Alaska Salmon Industry, Inc., until 1956 when 

 a contract for more extensive aerial surveys 

 of sea lions was arranged between the Fish- 

 eries Research Institute and the U.S. Fish 

 and Wildlife Service. Research under this 

 contract, which provided for several aerial 

 surveys of rookeries at different times of 

 the year, was conducted by Thompson and Ron 

 J. Lopp. 



Under another contract between the two 

 agencies, surveys were made in 1957 by Lopp 

 or by Lopp and Mathisen. In 1958, Lopp made 

 three surveys of rookeries in the Shumagin 

 Islands area. He also processed the film 

 each year and made most of the counts of the 

 sea lions on the finished photographs. Mathisen 

 compiled the tables, analyzed the data, and 

 wrote the report. 



METHODS OF ENUMERATING 

 MARINE MAMMALS 



The classical tagging and recovery methods 

 used in enumerating fish populations are not 

 practical for censusing marine mammals. An 

 exception is the northern fur seal (Callorhinus 

 uTsinus) on the Pribilof Islands where Kenyon, 

 Scheffer, and Chapman (1954) estimated popu- 

 lation size from the ratio of tagged-to-untagged 

 fur seals on the rookeries. Most of the fur 

 seals there are confined to a few rookeries 

 where they can be observed easily and where 

 many thousands are harvested each year. 

 Since sea lions are scattered on hundreds of 

 islands and are not harvested, their number 

 cannot now be estimated by the tagging and 

 recovery method. 



Usually, visual counts are used for es- 

 timating populations of seals and sea lions. 

 In California visual counts of sea lion rooker- 

 ies within the boundaries of the State have 

 been conducted systematically for a number 

 of years. The first survey dates back to 1927 

 (Bonnot, 1928). An account of the procedure 

 used follows: 



Tlie method used for taking the census in this report 

 was to approach the rookery under cover if possible, or 

 if tliis could not be done, to approach the animals very 

 slowly. V^hen within a reasonable distance, a count or 

 estimate was made and a picture, or pictures, taken. 

 A closer $xisition was then gained and the same proce- 



dure repeated. It was found that when counts were made 

 the photographs bore them out, but when estimates were 

 made, the photographs proved them to be high in nearly 

 all cases, (p. 27). 



Because there are few rookeries in Cali- 

 fornia and only three with more than 400 ani- 

 mals, results from the procedure described 

 by Bonnot were adequate. Similar surveys 

 followed (Bonnot, 1928, 1931,- 1937; Bonnot, 

 Clark, and Hatton, 1938), In 1946 Bonnot 

 and Ripley (1948) used airplanes and Navy 

 blimps to obtain suitable photographs of 

 rookeries. The photographs were used pri- 

 marily to check ground survey counts made 

 by two or three independent surveyors. One 

 apparent drawback to the aerial census was 

 the difficulty in distinguishing between the 

 Steller and the California sea lions 

 (Znlophus cali(omianus). This problem does not 

 exist in Alaska where the Steller sea lion is 

 the only species. The northern limit of the 

 range of the California sea lion is at Barkley 

 Sound in British Columbia (Scheffer, 1958). 



AERIAL PHOTOGRAPHIC CENSUS 

 IN ALASKA, 1956-58 



The districts surveyed aerially from 1956 

 to 1958 extend from Cape St. Elias (144° W.) 

 to the Islands of the Four Mountains (170° W.), 

 or about 1,100 miles in a straight line (fig. 1). 

 The actual flight line needed to cover all 

 coastal rookeries between these two limits 

 is considerably longer. 



Equipment and Techniques 



Among different planes used during the 

 investigations, a twin-engined amphibian most 

 adequately provided efficient cruising speed, 

 cruising range, and pxjwer to overcome treach- 

 erous downdrafts at the rookeries. 



While photographs were being taken, the 

 speed of the plane was about 100 to 120 miles 

 per hour, and the pilot maintained the plane 

 at a distance of 300 to 400 feet from the 

 animals. Generally all photographs were ex- 

 posed during the first circuit of the rookery, 

 but at rookeries with highly indented shore- 

 lines, sometimes a second or third coverage 

 was needed. 



