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the narratives of nineteenth century whaling and found that sperm whales usually, though not invariably, turned over when about to bite a whaleboat. The behavior extends to in- traspecific fighting in sperm whales (Clarke and Palita, 1988) because Hopkins (n.d.) watched a fight between rival bulls and saw how one, charging the other, turned over when about a hundred feet away.

The first author’s observation aboard the Soutbwn Harvester in 1948 goes far to answer Scamrnon’s rhetorical question (1874, p. 83) “when the creature [sperm whale] essays to grasp a large object on the water, it instantly rolls over to bite, but does it necessarily follow that the same attitude must be maintained when obtaining its food in the abyss beneath?” However, we cannot know all that goes on in the dark of the sea, and the sperm whale may sometimes use other stratagems to capture its prey like those discussed in the second hypothesis of Fristrup and Harbison (2002).

LITERATURE CITED

ANDRIASHEV, A. P. 1968. The problem of the life community associated with the Antarc- tic fast ice. Pages 147-155 in SCAR Symposium on Antarctic Oceanography, Santia- go, Chile, 13-16 September 1966. Scott Polar Research Institute, Cambridge.

BENNETT, F. D. 1840. Narrative of a whaling voyage round the globe, from the year 1833 to 1836. London, Richard Bentley. 2 vols: pp xvi, 402; viii, 395.

BUDKER, P. 1971. The life of sharks. Columbus University Press, New York, NY. CALDWELL, D. K., M. C. CALDWELL AND D. W. RICE. 1966. Behavior of the Sperm Whale,

Physeter catodon L. Pages 677-717 in K. S. Norris, ed. Whales, dolphins and por- poises. University of California Press, Berkeley and Los Angeles, CA.

CLARKE, R., AND 0. PALIZA. 1988. Instraspecific fighting in sperm whales. Report of the International Whaling Commission 38:235-241,

CLARKE, R., 0. PALIZA AND A. AGUAYO L. 1988. Sperm whales of the Southeast Pacific. Part IV. Fatness, food and feeding. Investigations on Cetacea, Berne, 21:53-195.

FRISTRUP, K. M., AND G. R. HARBISON. 2002. How do sperm whales catch squids? Ma- rine Mammal Science 18:42-54.

HOPKINS, W. J. n.d. She blows! And sparm at that! London, Constable & Co. Limited. (The American edition was dated 1922).

SCAMMON, C. M. 1874. The marine mammals of the north-western coast of North Arneri- ca, described and illustrated: Together with an account of the American whale fish- ery. San Francisco: John H. Carrnany and Company. G. P. Putman’s Sons, New York, NY.

ROBERT CLARKE AND OBLA PALIZA, Apartado 40, Pisco, Peru; e-mail: robertclarke007@ hotrnail.com.

MARINE MAMMAL SCIENCE, 19(1):608-612 (July 2003) 0 2003 by the Society for Marine Mammalogy

DIGITAL PHOTOGRAPHY IMPROVES EFFICIENCY OF INDIVIDUAL DOLPHIN IDENTIFICATION: A REPLY TO MIZROCH

We agree with Dr. Mizroch that the absolute resolution of film is higher than that of digital images. One need look no farther than the camera specifications published by Ni- kon, Canon, Kodak, and others to confirm this fact. However, the purpose of our note was not to examine the absolute resolution of the two media. In fact, we opted not to

LETTERS 609

use the highest resolution settings on the digital cameras. Beyond a threshold level, high- er resolution did not appreciably improve photograph quality in a way meaningful to our research. Fine resolution 2-3 megapixel JPEG files use 1-1.3 megabytes of memory per image, versus >10 megabytes per TIFF file in the highest resolution (>5 megapixel) mode. As our results did not vary with changes in resolution, and increased file size de- creased analysis speed due to processor, RAM, and hard drive limitations, we chose to use the second highest resolution setting. Further, when ordering a newer camera model for additional research, we chose the Nikon D1H over the Nikon DIX, as we preferred the lower cost and higher speed with slightly lower resolution offered by the D1H model. The optimal resolution settings will vary depending on the level of detail required to re- liably document distinctive individuals, the distance from the camera to the subject, the number of photographs taken, the size of the photo-catalog, and other particulars of each research project. However, we would not recommend resolution settings below 1-2 meg- apixels.

We agree with Dr. Mizroch that the ultra-high-speed film system may be more effec- tive for identification of some cetaceans at sea (e.g. , humpback whales, although research- ers in Hawaii commented on the MARMAM list serve that they found digital photography effective'). Our data presented in this note are in regard to dolphin photo- identification only. However, we are told by researchers working with a variety of whale specie^^'^'^ that digital photographs have also been found to be very effective for large whales.

We agree whole-heartedly with Dr. Mizroch that more side-by-side film ws. digital photo-identification efficiency tests should be conducted. Based on our work over the past three years with Nikon D1 and D1H cameras, as well as anecdotal remarks from col- leagues using similar digital SLR cameras (e.g., R. Connor'), we believe that further test- ing will lend additional support for the use of digital photography in field research with cetaceans. We wonder why Dr. Mizroch, having a Nikon D1X available for her research, did not use the opportunity to test the effectiveness of this system vs. her ultra-high- speed film system in the field with humpback whales rather than on newspaper print. We suggest that obtaining photographs of moving creatures with a hand-held camera from a vessel at sea is a qualitatively different undertaking than taking photographs of newspaper print from a set distance with a camera stabilized on a tripod. At any rate, the line/pixel resolution of film types, development considerations, etc., are already matters of written record. However, we look forward to further comparisons of film images and dig- ital images taken of cetaceans in the field with similar SLR-type cameras.

In regard to our research, we recently completed a brief field season with digital and film cameras to photographically identify New Zealand dusky dolphins. During this two- month period, we shot 4,520 digital images using the Nikon D l H , and 1,941 images on TMAX 100-400 speed films. Once again, we found a higher proportion of digital images to be of suitable quality for photo-identification, although both film and digital photo- graphs were >70% suitable due to extremely favorable photographic conditions. More im- portantly, the logistical advantages of the digital format once again were evident. In the

' Personal communication from A. A. Pack, Kewalo Basin Marine Mammal Laboratory, 1129 Ala Moana Blvd., Honolulu, Hawaii 96814, U.S.A., 21 August 2002. ' Personal communication from N. Jaquet, Texas A&M University, 5007 Avenue U, Galveston,

Texas 77551 U.S.A., 30 September 2002. Personal communication from D. W. Weller, National Marine Fisheries Service, NOAA, South-

west Fisheries Science Center, 8604 La Jolla Shores Drive, La Jolla, California 92037, U.S.A., 15 November 2001.

Personal communication from P. J. Clapham, Large Whale Biology Program, Northwest Fisher- ies Science Center, 166 Water Street, Woods Hole, Massachusetts 02543, U.S.A., 20 August 2002.

Personal communication from R. Connor, Biology Department, University Massachussets, Dart- mouth, 285 Old Westport Rd, North Dartmouth, MA 02747 U.S.A., 13 September 2001.

610 MARINE MAMMAL SCIBNCE, VOL. 19, NO. 3, 2003

field, we were able to collect more data per unit time, allowing us to photograph an esti- mated 93% of dolphins present using digital images versus 82% of dolphins present using film (estimates based on our field counts of dolphins, mean group size = 6 dolphins). A complete photographic sample of all individuals present was obtained for an estimated 76% of groups using digital images ( n = 150 groups) versus an estimated 64% of groups using film (n = 77 groups). In the laboratory, we spent hundreds of additional hours de- veloping, sorting, slide mounting and labeling film images, whereas digital images were ready to be input into our Finscan database immediately following a rapid onscreen initial sorting process. Computer-based photo-matching systems for dolphin identification (e.g., Finscan, Araabi et al. 2000) require analog film images to be converted into a digital for- mat, which adds additional time to analysis and results in a loss of resolution. We estimate from our own work that digital technology reduces the time required to prepare images for computer-based analysis by up to five minutes per image (Markowitz et al. 2001). We speculate that the use of digital photographs would equally increase the efficiency of other automated computer-based photo-cataloging systems (e.g., right whale identification soft- ware, Hiby and Lovell 2001, Rurnell and Shanahan 2001; gray seal identification software, Hiby and Love11 19%)).

As with 35-mm film cameras, the settings used on digital cameras, i .e., aperture, shut- ter speed, virtual ISO, image resolution, and white balance, will affect image quality. We encourage researchers to take the time to familiarize themselves with the optimal settings for the new professional digital cameras as they have with film cameras. One advantage of digital cameras is the ability to adjust virtual IS0 settings with changing light condi- tions in the field; no longer is i t the case that 36 frames must be shot with the same set- ting and developed in the same conditions (e.g., "pushing" film).

Not all digital cameras are of equal suitability for photo-identification. Professional SLR digital cameras we have field-tested are the equivalent of the Nikon F5 or Canon EOS 35- mm film cameras. One can no more expect to obtain good photo-identification results with a point-and-shoot digital camera than with a similar film camera.

We do not maintain that film photography should never be used or is ineffective in identifying individual whales and dolphins. On the contrary, we have used film photogra- phy for years and have been strong advocates for its use in cetacean research (e.g., Wursig and Wursig 1977, Wursig and Jefferson 1990, Markowitz et al. 1999). We firmly be- lieve, however, that digital technology represents a leap forward that is already resulting in new scientific advances and discoveries.

Questions and concerns expressed by Dr. Mizroch likely reflect those of other re- searchers who have years of experience with film-based photo-identification systems. We had much the same skepticism prior ro using the Nikon D1 digital system in the field. After three years of using digital photography in the field, we can confidently say that we have not only found it to greatly increase the efficiency of our dolphin identifi- cation efforts, but also that i t consistently outperforms film photography in the propor- tion of images of suitable quality for analysis. Were this not the case, and digital photography performed just on par with film photography, the logistical advantages of digital photography would still be considerable. For example, long-term storage of multiple copies of photographs in digital format is inexpensive (about 5,000 images before cropping can be saved on a single compact disk), and takes LIP very little space compared to storage of slide film or prints. Multiple copies of photo-identification cata- logs are good insurance against cataclysmic stochastic events, and storage on compact disks allows for easy transport between research field and lab sites, and for collaboration between research laboratories. There is no need to print digital images, as Dr. Mizroch did for her test. Printing, even on state-of-the-art-printers, increases time, increases cost, requires considerably more archival space, and generally reduces photo resolution or quality ( e . g . , the onscreen resolution of the image files shown in figure 1 of our note is higher than the resolution of the printed images that appeared in Markowitz et al. 2003).

LETTERS 61 1

The concern regarding the cost of a digital system is legitimate; however, we would argue that in the long-term, the initial investment in the digital camera is recouped by savings in film purchase and processing. With the understanding that the figures below are time-locked to the present, and can only be used for comparative purposes, we give several examples, using the discount prices quoted by the B&H Photo Compa- ny (http://www.bhphotovideo.com). Using the Fuji Neopan 1600 and TMAX 3200 ul- tra-high-speed films Dr. Mizroch recommends, the cost of the film alone before developing is approximately $3-$S per roll (all costs in U.S. dollars). Let us say that you shoot 15,000 images (not an unreasonable number for a Ph.D. project involving photo-identification). That is about 400 rolls of film, or a cost of $1,200-$3,600 be- fore developing, slide mounts, slide sheets, paper for enlargements, etc. Film processing costs about $1 per roll if developed “in-house,” and $6 or more if done professionally. Thus film and developing cost a minimum of $1,600-$ 6,000 in this system. The list price for the Nikon F5, a film camera body equivalent to the digital SLR we used, is $2,000-$3,000. The list price for the Nikon DlH, the digital camera body, is $3,600-$4,500. Digital cameras replace analog film with re-usable memory cards that generally cost <$1 per megabyte. One of the greatest attributes of memory cards is that, unlike film, they are a renewable resource. Therefore, after the initial investment in a digital camera system, the costs associated with film are eliminated. More impor- tantly, because memory cards do not require changing nearly as often as rolls of film, more photographic data can be collected in the field per unit time using digital media than using film. We doubt any of the readers of this journal would argue that more data collected per unit time in the field is anything but priceless.

In summary, we thank our colleague for her excellent comments, and for promoting healthy dialogue on this subject. We recommend that scientists conducting photo-identi- fication research consider trying digital photography as an alternative to 35-mm film photography. We believe they will be pleasantly surprised by the results.

LITERATURE CITED

ARAABI, B. N., N. KEHTARNAVAZ, T. MCKINNEY, G. HILLMAN AND B. WURSIG. 2000. A string matching computer-assisted system for dolphin photo-identification. Annals of Biomedical Engineering 28:1269-1279.

BURNELL, S. R., ANn D. SHANAHAN. 2001. A note on a prototype system for simple com- puter-assisted matching of individually identified southern right whales, Eubuluenu australis. Journal of Cetacean Research Management (Special Issue 2): 297-300.

HIBY, L., AND P. LOVELL. 1990. Computer aided matching of natural markings: a prototype system for grey seals. Reports of the International Whaling Commission (Special Is- sue 12):57-62.

HIBY, L., AND P. LOVELL. 2001. A note on an automated system for matching the callosity patterns on aerial photographs of southern right whales. Journal of Cetacean Re- search Management (Special Issue 2):291-295,

MARKOWITZ, T. M., A. D. HARLIN AND B. WURSIG. 1999. Photo-identification of New Zealand dusky dolphins. 13th Biennial Conference of the Society for Marine Mam- malogy, Maui.

MARKOWITZ, T. M., A. D. HARLIN AND B. WURSIG. 2001. The use of digital photography in photo-identification of a wild dolphin population. 14th Biennial Conference of the Society for Marine Mammalogy, Vancouver.

MARKOWITZ, T. M., A. D. HARLIN AND B. WURSIG. 2003. Digital photography improves efficiency of individual dolphin identification. Marine Mammal Science 19:217-223.

WURSIG B., AND T. A. JEFFERSON. 1990. Methods of photo-identification for small ceta- ceans. Reporrs of the International Whaling Commission (Special Issue 12):43-52.

612 MARINE MAMMAL SCIENCE. VOL. 19. NO 3. LOO3

WURSIG, B., AND M. WLJRSIG. 1977. The photographic determination of group size, com- position and stability of coastal porpoises (Tzlrsiops truncatm). Science 198:755-756.

T. M. MARKOWITZ, A. D. HARLIN, AND B. WURSIG, Marine Mammal Research Pro- gram, Department of Wildlife and Fisheries Sciences, Texas A&M University, 4700 Ave- nue U, Building 303, Galveston, Texas 7755 1 , U.S.A.; e-mail: tim-markowitz@ yahoo.com

MARINE MAMMAL SCIENCE, 19(1):612-614 (July 2003) 0 2003 by the Society for Marine Mammalogy

DIGITAL PHOTOGRAPHY IMPROVES EFFICIENCY OF INDIVIDUAL DOLPHIN IDENTIFICATION: A REPLY TO MARKOWITZ E T AL.

Mizroch and Bigg (1990) provided a short guide to photographing whales from small boats. Topics we covered included choice of film, framing and focusing tips, suggestions about exposure times, and tips and examples on processing and printing images. In the 12 yr since we published our note, our methods have remained virtually the same, but our choice of black and white negative film has evolved from Ilford HP-5 (rated at 400 ASA but usually shot at 1600 ASA) to Fuji Neopan 1600 (shot at 1600 ASA or shot at 800 ASA if light conditions permitted) and most recently to Kodak TMAX 3200 (shot at 800 or 1000 ASA). With some of the newer high-speed black and white films, the nominal ASA (ie., 1600 or 3200) is usually not the optimum film emulsion speed. The optimum speed for both Neopan and TMAX is closer to 800, and the optimum speed for HP-5 is 400.

Recently, researchers have begun exploring the use of high-resolution ( > S megapixel) digital cameras, most commonly the Nikon D1X. Some of the humpback whale research- ers working in the North Pacific have begun using the Nikon DIX, and their digital im- ages are decidedly better than their scanned color slides. Markowitz et al. (2003) have compared images from their existing dolphin fin catalog (shot with mostly slide film?) to digital images shot with the Nikon D1, and found that the digital images were better. However, the question remains for those of us using high-speed black and white film, is digital a better format for photo-identification than the film we currently use?

With the help of a Seattle, WA, professional black-and-white photo lab (Panda Photo- graphic Laboratories, Inc.), we devised a simple test to compare the two black-and-white films we commonly use (Neopan 1600 and TMAX 3200, both shot at 800 ASA), to the Nikon D1X (set at 800 ASA, high resolution, black and white, Y Cr Cb). We mounted a newspaper financial page with stock market tables in very small type and graphics on an easel set outside in natural lighting on an overcast day. We placed a Nikon 300-mm f4 ED-IF lens on a tripod and set the lens aperture at f8 and mounted first the film cam- eras then the digital camera back to the lens for the comparison test. The image in the camera viewfinder was 1.5 times larger in the digital camera than in the film camera, so when shooting with the digital camera, the tripod was moved back to ensure the exact same section of the newspaper was in all the shots.

Each camera meter was set to the spot meter setting and a photographic (18%) reflectance) gray card was used to determine the optimum exposure. We took one shot at this optimum exposure, then bracketed the exposure with shots at shutter speed one setting above and one setting below the optimum setting. Then we changed the exposure compensation (?) but- ton on the camera to an exposure value of +0.7, determined the optimum exposure with