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두 큰돌고래의 자연 방사 가능성을 연구한 논문입니다.
WELLS와 BASSOS-HULL 이 작성했습니다.
제목은 EXPERIMENTAL RETURN TO THE WILD OF TWO BOTTLENOSE DOLPHINS 입니다.
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Return to wild of bottlenose dolpins (Wells et al 98).pdf
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EXPERIMENTAL RETURN TO THE WILD OF
TWO BOTTLENOSE DOLPHINS
RANDALL S . WELLS
KIM BASSOS-HULL
Chicago Zoological Society,
'70 Mote Marine Laboratory,
1600 Thompson Parkway, Sarasota, Florida 34236, U.S.A.
E-mail: rwells@mote.org
KENNETH S . NORRIS
Institute of Marine Sciences,
University of California,
Santa Cruz, California 95064, U.S.A.
ABSTRACT
In the first scientific experiment of its kind, two young male bottlenose
dolphins (Tursiops truncatus) were captured in Tampa Bay, Florida, and then
returned to the wild at the same locale in October 1990, after two years in
captivity. The dolphins' agekex class and the capture and release site were
selected prior to their collection. The ranging and social association patterns
of the host community were examined prior to, and, including the two ani-
mals, after release. The dolphins remained together for the first month, then
began interacting more with other dolphins and less with each other. Within
the first year, one dolphin returned to the waters near his capture site and
has remained there a t least through September 1993. The other dolphin has
remained in his original home range at least through June 1996. Observations
of each dolphin have shown them to be fully integrated into the local dolphin
societies. They displayed typical behavioral, ranging, and social association
patterns. Their body condition has been excellent at each observation. They
have not been observed interacting with humans. The apparent success of this
experiment cannot necessarily be generalized to all potential candidates for
return to the wild, but the results can be used to guide future experiments.
Key words: return to the wild, reintroduction, bottlenose dolphin, Tursiops
truncatus, experimental design.
T h e controlled, experimental release of captive animals into t h e wild has
become an important conservation tool in recent years. I n cases such as red
wolves (Canis rufus) i n No r t h Carolina (Phillips and Parker 1988), golden lion
tamarins (Leontopitbecus rosalia) i n Brazil (Kleirnan et al. 1986), and Arabian
51 5 2 M A R I N E MAMMAL SCIENCE, VOL. 1 4 , N O . 1. 1998
oryx ( O r y feurwyx) in Oman (Price 1986), releases have taken the form of
reintroductions of caprive-bred animals to supplement endangered or threat-
ened populations ot to reestablish a population in a former range. These ex-
periments have had varying degrees of success. Because many are first-time
experiments, the risk of failure has been high. As biodiversity decreases, in-
terest in the development of protocols for reintroduction is increasing. From
a conservation biology perspective, cetaceans warranr consideration for rein-
troductions for two reasons. First, several species of small cetaceans, including
the baiji (Lipotes vexill;fer) and the vaquita (Phocoena sinus) are facing imminent
extinction. Second, large-scale mortality of dolphins and porpoises is occurring
with increasing frequency around the world (e.g., Duignan et al. 1996), re-
sulting in the depletion of populations. It has been suggested that returning
captive members of non-endangered cetacean species (e.g. , bottlenose dolphins,
Tursiops truncatus) t o the wild could be a means of developing and testing
methodology for reintroducing endangered cetaceans involved in captive-
breeding programs (Ames 1991, Brill and Fried1 1993).
Though the return of captive dolphins to the wild has become a source of
much public attention and controversy in recent years, the idea itself is not
new. According to the National Marine Fisheries Service, since 1964 more
than 7 0 dolphins in the U.S. have been returned to the wild for a variety of
reasons after periods in captivity ranging from days to 10 yr. Many dolphins
deemed unsuitable have been released by commercial dolphin collectors a t the
capture sites, or after brief periods in captivity if they did not adjust to the
captive environment, did not fit into established social situations, or did not
meet training standards. Research programs have used wild-caught dolphins
for brief periods of study in captivity and then returned them to the wild ( e . g . ,
Irvine and Wells 1972, Odell and Asper 1990).
A new set of considerations has driven some of the dolphin returns to the
wild in recent years. Improvements in the ability to treat sick and injured
dolphins have resulted in increasing numbers of successfully rehabilitated
stranded dolphins (Odell and Asper 1990, St. Aubin e t al . 1996). Arguments
questioning the appropriateness of dolphins in captivity have driven several
efforts to obtain dolphins from oceanaria or the military for the purpose of
return to the wild. A financial management decision to cease operations led
to t h e experimental release of all of the dolphins at a facility in Australia
(Gales and Waples 1993).
Inherent in most of the examples described above is the assumption that
return to the wild is in the best interest of the individual captive animal. It
is also assumed that returned dolphins will survive and thrive in the wild.
Few empirical data exist to support these assumptions, because few systematic
efforts have been made to conduct follow-up monitoring. In two of the few
published cases, bottlenose dolphins used in research were returned t o the
wild less than one year after capture. During 1971-1972, two dolphins were
freeze-branded, tagged, and released into their native waters near Sarasota,
Florida, after one year and 11 mo at Mote Marine Laboratory; no resightings
were obtained (Irvine and Wells 1972). During 1977-1980, Sea World of WELLS E T A L . : BOTTLENOSE DOLPHINS 5 3
Florida captured 10 dolphins, held them in captivity for up to 90 d to test
freezebrand development, and then returned the dolphins to their native In-
dian and Banana River, Florida, waters (Ode11 and Asper 1990). Nine of these
were resighted, 404-1,631 d post-release.
Several returns since the mid-1980s have involved dolphins held for mul-
tiple years in captivity, but few of these efforts have been documented ade-
quately for evaluation. In January 1992, nine dolphins were experimentally
released from Atlantis Marine Park at Two Rocks, Western Australia (Gales
and Waples 1993). Five of these had been captured nearby 10-11 yr previ-
ously, and the others were their captive-born offspring. The dolphins were
released after nearly a year of preparations which included efforts in a sea-pen
halfway house. Three of the dolphins were returned to captivity in poor con-
dition within 12, 13, and 48 d ; one newborn calf disappeared and is presumed
to have died within 30 d ; and no additional confirmed sightings of the others
were reported after 6-36 d post-release.
In May 1996 two adult male bottlenose dolphins captured in 1988 in
Mississippi Sound were released off Key West, Florida. One dolphin was re-
covered seven days later and the other after 1 2 d. Both were lacerated, un-
derweight, and dehydrated. Both were reported to have approached boats and
people, begging for food (T. Spradlin, National Marine Fisheries Service, per-
sonal communication).
In the absence of information on the fates of most of the dolphins involved
to date, and because some efforts have been unsuccessful, the return of dolphins
to the wild should still be considered experimental. Systematic experiments
examining the factors that may affect the survival and well-being of the in-
dividual dolphins and the host populations are necessary before returns can be
considered acceptable conservation or management tools, from either a prac-
tical or an animal-welfare perspective (Brill and Fried1 1993). Such experi-
ments should take into consideration a variety of concerns, such as the poten-
tial for disease transmission (Cunningham 1996), discreteness of genetic
stocks, social structure, the ability of the individual dolphin to recognize and
capture prey and avoid predators, the animal’s familiarity with the environ-
mental conditions at the release site, the animal’s physiological adaptations to
release-site conditions, and the potential impacts of the released dolphins on
the host population, including the ability of the release site to support the
host population as well as additional returned dolphins.
In July 1988 we initiated the first experiment to systematically evaluate
the return of captive dolphins to the wild. Two young male bottlenose dol-
phins were captured in Tampa Bay, Florida, were subsequently involved in
echolocation research at the University of California, Santa Cruz, and then,
according to plan, were returned to Tampa Bay two years later. Follow-up
monitoring has continued to date. This report summarizes the experimental
design, methodology, and the broader findings of the research. Detailed be-
havioral evaluations of the animals during captivity, release, and afterward have
been provided elsewhere (Bassos 1993). 5 4 M A R I N E M A M M A L SCIENCE. VOL . 14. N O . 1. 1998
METHODS
Experimental design-The criteria for selection of the dolphin subjects and
the release site were determined prior to the capture of the animals (Wells
1989). The criteria were designed to maximize the probability of a successful
return. We selected young male dolphins of similar age, already independent
of their mothers. Such independence ensured the dolphins were capable of
fending for themselves-this presumably indicated they were capable of prey
capture, and tha t they were sufficiently familiar with the local predators, en-
vironmental conditions, and the social structures of dolphin schools they might
encounter. Young males were chosen because members of this agehex class are
known to develop strong pair bonds in the wild (Wells e t al. 1987). We
hypothesized tha t the development in captivity of a functional social unit of
a kind commonly found in nature might benefit the animals upon release.
Young males approaching sexual maturity were selected in part because, in
the wild, maturing males begin to venture outside of the community home
range (Wells e t al. 1987). Thus, their absence while in Santa Cruz might
approximate this natural pattern. Finally, young animals were selected because
their behavioral flexibility would facilitate training for echolocation studies in
Santa Cruz (Howard 1995), and i t was hoped this flexibility would facilitate
the animals’ reacclimation to life in the wild.
Tampa Bay was selected as the site for the experiment for several reasons.
We wanted dolphins likely to be resident to a region. Residency has been
demonstrated in some, but not all, parts of the species’ range (Shane e t al.
1986). Such residency would define the subsequent release site and facilitate
follow-up monitoring. I t would also help to define the host population so
baseline studies could be conducted before the return of the subjects. Return
to an established home range should also provide the dolphins with familiar
habitat, resources, predators, and social system. The results of genetic and
behavioral studies (Duffield and Wells 1986, 1991; Wells 1986; Wells e t al.
1987; Wells 1991) have demonstrated that many of the dolphins along the
central west coast of Florida, including Tampa Bay, are residents of overlap-
ping, long-term community home ranges, and that genetic differences between
these communities exist. Such residency dictated returning the animals to the
waters of their origin in order to avoid artificial genetic mixing (IUCN 1995).
Another important site selection criterion was the quality of the habitat.
We selected southeastern Tampa Bay as an area with adequate resources and
modest human activity and impact. I t is largely undeveloped, supports large
numbers of dolphins that appear to maintain good body condition, and is used
by fewer boaters than many other portions of the bay.
Site selection was also based on monitoring considerations. An established
field station on Anna Maria Island, along southern Tampa Bay, made the search
area accessible t o our small vessels. A site adjacent to the ongoing Sarasota
Bay study area (Wells 1991) enhanced our ability to find the dolphins should
they venture south of Tampa Bay. We were also contracted by the National
Marine Fisheries Service to conduct annual photographic identification surveys WELLS E T A L . : BOTTLENOSE DOLPHINS 5 5
through Tampa Bay during 1988-1993 (Wells e t af. 1996). Thus, we were
able to define and monitor the ranging and social association patterns of the
Tampa Bay dolphins prior to and following the return of the released dolphins
and thereby evaluate the impact of the return upon the host dolphin com-
munity (Bassos 1993).
Subject collection-The dolphins were collected by an experienced team of
researchers, dolphin handlers, and veterinarians on 12-13 July 1988 using a
standard seine net technique (Asper 1975, Irvine e t af. 1981, Wells 1991). A
230-cm male (“Echo”) was captured on 12 July off the Interbay Peninsula and
transported to a temporary pen at Ruskin (Fig. 1). A 235-cm male (“Misha”)
was captured the next day near Bishop Harbor in southeastern Tampa Bay and
brought to the pen. At the capture sites, the ages of these dolphins were
estimated a t 6-7 yr based on body length (Read e t af. 1993).
The dolphins were maintained in the temporary bay pen for six days; they
began to demonstrate their compatibility, and they began to eat fresh dead
fish. In addition, veterinary examinations indicated they were in good health.
O n July 18 the dolphins were transported by air to the Long Marine Lab
(LML) dolphin research facility a t the University of California, Santa Cruz.
The LML facility consisted of three pools, including a 16.5 X 12.2 X 2.7 m
deep oval-shaped pool with non-parallel, sloped walls (for damping reverberent
sound) containing about 360,000 liters of water, interconnected with circular
pools 9.1 m in diameter and 2.1 m deep (about 140,000 liters) and 7.6 m in
diameter and 1.8 m deep (about 100,000 liters).
Laboratory experiments and observations-While a t LML, the dolphins were
trained for cognitive studies of echolocation information processing abilities
(Howard 1995). Other training was carried out for husbandry purposes and
for behavioral enrichment. The animals were maintained on a diet of herring,
capelin, Columbia River smelt, and mackerel. Veterinary examinations were
conducted quarterly.
Beginning in April 1989 and continuing until the dolphins returned to
Florida, weekly 24-h behavioral observations were conducted a t LML to doc-
ument the behavior and social interactions of Misha and Echo (Bassos 1993).
Focal animal observation techniques (Altmann 1974) were used to quantify
their activity patterns, their respiratory patterns, and the spatial relationships
between the two dolphins. Thus, i t was possible to monitor the development
of the social bond between the two males and to allow comparisons during
post-release monitoring. Observational data were also used to compare the
behavior of the dolphins relative to different pool sizes and features (Bassos
and Wells 1996). Observations continued after the dolphins were transferred
t o a temporary bay pen in Florida.
Preparation for release-Preparations began more than nine months before
the dolphins were returned to Florida. Ages were confirmed through exami-
nation of growth layer groups (GLGs) in a tooth taken from each animal (Hohn
e t af. 1989). At the time of capture, Misha was 7 yr old, and Echo was 6 .
The dolphins were freeze-branded with +digit, 5-cm-high numerals while at
LML so the numbers would be fully formed prior to their return to the wild. 56 M A R I N E MAMMAL SCIENCE, V O L . 1 4 , N O . 1, 1998
Figure I . Locations of capture and release sites and sighting locations of Misha and
Echo in Tampa Bay, Florida.
Their distinctive dorsal fin features were photographed to aid in their iden-
tification in the wild (Scott et al . 1990). I n addition t o several distinctive
natural features on i t s fin, upon close examination Misha was determined t o
have a notch tha t had resulted from a roto-tag applied in December 1984.
Misha had been captured, tagged, and released off Ruskin (Fig. 1) nearly four WELLS E T A L . : BOTTLENOSE DOLPHINS 57
years prior to his capture and transport to LML. His recapture in the same
region of Tampa Bay provided additional support for his residency.
In January 1990, a t LML, the dolphins were presented with a school of live
Pacific frigate mackerel (Auxis thazard) to test their ability to capture live
prey. Though they approached and in one case mouthed the fish, they did not
consume any of them. Similarly, when presented with dead Florida striped
mullet (Mugil cephalus), they refused to eat them. While this was a concern,
i t did not stop preparations for release. The research training was complete
by February 1990, after which training efforts emphasized husbandry, behav-
ioral enrichment, and body conditioning.
Initial plans called for Misha and Echo to return to Florida during winter/
spring 1990. This was delayed, however, because of a die-off of dolphins in
the northern Gulf of Mexico, followed by gastrointestinal concerns for Misha.
By summer, the unusual mortality event had run its course, and Misha’s illness
had responded well to treatment. O n 1 1 September 1990 the dolphins were
flown to Florida and placed in a 9 . 8 X 11.3 X 2 m deep temporary bay pen
a t Mote Marine Laboratory (MML) in Sarasota.
Preparation for release: Prey andfeeding-The dolphins ate their standard diet
of capelin immediately upon arriving in the pen. Their diet was soon switched
t o whole, local fish purchased from a local fish market and supplemented with
live fish caught by the MML collection staff. The dolphins were first presented
with fresh dead striped mullet (about 0.5 kg per fish) within 8 h of their
arrival at MML and they consumed these fish without hesitation. They con-
tinued to take fresh striped mullet (up to 1 kg per fish) whenever offered.
Food was offered to the dolphins three to five times each day; the number of
feeds varied with the availability of live fish and the sizes of the fish consumed.
The quantities of fresh fish were adjusted accordingly to maintain a stable
diet. We offered the dolphins a variety of species and sizes of locally abundant
fish known to be eaten by bottlenose dolphins. A base diet of 3.6-5.5 kg of
fish per dolphin per day was established, with the maximum determined by
their appetites. This was less than the 5.5-7.3 kg per dolphin per day that
they ate at LML. The difference was likely due at least in part to the higher
water temperature (about 11°C warmer) in Sarasota than at LML and perhaps
in part to differences in the caloric content of the food.
Once the dolphins ate fresh local fish reliably, we made the transition to
live local fish through a series of approximations. Initially, live fish were
stunned or otherwise incapacitated (e.g., by cutting their tails) before presen-
tation. As the dolphins demonstrated the ability to handle these fish, we
stopped incapacitating the fish. The difficulty of prey capture was increased
by tossing the fish into the water at increasing distances from the dolphins,
thereby creating the need for the dolphins to chase their prey. We then began
to present live fish at random times rather than during regularly scheduled
feeds. By 21 September 1990 both dolphins seemed to fully recognize live
fish as food rather than as diversions.
Preparation for release: Veterinary aspects-The behavior of the dolphins was
monitored around the clock during the entire readaptation period a t MML. 5 8 M A R I N E MAMMAL SCIENCE, VOL. 1 4 , N O . 1, 1998
Respiration rates were recorded three times daily. The first feeding session of
each day included examination of the head, mouth, eyes, and body condition,
when possible. Vitamin supplements were given each day, inserted in fish.
Veterinary examinations were conducted prior to transport, upon arrival in
Florida, and weekly thereafter until release. Examinations included physical
inspection, blood sampling, ultrasonic blubber depth measurement, and fecal
and gastric sampling. Broad-spectrum antibiotics were administered for the
first week following transport as a preventative measure.
Preparation for release: Human contact reduction a n d behavioral changes-The
dolphins showed progressively less interest in interactions with humans and
more interest in their environment while at MML. The dolphins’ responses to
familiar behavioral cues were strong a t first but diminished in time. This was
desired and was probably due in part to the fact that food reinforcements for
interactions wi th humans decreased from the 50-60 daily cut-fish rewards
during training sessions at LML to about five to seven whole-fish feedings each
day in Sarasota. The balance of the daily fish was provided without expectation
of a conditioned response, because the thrust of the training (except for health
monitoring) was now to encourage the animals to catch and eat live fish. In
addition, the number of people near the pen was controlled to reduce human
contact.
Release-Based on t h e satisfactory results of the final veterinary examination
and on the observations that the dolphins were reliably capturing and eating
live local fish, the release was scheduled for 6 October 1990. The dolphins
were transported by boat, in customized flotation transport boxes, to Misha’s
capture site (41 km from MML) off Bishop Harbor in southeastern Tampa Bay
(Fig. 1). This specific site was selected because (1) i t was an area of minimal
human activity and relatively undisturbed habitat within the previous “home
range” of at least one of the two dolphins (as defined from 1984 and 1988
captures of Misha and annual surveys since 1988 (Wells et al. 1996)), and (2)
i t was t h e part of the home range that was closest to our field station, thus
facilitating transport and monitoring.
During the t r ip to the release site, Echo was tagged with a small, bright
red Telonics MOD-050 VHF radio transmitter (148 MHz). The neoprene-
padded transmitter package was attached to the dorsal fin by two 0.64-cm-
diameter delrin pins. The pins were secured by corrosible magnesium nuts
backing on neoprene-padded washers. The attachments were designed to re-
main intact for 2-3 wk, then to release the package. Both dolphins were
readily identifiable from their freeze-brands (Misha = 202, Echo = 204) and
from their distinctive dorsal fin features. At the release site the animals were
lowered in slings t o handlers standing in water about 1.5 m deep. After
removal from the slings, the dolphins were oriented offshore and released at
about 1 2 1 5 on 6 October 1990.
Monitoring-Monitoring was accomplished primarily by direct observation
from small vessels but was supplemented with radiotracking, helicopter search-
es, and reports from the public. The primary observers were researchers who
were very familiar with Misha and Echo, having worked with them at LML; WELLS E T A L . : BOTTLENOSE DOLPHINS 59
i t was hoped that their experience would facilitate detection of subtle changes
in the animals. Radiotracking involved Telonics TR-2 receiver systems, with
an antenna array mounted on an 11-m vessel, and a hand-held Yagi antenna
operated from a 6-m boat. Helicopter searches were provided by a local tele-
vision station and were facilitated by the highly visible radio tag on Echo.
The reintroduction project generated media attention, which resulted in a
confirmed sighting report of Echo.
Contingency plans were developed prior to release to recover the animals
should monitoring indicate a failure to thrive in the wild. If necessary, the
dolphins would be recaptured and held in the temporary pen a t MML while
their conditions and our future plans were evaluated.
Observations from small vessels took two forms: photographic identification
surveys (Scott e t al. 1990, Wells and Scott 1990, Wells e t a / . 1996) and focal-
animal behavioral observations (Bassos 1993). For the first year following re-
lease, intensive efforts were made to search for the dolphins every day that
weather permitted. Searches were conducted primarily from a 5.8-m outboard-
powered boat and emphasized the southeastern shore of Tampa Bay for the
first six months following release. Every dolphin group encountered was ex-
amined closely, the dorsal fins were photographed, and date, time, location,
numbers of dolphins/calves, environmental features, and dolphin activities
were recorded. If Misha or Echo was identified, focal-dolphin behavioral ob-
servations were initiated, following protocols developed during the observa-
tions at LML and MML (Bassos 1993). Activities, surfacing and respiration
patterns, and spatial relationships between individuals were recorded a t five-
minute intervals. The physical conditions of the dolphins were evaluated at
each sighting, and we attempted to document the animals’ conditions and
behaviors with videotape.
Searches have continued opportunistically after the first year post-release.
Annual Tampa Bay photographic identification census projects were conducted
during September and October 1988-1993 (Wells e t al. 1996). As many as
four boats were operated in Tampa Bay each day during these surveys. In
September 1995 we conducted a one-week dedicated search for Echo and
Misha, using two boats each day (Bassos-Hull et a]. 1996).
RESULTS
Preparations-The dolphins made the transition t o a diet of live local fish
within only a few days. They ate live striped mullet, silver mullet (Mugzl
curemu), spotted seatrout (Cynoscion nebulosas), pinfish (Lagodon rhornboides), and
redfish (Sciaenops ocellata). They mouthed but dropped other species. The dol-
phins demonstrated a strong preference for silver mullet of about 15-20 cm
(about 0.2-0.6 kg each). The quantities of live fish consumed by each dolphin
increased over time. By the end of the readaptation period they were eating
more than 90% of the fully functional fish offered. The dolphins were also
observed chasing fish that entered the pen or that remained from previous
feeds. I t seems possible that the transition from a diet of dead fish to live fish 60 M A R I N E MAMMAL SCI ENCE , VOL. 14, NO. 1, 1998
may have been facilitated by the relative brevity of the dolphins’ time in
captivity ( 2 . 2 yr), and by the dolphins’ experience in prey capture prior to
collection.
T h e dolphins’ responses to interactions with humans changed during the
time they were in the bay pen at MML. During the first week the dolphins’
attentions were focused largely on the dock and training raft, from which their
familiar trainers fed and observed them. There was a gradual shift in attention
offshore, where boats passed in the distance and where dolphins and manatees
sometimes passed nearby. Misha and Echo were observed to orient toward these
objects. The dolphins maintained synchrony in respirations and movements,
with occasional brief bouts of independence.
Beginning about 24 September 1990 and continuing until release, both
dolphins produced tail-slaps, “chuff’ exhalations, and deep, concussive tail-
lobs and side-slaps with increasing frequency. The trainers interpreted these
behaviors as indications of restlessness, and the behaviors coincided with the
increased interest in activities and objects outside their pen. The dolphins
were easily distracted from bouts of these new behaviors by normal feedings
and other interactions with trainers.
Results of the first week’s veterinary exam indicated good health, so the
antibiotics were discontinued. Subsequent veterinary examinations continued
to indicate tha t both dolphins were in good health, and they were certified as
fit for release o n 4 October 1990. Misha, at 160 kg, had gained about 9 kg
during the readaptation process, while Echo maintained its LML weight of
151 kg. Both dolphins showed a decrease in blubber thickness to 1 4 mm,
similar to the summer values recorded for resident Sarasota dolphins (Wells
1993).
Release-Upon release, the dolphins swam amongst the handlers for several
minutes, then swam rapidly inshore, crossing one sandbar and a narrow chan-
nel, and then stranded in extremely shallow water near the mainland. We
released them again into deeper water. They swam rapidly several hundred
meters to the northeast, then moved into shallow water again. They stopped
over a sandbar where they could maneuver but could not fully submerge. Side
by side, they oriented offshore, moving their rostra from side to side in a
manner suggesting scanning. No approach was made for about 30 min in
order to allow the dolphins to become oriented. When no change in behavior
was forthcoming, two of the dolphin’s handlers approached the dolphins.
When they gently slapped the water about 3 m in front of the dolphins,
Misha and Echo slowly approached the handlers, then moved alongside as the
handlers walked to deeper water. Once the dolphins reached water about 0.8
m deep, they swam off together at moderate speed, first offshore, then along-
shore t o the northeast.
The radio transmitter failed within two hours of release. The transmitter
separated from the attachment package and was lost by 2 2 October 1990. The
attachment package came off Echo as designed, between 2 2 October and 31
October 1990. I t provided a reliable visual tag until its loss and even allowed
one confirmed sighting to be made from a helicopter. WELLS E T A L . : BOTTLENOSE DOLPHINS 61
Monitoring efforts began immediately following release and have continued
into 1996. Searches have been conducted on 66 d in 1990, 1 3 3 d in 1991,
39 d in 1992, 4 8 d in 1993, 7 d in 1994, 2 3 d in 1995, and 4 d in 1996.
Misha has been identified 64 times since release (Table 1). Echo has been
identified 32 times (Table 2).
Misha and Echo were observed together 19 times along 18.5 km of the
southeastern shore of Tampa Bay during the first 5 . 5 mo following release
(Fig. 1). During the first month, all of their sightings were together, mostly
in relatively shallow water. Initially, when Misha and Echo were seen near
other dolphins, they were typically on the periphery of the group. They were
first observed to be integrated into a group of dolphins on 22 October 1990.
Beginning on 5 November 1990, Misha and Echo were found together with
decreasing frequency, as they began to associate more with other dolphins in
the same area (Table 1, 2). The last sighting of Echo in southeastern Tampa
Bay occurred on 1 2 March 1991. The dolphin was next resighted in Old
Tampa Bay on 3 September 1991, during the annual Tampa Bay photographic
identification survey. This sighting was 31 km from its release site but within
four k m of its 1988 capture site. All subsequent sightings of Echo during
1991, 1992, and 1993 were in Old Tampa Bay, within nine k m of its capture
site (Fig. 1). The lack of sightings of Echo since 1993 is not surprising given
the size and complexity of the habitat within its home range, the large number
of dolphins in Tampa Bay (about 500, Wells e t al. 1996), and the logistical
difficulties of reaching the distant waters that comprise his range. All of Mi-
sha’s sightings during 1984 through 1996 have occurred along 29 km of
southeastern Tampa Bay, from Ruskin to the Manatee River, within 11 km of
i t s 1984 or 1988 capture sites (Fig. 1).
Therefore, both dolphins have returned to, or remained within, the home
ranges they occupied prior to capture (Bassos 1993). Each has ,been seen with
regular associates sharing its home range, and in some cases they have been
observed with associates from their capture days (Bassos 1993). Both dolphins
have remained in excellent body condition, with no indications of aggressive
encounters with conspecifics (Fig. 2). N o indications of adverse changes in the
activities, ranges, or social patterns of the host population members were ob-
served.
As might be expected, the dolphins’ activity patterns after release were
different from those observed at LML, but they were typical of those observed
for other dolphins in the wild. They surfaced together more often at LML and
MML than in the wild (Bassos 1993). When they surfaced synchronously, the
preferred formation was with Echo slightly ahead and to the right of Misha
a t all three sites. We observed more “milling” and “resting” in captivity and
more “traveling,” “foraging,” and “socializing” in the wild (Bassos 1993). In
the wild, feeding peaked in the morning and socializing peaked in the after-
noon, similar to findings for other wild dolphins (Bassos 1993). Mean dive
durations both in captivity and in the wild were within the range observed
for other dolphins (Bassos 1993). Except for bowriding, which is typical of
dolphins in the area, we have not observed any interactions with humans. Table 1 . Sightings of Misha, 1984-1996.
Sighting Group With
Date time size Location Echo?
20 Dec. 1984
13 Jul . 1988
6 Oc t . 1990
6 Oc t . 1990
8 Oc t . 1990
12 Oc t . 1990
15 Oc t . 1990
18 Oc t . 1990
22 Oc t . 1990
31 Oc t . 1990
3 Nov. 1990
6 Nov. 1990
12 Nov. 1990
1 9 Nov. 1990
20 Nov. 1990
21 Nov. 1990
24 Nov. 1990
29 Nov. 1990
6 Dec. 1990
11 Dec. 1990
4 J an. 1991
14 Jan. 1991
18 Jan. 1991
23 Jan. 1991
22 Feb. 1991
12 Mar. 1991
23 Mar. 1991
24 Mar. 1991
26 Mar. 1991
6 Apr. 1991
16 Apr. 1991
17 Apr. 1991
3 May 1991
1630
1230
1215
1700
1230
1512
1400
1026
1310
1345
1142
1329
1030
1010
0853
1024
1157
0904
0910
1000
1041
1350
1308
1410,
1035
0845
1245
1245
1030
1045
0952
0850
1400
4 Capture, tag, release-SE Tampa Bay, Ruskin N
6 Capture-SE Tampa Bay, Bishop Harbor N
2 Release-SE Tampa Bay, Bishop Harbor Y
2 SE Tampa Bay, Bishop Harbor Y
2 SE Tampa Bay, Ruskin Y
10 SE Tampa Bay, Little Manatee River Y
2 SE Tampa Bay, Piney Point Y
11 SE Tampa Bay, Cockroach Bay Y
9 SE Tampa Bay, Cockroach Bay Y
2 SE Tampa Bay, Port Manatee Y
6 SE Tampa Bay, Cockroach Bay Y
6 SE Tampa Bay, Piney Point Y
5 SE Tampa Bay, Ruskin Y
10 SE Tampa Bay, Bishop Harbor Y
7 SE Tampa Bay, Bishop Harbor N
14 SE Tampa Bay, Bishop Harbor N
12 SE Tampa Bay, Port Manatee N
16 SE Tampa Bay, Port Manatee Y
8 SE Tampa Bay, Bishop Harbor Y
22 SE Tampa Bay, Bishop Harbor Y
3 SE Tampa Bay, Sunshine Skyway N
11 SE Tampa Bay, Port Manatee Y
7 SE Tampa Bay, Piney Point Y
16 SE Tampa Bay, Port Manatee Y
6 SE Tampa Bay, Port Manatee Y
12 SE Tampa Bay, Bishop Harbor Y
7 SE Tampa Bay, Port Manatee N
15 SE Tampa Bay, Piney Point N
11 SE Tampa Bay, Cockroach Bay N
10 SE Tampa Bay, Cockroach Bay N
5 SE Tampa Bay, Port Manatee N
9 SE Tampa Bay, Port Manatee N
13 SE Tampa Bay, Port Manatee N Table 1. Continued.
Sighting Group W i t h
Date time size Location Echo?
18 May 1991
10 Jun. 1991
6 JuI. 1991
8 Jul . 1991
15 JuI. 1991
2 Aug. 1991
6 Aug. 1991
28 Aug. 1991
29 Aug. 1991
10 Sep. 1991
12 Sep. 1991
17 Sep. 1991
14 O c t . 1991
12 Nov. 1991
2 2 Jan. 1992
13 Feb. 1992
3 Mar. 1992
20 Jun. 1992
9 Sep. 1992
2 2 Sep. 1992
1 5 Dec. 1992
2 1 JuI. 1993
4 Aug. 1993
13 Sep. 1993
1 5 Sep. 1993
2 3 Sep. 1993
20 O c t . 1993
20 Mar. 1994
22 Oc t . 1994
2 1 Mar. 1995
2 2 Mar. 1995
18 May 1996
19 May 1996
14 Jun. 1996
1131
1356
1453
1420
101 1
1028
1043
1157
1010
1134
1241
1455
1010
1358
0907
1300
1434
1320
1123
1623
1139
0920
1540
1630
0858
1549
1526
0948
0902
1038
0803
1101
1102
1253
10
8
9
10
2
4
3
5
8
5
18
8
13
16
6
3
3
3
6
13
2
3
4
7
20
36
18
3
2
2
17
3
5
9
SE Tampa Bay, Piney Point
SE Tampa Bay, Terra Ceia Bay
Manatee River
SE Tampa Bay, Bishop Harbor
SE Tampa Bay, Bishop Harbor
SE Tampa Bay, Piney Point
SE Tampa Bay, Bishop Ha rbor
SE Tampa Bay, Port Manatee
SE Tampa Bay, Port Manatee
SE Tampa Bay, Bishop Harbor
SE Tampa Bay, Bishop Harbor
SE Tampa Bay, Sunshine Skyway
SE Tampa Bay, Piney Point
SE Tampa Bay, Ruskin
SE Tampa Bay, Bishop Harbor
SE Tampa Bay, Port Manatee
SE Tampa Bay, Cockroach Bay
SE Tampa Bay, Bishop Harbor
SE Tampa Bay, Cockroach Bay
SE Tampa Bay, Ruskin
SE Tampa Bay, Cockroach Bay
SE Tampa Bay, Bishop Harbor
SE Tampa Bay, Sunshine Skyway
SE Tampa Bay, Cockroach Bay
SE Tampa Bay, Ruskin
SE Tampa Bay, Ruskin
SE Tampa Bay, Cockroach Bay
SE Tampa Bay, Por t Manatee
SE Tampa Bay, Bishop Harbor
SE Tampa Bay, Bishop Harbor
SE Tampa Bay, Ruskin
SE Tampa Bay, Por t Manatee
SE Tampa Bay, Ruskin
Terra Ceia Bay
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N Table 2. Sightings of Echo, 1988-1993.
Sighting Group With
Date time size Location Misha?
12 J u l . 1988
6 O c t . 1990
6 Oc t . 1990
8 O c t . 1990
12 Oc t . 1990
15 O c t . 1990
18 Oc t . 1990
22 O c t . 1990
31 O c t . 1990
3 Nov. 1990
'5 Nov. 1990
6 Nov. 1990
12 Nov. 1990
16 Nov. 1990
19 Nov. 1990
20 Nov. 1990
24 Nov. 1990
29 Nov. 1990
4 Dec. 1990
6 Dec. 1990
11 Dec. 1990
16 Dec. 1990
17 Dec. 1990
14 Jan. 1991
18 Jan. 1991
20 J an. 1991
23 Jan. 1991
22 Feb. 1991
12 Mar. 1991
3 Sep. 1991
22 Sep. 1992
23 Sep. 1992
17 Sep. 1993
21 Sep. 1993
1434
1215
1700
1230
1512
1400
1026
1310
1345
1142
1325
1329
1030
1130
1010
1045
1337
0904
1047
0910
1000
1422
1545
1350
1308
1010
1410
1035
084 5
1353
1439
1050
0934
1415
27
2
2
2
0
2
1
9
2
6
15
6
5
10
10
10
6
16
16
8
22
I 0
2
11
7
12
16
6
12
8
8
7
3
33
Capture-Old Tampa Bay, S of Gandy Bridge
Release-SE Tampa Bay, Bishop Harbor
SE Tampa Bay, Bishop Harbor
SE Tampa Bay, Ruskin
SE Tampa Bay, Little Manatee River
SE Tampa Bay, Piney Point
SE Tampa Bay, Cockroach Bay
SE Tampa Bay, Cockroach Bay
SE Tampa Bay, Port Manatee
SE Tampa Bay, Cockroach Bay
SE Tampa Bay, Cockroach Bay
SE Tampa Bay, Piney Point
S E Tampa Bay, Ruskin
SE Tampa Bay, Ruskin
SE Tampa Bay, Bishop Harbor
SE Tampa Bay, Port Manatee
SE Tampa Bay, Cockroach Bay
SE Tampa Bay, Port Manatee
SE Tampa Bay, Cockroach Bay
SE Tampa Bay, Bishop Harbor
SE Tampa Bay, Bishop Harbor
SE Tampa Bay, Ruskin
SE Tampa Bay, Piney Point
SE Tampa Bay, Port Manatee
SE Tampa Bay, Piney Point
SE Tampa Bay, Piney Point
SE Tampa Bay, Port Manatee
SE Tampa Bay, Port Manatee
SE Tampa Bay, Bishop Ha rbor
Old Tampa Bay, N of Gandy Bridge
Old Tampa Bay, N o f Gandy Bridge
Old Tampa Bay, N o f H . Frankland Bridge
Old Tampa Bay, S o f Gandy Bridge
O l d Tampa Bay, S of Gandy Bridge
N
Y
Y
Y
Y
Y
Y
Y
Y
Y
N
Y
Y
N
Y
N
N
Y
N
Y
Y
N
N
Y
Y
N
Y
Y
Y
N
N
N
N
N WELLS E T A L . : BOTTLENOSE DOLPHINS 65
Fzgzrre 2. “Echo” on 15 December 1990 off Ruskin, Florida, 10 wk following
release, demonstrating normal body condition. Note the healing of the radio trans-
mitter attachment site on the dorsal fin.
DISCUSSION
Misha and Echo appear t o have successfully reacclimated t o life in the wild.
Both dolphins have maintained excellent body condition through all of their
sightings to date (3 yr and 5.6 yr, respectively), they have continued to inhabit
their original home ranges, they appear t o have been reintegrated into the
local dolphin societies, their activities appear normal, and they d o nor appear
to have negatively impacted the host populations.
A number of factors may have contributed t o this success. T h e release of a
natural functional social unit-a pair of bonded males-may have played a
role in the early stages following release. This pair bond remained strong
through the first month, the most critical period. The functionality of this
bond was suggested by observations a t LML, where Misha and Echo alternated
roles as resting or vigilant individuals. I t was only as they began associating
closely with other individuals in the wild that the pair bond weakened.
T h e ages of the dolphins and the relative brevity of t ime away from the
wild may also have been contributing factors. Young animals might be ex-
pected t o be more adaptable t o changing conditions than are older animals.
Misha and Echo were still sexually immature a t the time of release (Wells e t
al. 1987). The dolphins were away from the wild for only 2.2 yr; i t would 66 M A R I N E MAMMAL SCI ENCE . VOL. 14. NO. 1. 1998
have been surprising if such a brief absence from the wild had resulted in a
significant loss of ability to survive. Additional experiments with dolphins of
different ages and different periods away from the wild would help to define
the importance of removal time.
Acclimation in a bay pen prior to release may also have been important to
the success of the project. During this period, the dolphins demonstrated
physiological and behavioral acclimations to the local environment around
their temporary pen a t MML. Their blubber thickness decreased, their ability
to capture live prey developed swiftly, and their interest in natural environ-
mental features outside of their pen, including other dolphins and manatees,
increased progressively. The behavior of the dolphins upon release suggested
that a n extension of the bay pen concept to a “halfway house” and a “soft
release” might have been advisable. Their initial stranding and subsequent
shallow-water behavior suggested disorientation. Similar behavior has been
reported for some captive dolphins involved in open-ocean release work with
the U.S. Navy (Irvine 1971). In future experiments i t would be of interest to
see if reacclimation in a temporary pen a t the release site eliminates this
apparent disorientation.
Probably one of the most important factors contributing to the project’s
success was t h e return of the dolphins to their native waters. The importance
was indicated by Echo’s return to its original home range after release in
Misha’s home range, which was immediately to the south. Although prelim-
inary data had suggested that Misha and Echo originated from the same home
range, subsequent surveys and radio tracking indicated instead that they in-
habited adjacent, slightly overlapping home ranges (Mate et al. 1995, Wells
et al. 1996). T h e attraction of Echo’s home range apparently exceeded the
strength of t h e bond that had been formed between Echo and Misha, or later
between Echo and other members of Misha’s community. The subsequent site
fidelity of each dolphin underscores the importance of the native home range
to t h e animals and provides strong direction for future returns to the wild.
T h e return of Misha and Echo to the wild represented several departures
from previous dolphin releases. Ours was the first project in which (1) plans
for return were made prior to the collection of the dolphins, to the extent that
a particular agehex class and capture site were selected because of release
considerations; (2) a functional social unit, similar to those found in the wild,
was released; (3) background information on the ranging and social association
patterns of t h e host community were examined over periods of years prior to,
during, and after release; ( 4 ) detailed behavioral observations of social inter-
actions, activities, and dive patterns of the individuals while in captivity were
made i n such a way that comparative data could be collected after release; and
( 5 ) intensive, long-term follow-up monitoring was conducted.
T h e success of the Misha and Echo experiment should not be extrapolated
to suggest tha t any captive dolphin can be successfully returned to the wild.
Our project was conducted under strictly controlled circumstances and in-
volved young animals that were held in captivity for a modest period. Each
potential release should be considered individually in an experimental context, WELLS ET AL.: BOTTLENOSE DOLPHINS 67
with careful evaluation of the potential effects of the variables considered
above. O u r results provide guidelines for future experiments:
1. Return dolphins to the waters from which they were originally collected
or their stock originated. Familiarity with, or morphological or physio-
logical adaptations to, the physical habitat, environmental features (e.g.,
tides, currents, water temperature regimes), food resources, potential
predators, and resident dolphins and the social system seem likely to
play a role in increasing the chances for a successful reintroduction.
2 . Release dolphins as functional social units based on similar natural com-
binations of age and sex classes. Sex and age segregation are important
features of bottlenose dolphin societies.
3. Give careful consideration to the selection of individuals for return to
the wild. I t is likely tha t animals with precapture experience in fending
for themselves might have an advantage over either dolphins taken from
their mothers in the wild a t an age of 2-3 yr, or captive-born dolphins.
Also, older dolphins with a history of poor response to new situations
( e . g . , become inappetent, ill, or lethargic) might be poor candidates.
4 . Establish a “halfway house” a t or near the release site. Such a facility
might also provide a means of gradually returning the animals to the
wild, through open-ocean release training. If the facility was available
to the animals after release, i t might provide them a haven if they be-
came ill or otherwise incapacitated. Use of the facility would facilitate
monitoring their condition.
5 . Obtain background information on home ranges and social patterns of
resident dolphins prior to the release. This will facilitate selection of
appropriate monitoring methodology and logistics.
6. Make efforts to match blubber thickness and water temperature regimes
between the captive facility and the readaptation site well in advance of
the transfer. Body condition should be monitored prior to release and
compared to residents.
7. Learn about the local dolphin prey and locate soutces of fresh and live
prey for readaptation.
8. Make plans and obtain necessary funding and permits well in advance
for monitoring the reassimilation of the dolphins. There should be a
contingency plan for recapture during the first few weeks if i t appears
that an animal is not thriving, and for another release a t t empt or place-
ment of the animal after recapture.
Several factors that have contributed to this successful experiment appear
to have been important in reintroduction efforts with other mammals. The
release of functional social units, “packs” of wolves, into the Yellowstone eco-
system may have contributed to the success of the wolf reintroduction project
(Ferguson 1996, Milstein 1995). These wolves were involved i n a “soft-release’’
approach, in which they were released from pens and they were fed fresh-
killed local prey. Radiotracking was used to monitor the wolves, allowing the
researchers to observe how well they were acclimating to the new area. 6 8 M A R I N E MAMMAL SCIENCE. VOL. 14. N O . 1. 1998
I n o t h e r exampl e s c apt ive -br ed Ar abi an oryx were r e int roduc ed successfully
into O m a n , b y me ans of a soft-release approa ch involving a functional social
herd (Price 1 9 8 6 ) . Captive-bred g o l d e n l ion t a m a r i n s u b a d u l t s fared b e t t e r
t h a n captive-bred a d u l t s u p o n r e int roduc t ion i n t o a Brazilian forest ( K l e i m a n
e t af. 1986) . Translocated a d u l t male sea o t t e r s r e turned t o the i r or igina l cap-
tur e sites, s u g g e s t i n g t h a t s u b a d u l t ma l e o t t e r s (Enhydra futris) may be b e t t e r
candidates f o r translocation because of t h e i r t endency t o disperse f r o m t h e i r
natal sites g a m e s o n e t af. 1 9 8 2 ) . Cons ide r a t ion of t h e successes a n d failures of
a va r i e ty of expe r iment a l efforts c an benefit t h e d e s i g n of f u t u r e m a m m a l i a n
r e int roduc t ion projects.
M o r e research is needed before t h e release i n t o t h e wi ld of wi ld- c aught o r
captive-born bot t l enos e d o l p h i n s can be considered a rout ine tool for t h e con-
servation of t h i s or o t h e r d o l p h i n species. As has been f o u n d w i t h t h e rein-
t roduc t ions of o t h e r m a m m a l s , d o c u m e n t a t i o n of efforts is essential for p r o g -
ress to occur. Post-release m o n i t o r i n g has been identified by Kl e iman ( 1 9 8 9 )
and subs equent ly i n t h e IUCN “Guide l ine s for Re - Int roduc t ions ’ ’ ( I U C N
1995) as a r e q u i r e m e n t for r e int roduc t ions . T h e pre-, d u r i n g - , a n d post-release
m o n i t o r i n g of t h e hos t d o l p h i n c o m m u n i t y a n d Mi sha a n d Echo were c ruc i a l
e l ement s i n t h e success of t h i s project, a n d provided di r e c t ion for f u t u r e re-
search. For t h e success of t h e Mi sha a n d Echo proj e c t to have o p t i m a l va lue
as a conservation e x p e r i m e n t , i t wi l l be necessary t o c o n t i n u e t h e research
t h r o u g h a sys
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