DeMartIni et al.: Age and growth oi Xiphios glodius 



357 



Materials and methods 



Collections and measurements of fish 



All swordfish used for age determination in this study 

 were collected from within the general region of the 

 Hawaii-based pelagic longline fishery (Ito et al., 1998; 

 DeMartini et al., 2000, Fig. 2 therein). About 95% of the 

 specimens used were caught by commercial longlines 

 during March 1994-June 1997; specimen collections 

 were conducted and fish measurements were recorded 

 by National Oceanic and Atmospheric Administration 

 (NOAA) Fisheries, Southwest Region observers. The 

 remaining 57c of the fish were caught on research cruises 

 conducted during April-May 1992 and 1993, September 

 1996, and March-April 1997. Fish were measured (eye- 

 to-fork length, EFL, in cm) before dressing (removal 

 of head, entrails, tail, and fins) at sea. As they were 

 dressed, sex was scored according to macroscopic cri- 

 teria and later validated by microscopic evaluation of 

 histological preparations of gonads for subsamples of the 

 fish (DeMartini et al., 2000). When the fins of swordfish 

 were removed at sea, either a portion or the entire first 

 anal fin was collected and frozen. The braincase section, 

 including the region of the semicircular canals was col- 

 lected from juvenile and young adult swordfish, either 

 when fish were beheaded at sea or when whole frozen 

 bycatch specimens were thawed and dissected ashore. 

 Additional larval and early young-of-year specimens (4 

 mm to 20 cm EFL) were collected by a neuston trawl 

 (5-mm and 0.505-mm mesh in wings and codend, respec- 

 tively) leeward of Hawaii Island during 1995-97; intact 

 specimens were stored frozen before otolith extraction. 



Laboratory processing and specimen examination 



Frozen first anal fins were thawed, and the second spiny 

 ray was selected (Berkeley and Houde, 1983), removed, 

 and cleaned of all tissue. It was then dried in a dehydra- 

 tor for 24-48 h at about 60"^C, and three adjacent, trans- 

 verse sections were cut with a low-speed saw. The first 

 cut was made according to standard protocol (Ehrhardt 

 et al., 1996) but at a newly defined position (distal end of 

 the medial suture, hereafter "suture terminus") located 

 about 159f of the distance beyond the basal condyle. 

 Subsequent cuts were made distal to the first, spaced 

 to provide wafers =1 mm thick (Uchiyama et al., 1998). 

 The location chosen for the cuts was different from the 

 conventional standard (i.e., at a distance above the 

 basal condyle equal to one-half the condyle width=c?/2) 

 currently used in swordfish aging studies (Sun et al., 

 2002). The unconventional cut was necessary because 

 the condyle of the second ray is often severed or lost 

 during the removal of fins by fishermen at sea. A small 

 series of matched (same fish) fin ray samples were cut 

 at the suture terminus and at the d/2 positions; some 

 of these were also cut immediately distal to the condyle 

 (basal cut) and the numbers of annuli were counted 

 and compared. Cross sections of rays were preserved in 

 mounting media on glass microscope slides and stored 



(without cover slips) in sealed boxes. Otoliths (sagittae) 

 were dissected from frozen larvae and young adults at 

 the NOAA Fisheries, Pacific Islands Fisheries Science 

 Center (Honolulu Laboratory), and stored dry after 

 having been cleaned, rinsed with water, and dried with 

 95% ethanol (EtOH). 



Fin ray annuli, each defined as a single pair of 

 opaque and translucent bands completely encircling 

 the cross-section hemisphere without partial and split 

 checks (Ehrhardt et al., 1996; Sun et al., 2002), were 

 enumerated. At first examination, about 1% of all cross 

 sections were deemed unreadable and discarded. The 

 distances separating the distal edges of the translucent 

 band of each annulus were measured, the opaque versus 

 translucent nature of cross-section edges was noted, 

 and marginal increment ratios (MIRs) were measured 

 in marginal increment analysis (Campana, 2001). A 

 series of MIRs was calculated for each specimen of age 

 1 or older by using the formula (Prince et al., 1988; 

 Sun et al., 2002); 



M/i? = (/?,„, -i?„)/(fl„-i?„_i), 



where i?,^, = total radius of fin ray specimen; and 



R^ and fl„ j = the distance from ray focus to the nth 

 and (n-l)th annuli, respectively. 



The focus was identified at the proximal confluence of 

 growth striations (Ehrhardt et al., 1996). Because only 

 one image analyzer was available and multiple readers 

 had to work concurrently, several methods were used to 

 examine specimens: 1) slide-mounted ray cross sections 

 were viewed with a dissecting microscope (10-60x) by 

 reflected light against a black background; 2) grey-scale 

 TIFF file images of slide-mounted cross sections were 

 prepared by using a digital camera system (Sony DKC- 

 5000 and VCL-713BXS macro-zoom lens; Sony USA, 

 New York, NY), processed to enhance contrast and 

 sharpness using Adobe PhotoShop vers. 3, and viewed by 

 means of two shareware available in the public domain 

 (NIH Image vers. 1.58; National Institutes of Health, 

 Bethesda, MD; and Scion Image vers. Beta 4.0.2; Scion 

 Corporation, Frederick, MD), for MAC and PC, respec- 

 tively. Annuli were counted independently by two pri- 

 mary readers (1 and 2) without reference to length, sex, 

 or month of capture. Each reader made two or more 

 readings, spaced by at least several months to cloak the 

 identity of individual specimens. Presumed daily growth 

 increments (DGIs) were enumerated by using digitized 

 composite images ( scanning electron micrographs of 

 sagittae) (Humphreys, 2000). 



If known-age specimens are unavailable for use in cal- 

 ibrating age assignments, a reference collection should 

 be evaluated and a consensus or majority agreement 

 used to provide a reference standard (Campana, 2001). 

 We therefore enlisted the services of four other North 

 and South Pacific laboratories that either recently had 

 or were presently conducting aging studies of swordfish 

 (Institute of Oceanography, National Taiwan University 

 [NTU]; the National Research Institute of Far Seas 



