Methods for the Preparation of Pacifi c Spiny Dogfi sh, Squalus suckleyi, Fin Spines and Vertebrae and an Overview of Age Determination CINDY A. TRIBUZIO, MARY ELIZABETH MATTA, CHRISTOPHER GBURSKI, NIKKI ATKINS, and WALTER BUBLEY Introduction To be viable for an age determina- North Pacifi c Ocean, ranging from the tion study, a hard structure must form Koreas and Japan through Russian and Age determination of elasmobranchs visible, annually-formed growth pat- Alaskan waters to the North Ameri- presents unique challenges compared terns. Typically, these growth patterns can west coast, reaching as far south to that of teleosts. Elasmobranchs do consist of alternating light and dark as Baja California (Ebert et al., 2010). not have calcareous otoliths or scales, bands; each pair of growth bands is Squalus suckleyi was previously structures commonly used to age te- termed an “annulus,” representing 1 thought to be identical to its Atlantic leosts. Various techniques, including year of growth. Note that this differs counterpart, S. acanthias, but genetic, bomb-radiocarbon dating, histologi- from the standard English defi nition meristic, and morphological evalua- cal staining, and X-radiography, have of the word annulus, which is derived tion has proven them to be two distinct been applied to hard structures such from the Latin word “anus” meaning species (Ebert et al., 2010). Further, as fi n spines, vertebrae, and caudal “ring,” not “annus” meaning “year” S. suckleyi differs from S. acanthias thorns to age elasmobranchs (Cail- (Panfi li et al., 2002). in several key life history attributes, liet and Goldman, 2004; Carlson and In most elasmobranch studies, sag- including slower growth, larger maxi- Goldman, 2006). ittally sectioned vertebrae are selected mum size, and later maturity. Much of as the primary age structure (Cailliet the existing scientifi c literature from Cindy A. Tribuzio, corresponding author (cindy. and Goldman, 2004), although clarity the North Pacifi c Ocean refers to spiny [email protected]), is with the Auke Bay Labo- of annuli within vertebrae is largely dogfi sh collected there as S. acanthias, ratory, Alaska Fisheries Science Center, Nation- al Marine Fisheries Service, NOAA, 17109 Pt. species-specifi c. For some species, and it is important to note that the spe- Lena Loop Road, Juneau, AK 99801. Mary Eliz- vertebra growth patterns are not dis- cies name is now considered incorrect abeth Matta and Christopher Gburski are with cernible and thus alternative structures in previous literature and should be the Resource Ecology and Fisheries Manage- ment Division, Alaska Fisheries Science Cen- such as the neural arch (McFarlane et considered S. suckleyi. ter, National Marine Fisheries Service, NOAA, al., 2002) or dorsal fi n spine (Clarke The dorsal fi n spine method has 7600 Sand Point Way NE, Seattle, WA 98115. Nikki Atkins is with the Fishery Resource Anal- and Irvine, 2006) must be used. been used to age S. suckleyi and S. ysis and Monitoring Division, Northwest Fish- Squaliform sharks (dogfi shes) are acanthias since the 1930’s. In this eries Science Center, National Marine Fisheries one of two orders of elasmobranchs method, annuli on the enamel of the Service, NOAA, 2032 SE OSU Drive, Newport, OR 97365. Walter Bubley is with the South Car- possessing dorsal fi n spines (Clark and second dorsal fi n spine are viewed olina Department of Natural Resources, Marine Irvine, 2006). Pacifi c spiny dogfi sh, and counted using refl ected light and Resources Research Institute, 217 Fort Johnson Squalus suckleyi (hereafter termed a dissecting microscope or with im- Road, Charleston, SC 29412. “spiny dogfi sh”), is a species of Squal- age analysis software. However, this doi: dx.doi.org/10.7755/MFR.78.1–2.1 iform shark found throughout the may not be the best method to accu- rately describe age and growth of the species. Because the dorsal fi n spine ABSTRACT— The Pacifi c spiny dogfi sh, ability due to diffi culty in interpreting fi n extends from the body into the envi- Squalus suckleyi, is a small shark spe- spine growth patterns. A new method was ronment, breakage and erosion of the cies commonly found in the North Pacifi c recently developed for S. acanthias, a North fi n spine often occurs over time. Thus, Ocean. Age determination for this species Atlantic Ocean congener of S. suckleyi, us- larger, older spiny dogfi sh tend to have has historically been conducted by exami- ing histologically stained thin sections of fi n spines with more wear than small- nation of the dorsal fi n spine with little vertebrae instead of dorsal fi n spines for change in methodology since the 1930’s. age estimation. Here, we apply this histo- er, younger fi sh. Despite extensive use, there are two major logical method to vertebrae of S. suckleyi Ketchen (1975) developed an algo- caveats associated with fi n spines as age and describe the historic methodology for rithm to estimate the number of miss- structures: 1) fi n spines protrude from the dorsal fi n spines. This document presents ing annuli in the worn portion of the body and are subject to damage, requiring detailed procedures for both methods, in- estimation of annuli contained in missing cluding sample collection, sample prepara- fi n spine using the relationship be- portions of the fi n spine and 2) there is a tion, and age estimation criteria for each tween the enamel base diameter and high degree of inter- and intra-reader vari- structure. the number of annuli counted on un- 78(1–2) 1 worn fi n spines. An alternative analyti- vertebrae do not wear or break over southwestern edge of its range, in par- cal method for estimating lost annuli time as fi n spines do, therefore reduc- ticular, S. japonicus, S. blainville, and was proposed by Cheng (2012); how- ing one source of variability and error S. brevirostris. However, S. suckleyi is ever, few laboratories have adopted in the age determination process (i.e., generally easy to distinguish from the this method to date. the need to use a modeled estimate for other Squalus species because of the Taylor et al. (2013) conducted a de- the number of missing annuli in worn white spots along the sides and be- tailed examination of the Ketchen and fi n spines). Furthermore, age estimates cause the origin of the fi rst dorsal fi n Cheng analytical approaches and de- derived from vertebrae are far more spine is posterior to the rear free tips termined that both methods produced precise than those from spines (Bubley of the pectoral fi ns, whereas in most questionable age estimates for larger, et al., 2012). species of Squalus occurring in the older fi sh, and they further recom- Results are not presented in this western North Pacifi c Ocean the fi rst mended an examination of new meth- paper as it is intended solely as a dorsal fi n and spine are located above ods. Attempts to improve Ketchen’s technical guide for the collection, lab- the pectoral fi ns (Compagno, 1984). algorithm (McFarlane and King, 2009) oratory processing, and interpretation The fi rst steps in spiny dogfi sh col- have not addressed problems of error of age structures. This paper is part of lection are to sex and measure each from other sources (e.g., natural vari- a larger spiny dogfi sh age determina- fi sh. Sex can be determined externally; ability, reader error); therefore, the tion project. While both methods are males have paired claspers attached to historical method continues to be used presented here to improve precision the pelvic fi ns. Special care may be (Tribuzio et al., 2010). and document ageing criteria for use needed when identifying sex of very Fin spine-based age estimates of by other laboratories, it is important small (immature) animals, as male both S. suckleyi and S. acanthias have to note that at this time, the vertebra claspers can be small. There are four been validated using bomb-derived method does not appear to be appro- commonly used length measurements radiocarbon (Campana et al., 2006). priate for older spiny dogfi sh (Tibuzio for spiny dogfi sh (Tribuzio et al., Furthermore, annual periodicity of et al., in press). Documenting age de- 2009), measured from the tip of the the fi n spine banding pattern has been termination methods is imperative, as snout to 1) the dorsal pre-caudal pit verifi ed by oxytetracycline (OTC) in- criteria used for identifying annuli can (pre-caudal length, PCL); 2) the deep- jections and tag/recapture methods on drift over time and among agencies. est indentation of the tail fork (fork S. suckleyi that were at liberty up to This paper provides a central reference length, FL); 3) the dorsal tip of the 21 yr (McFarlane and Beamish, 1987; for all laboratories involved in spiny tail in its natural position (natural to- McFarlane and King, 2009). However, dogfi sh age determination and will tal length, TLnat); and 4) the dorsal tip the low precision of fi n spine-based promote consistency between the two of the tail with the upper lobe of the age estimates (CV = 19%; Rice et al., methods and among spiny dogfi sh age caudal fi n depressed to align with the 2009; Tribuzio et al., 2010) is prob- readers, in the hopes of improving in- horizontal axis of the body (extended lematic, and systematic bias among ter- and intra-laboratory precision. total length, TLext) (Fig. 1). However, age determination laboratories oc- PCL has the least amount of mea- curs despite age validation (Rice et Sample Collection surement error and is often the easi- al., 2009). Measurement errors among Squalus suckleyi is a small shark est to measure.