearshore waters. Group sizes ranged from 1-35 animals (mean=3.92±4.60). Groups of 1-10 animals composed 91% of total (27.9% single animals). An encounter rate of 0.07-0.17 dolphins km(-1) lacked a significant trend across survey years. A discovery curve remained steep after 87 dolphins were photo-identified, suggesting the population is vastly larger. In Sonmiani Bay, Balochistan, during 9 survey days in 2011-2012, group sizes ranged from 1-68 animals (mean=11.9±13.59; n=36), totalling 428 dolphins. Incidental entanglements, primarily in gillnets, pollution (especially around Karachi), overfishing and the ship breaking industry in Gaddani, pose major threats. Incidental catches occur along the entire Pakistani coast. Of 106 stranded cetaceans, 24.5% were S. plumbea. Directed takes in Balochistan, driven by demand for bait in shark fisheries, have reportedly declined following dwindling shark stocks. Habitat degradation threats include depletion of prey and increased maritime traffic. Domestic sewage and solid waste pollution are predominant on the Balochistan coast, especially at Miani Hor, Kund Malir, Ormara, Kalmat Lagoon, Pasni, Gwadar and Jiwani. An exhaustive habitat assessment combined with appropriate fishery management is the only way to safeguard the future of S. plumbea in Pakistan.

Humpback Dolphins: A Brief Introduction to the Genus Sousa

The delphinid genus Sousa has recently undergone a major revision, and currently contains four species, the Atlantic humpback (Sousa teuszii), Indian Ocean humpback (Sousa plumbea), Indo-Pacific humpback (Sousa chinensis), and Australian humpback (Sousa sahulensis) dolphins. Recent molecular evidence suggests that humpback dolphins in the Bay of Bengal may comprise a fifth species. These moderate-sized dolphin species are found in shallow (<30m), coastal waters of the eastern Atlantic, Indian, and western Pacific oceans. Abundance and trends have only been studied in a few areas, mostly in eastern Africa, China, and northern Australia. No global, empirically derived abundance estimates exist for any of the four species, but none appear to number more than about 20,000 individuals. Humpback dolphins feed mostly on small fishes, and sometimes shrimps; occur for the most part in small groups (mostly 12 or less); have limited nearshore movements; and in most parts of their range exhibit a fission/fusion type of social organization. Major threats that affect all the species are entanglement in fishing gear, and habitat degradation/destruction from various forms of coastal development. Impacts from vessel traffic (including behavioural disturbance and displacement, as well as mortality and morbidity from collisions with vessels) appear to be significant in most areas. Several other threats are apparently significant only in particular parts of the range of some species (e.g. high levels of organochlorine contaminants affecting Indo-Pacific humpback dolphins in Hong Kong). Direct hunting only occurs in limited areas and primarily on a small scale. Conservation actions so far have been limited, with most populations receiving little study and almost no management attention. Much more work is needed on humpback dolphin population status, threats, and how the major threats can be reduced or eliminated. Extinction risks for the four species and some populations are preliminarily re-assessed using the IUCN Red List criteria in the current volume. The results suggest that all four species in the genus are threatened at some level (suggested Red List status ranges from Vulnerable for S. chinensis and S. sahulensis to Critically Endangered for S. teuszii).