FISHERY BULLETIN: VOL. 74, NO. 2 



those for S. longirostris . Preliminary unpublished 

 results of our studies indicate that these two 

 species are probably disparate in such growth 

 parameters as length at birth, length at maturity, 

 and asymptotic length. Harrison et al. (1972) 

 stated that lengths of the fetuses examined indi- 

 cate that parturition occurs both in the spring 

 and in the autumn. They described in detail the 

 gross and microscopic histological appearances of 

 several pairs of ovaries. A maximum of nine cor- 

 pora albicantia were encountered. They con- 

 cluded that if all the corpora albicantia in ovaries 

 of specimens of this species do not represent past 

 pregnancies, either the fertility is very low or the 

 corpora are not permanent. 



Nishiwaki et al. (1965) published length- 

 frequency distributions of 34 fetuses (up to 106 cm 

 long) and 194 postnatal animals (104 to 208 cm) 

 from a school driven ashore in Japan. They esti- 

 mated that gestation lasts 1 yr, length at birth is 

 about 105 cm, juveniles reach 150 cm in 6 mo, and 

 adult size (180 cm for females and 190 cm for 

 males) is reached in 1 yr. They concluded that 

 there are two seasons for mating and parturition, 

 in the spring and in the autumn, and that there 

 are fewer males than females among adults. On- 

 togenetic changes in coloration, external propor- 

 tions, organ weights, the skeleton, parasite load, 

 and feeding habits have been described (Perrin 

 1970b, in press; Perrin and Roberts 1972; Dailey 

 and Perrin 1973; Perrin et al. 1973). 



Kasuya et al. (1974) recently published results 

 of a study of several hundred specimens caught in 

 the Japanese fishery for S. attenuata. Their re- 

 sults are discussed and compared with ours in the 

 body of this paper. 



METHODS AND MATERIALS 



Observer Program 



Beginning in 1968, NMFS placed observers 

 aboard U.S. tuna seiners to collect information on 

 the incidental take of cetaceans in the eastern 

 tropical Pacific. Observers were placed on 1 cruise 

 in 1968, 5 in 1971, 12 in 1972, and 22 in 1973. Most 

 of the cruises were 30 to 60 days long. In addition, 

 biological data were collected during chartered 

 cruises of commercial seiners: one in 1971, one in 

 1972, and two in 1973. 



The data collecting had to be carried out in 

 such a way as to not interfere with the fishing 

 operation. Hence, the amount of information col- 



lected on the animals killed in a net set varied 

 vddely, depending on the amount of time that was 

 available before the next set was made. Following 

 is the hierarchy of types of data that were col- 

 lected (sample sizes were largest for the first and 

 smallest for the last): 

 Animals killed were: 



1. Counted (estimates were made in cases 

 where counts were not possible), usually 

 on the deck or in the net, 



2. Identified to species (and race when 

 possible), 



3. (S. attenuata only) identified to develop- 

 mental color pattern phase (Perrin 1970b), 

 and sexed, 



4. Measured (to nearest centimeter with 2-m 

 calipers), and 



5. Dissected to collect information on repro- 

 ductive condition (for females, mammaries 

 were examined and reproductive tract col- 

 lected; for males, the right testis was col- 

 lected) and age (a section of the left lower 

 jaw at midlength was collected). The gonad- 

 al material and jaw sections were pre- 

 served in 10% Formalin.'* Small fetuses (^ 30 

 cm) were preserved in the uterus. Larger 

 fetuses were removed from the uterus and 

 frozen. 



For each specimen that was at least measured 

 (step 4 above), a field serial number was assigned, 

 and a specimen data sheet was filled out. Data for 

 specimens that were not at least measured were 

 collected on a running tally. 



The Study Area 



One of us has described the distribution ofS. 

 attenuata in the eastern tropical Pacific (Perrin 

 1975). The known occurrence of mixed aggrega- 

 tions of cetaceans and tuna is strongly correlated 

 with certain oceanographic conditions peculiar to 

 that region. The porpoise-tuna association is 

 known only in the eastern tropical portion of the 

 Pacific. That area, which has been called the 

 North Pacific Equatorial water mass (Seckel 

 1972), has an unusual oxygen-salinity- 

 temperature structure. The reason for this is not 



••Reference to trade names does not imply endorsement by 

 the National Marine Fisheries Service, NOAA. 



230 



