Length-Weight Relationships for 71 Reef and Bottomfish Species from Tutuila and Aunu'u, American Samoa

Length-weight Relationships for 71 Reef and Bottomfish Species from Tutuila and Aunu′u, American Samoa Toby Matthews1, Domingo Ochavillo2, Sean Felise2, Teejay Letalie2, Mika Letuane2, Ekueta Schuster2, Auva'a Soonaolo2, Saolotoga Tofaeono2, Alama Tua2, Faleselau Tuilagi2 1Pacific Islands Fisheries Science Center National Marine Fisheries Service 1845 Wasp Boulevard Honolulu, HI 96818 2American Samoa Department of Marine and Wildlife Resources P.O. Box 3730 Pago Pago, American Samoa 96799 Honolulu, HI 96818 April 2019 NOAA Administrative Report H-19-03 https://doi.org/10.25923/r3wq-ax31 About this report Pacific Islands Fisheries Science Center Administrative Reports are issued to promptly disseminate scientific and technical information to marine resource managers, scientists, and the general public. Their contents cover a range of topics, including biological and economic research, stock assessment, trends in fisheries, and other subjects. Administrative Reports typically have not been reviewed outside the Center. As such, they are considered informal publications. The material presented in Administrative Reports may later be published in the formal scientific literature after more rigorous verification, editing, and peer review. Other publications are free to cite Administrative Reports as they wish provided the informal nature of the contents is clearly indicated and proper credit is given to the author(s). Recommended citation: Matthews, T., D. Ochavillo, S. Felise, T. Letalie, M. Letuane, E. Schuster, A. Soonaolo, S. Tofaeono, A. Tua, and F. Tuilagi. 2019. Length-weight relationships for 71 reef and bottomfish species from Tutuila and Aunu'u, American Samoa. Pacific Islands Fish. Sci. Cent., Natl. Mar. Fish. Serv., NOAA, Honolulu, HI 96818-5007. Pacific Islands Fish. Sci. Cent. Admin. Rep. H-19-03, 9 p. __________________________ Copies of this report are available from Science Operations Division Pacific Islands Fisheries Science Center National Marine Fisheries Service National Oceanic and Atmospheric Administration 1845 Wasp Boulevard, Building #176 Honolulu, Hawaii 96818 Or online at https://www.pifsc.noaa.gov/library/ Table of Contents INTRODUCTION ............................................................................................................................................ iv MATERIALS AND METHODS .......................................................................................................................... 1 Data Source ............................................................................................................................................... 1 Data Manipulation .................................................................................................................................... 2 RESULTS ........................................................................................................................................................ 3 DISCUSSION ................................................................................................................................................... 3 ACKNOWLEDGMENTS ................................................................................................................................... 4 REFERENCES .................................................................................................................................................. 4 TABLES ............................................................................................................ Error! Bookmark not defined. iii iv Introduction Length and weight are two fundamental metrics used in studying fishes and almost any other living organism. The allometric growth equation (Weight = a * Lengthb) is typically used to define the algebraic relationship between increases in fish length and weight. Once developed, this formula can be used to estimate weight with respect to length, or vice versa. For example, in creel surveys conducted by the American Samoa Department of Marine and Wildlife Resources (DMWR), the catch is rarely weighed in the field. To limit the time requested of fishermen, fish and invertebrates are quickly measured (Oram et al., 2010a; Oram et al., 2010b), and an estimated weight is calculated later. When length measurements are entered into the computer, missing weights are estimated based on known allometric growth formulas, either derived locally (1st choice) or from the literature for other regions (2nd choice). Very little information has been published in the scientific literature regarding length-weight relationships for marine species in American Samoa. Some information exists for large pelagic species from the more prominent longline and purse seine fisheries (e.g. Curran and Bigelow, 2016). American Samoa’s smaller-scale fisheries are very diverse and important to its culture and economy, yet much less well known. This study analyzes length-weight data collected from small-scale fisheries on the islands of Tutuila and Aunu′u, American Samoa, and summarizes allometric growth relationships determined for 71 fish species (and one invertebrate) for which sufficient data were available. Materials and Methods Data Source Data collected in American Samoa through the Pacific Islands Fisheries Science Center (PIFSC) Commercial Fisheries Bio-sampling (CFBS) Program were retrieved from a database maintained by the Western Pacific Fishery Information Network (WPacFIN). Bio-sampling data were collected by DMWR staff working with the CFBS from October 9, 2010, through September 26, 2015. Over this period, 2290 fishing trips were sampled. Trip breakdown by fishing method was 92.1% spearfishing (without scuba), 6.3% bottomfishing, 0.9% bottomfishing/trolling mixture, and 0.7% atule (hook and line used for catching bigeye scad). Most of the catch from these trips was identified to species, and fish-fork length in centimeters (cm) and weight in grams (g) were recorded for most specimens. For crustaceans, carapace width (crabs) or carapace length (lobsters) was used. Data were collected for 257,110 specimens, representing 282 species and/or major taxa. Generally, weight measurements were not made once sufficient amounts of paired length-weight data were collected. Paired length-weight measurements were collected for 99,780 specimens. Only paired length-weight measurements for organisms identified to species were included in the present analysis. 1 Data Manipulation Paired length-weight measurements were analyzed by species using the statistical language R (R Core Team, 2015). Code used in a similar analysis of CFBS data from Guam (Kamikawa et al., 2015; Branch and Essington, 2014) to automatically remove apparent outliers and produce parameters of the length-weight regressions was replicated for the American Samoa CFBS data. A few more stringent requirements were applied to screen out species with insufficient data quality and range. The general methodology is described below, including the differences between this and the previous study. For each species, paired length-weight measurements were fit to the model: W = a * Lb where W is the weight (g), L is the fork length (cm), and a and b are model parameters. To estimate the parameters via linear regression, a natural log transformation was applied, yielding: ln(W) = ln(a) + b * ln(L) Linear regression of the logged weight onto the logged length measurements produced estimates of ln(a) and b. The value of a was then estimated as eln(a). After running the initial regression for each species, outliers were identified in ln-ln space as those points at a distance greater than four residual standard error measurements away from the regression line. Outliers were removed and the remaining paired length-weight measurements were re-fit to the model. Although the code produced length-weight regression parameters for all species, only species deemed to have sufficient data for a reliable regression are reported. This was determined, based on three criteria: • There must be 100 or more paired length-weight measurements for each species. This limit was increased from 50 in the Guam study to ensure that sufficient data were available to compute a reliable regression. • The coefficient of determination (r2) of the linear regression must be greater than or equal to 0.9 (r2 ≥ 90%). This limit was increased from 0.8, which was used previously for Guam. • Length-weight data must cover at least 30% of the total length range for the species. The total length range was defined as being from zero to the maximum known length for a given species. This maximum was defined as whichever length was greater, the maximum value reported in FishBase (Froese and Pauly, 2016) or the maximum length found in American Samoa CFBS data. 2 Results Seventy-one species had sufficient paired data for a reliable length-weight regression (Table 1). One of these species, Panulirus penicillatus, is an invertebrate (spiny lobster) and the others are fish. Of the fish species, none had length-weight regression data from American Samoa and 12 had no length-weight regression data from any location in FishBase (Froese and Pauly, 2016). Table 2 provides length-weight regressions for nine additional species. These species did not meet all three criteria for inclusion but are still mentioned due to their importance in fisheries. This includes the two surgeonfishes that are the most abundant species in the bio-sampling data (Acanthurus lineatus and Ctenochaetus striatus). The other 7 species are amongst the 30 most abundant

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