Abstract

Periodic measurements of weight and length were taken of 9 Nest Indian manatees (Trichechus manatus) raised in captivity. Seven were ronceived and born in captivity and therefore, precise birth data is available for these animals. One manatee, conceived in captivity, was stillborn. Birth weight and length of this animal are noted in the data. In addition, 2 wild-born animals were rescued as neonates (less than one month old), brought to the Miami Seaquarium, and successfully rehabilitated. Measurements of 8 animals were taken on a monthly basis, and then on an annual basis beginning at age one year. Data is presented with the intent of providing a baseline for comparison of normal birth weights and lengths, and normal growth rates for future studies dealing with both captive and wild animals. Finally, comparison of the data is made with two other West Indian manatees born in captivity for which birth weights and measurements are available.

Introduction

The West Indian manatee (Trichechus manatus) is a severely endangered species for which little baseline data is available. Recent improvements in husbandry and nutritional programs have resulted in repeatedly successful reproduction of these rare animals (1). Seven live calves have been produced from eight pregnancies in the last 8 years (2,3). Accurate length and weight measurements at specific ages is available for several animals of each sex. Data is also available on two animals rescued from the wild as neonates (less than one month old).

Growth of neonates was recorded on a monthly basis for the first six months of life, and then on an annual basis beginning with the first birthday. All animals were considered clinically normal throughout the period of data collection.

Materials and Methods

The subjects of this study are 7 West Indian manatees--3 females and 4 males-­conceived and born in captivity. Additional data is provided for two animals born in the wild, but brought into captivity as neonates of less than one month old. One of these was female, the other was a male. Finally, birth length and weight are noted for a deformed stillborn calf conceived in captivity and delivered at or near "term".

Measurements were taken on a monthly basis as conditions permitted until the first birthday, following which measurements were taken annually.

Neonates were measured by lifting them out of the pool and placing them on a foam pad. This did not seem to elicit a stress response in either the mother or the infant. Length measurements were made with a 0.25 inch nylon rope extended from the nose to the tip of the tail; the rope was then marked and measured. Neonates were carried onto a scale, weighed, and placed back into the pool; the handler was then weighed and then his weight subtracted from the original combined weighing to achieve the true weight of the animals.

As the animals grew, it become necessary to drain all water from their pool and "beach" them prior to manipulation. Weights were obtained by placing each animal in a sling attached to a scale. The entire apparatus was then lifted by a pulley vstern; the weight recorded, and the weight of the sling ropes arid poles subtracted to give, the true weight of the animals. Body length Was measured as described above. Care was taken to keep the nylon rope straiqht, rather than allow it to curve aver the body of the animal, resulting in as accurate a measurement as possible.

Results

Birth weight and length for the seven live births at the Miami Seaquarium are presented in Table 1. Data analysis indicates a mean birth weight of 33.9 kg with a 95% confidence interval of .3.24 kg. Birth weights ranged from 28.6 to 40.0 kq. Similar analysis was performed Tor length at birth, yielding a mean length of 116.1 cm with a 95% confidence interval of 11.15 cm. The range was from 96.5 to 132.0 cm. No significant difference in inean birth weight or, length was detected between male and female calves using a student's t-test at alpha = 0.05.

Analysis of growth in total length and body weight was performed according to least squares regression and analysis of covariance using SPSS release 7-9 (4). Data obtained froin animals born in captivity was pooled with growth data of two wild-born neonates maintained in captivity. Figure I shows growth in length (cm) against age in months. Figure 2 shows growth in weight (kg) against age in months. Growth in weight and length was linear for measurements taken during the study period.

The data regressed against age yielded the following equations:

Eq. 1: length (cm) = 128.14 + 3.399 age (mos)
R² = 0.83
Eq. 2: weight (kg) = 45.546 + 4.85 age (mos)
R² = 0.69

Separation of the growth curves into two components at 1 year of age, as suggested by O'dell (5), did not yield a significant improvement, in the equations based upon a reduction of the residual mean squares of an increase in R².

Further analysis of the data, using both analysis of covariance (SPSS) and the general linear test approach for comparison of regression lines (6,7), failed to detect differences among sex, or captive-born versus wild-born calves at alpha = 0.05. A significant difference was detected among calves; the equation for the calf born 5/3/75 fell significantly below that of the other calves, alpha = 0.05. This trend is indicated by Figure 2. Removal of data for this calf produced the following equation for the seven remaining animals (Figure 3):

Eq. 3: weight (kg) = 40.196 + 7.737 age (mos)
R² = 0.85

Table 1. Birth Weight and Length for Six Live Captive Born Manatees at the Miami Sea quarium

Discussion

The calf born in 1975 demonstrated a significantly slower growth rate than the calves born after 1980 (Figure 1, Equation 3). This may be related to an improvement in the nutritional program which was instituted in 1980 (1).

In addition to the 6 live captive-born calves listed in Table 1, a seventh calf was born into the colony on 6/15/81. This calf was stillborn and physically deformed. Its birth length was 115 cm which is approximately equal to the mean length of the 6 healthy animals born into the colony. It is of interest to note, however, that the birth weight of this calf was only 21.4 kg, about 33% less than observed with healthy calves. This is supportive of the fact that this information may be directly relevant to evaluating the health status of young animals.

It is of interest that there is no significant difference in the growth rate of captive-born versus wild-born animals. Animals which were in poor condition when brought in demonstrated a temporary decrease in growth rate, particularly weight (kg) which seemed to resolve as their general health and nutritional status improved. It is logical that weight would fluctuate more readily and thus reflect the animal's current health or nutritional status, whereas length would be stable and therefore a better indicator of age.

Birth weight and length of two other calves which were born in captivity are within the range observed with the Miami Seaquarium calves. A calf born in Miami in the 1930's was reported as weighing 28.6 kg and measuring 99 cm in length (7). This is a small calf but still within the range recorded in Table 1. A second calf born in Holland measured 104 cm in length at 16 days. It was weighed when one month old and was 28.0 kg; it's length had increased from 104 cm at 16 days to Ill cm (8). Again, this is a small calf according to the data presentpd but is reasonable. Husbandry conditions have improved markedly within the past few years (1), therefore it is not unreasonable to expect birth weight and length to increase as these improvements continue.

References

1. White, J.R. "Man Can Save The Manatee". Nat. Geo. (Sept., 1984).
2. Francis-Floyd, R.; White, J.R.; Chen, D.; and Cardeilhac, P.T. Age of puberty estimation in captive female manatees by blood hormone levels (in press).
3. White, J.R.; Francis-Floyd, R.; and Cardeilhac, P.T. Gestation period and observations of births of captive West Indian manatees (Trichechus manatus) (in press).
4. Nie, N.H.; Hull, C.H.; Jenkins, J.G.; Steinbrenner, K.; and Brent, D.H. Statistical Package for the Social Scientist, Release 7-9, SPSS, Inc. McGraw-Hill Book Co., New York, NY, 1981.
5. O'dell, D.K. Growth of a West Indian manatee, Trichechus manatus born in captivity. In: The West Indian Manatee in Florida, R.C. Browne[[ and K. Rails, Eds. T­lorida Audubon Society, Maitland, FL, 1978, pp. 131-140.
6. Neter, J.and Wasserman, W. Applied Linear Statistical Models: Regression, Analysis of Variance, and Experimental Design. Richard D. Irwin, Inc., Homewood, IL, 1974.
7. Barbour, T. Birth of a manatee. J. Mamm. 18: 106-107 (1937).
8. Dekker, D. Birth of a sea cow in captivity. Artis. 23(4): 111-119 (1977).