The Tees seals project was initiated by David Bellamy Associates (DBA) and funded by the Teesside Development Corporation (TDC) in 1989, following the devastation of harbour seal populations on the east coast of Britain by the epidemic of phocine distemper virus (PDV). The Tees – a highly industrialised estuarine environment – was at that time home to about 20 harbour seals, and because of its small size, this group was considered to be at risk from the PDV outbreak or other environmental factors. Prior to the Industrial Revolution in the mid-19th century, there were believed to be a resident breeding population of harbour seals numbering approximately 1000 animals, but following industrialisation of the estuary, the population was virtually extinct by the turn of the 20th century. The tentative return of the seals to the Tees was – and is – therefore something of a cause for celebration mingled with concern for the health of the seals in an industrial environment which was still polluted to some extent.

In 1989 two scientific personnel were employed by DBA (in association with Durham University Biology Department) to investigate the status quo of the population and assess the feasibility of establishing seal sanctuary facilities at Teesside. The proposed sanctuary was researched and designs suggested, but was finally assessed to be inappropriate for the area. However, the results of the seal monitoring programme attracted considerable interest. The harbour seal population was found to number about 23 individuals in 1989; one pup was born to the colony, but died at five days of age. Post-mortem examination revealed high levels of PCBs in the dead pup's blubber. These findings were included in the final project report:

  • Jackson, D.B. & Wilson, S.C. 1990. Tees Seals Programme: the feasibility study. Report no. 1 prepared for Teesside Development Corporation. David Bellamy Associates, 208pp.
    The findings in this report generated an extension of the monitoring programme, again funded by TDC through DBA, during which organochlorine pollutants (including PCBs) in the Tees fish were investigated. Following this extension, a long term monitoring programme for the Tees seals was developed and again funded by TDC with significant contributions from several local Teesside industries. Eventually, in 1993, the newly formed INCA (Industry and Nature Conservation Association) was formed, and adopted the running of the Tees Seals monitoring programme. Annual reports on the results of the population monitoring were prepared. From 1997, INCA took the programme over completely.

The results of the monitoring programme from 1989 to 1997 are reported in the published paper, which may be downloaded below:

  • Wilson, S.C. 2001. Population growth, reproductive rate and neo-natal morbidity in a re-establishing harbour seal colony. Mammalia, 65 (3): 319-334.
    Abstract – Harbour seals, Phoca vitulina vitulina were exterminated from the Tees estuary in north-east England during the industrial revolution in the middle of the 19th century. Industrial chemical plants now occupy reclaimed land on much of the former estuarine sand flats. Since the 1980s a breeding colony of harbour seals has been re-establishing together with a small, non-breeding group of grey seals, Halichoerus grypus. Between 1989 and 1997 the harbour seals increased from about 24 to 50 individuals, although the birth rate has been <10% of the population.
    Of 12 pups born live between 1989 and 1997, seven have stranded in a moribund condition, while five have appeared healthy at approximately one month of age. Observations of the seven non-viable pups revealed a common pattern of apparently normal maternal care, but gradual weakening of the pup with progressive inability to follow its mother preceding the final stranding. Analysis of chemical contaminants of the tissues of the first three pups revealed elevated levels of polychlorinated biphenyl compounds (PCBs) in the blubber. Analysis of local fish and invertebrates revealed elevated levels of PCBs. A possible causal link between the elevated PCB levels and the poor reproductive performance is suggested.