Trends and status of liver neoplasms in flatfish from UK waters collected between 2004 and 2015

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The 2016 assessment of the UK's Clean Seas Environment Monitoring Programme described the status and trends of contaminant concentrations and biological effects measurements in biota and sediment at monitoring stations in waters around the UK. Liver neoplasm assessment was conducted on simplified data previously submitted to the MERMAN database between 2004 – 2015. All data were quality assured in accordance to the Biological Effects Quality Assurance in Monitoring Programmes (BEQUALM) Fish Disease Measurement scheme. The E&W CSEMP programme was redesigned in 2011 to adopt a biennial sampling cycle to include the Greater North Sea one year, followed by the Celtic Seas the next. This redesign resulted in an inability to conduct a continuous year-on-year temporal trend assessment. A preliminary analysis was conducted to ensure the most appropriate use of the data collected. Specifically, this was to avoid any bias caused by potentially disproportionate numbers of fish within a given age class. Data were subsequently split into two periods to include a baseline (2004-10) and assessment (2011-15) period. Furthermore, the Scotland data were collected from 2010-15, therefore the Scotland data for 2010 was removed from the analysis because it fell outside of the assessment period assigned to the E&W data (2011-15). This was done because the analysis of data periods, comprised of different durations, are not directly comparable i.e. comparing 5 years of E&W data (2011-15) to 6 years of Scotland data (2010-15). The treatment of the data in this manner allowed for efficient use of UK data for the purposes of conducting a UK-wide assessment. The results of the preliminary data analysis, used to develop the assessment tool, are located within the Results (extended) section of the indicator assessment. Following the preliminary data analysis, a generalised linear model (GLM) was used to normalise for the effects of sex and age, and determine any temporal trend increase or decrease in the prevalence of neoplasms between the baseline and assessment periods. Two levels of assessment were conducted using E&W data: (1) MSFD sub-Regions and (2) UK biohydrographic marine regions (UKMMAS, 2010). The prevalence range of liver neoplasms in E&W waters is reportedly the highest observed within the OSPAR region of the North East Atlantic (Stentiford et al., 2009; Stentiford et al., 2010; Lang et al., 2015). Thus, the indicator response was classified into three categories of background, elevated and significant, by separating the total observable range of liver neoplasm prevalence, corresponding to MSFD sub-Region or UK marine region, into thirds. Scotland data were treated independently of E&W data resulting from (a) limitations in the number of fish and (b) lack of data from baseline period (2004-2010). As a result, the E&W and Scotland data were not directly comparable. Consequently, it was not possible to incorporate Scotland data into the GLM, alongside E&W data, for an assessment at the MSFD sub-regional level, or for the development of assessment criteria thresholds. However, an indicative assessment of Scotland data at the UK biohydrographic regional level was conducted against proposed assessment criteria derived from E&W marine regional data, although this data could not be normalised for age or sex. One level of assessment was conducted using Scotland data: UK biohydrographic marine regions (UKMMAS, 2010). Since older age and the number of females has a positive influence i.e. liver neoplasms increase; a brief analysis of age and sex distribution using the Scotland data was conducted to inform any assessment as best as possible. The results of this analysis are located within the extended results section of this indicator assessment. There has been a significant decrease in the prevalence of toxicopathic liver neoplasms (cancer) in flatfish from the Celtic Seas and Greater North Sea MSFD sub regions. Whilst Celtic Seas fish still exhibit a ‘significant response’, Greater North Sea fish exhibit an ‘elevated response’ and are marginally above background levels. The evidence provided in this assessment indicates that pollution effects in the marine environment are decreasing, specifically concerning the formation of liver neoplasms. This finding informs good progress towards reducing chronic pollution effects.