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BPA Welcomes Independent Report into NE England 2021 Crustacean Die-Off

The British Ports Association has welcomed a new report from a panel of independent scientists into the cause of a mass mortality incidence affecting crustaceans off the north east coast of England in late 2021.

On dredging, the report confirms earlier analysis of available evidence by a joint agency investigation into the incident that concludes that it was not the cause of the 2021 crustacean die-off. The BPA has been disappointed that misinformation about dredging has proliferated since the incident. The report can be found here.

On maintenance dredging, the report said that dredging in the offshore channel, which has been scrutinised by some, mobilised less material than that moved during storms and was “not considered a contribution to the unusual mortality”. The report concluded that “overall, the possibility that maintenance dredging contributed to the unusual mortality is very unlikely“. Very unlikely is defined as less than a 10% chance. It also said that “the absence of any capital dredging in the area between December 2020 and September 2022 make it exceptionally unlikely that capital dredging is responsible for the unusual mortalities commencing in October 2021″. ‘Exceptionally unlikely’ is defined as less than a 1% chance.

This authoritative report again clearly underlines that there is no credible evidence to suggest that either capital or maintenance dredging has had any impact on this event. This sits on top of a joint-agency report from marine experts at several regulators that ruled out dredging in May 2022.

Dredging and the disposal of dredged material is a routine activity for almost every UK port and is subject to strict regulatory processes in line with internationally agreed standards. Dredging is critical to keeping ports open.

We would support further research into possible pathogens although we recognise that a lack of evidence in this area means that a definitive cause may never be found.

We support calls to Government to consider how it can help local fishermen who have suffered financially to recover. The BPA represents almost every fishing port in the country and this event has robbed communities of their livelihoods.

Mark Simmonds, Director of Policy & External Affairs

On pyridine, which has been the focus of one group of researchers, the panel of experts said that it is exceptionally unlikely that a reservoir of toxic contaminants (such as pyridine) exists or existed beneath or adjacent to the surface sediments disturbed and removed by the Orca’s maintenance dredging activity. Exceptionally unlikely is defined at less than a 1% chance of likelihood and as close as scientists usually get to saying something is impossible. As the BPA noted recently in a letter published in The Times, the dredger would have had to have made 5,000 trips (approximately five years worth) to deposit enough pyridine to have this effect, when in fact it made 52 trips in the time it was active.

The British Ports Association supports further research into the areas identified in the report as well as further consideration from Government of support for affected fishermen.

The panel concluded:

  • It is about as likely as not that a pathogen new to UK waters – a potential disease or parasite – caused the unusual crab mortality. There are pathogens known to cause similar symptoms to those observed in the north-east and these pathogens have caused mortality events and declines in crustacean populations around the world. No significant pathogens were identified in the north-east crabs but full molecular screening was not conducted at the time of the initial investigation.
  • It is unlikely that a harmful algal bloom or that a loss of oxygen in the water associated with the algal bloom caused the crab deaths. The panel assessed satellite data and water-column measurements and concluded that the presence of an algal bloom in the area during September 2021 was likely but it was unlikely that the bloom persisted beyond October 2021.
  • It is very unlikely that pyridine or another toxic pollutant caused the crab deaths. The panel considered industries on Teesside and concluded they could not be sources of any significant volume of pyridine during the period of the crab deaths. Measurements of seawater by the Environment Agency and York University could not detect pyridine. Sediment measures of pyridine from dredged material and other toxic chemicals found in sediments in the Tees are significantly lower than the levels which would cause crab mortality.
  • It is very unlikely that maintenance dredging, as required to keep the port open, was the cause; a dredger operated in the channel offshore Teesside during late September and early October 2021 but the maximum possible release of toxic chemicals, including of pyridine, caused by this activity is significantly too small to cause crab mortality.
  • Capital dredging (i.e. as required to expand the port) was last carried out in December 2020, some time before deaths started in October 2021. Further capital dredging did not commence until September 2022. It is therefore exceptionally unlikely that capital dredging on the Tees caused the crab mortality seen in the region.

From the report, on Maintenance Dredging:

[Maintenance dredging removes recent infill material to provide safe operating conditions in the context of the original or ‘declared’ channel (or berth) depth.]

Maintenance dredging by PD ports dredgers, and by Able UK, during September and October 2021 was part of normal long-term dredging and moved relatively small amounts of sediment from areas routinely dredged. There is no evidence that this dredging differed from that in previous months and years, and no evidence that it dredged material with an unusual concentration of toxic chemical. It is very unlikely that this routine maintenance dredging contributed to the unusual crustacean mortality events.

Page 45, Independent Expert Assessment Report

From the report, on Capital Dredging:

[Capital dredging generally excavates geological or historically accumulated sediments to create a new or deeper channel or berth]

No capital dredging was undertaken in the Tees area in the period before or during the unusual mortality event. The last capital dredging before this period was in December 2020, and the new capital dredging at Teesworks did not commence until September 2022. The panel therefore considers it exceptionally unlikely that capital dredging on the Tees caused the unusual crustacean mortality seen in this region between these dates.

Page 9, Independent Expert Assessment Report

From the report, on Pyridine:

A larger than normal dredger was operating in the channel offshore Teesside during late September and early October 2021. The vessel was dredging recently mobilised sandy material deposited in the channel by storm events. Although larger than normal volumes of sediment were mobilised, maximum possible release of toxic chemicals, including pyridine, is significantly too small to cause crab mortality. Other routine dredging was also underway in the Tees Estuary by the port’s dredgers. This was similar to activity conducted every month to keep the port operational and followed normal regulatory procedures. Considering all available evidence about Teesside dredging the panel considers it very unlikely that release of any toxic chemical, including pyridine, due to maintenance dredging could have caused the deaths. This conclusion is supported by the broad geographic spread and long duration of crustacean mortality.

Page 9, Independent Expert Assessment Report

…it is exceptionally unlikely that a reservoir of toxic contaminants (such as pyridine) exists or existed beneath or adjacent to the surface sediments disturbed and removed by the Orca’s maintenance dredging activity.

Page 43, Independent Expert Assessment Report

In total the Orca dredged approximately 150,000 tonnes of sediment… over 52 cycles of dredging and disposal. N.B. This latter figure is notable insofar as it represents only 1% of the c.5000 transits of the dredger highlighted in the October 2022 North East Research Group Investigation Report as being needed to reach the threshold used in the pyridine plume modelling (NEFC et al., 2022)

Page 61, Independent Expert Assessment Report

The report, and associated data can be found here.

The Joint agency investigation from May 2022 can be found here.