Abstract
Cetacean brucellosis is a long-lasting debilitating disease that induces abortion, death, and causes lesions in organs and bones, which hamper the dolphins’ physiological performance and development.1 The primary cause of most striped dolphin strandings in Costa Rica is neurobrucellosis, with close to 95% of seropositive animals and 77.5% successful isolation of B. ceti. This neurological infection impairs the survival of animals because of swimming and buoyancy problems, also hunting and feeding difficulties demonstrated by the absence of stomach contents in these dolphins.1-3 These stranded animals are usually smaller than expected for the specie, but there has never been a study comparing the age and sexual maturity in relation to their size.
Life history parameters in cetacean populations allow an overview of the state of conservation and show in ill individuals the possible grade of developmental affection. Therefore, a study of 51 striped dolphins stranded on Costa Rica’s Pacific coast for the past 15 years, was conducted. To ascertain the dolphins’ ages, measures of length,4 dentin-layer group counts (GLGs),5 flipper bone radiography assessment,6 were examined to evaluate the age of the individuals. Sexual maturity was determined through gonadal histology7,8 and sexual hormone serum levels9.
Compared with a model based on S. coeruleoalba ages estimations in other latitudes4 the striped dolphin studied displayed deficient growth parameters, with considerable variability in length, teeth, and flippers bone development. The majority were juveniles. Close to 43% (n=15) of GLGs’ measurements were below the body length average ranges for the predicted age, likewise, 34.4% of the flipper assessed were also below based on age prediction curves, all of these results alerting developmental abnormalities. Regarding sexual maturity, results behave differently in males and females. While the vast majority of males (20/28) were immature, only 6 females were pre-pubertal. Hormone levels were as expected in immature and mature animals.9 The histopathological analysis of animals showing signs of meningoencephalomyelitis compatible with active brucellosis infections was 98%.2 Other diseases such as morbillivirus and herpes virus, or parasites such as toxoplasmosis, were discarded.
Although the different oceanic settings, such as pollutants, food resources, and stress among several features, may be factors influencing size variation, data indicate that a significant number of the dolphins studied (~45%) were below the expected length, bone, and teeth parameter proportions, indicating developmental deficiencies and pinpointing other causes. Brucellosis hampers reproduction in females and males, affecting the secondary reproductive organs in cetaceans.3 As in cows, calves born from Brucella infected mothers may be premature, weak, and unhealthy,10 affecting their performance in a highly competitive environment such as the open ocean. These results are a first sight of the prevalence of abnormalities in a dolphin population with a chronic infectious disease such as brucellosis, which should be aware of the deleterious consequences of this disease in animals already confronting distressful conditions in the oceans.
Acknowledgments
The authors wish to thank to all the personnel at the National University of Costa Rica who collaborated in this study. Also thank the Municipal Police, the Coastguard of Costa Rica, and the Tropical Disease Investigation Program (PIET) personnel for their collaboration in the recollection of the carcasses. This work was supported and approved as part of the National Program of Wildlife of SENASA San José, Costa Rica.
*Presenting author
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