Organ Weight and Growth Profiles of Stranded Bottlenose Dolphins from the Western Gulf of Mexico
Abstract
Organ weights and standard body length were examined in 48 stranded bottlenose dolphins (Tursiops truncatus) collected from coastal Louisiana and Texas. Mass was available for 35 of the animals sampled. Age was estimated in a sub-sample of these animals (n=29) using growth layer groups (GLG's) found in the teeth. Growth curves (age versus standard length) were produced from a larger group of stranded bottlenose dolphins (n=170) recovered along the coasts of Florida, Mississippi, Louisiana, and Texas. Pearson's correlation coefficients were calculated between length, age, and various organ weights, including: lungs, heart, liver, pancreas, adrenal glands, kidneys, testes, ovaries, brain, pituitary, thyroid, thymus, and spleen. Allometric relationships between organ mass and body mass were similar to those described for other mammalian species. Individual organs exhibited mass changes consistent with pathologies noted during necropsy. Strong positive correlations were found between length and all non-endocrine organs. There was a weaker correlation between age and all organ weights.
This was consistent with previous work by Cowan1 on pilot whales (Globicephala melaena) sampled in a commercial hunt from the Northwestern Atlantic in which all non-endocrine organs were correlated with length. Standard body length was not found to be an accurate predictor of age, with a correlation coefficient of 0.602 (p<0.0001). During examination of several animals, DFC noticed separation in organ weights of Tursiops at approximately 225 cm in standard body length. Animals were divided into three groups, to further facilitate the comparison of future animals in the data set. Animals were separated into group A, including those 175 cm, group B, with body lengths between 175 and 225 cm, and group C, with animals over 225 cm in length. The mean, standard deviation and number of animals in each group were calculated and are presented in Table 1.
Though the groups were initially determined through gross examination, they are in fact based upon the developmental growth curves of these animals. Standard body length of 225 is consistent with the transition between exponential growth and a phase of negative growth acceleration in several studies of growth and development and is well within the range of sexual maturity values of Tursiops in the Atlantic and Gulf of Mexico.2,3,4,5 The two groups DFC described were actually juvenile animals undergoing ontogeny and then adults from maturation onward. The further division of animals # 225 cm separates newborn calves, which undergo extensive exponential growth, from juveniles, approaching the phase of negative growth acceleration. Standard length parameters used to separate animals were based upon growth curves for Tursiops from the Atlantic coast of the United States as well as the Gulf of Mexico. Data on organ weights of bottlenose dolphins in the Gulf of Mexico, correlated with standard body length and age, offers an important tool for pathologists and veterinarians in the interpretation of health status.
Table 1. Organ weights grouped by body size parameters.
|
|
Group A (<175 cm) |
Group B (>175<225) |
Group C (>225) |
|
Organ |
Mean |
SD |
N |
Mean |
SD |
N |
Mean |
SD |
N |
|
Length (cm) |
149.3 |
25.3 |
5 |
205.1 |
12.6 |
15 |
247.4 |
12.8 |
28 |
|
Age (glg's) |
2.0 |
-- |
1 |
3.7 |
1.4 |
5 |
18.1 |
7.5 |
14 |
|
Mass (kg) |
52.3 |
11.2 |
4 |
91.0 |
19.6 |
12 |
169.7 |
48.6 |
20 |
|
L. Lung (g) |
686.1 |
286.7 |
5 |
1347.0 |
538.5 |
13 |
2910.1 |
934.0 |
27 |
|
R. Lung (g) |
814.9 |
404.0 |
5 |
1441.6 |
602.1 |
13 |
3239.1 |
929.7 |
26 |
|
Heart (g) |
269.8 |
86.1 |
5 |
467.4 |
102.2 |
13 |
954.6 |
235.8 |
28 |
|
Liver (g) |
1108.9 |
571.5 |
5 |
2569.0 |
737.8 |
13 |
4373.3 |
1568.2 |
26 |
|
Pancreas (g) |
153.6 |
154.9 |
2 |
230.3 |
84.3 |
8 |
395.3 |
132.2 |
15 |
|
L. Adrenal (g) |
2.9 |
1.2 |
5 |
6.4 |
1.8 |
14 |
11.7 |
3.2 |
28 |
|
R. Adrenal (g) |
2.7 |
1.3 |
5 |
6.2 |
1.5 |
12 |
12.0 |
3.6 |
28 |
|
L. Kidney (g) |
153.4 |
70.1 |
5 |
323.9 |
123.6 |
12 |
637.9 |
139.1 |
28 |
|
R. Kidney (g) |
163.6 |
88.7 |
5 |
307.3 |
113.2 |
11 |
618.7 |
150.4 |
28 |
|
Brain (g) |
935.3 |
232.9 |
5 |
1350.4 |
117.9 |
10 |
1464.7 |
104.1 |
20 |
|
Pituitary (g) |
0.7 |
0.1 |
4 |
1.1 |
0.3 |
10 |
2.0 |
0.5 |
20 |
|
L. Testis (g) |
-- |
-- |
0 |
17.3 |
5.9 |
8 |
557.3 |
345.0 |
10 |
|
R. Testis (g) |
-- |
-- |
0 |
17.2 |
6.1 |
8 |
548.5 |
369.5 |
9 |
|
L. Ovary (g) |
0.9 |
0.8 |
2 |
2.9 |
1.0 |
4 |
13.2 |
9.6 |
9 |
|
R. Ovary (g) |
1.0 |
0.9 |
2 |
2.4 |
0.8 |
4 |
6.4 |
2.7 |
9 |
|
Thyroid (g) |
24.5 |
3.8 |
2 |
27.1 |
6.2 |
7 |
33.0 |
11.7 |
19 |
|
Thymus (g) |
85.8 |
69.4 |
3 |
47.5 |
27.5 |
2 |
38.0 |
11.9 |
5 |
|
Spleen (g) |
63.3 |
51.1 |
4 |
75.0 |
29.9 |
13 |
95.0 |
48.0 |
28 |
Acknowledgements
The authors would like to thank the many dedicated volunteers of the Texas Marine Mammal Stranding Network, without whom, none of this would be possible.
References
1. Cowan DF. 1966. Observations on the pilot whale Globicephala melaena: organ weight and growth. Anat. Rec., 155: 623-628.
2. Fernandez SP. 1992. Composicion de edad y sexo parametros del ciclo de vida de toninas (Tursiops truncatus) varadas en el noroeste del Golfo de Mexico. Tesis de Maestria. Instituto Tecnologico y de Estudios Superiores de Monterrey, Guaymas, Mexico. 109pp.
3. Mead JG, CW Potter. 1990. Natural history of bottlenose dolphin along the central Atlantic coast of the United States. In The Bottlenose Dolphin. S. Leatherwood and R. R. Reeves, eds., pp.165-195. Academic Press, San Diego.
4. Read AJ, Wells RS, Hohn AA, MD Scott. 1993. Patterns of Growth in Wild Bottlenose Dolphins, Tursiops truncatus. J. Zool., Lond. 231, 107-123.
5. Turner JP. Unpublished data.