2013 85 Ecology and Conservation of the Sirenia. Dugongs and Manatees

2013 BOOK REVIEWS 85 Ecology and Conservation of the Sirenia. Dugongs and Manatees By Helene Marsh, Thomas J. O’Shea and John E. Reynolds III. 2011. Conservation Biology 18, Cambridge University Press, Cambridge, U.K. 521 pages, 65.00 USD, Paper. There is no doubt that this is a scholarly treatise of extinct Stellar’s Sea Cow, evolution, feeding biology, the Dugongs and Manatees of the world. The authors behaviour and habitat use, life history and population have combed the scientific literature to compile an dynamics, threats, conservation status, and conservation exhaustive summary of the evolutionary history, biol- opportunities. For each topic, the available science is ogy and conservation status and challenges of the Sire- presented in a systematic and progressive manner for nia (Manatees and Dugongs) of the world. As such, it each of the four extant species, on occasion also refer- is of primary interest to Sirenian researchers and con- encing the Stellar’s Sea Cow and ancestral Sirenians. servation biologists. However, there is still much here Chapters end with an excellent summary comprising of interest to the general reader with a broad interest conclusions, implications for conservation and sug- in natural history and conservation. gestions for future research. Surprisingly little is known Four Sirenian species are distributed in warm, shal- about several aspects of Sirenian biology and ecology, low tropical and subtropical waters around the globe and the authors do an excellent job of weaving togeth- today – the Dugong, West Indian Manatee, West Afri - er disparate research on the various Sirenian species can Manatee and Amazonian Manatee. This book deliv- into a cohesive, logical and comprehensive compila- ers on the promise of its title. Every aspect of the ecol- tion. The subject is extremely well researched, and the ogy of present day Manatees and Dugongs, as well as reader gets the impression that virtually every published other species from the evolutionary past, is detailed in source dealing with Sirenian life history and conserva- a few very detailed and very comprehensive chapters, tion has been consulted in the writing of this treatise. with a common and recurring focus on the conserva- Even interesting minor facts are included, such as the tion status and recovery potential of this imperilled facts that both Dugongs and Manatees have died order of marine mammals. through impalement on the barbs of rays, that Mana- The biology of all four Sirenian species is covered in tees are less tolerant of approaching scuba divers than a thorough and well organized manner, covering exten- snorkellers, that there were past attempts to harness sive subject matter in broad chapters devoted to the Manatees to clear vegetation-infested canals, and that 86 THE CANADIAN FIELD -N ATURALIST Vol. 127 there is an international citizen science initiative (Sea - that is required, simply because it is easier, and that grass-Watch) devoted to the monitoring of coastal sea - sometimes the main threat to conservation is “our in - grass communities (the principal forage of Sirenians). ability to solve conservation problems, even when the The chapter on evolutionary history is the only one issues and potential mitigation options are identified that is perhaps too detailed for the general reader. While proactively”. the topic is thoroughly and exhaustively covered, the The book is well produced technically. It is well sup - complexity of various prehistoric species – the fossil plied with interesting and informative figures, photo - record, the intricacies of their evolution and phylogeny, graphs and tables portraying various aspects of Siren - their scientific names and places in the family tree, ian life history and ecology. Additionally, there are their DNA and genetic linkages, may be too much for many insert boxes distributed throughout the text that all but the most dedicated and most interested reader. provide interesting supplemental details on the general In contrast, one extremely fascinating and illuminat - topic being discussed. There are only a few puzzling ing chapter is devoted to the natural history and mod - and less than ideal uses of figures and tables. The ern-day extinction of the Stellar’s Sea Cow, the only numerous black and white photographs are placed modern-day Sirenian that occurred in cool northern throughout the text, readily located immediately after latitudes, and whose large size, slow movements, and their reference in the text. However a subset of colour incomplete diving behaviour made it extremely attrac - photographs is also inserted in the centre of the book tive as an easy food source for 18 th century explorers without any specific reference or rationale for why they and a prime and very vulnerable candidate for early are included, and duplicating only a small portion of the extirpation. many black and white figures. While the photographs Conservation challenges are many and varied. Be - undoubtedly add value, they also provoke confusion as y ond the general exposure to a fascinating and little there is no hint to the reader or any apparent logic as known order of marine mammals that faces serious to when there is a duplicate colour copy of the image conservation challenges world-wide, by far the most that could be referred to, and they appear almost an interesting aspects of this book to general naturalists afterthought. Another irksome detail pertains to the and non-marine mammal specialists are likely to be the inset of multiple (14) small boxes over a span of 60 sections on the current status, threats and conservation pages all pertaining to various threats to Sirenian pop - opportunities for all four species. There are many gen - ulations as they were individually identified in the text. eral conclusions and observations that are relevant to The first few boxes were very difficult to understand, the conservation of many marine mammal species. The as they show only a single bar for each species, with multiple threats from climate change are clear and wor - text indicating that the degree of shading reflects the risome globally, as are the effects of harvest and habi - severity of the threat. The meaning of the reference is tat degradation. Harvest, both intentional and inciden - only discerned after viewing several of these miniature tal, is still an issue for all Sirenians except the Florida charts, particularly as the bars in the first chart were Manatee; in many areas of the globe a Manatee or only black and white. It would have been much clear - Dugong carcass provides a substantial enhancement er and much more useful to have compiled all of these to family income or food. It is clear that there is much threats and their degree of severity into a single com - more research and management effort directed towards prehensive table. Another cumbersome use of the oth - the West Indian Manatee, particularly in Florida, than erwise very informative inset boxes was a box (7.6) that for the other Sirenian species; yet even for that species, asked several questions raised about the adequacy of there are clearly significant knowledge gaps. Mortal - warm-water refugia for Florida Manatees; a second ity from motorboat strikes remains a major mortality box (7.7) two pages later repeated these same ques - factor for Florida Manatees; even with some regula - tions with very short answers; one inset box would tions on motorboat speed the authors note that Florida have sufficed. But these are admittedly minor criticisms Manatee conservation is hampered by the “perceived in an extremely well-written and well-researched book. right to travel by boat over publicly owned waters at Ecology and Conservation of the Sirenia. Dugongs unregulated speeds wherever they wish”. and Manatees is an obvious labour of love, and an Beginning with the chapter on Threats, the tone of encyclopaedic summary of research on four widely the book gradually and subtly shifts from the presenta - dispersed Sirenian species facing many different life tion of objective scientific data to that of science-based history challenges and human threats throughout their advocacy, for example challenging ‘slow-moving sci - range. It is also a call to action for difficult decisions entific and management communities”. The authors and essential conservation actions, a call that will res - challenge Sirenian managers and those managing other onate with all conservation-minded readers. similarly-challenging species, pointing out that addi - tional research and monitoring of Sirenian populations TED ARMSTRONG is often undertaken when it is urgent management action 615 Rosewood Crescent, Thunder Bay, Ontario, P7E 2R5.

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