21 newborn seal pups found dead in Tees Estuary

Harbor seals have been living in the Tees Estuary for more than 100 years. After almost facing extinction in the early 20^th century, the seals have been making a comeback, and in the last two years, the Tara Seal Research team has been monitoring them.

This year, as a part of the Tees Estuary Seal Study (TESS), the team counted a total of 21 pups at Seal Sands, Teesmouth National Nature Reserve. This study followed on from the Industry and Nature Conservation Association’s monitoring programme and the original Tees Seal Project 1989-94’s study on seal pup morbidity.

It all began when concerns were raised about the health of the seals living in an industrial environment where pollution was still an issue. In 1989, a post-mortem examination of a newborn seal pup revealed high levels of PCBs (toxic industrial chemicals) in its blubber. Since then, the seal population in the Tees Estuary has been monitored.

More recently, the 21 seal pups that were counted this year all succumbed to a disease known as mouth rot; this causes swelling, wounds, and abscesses in the mouth, which can lead to difficulty eating and respiratory issues. Conservationists at Tara Seal Research have been aware of mouth rot in the Tees Estuary’s seals since 2022, but report that this year is the worst they’ve seen.

The research team has attempted to investigate PCB levels in association with mouth rot infections. Studies are reporting that high concentrations of PCBs could be responsible for a weakened immune response in the seal pups towards infections, though further investigation is required for a better understanding of seal pup morbidity.

Due to these recent deaths, the conservation team has requested that further research be done into the cause of the seal pups’ mouth rot. They expect that seal mortality levels will continue into 2026, and have stated that they will continue investigating the cause.