AN ABSTRACT OF THE THESIS OF
Kelly Ann Rossbach for the degree of Master of Science in Wildlife Science presented on
November 14, 1997. Title: Distinguishing Inshore and Offshore Communities of
Bottlenose Dolphins (Tursiops truncatus) near Grand Bahama Island. Bahamas.
Abstract approved: Redacted for Privacy Bruce R. Mate
Little is known about the behavior of offshore dolphin populations. The purpose of
this study was to distinguish stable social groups of bottlenose dolphins (Tursiops
truncatus) from inshore and offshore West End, Grand Bahama Island (26°42'N,
79°00°W). The unprotected study area extended from shore, to 56 km north, due offshore, and 5 km east/west, along the western edge of Little Bahama Bank. Water depth ranged between <1 - 20 m. Photo-identification was conducted between May and
September, 1994 to 1996. Simple ratio index was used to describe association patterns between dolphin pairs. Of 212 dolphins identified, 59 non-calves were photographed >5 times in sightings where all dolphins were photographed. Underwater observation determined the gender of 66% of the 59 non-calves. Multidimensional scaling of association indices (n = 1711 dolphin pairs) suggested two large groups of dolphins consisting of 15 dolphins (12 of known sex) and 28 dolphins (19 of known sex).
Members of the two of the groups were labeled Southern and Northern communities based on members' relative ranges in the study area, and were probably core to larger communities.
Members of the Northern community were sighted a minimum of 27 km offshore, and 12 of the 15 dolphins had been opportunistically photographed in the same region between 1987 and 1993. The Northern community was found in deeper water (Mann-
Whitney U-test, p < 0.01) and over predominantly sand bottoms, compared to the
Southern inshore community which was sighted in shallower water and primarily over grassy bottoms (Kruskal Wallis test, p < 0.01). Members of the two communities were observed using different bottom-foraging strategies. Northern dolphins primarily crater- fed in sand. Southern dolphins used several feeding techniques, with little crater-feeding.
Some dolphins, which were not associated with either community, fed cooperatively.
These dolphins were rarely observed with the Southern dolphins (7( = 0.03, SD = 0.04, n
= 112 dolphin pairs), though they overlapped in range.
Northern and Southern community members that were sighted >15 times interacted with a similar number of different individuals (t-test, p > 0.05), averaging 48 associates
(SD = 11, n = 28). A dolphin's closest associate was of the same sex 74% of the time, and the opposite sex 26% of the time. This study is the first to report long-term site fidelity and social structure of bottlenose dolphins found far from shore. °Copyright by Kelly Ann Rossbach November 14, 1997 All Rights Reserved Distinguishing Inshore and Offshore Communities of Bottlenose Dolphins (Tursiops truncatus) near Grand Bahama Island, Bahamas
by
Kelly Ann Rossbach
A THESIS
submitted to
Oregon State University
in partial fulfillment of the requirements of the degree of
Master of Science
Completed November 14, 1997 Commencement June 1998 Master of Science thesis of Kelly Ann Rossbach presented on November 14. 1997
APPROVED:
Redacted for Privacy Mai rofessor, representing Wildlife Science
Redacted for Privacy Chair of Department of Fisherie
Redacted for Privacy Dean of Gradu School
I understand that my thesis will become part of the permanent collection of Oregon State University libraries. My signature below authorizes release of my thesis to any reader upon request.
Redacted for Privacy Acknowledgements
This was a research project that required a TON of people. This project would not have come to pass if it were not for all the people who so generously gave of their time and sweat. Living and working conditions in the field were less than ideal. Field assistants were tough in the truest sense of the word. From eating cold canned food and granola day after day and taking insect bites in stride, to having tents (our home) periodically torn up in rain storms, these people stuck it out. They worked harder than is reasonable to expect of a person. I am truly grateful to all the field assistants: Mike
Adam, Michelle Armstrong, Sallie Beavers, Dave Beran, Michael Buchal, Susan Drew,
Terri Herbert, Barb Losch, Andrew Mason, Rob Mate, Nicole Matlack, Marlene
Mendes, Sharon Nieukirk, Beth Stark, Laura Urian, John Vichnicki, Ivfindy Zuschlag, and especially Robin Lawford and Tina Toms.
I would further like to thank the residents of West End, especially the fishermen who reported sightings, and taught me about the area. Capt. Dick Rhinehart and the
Bahamian Department of Fisheries permitted me and my assistants to camp at the Jack
Tar Marina. The employees of the marina provided abundant miscellaneous services.
They were always willing to help with engine problems, moving heavy things (like the boat!), equipment mishaps, and just kept a watchful eye on us. Capt. Bob Rhinehart provided our camp with electricity in 1996. Garvin Green was especially kind and willing to assist whenever necessary.
I would like to thank Scott Smith of the Dream Too who provided occasional transportation, miscellaneous supplies, and an occasional warm meal. The crews from the Gulf Stream Eagle, Bottom Time II, Sea Fever, Ocean Explorer, Calypso Poet, and
Calypso Spirit also provided occasional transportation, sighting reports, and dolphin
videos/slides with date, time, and location.
Financial support for this project was provided by the Oregon State University
Endowed Marine Mammal Program and the Wild Dolphin Project (WDP). William
Rossiter and Cetacean Society International also supported this project. Ken Balcomb
and Diane Claridge loaned me an inflatable (workhorse) boat and assisted with delivery.
Tazmanian Freight Forwarding delivered the 1994 inflatable. I thank Veryl Barry for
clerical support, Toby Martin for computer programming, Fred Ramsey, Dale Usner and
Martha Winsor for statistical support, Tomas Follett and Martha Winsor for assistance with figure preparation, and Sallie Beavers, Bruce Mate, and Susan Shane forcomments on manuscript drafts. Sallie Beavers, Terri Herbert, Toby Martin, Bruce Mate, Sharon
Nieukirk and Susan Shane provided stimulating and thought provoking conversations, and were especially supportive of this project. I would like to thankmy graduate committee, Joe Beaty, Denise Herzing, Bruce Mate, Fred Ramsey, Cliff Ryer, and Susan
Shane for their advice, direction, and support.
This study was conducted in collaboration with the Wild Dolphin Project (a private non-profit, research organization) and under their research permit with the Bahamian
Department of Fisheries. It was conducted in conjunction with a the WDP's long-term, spotted dolphin (Stenella frontalis) study by Denise Herzing. Denise was one of two people who especially made this project possible. I am indebted to Denise and her staff,
Tim Barret, Barbara Brunnick, Will Engleby, Nicole Matlack, and Dan Sammis, for dealing with my constant needs for provisions and assistance. They never said no. Bruce Mate, my major professor, was the key person in this whole thing. I thank him especially for his confidence in me, and for his moral support. I am grateful to
Bruce for providing me with this experience of a lifetime.
I thank Mike Adam, my husband, for his love and support during all of this, and my parents, Claire and Chuck Rossbach who always encouraged me to follow my dreams.
Finally, I thank the dolphins; they put up with me and my boat. Contribution of Authors
Dr. Denise Herzing assisted in data collection and edited the manuscript of chapter two. Table of Contents
Page
Introduction 1
Inshore and Offshore Bottlenose Dolphin (Tursiops truncatus) Communities Distinguished by Association Patterns near Grand Bahama Island, Bahamas. 3
INTRODUCTION 4
METHODS 5
RESULTS 17
DISCUSSION 59
Underwater Observations of Benthic Feeding Bottlenose Dolphins (Tursiops truncatus) near Grand Bahama Island, Bahamas 74
INTRODUCTION 75
METHODS 75
RESULTS 77
DISCUSSION 81
Cooperative Feeding Among Bottlenose Dolphins (Tursiops truncatus) near Grand Bahama Island, Bahamas 84
INTRODUCTION 85
METHODS 85
RESULTS 87
DISCUSSION 90 Table of Contents (Continued)
ata
Summary 93
Bibliography 95
Appendices 101 List of Figures
Figure Page
1.1. The study area is located on the western edge of Little Bahama Bank, Bahamas 6
1.2. Locations of bottlenose dolphin sightings, during 1994-1996 18
1.3. Decreasing rate of discovery of new dolphins in the study area (n = 212) 21
1.4. Number of sightings per dolphin (n = 212 dolphins), during 1994-1996 23
1.5. Latitudinal ranges of 98 non-calves sighted >5 times (ordered by mean latitude), during 1994-1996 25
1.6. Latitudinal ranges of 98 non-calves sighted <5 times (ordered by mean latitude), during 1994-1996 26
1.7. Latitudinal ranges of 51 dolphins (ordered by mean latitude) photographed before 1994 28
1.8. Results of multidimensional scaling show the relative distance between association indices of 59 non-calves photographed >5 times in fully- photographed sightings 30
1.9. Cluster analysis (group average method) dendogram of simple ratio indices of 59 non-calves seen >5 times in fully-photographed sightings 31
1.10. The agglomeration distance plot shows the distance between groups when they were combined by cluster analysis 32
1.11. Latitudinal ranges of dolphin cluster members 33
1.12. Range of school size of 363 dolphin schools sighted during 1994-1996 39
1.13. Range of school size of 263 dolphin schools photographed during 1994-1996 40 List of Figures (continued)
Figure Page
1.14. Number of associates of each dolphin (n = 194) based on the number of the dolphin's sightings 42
1.15. Number of associates of Northern dolphins (n = 12) vs. Southern dolphins (n = 14) photographed >15 times 43
1.16. Comparison of simple ratio indices between sexes of Northern dolphins 45
1.17. Comparison of simple ratio indices between sexes of Southern dolphins 46
1.18. Range of simple ratio indices for 59 dolphins' closest associate 47
1.19. Number of associates of 12 males vs. 12 females seen >15 times, during 1994-1996 48
1.20. Depth of sightings in which Northern (n = 37) or Southern (n = 81) dolphins were present 51
1.21. Water depths at the latitudes of 252 dolphin sightings 52
1.22. Latitudes of dolphin sightings over crusty sand (n = 48) vs. loose sand (n = 27) 53
1.23. Latitudes of dolphin sightings at different vegetation types 54
1.24. Dominant benthic characteristic at the latitudes of dolphin sightings 55
1.25. Latitudinal ranges of 28 non-calves sighted >15 times (ordered by mean latitude), during1994-1996 61
1.26. Latitudinal ranges of 8 non-calf dolphins (ordered by mean latitude) with the highest number of associates 63
2.1. The study area 76
2.2. The dolphin searches the sand bottom with head moving side to side, and oriented downward 78 List of Figures (Continued)
Figure Page
2.3. The dolphin dives into the sand, flukes moving vigorously, and digs, burying itself nearly to the flippers 79
2.4. As the dolphin lift its head, a small fish is visible in its mouth 80
2.5. After a group has fed, the bottom resembles a moonscape 82
3.1. The study area 86 List of Tables
Table 2
1.1. Field effort and success rate of dolphin observations, during 1994-1996 19
1.2. Individual dolphin records collected 20
1.3. Number of male and female dolphins identified, and the method of gender determination 22
1.4. Medians, means, and standard deviations of dolphin clusters: Within and between 36
1.5. Number of pair-wise dolphin associations observed within and between 4 cluster groups 36
1.6. Percentage of closest associates that are same sex vs. opposite sex of partner 49
1.7. Medians, means, and standard deviations of association indices for non-calves and their closest associate, photographed >5 times in fully- photographed sightings 49
1.8. Dolphin foraging strategies observed, during 1994-1996 58
3.1. Six sightings of cooperatively feeding bottlenose dolphins near Grand Bahama Island 88
3.2. Reports of presumed cooperation in feeding bottlenose dolphins 91 List of Appendices
Appendix Ego
A.1. Sighting Log 102
A.2. Daily Summary 103
A.3. Photo Log 104
B. Body markings of 212 individual dolphins identified near Grand Bahama Island, during 1994-1996 105
C. Life history parameters of 212 individual dolphins identified near Grand Bahamas Island, during 1994-1996 112
D. Number of sightings of 212 individual dolphins identified near Grand Bahama Island 119 Distinguishing Inshore and Offshore Communities of Bottlenose Dolphins (Tursiops truncatus) near Grand Bahama Island, Bahamas
Introduction
The bottlenose dolphin (Tursiops truncatus) is cosmopolitan in its distribution
(Leatherwood and Reeves 1983). The species occurs in shallow coastal waters, bays,
and estuaries, as well as offshore (Leatherwood and Reeves 1983). Movement patterns
range from residential (Wells 1978, Connor and Smolker 1985, Brager 1993, Harzen
1995, Wilson 1995) to wide-ranging and migratory (Hansen 1990, Wellset al. 1990).
Two ecotypes of the bottlenose dolphin are generally known as coastal and offshore
(Hersh and Duffield 1990). However, the coastal ecotype can be found far from shore when the continental shelf extends away from land, and the offshore ecotype can be found near shore when the shelf is close to land (Kenny 1990). Bottlenose dolphins occurring coastally are easily accessible to researchers and have been well studied.
However, little known about either ecotype as the species occurs further from shore.
Photo-identification studies have become a proven method to study numerous aspects of wild bottlenose dolphin populations. These studies have resulted in increased knowledge of population size, range, ecology, social structure, and behavior of bottlenose dolphins around the world (Wursig and Wursig 1977, Wells 1980, Shane
1990a, Weller 1991, Smolker et al. 1992, Brager 1993, Claridge 1994).
In the photo-identification study presented here, I observed free-ranging bottlenose dolphins near West End, Grand Bahama Island, Bahamas. Bottlenose dolphins found along the western edge of Little Bahama Bank appear to be the coastal ecotype (Hersh 2
and Duffield 1990). They measure about 2.4 m in length, and are small compared to dolphins seen in the gulf stream just to the west. Underwater observation provided a closer look at behavior and the opportunity to determine dolphin genders in order to describe social structure. 3
Chapter 1
Inshore and Offshore Bottlenose Dolphin (Tursiops truncatus) Communities Distinguished by Association Patterns near Grand Bahama Island, Bahamas
Kelly Ann Rossbach
Department of Fisheries and Wildlife Oregon State University, Corvallis, OR 4
INTRODUCTION
Patterns of association between individual bottlenose dolphins (Tursiops truncatus)
vary from dynamic and temporary, to stable and long-term (Wursig 1978, Wells et al
1987, Ballance 1990, Wursig and Harris 1990, Weller 1991, Smolker et al. 1992, Brager
et al. 1994, Harzen 1995). Association patterns are useful in defining a community
(Wells et al. 1987). Community members typically interact closely and frequently with
one to several particular individuals, less so with other members of the community, and
least with dolphins of surrounding communities (Wells et al. 1987).
Coastal bottlenose dolphins are most accessible to researchers, and therefore, their
association patterns and movements are best understood. Site fidelity is a typical feature
of these dolphins (reviews by Leatherwood and Reeves 1982, Shane et al. 1986). For
example, in a resident community in Sarasota Bay, FL, only about 17% of sightings
contain identifiable individuals of adjacent communities (Wells et al. 1987).
Every study of bottlenose dolphin association patterns has occurred in bays, or
within a few miles of shore (Wells 1986, Wells et al. 1987, Weller 1991, Smolker et al
1992, Brager et al. 1994, Harzen 1995, Wilson 1995, Felix 1997). Little is known about
how communities interact further from shore. The purpose of this study was to
distinguish and describe dolphin communities based on association patterns and ranges of
individuals from West End, Grand Bahama Island, due offshore for about 56 kin, along the western edge of Little Bahama Bank, Bahamas. 5
METHODS
Study Area
The study area (Figure 1.1) follows the western edge of Little Bahama Bank, between West End, Grand Bahama Island (26°42'N, 79°00'W) and the White Sand Ridge
(27°15'N, 79°08'W). It is approximately 280 km2, spanning 56-km north to south, and about 5 km east to west. Water depth varies between <1 - 20 m, and generally increases in depth from south to north. The unprotected study area is characterized by a sand bottom with small and large patches of turtle grass (Thalassia testudinum), and scattered areas of rock and reef bottom. Water temperature during the study period (May-
September) averages around 29°C.
Little Bahama Bank extends more than 160 km along the north side of Grand
Bahama Island, from West End to Abaco, Bahamas, and is about 80 km north to south at its widest point. The western border of the study area is a steep drop-off leading to the eastern edge of the Gulf Stream, which is over 500 m deep.
Materials
A 20-m power catamaran (M/V Stenella) and 5.3-m inflatable boat with a 25-hp
(1994) or a 75-hp (1995, 1996) motor were used to search, and photograph dolphins.
Occasionally, photos were obtained from the Stenella's 3-m dinghy. I used a 6
tinge/Ridg
27 00' Memo L TTIB AbOCO Rock Island
Son Gay
West En / rand Baham Island
26 00
Study Area Little Bahama Bank
79 30 79 00 7e 30 78 00
Figure 1.1. The study area is located on the western edge of Little Bahama Bank, Bahamas. 7
Canon AE-1 35 mm camera with a 300-mm telephoto lens, and Kodachrome 64, 200 or
Fujifilm 100 film to photograph dolphin dorsal fins at the surface. Underwater photos of
fin notches, body scars, and genital regions were taken with a Nikonos V 35 mm camera
and Kodachrome 200 film. I used 10 X 50 Nikon binoculars to search for dolphins from
land. A Garmin 70 or Magellan GPS recorded vessel courses and locations of dolphins.
A Humminbird Wide 100 Fishfinder measured water depth from the inflatable. The
Stenella was equipped with a fathometer. A small, hand-held tape recorder was used to record sighting data.
Search Procedure
A pilot study was conducted from May 20 to June 15, 1994 to investigate feasibility, determine field methods, and prepare data collection techniques. Sighting data collected during the pilot study were not used in the final analyses due to variable methodology in the data collection.
The study area was divided latitudinally into three sections (Southern, Central, and
Northern). The Southern section extended from West End (26°42'N), about 19 km offshore to 26°54'N. Portions of it were searched from land or with the inflatable boat, starting from base camp at West End. I searched the Northern section (27°03'N -
27°15'N) in collaboration with the Wild Dolphin Project (WDP), during their ongoing research of spotted dolphins (Stenellafrontalis). Spotted dolphins are primarily sighted on the bank, north of 27°03', and therefore, the Northern area was searched regularly. I alternated periods of searching the Northern and Southern sections of the study area. 8
The Central section (26°54'N - 27°03'N) was infrequently searched because it was most
difficult to reach from shore-based camp and of less interest to the spotted dolphin
project.
South
Periods of approximately one to five weeks, were spent searching for dolphins in the
Southern section of the study area. Most searches were conducted from the 5.3-m
inflatable boat under fair to excellent weather conditions. Three observers rotated
between one driving and two searching stations. Each observer stood at the bow of the
vessel and searched from the bow to abeam (90°) on their respective sides. The course
of travel was plotted by recording the time, position (latitude and longitude), and
heading, at each change in course. This plot provided an estimate of search effort.
Searches were conducted at all times of day between dawn and dusk.
Land-based searches were conducted around dawn, and during questionable weather
conditions. Observers used binoculars, from the beach of the Jack Tar Marina, West
End, or from the roof of a three-story building about 100-m east. When observers
sighted dolphins, I followed the dolphins with the inflatable boat to obtain identification
photographs. When dolphins were sighted from camp at times other than searches, they were immediately followed by boat.
North
I searched the Northern region of the study area for periods ofone to two weeks. A dolphin search was conducted continuously from the Stenella, between 0700 and 1900 h, 9
during all but severe weather conditions. Two observers searched in 2-h shifts, from
abeam port-side to abeam starboard-side when underway, and in a 360° area, when
anchored. The vessel's course was recorded by taking a position and heading, every 15
min when underway, and at each change of course, and provided an estimate of search
effort. Eight observers usually shared search duties each day.
Central
Occasionally, I was able to reach the Central section of the study area from the South
in the inflatable boat, or from the North in the Stenella. The search procedure was the
same as described above.
Data Collection
A dolphin "sighting" was defined as all dolphins in sight, moving in the same
direction, and usually involved in similar activity (termed `pod' in Shane 1990a). Data
were recorded in real time on a tape recorder and consisted of: date, start time, start
location (latitude and longitude), end time, end location, and numbers of bottlenose
dolphins, young-of-the-year (about half adult size, or smaller, and surfacing in echelon position with larger dolphin), calves (greater than half adult size, but still with presumed mother), and spotted dolphins. I also recorded pod form (tight, loose, dispersed, mixed; see Shane 1990a), direction of dolphin movement, behavior (travel, feed, social, rest; see
Shane et al. 1986, Shane 1990a), water depth, bottom type (sand, rocks, reef, unknown), vegetation type (turtle grass, other, absent), dominant benthic feature 10
(bottom or vegetation), sea state (Beaufort Scale), swell height, and the identity of all
recognizable dolphins.
Photographs of dorsal fins were used to identify individual dolphins at the surface
(Wursig and Wursig 1977, Wursig and Jefferson 1990). Every attempt was made to
photograph the dorsal fins of all dolphins in each sighting. Previously unknown individuals were photographed several times. Film roll and exposed frame numbers were recorded for each dolphin sighting. A "spacer" photograph separated dolphin sightings on each roll of film.
After the sighting was photographed, if weather conditions were acceptable, and if dolphins were not traveling, I entered the water with snorkel gear to obtain further identification markings on individuals, to determine the gender of dolphins, and to observe behavior. Dolphin gender was determined by observation of the genital region.
A large gap between genital slit and anus, and lack of mammary slits, or observation of an erection, identified a male. Females were identified by observation of mammary slits or by regular accompaniment by a smaller animal (presumed to be her calf). A concerted effort was made to photograph the genital area when possible. Without a photo, gender confirmation by a second observer, or on a second occasion by the same observer was attempted.
The sighting data were transcribed to a data sheet (Appendix A.1) at the end of each day. Additionally, I plotted the vessel's course, calculated distance traveled, and recorded a daily summary report (Appendix A.2). 11
Photo Management and Manipulation
Slides were labeled with date, roll and frame number. It was necessary for all slides of a specific sighting to be available before beginning the analysis of that sighting. Slides were examined, one sighting at a time, with a 10x magnifying loupe. Like dorsal fins were matched within each sighting. The total number of photo-identified individuals in a sighting was recorded.
The number of photo-identified dolphins was then compared to the field estimate. If the number of photo-identified dolphins was equal to or greater than the field estimate
(excluding unidentifiable calves), the field estimate was adjusted (if lower) to the number of photo-identified dolphins (plus unidentifiable calves). However, it is impossible to know if all members of a sighting are identified. Dolphins could be part of a sighting acoustically, or a dolphin could be missed both in the field estimate and in the photographs. With these factors in mind, a "filly-photographed" sighting was defined as one with an equal number (or greater) of dolphins identified photographically, as recorded in the field estimate. If the number of photo-identified dolphins was smaller than the field estimate (excluding unidentifiable calves), the sighting was considered not fully- photographed. Sightings which included unidentifiable non-calves were also considered not fully-photographed.
Distinct fins were named with a combination of three letters and numbers, and entered into a catalog by grouping similar fin notches and shapes. The catalog contained prints of the highest quality dorsal fin photos of each animal. Dorsal fin photographs from each sighting were compared to the catalog of all previously photographed fins, 12
and matched. Confirmation of a match was made with original slides. Notches and scars
on the pectoral fins, flukes and body assisted in matching dolphins, however they were
not used to define a new individual. A Photo Log (Appendix A.3) recorded the dolphin
name for each frame on a roll of film, during the matching process. Photo-identified
individuals in a sighting were then recorded onto the original field data sheet.
Additional photo-identified individuals were recorded when they appeared in photos
or videos from the WDP or other reliable sources, and were supplied with at least date
or location. The effort for these records is not included in this paper. Identified
individuals were later compared to photos of a residential population of dolphins
described in central Abaco, Bahamas (Claridge 1994) about 160 km east of my study
area.
Data Management, Manipulation and Analysis
All data were entered into a Microrim RBase® 4.0 database. Analyses were conducted using Statgraphics Plus® 2.1 on an IBM compatible PC. Results were plotted with the use of SigmaPlot® 4.0.
The database consisted of three primary tables: Sightings, Individuals, and Daily
Summaries. The Sightings table consisted of data collected at each bottlenose dolphin sighting (Appendix A.1). Water depths at sightings were compared using the Mann-
Whitney U-test (Sokal and Rohlf 1981). Benthic characteristics at sightings were compared by use of the Kruskal-Wallis test (vegetation) (Sokal and Rohlf 1981) and the
Mann-Whitney U-test (bottom-type and dominant benthic feature). 13
The Individuals table contained one "record" for each sighting of each photo-
identified individual. A record included: Dolphin ID (name), date, sighting start time,
start location, number of dolphins in the sighting, number of photo-identified dolphins in
the sighting, photographic success rate of the sighting (e.g., fully-photographed), type of
feeding (if present), presence of spotted dolphins, and photographer's name. A dolphin's
presence was recorded one time each day, unless it was seen with different dolphins later
in the day to justify a separate record.
The Daily Summary (Appendix A.2) table recorded daily field effort and sighting
success. Field effort included: date, area searched (Southern, Central, Northern), time
searched from the inflatable boat, time searched from Stenella, time searched from land,
and distance traveled by boat. Sighting success included: number of sightings, total
number of dolphins, number of calves and young-of-the-year, number of sightings
photographed, number of mixed species sightings, number of spotted dolphins in mixed
sighting, total time spent observing bottlenose dolphins, number of sightings that
included more than one school, and comments.
Five secondary tables were generated from the primary tables. First, ID Summary was produced from the Individuals table. It contained one row for each identified individual, age class (Calf: included young-of-the-year and calves defined on p. 9;
Juvenile/Sub-adult: relative small size and girth; Adult: relative large size and girth; adult female - regular presence of calf, adult male - heavily scarred), gender, the number of sightings each season, number of sightings before 1994, and total number of sightings.
Second, the School Size table was generated from the Sightings table. In orderto determine school size most accurately, schools were defined differently than sightings. A 14
sighting included the maximum number of dolphins seen between the time they were
approached by the vessel until the time they were left or were lost. However, I had the
opportunity to remain with some sightings for an extended period of time. The size of
the sighting sometimes changed as new dolphins arrived, and others left. In these cases,
the number of dolphins present was recorded at the time of approach and then again each
time the number changed. These numbers were termed "school size". When the number
of dolphins remained constant throughout the observation period, then school size was
the same as sighting size. This table was used only to determine average school size.
School size was determined from photo-identified schools as well as from all schools.
The first data set was a subset of the whole. It included only schools that contained at
least one photo-identified dolphin. This subset was used, because schools that were not
photographed were either seen in rough seas or lost soon after first sighting, and
therefore had a less accurate field estimate. The second data set contained all data,
including schools in which no dolphins were photo-identified. The whole data set was
used because schools that were not photographed may have tended to be smaller than
average, and therefore, more difficult to keep in sight. By excluding non-photographed
schools the average size would likely be biased upward. Comparison of school size by
latitude was conducted using simple linear regression (Sokal and Rohlf 1981).
The third and fourth secondary tables, also produced from the Individuals table, were
called the Associate table, and Full-Photo Associate table. Dolphin association indices were calculated for all dolphin pairs photographed in each sighting. Calves were excluded from all analyses, because it was expected that range and association patterns were dependent on that of the mother. 15
Association indices were determined with the use of the simple ratio (SR) (Ginsberg
and Truman 1992):
x/(x + Y. + Yb)
where x = the number of times dolphin 'a' and dolphin 'b' were sighted together, Y,= the number of times dolphin 'a' was seen without dolphin `1)', and Yb = the number of times dolphin 'b' was seen without dolphin 'a'.
The Associate table contained every pair combination of all photo-identified dolphins. It included the number of times each dolphin of the pair was sighted (during
1994-1996), the number of times the pair was sighted together, the SR, and the known genders of each dolphin in the pair. The Full-Photo Associate table was a subset of the
Associate table. It contained sightings of animals in fully- photographed sightings only.
This table contained the same number of rows and columns as the Associate table, but the values in each row were equal to or (usually) lower than the Associate table.
The Full-Photo Associate table was used primarily to distinguish "groups". A group was defined as a social unit, somewhat stable over time (Wells et al. 1987). All analyses of association indices were conducted using the SR of dolphins photographed >5 occasions.
I used multidimensional scaling (MDS; Mardia et a/. 1979) and cluster analysis
(group average method; Mardia et al. 1979, Manugistics, Inc. 1995) to distinguish groups. MDS and cluster analysis are multivariate techniques that group data. Group average method of cluster analysis is a hierarchical method that has been used in many 16 studies of dolphin social systems (Wells et al. 1980, Ballance 1990, Heimlich -Boran
1993, Slooten et al. 1993, Wilson 1995, Harzen 1995). However cluster analysis is a subjective tool that will group data even when there are no reasonable bases for the existence of clusters. In contrast, MDS is an objective tool that only groups data that are related. I used the Kruskal-Wallis test to compare association indices by gender, within groups.
The Associate table provided information on the number of associates. Student's t- tests (Sokal and Rohlf 1981) were used to compare the number of associates by community, and the number of associates by gender. Data from the Associate table was also used to distinguish further possible groups in which members were excluded from the cluster analysis due to an insufficient number of fully- photographed sightings. Non- calf dolphins photographed >5 times in all sightings were used in these analyses.
The fifth secondary table was termed the Closest Associate table, and was produced from the Full-Photo Associate table. This table contained non-calf dolphins photographed >5 times in filly-photographed sightings. It included each animal's closest associate (also non-calves photographed >5 times in fully- photographed sightings), SR, and the genders of each pair, when known. The Mann-Whitney U-test was used to compare medians of individuals' closest associate by gender. 17
RESULTS
Effort
Field effort totaled 341 days between 1994 and 1996, of which 256 days were workable (i.e., dry, with winds less than 28 km/h). Full or partial days were spent searching in the following areas: 86 days in the North; 169 days in the South; and 54 days (50 of which were partial, and averaged only 3 h/day) in the Central region.
Overall, the study area was searched for 2162 h: about 37% in the North, 9% in the
Central region, and 54% in the South.
Two-hundred-ninety-five sightings of bottlenose dolphins were recorded (Figure 1.2) during 167 (65%) of the workable days (Table 1.1). An average of 1.2 sightings was observed per day (295/256). On average, 66 min were spent with each sighting, and 322 h (15% of total hours of searching) were spent in direct observation of dolphins during daylight hours. Sightings were rare during severe weather conditions, or when sea states were greater than Beaufort 3.
I analyzed 267 rolls (9608 frames) of film. Of these, 224 rolls were taken with the
Canon AE-1, and 43 rolls were taken with the Nikonos (underwater photos of body scars, gender, and behavior). Of the 295 sightings, 203 were photographed. In the 203 sightings, I collected 1083 dolphin records, including identifiable calves (380 North, 153
Central, and 550 South) although not all dolphins were photographed in each sighting.
In addition, over 5300 photos were analyzed from the Wild Dolphin Project's collection, dated between 1985 and 1996. These photos provided 763 records, 528 of 18
Y. i'"811.
27 V
Mt.
27 00
Memory Rock Ritr
.-.
lo
26 ...... Sandy . . IV. Coy
.26 40 West E
Grand Bahama Sighting Location Island * Point of Land
79 V 79 00
Figure 1.2. Locations of bottlenose dolphin sightings, during 1994-1996. Dotted lines show boundaries between North, Central, and South regions of the study area. 19
Table 1.1. Field effort and success rate of dolphin observations, during 1994-1996.
1994 1995 1996 TOTAL
5/3 - 6/5, Dates in the field 6/18 - 9/22 5/3 - 9/21 N/A 6/22 - 8/28 Days in the field 97 142 102 341 Workable* days in the field 85 117 54 256 Hours of searching 731 945 486 2162 Days of sightings 49 81 37 167 Number of sightings** 80 123 92 295 Sightings photographed 43 93 67 203 Avg. no. of sightings per day of searching 0.9 1.1 1.7 1.2 Avg. min. spent with each sighting 44 96 45 66 Hours of direct dolphin observation 60 197 65 322 Percent of time in direct observation of dolphins 8.2 20.8 13.9 14.9
*Workable days were dry with winds <28km/h. **Includes 5 sightings observed from land (no photos) on days of no searching
which were additional to the 1083 records. I obtained an additional 103 records during times other than the field season, and 37 records were received from other reliable sources. These 668 additional records were located as follows: 522 North; 73 Central;
29 South; 44 unknown location. Therefore, the number of individual records totaled
1751 (Table 1.2). 20
Table 1.2. Individual dolphin records collected. A record is defined as a photo of an identified individual with information on date, time, and location.
re-1994 1994 1995 1996 TOTAL My Effort 0 178 627 278 1083 Wild Dolphin Project* 193 119 132 84 528
Others 12 4 20 1 37 Additional Data** 0 51 9 43 103
Total 205 352 788 406 1751
* additional to my effort ** I collected at times other than during the study.
Site Fidelity
General
During three field seasons, 212 individual dolphins were identified and described
(Appendix B, C). Of these, 105 were first recorded during 1994. In 1995, 92 new
individuals were sighted (49% of 188 individuals identified in 1995) and in 1996, only 15
new dolphins were identified (11.5% of 130 individuals identified in 1996). The
substantial decrease in new individuals identified in 1996 suggested that most dolphins inhabiting the area between May and September were identified by the end of the study
(Figure 1.3). Gender was determined for 77 (36%) of the identified dolphins (Table
1.3). 21
220
200
180
160
140
120
100
80
60
40
20
0 1994 1995 1996 Year
Figure 1.3. Decreasing rate of discovery ofnew dolphins in the study area (n = 212). 22
Table 1.3. Number of male and female dolphins identified, and the method of gender determination.
Method of Gender Females Males Determination
Observation of genital region 26 (10) 12 (11) (with confirmation photo)
Regular association with calf 20 N/A Observation of erection N/A 19 (16) (with confirmation photo) Total number of dolphins of 46 known gender 31
Of the 212 individuals identified, 173 (82%) were photographed >2 times, 110 dolphins (52%) were photographed >5 times, and 57 (27%) were photographed >10 times between 1994 and 1996 (Figure 1.4, Appendix D). On average, individuals were seen 7 times (SD = 7, n = 212) during the three field seasons. On 35 occasions (2% of
1751 records), a dolphin was counted as present two times in one day, due to being photographed with different dolphins in the two sightings.
Sixty-two (29%) dolphins were photographed during all three years. Gender was determined for 42 (68%) of these, which accounts for 55% of all dolphins of known gender. Fifty-four dolphins (205 records) were matched to photos taken opportunistically between 1985 and 1993. Many of these dolphins were photographed numerous times before 1994 (Appendix D). One dolphin was photographed 14 times 23
Number of Sightings per Individual
Figure 1.4. Number of sightings per dolphin (n = 212 dolphins), during 1994 and 1996. 24 between 1990 and 1993. These photographs suggest long-term site-fidelity for at least some individuals during the summer months.
Thirty-nine dolphins were photographed only one time during this study, although four had been photographed one to four times before 1994 by the WDP. Fifteen of these
39 dolphins were sighted within 6 d of each other (9 in the same group on 8/21/95), and may be transients.
No overlap was found between individual dolphins of the present study and those of the Central Abaco population. However, in July 1997, seven dolphins photographed in south Abaco were matched to dolphins that had been previously identified in the
Northern region of my study area (Claridge, pers. com.). The seven dolphins were photographed in my study area 1-8 times, during 1994-1996. They presumably traveled about 225 km.
Specific
All non-calves photographed >5 times (n = 98) showed site fidelity to a specific region within the study area. No single dolphin was sighted throughout the study area
(Figure 1.5). Ninety-eight non-calves were sighted <4 times during the study (Figure
1.6). Thirty-two of these dolphins were seen only at the northern border of the study area, and seven were seen only at the southern border. Of the remaining 59 dolphins sighted <4 times, 22 were seen primarily in and near the less thoroughly searched Central region, and 24 were found at least once in or near a poorly searched area. None of the dolphins seen <4 times were found predominantly in the well-searched Northern or Dolphin I. D. Figure 1.5. Latitudinal ranges of 98 non-calves sighted >5 times (ordered by mean latitude), during 1994-1996. 2718' - °, o. I . . t !I 0841 lboo. : 0 27°12' -
2706' -
5 00000 . 11141 .
8 2700' . . . 4.
26°54'
26°48' - 60(00
26°42' I 5 11111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111 RIMMAPWWWWWWWORMIXWOIRWIWININPRIPOVWVOINRUMM9 Dolphin I.D. Figure 1.6. Latitudinal ranges of 98 non-calves sighted <5 times (ordered by mean latitude), during 1994-1996. 0.") 27
Southern areas, suggesting that most dolphins regularly inhabiting the well-searched regions were known, and that many other dolphins inhabit nearby areas.
Although the 205 pre-1994 dolphin records taken in the study area were not included in these analyses, locations of individuals' sightings were consistent with the 1994-1996 findings (Figure 1.7). However, in 1992 one dolphin (ROC) was photographed about 40 km east of its locations in the present study area (Claridge, pers. com.).
Association Patterns
Primary Groups
A total of 821 individual records (see p. 13) were documented in 158 fully- photographed sightings (including additional data, see Table 1.2). The success of photographing all individuals in a sighting increased each season due to my increased experience (1994 = 22%, 1995 = 58%, 1996 = 75% estimated success from all sightings). Between 1994 and 1996, 73% of dolphins identified south of 26°59'N (the approximate latitudinal halfway point in the study area) were recorded in fully- photographed sightings (n = 644 records), compared to only 39% of the dolphins identified north of 26°59'N (n = 902 records). Unless otherwise specified in the remainder of the results, 'dolphin' or 'individual' refers to a non-calf dolphin.
A total of 148 dolphins were recorded in >1 fully-photographed sighting.
Association indices showed that less than 17% of all possible pair-wise interactions between dolphins (1827/10878 pairs) in these sightings were observed. 28
27°18' II 00o. : 27°12' So 4111...04 I 27°06' 0000 000 .0 00 27000.
26°54'
26°48'
26°42'
26°36' 1 1 1111111111111111111111111111111111111111111111111 gglIgNPRQMOVIM5PlianSlIM§WMPR§"2§i
Dolphin I.D.
Figure 1.7. Latitudinal ranges of 51 dolphins (ordered bymean latitude) photographed before 1994. 29
Multidimensional scaling of 59 dolphins photographed >5 times in fully-photographed sightings (n = 1711 dolphin pairs) suggested three primary clusters (Figure 1.8). Cluster analysis of the same data indicated four primary clusters (Figure 1.9) based on a distance of 110 as a divider of clusters. I chose 110 as a divider for three reasons: 1) It was most similar to the MDS plot; 2) The agglomeration distance plot (Figure 1.10) shows the distance between groups when they were combined by cluster analysis. "A sharp jump at some location may indicate that a good choice for the number of clusters is just to the left of the jump" (Manugistics, Inc.1995); and 3) It was congruent with what I observed in the field.
Members of the same cluster shared similar ranges (Figure 1.11). The range of some members of each cluster overlapped with the range of some or all members of other clusters. A large cluster of 15 dolphins was called the "Northern dolphins" because of the dolphins' relative range within the study area. Twelve of the 15 individuals were of known sex (6 males; 6 females, 3 with a calf). Northern dolphins were sighted a minimum of 27 km from shore, and were considered offshore relative to a large cluster of 28 dolphins which was termed the "Southern dolphins" because of their inshore range.
Nineteen of the Southern dolphins were of known sex (9 males; 10 females, 7 with a calf). Members of the two clusters were photographed in the same sighting in only 1.3%
(2/158) of all fully-photographed sightings.
Most dolphins in these two clusters were sighted frequently. Northern dolphins were sighted an average of 22 times each (SD = 9, n = 15), and Southern dolphins were seen an average of 16 times each (SD = 6, n = 28) between 1994 and 1996. Northern and
Southern dolphins were sighted well above the overall average of 7 sightings per dolphin Central Dolphins
ZEE FIS ECL SEpooLIAB BRE COR c=? IiIP MA pifAR SOPA CRA RO BA a ROO PEHAlscAlk-FIEHRYAN FRI MOM BIN
-0.2 0.0 0.2 Coordinate 1 INorthern Dolphins I Southern Dolphins
Figure 1.8. Results of multidimensional scaling show the relative distance between association indices of 59 non-calves photographed >5 times in fully-photographed sightings. Three groups can be suggested by the diagram. About 10 dolphins that neared the center point (0,0), showed no strong affinity to any group or to each other, and were not assigned to any of the three groups. 4§1-jWili§ttZ0:4i0.1:',6,1i2;4,0,W-.§VIEN504§i§WIDARVINmiEIVI k /- H k .14 NORTHERN CENTRAL SOUTHERN COOPERATI DOLPHINS DOLPHINS DOLPHINS FEEDERS
Figure 1.9. Cluster analysis (group average method) dendogram of simple ratio indices of 59 non-calves seen >5 times in fully-photographed sightings. Four clusters are shown at a distance of 110. In cases where the first association between two dolphins was greater than a distance of 30, the two dolphins were not fit into a new or existing cluster because the indices showed that the two dolphins associated with other dolphins more than with each other. 120
90 oeu g i\N ...v) A 60
30
o
10 20 30 40 50 60 Stage
Figure 1.10. The agglomeration distance plot shows the distance between groups when they were combined by cluster analysis. A sharp jump at some location may indicate that a good choice for the number of clusters is just to the left of the jump (StatgraphicsPlus 2.1). Arrow indicates the distance of 110, which I chose as a divider of clusters. 27°18' 00 SI 27°12' :1::: .11...8 8114111.111;1. 2706' l:i ,1111 ips 27oo. SS 0. as 8 t
26°54' :
26°48' SI lie 11 e 1; .1: 111;8
$ $ $ 11 26°42' : : IS hi
26°36' North Central South Cooperative Feeders n = 15 n = 5 n = 28 n = 4 Cluster
Figure 1.11. Latitudinal ranges of dolphin cluster members. 34
(n = 212). Also, most sightings of each dolphin were spread over time. Fourteen of the
15 Northern members were sighted during all three field seasons, and all but 3 dolphins
were photographed in the area prior to 1994. Fifteen of the 28 Southern dolphins were
sighted during all three seasons, and the remaining, during two seasons. Four Southern
dolphins were photographed prior to 1994.
The Northern dolphins were photographed over a longer period of time than the
Southern dolphins for two reasons. First, the Northern region of the study area was
regularly searched by the Wild Dolphin Project prior to 1994, whereas the Southern
region was rarely searched. Second, during 1994, the Central region of the study area
was rarely searched. Many of the Southern dolphins were frequently found in the
Central region.
The two large clusters of dolphins were considered "communities". A community was defined as a group of dolphins that included both genders, showed long-term site fidelity, relatively high association between members, low association with neighboring individuals, and shared similar habitat and feeding habits. The Northern and Southern members were probably core to larger communities, because other probable members were excluded from analyses simply due to insufficient number of photographs (i.e., <5 records) in fully-photographed sightings.
A smaller cluster was also shown by MDS and cluster analysis. It consisted of five dolphins (FOL, JIG, ALF, CUR, MEM). Three were known females; two with calves.
The sexes of the other two were unknown. This small cluster was located between the range of the Northern and Southern dolphins, and was termed the "Central group".
These five dolphins could be a female "band" (Wells 1991) or "clique" (Smolker et al. 35
1992), belonging to the Northern or Southern communities, or could be part of a Central
community. They interacted slightly more with the Southern dolphins, with which their
range overlapped to a greater degree.
A small cluster suggested by cluster analysis but not MDS consisted of four dolphins.
These dolphins were not distinguished by MDS probably due to the low number of fully-
photographed sightings of each individual. Each of the four dolphins was only identified
five times in a fully-photographed sighting, compared to Northern community members,
which averaged 22 sighting per dolphin, and Southern dolphins, which averaged 16
sightings per individual.
These dolphins were rather easily distinguished in the field because of their unique
method of feeding. When sighted, they were usually feeding. I called them
"Cooperative Feeders" because of their feeding behavior (Chapter 3). The four
Cooperative Feeders were probably part of a larger group. However, other presumed
members were photographed an insufficient number of times in fully-photographed
sightings to be included in the analyses. They were relatively highly associated and,
though overlapping in range, were rarely associated with the Southern dolphins.
Simple Ratios were substantially higher between pairs of dolphins within each of the
four clusters, than between pairs of dolphins in different clusters (Table 1.4). All
members of the Cooperative Feeders interacted with each other, as did all members of the Central group. A total of 99% of possible associations between pairs of Northern dolphins (n = 105) were observed, and 94% of possible associations were observed within the 28 Southern dolphins (n = 378). Overall, 95% of possible interactions within clusters were observed, and only 18% were observed between clusters (Table 1.5). 36
Table 1.4. Simple ratio medians, means, and standard deviations of dolphin clusters: Within and between.
Simple Ratio Median Mean SD N
North/North 0.18 0.21 0.13 105
North/South 0 0.01 0.02 420
North/Central 0 0.01 0.02 75
North/Cooperative 0 0 N/A 60
South/South 0.16 0.19 0.15 378
South/ Central 0 0.01 0.03 140
South/Cooperative 0 0.03 0.04 112
Central/Central 0.5 0.57 0.2 10
Central/Cooperative 0 0 N/A 20
Cooperative/Cooperative 0.34 0.43 0.29 6
Table 1.5. Number of pair-wise dolphin associations observed within and between 4 cluster groups.
Association Pair-wise Associations Type Possible Observed % Observed
Within 4 groups 499 476 95
Between 4 groups 827 150 18 37
Other Possible Groups
Two range tendencies of dolphins shown in the latitudes of individuals (Figure 1.5) were not distinguished by the cluster analysis results of association indices. This was because most dolphins in these two ranges were photographed an insufficient number of times in fully-photographed sightings to be included in the cluster analysis. However, when non-calves sighted >5 times in all sightings (n = 98 dolphins) were considered, most dolphins within each of these two ranges were relatively highly associated.
Five dolphins found around latitude 27°03'N were termed the "Central/North group", and 8 individuals found only north of 27°12'N were named the "Far North dolphins". The Central/North group (DIP, SIC, SPI, VOL, ZEE) was suggested by overlapping range and high association indices (SR median = 0.21, R = 0.22, SD = 0.07, n = 10 pairs in all sightings). All 5 dolphins were known females (4 with calves) and may be a female band belonging to one of the two communities, or they could be part of a
Central community. They interacted more often with the Northern dolphins.
Though the Central and North/Central groups were found in similar ranges, they were sighted together rarely (Central/North to Central dolphins: SR median = 0, R =
0.02, SD = 0.03, n = 25 pairs in all sightings). However, the Central/North dolphins may interact with other dolphins more often than shown in results, because many sightings in which they occurred were not fully- photographed.
Far North dolphins were sighted only north of 27°12'N (>48 km from shore), although the area just to the south was searched heavily. These 8 dolphins (MAR, SQU,
TWE, FIG, DBL, SCO, SLA, BEE) were sighted 5 - 9 times each in all sightings and were associated (SR median = 0.09, R = 0.10, SD = 0.10, n = 28 pairs in all sightings). 38
The Far North dolphins rarely interacted with the Northern dolphins (SR median = 0, 5:
= 0.01, SD = 0.02, n = 120 pairs in all sightings) although they overlapped somewhat in range. Thirty-two other dolphins sighted 1 - 4 times each were seen only at the northern edge of the study area. These dolphins could be members of the Northern community, but because not all dolphins were photographed in most of their sightings, it is not known to what extent they interact with other dolphins. The seven dolphins sighted 225 km southeast of my study area in 1997, were not presumed members of the Far North group or the Northern community.
Long-term Associations
Forty-nine percent of dolphin pairs opportunistically photographed in the same sighting between 1990-1993 (n = 97 different dolphin pairs) were sighted together at least once during the study. Of 12 different dolphin pairs photographed in the same sighting prior to 1990, seven pairs were sighted together at least once during the study.
With one exception, all pre-study associations were sighted in the Northern section of the study area.
School Size
The size of all bottlenose dolphin schools (calves included) averaged 5.8 dolphins
(SD = 5.3, median = 4.0, n = 363) (Figure 1.12). The size of photographed schools
(calves included) averaged 6.7 dolphins (SD = 5.8, median = 5.0, n = 263) (Figure 1.13), 39
80
70
60
50
40
30
20
10 -
77:77
0 "77 0 5 10 15 20 25 30 School Size
Figure 1.12. Range of school size of 363 dolphin schools sighted during 1994-1996. 40
School Size
Figure 1.13. Range of school size of 263 dolphin schools photographed during 1994-1996. 41
11.8% (n = 31) of which consisted of only one dolphin. School size (of all schools and
of photographed schools) did not vary significantly by area (p > 0.05 for all schools; p >
0.05 for photographed schools).
Schools in which at least one dolphin in the school was photographed a total of only a
single time (36 non-calves) averaged 12 dolphins per school (SD = 7, n = 24 dolphins),
well above the overall average. Presumed transient schools were larger in size than other
schools.
Number of Associates
The number of associates sighted with an individual dolphin leveled off after the individual was sighted >15 times (including non-fully-photographed sightings; Figure
1.14). Overall, dolphins photographed >15 times averaged 48 associates (SD = 11, range = 32 - 77, n = 28). The animals photographed most often (MIN, a female and
SAW, a male) were photographed on 44 and 31 occasions. They associated with 53 and
48 dolphins, respectively. Southern dolphins sighted >15 times associated with more dolphins (R = 53, SD = 12, n = 14) than did Northern dolphins sighted >15 times (g =
44, SD = 9, n = 12; Figure 1.15), but the difference was not significant (p > 0.05). 42
80
60
0
40 o -4- I
20
0
1-4 5-9 10-14 15-19 20-24 >24 n = 96 n = 47 n = 23 n= 11 n = 6 n = 11
Number of Sightings per Dolphin
Figure 1.14. Number of associates of each dolphin (n = 194) based on the number of the dolphin's sightings. The number of associates leveled off when a dolphin was seen about 15 times. All dolphins and associates are non-calves. 43
North - H
South - H H
40 60 80 Number of Associates per Dolphin
Figure 1.15. Number of associates of Northern dolphins (n = 12) vs. Southern dolphins (n = 14) photographed >15 times. 44
Gender
Many northern male/male associations were closer than male/female and
female/female associations but the difference was not significant (p > 0.05; Figure 1.16).
All 12 Northern dolphins of known sex associated with each other at least once (in fully-
photographed sightings). Southern males and females associated differently (p < 0.01).
Male/male and male/female associations were significantly higher than female/female
associations (Figure 1.17). Ninety-seven percent of male/male, 91% of female/female,
and 93% of male/female possible dolphin-pair associations were observed among
Southern community members.
Association indices of 59 dolphins and their closest associate averaged 0.58 (SD =
0.26, n = 59; Figure 1.18). Forty of the 59 dolphins were of known sex, and 31 had a closest associate of known sex. The closest associate for a particular animal was of the same sex 74% of the time (Table 1.6). Simple Ratios of the closest associate for male/male pairs were not significantly different than for females/female pairs (p > 0.05;
Table 1.7).
Males associated with slightly more individuals than did females. Males seen >15 times averaged 48 associates (SD = 9, n = 12), and females seen >15 times averaged 42 associates (SD = 7, n = 12) but the difference was not significant (p > 0.05; Figure 1.19). 45
1.0
0.8 -
.
s T T 0.2 -
0.0 I I Male/Male Female/Female Male/Female n= 15 n = 15 n = 36
Gender Combination
Figure 1.16. Comparison of simple ratio indices between sexes of Northern dolphins. 46
1.0
0.8
a
I
0.2
i 0.0 Male/Male Female/Female Male/Female n = 36 n = 45 n = 90
Gender Combination
Figure 1.17. Comparison of simple ratio indices between sexes of Southern dolphins. 47
12
10
0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00 Simple Ratio
Figure 1.18. Range of simple ratio indices for 59 dolphins' closest associate. 48
60 - T
50 - T
40
i' 30 Males Females Gender
Figure 1.19. Number of associates of 12 males vs. 12 females seen >15 times, during 1994-1996. 49
Table 1.6. Percentage of closest associates that are same sex vs. opposite sex of partner. Dolphins and their closest associate are non-calves of known sex, photographed >5 times in fully- photographed sightings.
Number of Percentage Closest Pairs Occurances of N Same sex 23 74 31 dolphins Male/male 12 92 13 males Female/female 11 61 18 females Opposite sex (1 mit 7 f/m) 8 26 31 dolphins
Table 1.7. Medians, means, and standard deviations of simple ratio association indices for non-calves and their closest associate, photographed >5 times in fully- photographed sightings.
Closest Associate Median Mean SD Overall 0.55 0.58 0.26 59 Male/male 0.79 0.76 0.15 12 female/female 0.71 0.68 0.22 11 male/female N/A N/A N/A 1 female/male 0.33 0.38 0.14 7
Spotted Dolphin Interaction
Interactions with spotted dolphins (n = 30 mixed-species schools) primarily occurred in the Northern region of the study area (90% of mixed-species schools). The remaining interactions occurred in the South, near Grand Bahama Island. Mixed-species schools were usually socializing and averaged 5 bottlenose dolphins (SD = 4, calves included) and 16 spotted dolphins per school (SD = 12, n = 30 schools). 50
A total of 76 different bottlenose dolphins were photographed in the presence of spotted dolphins. Gender was determined for 14 of 15 bottlenose dolphins (11 males, 3 females) that interacted with spotted dolphins >3 times.
Environmental Factors
Dolphins were sighted in water depths typically ranging between 1 - 15 m. On two occasions, dolphins were followed off the edge of Little Bahama Bank. On 8/8/95 a dispersed school of 20 dolphins moved west, off West End, fluldng-up in water over 30 m as darkness approached. On 8/16/95, a school of 20 dolphins was headed west, about
35 km north of West End, toward deep water as dusk approached. Depth measured 200 m before losing sight of the dolphins due to darkness. Individuals identified in the two sightings were different.
Environmental factors differed between sightings of the Northern and Southern community members. Water depth was significantly deeper for Northern dolphin sightings (p < 0.01, Figure 1.20). Overall, dolphin sightings north of 26°59'N typically were in water 5 - 12 m deep (117 of 131), and all depths were greater than 4 m (5-( = 7.6,
SD = 2.4 ). In contrast, typical depths south of 26°59'N ranged between 1 - 3 m (108 of
121; 5-( = 3.0, SD = 1.8) (Figure 1.21).
Benthic characteristics also differed by latitude. Loose sand bottom was the dominant feature in the Northern region, and grass and patchy grass areas were most common in the South (bottom p < 0.01, vegetation p < 0.01, and dominant feature p <
0.01; Figures 1.22, 1.23, 1.24). 51
North
.a
0
South I
0 2 4 6 8 10 12 14 16 Depth (m)
Figure 1.20. Depth of sightings in which Northern (n = 37) or Southern (n = 81) dolphins were present. 52
27°18' O. 00 I os 27°12' . 41 41, : :8 27°06' ,41:41:4,. 8 -o 24/00, . -4 . 14, 26°54' :8 .1: 8 26°48' - ::
26°42' - 1.0111:
26°36' 0 2 4 6 8 10 12 14 16 Depth (m)
Figure 1.21. Water depths at the latitudes of 252 dolphin sightings during 1994-1996. 53
27°24'
27°12' -
-o .4 rfoo. 41
26°48' - I
26°36' Crusty Sand Loose Sand
Bottom Type
Figure 1.22. Latitudes of dolphin sightings over crusty sand (n = 48) vs. loose sand (n = 27). 54
Patchy Grass Other/unknown Absent n = 40 n= 19 n = 9
Vegetation Type
Figure 1.23. Latitudes of dolphin sightings at different vegetation types. 55
27°241
27°12'
to -es viB 27°00' 1.1 T 26°48' I t -V-
26°36' Bare Bottom Vegetation n = 153 n = 57
Dominant Benthic Characteristic
Figure 1.24. Dominant benthic characteristic at the latitudes of dolphin sightings. 56
Foraging Strategies
I observed a total of five different foraging strategies, although it is likely that
dolphins in the study area use other strategies as well. Cooperative feeding was
observed during six sightings in the Southern region of the study area (Chapter 3). A
total of 34 identified dolphins fed cooperatively, 19 of which were seen in cooperative-
feeding sightings for at least 50% of their total sightings.
Crater feeding was primarily observed around latitude 27°08'N, and secondarily,
near Grand Bahama Island, at depths averaging 8.5 m (Chapter 2). A total of 36
individuals (including 3 identifiable calves) were photographed crater feeding (35 were
identified by 1995), 20 of which were observed using this method to feed >4 times
between 1994 and 1996. In 1996, the only additional dolphin seen in crater-feeding
sightings was a newly identifiable yearling whose presumed mother regularly crater-fed.
All 15 Northern Dolphins were found in crater-feeding sightings on at least two
occasions (51 = 6 sightings, SD = 3, n = 15).
A variation of crater feeding was seen throughout the study area, mostly in shallower
regions (about 2 - 7 m) sometimes covered with turtle grass. Dolphins' heads circled as
they "scanned" the bottom with rapid clicks, from mid-water or high in the water
column. Little scanning was done directly on the sand (as in crater feeding), until prey
was presumably detected. The dolphin then scanned intensely at one spot before digging,
less vigorously than in crater feeding. Another variation of crater feeding was often seen just north of West End, where water depths average around 2 m. Dolphins fed in holes,
sometimes inhabited by squirrel fish (Holocentrus sp.), in a similar manner as just 57
described. It is not known what species were taken, but sand tile fish (Malacanthus plumieri), as well as small eels, frequently inhabit such holes.
A fourth foraging strategy took advantage of what Bahamian fishermen term a
"snapper run", which occurs near West End in late June and early July, when lane
snapper (Lutjanus synagris) move close to shore to spawn. Dolphins were occasionally
seen fluking -up in an area where numerous fishermen were successfully landing lane snapper with a hand-line from a jetty. Many Bahamians reported dolphins following or feeding on lane snapper during this time of year. This feeding strategy was the only one not observed from underwater.
Finally, some Southern dolphins foraged on fish in fishermen's traps. In early July,
1995 and 1996, fishermen and boaters reported fish traps near West End being dismantled and tossed at the surface by bottlenose dolphins. On 18 June 1995, I observed two dolphins (an adult female, and approximately 3 yr.-old female calf) at a fish trap made of wire-mesh. The trap measured about 1.2 m by 1.8 m, and 0.3-0.6 m high, and was in water less than 2 m deep. The dolphins remained at the trap for 49 min, and about 2 h later, returned and remained for another 25 min. Underwater, I observed the adult capture two lane snappers by aggressively thrusting her rostrum into the trap and pulling out a fish. At one point, the adult lifted the entire trap onto its side with her rostrum. The trap remained on its side for a few minutes before it was knocked down by one of the dolphins.
All of the described foraging strategies (with the exception of crater-feeding variation) were observed in specific and unique regions of the study area (Table 1.8).
Northern dolphins primarily crater-fed in sandy bottoms. Southern dolphins bottom-fed Table 1.8. Dolphin foraging stategies observed, during 1994-1996.
Foraging Primary Dolphins Primarily Typical Water Type Locations Involved (Secondarily) Depth (m) Northern region, Sandy Crater feeding North (South) 10 Cay, south of West End Crater feeding variations/ whole study area South and Central (North) 5 other bottom feeding
Cooperative feeding around Sandy Cay Cooperative Feeders (South) 3.5
Snapper run north of West End South 2
Fish traps north of West End South 2 59
in grassy areas or in holes. Seasonally, they also fed on lane snapper, and occasionally
from fish traps. No single dolphin was observed using all the above-described foraging
strategies.
DISCUSSION
Site Fidelity and Range
Eleven percent of identified non-calf dolphins (21/194) in the present study, were matched to photos opportunistically taken between 1985 and 1989. Seventeen of the 21 dolphins were photographed in the Northern region of the study area in the past, and during the study. Thus, long-term site fidelity of 5 - 11 years exists for at least some individuals >27 km offshore Grand Bahama Island. Site fidelity is a typical characteristic of coastal bottlenose dolphins (reviewed by Leatherwood and Reeves 1982, and Shane et aL 1986; Connor and Smolker 1985, Wells 1986, Mate et al 1995, Harzen 1995).
However long-term site fidelity has not been previously reported for bottlenose dolphins found far from shore.
Covering a study area over twice the size of most others (Weller 1991, Harzen 1995,
Smolker et aL 1992, Shane 1990b, Brager et aL 1994, Wilson 1995, Wells et aL 1987) allowed for the determination of range differences between identified individuals and for the distinction of communities. Wells (1978) estimated that with 15 sightings of an individual, a dependable home-range estimate could be made for that animal, within the 60
study area. In the present study, 28 non-calves were photographed on 15 or more
occasions. Each dolphin's range was characteristic of one of two broad range
tendencies, offshore and inshore (Figure 1.25). Coastal adjacent communities have been
reported by Irvine et al. (1981). They repeatedly observed certain identifiable dolphins
only around the edge of the Sarasota study area. Wells et al. (1987) reported that about
17% of sightings contained identifiable residents from adjacent communities. Dolphins
found off northern Mexico and southern California also appear to have inshore adjacent
home ranges (Hansen 1990, Caldwell 1992) that may be dependent on environmental
conditions (Wells et al. 1990). The current study demonstrates that adjacent
communities occur offshore, also.
A community's range may be dependent on suitable foraging habitat. Environmental conditions differed between the Northern and Southern communities' ranges. The area of overlap between the two communities is an area of transition from shallow to deep water and from grassy bottom to sand. Foraging strategy may be determined by or limited by bottom-type. Therefore, benthic, environmental factors may play a role in determining individual range, since many dolphins are bottom-feeders.
Number of Associates
Dolphins photographed >15 times averaged 48 associates (n = 28 dolphins). The number of associates affiliated with a dolphin was higher for dolphins more centrally located in the study area. Of 51 dolphins photographed >10 times (which averaged 45 27°18'
: a s I I s s .i :1 : 1 s . 27°12' I a a a . 1 $ $ 4 a ! 1 . I I I I I I 27°06' I I 1 I. ! 4 s I Iiiii II5 g 27°00' 8 ,Z1 i
26°54' II a a a 1 a 1 I I 26°48' I ! ! i $ : ! ! ; 1 26°42' I i S :II 4! 1 1 1 1 I I
26°/36' a. 1111111111IIIIIIIIIiiiiill9, 8 g 6 . - 1 8, 0 i i i 4 11 Z N 5ia COCO 1 co) CO "4 8 P I A 4h4j 0 Dolphin I.D.
Figure 1.25. Latitudinal ranges of 28 non-calves sighted >15 times (ordered by mean latitude), during 1994-1996. cA 62 associates), eight had greater than 60 associates. They included one Northern dolphin
(ART), and 7 Southern dolphins which were most centrally located (5PP, ATT, BAK,
BIN, CRA, HAM, MAG) (Figure 1.26). The higher number of associates for these dolphins could be explained if the Central area represented the northernmost and southernmost border of the Northern and Southern communities, and therefore the dolphins' interactions with neighbors on both sides were observed. Though observation of all associates is not possible, associations are most difficult to determine for dolphins that may interact with neighbors outside the study area. Still, a trend toward a finite number of associates was observed in the study area. The number of associates is probably most accurate for those dolphins with a larger number of associates. Until the home range limits of the Northern and Southern communities are known, it is difficult to estimate the number of associates.
Other bottlenose dolphin studies have found varying numbers of associates.
Dolphins seen >4 times in Galveston Bay, Texas associated with an average of 39.3 individuals (Brager et al 1994). In Sarasota Bay, FL dolphins averaged a minimum of
61 associates (range of 25 - 91) (Wells et aL 1987). In contrast, dolphins sighted >15 times in Southern California range more widely and were seen with over 200 affiliates
(Weller 1991). Dolphins with larger ranges probably interact with more dolphins. 27°18'
27°12'
27 06'
2100' as S 04
26°54 -
26 48'
26°42' -
26°30' I I I I g 9 02 c.)
Dolphin I.D.
Figure 1.26. Latitudes of 8 non-calves (ordered by mean latitude) with highest number of associates. 64
Association Patterns
Dolphins off Grand Bahama Island showed repeated associations (up to 8 yr.) between individuals found >27 km offshore. Long-term associations between coastal bottlenose dolphins have been described previously for dolphins in Sarasota, FL (Wells et al. 1987) and Shark Bay, Australia (Smolker et al. 1992). Long-term associations may increase the overall fitness of individuals by increasing their ability to locate food sources and detect predators. This study provides the first record of long-term associations of bottlenose dolphins found far from shore.
Bottlenose dolphin studies on association patterns report a wide range of mean and median levels of association (Wells et al. 1987, Weller 1991, Smolker et al. 1992,
Brager et al. 1994, Harzen 1995, Wilson 1995, Felix 1997). The variation of association values between studies may be due to real differences in social structure or could be due to differences in the data collection, manipulation, analyses, and interpretation.
Association analyses of dolphins are not currently standardized, and the methods used by researchers vary considerably. At least five factors can seriously affect the meaning and interpretation of results: 1) the association index applied, 2) choice of data applied to the index; a. which sightings/schools were used, b. minimum number of sightings per dolphin used, 3) sampling method of data used, 4) method used to identify dolphins, and 5) the location of the sampled area in relation to the range of the dolphins.
Index choice: The two indices most commonly used to measure association patterns in dolphins are the simple ratio and the half-weight index (HWI). The HWI (Dice 1945) follows: 65
2j/a + b
where a = the number of times dolphin 'a' was sighted, b = the number of times dolphin
`b' was sighted, and j = the number of times dolphin 'a' and dolphin '1;1' were seen together, scored once for each occurrence of both individuals together.
According to Cairns and Schwager (1987), the choice of formula should be based on the sampling method used. They recommend that the HWI is the most appropriate when a pair is more likely to be sighted when apart than when together, because it controls for this sampling bias. All photographic identification studies have this bias because it is more difficult to record the presence of two dolphins in a school than one. Further, when two dolphins are separate only one of the two schools needs to be sighted whereas when they are together only one school can provide the necessary data (Slooten et al.
1993). Cairns and Schwager (1987) state that the SR describes the associations that were actually observed, and that it is least biased when the sample is random. Ginsberg and Young (1992) argue that the HWI controls for the direction of the bias but is not able to control for the extent of the bias and therefore recommend that the SR be used in all cases (except where a maximum likelihood estimator can be used) and for the researcher to detail biases in the data.
Previous to the findings of Ginsberg and Young (1992), bottlenose dolphin association studies most often used the HWI (Wells et al. 1987, Weller 1991, Smolker et al. 1992). More recently, the SR has been used for bottlenose dolphins (Wilson
1995), pilot whales (Heimlich-Boran 1993), and spotted dolphins (Dudzinski 1996). 66
Two recent studies conducted analyses with both indices (Slooten et al. 1993, Harzen
1995). Only Brager et al. (1994) and Felix (1997) have used the HWI recently.
Data choice: The choice of data applied to the index formula affects the association analyses. Was data used from all sightings or some? In Australia, all sightings of single individuals (and lone mother/calf pairs) were excluded from association analyses
(Smolker et al 1992). This exclusion biases association indices upward for dolphins that are sighted alone.
It is also important to know if a subset of the entire data set was used for analyses.
Were only fully-photographed sightings used? How was filly-photographed defined? It is never possible to know if a sighting is filly-photographed. However, many times it is fairly clear that all dolphins in a sighting are not photographed (in the current study, at least 61% of dolphin records in the northern half of the study area, and 27% of dolphin records in southern half were not fully-photographed). I used data from fully- photographed sightings (a subset of the whole) for the primary analyses. I used data from all sighting to distinguish possible groups in which members were excluded from the previous analysis due to insufficient number of fully-photographed sightings.
Few studies state their photographic success rate of dolphin sightings. It is unclear in many studies whether selective criteria were used to create a subset of the data in order to perform association analysis. Wilson (1995) analyzed data from all sightings and from fully-photographed sightings. Dudzinski (1996) analyzed data from sightings in which all members were of known identity, but does not report how it was known that all members present were known. Wells et al. (1987) reports that "on average, unidentified noncalves comprised 18.5% of the dolphins in the 536 sightings in which only Sarasota 67
community members were identified", but it is not clear if sightings that included
unidentified animals were excluded from association analyses. Felix (1997) used data
from schools where at least 50% of the dolphins were identified. Weller (1991) used
data from all sightings for the analyses, regardless of photographic success, which was
not known at the time of the analysis. As photographic success rate decreases, the
resulting association indices are lower and less accurate. Photographic success rate is
not reported in other studies (Smolker et al 1992, Brager et al 1994, Harzen 1995).
A second important aspect in the choice of data applied to the index is how many
sightings of an individual were necessary for that dolphin to be included in the analysis.
All identified dolphins were included in the analyses of Heimlich-Boran (1993), Harzen
(1995) and Dudzinski (1996). Brager et al. (1994) used dolphins photographed >4 times for their analyses. Wells et al. (1987), Weller (1991) and Felix (1997) used individuals photographed >5 times, and Smolker et al (1992) reported association
patterns of dolphins of known sex photographed >10 times. Wilson (1995) used dolphin
pairs in which, when combined, the two dolphins were seen a total of >7 times.
Choosing a minimum number of sightings may depend on the research question.
Descriptive information may include all individuals, whereas distinguishing long-term or
`important' associates requires more sightings per dolphin. The lower the number of
sightings per dolphin, the increased chance of a bias in either direction due to smaller
sample size. A larger sample size lessens the weight of two dolphins reported as found together when they are actually usually found apart (and visa versa). Additionally, less weight is given to errors (i.e. a sighting that may actually include a dolphin thought to be absent). 68
Sampling method: For example - How was a school or sighting defined; was the data
(i.e. presence/absence of a dolphin) taken once during an observation period, each time school composition changed, or periodically over time? The method of defining which dolphins are associates varies. I defined a dolphin "sighting" as all dolphins in sight, moving in the same direction, and usually involved in similar activity (termed 'pod' in
Shane 1990a). On only a few occasions did it appear clear that two separate sightings were present at the same time. In these instances the dolphins in each sighting either never interacted or only briefly interacted and then separated again. This definition of sighting is similar to that used in many other association studies (Brager et a/.1994,
Harzen 1995, Wilson 1995, Felix 1997). Wells et al. (1987) and Smolker et at (1992) use a more spatial definition. However, most variability between studies may occur in cases where dolphins join and separate from a school during the observation period.
Biases in the data may be present depending on how these "sub-groups" are manipulated with regard to association between individuals. In the present study, a sighting included the maximum number of dolphins seen between the time they were approached by the vessel until the time they were left or were lost. One disadvantage to this method is that in cases when some dolphins leave a sighting before new dolphins arrive, the two sub- groups could be considered associated when in fact they were not. This bias possibly occurred on at least one occasion during the current study.
A dolphin's presence was recorded once each day, unless it was later found in another sighting with different dolphins, then it was recorded again (2% of dolphin records). Only Wells et al. (1987) and Smolker et al. (1992) discussed challenges brought on by changing school composition. In Sarasota, a dolphin's presence was 69
recounted if the two sightings were greater than 1 h apart or if school composition
changed during observations. In Shark Bay, a dolphin's presence was recounted when
the second sighting was greater than 1 h from the first and the school changed by at least
30% of its original composition.
Identification technique: The method used to positively identify dolphins varies between studies. Most researchers use photographs to make a positive identification
(Wells et al. 1987, Weller 1991, Heimlich-Boran 1993, Harzen 1995), whereas photos are not required in other studies to positively identify an individual (Smolkeret al.. 1992,
Dudzinski 1996). The method of identifying dolphins may produce differing results.
First, if or when a less experienced observer identifies dolphins without a photo, the risk of a wrong identification and the chance of missing dolphins present increases. In contrast, an experienced observer may be able to identify a greater percentage of animals in schools, if it requires less time to observe dolphins than to photograph them.
Area Sampled: The area sampled in relation to the sampled dolphins' ranges can play a role in determining the outcome of the association values. Are all dolphins part of the same community? If sampling occurs in an area that is between communities, the resulting index may show how the dolphins of different communities interact, which results in different meaning than if sampling were done in the middle of a community's range.
Mean association values have a range of meanings and interpretations depending on the factors discussed above. As much detail as possible should be used in describing methods used to calculate association indices (Ginsberg and Young 1992). Each factor should be clearly defined and explained. Straight comparisons between studies should be 70
avoided, and when done, must be viewed with caution (Ginsberg and Young 1992).
Analyses of association patterns will differ depending on the circumstances of the study
(time frame, vessel, observers, and equipment), the environment, the dolphins, and the
study questions.
Gender
Gathering gender data on wild bottlenose dolphins is difficult. The success of this
study in determining the sex of 36% of all identified individuals (74% determined by
direct observation) and 78% of dolphins sighted >10 times, was due to the ability to
observe from underwater. The somewhat habituated nature of the animals allowed
relatively close human approach, and excellent underwater visibility (about 30 m)
provided the opportunity to photograph 65% of the observed genital regions for
confirmation. Crater-feeding dolphins (Chapter 2) made observation of the genital slit
easier because the belly was more visible. Additionally, socializing males often had
erections.
Only a few other studies succeeded in determining the gender of free-ranging
bottlenose dolphins by direct observation of the genital region. In Sarasota, dolphins are temporarily handled to collect various physiological data, including gender (Wells 1978,
1986). In Shark Bay, Australia, and Moray Firth, Scotland, some dolphins turn belly-up
at the surface near the vessel, or breach nearby, providing researchers a view of the
dolphins' genital regions (Smolker et al. 1992, Wilson 1995). 71
Gender is an important component of dolphin social structure. Offshore and inshore
Grand Bahama Island, dolphins associated most closely with a dolphin of the same gender. Similarly, coastal dolphins in Sarasota, FL and Shark Bay, Australia form stable
social bonds, and are organized by sex and age class (Wells et al 1987, Smolker et al.
1992). Females associate with a network of other females, and many adult males form close bonds with one or two other males. In Moray Firth, Scotland, males may associate with a network of dolphins, more similar to the patterns of females (Wilson 1995). This study is the first to report social structure of bottlenose dolphins found far from shore.
In the Bahamas, 92% of closest associates of males were males, and 61% of closest associates of females were females. In Australia, the closest associate was of the same sex 98% of the time for males, and 90% of the time for females (Smolker et al. 1992).
Association indices of male/male closest associate were higher than for female/female closest associate in both studies (though not significant in Bahamas).
In the present study, all 6 Northern females interacted with each other. Between
1994 and 1996, 91.1% of Southern associations among 10 females (n = 45 pairs) were observed, and many of the Southern dolphins were first identified in 1995. In Sarasota, females are seen with almost every other female in the community. During 1975-1978,
82.4% of 14 females' possible association were recorded, but many females were first identified toward the end of the first study year. During 1980-1984, 95.8% of 27 females' possible associations were recorded (Wells et al. 1987). However, the small sample size in the Bahamas may be describing interaction within or among a couple of female bands rather than within a whole community. Until further members of the two 72 communities in the Bahamas are identified, it is difficult to describe a detailed social
structure among females.
Southern males near Grand Bahama Island interacted with more males than Southern females did with other females. Only 2.8% of interactions among 9 known Southern males were not observed. All 6 Northern males interacted. Male/male interactions among Sarasota dolphins are less frequent than female/female interactions (Wells et aL
1987). In 1980-1984, 76.2% of possible associations were observed among 15 Sarasota males. As more males are identified as community members in the Bahamas, a more detailed description of male social structure will be possible.
Males and females photographed >15 times in the Bahamas interacted with 48 and
42 individuals, respectively. Similarly, males in Moray Firth associated with significantly more dolphins than did females (Wilson 1995). Males and females averaged 52 and 42 associates, respectively. However, comparisons between studies should be treated with caution due to small sample sizes, and unknown community size, in the Bahamas.
Ecological Concerns
Many dolphins fed on lane snapper during spawning season. The extent to which they are dependent on the fish is unknown. According to Bahamians, the lane snapper run is decreasing at an alarming rate. In the past the snapper run was in full force for over a month. In 1994, fish numbers were high for about a week, and in 1996, the primary run lasted for only two days. Heavy fishing may be the culprit. 73
Though commercial fishing is not common in the area, it is on the rise. West End is less than 100 km from West Palm Beach, and the study area is a very popular vacation
spot for sport fishermen. As West End, Grand Bahama Island becomes more developed, and as fishing increases, dolphin populations should be monitored. This study provides baseline data on the range and association patterns of bottlenose dolphins off West End,
Grand Bahama Island. 74
Chapter 2
Underwater Observations of Benthic Feeding Bottlenose Dolphins (Tursiops truncatus) near Grand Bahama Island, Bahamas
Kelly A. Rossbach and Denise L. Herzing
Marine Mammal Science, 1997 13(3):498-504 Reprinted with Permission 75
INTRODUCTION
Bottlenose dolphins (Tursiops truncatus) are known to feed on a variety of fish
and non-fish species (reviewed by Leatherwood 1975; Barros and Odell 1990, Cockcroft
and Ross 1990). The opportunistic feeding habits of the species are demonstrated by its use of various foraging strategies (reviewed by Shane 1990b; Bel'kovich 1991). We describe a benthic-feeding method, observed underwater near Grand Bahama Island,
Bahamas.
METHODS
From May to September, during 1994 and 1995 we observed feeding bottlenose dolphins as part of a larger photo-identification study of the species in the northwest
Bahamas. The study area (Figure 2.1) ranges along the western edge of Little Bahama
Bank, between West End, Grand Bahama Island (26°42'N, 79°00'W) and the White Sand
Ridge (27.15'N, 79°08W). Water depth varies between about 1 - 20 m. Groups of dolphins were sighted and photographed from either a 20 m power catamaran or a 5.3-m inflatable boat with a 70-hp motor, between dawn and dusk. After photographing dorsal fins from the surface, we occasionally entered the water with snorkel gear to photograph animals underwater, determine their sex, and observe their behavior. Behavior was positively identified only when observed from underwater. All feeding sightings reported here were observed from underwater. The excellent underwater visibility (up to 30 m) 76
TTIB ADOCO Island
Study Area Little Bahama Bank
SO CO 79 30 79 00 7a 30 713 CO
Figure 2.1. The study area. 77
and warm temperatures (around 30°C) allowed observers to remain in the water for
prolonged periods. A Sony Hi-8 video camera with underwater housing and a Nikonos
V still camera were used to identify individuals and to record behavior.
RESULTS
Benthic-feeding groups of wild bottlenose dolphins were observed from underwater between 0.2 - 64.8 km offshore of Grand Bahama Island on 20 occasions, for a total of 33.2 h (0.3 - 5 h per session). Groups of 3 - 16 dolphins (5z = 7.5 dolphins) fed at bottom depths of 7 - 13 m = 8.5 m), with little change in location throughout each observation period. Feeding groups were observed during most hours of the day between sunrise and sunset. Typically, a dolphin's feeding pattern was to search the sand bottom for several seconds with its head moving side to side and oriented downward
(Figure 2.2). Individuals swam slowly in different directions along a sand bottom. The dolphins foraged independently but behaved similarly. Fish were not visible in the immediate vicinity, and echolocation clicks were audible in the water (described in
Herzing 1996). When forward movement stopped, clicks increased in repetition rate, suggesting that the dolphin detected some cue. The dolphin then dove into the sand, continuing to echolocate, flukes moving vigorously, and dug, occasionally burying itself nearly to the pectoral fins (Figure 2.3). As the dolphin lifted its head, a small fish was sometimes visible in its mouth (Figure 2.4). Scanning usually resumed immediately. We termed this foraging behavior 'crater-feeding' because a crater (7( diameter = 47.3 cm, 78
Figure 2.2. The dolphin searches the sand bottom with head moving side to side, and oriented downward. Echolocation clicks are audible. (Photographs by Dan Sanunis) 79
Figure 2.3. The dolphin dives into the sand, flukes moving vigorously, and digs, burying itself nearly to the flippers. Figure 2.4. As the dolphin lifts its head, a small fish is visible in its mouth. 81
ii depth = 14.9 cm, n = 7) was left in the sand after a dolphin fed. After a group of
dolphins fed, the bottom resembled a moonscape (Figure 2.5).
Of 195 individuals identified in 1994 and 1995, 35 (18%) were photographed in
crater-feeding groups. About half of these (17) were photographed frequently (4 - 9
times) during the 20 feeding sessions. Each of the 17 dolphins was photographed
between 9 - 34 times overall (including sightings only at the surface), and each was seen
in crater-feeding groups 18% to 47% of those times. All 17 animals were sexed (9
females, 8 males). Sex was confirmed on 14 animals with a photo that included both the
genital area and I.D. mark (i.e. fluke or flipper notch, body scar), and three animals were
sexed by visual observation of the genital area.
The only prey we were able to positively identify was one conger eel (family
Congridae), which was dropped by a crater-feeding dolphin. Other benthic fish species occurring in the area include wrasses (family Labridae) and clinids (family Clinidae).
Dolphins may consume more than one fish species from the sand. We did not observe dolphins taking crustacean species from the sand.
DISCUSSION
It appears that, at least for the 17 most often-sighted dolphins, crater-feeding is an important feeding strategy. Some dolphins apparently spend a substantial amount of time crater-feeding. Feeding periods (0.3 - 5 h) are minimum actual feeding durations 82
Figure 2.5. After a group has fed, the bottom resembles a moon scape. 83
because feeding sessions were never observed from start to finish. The total number of
sightings per animal that were in crater-feeding groups (18% - 47%) is also a minimum
because we did not enter the water to positively identify behavior at every sighting.
Dolphins may have been crater-feeding at times when we did not enter the water. At the
surface, flukes-up diving (Shane 1990a) was often associated with, but not a positive
indicator of crater-feeding.
Other marine vertebrates are known to leave a distinct record of their bottom
feeding behavior. Gray whales (Eschrichtius robustus) feed on ampeliscid amphipods
and other infaunal invertebrates found in the upper 2 cm of sediment (Oliver et al.
1983b, Nerini 1984). They are thought to use suction to capture prey from sediment
(see Ray and Schevill 1974), occasionally coming into physical contact with the bottom
(Kasuya and Rice 1970). Walruses (Odobenus rosmarus) use their snout and vibrissae in
excavating bivalves from the sea floor by hydraulic jetting (Oliver et al. 1983a).
Dugongs (Dugong dugon) graze on seagrass meadows and consume a substantial
amount of below-ground plant material (Preen 1995). Sea turtles (Caretta caretta) are also known to produce pits in sand during infaunal feeding (Preen 1996). All of these species considerably impact the local benthic community (Johnson and Nelson 1984,
Oliver and Slattery 1985, Nelson and Johnson 1987; Preen 1995, 1996). Further studies in the Bahamas may shed light on the ecological significance of crater-feeding bottlenose dolphins. 84
Chapter 3
Cooperative Feeding Among Bottlenose Dolphins (Tursiops buncatus) near Grand Bahama Island, Bahamas
Kelly Ann Rossbach
Department of Fisheries and Wildlife Oregon State University, Corvallis, OR 85
INTRODUCTION
Dolphin schools are thought to benefit individuals in the detection of predators
and prey (Norris and Dohl 1980). Cooperation among dolphins in a school has been
reported during searching for and capturing prey (reviewed by Leatherwood 1975,
Norris and Dohl 1980, Wursig 1986). According to Norris and Dohl (1980), schools of
dolphins capture prey by use of two methods: a) spread-school formation, and b)
cooperative-capture methods. This paper describes observations of the latter method.
METHODS
In 1995 and 1996, between May and September, I observed cooperative behavior
of bottlenose dolphins (Tursiops truncatus) as part of a larger photoidentification study
of the species in the northwestern Bahamas. The study area follows the western edge of
Little Bahama Bank, between West End, Grand Bahama Island (26°42'N, 79°00'W) and the White Sand Ridge (27°15'N, 79°08'W) (Figure 3.1). Water depth varies between 1 -
20 m, and generally increases in depth from south to north. The study area is
approximately 280 km2, 56 km north to south, and about 5 km east to west. It is characterized by mostly sand bottom with small and large patches of turtle grass
(Thalassia testudinum), and scattered areas of rock and reef bottom.
Cooperatively feeding schools of dolphins were sighted and photographed from a
5.3-m inflatable boat with a 70-hp motor. After photographing dorsal fins from the 86
1:T Y13 ADOCO Island
Study Area Little Bahama Bank
SO 00 79 30 79 03 73 30 78 00
Figure 3.1. The study area. 87 surface, I occasionally entered the water with snorkel gear to photograph animals underwater, determine dolphin gender, and observe behavior. Time, location, and description of behaviors were recorded on an audio tape, and transcribed the evening of the observations. Association indices (Chapter 1) were determined for dolphin pairs photographed in cooperatively feeding schools.
RESULTS
I observed 79 occurrences of cooperative-feeding behavior during six sightings of bottlenose dolphins, in 1995 and 1996 (Table 3.1). Cooperative feeding sightings averaged 11 dolphins (SD = 5, n = 6), and were seen at depths of 3 - 4 m. The cooperative-feeding behavior pattern began with dolphins swimming fast in a dispersed line abreast, occasionally porpoising. They then began to curve around and form a large, loose circle, and continued to swim swiftly toward each other, presumably herding fish to the center. As the dolphins approached each other, they lunged, and dove synchronously toward each other in a rather tight circle formation (about 8 - 10-m diameter). Dolphins typically remained underwater for 30 - 90 s (samples collected on
7/2/95: x = 54 s, SD = 19, n = 10 circle formations). One dolphin usually surfaced briefly one time, several seconds before the others. After 30 - 90 s, all dolphins surfaced several times, and dove (tail-stock dives and fluke-up dives; Shane 1990a) in the immediate area for 3 - 5 min. The dolphins then dispersed to start the pattern again.
The next circle formation (occurrence) typically took place in 5 - 10 min (samples Table 3.1. Six sightings of cooperatively feeding bottlenose dolphins near Grand Bahama Island.
7/2/95 7/5/95 11/11/95 9/7/95 9/20/95 6/27/96
Time start observation 9:21 11:17 10:40 10:06 12:32 10:20
Time end observation 13:13 17:28 16:37 15:39 17:36 13:04
Start of first occurrence 9:57 16:27 10:50 10:31 12:57 10:47 Location of first 2648.98 2648.94 2654.3 7901.22 2647.9 7900.56 2642.78 7859.65 2646.39 7900.20 occurrence 7901.87 7900.77
Start of last occurrence 13:09 N/A 15:19 13:57 15:32 11:29 Location of last 2654.87 7902.44 N/A 2652.09 7902.06 occurrence 2649.00 7900.79 2649.44 7900.07 2649.46 7900.9
Number of occurrences 29 1 19 16 9 5
Number of dolphins 10 13 11 19 10 4
Number of calves 1 2 2 3 2 1 6 females, 3 Known genders 1 female 3 females 4 females 2 females males 3 females AU, BAR, BEA, 5X, 5BJ, 5BL, 5BM, 5CC, 5X, 5Y, 5Z, BIN, BLU, COS, 5BJ, 5BL, 5BM, ACE, 5BR, 5BS, ACE, ALP, 5X, 5BJ, 5BL, 5BM, ACE, Positively Identified BLU, LIP, PEA, ALP, DER, GLA, HAN, LEF, LIP, ALP, DER, GLA, ICE, BLU, DER, GLA, ICE, ALP, JOK, LAC, LIE, Individuals SPA TEA MEG, PIV, ROC, JOK, LAC, PUN JOK, LAC, LIE, LIP, PUN ROO PUN, TEA Water depth (m) 4 3.75 3.5 3 3 3.5
Bottom type grass and sand grass and sand grass and sand grass and sand grass and sand grass and sand School is tight, looking in grass on bottom. No Dolphins picking up Underwater observation none none digging. Nothing small fish in the grass. none none happening in water Tight podform. column. Some clicks. In eight of ROO & SPA, One dolphin Comments Probably not all Passed through Southern but no interaction. Not all surfaces early. animals involved. dolphins 11:22-49. dolphins involved in each formation. 89
collected on 7/2/95: x = 7 min, SD = 4, n = 25 intervals measured between circle formations), although periods of up to 90 min occasionally occurred between formations.
During two of the sightings, immediately after a few of the circle formations occurred, I positioned the boat within 2 m of the dolphins. Underwater, I observed the dolphins in a tight pod form (<1 body length between dolphins; Shane 1990a), oriented toward the grassy bottom where they presumably herded the fish. Echolocation clicks were audible. Dolphins moved casually, and picked small fish (<12 cm) out of the grass.
Fish may have been disoriented because they seemed easily caught. I did not see fish readily and was unable to determine fish species.
I photographically identified a total of 34 individuals in schools that cooperatively fed. Cooperatively feeding schools did not include newborns (calves less than one year).
Eleven of the 34 dolphins were seen in cooperatively feeding schools every time they were sighted. Seven others were sighted feeding cooperatively in 50% - 75% of their total sightings. One dolphin was cooperatively feeding in two of five sightings. These
19 dolphins are referred to as "Cooperative Feeders" for the rest of this paper. I sighted these 19 dolphins a total of 1 - 6 times each (Fc = 3.2, SD = 1.7), compared to the overall average number of sightings for dolphins in the study area OR = 7 sightings per dolphin, n
= 212 dolphins). This average is low, especially considering that the sightings of the
Cooperative Feeders were primarily located in a heavily searched section of the study area. Association indices for Cooperative Feeders seen >5 times in fully-photographed sightings (n = 4 non-calves) show they associated closely with each other (Sc = 0.43, SD
= 0.29, n = 6 non-calf pair combinations), and infrequently associated with Southern 90
community members (Chapter 1) = 0.03, SD = 0.04, n = 112 non-calf pair combinations ). The Cooperative Feeders may be transients, which occasionally move
into the study area to feed.
Eleven of the remaining 15 identified dolphins were present in only one of the 79
circle formations. The other four dolphins were Southern community members (Chapter
1). Two of these four were seen cooperatively feeding on five occasions during one sighting, and two (an adult female and approximately 2-3 yr.-old calf) were present during three sightings. With the exception of the mother/calf pair, Southern community members only took part in six of the 79 cooperative feeding, circle formations.
DISCUSSION
Bottlenose dolphins have been reported feeding cooperatively in many parts of the world (Table 3.3). Past descriptions are similar to my observations, however some differences were noted. Past reports describe dolphins herding fish toward the surface, the shore, or each other (Table 3.3). In my study dolphins herded fish to the grassy sea bottom, and fish were possibly disoriented.
Cooperative feeding by dolphins often involves high-energy movements (e.g. fast swimming, quick movements, leaps, apparent chasing; Saayman et al. 1973, Shane
1977). Although dolphins near Grand Bahama Island swam fast, occasionally porpoising during herding of fish, I did not observe high-speed chasing after initial lunging in the 91
Table 3.2. Reports of presumed cooperation in feeding bottlenose dolphins.
Number of Dolphins Location Cooperating Cooperative Feeding Behavior Reference Dolphins herd fish to a sloping bank and thrust Georgia 2 themselves onto the bank to capture fish during low Hoes. 1971 tide.
Dolphins herd against shoreline with apparent Taylor and South Africa unknown division of labor patrolling near and offshore. Saayman 1972
Dolphins swim toward shore as fishermen pound Western Africa 5 to 10 stick on water. Dolphins feed while fishermen net Busnel 1973 fish. Dolphins swim at high speed, herding fish, and Saayman et et. Indian Ocean 200 performing crisscrossing maneuvers to trap fish 1973 schools.
Louisiana, Baja Dolphins herd small schooling fish to tight circle CA, near San 2 to 14 Leathetwood 1975 and take turns darting in to catch fish. Clemente Isl. CA
Northern Gulf of Dolphins form a half circle and drive school b3 31b 6 Leatherwood 1975 Mexico shallow water keeping the formation.
Dolphins swim rapidly in a row underwater, causing a wave at the survace, then swim in different Texas unknown Shane 1977 directions and make circular movements. Fish are seen jumping ahead of the dolphins chasing them.
Dolphins are seen in spread-school formation (up to Argentina unknown 35 m apart) and then herd fish to ocean surface to Wursig 1979 feed on them.
Dolphins converge in 200-m radius, and submerge Gulf of Mexico near for 30-90 s. Then large numbers of fish jump at 20-30 Irvine et el. 1981 Sarasota FL surface and are caught by dolphins, occasionally in midair.
Dolphins split into two groups of 2-3 individuals and Wursig 1988, Kino Bay, Mexico -5 meet in the middle with fish. Salience 1992
Dolphins move synchonously in a spiral or circle, presumably herding fish, then move into a line, Black Sea 5 to 32 Bel'kovich 1991 simuttaniously dive for 30 s, surface together in a line formation, and dive again for 30-70 s.
Dolphins surround fish and force school to tighten Black Sea 3 to 15 (termed "carouser), with dolphins individually Berkovich 1991 swimming through the fish ball (termed "kettle").
Dolphins heard fish from one side, moving them Black Sea 2 to 15 Bel'kovich 1991 against shore. 92
circle formation. Dolphins appeared to capture prey easily possibly due to disoriented
fish.
The duration of cooperative feeding is infrequently reported. Bottlenose
dolphins near Grand Bahama Island typically fed for only 3 - 5 min at a time, before
beginning the cooperative feeding procedure again. However, the circle formation
behavior was observed repeatedly (with exception of 7/8/95), up to 29 times, during
each observation of cooperative feeding. Fertl and Wursig (1995) observed spotted
dolphins (Stenella frontahs) feeding in a coordinated manner for over 1 hr. Killer whales
in Norway herd fish into a tight ball at the surface and feed for up to 3 hr or longer
(Siniila and Ugarte 1993), and dusky dolphins (Lagenorhynchus obscurus) in the South
Atlantic herd fish toward the surface and feed for up to several hours (Wursig 1986).
Only specific dolphins in my study fed cooperatively. Of 212 dolphins identified,
only 34 dolphins were observed in cooperatively feeding schools. Nineteen of these
dolphins were seen cooperatively feeding during >50% of their total sightings. A small percentage of dolphins in the area appear to utilize this type of foraging behavior.
Although cooperative feeding has been reported often, little is understood about how it works, and why some dolphins feed cooperatively while others in the same area feed individually. All reports of bottlenose dolphin cooperative feeding have been opportunistic observations. Studies concentrating on specific questions concerning cooperation will provide a better understanding of the mechanics and advantages of cooperative feeding, and will offer further insight into dolphin social behavior and communication. 93
Summary
Two communities of bottlenose dolphins were identified along the western edge of
Little Bahama Bank, Bahamas. A Northern community included 15 dolphins that were closely associated. Members were sighted at least 27 km from Grand Bahama Island.
Northern dolphins rarely interacted with the Southern community, which included 28 dolphins, and little overlap in range was observed between members of the two communities.
Environmental conditions varied between the two communities. Northern dolphins were sighted in deeper water, over loose-sand bottom; and Southern dolphins were found in shallow water, primarily over grassy bottom. Bottom-feeding behavior also differed, possibly due to varying environmental conditions. Northern dolphins primarily crater-fed in sand, whereas Southern dolphins mostly fed in holes, and in grass.
Four other dolphin groups were described. Two presumed female bands of five dolphins each were named the Central group and the Central/North group, respectively.
They were found between the ranges of the Northern and Southern communities. These two groups could be female bands belonging to either of the two communities, or could belong to a Central community.
A third group was named the Cooperative Feeders. These dolphins were sighted infrequently. When seen, they were located in the Southern community's range.
However, they rarely interacted with the community members. These dolphins had a unique method of feeding that was rarely seen in other dolphins. 94
A fourth presumed group was named the Far North group. Many dolphins were sighted only at the northern edge of the study area and infrequently interacted with the
Northern community. They could belong to the Northern community or could be part of a Far North community.
The findings of this study are unique. I identified and described ranges and association patterns of inshore and offshore, adjacent communities. Site fidelity was shown to occur far from shore, as well as inshore. Offshore and inshore Grand Bahama
Island, dolphins associated most closely with a dolphin of the same gender. This study is the first report of long-term site fidelity and social structure of bottlenose dolphins found far from shore. 95
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Appendices 102
Appendix A.1
subgroups? 1996 anch/uway anch/uway Date T.t. STG * Sighting Log Vessel stg Vessel photoed CONTACT muvrnax /BREAK I CLVS/ DIR OF H2O POD TIME LAT/LONG T.t. NUN TRVL DP-114 BOT VEGE FORM BEH S.f.
UW OBS: START ENO DURATION SEA STATE SWELL HT
FIELD KELLY WOP ROLL 0 FRAMES DESCRIPTION 0 PHOTO VIDEO PHOTO VIDEO
Comments
TIDAL STATE at cnt time
LOST THEM or LEFT THEM? WHY:
BOTTOM VEGETATION POD FORM BEHAVIOR SI Sc L At Ro X GGpSCUAX TLDIA Tf Ts Fc FI F S I 1996 DAILY SUMMARY
HEADER EFFURT D_ OLPHINS Study Outbd Time Land Watch Sten Uway Outbd Sten N TA. sub estgs Total I N Time w/ T.I. I T.t./ N Dale Area Vessels his min hrs min hrs min Dist 01st slgs me photoec Tura lops'calves his min Si. grps Si.
-i- 104
Appendix A.3
1996 PHOTO LOG ROLL # DATES
FRAMES
1 19
2 20
3 21
4 22
5 23
6 24
7 25
8 26
9 27
10 28
11 29
12 30
13 31
14 32
15 33
16 34
17 35
18 36
37
38 105
Appendix B
Body markings of 212 individual dolphins identified near Grand Bahama Island, during 1994-1996.
Key to Abbreviations:
Abbreviation Definition
unknown markings blank space (except column "white": blank = no)
chp chopped
cln clean
ctr center
hi high
I left
lg large
med medium
nch notch
pc piece
r right
sig significant
sm small
y yes 106
Appendix B (Continued)
4A ctr nch 4BB sm nch hi 5AB med chp 5AD multi nch I r nch 5AE low nch 5AF sm nch hi sm nch I 5AG ctr nch sm nch 5AH Ig nch hi 5AI sm nch hi 5AJ sm nch hi 5AK sm nch low 5AL sm nch hi 5AM sm nch hi 5AP sm nch low 5AQ sm nch ctr 5AR sm nch hi 5AS ctr nch sm nch 5AT sm nch ctr 5AU med chp 5AV leading edge 5AW Ig nch hi 5AX Ig nch hi 5AY multi nch 5AZ sm nch ctr 5BA low nch sm nch 5BC sm nch hi 5BD top nch 5BG pc out 5BI sm nch hi 5BJ sm nch ctr 5BK sm nch hi 5BL sm nch ctr 5BM sm nch hi 5BR sm nch ctr Ig nch 513S pc out 5BV sm nch hi 5CC Ig nch hi 5D multi nch 500 multi nch I nch r cln I nch r cln Ig nch 5PP sm nch ctr 5R sm nch hi cln I r 5S sm nch ctr 107
Appendix B (Continued)
c ii .c z0 0. 8 low nch sm nch 5X low nch Ig nch 5Y sm nch hi 5Z multi nch 52Z wide ctr dent 6A top nch 6C sm nch ctr 6F sm nch hi sm nch 6G low nch 6H clean Ig nch 61 med chp OK top nch 6L sm nch low ON sm nch ctr sm nch OP dean ACE multi nch ALF ctr nch sm nch ALP sig chp I r nch cln AMY clean I r nch dn sm nch r I r AQU shape ARR low nch ART leading edge r chp Ig nch ATT low nch BAK sig chp I r nch chi dn BAN med chp r dn BAR pc out BEA clean I dn r nch do sm nch I BEE leading edge r do do BIN sm nch hi BIR med chp BLA multi nch BLI sig chp BLU sm nch hi BRA Ig n hi BRE sm nch low BRU low nch BUM sm nch hi I r nch dn I tip nch BUZ med chp CAR med chp CAS leading edge sm nch CHI top nch Ig nch CHU pc out r nch sm nch 108
Appendix B (Continued)
o c E u- O 3 c z co 0 = E. 1 .1C = i LI leading edge I r nch nch Irnch COA Ig nch hi sm nch COC top nch COG top nch COO sig chp Y COR ctr nch I sm nch COS med chp I rnch tin cln CRA sm nch hi CUR sig chp Ig nch DAN top nch I rnch cln Irnch DBL dull tip
DEL sm nch hi I r nch chp Irnch Y DER sig chp sm nch DIM clean DIN top nch nch DIP top nch I chp r cln DIV leading edge Ig nch DIZ sm nch ctr DOP low nch I r nch cln cln DRE shape r chp I r ECH low nch ECL multi nch EDI sm nch hi I r nch cln cln EDW sm nch hi I nch MC top nch I r nch nch nch FEA top nch FIG dull tip r nch I cln cln FIS sm nch low FLA multi nch I sm nch Y FLO sig clip I r nch nch FOC low nch FOL Ig nch hi FRI leading edge sm nch FUL Ig nch hi GLA pc out Y HAL low nch HAM Ig nch hi HAN Ig nch hi HAR top nch HAY low nch ICE pc out Y ISO sig chp 109
Appendix B (Continued)
O c c U.. o .
JAC leading edge JAV Ig nch hi JIG multi nch JOK multi nch I cln JP low nch I (An r KEY top nch nch LAC low nch LED low nch I chp LEF ctr nch I chp y LEG ctr nch LIE wide ctr dent y LIG ctr nch LIN sig chp LIP sm nch hi I nch LLO top nch LOO med chp I r nch nch I r nch y LUC sm nch hi I r nch cln cln MAG wide ctr dent r chp I cln sm nch MAR multi nch MAX clean I r nch cln sm nch r r MCM sig chp MEA pc out MEG low nch I cln rnch cln MEM sm nch ctr MIC sm nch hi MIN Ig nch hi I r nch cln cln MIR top nch I nch MOC sm nch hi MOO Ig nch hi MOR sig chp sm nch y NAK sm nch ctr NOS ctr nch I r nch cln I r nch PEA ctr nch PER low nch I rnch cln r nch I r PEW sm nch ctr r nch r PIE low nch PIV shape nch POP shape PUN top nch PUZ Ig nch hi QUA sig chp sm nch RHY Ig nch hi Ism nch I nch 110
Appendix B (Continued)
T.5
e, _ _ U. _ et. 41 multi nch r cln r nch sm nch RID Ig nch hi I tear? RIP leading edge ROC leading edge ROO sig chp SAD ctr nch I dn I r nch Ig nch SAW multi nch I r nch cln r nch SCO Ig nch hi SEE Ig nch hi I nch I r nch SIC shape SIG Ig nch hi SLA leading edge SLI sm nch ctr SLY ctr nch I chp r nch cln SNA multi nch SPA Ig nch hi r nch Ig nch r SPI wide ctr dent SPO low nch SPR multi nch sm nch SQU sig clip I r nch cin r sm nch STA low nch I r nch nch Ig nch STI sm nch hi I r nch c.In cln STR pc out I chp r nch I r nch STU sig chp I chp r nch TAL top nch TAZ med clip r round Ig nch TEA sig chp sm nch THR Ig nth hi TOP Ig nch hi TRI top nch TRO dull tip I nch r cln I r nch sm nch TUR wide ctr dent TWE top nch VIC sm nch hi VOL med clip r chp I cln cln sm nch I r WAT med chp WAV shape WIL Ig nch hi Ig nch WIN sm nch hi sm nch WRE multi nch YEL sm nch hi YOS sig chp I rnch dn 111
Appendix B (Continued)
o c E b. e 8 0 S Je0 c 0g 2 0 u_ a_ 1 ZEEE ig nch hi ZIP multi nch I r nch cln I nch sm nch 112
Appendix C
Life history parameters of 212 individual dolphins identified near Grand Bahama Island, during 1994-1996.
Key to Abbreviations
Abbreviation Definition
A adult
C or c calVnewborn crater var crater feeding variation
F female
F* unconfirmed female
m mother
M male
S juvenile/subadult 113
Appendix C (Continued)
0 .._0 0 = a) O. 0) 0 cu 7 < 0 0 ,- Cu cu 0 z a) .c = 46 45 715 g c) = -0 § 16 oa cl) E 2 tn g a '6 ( D a. cv a = an .., in ^ o cl) 1) IFS C / 3 E 0 7) 7:5- (1) 12n, E a >- o ui o a. 2 TS LU 0 U. .7. = 4A 1990 4BB 1994 5AB 1995 5AD 1995 5AE 1994 5AF 1995 F A 5AG 1991 1996 5AH 1995 5AI 1995 5AJ 1995 5AK 1994 5AL 1995 F* 1995? 5AM 1995 5AP 1995 C m = SAO 5AQ 1995 F* A c = 5AP <1995 5AR 1995 5AS 1995 F A 5AT 1994 5AU 1995 5AV 1995 5AW 1995 5AX 1994 5AY 1995 5AZ 1995 5BA 1995 5BC 1995 5BD 1995 5BG 1995 5BI 1995 5BJ 1995 cooperative 5BK 1995 5BL 1995 F* A c = 5BM <1995 cooperative 5BM 1995 C m = 5BL cooperative 5BR 1995 5BS 1995 5BV 1995 5CC 1995 5D 1994 crater 500 1995 A 1995 5PP 1995 S 5R 1995 114
Appendix C (Continued)
L..0 o L 0 w co .c o cu a_ < >- 0 coti v 61) 0 8 2 v = " 43 11 E v .E 2 c:172 0. as c O .E. g a o a) a) f) ig 0 ,,_ r; TO 0 >' 0 WO a. 2 0 tu c..) 5S 1995 5U 1995 5X 1995 cooperative 5Y 1995 5Z 1995 5ZZ 1995 6A 1996 6C 1996 6F 1996 6G 1996 6H 1996 61 1996 6K 1996 6L 1996 6N 1996 6P 1996 C m = LLO ACE 1995 A cooperative ALF 1995 F A 1996 ALP 1995 C m =LAC cooperative AMY 1987 F A c = PIE 1995 crater AQU 1995 ARR 1994 ART 1994 crater ATT 1995 BAK 1990 M S BAN 1989 BAR 1994 A BEA 1994 F S crater, holes BEE 1995 1996? BIN 1995 F A BIR 1994 BLA 1994 BLI 1989 1994? BLU 1994 C m = LIP cooperative BRA 1988 BRE 1994 F A c = JP <1994, 1996 traps BRU 1994 BUM 1990 F S crater BUZ 1989 CAR 1995 F A c = LUC 1994 CAS 1992 115
Appendix C (Continued)
o o s_ o a) co c» a) 0_ < 0 >- 7 o TA I, -0 To .c mi .c -0 a) $2 .0 c) ?- of)- `) 46 :5e 0 ...... g 2 e9 2 8 iii 0 U) 0.) 0 0 1Z La T5 t 7 6 , 1 ) a >- tu o o_ 2 13- Lu 0 CHI 1994 F A 1995 CHU 1993 F A 1995 crater CLI 1989 M A crater COA 1994 COC 1995 COG 1995 COO 1995 S m = WIL COR 1995 M A COS 1991 F A c = MEG 1993, 1996 crater CRA 1995 F A c = JAC 1994 CUR 1992 DAN 1994 M S holes DBL 1994 DEL 1994 M A DER 1995 F A cooperative DIM 1994 1994? DIN 1993 M S DIP 1995 F A 1993, 1996 DIV 1994 DIZ 1995 F C m = DOP crater DOP 1986 F A c = DIZ 1994, 1995 crater DRE 1995 crater ECH 1995 ECL 1994 1996? EDt 1994 F C m = NOS crater EDW 1991 M FAC 1987 M A crater FEA 1989 FIG 1994 FIS 1995 F S crater var FLA 1991 F A crater FLO 1986 M A FOC 1994 F A 1996 FOL 1995 FRI 1994 FUL 1987 F A 1995 GLA 1995 cooperative HAL 1994 HAM 1995 S HAN 1991 M A crater HAR 1994 116
Appendix C (Continued)
0 .0 o 0 tr _ 0 0 a Q ,_ o >- a) 2= .c 0 .c 48 cii 715 a e ;) .= o -o § 11 0 c E a 8. E .F: O 0 2, "a 2 IT 0 to Tli O 2 E o )- V) w0 a_ 2 5 to (..) u_ ...... = HAY 1991 ICE 1995 cooperative ISO 1994 JAC 1995 M C m = CRA JAV 1995 C m=MOC JIG 1994 F S JOK 1995 M A cooperative JP 1994 F C m = BRE traps KEY 1995 F A 1996 LAC 1995 F A c = ALP 1994 cooperative LED 1990 crater LEF 1990 M A crater LEG 1990 LIE 1995 F* 1995? cooperative LIG 1995 LIN 1995 LIP 1994 F A c = BLU 1993 holes, cooperative LLO 1994 F* c = 6P 1996? LOO 1989 M A crater LUC 1995 S m = CAR MAG 1995 S MAR 1994 MAX 1993 M S crater MCM 1996 MEA 1989 MEG 1994 F C m = COS crater MEM 1995 F A 1996? crater var MIC 1995 MIN 1990 F A crater MIR 1995 MOC 1995 F A c = JAV <1994 MOO 1990 MOR 1990 F A 1996 NAK 1995 NOS 1993 F A c = EDI <1994 crater PEA 1994 F A c = STI <1994 cooperative PER 1994 M A crater PEW 1994 M S holes PIE 1996 F C m = AMY PIV 1994 M A POP 1994 C m = SIC 117
Appendix C (Continued)
0 .46 0 0 i(5 .0 0) a) a_ < _ 0 >- 7 0 "V -0, v .2 73 -iia 3 :g . t a, o E° .. 45 .05 C -0= g E 0. as E 2 1=1', fin) i 15 a) N=o .c''' a) ii C I) 410 2 E Ci >- (9 UJ 0 8E 15 WOLi.i O u_ = PUN 1995 cooperative PUZ 1994 QUA 1995 RHY 1989 F RIB 1993 F RID 1989 F A ? RIP 1994 F A c = 1995 1995 ROC 1994 A ROO 1994 F A 1994, 1996 holes, crater var SAD 1991 M crater SAW 1987 M A crater SCO 1994 SEE 1987 A SIC 1990 F A c = POP <1994 SIG 1992 M A SLA 1994 SLI 1994 SLY 1990 M S/A crater SNA 1994 M SPA 1994 F crater var, cooperative SPI 1994 F A 1996 SPO 1996 S SPR 1993 SQU 1994 M STA 1994 M S STI 1994 S m = PEA STR 1989 M A crater STU 1994 M S TAL 1995 TAZ 1994 M S TEA 1995 cooperative THR 1991 TOP 1994 TRI 1994 TRO 1994 M S TUR 1995 F* TWE 1991 A VIC 1995 M S crater var VOL 1991 F A c = 1996 1996 crater WAT 1995 WAV 1996 C m = SPI? ir41 8 III * * olphin ID sill-mor-mzF
CD CD CO tO CD CO CD ear of 1st Photo 1:00 000 al: g g cen el
71 ender
stimated Age lass
II resumed 0 other/Calf M-8 0 f Dolphin ID 1-- co 0
A stimated Year of 8 co co co o) aif Births ..3
eeding observed >1 ime) 119
Appendix D
Number of sightings of 212 individual dolphins identified near Grand Bahama Island.
Pre - Study AN Pre - Study AN ID Study 1994 _1995 1996 Years Years ID 1994 1995 1996 Years Years
4A 1 1 0 0 1 2 5Z 0 1 1 0 2 2 48B 0 1 1 0 2 2 6ZZ 0 0 2 0 2 2 5AB 0 0 2 0 2 2 M 0 0 0 1 1 1 MD 0 0 1 0 1 1 6C 0 0 0 3 3 3 ME 0 1 2 0 3 3 6F 0 0 0 4 4 4 5AF 0 0 1 5 6 6 6G 0 0 0 2 2 2 5AG 1 0 2 1 3 4 6H 0 0 0 3 3 3
5AH 3 0 1 1 2 5 61 0 0 0 1 1 1
MI 0 0 2 1 3 3 6K 0 0 0 1 1 1
5AJ 0 0 1 0 1 1 6L 0 0 0 1 1 1
5AK 0 1 2 0 3 3 6N 0 0 0 1 1 1
5AL 0 0 1 0 1 1 6P 0 0 0 1 1 1
5AM 0 0 1 0 1 1 ACE 0 0 5 1 6 6
5AP 0 0 1 0 1 1 ALF 0 0 2 3 5 5
5AQ 0 0 1 0 1 1 ALP 0 0 5 1 6 6
MR 0 0 1 2 3 3 AMY 8 3 11 5 19 27
MS 0 0 2 1 3 3 AQU 0 0 1 0 1 1
5AT 0 1 1 0 2 2 ARR 0 1 0 0 1 1
MU 0 0 1 0 1 1 ART 0 4 13 6 23 23 MV 0 0 2 0 2 2 ATT 0 0 13 3 16 16
MW 0 0 2 0 2 2 BAK 1 0 11 4 15 16 5AX 0 2 1 0 3 3 BAN 2 3 0 0 3 5
SAY 0 0 1 0 1 1 BAR 0 4 5 1 10 10
5AZ 0 0 1 0 1 1 BEA 0 6 7 0 13 13
5BA 0 0 1 0 1 1 BEE 0 0 4 1 5 5
5BC 0 0 1 0 1 1 BIN 0 0 9 4 13 13
580 0 0 1 0 1 1 BIR 1 2 1 0 3 4
5BG 0 0 1 0 1 1 BLA 0 1 2 4 7 7 5BI 0 0 1 0 1 1 BLI 2 1 1 0 2 4 5BJ 0 0 3 0 3 3 BLU 0 4 9 6 19 19 5BK 0 0 2 0 2 2 BRA 3 0 2 3 5 8 5BL 0 0 3 0 3 3 BRE 0 2 12 3 17 17 5BM 0 0 3 0 3 3 BRU 0 4 0 0 4 4 5BR 0 0 1 0 1 1 BUM 3 8 5 5 18 21 5BS 0 0 1 0 1 1 BUZ 2 1 7 0 8 10
5BV 0 0 1 2 3 3 CAR 0 0 3 1 4 4 5CC 0 0 1 0 1 1 CAS 1 3 4 0 7 8 5D 0 1 2 3 6 6 CHI 0 7 5 0 12 12
500 0 0 2 1 3 3 CHU 1 2 9 3 14 15 5PP 0 0 4 7 11 11 CLI 10 4 6 3 13 23
5R 0 0 1 4 5 5 COA 0 1 3 1 5 5 53 1 0 2 0 1 2 COC 0 0 7 4 11 11
5U 0 0 1 1 2 2 COG 0 0 1 3 4 4 5X 0 0 3 0 3 3 COO 0 0 5 3 8 8 5Y 0 0 1 1 2 2 COR 0 0 4 5 9 9 L- 1 1 1 1 .71 MMITIM>V000<>0>orTIDD>»rC13006(no635IXxxx0-11-n nini ni >0000m0R
00C110/00430+000 = CA O+ 0 0 + 0 CO CA Co 0 Al CO CO N.1 O+ O+ 0 0 0 =0011341000
CA N.) Co) W+ CA 0 A N+ CO = 1,3 an 0 CO A/ CA CO CO A CI CO CA CO 0 IQ A. A 0 = 0) = = 0 CO F.O. CO CO CO 0) CO
Is.) 0 0) O+ Is) O+ CO CO A O+ 0 0 CO 01 0 0 14 A 01 A. 0 0 CO 0 0 = Is3 13 W K.) 0 CA 0 CA 0 0 NI 0 W CO A
= Cf CO CA A CI Of 0 0 O n) CA 4.3 N V 7.4.1 = CO A 808oNo -4 O1 R.; 0 13 V CO 41 iJ W 1.) CO = A tg 0 V CO 41 A.
01 CA 0 A 41 0 CA 0 an PJ CO 0/ IV V 47; + W an O ao O i0 4f o 1 1 N V N V W W N.) CO A A tg CA tA 4 17; 0')
4"" f. 6 -0 z cn""nw"-°°V§A-""-'$"2-2281-1174i36f5554-4.4iiV)f0 0 [11 8*0 -c":" >rsiz-0 m 0;c007Jz°E0 x2300 g=8 00.0.00= A 0104 =00011.-.P.4000000000=0A 44001:000=041000020000
= A 1 0 = O CO A. CO W+ N 0 O+ 0 43 CA 0 CO CO CO 0:1 0 = 0 0 V 0 0 0 = 0 CO A. 0 0 ".4 01 0 0
ca 1.3 71:: 0 8 0) 0) CO A CO K., ca o 8 A O+ + 41 o co co W O ++ N e.4 N1
0 0 N+ 0 CA Al A 44 4 0 A CO O+ = N 0 0 = V CO = O CO 0 A 0 CO 0 V 0 CO 0 PO 41 0 0 01 AI V+ V CO 0
O CA = CO O r.) iD Ul O A A A CO 01 c, OD = CO = = A+ 0) CO CA CO A 0 7.1 A ti CO N
p,) m 6) 0"1 a CA t N 40 W + CA A. A CO CA CI CA 4 CO N+ Co = Cf 7.0; 4 41 N 01 Z11. A a CO ill ut O 121
Appendix D (Continued)
Pre - Study AN ID Study 1994 1995 1996 Years Years SPI 0 2 5 5 12 12 SPO 0 0 0 4 4 4 SPR 2 2 2 2 6 8
SOU 0 5 2 1 8 8 STA 0 1 4 0 5 5 STI 0 2 7 6 15 15
STR 5 10 1 2 13 18
STU 0 3 1 0 4 4
TAL 0 0 1 1 2 2 TAZ 0 3 3 0 6 6 TEA 0 0 2 0 2 2 THR 2 3 3 0 6 8 TOP 0 2 0 0 2 2
TRI 0 1 0 0 1 1 TRO 0 3 3 2 8 8 TUR 0 0 2 4 6 6
TWE 3 3 3 1 7 10 VIC 0 0 3 3 6 6 VOL 2 3 8 5 16 18 WAT 0 0 2 2 4 4
WAV 0 0 0 1 1 1
WIL 0 0 1 0 1 1 WIN 0 0 2 0 2 2 WRE 0 1 2 0 3 3
YEL 0 0 0 1 1 1
YOS 8 0 1 2 3 11 ZEE 4 2 3 5 10 14 ZIP 3 4 12 3 19 22