Age estimation of billfishes (Kajikiaspp.) using fin spine cross-sections: the need for an international code of practice

Abstract

-Fin spine ageing is the most common technique used to estimate age and growth parameters of large pelagic billfishes from the families Istiophoridae and Xiphiidae. The most suitable methods for processing and interpreting these calcified structures for age estimation have not been clearly defined. Methodological differences between unvalidated ageing studies are of particular concern for highly migratory species because multiple researchers in different regions of the world may conduct age estimates on the same species or stock. This review provides a critical overview of the methods used in previous fin spine ageing studies on billfishes and provides recommendations towards the development of a standardized protocol for estimating the age of striped marlin, Kajikia audax and white marlin, Kajikia albida. Three on-going fin spine ageing studies from Australia, Hawaii, and Florida are used to illustrate some of the considerations and difficulties encountered when developing an ageing protocol for highly migratory fish species. Particular areas of concern that may influence age and growth estimates included differences in fin spine selection, sectioning methods, criteria for identifying and measuring annuli, distinguishing false annuli, validation procedures, identification of the first annulus, and methods used to replace annuli lost due to vascularization of the fin spine core. Key words:Age determination / Sclerochronology / Growth / Population dynamics / Marlin / Tuna longline fisheries Résumé -Déterminer l'âge à partir des rayons épineux des nageoires est la technique la plus commune pour déter-miner l'âge et les paramètres de croissance des grands poissons pélagiques à rostre de la famille des Istiophoridés et Xiphiidés, marlins, voiliers et espadons. Les méthodes les plus adaptées pour interpréter et traiter ces pièces osseuses pour l'estimation de l'âge n'ont pas été clairement définies. Des différences méthodologiques entre des études nonvalides d'âge prêtent à conséquence pour ces grands migrateurs car de nombreux chercheurs de différentes régions du monde peuvent faire des déterminations d'âge d'une même espèce et d'un même stock. Cette synthèse présente une analyse critique des méthodes utilisées antérieurement dans les études sur la détermination de l'âge à partir des rayons des nageoires de marlins et elle fournit des recommandations afin de développer un protocole standard pour détermi-ner l'âge du marlin rayé, Kajikia audax (ex. Tetrapturus audax), et du marlin blanc, Kajikia albida (ex. Tetrapturus albidus). Trois études en cours, en Australie, Hawaï et Floride, sont utilisées pour illustrer certaines des considérations et difficultés rencontrées lors du développement d'un protocole pour déterminer l'âge des poissons grands migrateurs. Les points pouvant influencer l'estimation de l'âge et de la croissance comprennent, en particulier, les différences dans la sélection des rayons d'une nageoire, les méthodes de coupe fine, les critères d'identification et de mesure des annuli, la distinct...

Direct ageing of Thunnus thynnus from the eastern Atlantic Ocean and western Mediterranean Sea using dorsal fin spines

“…Further research is required in this context for reliable indirect validation of the ageing method using R MI analysis. Sectioning location is an important factor to be considered because the appearance and location of annuli may vary between sectioning levels (Kopf et al, 2010). In this context, how an alternative sectioning location (S1⋅5) could reduce the influence of nucleus vascularization to improve recognition of the innermost translucent bands was analysed.…”

“…The formation of sub-annual bands has been related to migrations or different diet regimes (Compeán-Jimenez & Bard, 1983;Cort, 1991;Tserpes & Tsimenides, 1995;Sun et al, 2002) as well as to spawning events when animals invest more energy in producing gametes than in somatic growth (Sun et al, 2001;Cerna, 2009). Even though analysis of the cause of their formation is beyond the scope of this study, discrimination of false increments from true annuli is a key factor in ageing analysis and has the potential to be a large source of error (Kopf et al, 2010). Based on observations, these double translucent bands appeared too close together to be considered a year mark and they were usually distinguishable within the general pattern of wide summer opaque bands.…”

“…Fin ray spines have been used to age pelagic fishes such as billfishes and tuna species (Beamish, 1981;Prince & Pulos, 1983;Kopf et al, 2010) mainly because sampling is easy and does not damage the fish, which is impractical in certain fisheries such as the Atlantic traps. In addition, the preparation of spines is less time-consuming than other structures such as vertebrae, as only transverse sections are needed and staining is not necessary .…”

“…As the fish grow, the spine nucleus is reabsorbed replacing the earliest annuli by vascular tissue (Rooker et al, 2007). This process, known as nucleus vascularization, is the greatest disadvantage of using this calcified structure for ageing purposes, as it might result in significant age underestimation and growth overestimation (Panfili et al, 2002;Drew et al, 2006;Kopf et al, 2010). Nucleus vascularization has been reported in several tuna species with frequent use of the method developed by Hill et al (1989) to replace lost annuli (Compeán-Jimenez & Bard, 1983;Tserpes & Tsimenides, 1995;Chiang et al, 2004;Zaboukas & Megalofonou, 2007;Duarte-Neto et al, 2012;Farley et al, 2013).…”

Identification of a nonlethal method for aging tautog (Tautoga onitis)

“…The precision of age estimates was higher for pelvic-fin spines in comparison with final ages than from any other structure tested. Furthermore, with the pelvic-fin spines used in this study, we did not find the core to be obscured by vascularization as has been seen in fin spines of other species (e.g., Keller Kopf et al, 2010;Kopf and Davie, 2011;Landa et al, 2015). Although the tautog in our study reached only age 12, we believe that the growth bands in the spines would be discernible in tautog of considerably older ages.…”