A Comparative Analysis of Growth Zones in Four Calcified Structures ofPacific Blue Marlin, Makaim nigricans Kevin T. Hill, Gregor M. Cailliet, and Richard L. Radtke ABSTRACT: Sagittae, vertebrae, and anal and Various calcified structures have been utilized dorsal fin spines collected from Pacific blue marlin for age estimation of the Istiophoridae. Dorsal in Kona, Hawaii were evaluated for legibility and spine sections have provided age estimate data interpretability of growth patterns, ease of collec­ for Atlantic sailfish, Istiophorus platypterus tion and processing, and the precision of the resul­ (Jolley 1974, 1977; Hedgepeth and Jolley 1983), tant annulus counts for use in estimating age. Atlantic white marlin, Tetrapterus albidus, and Sagittae, and anal and dorsal fin spine sections contained growth zones assumed to be annual Atlantic blue marlin, Makaira nigricans (Prince events and there was a linear relationship between et a1. 1984). Sagittal otoliths have been described age estimates of corresponding samples. Vertebrae as potentially useful structures for ageing most had numerous minute growth increments, but con­ billfish species (Radtke 1981, 1983; Radtke and tained no marks' which could be interpreted as an­ Dean 1981; Radtke et al. 1982; Prince et al. 1984; nual. While nonparametric tests revealed no signifi­ Wilson 1984; Cyr 1987). Jolley (1974) described cant difference between age estimates from differ­ numerous circuli in the vertebrae of sailfish; ent hardparts of the same fish, dorsal and anal however, both scales and vertebrae have now spine counts had the best agreement. Anal and been dismissed as stmctures for age estimation dorsal fin spines were more practical in terms of in billfish (Prince et al. 1984). ease of collection, processing, legibility, and inter­ Age estimation of Pacific blue marlin is still pretation; however, age estimates of spine samples from larger fish required a statistical replacement in the developmental stages, and most data of inner growth zones that were destroyed by have focused on sagittae (Radtke 1981; Wilson matrix expansion. Although more difficult to col­ 1984), with little effort on other skeletal lect and interpret, sagittae provide more detailed structures. The objective of the present study age information. Mean length-at-estimated age was to examine, interpret, and quantitatively data based on anal spine band counts are also pre­ compare growth patterns in the sagitta, sented. vertebrae, and dorsal and anal fin spines of blue marlin from Kona, HI. Each structure was evaluated in terms of ease of collection and Increased knowledge of billfish age and growth processing, legibility of growth patterns, and is essential for sensible management of these the relative precision of the resulting age fisheries. Although there is a paucity of such estimates. information for most billfish species, the West­ ern Pacific Fisheries Management Council was MATERIALS AND METHODS forced to draft a management plan for the Pacific blue marlin, Makai-ra. nigricans, with only Pacific blue marlin were sampled at the cursory data (WPFMC 1985). This lack of infor­ Hawaiian International Billfishing TOl.uonaments mation is due to the many difficulties involved in Augusts 1982 (n = 48), 1983 (n = 113), and with studies of large pelagic fish species (Prince 1984 (n = 98), and at the Kona Gold Jackpot and Pulos 1983), compounded by lack of routine tournament in May 1983 (n = 20>, Kailua-Kona, sampling programs by research agencies in the HI. Additional spine samples were obtained Pacific region. from the Pacific Gamefish Research Foundation (n = 32), the Hawaii Fishing Agency (on = 2), Kevin T. Hill. University of Hawaii. Depart.ment of Zoology. and the National Marine Fisheries Service, 2538 The Mall, Honolulu. HI 96822. Southeast Fisheries Center (a specimen from Gregor M. Cailliet. Moss Landing Marine Laboratories. Kona which was shipped to Miami for taxi­ P.O. Box 450, Moss Landing. CA 95039-0450. Richard L. Radtke. University of Hawaii, Oceanic Biology. dermy). Meristic data collected for each fish Hawaii Institute ofGeophysics. Honolulu, HI 96822. included lower jaw-fork length (LJFL to 0.1 cm), Manugcript accepted Apl·ill989. 829 Fishery Bulletin. U.S. 87: 829-843. FISHERY BULLETIN: VOL. 87. NO.4, 1989 roundweight (W to 0.5 lb converted to kg), sex, growth bands per millimeter of radius in the core and date of capture (Hill 1986). matrix, and that the first several visible bands were analogous in age to matching bands of the Anal and Dorsal Fin Spine Analyses compiled radius data. Anal and dorsal fin spines were collected and Sagitta Analyses prepared for analysis following modified meth­ ods of Prince et al. (1984) (Hill 1986). The second Sagitta were cleaned, prepared, and examined anal spine and sixth dorsal spine were selected following the methods of Radtke (1983) and Hill for age analysis. These were chosen because (986). Terminology for sagitta orientations is they were the thickest ofthe spine complex, and based on Prince et al. (1986). Sagittal otolith sections taken from spines anterior to these had weight (SW) was measured to the nearest 0.005 more prominent core matrices. mg. Age assignments were based on combined Spine length, defined as the distance from the counts of external growth features present on hole at the center of the condyle base to the spine the sagittae, which included lidges along the tip, was measured to the nearest millimeter. anterior rostrum edge on the ventral plane of Thin cross sections from anal and dorsal fin growth and ridges along the ventral surface of spines were taken at positions marked at 10% the medioventral mId medial planes of growth. and 5% (respectively) of the spine length from Previous studies of Istiophorid sagitta have the condyle hole. Spine sections were examined supplemented age estimates based on external using a compound stereoscope at 63 x and 120 x features with examination of internal growth magnification using either transmitted light or features using thin trmIsverse sections and light reflected light with a black background. The microscopy (Wilson 1984; Prince et al. 1986). focus of the spine was defined as the midpoint of However, Hill (1986) statistically compared age the distance between the anteriOl' and posterior estimates using external and internal growth portions of the spine along the midsagittal plane. features and found no significant difference be­ All growth bands were counted and their radii tween the two methods. Therefore, age esti­ measured with an ocular micrometer along the mates reported in this study were based only plane from the focus of the spine to the widest upon examination of external features. radius of the spine section. Spine radius (anal spine radius = AR; dorsal spine radius = DR) Vertebrae Analyses was defined as the distance from the focus to the outside edge of the spine along the same plane. Caudal vertebrae numbers 22 and 23 were re­ Statistical replacement of early missing anal moved from the area between the posterior por­ and dorsal spine growth bands in larger fish was tion of the second dorsal fin and the base of the accomplished by summmizing band radii statis­ caudal fin. These were the only vertebrae which tics from smaller, younger specimens in which could be removed without loweling the market these early bands were visible. Compiled band value of the fish. Vertebrae were simmered for radius statistics included spine samples which several hours in hot water to remove extraneous had at least the first or second band visible. tissues and then air dried for at least 72 hours. Unpaired t-tests were applied to compare corre­ Vertebral spines and arches were removed, sponding radii between those specimens contain­ anterior and posterior centra separated, cut ing the first and second bmId and to compare longitudinally along the dorsoventral plane, and corresponding band radii between sexes. stored in 95% isopropyl alcohol. Final corrected age estimates were assigned Vertebral cone depth (CD) (as defined by to spine samples missing early bands by compar­ Johnson 1983), referred to in this paper as cen­ ing the radii of the first four visible bands to the hum cone depth was measured to the nem'est means and 95% confidence limits of the compiled 0.05 mm. Growth rings were observed after data. When the radii of at least three successive carefully peeling away the thin layer of carti­ bands of the first four visible bands fitted well laginous tissue which covers the bony face of the within the 95% confidence limits of three or four centra. Centrum length, from focus to outside bands of the compiled data, corresponding ages edge, was divided into approximately 5 mm sec­ were assigned. The use of this technique to pro­ tions and the average number of rings per milli­ vide f'mal age estimates was based upon the as­ meter was calculated for each section by count­ sumption that there was a predictable number of ing three 1 mm portions in each section. Total 830 HILL ET AL.: ANALYSIS OF GROWTH ZONES IN PACIFIC BLUE MARLIN increment number was extrapolated from these Zar 1984). The significance of correlation coeffi­ data. cients (r) of the comparisons was tested using methods outlined by Schefler (1979). These rela­ Assessment ofAgeing Techniques tionships were also tested using a Wilcoxon Signed Ranks test <Sokal and Rohlf 1981). Owing The usefulness of each hardpart for estimating to the difference in increment types, vertebrae age in blue marlin was assessed by considering were not considered in these comparisons. ease of collection, hardpart growth, precision of To test the consistency of age estimates within age estimates, and the legibility of each hard­ and between readers, a subsample of 20 of each part. hardpart was read three times each by two To test the hypothesis that hardpart growth readers. Age estimates were compared using the was proportional to somatic growth of the ani­ Average Percent Error <APE) method of mals, both LJFL and W were modeled with AR, Beamish and Fournier (1981).