Relationships Between Otolith Size and Body Size for Hawaiian Reef Fishes1
By Longenecker, Ken
Abstract: Estimating body size of fishes from remains recovered from piscivores, archaeological sites, and sedimentary deposits is desirable but rarely accomplished because the relationships between the size of a fish and its durable anatomical structures are largely unknown. Regression equations to predict the size or weight of 41 common Hawaiian reef fishes from sagittae (saccular otoliths) are presented. Data are also grouped into higher taxa to permit size predictions when otoliths cannot be assigned to species. ANIMAL REMAINS are frequently used to reconstruct faunal assemblages in dietary analysis, archaeology, geology, and paleontology. This work on fishes is difficult because bones and scales can be hard to identify, their numbers may vary among individuals, and the relationship between the size of a bone or scale and the size of the fish that produced it may be unknown.
Otoliths, particularly sagittae or saccular otoliths, may be used to circumvent these problems because they are taxonomically distinct and the number per individual does not vary. Further, they are harder and more durable than skeletal components and are often the only identifiable remains found in geological strata (Rivaton and Bourret 1999). Otoliths are common fossils throughout broad geographic and stratigraphic ranges (Hecht 1990), may be the only evidence that a fish species was present at archaeological sites (Weisler 2002), and are often the only identi- fiable fish remains found in the stomachs or feces of predators (Hecht 1990). Finally, the size of otoliths can be used to estimate fish size, and a fair number of these relationships have been described for fishes worldwide (Frost and Lowry 1981, Echevierria 1987, Gamboa 1991, Plotz et al. 1991, Smale et al. 1995, Granadeiro and Silva 2000, Harvey et al. 2000, Mikkelsen et al. 2002, Naya et al. 2002, Waessle et al. 2003).
No large-scale analysis of otolith-fish size relationships has been conducted for Hawaiian fishes. With 1,250 species of which 22.3% of coastal species are endemic (Mundy 2005), this information is needed for research on resource use by early Hawaiians, dietary analysis of piscivores, and reconstruction of ancient marine environments. Here I present analyses of the relationship between otolith length and fish length or weight. These results complement a guide to the identification of Hawaiian fish otoliths (Dye and Longenecker 2004).
MATERIALS AND METHODS
Fishes were collected from May 2000 through September 2002 from the forereef of Kane’ohe Bay. Collecting area boundaries were the 5.5 m isobath shoreward (parallel to the barrier reef ), the 30.5 m isobath seaward (the bottom of a drop-off at the mouth of the bay), and boating channels laterally. All specimens were identified, then standard length (in millimeters) and total body weight (in grams) were measured. Sagittae were removed and stored dry in tissue culture plates, with one species per plate and one individual per well. One otolith per fish was haphazardly chosen (or the lone otolith if one was broken or missing) and measured with digital calipers along the rostrum to postrostrum axis (nomenclature of Secor et al. ).
Least squares regression analysis of otolith length versus standard length and otolith length versus total body weight was performed for each species. Data were also combined to search for the same relationships within all higher taxa. Equations are presented only for regressions with P
RESULTS AND DISCUSSION
Standard length can be modeled as a linear function of otolith length (Appendix 1), and total body weight can be predicted using a power function of otolith length (Appendix 2). For all but two cases, the otolithweight relationships could be modeled with two parameters. The exceptions were threeparameter power functions.
Both appendixes are organized phylogenetically. Species included in supraspecific analyses are either annotated at the end of the appendix (for space considerations) or listed parenthetically adjacent to taxon name if no significant relationship was found for that species alone. Species with significant otolith-fish size relationships are listed along with their regression equations below the supraspecific taxon heading. For example, results for the length regression of the subfamily Pomacentrinae (Appendix 1) include four species: Stegastes marginatus, which did not yield a significant regression on its own, listed parenthetically beside the subfamily name; Abudefduf abdominalis, which did have a significant relationship, listed below the subfamily name; and Plectroglyphidodon imparipennis and P. johnstonianus, indicated by an annotation to the generic name. A significant regression could not be constructed for either species alone; however, a genus-level relationship was significant.
This phylogenetic grouping serves three purposes. First, it can be used to predict the size of a fish from otoliths larger or smaller than those used in the analyses. Although linear relationships with high coefficients of determination, such as many of those in Appendix 1, might reasonably be used for extrapolation, doing so with curvilinear relationships (Appendix 2) is likely to provide unrealistic estimates. Using a relationship for a higher taxon, based on a wider size range of individuals, may help avoid the need for extrapolation. Second, because otoliths are more easily assigned to higher taxa than to species, the groupings provide reasonable predictions of fish size when a species-level identification of an otolith is not feasible. The more-general higher-taxa regressions should be used in such cases. Third, these groups also provide predictions for species not included in the analysis. With 1,250 fishes known from Hawai’i, the equations presented here represent just a fraction of the work necessary for detailed reconstruction of fish assemblages. In the interim, these higher-taxa relationships may suffice for predicting fish sizes.
I thank Annmarie Dehn, Ross Langston, and Joanna Philippoff for donating or helping collect many of the specimens; and Klahzia Longenecker for assisting with otolith extractions.
1 This paper is funded in part by a grant/cooperative agreement from the National Oceanic and Atmospheric Administration, Project no. R/FM-8, which is sponsored by the University of Hawai’i Sea Grant College Program, SOEST, under Institutional Grants No. NA86RG0041 and NA16RG2254 from NOAA Office of Sea Grant, Department of Commerce. The views expressed herein are those of the author and do not necessarily reflect the views of NOAA or any of its subagencies. UNIHISEAGRANT-JC-02-32. NOAA Fisheries, Pacific Islands Fisheries Science Center supported preparation of the manuscript. This is Hawai’i Institute of Marine Biology contribution no. 1297 and contribution 2007-014 of the Hawai’i Biological Survey. Manuscript accepted 28 November 2007.
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2 Hawai’i Institute of Marine Biology, P.O. Box 1346, Kane’ohe, Hawai’i 96744. Current address: Bishop Museum, 1525 Bernice Street, Honolulu, Hawai’i 96817 (e-mail: email@example.com).
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