Low CPUE levels of black marlin, < 0.5 marlin/1,000 hooks, 

 are common throughout most of the southwest Pacific from lat. 

 30°S northward during every month of the year. The southerly 

 limit in the summer through fall (January-May) is about lat. 40°S. 

 The only area commonly showing a low CPUE level throughout 

 the year is the area from New Caledonia east, in a latitudinal band 

 of lat. 10° to 20°S. A retraction of the low CPUE levels to the 

 northwest from the New Zealand area is observed in October 

 through December. CPUE data indicate that minor catches of 

 black marlin could be expected in many areas of the southwest 

 Pacific in most months. 



To better define the changes in areas of high CPUE, the ap- 

 proximate center of high CPUE was estimated and its 

 geographical position by month is given in Figure 15. A pro- 

 gressive southward movement of high CPUE areas from the tag- 

 ging area is observed for December and January, reaching its 

 southern-most limit by February. A substantial geographical shift 

 in high CPUE center from about lat. 28° to 18°S has occured. In 

 April, the shift is northeastward to the Solomon Islands area Oat. 

 10°S). CPUE center moves northwestward to about lat. 5°S in 

 May and June. The southward movement is again evident in July- 

 September, shifting the high CPUE center from lat. 5°S to about 

 lat. 10° to 11°S between New Guinea and the Solomon Islands. 



Figure 15. — Monthly movements of the approximate center (as determined by eye- 

 fit) of high longline CPUE for black marlin as observed in Figure 14a, b, c. 



DISCUSSION AND SUMMARY 



The north Queensland, Australia, area is one of the most pro- 

 ductive locations in the Pacific for anglers using rod-and-reel to 

 catch black marlin. The excellent fishing attracts anglers from 

 about the world, as indicated by the several countries represented 



in the tag recovery summary (see Table 2). An important factor 

 was that many of the anglers and charterboat operators in this 

 area were willing to tag and release black marlin. The number of 

 black marlin tagged off north Queensland (2,576) is the sum of 

 tag report forms returned by cooperating anglers. This represents 

 a minimum number of fish tagged, since some report forms are 

 not returned to the tagging agency (Squire 1974). The extent of 

 nonreporting of releases is assumed to be minimal in this area 

 because of the excellent management of the tagging effort by the 

 Cairns Game Fishing Club which distributed the tagging equip- 

 ment and maintained accurate records. 



Of the black marlin reported tagged during 1968-78, 60 tags 

 were returned for an overall return rate of 2.3"%. The maximum 

 return rate was observed in 1974, 5.1% for 335 marlin tagged with 

 H-type tags. This is a greater return rate than the 0.9% rate ex- 

 perienced for striped marlin tagged by anglers in the northeastern 

 Pacific (Squire 1974). For recapture data having information on 

 sex, 89% were reported to be males. 



The average weight of black marlin, as estimated at the time of 

 tagging, was approximately 175 kg (385 lb) each. Table 5 indicates 

 that substantial overestimates of black marlin weight at tagging 

 were recorded. The ability of an angler to estimate accurately the 

 weight of a large fish such as a black marlin actively swimming in 

 the water is subject to considerable error. The data presented in- 

 dicate that a reasonable level of accuracy (one that might produce 

 growth rate data or allow estimates of annual average size) is not 

 possible without the application of correction values. Estimated 

 weight data, given by average weight per year (Fig. 3), indicate 

 that estimated weights peaked in 1974 at 201 kg (445 lb)/fish. 

 Average shoreside landing weights, as recorded by the Cairns 

 Game Fishing Club, are about twice the estimated average weight 

 of tagged fish (Table 4). This would indicate that the fish being 

 landed for weighing are the large ones, and are not representative 

 of the average weight of all marlin caught. Landing larger marlin, 

 rather than tagging and releasing them, would tend to bias the 

 average estimated tagging weight lower. Figure 3 also shows an in- 

 crease in tagging effort northward along the Great Barrier Reef to 

 latitudes < 15°30 'S from the area immediate to Cairns, Australia 

 (lat. 17°S). This increase in tagging is evident in the latitudinal 

 band 15°30' to 14°30'S, beginning in 1972. 



The fish recaptured at 1 , 2, and 3 yr after tagging, were recap- 

 tured relatively close to the point of tagging. Fish released about 1 

 yr earlier were recovered a mean distance of 38.4 nmi, and 2 yr 

 earlier, at 58.3 nmi, from the point of tagging. The recovery of 

 tagged fish at annual increments near the tagging location in- 

 dicates that there is a tendency for at least some tagged black 

 marlin to return to the northwestern Coral Sea. 



To better define seasonal migratory patterns, tagging effort 

 should be distributed throughout the species range. In most cases 

 where tagging of oceanic species is conducted, the ideal distribu- 

 tion is not achieved. The tagging effort reported on in this paper is 

 from one portion of the black marlin distributional range in the 

 western Pacific and the associated Indo-Pacific area (Fig. 1). 

 Black marlin are presumed to spawn in the Coral Sea between Oc- 

 tober and December (Ueyanagi 1960), and tagging takes place at 

 this time at or near the spawning area. Black marlin are usually 

 caught by anglers in proximity to the outer edge of the Great Bar- 

 rier Reef, and most tagging takes place in this area. The commer- 

 cial longline fishing operations take place offshore from the tag- 

 ging area. The tagging area is within the high black marlin CPUE 

 area for commercial longline gear during the September-Decem- 

 ber period (see Fig. 14a, b, c) and is also within an area of 



17 



