Perrin, W. F., Wilson, C. E., and Archer, F. I. (1994). Striped dolphin Stenella coeruleoalba (Meyen, 1833). In “Handbook of Marine Mammals, Vol. 5: The First Book of Dolphins” (S. H. Ridgway, and R. Harrison, eds), pp. 129–160. Harcourt Brace and Company, London. Perrin, W. F., Mitchell, E. D., Mead, J. G., Caldwell, D. K., and van Bree, P. J. H. (1981). Stenella clymene, a rediscovered tropical dol phin of the Atlantic. J. Mamm. 62, 583–598. Ringelstein, J., Pusineri, C., Hassani, S., Meynier, L., Nicolas, R., and Ridoux, V. (2006). Food and feeding ecology of the striped dolphin, Stenella coeruleoalba, in the oceanic waters of the north-east Atlantic. J. Mar. Biol. Assoc. U.K. 86, 909–918.
KARIN A. FORNEY
urveys are used to address many different marine mammal research questions, including distribution, abundance, trends, and habitat associations. Equipment and methodology vary depending on the species of interest, ﬁnancial resources, availability of research platforms, and survey objective. Marine mammals at sea are most commonly surveyed aboard ships or large boats (Øien,1991; Wade and Gerrodette, 1993; Barlow, 1995), or from ﬁxed-wing aircraft (Heide-Jørgensen et al., 1993; Forney et al. 1995; Garner et al., 1999). Small boats, helicopters, airships, and land-based viewing stations are also used when appropriate (Kraus, et al., 1983; Rathbun, 1988). Linetransect methods (Buckland et al., 2001) are often the most effective for estimating the abundance of marine mammals at sea, although other survey techniques are also used (Hiby and Hammond, 1989; Garner et al., 1999). Marine mammals on or near land, such as pin nipeds, sea otters or walruses, are more commonly counted from landbased viewing points or using aerial photography (Lowry, 1999).
Figure 1 NOAA ship McArthur, which has been used for many marine mammal surveys in the eastern Paciﬁc Ocean (Photo: K. Forney).
I. Vessel Surveys Large oceanographic research vessels (Fig. 1), are the most versa tile platform for at-sea surveys of marine mammals. They can carry a dozen or more researchers and remain at sea for weeks at a time, pro viding the ability to cover extensive marine areas. Search efﬁciency is greatest aboard these large vessels, because observers can search from a greater height above the water (on the ﬂying bridge, bridge, or in a crow’s nest) and use high-power, deck-mounted binoculars (“big eyes”) (Fig. 2) when searching for and identifying marine mammals. Large research vessels usually also have equipment for collecting oceano graphic data for marine mammal habitat studies (Fiedler and Reilly, 1994), and they may be able to tow hydrophones to detect marine mammals acoustically. Auxiliary studies including photography, biopsy sampling, diving behavior, and prey sampling are also often possible during vessel surveys. A signiﬁcant disadvantage to large research ves sels, however, is their great operating cost: approximately US $10,000 per day. Small- or medium-sized vessels (Fig. 3), including a variety of ﬁshing boats and sail boats, have successfully been used for sur veys at a signiﬁcantly reduced cost (Vidal et al., 1997). This is the most feasible option in many parts of the world, particularly in developing countries (Aragones et al., 1997). On these smaller vessels, searching is usually conducted with hand-held binoculars or by naked eye, from the highest stable deck or platform on the ship. In some shallow bays and rivers, even smaller boats (e.g., rigid-hull inﬂatable boats, whalers) may be required for safe navigation.
Figure 2 “Big eyes” used to search for marine mammals on large survey vessels. (Photo courtesy of Protected Resources Division, Southwest Fisheries Science Center, NOAA).
II. Aircraft Surveys The main advantages of aerial surveys are the ability to cover large areas quickly and the lower cost of aircraft compared to large ships. They are particularly useful for rapid assessments and prelimi nary studies to determine the relative distribution and abundance of species in a particular region. Using strip or line-transect methods, aerial survey can be used to estimate abundance and monitor trends. Aircraft with high wings and bubble windows (Fig. 4) are best suited, because they allow lateral viewing as well as some downward vis ibility. An additional downward-viewing (“belly”) window enhances sighting efﬁciency considerably, because marine mammals are most easily seen from the air when viewing perpendicular to the water surface. A typical aerial survey observer team consists of two observ ers searching through the two side windows, one data recorder, and, if possible, a belly observer. Aircraft can also be outﬁtted with downward viewing instrumentation (e.g., radiometer, hyperspectral imager) to measure ocean surface properties, such as sea surface temperature and ocean color, to provide habitat information during surveys.
Small survey vessel used in the Philippines (Photo: W. Perrin).
Figure 4 NOAA Twin Otter survey aircraft with bubble window (under propeller) and belly window port (above tire) (Photo: K. Forney).
S III. Land-Based Surveys
viewing stations, such as cliff-tops, although aerial photographs can A few populations of whales reliably migrate close to shore and provide an excellent alternative means of surveying these animals have successfully been surveyed from land-based stations. These along the coastline (Lowry, 1999). include bowhead whales, Balaena mysticetus, at Point Barrow,
IV. Methodological Considerations Alaska, and gray whales, Eschrichtius robustus, along the California coast (Buckland et al., 1993). During these surveys, visual and acousDetectability of marine mammals is a key factor in deciding what tic means may be used to record all whales that travel past the obser- type of survey platform to use (Hiby and Hammond, 1989; Buckland vation point during the migratory period. Adjustments are made for et al., 2001; Garner et al., 1999). Animals that dive for prolonged unobservable periods, such as night-time and times of poor weather periods, such as sperm whales (Physeter macrocephalus) and beaked conditions. Pinnipeds are most commonly counted from land-based whales (Ziphiidae), will be missed much more frequently during
aerial surveys than from ships, because the aircraft travels much faster. For some species, correction factors have been developed to correct for the proportion of animals missed from airplanes or ships. Vessel attraction or avoidance is another concern when designing shipboard marine mammal surveys. For example, harbor porpoise are known to avoid vessels, and if animals are not detected before they react, result ing abundance estimates may be too low. The opposite problem exists for species that are attracted to vessels to “ride the bow”; in these cases abundance estimates may be too high. Both of these problems can be minimized by using a larger vessel that allows viewing from a greater height and with high-power binoculars; animals can then be detected at a greater distance before they react to the vessel. There is increasing recognition that marine mammal surveys are most effectively interpreted in the context of the habitat conditions at the time of the survey. Marine ecosystems are very dynamic, and the concurrent collection of real-time ecosystem data during surveys pro vides an ecological context for the observed patterns in marine mam mal distribution and abundance. Physical oceanographic measurements and indices of biological productivity can readily be obtained through shipboard sampling, aerial instrumentation, or satellite data. Biological measurements generally require shipboard sampling, such as net tows and hydroacoustic measurements. With the addition of such ecosystem data, survey results can be used to model ecological relationships and evaluate the effect of environmental variability on marine mammal spe cies (Hedley et al., 1999; Forney, 2000; Ferguson et al., 2006).
Hedley, S. L., Buckland, S. T., and Borchers, D. L. (1999). Spatial mode ling from line transect data. J. Cetacean Res. Manage. 1(3), 255–264. Heide-Jørgensen, M. P., Teilmann, J., Benke, H., and Wulf, J. (1993). Abundance and distribution of harbor porpoises Phocoena phoc oena in selected areas of the western Baltic and the North Sea. Helg. Meeresunter. 47, 335–346. Hiby, A. R., and Hammond, P. S. (1989). Survey techniques for estimat ing abundance of cetaceans. Rep. Int. Whal. Commn. (Spec. Iss. 11), 47–80. Kraus, S. D., Gilbert, J. R., and Prescott, J. H. (1983). A comparison of aerial, shipboard, and land-based survey methodology for the harbor porpoise, Phocoena phocoena. Fish. Bull. 81, 910–913. Lowry, M. S. (1999). Counts of California sea lion (Zalophus califor nianus) pups from aerial color photographs and from the ground: a comparison of two methods. Mar. Mamm. Sci. 15, 143–158. Øien, N. (1991). Abundance of the northeastern Atlantic stock of minke whales based on shipboard surveys conducted in July 1989. Rep. Int. Whal. Commn. 41, 433–437. Rathbun, G. (1988). Fixed-wing airplane versus helicopter surveys of manatees (Trichechus manatus). Mar. Mamm. Sci. 4, 71–74. Vidal, O., Barlow, J., Hurtado, L. A., Torre, J., Cendon, P., and Ojeda, Z. (1997). Distribution and abundance of the Amazon river dolphin
(Inia geoffrensis) and the tucuxi (Sotalia ﬂuviatilis) in the upper
Amazon River. Mar. Mamm. Sci. 13, 427–445.
Wade, P. R., and Gerrodette, T. (1993). Estimates of cetacean abun dance and distribution in the eastern tropical Paciﬁc. Rep. Int. Whal. Commn. 413, 477–494.
See Also the Following Articles
Abundance Estimation Management
CHARLES W. FOWLER AND MICHAEL A. ETNIER
References Aragones, L. V., Jefferson, T. A., and Marsh, H. (1997). Marine mam mal survey techniques applicable in developing countries. Asian Mar. Biol. 14, 15–39. Barlow, J. (1995). The abundance of cetaceans in California waters. Ship surveys in summer and fall of 1991. Fish. Bull. 93, 1–14. Buckland, S. T., Breiwick, J. M., Cattanach, K. L., and Laake, J. L. (1993). Estimated population size of the California gray whale. Mar. Mamm. Sci. 9, 235–249. Buckland, S. T., Anderson, D. R., Burnham, K. P., Laake, J. L., Borchers, D. L., and Thomas, L. (2001). “Introduction to Distance Sampling: Estimating Abundance of Biological Populations.” Oxford University Press, New York, 432 p.. Buckland, S. T., Anderson, D. R., Burnham, K. P., Laake, J. L., Borchers, D. L., and Thomas, L. (2004). “Advanced Distance Sampling.” Oxford University Press, New York, 434 p.. Ferguson, M. C., Barlow, J., Fiedler, P., Reilly, S. B., and Gerrodette, T. (2006). Spatial models of delphinid (family Delphinidae) encoun ter rate and group size in the eastern tropical Paciﬁc Ocean. Ecol. Modell. 193, 645–662. Fiedler, P. C., and Reilly, S. B. (1994). Interannual variability of dolphin habitats in the eastern tropical Paciﬁc. I: Research vessel surveys, 1986–1990. Fish. Bull. 92, 434–450. Forney, K. A. (2000). Environmental models of cetacean abundance: reducing uncertainty in population trends. Conserv. Biol. 14(5), 1271–1286. Forney, K. A., Barlow, J., and Carretta, J. V. (1995). The abundance of cetaceans in California waters. Part II. Aerial surveys in winter and spring of 1991 and 1992. Fish. Bull. 93, 15–22. Garner, G. W., Amstrup, S. C., Laake, J. L., Manly, B. F. J., McDonald, L. L., and Robertson, D. G. (1999). “Marine Mammal Survey and Assessment Methods.” A.A. Balkema, Rotterdam.
ustainability has been elusive in spite of its ubiquitous appear ance in the goals for management. Human impacts need to be sustainable, whether they are the harvest of a marine mam mal population, the harvest of ﬁnﬁshes in the marine environment, our production of CO2, or the genetic effects we have on other spe cies. Sustainable human interactions with other systems must be established in ways that account for the suite of factors involved in ecosystems and the complexity of the biosphere to include both our direct effects and our indirect effects on such systems. It is unlikely that historical harvests of marine mammal populations are sustain able, partly because of their low productivity levels (Perrin, 1999). Thus, deﬁning sustainability, whether it involves our interactions with marine mammals, ﬁsheries resources, or ecosystems, remains an important objective. Historically, the concept of Maximum Sustainable Yield (MSY) has played a major role in the management of our utilization of natu ral resources. This approach has yet to be assessed in its contribution to worldwide problems such as over-harvested ﬁsh populations (Rosenberg et al., 1993; Committee on Ecosystem Management for Sustainable Marine Fisheries, 1999). Commercial whaling and seal ing have also involved concepts derived from the MSY approach. The inadequacies of management based on MSY have been recognized [e.g., it is illogical (Fowler and Smith, 2004)]; such approaches are not sustainable. Progress in understanding such problems involve the development of other methodologies, e.g., the Catch Limit Algorithm of the International Whaling Commission (Slooten, 1998) and the Potential Biological Removal approach being used by the National Marine Fisheries Service in the United