The first four chapters of this book present an overview of the ecology of the 13 otter species, their distribution, distinctive features, ecology, evolutionary relationships and habitats. The author reports his vast experience in studies with otters, especially with the Eurasian otter, and whenever possible compares the results with other otter species. To do that, the author traveled around the world visiting otter habitats in Alaska, Thailand, Africa and South America. There is a very good review of the evolution of otters in Chapter 3, which also deals with research and field methods. However, I missed in this section the playback technique, which is giving excellent results with giant otters: it attracts them, thereby permitting researchers to record the gular patches, which can be used to identify individuals and which will probably be similarly successful with other otter species.
There are some typographical errors, including the scientific names of the sea otter on pages 10, 30 and 64 (it should be Enhydra lutris and not Enhydra lutra) and the elephant seal on page 181 (Mirounga angustirostris instead of Mizounga angustirostris). However, these do not detract from the work as a whole. When describing the mating system of the Eurasian otter in chapter 6 the author mentions that this species appears to be polygynous as well as polyandrous. This, in other words, means promiscuity, as polygyny and polyandry together leads to a promiscuous mating system. Another confusion seems to occur on page 81 when describing scent communication amongst otters. It is said that giant otters have interdigital or pedal glands that participate in scent marking. What happens is that, while defecating or urinating, giant otters also liberate scent from the anal and proctodeal glands, spreading everything with their feet. The feet movements may cause the false impression that they possess scent glands on their paws, which to my knowledge have never been described in this species.
Another question is raised when dealing with feeding habits (chapters 7, 8 and 9). The book stresses that Eurasian otters select their prey and that several otter species have been shown to select especially slow, bottom-living fish species rather than fast, pelagic species, noting that this preference probably holds true for all otter species. On the other hand, the author also mentions that otters seem to feed on prey according to their availability. This therefore suggests that otters tend to be opportunistic feeders, at least during some times of the year. Probably what happens is that otters can select their prey when availability is high but feed opportunistically during those periods when prey items are less available. Perhaps more than a preference, otters prey on certain species according to their catchability, i.e. those prey that suit the otters’ hunting ability.
Chapters 10, 11 and 12 deal with thermo-insulation, populations, recruitment, competition, survival and mortality, and present a fantastic review of several aspects of the biology and physiology of otters. However, chapter 11 mentions the black caiman Melanosuchus niger, which would 'frequently steal fish from neotropical otters in the Pantanal'. However, there are no black caimans in the Pantanal, and the caimans that could compete with otters there are probably those of the genera Paleosuchus or Caiman. Chapter 13 presents an excellent synthesis of the subjects from previous chapters, with an emphasis on habitat, foraging and population dynamics. Finally, chapter 14 deals with the anthropogenic actions that influence the conservation of otters.
Overall, I found this book an excellent reference work, providing a great deal of relevant information that will help everyone, from students to researchers, engaged in the study of otters. In particular, several overview chapters provide in depth comparisons and syntheses of otter ecology and conservation. I highly recommend this book.
