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Journal of Experimental Marine Biology and Ecology 244 (2000) 157–158
www.elsevier.nl / locate / jembe
Book review
Marine Mammal Survey and Assessment Methods
Edited by G.W. Garner, S.C. Amstrup, J.L. Laake, B.F.J. Manly, L.L. McDonald, and D.G. Robertson, Balkema, Rotterdam; 1999; 287 pp.; GBP 80.00; ISBN 90-5809-043-4.
This book comprises the proceedings of a Symposium on Surveys, Status and Trends of
Marine Mammal Populations, which took place in Seattle, Washington, USA, 25–27 February 1998. The aim of the Symposium was to ‘‘gather top international marine biologists and biometricians to present and discuss state of the art methods and theories for estimating marine mammal populations’’.
Estimates of marine mammal population size are important for conservation and management: ‘‘population estimates are the most direct method for monitoring popula-tion status’’ (p. 28). However, obtaining estimates with a good degree of certainty is at present all but impossible. Survey estimates have wide confidence limits due mainly to the lack of prior knowledge about the populations and the low densities encountered. Other problems include non-homogeneous populations, animals avoiding or being attracted to survey boats, sensitivity to weather conditions, and expense in terms of money, personnel and platforms (ship or airline time). A particular problem for surveys of mammals in the sea is that animals on the transect line are not necessarily visible.
The book is a compilation of papers from the symposium and is divided into three parts: Survey design and application, Visibility bias and missed observations and
Modelling. Each section consists of a series of contributed papers and, perhaps inevitably, there is some overlap in subject matter between sections. There is a preface, but otherwise the editors do not summarise or comment on the outcome of the symposium. I would have liked to see an introduction dealing with more general terms and explaining the methods employed nowadays to estimate marine mammal popula-tions, their pros and cons – perhaps, as Hiby and Hammond (1989) put it, ‘‘a comprehensive how-to-do-it guide for researchers about to embark on a survey’’.
The first part of the book comprises seven papers from the introductory session of the original symposium and a session on low density over large areas. Although the introductory session included presentations on ‘‘the status of attempts to estimate marine mammal populations’’, this part of the book places more emphasis on details of possible modifications to improve survey design and deal with particular biases. It does not attempt to provide a review or introduction to the subject. The subjects of the papers include:
158 Book review / J. Exp. Mar. Biol. Ecol. 244 (2000) 157 –158
• application of adaptive line transect sampling and how this method fared against traditional line transect sampling in estimating number of harbour porpoises in the Gulf of Maine (it was 8% better);
• application of an aerial survey method (with intensive searches within portions of strip transects) to estimate sea otter numbers in Prince William Sound in Alaska; • analysis of the utility of aerial transect methods to estimate population numbers of
polar bears in the Barents Sea;
• evaluation of line transect methodology for the assessment of polar bear population size in Northern Alaska;
• a simulation to study the effect of survey interval on estimated abundance.
The ten papers in the second part of the book deal with ‘‘describing methods for estimating density when an unknown proportion of the animals being surveyed are unavailable for sightings at the time of the survey . . . or when an unknown proportion of the animals being surveyed are visible but missed during the aerial survey’’. These papers indeed cover the problem of detectability in considerable detail, including derivation of the mathematical formulae required for estimation of abundance. However, they also contain much information on proposed modifications to survey design, including use of combinations of design types such as line transect and capture-recapture methods. Thus, there is some overlap with the first section of the book.
Finally, in the third and potentially most interesting part of the book, survey data and life history parameters are used to assess population status. Sadly, this is the part with fewest contributions (only 4 papers). The book also includes an index of keywords and an author index.
In summary, this book tells you a lot about possible detailed technical improvements to survey methods without telling you how to do a survey in the first place. Thus it is aimed at the specialist rather than the general reader.
Reference
Hiby, A.R. and Hammond, P.S., 1989. Survey techniques for estimating abundance of cetaceans. Rep. Int. Whal. Commn., Special Issue 11, pp. 47-80.
´ M.B. Santos Vazquez
Zoology Department Aberdeen University Tillydrone Avenue Aberdeen AB24 2TZ
