Ingestion of plastic and unusual prey by a juvenile harbour porpoise


Robin W. Baird and Sascha K. Hooker. 2000.

Marine Pollution Bulletin 40: 719-720.

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Summary

Since many species of whales and dolphins live in waters far from shore, and may sink upon death, opportunities to record instances of ingestion of marine debris by cetaceans are infrequent. Here we document the third reported case of plastic ingestion by a harbour porpoise, and discuss factors that might have contributed to ingestion. A 95 cm harbour porpoise was found dead on a beach near Pictou, Nova Scotia, and was visibly emaciated, with a distinct concavity of the dorsal surface on both sides of the body, indicating atrophy of the epaxial muscles. Upon examination of the esophagus, a balled up piece of black plastic (measuring when stretched out about 5 by 7 cm, weighing 0.36 grams) was found adjacent to the junction with the stomach. Immediately cranial to this plastic was a mass of fish bones, partially digested fish, and three intact fish (a total of 2.7 grams), all occluding the esophagus. The fish remains recovered were identified as three-spined stickleback (a species not previously reported as prey of harbour porpoise); a total of 18 individuals were represented, ranging in size from 22-28 mm standard length, and all had been recently ingested. The ingested plastic probably blocked the esophagus, although for how long is not clear, though it is unlikely to have been for very long, given there was no necrosis associated with the blockage. We do not know whether this plastic caused the death of the individual, but its emaciated state and the presence of a previously undocumented prey species suggests that the porpoise may have been investigating inappropriate prey items. Based on its size and timing of the stranding, it is likely that this individual was only a few months of age, and likely had not yet been weaned, thus pre-weaning separation from its mother may have led to the ingestion of inappropriate items.


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