SPEARFISHES OF THE CENTRAL PACIFIC 



533 



and first dorsal is the best clmracter we liave 

 found for distinguishing ampla from audai. In 

 ampla, the height of the first anal averaged 86 

 percent of the height of the first dorsal with a 

 range of 76 to 100 percent; in audax, the range was 

 from 50 to 76 percent %vith an average of 66 

 percent. The center of the first dorsal fin is low 

 and in our specimens there is a suggestion of an 

 actual decrease in the average length of the 20th 

 ray with the growth of the fish up to 200 cm. ; but 

 in the specimens of more than 200 cm. fork length 

 the length of the 20th ray is nearly constant. 

 Tlie average lengtli of the ray in ampla is appro.xi- 

 mately 6 cm. with the range in our specimens from 

 3 to 9 cm. ; in audax, which has a similar growth 

 pattern, the range is from 8 to 14 cm. with an 

 average of 10 cm. The length of the pelvic fin is 

 comparable to that of audax and longer than that 

 of marlina, averaging about 34 cm. in our speci- 

 mens with no change in size according to length 

 of fish. 



This species appears to be unique among the 

 marlins in the growth relation of mandible and 

 snout (fig. 13).' In audax and marlina the snout 

 and mandible grow approximately isometrically, 

 whereas in ampla the mandibular growth definitely 

 is negatively allometric. As a result the snout 

 appears long in very large individuals. 



The lumping of the Atlantic and Pacific forms 

 of this marlin in the single species ampla will no 

 doubt be contested by people who automatically 

 consider that such geographic separation indicates 

 distinct species. However, in none of the char- 

 acters considered in the preceding pages do we 

 find a difference that even approaches the sub- 

 specific level. Until morphological differences can 

 be found it seems preferable to consider both 

 forms as belonging to the same species. 



Color 



In the living specimens of ampla that we have 

 seen in the Pacific, the predominant color of tlie 

 upper parts is a brilliant, deep metallic blue which 

 fades rapidly after death to a lead-gray color 

 mixed with browns wherever the fish has been 

 rubbed or scraped. Stripes usually are present 

 on the sides immediately after death but are rarely 

 conspicuous, and generally some are so faint that 



' Dr. Hiroshi Xakamura, in a [HTSonal ctimniunication, jwinted out that 

 allometric p-owth of the snout occurs in Istiophonts oritntaliti. At about 

 140 mm. the snout is extraordinarily long in relation to body lenpth and, as 

 the fish grows, the length of .snout in relation to body length decreases. 



it is difficult to count them. They may be absent 

 or remain conspicuous after death and cannot be 

 relied on to distinguish the fish from either marlina 

 or audax. 

 Distribution in the Pacific 



This is the predominant marlin of the central 

 tropical Pacific, having been taken in all of the 

 tropical areas fished by POFI, from 110° W. longi- 

 tude to 180° longitude, with catch rates up to 0.35 

 per 100 hooks (fig. 27). West, along the Equator 

 in the Marshall and Caroline Islands area, the 

 Japanese mothership expeditions of 1950 and 1951 

 found it even more abundant, for they had an 

 average catch rate of 0.53 per 100 hooks. Off 

 Formosa it is taken in lesser quantities than 

 marlina and orientali.'^ (Xakamura 1951 , table 1 14). 

 Northward from the Equator its abundance de- 

 clines with latitude and, according to Nakamura 

 (1951, fig. 31), for the zone from 143° to 150° E. 

 longitude just off the coast of Japan ampla be- 

 comes less abundant than audax at about 15° N. 

 latitude, but moderate quantities are caught as 

 far north as 40°. It has been reported recently 

 off Australia by Whitley (1954). LaMonte (in 

 Gabrielson and LaMonte 1950, p. 515) showed a 

 photograph of a black marlin from off Acapulco 

 which almost certainly is of this species because 

 the fin is folded against the side, and the body 

 shape, height of first dorsal, and the very short 

 mandible are typical of ampla. 



The localities where ampla has been taken by 

 the Japanese longline fishery are shown in the 

 atlas prepared by the Nankai Regional Research 

 Laboratory (Yabuta 1954). Catches are reported 

 from the South China Sea off Hainan Island, from 

 the Celebes Sea just east of the Philippines off 

 northern New Guinea, and then almost continously 

 along the Equator east to 155° W. longitude. The 

 best catches were made during the summer months 

 at 10° to 15° N. latitude north of the Caroline 

 Islands. A few were taken during winter months 

 in the albacore fishery along 30° N. latitude, east 

 of Japan as far as 175° W. longitude, north of 

 Midway. They also were taken at fishing stations 

 in December and January in the Indian Ocean 

 along the coasts of Java, Sumatra, and in the 

 vicinity of the Nicobar Islands. Special concen- 

 trations were found during February 1952 off 

 northwest Australia at about 15° S. latitude, 118° 

 E. longitude, and in the vicinity of the Solomon 

 Islands. In the Hawaiian longline fishery, ampla 



