«A DISSERTATION SUBMITTED TO THE GRADUATE DIVISION OF THE UNIVERISTY OF HAWAI‘I AT MĀNOA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE ...»
ECOLOGY AND SOCIAL BEHAVIOR OF A RESIDENT MANTA RAY
(MANTA ALFREDI) POPULATION OFF MAUI, HAWAI‘I
A DISSERTATION SUBMITTED TO THE GRADUATE DIVISION OF THE
UNIVERISTY OF HAWAI‘I AT MĀNOA IN PARTIAL FULFILLMENT OF THE
REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHYIN
PSYCHOLOGYDECEMBER 2010 By Mark H. Deakos
Karl A. Minke, Chairperson Patricia A. Couvillon Louis M. Herman Adam A. Pack Joseph R. Mobley, Jr
TABLE OF CONTENTSLIST OF TABLES
LIST OF FIGURES
1 GENERAL INTRODUCTION
1.2 A Brief Evolutionary History of Elasmobranchs
1.3 Manta Rays
1.3.2 Sensory Systems
1.3.5 Range and Habitat
1.3.6 Food and Foraging
1.3.7 Population Size
1.3.12 Manta Ray Protection
1.4 Dissertation Overview
1.5 General Methods
2 USING PAIRED-LASER PHOTOGRAMMETRY AS A SIMPLE AND
ACCURATE SYSTEM TO MEASURE THE BODY SIZE OF FREE-RANGINGMANTA RAYS (MANTA ALFREDI)
ii 2.1 ABSTRACT
2.3.1 Study Area and Population
2.3.3 Accuracy and Precision
2.3.4 Manta Ray Measurements
2.4.1 Accuracy and Precision
2.4.2 Manta Ray Measurements
2.5.1 Accuracy and Precision
2.5.2 Manta Measurements
2.5.3 Future Research
3 CHARACTERISTICS OF A MANTA RAY (MANTA ALFREDI) POPULATIONOFF MAUI, HAWAI‘I, AND IMPLICATIONS FOR MANAGEMENT................ 49 3.1 ABSTRACT
3.3.1 Main study area
3.3.4 Abundance and Survivorship
3.3.5 Population Range
3.3.6 Population Structure
iii 3.3.7 Use of the Aggregation Area
3.4.2 Abundance and Survivorship
3.4.3 Population Range
3.4.4 Population Structure
3.4.5 Use of the Aggregation Area
3.5.1 Abundance and Survivorship
3.5.2 Population Range
3.5.3 Population Structure
3.5.4 Use of the Aggregation Area
3.5.6 Population Management
4 THE REPRODUCTIVE ECOLOGY OF MANTA RAYS (MANTA ALFREDI) OFFMAUI, HAWAI‘I, WITH AN EMPHASIS ON BODY SIZE
4.2.1 Reproductive Cycles
4.2.2 Role of Body Size
4.3.1 Data Collection
4.3.2 Data Analysis
4.3.3 Reproductive Cycles
iv 4.3.4 Role of Body Size
4.4.1 Reproductive Cycles
4.4.2 Role of Body Size
4.5.1 Reproductive Cycles
4.5.2 Role of Body Size
5 SUMMARY AND GENERAL DISCUSSION
5.1 Using paired-laser photogrammetry as a simple and accurate system to measure the body size of free-ranging manta rays (Manta alfredi)
5.2 Characteristics of a manta ray (Manta alfredi) population off Maui, Hawai‘i, and implications for management
5.3 The reproductive ecology of manta rays (Manta alfredi) off Maui, Hawai‘i, with an emphasis on body size
Table 2. The total number of different individuals photo-identified and the estimated abundance, where available, for manta ray (Manta alfredi) populations around the globe
Table 3. Comparison of the mean disc ratio (DR) between male and female, and between adult male and juvenile male manta rays (M.
Table 4. The number of surveys conducted and mean sighting rates for years 2005 through 2009, broken down into time of day (600-1000, 1000-1400, 1400-1600) and season (Nov-Apr, May-Oct).
Sighting rates are calculated as the mean number of manta rays observed per hour of survey effort.
Table 5. Surveys, mean sighting rates, mean rate of new individuals, proportion of males, and proportion of mating trains with standard deviations (SD) listed by month and season.
Table 6. Summary of surveys conducted by month and season showing the total number and proportion of surveys observed with mating trains and pregnant females.
The proportions of surveys with trains and pregnant females were significantly higher during the winter season.
Table 7. The resight history of 21 nuclear females (NF) observed between years 2005 and
2010. Numbers indicate the month in which they were observed as a NF during that year with train size indicated in brackets. Bolded IDs indicate females observed in a train during a summer month.
Table 8. The resight history and disc width (DW), if available, of 20 pregnant females during the years 2005 through 2010.
P indicates she was observed pregnant and her pregnancy was new for that year; N indicates she was observed enough times during that year to determine she was unlikely pregnant; U indicates the she was observed during that year but not sufficiently often to determine if she was visibly pregnant;
and a dash (-) indicates she was not sighted during that entire year. Bolded IDs indicate females observed pregnant during a summer month. Estimated Pregnancy Rates (EPR) based on a minimum of 3 yrs with sufficient data, and Estimate Consecutive Pregnancy Rates (ECPR) based on a minimum of 2 consecutive yrs with sufficient data are shown.
Table 9. The resight history and disc width (DW), if available, of 22 individual nuclear primary escorts (N1Es) during the years 2005 through 2010.
N1E indicates he was the primary escort in a mating train, and the bracketed numbers represent the month followed by the train size. S indicates the male was sighted but not as a N1E during vi that year. A dash (-) signifies he was not sighted during any surveys for that entire year. Bolded IDs indicate a male observed escorting in a train during a summer month.
Figure 2. A pair of green, underwater laser pointers mounted in parallel to an underwater video housing.
Figure 3. (a) Pipe of known length being measured on the ocean floor showing the projected points of light 60 cm apart; (b) a photograph of a manta ray (M.
alfredi) from above showing the projected points of light along the spinal axis of the disc from which a DL measurement can be obtained.
Figure 4. A plot of the expected, undistorted length of an object (in pixels) if measured with a flat lens against the actual measured length of the same object (in pixels) distorted by the wide-angle lens.
The data are fitted with a linear regression equation
Figure 5. Sixty-four manta ray DW measurements plotted against its corresponding DL measurement and fitted with a linear regression.
Measurements are in meters........ 41 Figure 6. The distribution of manta ray (M. alfredi) disc widths by gender and age class.
Females were considered adults if obviously pregnant or showed visible mating scars. Not all nuclear females were pregnant or had mating scars. Males with clasper lengths extending beyond the pelvic fins were classified as adult, even with the pelvic fins were classified as transition, and shorter than the pelvic fins were classified as juvenile. White boxes represent female categories, gray boxes represent male categories, numbers represent sample sizes, and circles represent outliers. All measurements are in millimeters.
Figure 7. The proportion of males which are sexually mature for each disc width size category.
The black column indicates the size category for which nearly 50% of the males can be considered mature (DW50). Numbers above the column indicate the sample size.
Figure 8. Map showing the study area 450 m from the shoreline.
The start point of each survey and the clockwise survey route are shown.
Figure 9. Discovery curve illustrating the cumulative number of new manta ray identifications against the cumulative number of all identifications.
Dark circles represent surveys conducted in the winter (November – April) and light circles represent surveys conducted in the summer (May - October).
Figure 10. Map showing the range of individual manta rays (M.
alfredi) either matched with photo-identifications (solid arrows) or tracked with an acoustic tag (dashed arrows).
Figure 12. The sighting history of a notable female (ID#5003) observed multiple times as a NF.
Numbers in brackets indicate the number of animals in the mating train....... 94 Figure 13. Distribution of manta ray disc widths. Heavy black lines = means, box boundaries = 25th and 75th percentiles, whiskers = smallest and largest observed values that are not statistical outliers, circles = statistical outliers, numbers = sample sizes. *not significantly different, p = 0.232, #not significantly different, p = 0.363.
Figure 14. The sighting history of a notable male (ID#13007) with a DW of 2.
94 m, observed pursuing a female on seven occasions. The behavioral role(s) observed are indicated for each sighting as well as the train size in brackets
ACKNOWLEDGMENTThe completion of this dissertation could not have been completed without the support, hard work, dedication, collaboration and patience of many people. To my dive buddies, Robin Deakos, Jonathan Whitney, Allan Ligon, Edward Lyman, Donna Brown, Lars Bejder and Jason Larese who often endured ankle breaking surface swims, crippling winds and swell, merciless currents, and horrendous visibility to assist with data collection, my sincere gratitude. For their assistance with the paired-laser photogrammetry design and calibrations, my thanks go out to Robin Deakos, Scott Spitz, and Brian Brainstetter. For the grueling task of matching hundreds of manta ray photoidentifications, thank you to Allan Ligon, Jonathan Whitney, Lesley Czechowic and Elisa Weiss. The active tracking portion of this study could not have been achieved without the expertise of Tim Clark, and the commitment of Jonathan Whitney and Lee James. A big mahalo to Ultimate Whale Watching Adventures for providing the research vessel and the University of Hawai‘i Zoology department for supplying the Vemco VR100 acoustic receiver and the VH110 directional hydrophone. To my committee members Louis Herman, Adam Pack, Joe Mobley, Karl Minke, and Patricia Couvillon, thank you for your support, patience, and guidance. For their valuable feedback on earlier versions of this manuscript I give my utmost appreciation to my committee, Tracy Adams, John Deakos, Mari Smultea, William White, Jill Kubatko, Susan Yin, Scott Spitz and anonymous reviewers. A special thanks to G. Scott Mills for his constructive comments, edits and advice while we cruised the open ocean aboard the Oscar Elton Sette. Jason Baker and Lars Bejder were particularly helpful with comments on the population chapter. I look forward to publishing collaborative works with them on manta ray population modeling in the near future. To Hal Whitehead, thank you for the development of SOCPROG and for the advice on computational analysis. Additional gratitude goes to Andrea Marshall (a.k.a. Manta Queen), William White, and Guy Stevens for sharing their observations on manta ray populations on the other side of the globe. I wish them the very best in their continued efforts to understand and protect manta rays worldwide. Thanks to Joe Mobley for assistance with the animal care permit issuance through the University of Hawai‘i and to Dave Pence who’s training and x guidance gave me the skills to conquer the underwater world. Research was conducted under the University of Hawai‘i Animal Care & Use Committee, Protocol No. 08-591-2, and Assurance number A3423-01. I am indebted to Tracy Adams for her relentless support, endurance to see me through this project, for tolerating my many years without a real job, and for not asking me when I would be finished during my final year of writing.
My thanks to the Adams family for their generous hospitality and allowing me into their home. And lastly, I am grateful to my primary advisor, Louis Herman, and the Deakos family for their continued support throughout this extended endeavor.