Abstract

Swallowing foreign objects is a common cause of gastric disorders in captive dolphins; without intervention, it can lead to mortality. In 2002, one of the dolphins in a captive group of eight began swallowing leaves fallen into the sea-pens. Subsequently, all the remaining dolphins followed and exhibited the behaviour. Intervention and routine clinical monitoring were clearly indicated.

The dolphin group was maintained in a semi-natural facility in the Republic of Palau (North Pacific Ocean). It was constituted of eight inter-connected sea-pens bordered by over-hanging foliage of trees, such as Rubiaceae, Pandanales and Arecaceae, that densely populate the Rock Islands. The size and physical characteristics of the leaves of these trees vary: some were large elliptic or palmate while others were smaller and lobular. The margins of these leaves ranged from smooth to doubly serrated. Cutting trees on the Rock Islands is prohibited by law, therefore, training techniques to modify the leaf swallowing behavior was devised to reduce ingestion by the dolphins. Basically, dolphins were reinforced with food for leaves retrieved on cue during scheduled training sessions and sometimes on a random-casual basis.

To monitor the effect of leaf ingestion on the dolphins' health, gastric fluid was collected monthly under voluntary behavior. Hematology and endoscopic examinations of the gastro-intestinal tract were conducted routinely, or when indicated. When leaves were visualized in the first compartment of the stomach, they were manually removed by insertion of the forearm into the esophagus. On gross physical examination, gastric fluid collected from a stomach congested with leaves was dark brown and oily in texture. Gastric samples appear to increase in darkness and strength in occult blood according to the length of time and the amount of leaves present in the stomach. Lower hematocrits (< 30%) appear to be associated with the presence of leaves. This is likely to indicate gastric hemorrhage, which can partly be explained by mechanical abrasion on the mucosa due to the sharp margins of the leaves and gut motility. Ferrous-sulfate (300mg/BID per animal) and Phytonadione (vitamin K; 50mg/BID per animal) were administered to dolphins with less than 30% hematocrits. Hematocrits returned to normal levels within a month after leaves were removed. A maximum of about seven kg leaves (wet weight) was removed from the stomach of a 200 kg female dolphin.

Despite efforts of the trainers to reduce leaf ingestion, the problem is on-going. The procedure of manual leaf removal is repeated approximately once a month for those individuals deemed 'heavy leaf-eaters'. For the rest, the procedure is carried out less frequently.