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Marine litter indicators: plastic in fish stomachs

Pioneering protocol established by ICES to monitor plastics in the marine environment.
Published: 3 June 2015

​​​​​​​​​​​​​​​​​​​The EU Marine Strategy Framework Directive (MSFD) aims to protect the marine environment by achieving Good Environmental Status (GES) throughout the region. Marine litter is addressed by Descriptor 10, which states that for GES to be achieved, "Properties and quantities of marine litter do not cause harm to the coastal and marine environment".

Plastic is a major contaminant in the marine environment that never fully biodegrades, instead photodegrading into smaller pieces that are ingested by fish and other animals in the marine environment.  Fish stomachs, should therefore provide an accurate indication of plastic levels in the marine environment and have as such been named as an indicator for GES under MSFD Descriptor 10.

OSPAR​ has requested that ICES establish a monitoring protocol that will enable the analysis of fish stomachs for plastic particles in the marine environment. Fish stomachs have previously been checked for visual plastic pieces but this overlooks microplastic particles. The resulting protocol released by ICES today is the first of its kind globally and defines the steps required in the practical work. If adopted, this protocol will establish a baseline with which to gauge whether or not trends in plastic are increasing or decreasing in the future, leading to possible management actions.

As a new area of research, ICES advises that if adopted, "this protocol is reviewed at regular intervals and improved on the basis of experience". Lisa Devriese, a member of the advice drafting group, points out the timeliness of the new protocol, "Based on current knowledge, microplastics should be considered as contaminants of emerging concern. Still, there is a lack of knowledge on the presence and impact (and biological effects) of microplastics in the water column or sediments. Besides the plastic itself, absorbed chemicals or adhered bacteria may pose additional risk to the aquatic ecosystem." ​​

A challenge that has been acknowledged when processing samples is the possibility of contamination. Plastic is prevalent in our environment and this is no different on board research vessels. Contamination sources range from clothing fibres to containers to the paint on the walls of the ship. To counter this environmental interference, it is suggested that freezing fish stomach for later analysis within clean labs should be carried out.

Devriese also adds data management, integrated assessments in the OSPAR region, harmonization of monitoring procedures (sampling, extraction, identification, airborne contamination), and quality assurance (implementation of interlaboratory exercises, procedural blanks, detection limits, etc) as further challenges that were addressed.

If adopted, this new protocol can be added to the work already carried out by fish disease surveys, which are currently carried out in OSPAR waters to monitor the health of wild fish and fish stock surveys. However, the experts drafting this advice point out a "power analysis", which evaluates a sufficient number of samples to detect a trend, should be carried out. They also suggest that further monitoring, possibly by commercial vessels, will be necessary for an OPSAR-wide assessment.

Stocks that have been recommended for sampling include mackerel, herring, cod, flounder, and shellfish, such as Blue and Mediterranean mussels.​​

Read the full text of ICES advice to OSPAR on the development of a common monitoring protocol for plastic particles in fish stomachs and selected shellfish on the basis of existing fish disease surveys​.

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​Members of ADGPLAST, the advice drafting group on plastics in fish stomachs and a fish made from about 300 kg of plastic taken from the sea. Copenhagen, May 2015.

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Marine litter indicators: plastic in fish stomachs

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