DATA COLLECTION 



Field Procedure 



Purse seine vessels (Append. Fig. A-ll) were used by the 

 United States for conducting pelagic research, with only a few 

 exceptions. This type of vessel with the wheelhouse and flying 

 bridge forward of amidship permitted greater visibility for 

 sighting and following seals. The sizes of the chartered vessels 

 were between 19.4 and 29.4 m (65-96 ft) registered length with 

 a cruising speed of about 8 to 10 kn, with fuel, water, and food 

 storage capability to stay at sea for at least 1 mo. The vessel 

 complement normally consisted of eight men, including four 

 crew, a captain, engineer, deckhand, and a cook with four 

 wildlife biologists aboard. The vessel crew assisted the three to 

 four scientists in all phases of research including sighting, 

 tracking, shooting, and recovering seals. Fur seals were shot 

 with 12-gauge shotguns using magnum loads of 00-buckshot. 

 The scientists or biological crew collected the biological data 

 and samples from each animal collected at sea. 



Biological data collected from each seal included sex, 

 length, weight, and any external irregularities which were 

 recorded on field data cards (Append. Fig. A- 12) before any 

 biological specimens were removed from the animal. Both up- 

 per and lower jaws were cut off, and these sections boiled until 

 the teeth could be easily removed. The four canines were 

 labeled and tagged for final processing in the laboratory where 

 age was determined. 



Upon opening the abdominal cavity, if the seal was a 

 female, the reproductive condition was determined by exam- 

 ining the uterine horns. The entire female genital tract was 

 then removed as was the entire stomach and preserved in 10% 

 Formalin for detailed examination in the laboratory. 



Laboratory Procedure 



The examination of female reproductive organs in the lab- 

 oratory consisted of a thorough macroscopic examination of 

 the uterine horns to verify field diagnosis. The ovaries were 

 then sliced (1 mm thickness) and examined for Graafian folli- 

 cles (size and ovulation) and the presence or absence of cor- 

 pora albicantia or corpora lutea indicating past and present 

 reproductive history. Age specific pregnancy rates are a major 

 factor in assessing the overall health of the fur seal population 

 (pups born) as an indication of its present status and in esti- 

 mating future herd size for making management decisions. 



The ages of all seals collected are determined by counting 

 the annual growth layers in the dentine of the canine teeth 

 which appear as alternate clear and opaque layers under trans- 

 mitted light (high intensity lamps) and with the aid of magni- 

 fiers and dissecting microscopes. The ages of most young fur 

 seals through age 6 yr can be determined with acceptable ac- 

 curacy by counting the external growth increments on the up- 

 per canine; however, for older seals, the ages are determined 

 by counting the internal annuli from longitudinal half sections 

 of canine teeth. 



All canine teeth of fur seals taken at sea were sectioned lon- 

 gitudinally (lengthwise), just off center, with a bandsaw. Lapi- 

 dary equipment utilizing horizontal grinding wheels of various 

 coarseness was used to grind the rough surface as close to mid- 

 line as possible. The plane of cut and the degree to which the 

 tooth is ground to the midpoint is critical in obtaining readable 



annual growth lines. For those teeth that do not show annual 

 growth layers clearly, a technique reported by Pierce and Kaji- 

 mura (1980) on acid etching and highlighting for defining 

 growth layers will be of use in age determination. 



The stomach was cut open by slicing the entire length of the 

 stomach lining, cutting with care so food organisms would not 

 be damaged. When the stomach contained whole fish or 

 squids, the contents were placed directly into a weighing pan. 

 If the contents were largely liquid they were placed in a sieve to 

 drain. The contents were then transferred into the weighing 

 pan. The stomach lining was rinsed to obtain all food parti- 

 cles, as otoliths and squid beaks often adhered to the stomach 

 wall. Excess fluid was drained from the weighing pan prior to 

 each weighing. Large stomachs required two or more weigh- 

 ings as did the volumetric measurements. 



Stomach contents weighing < 10 g (or digested fish, squid 

 remains, otoliths, squid beaks and pens, or vertebrae frag- 

 ments) were recorded as "trace" amounts unless a whole spec- 

 imen or fleshy parts were present. For contents with a weight 

 of 100 g or less, the volume was not measured but was assigned 

 a value as though the contents had the same density as water 

 (e.g. , if weight equals 55 g, the volume equals 55 cm J ). Weight 

 and volume < 100 g were checked early in the program and 

 found not to vary significantly. Nonfood items such as rocks, 

 pebbles, shells, etc. were not entered on food data sheets as 

 part of the total weight and volume. Stomach content volumes 

 (cc) were obtained by the water displacement method in large 

 graduated beakers capable of holding 2,000 cc. 



A number was assigned to each specimen and recorded on a 

 food card (Append. Fig. A-13). When the stomach was 

 opened, weight and volume of contents were entered on this 

 card and the contents identified. When two or more species 

 could not be easily separated, the examiner estimated their 

 proportionate volume to the nearest 5%. The weight and vol- 

 ume of each individual species were calculated by multiplying 

 estimated percentage times total weight and volume. Specimens 

 were identified by comparing them with known preserved 

 whole specimens or known skeletal material in the laboratory 

 collection and by using various cephalopod and fish identifica- 

 tion keys. A direct count of complete specimens, squid beaks 

 (dorsal and ventral), and fish skeletal remains such as total 

 skulls, otoliths, or numbers of vertebrae approximating a com- 

 plete fish skeleton was used to estimate the numbers of squid 

 and fish in the stomach. Length and weight measurements of 

 prey were taken whenever possible (measurement examples: 

 snout to fork of tail; length of all vertebrae of fish, snout to 

 hypural plate, and dorsal mantle length of squid). 



FUR SEAL FEEDING AT SEA 



Although fur seals are usually solitary at sea, they tend to 

 congregate loosely in areas of abundant food supply and are 

 most frequently seen from about 70 to 130 km from land and 

 near the continental shelf and slope. Fur seal densities are 

 often greatest near sea valleys, submarine canyons, seamounts, 

 and along the continental shelf and slope where abrupt 

 changes occur in depths and upwellings of nutrient-rich water, 

 which influence productivity and concentrate primary pro- 

 ducers and zooplankton. This, in turn, gives rise to the attrac- 

 tion, distribution, and recruitment of fishery resources which 

 then become food for fur seals and other predators in the 

 marine environment. 



