Non-Indigenous Species Thematic Assessment

Pressures associated with non-indigenous species

The assessment of the Trends in New Records of Non-Indigenous Species Common Indicator demonstrates an overall reduction in their rate of introduction (trend). The pressure from new arrivals of NIS on marine biodiversity state is generally decreasing for Greater North Sea (Region II), Celtic Seas (Region III) and Bay of Biscay and Iberian Coast (Region IV). No assessment was made for Arctic Waters (Region I) and Wider Atlantic (Region V). For Regions II, III and IV there was a statistically significant decrease in introduction rates over time, in particular between period 1 (2003–2008) and period 3 (2015–2020), and especially for Region II (Celtic Sea), for which there were only very few new NIS recordings (Figure P.1). Overall, this assessment is associated with high confidence where sources of information are concerned. However, there is uncertainty about the monitoring effort and the publication time lag. Thus, while the rate of new NIS introduction is high (range 0,5 – 9,3 new NIS per year), the provided data indicate a downward trend towards the most recent assessment period, which might be the effect of the current measures to reduce the introduction and spread of NIS in the OSPAR Maritime Area. This conclusion should, however, be treated with great caution owing to the lack of a harmonized NIS monitoring programme across OSPAR Regions.

Figure P.1: Graphical summary of the pressure associated with non-indigenous species (NIS) rate of introduction observed in the data used in the QSR 2023 thematic assessment

The following text gives a detailed description of the OSPAR assessment of trends in new records of NIS introduced by human activities.

Despite the overall decreasing trends, several new NIS were introduced to each OSPAR Region during the latest assessment period. This shows that continued effort is required in order to reduce and prevent new NIS introductions. It should also be noted that there is substantial uncertainty as to whether the observed decline is due to an actual reduction in introductions or to a change in the monitoring effort, which it was not possible to account for. Also, the current assessment is potentially biased owing to a delay in the reporting of new NIS in the most recent years and to gaps in monitoring in general (Tsiamis et al., 2019, 2021). These conditions weaken the interpretation of decreasing trends, which should be investigated further in future assessments.

Newly introduced NIS are extremely difficult to detect. The assessment of new NIS is therefore ideally based on efficient and standardized monitoring approaches which reduce potential bias among Contracting Parties arising from differences in applied methodologies, as these may affect the quality and quantity of collected NIS data. Such harmonisation is necessary in order to enhance the quality of future regional assessments of trends in new NIS arrivals (see:  Trends in New Records of Non-Indigenous Species Common Indicator ). To optimise the monitoring effort and reduce costs, the implementation of a harmonised monitoring programme should apply a cost-efficient and risk-based approach, with the emphasis on high-risk areas such as harbours (from commercial ports to marinas) and marine aquaculture sites. The existing monitoring may need to be complemented and supplemented with efficient new techniques which reflect the importance of adapting sampling effort to regional needs and current data gaps. For this purpose, efficient new technologies such as those based on DNA studies (e.g. metabarcoding) or deep-learning techniques (e.g., image analyses) may be useful. Although monitoring per se does not reduce the risk or rate of new NIS introductions, early detection in risk areas and up-to-date information on NIS introductions and spread are essential in order to improve the future assessment and management of NIS spread and NIS impact. Indeed, it is well documented that cost-efficient management needs to be implemented at the start of the introduction process. Furthermore, cost-efficient monitoring is important for assessing the effectiveness of the NIS management efforts aimed at reducing their impact. These considerations relate primarily to the Ballast Water Convention and the International Convention on the Control of Harmful Anti-fouling Systems on Ships, both IMO instruments.

There are considerable differences in rates of introduction between Regions and Contracting Parties, with lower rates in Celtic Seas (Region III) indicated by the available NIS observations (Figure P.1). As the NIS monitoring effort (e.g., number of samples taken per year) for each Contracting Party is not known, it is possible that the observed trends in new NIS introductions partly depend on variation in monitoring activity. It is also not possible to determine the reasons for the observed differences between Contracting Parties. Two factors in particular may explain the observed discrepancies: there was no control for the length of the coast that was monitored and none for the type of habitats that were surveyed. Part of the explanation might relate to the number of high-risk areas that were surveyed.

Regarding the effects of responses (management), it is of interest to identify the most important pathways of NIS introductions. According to the records provided by 11 Contracting Parties, the pathways of 56% of the species remain uncertain/unknown. Many NIS may be introduced through multiple pathways and from multiple sources, making it difficult to identify a specific one. This could partly explain the large unknown group. Of the known pathways, introduction via ships hull fouling (14%) or ballast water (13%) are the most important, followed by aquaculture/mariculture and associated epibionts (12%). Natural spread only accounted for 5% of NIS introductions, but as such spread may result from a combination of natural dispersal and human-mediated dispersal, it could be argued that this vector should not be specified. The remaining pathways (1,6%) relate to game fishing, intentional release, bait escape and nursery material. Given the absence of a standardised method offering quantifiable quality assessment for determining pathways of introduction, it is currently very difficult to assess their relative importance.