Multiple stressors and data deficient populations; a comparative life-history approach sheds new light on the extinction risk of the highly vulnerable Baltic harbour porpoises (Phocoena phocoena)

Many endangered marine mammal populations are difficult to study, spread out over large areas, and capturing them for branding and research purposes would be unethical. Yet, they are in urgent need for assessment and conservation actions. We suggest collecting data from other more abundant populations of the same species, with careful consideration of body size, age at sexual maturity, and ecological conditions to produce scientifically sound best approximations of vital rates of data deficient endangered populations. The genetically distinct Baltic Sea harbour porpoise population amounts to about 500 animals and is classified as 'Critically Endangered' according to the IUCN red list. Data deficiency on nearly all demographic parameters have precluded systematic investigations of the relative importance of stressors affecting population viability. We took a comparative life history approach and investigated the phenotypic plasticity in somatic and demographic vital rates of seven larger, well studied North Atlantic harbour porpoise populations, enabling us to approximate the missing pieces of the life history of the Baltic population. We parameterized a stochastic, individual-based population model, and performed a population viability analysis for a range of biologically realistic parameter values and scenarios of environmental stressors. The baseline scenario was based on the most representative samples of healthy harbour porpoise populations and challenged with three different levels of bycatches. Due to high levels of endocrine disruptive contaminants observed in Baltic harbour porpoises, we also investigated the effect of a possible reduction in fecundity. Subsequently, the combined effects of bycatches and reduced fecundity were investigated in terms of population growth rate and quasi-extinction risk. The Baltic harbour porpoise population is viable in the baseline scenario without anthropogenic stressors. However, even the lowest estimated bycatch level of 7 individuals per year will lead to a population collapse to ≤50 animals with high probability (0.4-1.0) over the next century, assuming an intermediate or low (<73%) fecundity. Adult survival is of critical importance and mitigation of fishery impacts and reduction of anthropogenic disturbances in the identified main breeding areas are recommended.

How 'Blue' Is 'Green' Energy?

Often perceived as environmentally benign, 'green' renewable energy technologies have ecological costs that are often overlooked, especially those occurring below the waterline. After briefly discussing the impacts of hydropower on freshwater and marine organisms, we focus this review on the impacts of marine renewable energy devices (MREDs) on underwater marine organisms, particularly offshore wind farms and marine energy converters (e.g., tidal turbines). We consider both cumulative impacts and synergistic interactions with other anthropogenic pressures, using offshore wind farms and the Taiwanese white dolphin (Sousa chinensis taiwanensis) as an example. While MREDs undoubtedly can help mitigate climate change, variability in the sensitivity of different species and ecosystems means that rigorous case-by-case assessments are needed to fully comprehend the consequences of MRED use.

Severe mutilation of a Critically Endangered Taiwanese humpback dolphin Sousa chinensis taiwanensis by fishing gear

Direct observations of the causes of injuries to cetaceans are rare events. For very small and declining populations, such events may be even less likely to be observed because of the few individuals that remain. A long-term monitoring program using photographic identification of individuals resulted in the documentation of an individual Taiwanese humpback dolphin Sousa chinensis taiwanensis that survived a harmful interaction with fishing gear. An adult female that was accompanied by a young calf sustained massive damage to several tissue types on her dorsal surface. From the injuries, it is clear that the animal had suffered intense trauma that likely caused pain for several months as the fishing gear sliced through its dorsal hump and fin. Given the incredible mutilation, the animal is likely compromised at some level and probably continues to experience ongoing pain. This case, along with observations of other individuals in this population bearing serious injuries or being entangled in fishing gear, is direct evidence that the impacts of local fisheries on this subspecies are almost certainly unsustainable.

Unsustainable human-induced injuries to the Critically Endangered Taiwanese humpback dolphins (Sousa chinensis taiwanensis)

The Critically Endangered Taiwanese humpback dolphin (Sousa chinensis taiwanensis) is endemic to inshore and estuarine waters of central western Taiwan. It numbers fewer than 75 individuals, is declining and faces a myriad of human threats. Data from a long-term photo-identification program on these dolphins allowed major injuries to be examined quantitatively. A large proportion (57.7%) of individuals had suffered major human-induced injuries that likely compromised their health, survivorship or reproductive potential and thus, the future of this subspecies. Considering major injuries as "takes", the injury rate (1.13 dolphins/year) for the population was 8-8.5 times higher than its Potential Biological Removal rate. Observations of new injuries and fishing gear entanglements on several dolphins showed that fisheries continue to be the predominant cause of these major injuries. Unless immediate action is taken to reduce harmful fisheries, extinction is imminent for Taiwan's only endemic dolphin.

Re-assessment of the Conservation Status of the Indo-Pacific Humpback Dolphin (Sousa chinensis) Using the IUCN Red List Criteria

The IUCN Red List designation of the Indo-Pacific humpback dolphin (Sousa chinensis) is re-assessed in light of its newly recognized taxonomic status (it has recently been separated into three species) and findings that humpback dolphins along the coast of Bangladesh, and possibly eastern India, are phylogenetically distinct from other members of the Sousa genus. Sousa chinensis is found in Southeast/South Asia (in both the Indian and Pacific oceans), from at least the southeastern Bay of Bengal east to central China, and then south to the Indo-Malay Archipelago. There are no global population estimates, and the sum of available abundance estimates add up to about 5700 individuals, although only a portion of the range has been covered by surveys. This species occurs in shallow (<30m deep), coastal waters of the tropics and subtropics, and feeds mainly on small fishes. It has a similar reproductive biology to other large dolphins, occurs mostly in small groups, and generally has individual movements of about 50-200km(2). Major threats throughout the range include entanglement in fishing nets (primarily gillnets) and habitat destruction/degradation, although in some more industrialized areas, vessel traffic, and environmental contamination from organochlorines are also serious issues. Conservation management is largely lacking in most parts of the species' range, although there has been significant (though still inadequate) attention in some parts of China (e.g. Hong Kong and adjacent areas, and Taiwan). Much greater efforts are needed toward conservation of Indo-Pacific humpback dolphins to stop apparent declines, and to lower the species' extinction risk. Sousa chinensis meets the IUCN Red List requirements for Vulnerable (under criteria A4cd), with fisheries bycatch and habitat loss/degradation being the main pervasive threats.

Biology and Conservation of the Taiwanese Humpback Dolphin, Sousa chinensis taiwanensis

The humpback dolphins of the eastern Taiwan Strait were first discovered scientifically in 2002 and since then have received much research attention. We reviewed all information published in peer-reviewed scientific journals on these dolphins and where appropriate and available, peer-reviewed scientific workshop reports and graduate theses were also examined. Recent evidence demonstrated that this population warranted recognition as a subspecies, Sousa chinensis taiwanensis. It is found in a highly restricted and linear strip of coastal waters along central western Taiwan. Numbering fewer than 80 individuals and declining, five main threats (fisheries interactions, habitat loss and degradation, loss of freshwater to estuaries within their habitat, air and water pollution, and noise) threaten the future existence of this subspecies. These dolphins have cultural and religious importance and boast the highest level of legal protection for wildlife in Taiwan. However, despite enormous efforts by local and international non-governmental groups urging immediate conservation actions, there have been no real government efforts to mitigate any existing threats; instead, some of these threats have worsened. Based on recent studies, we suggest the IUCN Red List status be revised to Critically Endangered CR 2a(ii); D for the subspecies.

Diagnosability and description of a new subspecies of Indo-Pacific humpback dolphin, Sousa chinensis (Osbeck, 1765), from the Taiwan Strait

BACKGROUND

Subspecies recognition can affect how people (scientists and non-scientists alike) view organisms and thus has important implications for research on, as well as the conservation of, these entities. Recently, a small group of Indo-Pacific humpback dolphins was discovered inhabiting the waters off central western Taiwan. This geographically isolated population possesses pigmentation patterns that are subtly, but noticeably, different from their nearest conspecifics in the neighbouring waters of the Jiulong River Estuary and Pearl River Estuary of mainland China. Due to this population's low and declining numbers and the numerous threats it faces, it was assessed as critically endangered by the Red List of Threatened Species of the International Union for Conservation of Nature. The purpose of this study is to examine the degree of differentiation of the Taiwanese population to determine if subspecies recognition iswarranted.

RESULTS

Analysis of the degree of differentiation in pigmentation patterns revealed nearly non-overlapping distributions between dolphins from Taiwanese waters and those from the Jiulong River + Pearl River estuaries of mainland China (the nearest known populations). The Taiwanese dolphins were clearly diagnosable from those of the Jiulong River + Pearl Riverestuaries under the most commonly accepted '75%rule' for subspecies delimitation (with 94% of one group being separable from 99+% of the other). Evidence of geographical isolation and behavioural differences also provided additional support for the distinctiveness of the Taiwanese dolphins.

CONCLUSIONS

Together, the evidence strongly demonstrated that the Taiwanese humpback dolphin population is differentiated at the subspecies level and on an evolutionary trajectory that is independent from that of dolphins from adjacent waters of mainland China (i.e. Jiulong River + Pearl River estuaries). As a result, the taxonomy of Sousa chinensis was revised to include two subspecies: the Taiwanese humpback dolphin, Sousa chinensis taiwanensis subsp. nov., and the Chinese humpback dolphin, Sousa chinensis chinensis (the nominotypical subspecies). These subspecies are described, and the holotype and paratype specimens for S. c. taiwanensis are established.