NOAA Technical Memorandum NMFS DECEMBER 2020 MEASUREMENTS AND REGRESSIONS OF OTOLITHS, CEPHALOPOD BEAKS, AND OTHER PREY HARD PARTS USED TO RECONSTRUCT CALIFORNIA CURRENT PREDATOR DIET COMPOSITION 1Mark S. Lowry, 1K. Alexandra Curtis, 2Christiana M. Boerger 1Southwest Fisheries Science Center National Marine Fisheries Service National Oceanic and Atmospheric Administration 8901 La Jolla Shores Dr. San Diego, CA 92037 2California State University Northridge Northridge, CA NOAA-TM-NMFS-SWFSC-637 U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Marine Fisheries Service Southwest Fisheries Science Center About the NOAA Technical Memorandum series The National Oceanic and Atmospheric Administration (NOAA), organized in 1970, has evolved into an agency which establishes national policies and manages and conserves our oceanic, coastal, and atmospheric resources. An organizational element within NOAA, the Office of Fisheries is responsible for fisheries policy and the direction of the National Marine Fisheries Service (NMFS). In addition to its formal publications, the NMFS uses the NOAA Technical Memorandum series to issue informal scientific and technical publications when complete formal review and editorial processing are not appropriate or feasible. Documents within this series, however, reflect sound professional work and may be referenced in the formal scientific and technical literature. SWFSC Technical Memorandums are available online at the following websites: SWFSC: https://www.fisheries.noaa.gov/about/southwest-fisheries-science-center NOAA Repository: https://repository.library.noaa.gov/ NTIS National Technical Reports Library: https://ntrl.ntis.gov/NTRL/ Accessibility information NOAA Fisheries Southwest Fisheries Science Center (SWFSC) is committed to making our publications and supporting electronic documents accessible to individuals of all abilities. The complexity of some of SWFSC's publications, information, data, and products may make access difficult for some. If you encounter material in this document that you cannot access or use, please contact us so that we may assist you. Phone: 858-546-7000 Recommended citation Mark S. Lowry, K. Alexandra Curtis, Christiana M. Boerger. 2020. Measurements and regressions of otoliths, cephalopod beaks, and other prey hard parts used to reconstruct California Current predator diet composition, U.S. Department of Commerce, NOAA Technical Memorandum NMFS-SWFSC-637. i Measurements and regressions of otoliths, cephalopod beaks, and other prey hard parts used to reconstruct California Current predator diet composition Mark S. Lowry1,*, K. Alexandra Curtis1, and Christiana M. Boerger2,a 1 Southwest Fisheries Science Center National Marine Fisheries Service National Oceanic and Atmospheric Administration 8901 La Jolla Shores Drive La Jolla, CA 92037 Email: [email protected] 2 California State University Northridge Northridge, CA * Retired a Current address: Naval Facilities Engineering Command Southwest Environmental Division San Diego, CA i Table of Contents Abstract .................................................................................................................................... 1 Introduction .............................................................................................................................. 1 Methods.................................................................................................................................... 2 Results ...................................................................................................................................... 3 Discussion ................................................................................................................................ 3 Data Accessibility .................................................................................................................... 4 Acknowledgments.................................................................................................................... 4 Author Contributions ............................................................................................................... 5 Literature Cited ........................................................................................................................ 5 Tables Table 1. Whole-specimen and hard-part dimensions measured .............................................. 8 Table 2. Summary of reference specimen measurements ........................................................ 9 Table 3. Regression summaries for prey size and hard part dimensions ............................... 15 Table 4. Regression summaries for otolith morphometrics ................................................... 20 Appendix A. Paired Comparisons of Left and Right Sagittal Otoliths Figure A1. Distribution of paired differenced left and right otolith length by species .......... 28 Figure A2. Distribution of paired differenced left and right otolith width by species........... 29 Table A1. Paired t-tests of left and right otolith lengths by species ...................................... 30 Table A2. Paired t-tests of left and right otolith widths by species ....................................... 32 ii Abstract Prey hard parts are used to reconstruct species composition and prey sizes from analyses of scats or stomachs of many marine predators. Measurements of prey hard parts are often closely related to prey size, allowing estimation of lengths and weights of prey consumed. In addition, otolith morphometrics, such as length, weight, and surface area, are related to otolith survival in predator digestive tracts and may thus help predict recovery rates in scats. Measurements were taken of prey hard part dimensions, additional morphometrics for otoliths, and/or prey size (length and weight) of reference specimens for 158 prey species found in the California Current Large Marine Ecosystem (CCLME), including 137 teleosts, twelve cephalopods, two batoids, one decapod, one myxinid, and one tunicate. Regression relationships of prey size to hard part measurements, among different prey hard part measurements (e.g., otolith length to width), and among different prey size measurements (e.g., weight to length) are provided for most species to facilitate application of these data to reconstruction of predator diets in the CCLME. Introduction Digestion-resistant prey structures, such as teleost otoliths and cephalopod beaks, are used to reconstruct diet composition of a wide range of marine predators, from jellyfish to cetaceans (e.g., Scott 1902; Clarke 1962; Purcell 1984). Many prey hard parts can be used not only for taxonomic identification of prey, but also to estimate prey size, based on species-specific regressions of prey hard part size to prey size (e.g., Clarke 1962; Antonelis et al, 1984). Information on species composition and length frequencies of prey in marine predators has a wide range of applications, from informing our basic understanding of marine trophic ecology, to grounding the use of predator population dynamics as ecosystem indicators (e.g., Sydeman et al., 2001; Melin et al., 2012), informing ecosystem models (e.g., Kaplan et al., 2017), and supporting fisheries management (e.g., Field et al., 2007; Velarde et al., 2015). Otoliths have also been used to characterize teleost fauna in middens and sediment deposits (e.g., Fitch 1964; Fitch 1969), including deep-sea sediment cores for paleoecological research (Jones 2016). Available identification guides for prey hard parts of species occurring in the California Current Large Marine Ecosystem (CCLME) have become increasingly comprehensive over time (Fitch and Brownell, 1968; Pinkas et al., 1971; Wolff 1984; Harvey et al., 2000; Lowry 2011). Some guides also contain regression relationships for prey hard parts to prey size (Wolff 1984; Clarke 1986; Harvey et al., 2000; Kubodera 2005). However, many prey species in the diverse forage assemblage of the CCLME have no data published to support size reconstruction, and sample sizes for many others remain limited, exacerbating the potential for considerable bias in calculating prey sizes from prey hard parts. Otolith morphometrics may also contain information on resistance to dissolution, and thus probability of surviving passage through a predator’s digestive tract, or through the water column and bioturbated surface sediment layers prior to incorporation into varved sediment layers that can be used for paleoclimate and paleoecological reconstruction. Information on otolith morphometrics may support at least partial correction for biases introduced by differential recovery rates for different fish species and sizes in diet and sediment samples. Several studies have found consistent relationships between otolith morphometrics, such as length and mass-to- 1 length ratio, and their recovery rates in pinniped scats (Harvey 1989; Tollitt et al., 1997; Sweeney and Harvey 2011). However, only one published data source provides such morphometrics for a suite of species, and its focus is primarily on mesopelagic forage species (Jones and Morales, 2014). We provide extensive additional data on prey length, weight, and hard part measurements and on additional otolith morphometrics for a wide array of forage species and sizes, most of which are consumed by California sea lions (Zalophus californianus; M. Lowry, unpublished data, NOAA SWFSC). We also provide regression relationships among prey length, prey weight, prey hard part measurements,