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Scyphozoan Jellies As Prey for Leatherback Sea Turtles Off Central California

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Scyphozoan Jellies As Prey for Leatherback Sea Turtles Off Central California San Jose State University SJSU ScholarWorks Master's Theses Master's Theses and Graduate Research 2009 Scyphozoan jellies as prey for leatherback sea turtles off central California Tanya R. Graham San Jose State University Follow this and additional works at: https://scholarworks.sjsu.edu/etd_theses Recommended Citation Graham, Tanya R., "Scyphozoan jellies as prey for leatherback sea turtles off central California" (2009). Master's Theses. 3692. DOI: https://doi.org/10.31979/etd.kpj2-ubtw https://scholarworks.sjsu.edu/etd_theses/3692 This Thesis is brought to you for free and open access by the Master's Theses and Graduate Research at SJSU ScholarWorks. It has been accepted for inclusion in Master's Theses by an authorized administrator of SJSU ScholarWorks. For more information, please contact [email protected]. SCYPHOZOAN JELLIES AS PREY FOR LEATHERBACK SEA TURTLES OFF CENTRAL CALIFORNIA A Thesis Presented to The Faculty of Moss Landing Marine Laboratories San Jose State University In Partial Fulfillment of the Requirements for the Degree Master of Science by Tanya R. Graham August 2009 UMI Number: 1478582 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. UMT Dissertation Publishing UMI 1478582 Copyright 2010 by ProQuest LLC. All rights reserved. This edition of the work is protected against unauthorized copying under Title 17, United States Code. ProQuest LLC 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106-1346 ©2009 Tanya R. Graham ALL RIGHTS RESERVED MOSS LANDING MARINE LABORATORIES SAN JOSE STATE UNIVERSITY The Undersigned Faculty Committee Approves the Thesis of Tanya R. Graham: SCYPHOZOAN JELLIES AS PREY FOR LEATHERBACK SEA TURTLES IN CENTRAL CALIFORNIA Jamst* 'AIf Dr. James T. Harvey, U Moss Landing Marine Laboratories ' // Dat<e £ 5U 5"-/ l-i?J Dr. Erika McPhee-Shaw, Moss Landing Marine Laboratories Date l£)£L- C-ll-OCf Dr. David A. Demer NMFS Southwest Fisheries Science Center Date APPROVED FOR THE UNIVERSITY \y*4 t^p^L^ 1r fitly Associate Dean Office of Graduate Studies and Research Date ABSTRACT SCYPHOZOAN JELLIES AS PREY FOR LEATHERBACK SEA TURTLES OFF CENTRAL CALIFORNIA by Tanya R. Graham Size and nutritional value of four species of scyphozoan jelly (Aurelia spp., Chrysaora colorata, Chrysaora fuscescens, and Phacellophora camtschatica) were examined as prey for leatherback turtles (Dermochelys coriacea) in a central California foraging area. Chrysaora fuscescens and C. colorata were larger and more nutritionally beneficial than Aurelia spp. and P. camtschatica, and jellies contained more carbon and nitrogen during the post-upwelling season when turtles were most abundant. This indicates leatherback turtles maximized foraging success by timing their arrival when prey was larger, more abundant, and more nutritionally beneficial than during other seasons. Acoustic sampling techniques were developed to characterize the distribution and abundance of scyphozoan jellies in the leatherback turtle foraging area off central California. Acoustic target strength (TS, dB re 1 m2) values were estimated for scyphozoan jellies using a distorted-wave Born approximation scattering model (mean = -61.9 at 38 kHz and -70.5 at 200 kHz) and in situ data (mean = -54.9 at 38 kHz and -63.7 at 200 kHz). Using these data, an algorithm was developed to identify acoustic backscatter from jellies that can be used to characterize the distribution and abundance of scyphozoan prey for leatherback turtles in central California. ACKNOWLEDGEMENTS I would like to thank Jim Harvey, Scott Benson, Erika McPhee-Shaw, and David Demer for their intellectual contributions throughout this course of this project. I would also like to thank Josiah Renfree for his invaluable assistance with Matlab, and Gareth Lawson and Dezhang Chu for their generosity in sharing the DWBA model program. Thanks to all those who helped in the field, with particular thanks to Laurie Hall, Luke Beatman, Kelly Newton, and Erin LaCasella for their assistance with collecting the best data possible. Thanks to Craig Hunter for his help with elemental analysis, to Kate Thomas for help with figures, and to Matt Wilson from SonarData for generously extending the use of Echoview software. I would especially like to thank my friends and family, whose love and support helped me to overcome many personal and academic challenges along the way and made completion of this project possible. Funding for this project was provided by the NOAA/NMFS Southwest Fisheries Science Center, Marine Turtle Research Program, and Advanced Survey Technologies Program, as well as the Monterey Bay National Marine Sanctuary Foundation. Additional funding was provided by the Earl and Ethel Myers Oceanographic and Marine Biology Trust and the American Cetacean Society (Monterey Bay Chapter). v INTRODUCTION This thesis is divided into two independent chapters which each address different aspects of the role of scyphozoan jellies as prey for endangered leatherback sea turtles (Dermochelys coriacea) off central California. The first chapter discusses the nutritional value of scyphozoan jellies, and the second chapter addresses the acoustic characterization of scyphozoan jellies as prey for leatherback sea turtles. Each chapter has an abstract, an introduction, methods, results, discussion, and literature cited section, with figures and tables embedded within the text. VI TABLE OF CONTENTS LIST OF FIGURES - CHAPTER 1 viii LIST OF TABLES - CHAPTER 1 ix LIST OF FIGURES - CHAPTER 2 x LIST OF TABLES - CHAPTER 2 xii CHAPTER 1 ABSTRACT 2 INTRODUCTION 3 METHODS 8 RESULTS 13 DISCUSSION 21 LITERATURE CITED 27 CHAPTER 2 ABSTRACT 32 INTRODUCTION 33 METHODS 39 RESULTS 50 DISCUSSION 56 LITERATURE CITED 62 vn LIST OF FIGURES - CHAPTER 1 FIGURE TITLE PAGE 1. A record of cruise effort aboard the R/V John Martin. 9 Horizontal position of marker indicates approximate date of the cruise within the month noted. (•) Center for Integrated Marine Technologies (CIMT) cruises, (•) Moss Landing Marine Laboratories (MLML) cruises. 2. All net sampling locations off central California. Locations 10 selected for additional analysis of accompanying acoustic data when jellies were present (•) or absent (o), all other tow locations (•). 3. Distribution of bell diameter (cm) of jellies Aureliajapp. 14 (AULA), Chrysaora colorata (CHCO), Chrysaora fuscescens (CHFU), and Phacellophora camtschatica (PHCA) for all cruises off central California from 2003 through 2007. 4. Mean (± standard error) and distribution of bell diameters 15 and of Aureliajspp. (AULA; •) and Chrysaora fuscescens (CHFU; •) by oceanographic season (Upwelling = Mar through Aug; Post-upwelling = Sep through Nov) off central California from 2003 through 2007. 5. Mean percentage of dry weight (± standard error) carbon (C; 16 o) and nitrogen (N; A) in AULA and CHFU between upwelling (open symbol) and post-upwelling (closed symbol) seasons. For AULA during post-upwelling season, n = 16, AULA upwelling season, n = 9, CHFU post-upwelling season, n = 9, CHFU upwelling season, n = 19. 6. Cumulative coefficient of variation (CV) of carbon (C) and 19 nitrogen (N) in bell, oral arms/gonads, and whole Aurelia spp. (AULA; top) and Chrysaora fuscescens (CHFU; bottom) as an indicator of sample precision. 7. Cumulative coefficient of variation of carbon (•) and nitrogen 20 (A) of Phacellophora camtschatica as an indicator of sample precision. Vlll LIST OF TABLES - CHAPTER 1 TABLE TITLE PAGE 1. Mean, standard deviation, and sample size (n) of bell 13 diameter (cm) of jellies Aurelia_spp. (AULA), Chrysaora colorata (CHCO), Chrysaora fuscescens (CHFU), and Phacellophora camtschatica (PHCA) for all cruises off central California from 2003 through 2007. 2. Mean, standard deviation (SD) and sample size (n) of bell 17 diameter (cm), carbon (C) and nitrogen (N; %DW), and ratio of C to N (C:N) of whole jellies (W), oral arms and gonads (OAG), and bell (B) of Aureliajspp. (AULA), Chrysaora colorata (CHCO), Chrysaora fuscescens (CHFU), and Phacellophora camtschatica (PHCA). IX LIST OF FIGURES - CHAPTER 2 FIGURE TITLE PAGE 1 • A record of cruise effort aboard the RV "John Martin". 40 Horizontal position of marker indicates approximate date of the cruise within the month noted. (•) Center for Integrated Marine Technologies (CIMT) cruises, (•) Moss Landing Marine Laboratories (MLML) cruises. 2. Distribution of jelly bell diameter (D; cm) which was used as 41 an input parameter in the DWBA model. This distribution includes data from Chapter 1 and additional data from a cruise aboard RV "David Starr Jordan"; mean D = 26.2; SD = ±10.6cm, n = 595. 3. Parameters incorporated in the DWBA model included 42 sound speed (c = 1500 m s"1), density {g) and sound speed (h) contrast, and height:radius and radius:radius ratios for a jelly with a relaxed- and contracted-bell (figure recreated from Monger etal., 1998). 4. All net tow and acoustic sampling locations off central 44 California. Locations selected for additional analysis of accompanying acoustic data when jellies were present (•), or absent (O); all other tow locations (•). 5. TS (dB re 1 m2) of all targets detected greater than 4 m and 46 less than 20 m depth at 38 kHz and 200 kHz versus depth (m). 6. TS (dB re 1 m2) of all targets detected at 200 kHz versus 47 angle (degree) off the major beam axis. 7. TS (dB re 1 m2) of targets detected at 200 kHz restricted in 47 depth (4 to 10 m) and off-axis angle (< 2 °) to reduce positive bias associated with the range from the transducer and possible false detection of multiple targets as a single target. x 8. Algorithm to extract echoes of jellies from multi-frequency 49 volume-backscatter data. A Boolean mask, defined by the differences in Sv at 200 and 38 kHz, is used to identify echoes from jellies. 9. Mean TS values (dB re 1 m2) by frequency (kHz) estimated 51 from the DWBA model (O) ± one SD (--) and TSfrom detected in situ single targets when jellies were present (X) and absent (—) ± one SD.
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