Serious threat as sharks become pet food

A recent analysis of commercially available pet foods found that it contained shark as an ingredient, although the ingredient was not explicitly listed in the ingredients list.

Pet foods often list ingredients from the ocean using generic terms like "fish," "whitefish," "whitebait," or "ocean fish." The researchers wondered if genetic testing could reveal information missing from the label.

Shark populations are critically endangered by commercial fishing to sell shark fins.

The researchers collected and sequenced samples from 45 pet food products of 16 brands sold in Singapore. Although no product labels listed shark among the ingredients, the researchers found that 31% of the samples contained shark DNA.

In some cases, researchers found DNA from a species of shark that the International Union for Conservation of Nature (IUCN) considers vulnerable; Such species include: the silky shark (Carcharhinus falciformis) and the white-headed reef shark (Triaenodon obesus).

The scientists examined samples with DNA barcodes, identifying species by comparing short DNA sequences with databases of so-called genetic barcodes from the genomes of known species.

Because canned pet food is highly processed, which can damage DNA, the researchers used a technique known as mini barcoding, which can amplify even very small gene sequences in decomposition samples.

The blue shark (Prionace glauca) is the most common of the test samples, appearing seven times, this shark is classified as Vulnerable by the IUCN. Other studies have shown that blue sharks are commonly caught by commercial fishing and that they are prevalent in the shark fin trade in Southeast Asia.

After the blue shark, the silky shark and the white reef shark are also most common in the patterns. The researchers identified all nine species, including the spotted-tailed shark (Carcharhinus sorrah), the red-eyed shark (Loxodon macrorhinus) and the sand tiger shark (Carcharias taurus).

Although pet food companies do not specifically mention shark meat in these products, the ambiguity of terms like "ocean fish" has kept pet food buyers from know about what they are feeding their pets.

This has caused a dramatic decline in global shark populations, reducing shark populations worldwide by more than 70 percent over the past 50 years, the study authors report.