(lower panel) by quarters, 1963-1970. Hook rates on 

 the average are lower in the south than in the north, 

 even after allowing for differences in efficiency due 

 to setting time. Catch rates also seem to be more 

 variable in the north than in the south. There is a 

 marked seasonal pattern, with highest hook rates 

 generally during the fourth quarter in the north but 

 such a pattern is not evident in the south. The 

 fourth quarter peaks do not appear to be related to 

 corresponding variations in fishing effort and vessel 

 concentration, but likely represent changes in 

 catchability. 



Slight upward trends in catch rates are detectable 

 in both the north and the south, probably due to 

 increased efficiency as a result of increased night 

 sets and concentration on the more productive 

 swordfish grounds. 



The catch of swordfish (Fig. 6) on the average 

 has increased steadily since 1956. The peak year 

 was 1969 when about 1 12.000 swordfish were taken 

 and effort was at a maximum. Both effort and catch 

 decreased in 1970 but catch per effort in the north 

 did not decrease. In the south, a decrease in catch 

 per effort was noted during 1970. 



Before catch per effort can be used as a very good 

 indicator of swordfish abundance it will be neces- 

 sary to adjust all data for the effect of night sets. It 

 is also essential that the amounts captured by 

 coastal fisheries (which may be substantial) be ac- 

 counted for in the analysis; for example during 

 1970, nearly one million pounds of swordfish were 

 taken in the California surface fishery. Without the 

 inclusion of such data it is useless to speculate on 

 interpretation of the data represented herein as far 

 as stock assessment analyses are concerned. 



CONCLUSIONS AND 

 RECOMMENDATIONS 



The importance of billfishes to man has been 

 abundantly demonstrated and documented. Large 

 and important longline fisheries exist for billfishes 

 throughout the oceans of the world, especially in 

 the eastern Pacific Ocean. Important sport fisheries 

 upon which the economy of local communities de- 

 pend exist for billfishes, not to mention the impor- 

 tant recreational aspects of the fisheries to a large 

 segment of the population. Many subsistence 

 fisheries depend upon billfishes as their sole supply 

 of raw material. 



To insure rational utilization of this resource (ra- 

 tional in this sense implies some sort of sustained 



harvests for all categories of use) the effect of man's 

 exploitation on subsequent recruitment and average 

 size of the stock needs to be analyzed. This has not 

 been done for the billfishes of the eastern Pacific 

 Ocean, nor for the billfish of the Pacific Ocean gen- 

 erally, nor for any other ocean to our knowledge. 



In this paper we were unable to comment, except 

 in a very general way for some species, on the con- 

 dition of the billfish stocks in the eastern Pacific. 

 The reasons for this were primarily due to the fact 

 that the statistical data were limited, the area of 

 study extended to only long. 130°W, and vital statis- 

 tics concerning the population were not available. 



If it is the desire of mankind to manage the 

 fisheries for billfish so as to insure sustained har- 

 vests, at whatever level is deemed desirable, then 

 certain basic data and studies are needed. Some 

 idea of the relative distribution of the population 

 under study needs to be established. If the popula- 

 tion is divided into distinct units on the basis of 

 biological characteristics and/or distributional 

 characteristics of the fish and fishery, then this 

 must be determined; these units cannot be estab- 

 lished on the basis of jurisdictional limits. For each 

 of the population units, estimates of the total catch 

 are needed; these should include catches from 

 commercial, sport, or any other fishery which might 

 take meaningful quantities of billfish. Some idea of 

 fishing mortality is required; this is generally esti- 

 mated as a function of fishing effort. Therefore es- 

 timates of fishing effort for a major share of the 

 catch are needed as an index. The size composition 

 of the catch by strata of time and area are useful for 

 conducting studies of growth rates and mortality 

 rates, and are a necessary ingredient to the deter- 

 mination of the relationship between stock size and 

 subsequent recruitment. A sampling program to ob- 

 tain such measurements should include samples 

 from all important fisheries. 



From the discussions presented in this report it is 

 clear that all six of the billfish which occur in the 

 eastern Pacific Ocean are found all the way across 

 the Pacific. The longline fishery which takes these 

 six species exploits nearly every 5-degree square 

 over the range of each species. Evidence from bill- 

 fish tagging demonstrates that some species un- 

 dergo extensive migration in the Pacific Ocean 

 (Mather, 1969; James L. Squire, Jr. pers. comm.). 

 Such migrations have been demonstrated in other 

 oceans as well (Mather, 1969). 



It is clear that the scope of billfish studies needs 

 to be extended throughout the Pacific Ocean. Such 



329 



