RALSTON ami POLOVINA: COMMERCIAL DKhT-SKA HANDLINK FISHERY 



240 



— 200 



-i i r 



J I I I I I l I i 



J L 



400 600 800 1000 



EFFORT ( FISHERMAN - DAYS ) 



1200 



1400 



Figure 3.— Fitted production curves of CPUE and catch on 

 fishing effort for the total aggregate landings of commercial 

 bottom fish species from the Maui-Lanai-Kahoolawe-Molokai 

 bank. 



probably low. The HDFG data provide informa- 

 tion on only a portion of the harvest of these 

 species. Recreational bottom fishing is very 

 popular around the main islands of the Hawaiian 

 Archipelago but its relative impact is completely 

 unknown. Furthermore, underreporting by 

 commercial fishermen is also likely but its extent 

 is hard to determine. Based on these considera- 

 tions, the overall estimate of annual production 

 calculated for the MLKM bank (272 kg bottom 

 fish/nmi 100-fathom isobath) is best considered a 

 lower bound for the surplus production obtain- 

 able from this type of fishery. In spite of the 

 difficulty in determining precise estimates of 

 productivity it would appear that the added 

 effects of commercial and recreational fishing 

 are close to fully exploiting the fishery (Fig. 3). In 

 1978 over 96 t (metric tons) of bottom fish were 

 harvested from the MLKM bank by commercial 

 fishermen. 



DISCUSSION 



Fishing Effort 



One of the primary goals of this study has been 

 to estimate the commercial productivity of 

 Hawaii's offshore bottom fish resources. We have 

 met with mixed success in our attempt because 



only one of the four study banks (Fig. 2) con- 

 sistently provided significant results. In spite of 

 this difficulty the MLKM is the largest of the 

 four, producing well over half the total catch of 

 bottom fish. The lack of statistical significance 

 from the remaining banks may be due to several 

 factors. 



The impact of fishing is measured by 

 correlating changes in fishing effort with catch 

 rate (CPUE). If the observed range of fishing 

 effort is too small to render an appreciable 

 change in stock density then the impact of 

 fishing cannot be measured. This hypothesis of 

 insufficient variation in fishing mortality does 

 not explain the lack of correlation between 

 CPUE and effort from the Hawaii, Oahu, and 

 KNK banks, however. The range in fishing 

 intensity (defined as fisherman-days/nmi 100- 

 fathom isobath or fishing effort per unit area) 

 between the period 1959 and 1978 was the least 

 for the MLKM bank where only a threefold 

 difference in intensity was experienced. In 

 contrast, fishing intensities ranged upwards 

 from 4-fold (KNK) to 26-fold (Oahu) among the 

 remaining banks. The range of fishing intensity 

 to which the MLKM bank has been exposed is the 

 least of all four sites and from this observation it 

 would be reasonable to assume that all banks 

 have experienced substantial variation in 

 fishing mortality. 



This follows logically only if the catchability 

 coefficients for all banks are similar. It is 

 probable, however, that these four regions differ 

 with respect to the impact of one unit of fishing 

 effort on the various stocks. If differences in 

 fishable area are corrected for, a fisherman-day 

 recorded from Oahu may well represent less 

 fishing mortality than the same figure from the 

 MLKM bank. In this regard, preliminary 

 analyses based on fishing intensity rather than 

 fishing effort showed that significant differences 

 exist among the four banks in the relationship of 

 CPUE to fishing intensity, precluding the option 

 of pooling the data across banks (see Munro 1978 

 for a production analysis based on fishing 

 intensity). In principle then, differences in catch- 

 ability could explain the poor results from 

 Hawaii, Oahu, and KNK if the catchability co- 

 efficient equating fisherman-days to fishing 

 mortality from these areas is substantially less 

 than that for MLKM. Variation in the extent of 

 unreported catch among banks could compound 

 this effect. 



Other factors which remain unaccounted for 



443 



