356 



Abstract — We verified the age and 

 growth of swordfish (Xiphias gla- 

 dius) by comparing ages determined 

 from annuli in fin ray sections with 

 daily growth increments in otoliths. 

 Growth of swordfish of exploitable 

 sizes is described on the basis of 

 annuli present in cross sections of 

 the second ray of the first anal fins 

 of 1292 specimens (60-260 cm eye- 

 to-fork length, EFL) caught in the 

 region of the Hawaii-based pelagic 

 longline fishery. The position of the 

 initial fin ray annulus of swordfish 

 was verified for the first time with 

 the use of scanning electron micro- 

 graphs of presumed daily growth 

 increments present in the otoliths of 

 juveniles. Fish growth through age 7 

 was validated by marginal increment 

 analysis. Faster growth of females 

 was confirmed, and the standard 

 von Bertalanffy growth model was 

 identified as the most parsimonious 

 for describing growth in length for 

 fish greater than 60 cm EFL. The 

 observed growth of three fish, a 

 year-old in size when first caught 

 and then recaptured from 364 tol490 

 days later, is consistent with modeled 

 growth for fish of this size range. Our 

 novel approach to verifying age and 

 growth should increase confidence in 

 conducting an age-structured stock 

 assessment for swordfish in the North 

 Pacific Ocean. 



Age and growth of swordfish (Xiphias gladius) 

 caught by the Hawaii-based pelagic longline fishery 



Edward E. DeMartini (contact author) 



James H. Uchiyama 



Robert L. Humphreys Jr. 



Jeffrey D. Sampaga 



Happy A. Williams 



Email address for E, E. DeMartini: Edward. DemartinKginoaa.gov 



Pacific Islands Fisheries Science Center 

 National Manne Fisheries Service, NOAA 

 2570 Dole Street 

 Honolulu, Hawaii 96822-2396 



Manuscript submitted 21 September 2006 

 to the Scientific Editor's Office. 



Manuscript approved for publication 



20 December 2006 by the Scientific Editor. 



Fish. Bull. 105:356-367 (20071. 



Swordfish (Xiphias gladius) consti- 

 tute an economically important fish- 

 ery resource and have historically 

 supported many large-scale commer- 

 cial fisheries throughout the world's 

 oceans. During the 1990s, however, 

 declining catches and average sizes 

 of swordfish in Atlantic and Mediter- 

 ranean fisheries indicated possible or 

 likely overexploitation of these popu- 

 lations, and the status and manage- 

 ment of these stocks became a highly 

 publicized issue. 



Swordfish began to be a major spe- 

 cies targeted by the Hawaii-based 

 pelagic longline fishery in 1990 and 

 continued as such through the late 

 1990s, with landings peaking at 

 4000-6000 t in 1991-93 (Ito et al., 

 1998). This longline fishery targeted 

 swordfish within, and adjacent to, 

 fronts of the Subtropical Conver- 

 gence Zone north of Hawaii during 

 winter and late spring (Bigelow et 

 al., 1999). Beginning in 1999, gear 

 restrictions were imposed and in 

 mid-2001 a moratorium on shal- 

 low-set (swordfish style) longlining 

 within the swordfish fishery grounds 

 north of the equator was instated to 

 reduce interactions of fishing gear 

 with, and incidental take of, pro- 

 tected species — primarily loggerhead 

 turtles {Caretta caretta). The morato- 

 rium was lifted in March 2004 and 

 a regulated (by annual effort cap, 

 gear restrictions, take limit) longline 

 fishery was reinstated. 



A preliminary stock assessment for 

 swordfish caught in the North Pacific 

 Ocean, based on surplus production 

 models, was conducted in early 1999 

 and was updated in early 2002 to 

 include body length composition. No 

 age-structured assessment as yet ex- 

 ists for swordfish in the central North 

 Pacific. With the subsequent re-open- 

 ing of the Hawaii-based fishery, there 

 has been renewed interest in sword- 

 fish management in the North Pacific 

 and a recognized need for a more ro- 

 bust, age-structured basis for stock 

 assessment and documentation of age 

 distributions and growth rates. For 

 example. Sun et al. (2005) recently 

 assessed the population status of 

 swordfish taken by the tuna longline 

 fishery in the waters around Taiwan 

 in the western North Pacific. 



Our objectives in this study were 

 the following: 1) to evaluate the ac- 

 curacy and precision of our age 

 estimates; 2) to provide several 

 complementary data supporting a 

 predictable periodicity (on a yearly 

 basis) of annulus formation in cross 

 sections of anal-fin rays of swordfish 

 caught in the region of the Hawaii- 

 based longline fishery and examine 

 evidence verifying our age estimates 

 for these specimens; and 3) to esti- 

 mate sex-specific patterns of size-at- 

 age and growth to provide input for 

 pending age-structured assessments 

 of swordfish stock(s) in the central 

 North Pacific. 



