Abstract
A study was made on captive births recorded at Marineland of Florida over a period of 40 years (1947-1987). The colony has been maintained at a constant size of about 18 animals with approximately 6 mature females. Twenty three (23) animals have produced 30 live births and 22 stillborn calves or premature births. One female, born in the colony, gave birth to a live calf at 7 years of age; therefore, a minimum age at puberty was considered to be 6 years. Most females began to calve at approximately 12 years of age. Gestation period is 1 year. The minimum interval between live births (calving interval) was 1.9 years but mean interval between all births was 3.3 years. A tendency for regular cycling was observed, with many births occurring near the same date for a single animal. Most of the births (71%) occur in February, March, April and May. One 32 year-old animal gave birth to a healthy calf. This animal had a reproductive life span of 26 years at the time of the birth, if puberty occurred at 6 years of age. The female was still alive and healthy at the end of the study. A maximum of six births have been recorded for a single animal in the colony. Reproductive rate for the colony is 1.3 births per year; while mean reproductive rate for each mature female is 0.2 births per year. Reproductive efficiency for the mature females was about 50%. It was estimated that a group of 3 or 4 well managed breeders could maintain the colony.
Introduction
Marineland of Florida (MLF) has kept Atlantic Bottlenosed Dolphins (Tursiops truncatus) since 1939 and described preproductive parameters (1,2,3,4). In the early years it was more convenient and economical to capture wild replacements than to seriously consider a breeding program (2). The Marine Mammal Protection Act and other changes made it desirable to maintain, at least partially maintain, the colony by reproduction. This study is a current report on reproductive parameters determined for the colony from records kept over 40 years (1947-1967).
Colony
The colony was started in 1939 but discontinued during World War II and the animals released. A new colony was collected in 1946 and detailed records for each animal maintained (1). Colony size has been constant at about 18 animals and approximately 6 mature females. The animals are kept in a 3,000 sq ft stadium tank, average of 8 ft deep, a 4,400 sq ft circular tank, 12 ft deep and 10 holding tanks. The tanks are supplied with flowing filtered seawater at oceanic salinity (34 +/- 5 parts per thousand) with 0.2 - 0.4 ppm copper added. Mature males and females are not always kept together.
Age at Puberty and Gestation
The youngest animal in the colony to produce a live calf was a known age of 7 years old. Age at the first calving varied considerably but most of the animals were from an estimated 10 to 15 years old. Gestation period is 1 year (1). It was concluded that a minimum age at puberty is 6 years.
Calving Interval
The shortest interval between live births was 1.9 years. Mean interval for 31 observations was 3.3 years. Mean value for 21 intervals beginning with a live birth was 3.6 years; while, the mean value for 8 intervals beginning with a stillborn calf was 2.4 years. Mean value 16 intervals beginning with a calf that survived at least 1 year was 3.8 years.
Post-Partum Infertility
This period is calving interval minus gestation. The mean value when nursing did not occur (intervals beginning with a stillborn calf) was 1.4 years. The mean value when nursing did occur was 2.6 years and when the calf survived at least one year it was 2.8 years.
Reproductive Lifespan
One animal, born in the colony, produced a live birth at 32 years of age. Assuming puberty occurred at 6 years, the maximum observed reproductive lifespan for this colony was 26 years (the animal was alive and healthy at the end of the study).
Seasonality
Calving tended to be seasonal with most of the births (71%) being born during February, March, April and May. A sharp (6 fold over January) increase in calf production is seen in February which has the highest incidence of births. The highest percentage (75%) of live births occurs in March, April, May and June; while, 38% live births were seen in the other 8 months. Calving for individual animals often occurred near the same date each time.
Reproductive Rate and Efficiency
Mean reproductive rate for the colony over 40 years is 1.3 births per year; while, the mean rate for each mature female was approximately 0.2 births per year. The shortest calving interval observed (704 days) that resulted in a live calf was considered a minimum for this colony. Thus, maximum reproductive rate for a female would be 0.52 calves per year using this interval. Reproductive efficiency for females in the colony would be 39% (0.20 0.52).
Discussion
Reproduction in the MLF colony has characteristics that may be unique. Seasonality may be concerned with water temperature since the incidence of live births increases with warmer temperatures. A colony 250 miles south produces more calves in the fall (5). Reproductive rate for the colony may be reduced because mature females and males were not always together. The reproductive rate is also dependent on many factors that are based on behavior of the animals and management of the colony (1,2,3,4). Calving interval depends upon the period of postpartum infertility which appeared to have two parts in our study. The first part is approximately 1 year long and was present whether the interval began with a live birth or a stillborn calf. This was believed to result from the presence of a relatively short breeding season and because the average female in this colony appear to have only I (productive) cycle each year. Thus, an animal that produces a stillborn calf misses her season or cycle and usually does not become pregnant until the next year. The second part of the period of postpartum infertility was also approximately 1 year in length and was observed when the period began with a live calf. This period of infertility increased with the survival time of the calf and was believed to result from lactation. Female Tursiops in other colonies have been reported to cycle as follows: 1. be anestrus for 1 year; 2. cycle once for the year; 3. cycle 2-3 times in I year (5).
Reproductive lifespan of captive dolphins can be long (26 years). A single female should be capable of producing 10 or more calves; although, the highest calf yield observed for a single animal was 6 for the MLF colony. Our study suggests that careful management of 3 or 4 breeders should maintain the MLF colony.
References
1. McBride, A.F. and H. Kritzler. 1951. Observations on pregnancy,, parturition and postnatal behavior in the bottlenosed dolphin. J. Mammol. 32: 251-266.
2. Essapian, F.S. 1953. The birth and growth of a porpoise. Natur. Hist. Mar. April pp 1-6.
3. Talvolga, M.C. and F.S. Essapian. 1957. The behavior of the bottlenosed dolphin (Turisops truncatus): Mating, pregnancy, parturition and mother-infant behavior. Zoologica 42: 11-31.
4. Wood, F.G. 1977. Birth of porpoises at Marineland, Florida. 1939 to 1969, and comments on problems involved in breeding small cetacea. In; Breeding Dolphins; Present Status, Suggestions for the Future. Marine Mammal Commission, Washington, D.C. pp 47-60.
5. Zeiller, W. 1977. Miami Seaquarium breeding program. In: Breeding Dolphins, Present Status, Suggestions for the Future. Marine Mammal Commission, Washington, D.C. pp 61-65.
6. Kirby, V.L. 1984. Hormonal evaluations of ovulation and pregnancy in captive Tursiops truncatus In Reproduction in Whales, Dolphins and Porpoises, W.F. Perrin, R.L. Brownell Jr. and D.P. DeMaster (eds.) International Whaling Commission. Cambridge. p 479.