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    "@type": "Dataset",
    "@id": "http://portal.medin.org.uk/portal/json-ld/Marine_Scotland_FishDAC_1506.jsonld",
    "identifier": "Marine_Scotland_FishDAC_1506",
    "url": "http://portal.medin.org.uk/portal/?details&tpc=Marine_Scotland_FishDAC_1506",
    "name": "Assessment of the \u201cState\u201d of the Demersal Fish Communities in UK waters",
    "description": "To date, OSPAR has largely been responsible for the development of an ecosystem\r\napproach to the management of marine natural resources within the convention area. Ten\r\nEcological Quality Issues have been identified, with the intention of setting Ecological Quality\r\nObjectives (EcoQOs) for each issue. Since 2000, this scheme has been developed and\r\npiloted in the North Sea. Fish Communities is the fifth in the list of Ecological Quality Issues,\r\nand is considered to be one of three community-level issues. In addressing concerns\r\nregarding anthropogenically induced change in fish communities therefore, a communitylevel\r\napproach has been widely adopted. This has generally involved the application of\r\nunivariate metrics to groundfish survey data to quantify change in various aspects of the\r\ncommunity\u2019s composition, structure and function. The element of Ecological Quality for the\r\nNorth Sea fish community focuses on \u201cchanges in the proportion of large fish and hence the\r\naverage weight and average maximum length of the fish community\u201d, thus clearly identifying\r\nthe need for a community size composition metric as the \u201cindicator\u201d on which to base an\r\nEcoQO for the \u201cfish community\u201d Ecological Quality Issue. The chosen metric, the Large Fish\r\nIndicator (LFI) was eventually defined as \u201cthe proportion by weight of fish greater than 40cm\r\nin length\u201d, based on ICES first quarter (Q1) International Bottom Trawl Survey (IBTS) data.\r\nThe LFI was intended to be an indicator of the \u201cgeneral health\u201d of the demersal fish\r\ncommunity. Indeed DEFRA have adopted the LFI as a means of monitoring change in the\r\ntrophic structure of demersal fish communities, since in marine systems, ontogenetic change\r\nand inter-specific variation in diet is so strongly linked to predator body-size. However, other\r\naspects of the composition, structure and functioning of fish communities, such as\r\nabundance, biomass, productivity, species richness, species diversity and mean life-history\r\ntrait composition, can also be summarised using univariate metrics. Any one, or all, of these\r\nalternative metrics might also be considered to be indicative of the \u201chealth\u201d of fish\r\ncommunities. The LFI was chosen ahead of these alternative metrics because it was\r\nbelieved to be particularly sensitive to variation in fishing pressure, and therefore to indicate\r\ndirectly the effect of fishing on the state of the fish community. But this raises the question\r\nas to whether one indicator is sufficient to inform on the general health of the demersal fish\r\ncommunity, or is a suite of indicators necessary in order to provide information on various\r\ndifferent aspects of a community\u2019s composition, structure and function? In this assessment\r\nof the state of the demersal community in UK waters, fifteen univariate metrics are applied to\r\ngroundfish survey data to quantify changes in five main aspects of community composition,\r\nstructure and function: abundance/biomass/productivity; size composition; species richness;\r\nspecies diversity; and life-history trait composition (Table 1).\r\nBottom trawl surveys have been carried out as part of the traditional annual fisheries\r\nmanagement process for several decades. These surveys routinely provide point estimates\r\nof the abundance at length of each species sampled; therefore providing the ideal data sets\r\nfor the application univariate community metrics. Many of these surveys have run for two or\r\nthree decades now, providing appropriate time series with which to evaluate changes in the\r\ncomposition, structure and function of fish communities. Furthermore, most coastal\r\nEuropean nations have been involved in survey activity, providing data from most western\r\ncontinental shelf waters. In this assessment, otter trawl survey data is analysed to assess\r\nchanges in the demersal fish communities present in the sea area that constitutes the UK\u2019s\r\nExclusive Economic Zone (EEZ). The UK EEZ has been divided into nine principal subregions\r\n(Figure 1), and assessment of the state of the fish community in each sub-region\r\nwas required. However, one of the sub-regions, the Scottish Continental Shelf, straddled the\r\nboundaries between OSPAR Regions II and III, and between ICES area IV and VI.\r\nConsequently, none of the groundfish surveys, which are normally aligned with the ICES\r\ndesignated marine regions, covered the entire Scottish Continental Shelf sub-region. A\r\nsingle assessment for the Scottish Continental Shelf was therefore not possible. The subregion\r\nhad to be further sub-divided in line with the data available for analysis, and three\r\nAssessment of the \u201cState\u201d of the Demersal Fish Communities in UK Waters\r\n2\r\nseparate assessments made for the southwestern and northeastern sectors of this large\r\narea (Figure 1).\r\nTo assess the state of the demersal fish community and make a judgement on the changes\r\nobserved, it was necessary to decide what constituted \u201cbeneficial\u201d and \u201cdetrimental\u201d change.\r\nEmphasis is generally placed on conserving and restoring biodiversity; implying that declines\r\nin species diversity (both richness and evenness) are detrimental. The converse was\r\ntherefore also assumed to hold. The life-history trait composition responses of populations\r\nand communities to anthropogenically raised levels of mortality have recently received\r\nconsiderable attention. Declines in population age and length at maturity, decreased\r\ncommunity average ultimate body length, and increased in community average growth rate\r\nare all considered to be detrimental consequences. Improved management would therefore\r\nbe expected to induce the opposite, beneficial trends.\r\nEstablished population dynamics theory predicts that size-related fishing mortality reduces\r\nthe mean size and proportion of large fish in exploited populations (including non-target\r\nspecies taken as by-catch). This concept underpins development of the LFI as the basis for\r\nthe OSPAR North Sea Fish Community EcoQO. Reductions in LFI are therefore considered\r\ndetrimental. Changes in LFI were generally inversely correlated with changes in the\r\nabundance, biomass and (growth) productivity of the fish community, implying that declining\r\nabundance, biomass and productivity are indicative of a fish community returning to a more\r\nnatural undisturbed state. The von Bertalanffy growth equation makes it clear that larger\r\nfish, closer to their ultimate body length (L8), have lower daily specific growth rates. Large\r\nfish exert a strong predation loading on small fish abundance. Since trophic transfer\r\nefficiency is around 10%, every kg of production by larger fish requires 10kg of production in\r\ntheir smaller prey fish populations. Specific growth rates among smaller fish are\r\napproximately twice that of larger fish, so 5kg of prey fish are required to support every kg of\r\nlarger fish. Reductions in the abundance of larger fish, with the consequent reduction in\r\npredation loading on smaller prey fish, would therefore tend to result in a rapid increase in\r\nthe abundance and biomass of small fish; a typical trophic cascade effect.\r\nIn assessing the state of the demersal fish community, two questions were addressed.\r\nFirstly, how has the state of the community changed over the last decade, from 1999 to\r\n2008; the period of particular interest to the current report. Secondly, how does the state of\r\nthe community over the period 2004 to 2008 (i.e. now) compare with that prevalent during\r\nthe eight-year period when data were first available for analysis. Detrimental trends were\r\nassigned a \u201cred\u201d colour code and beneficial trends \u201cgreen\u201d (e.g. Table 2). Where no\r\ndiscernable trend was apparent, an \u201corange\u201d colour code was applied. Five separate\r\naspects of composition, structure and function of the demersal fish community were\r\nconsidered, and a judgement was made based on the trends observed in the 15 univariate\r\ncommunity metrics applied to the groundfish survey data. Linear regression was used to\r\nmake an assessment of metric trends over the last decade. In comparing the current\r\nsituation with the earlier \u201creference period\u201d, mean metric values over the period 2004 to 2008\r\nwere determined and the assessment was scored red or green depending on whether the\r\nrecent mean value differed by more than one standard deviation either side of the mean\r\nvalue determined for the earliest possible \u201creference period\u201d.",
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        "description": "The MEDIN portal contains information about 19493 marine datasets from over 600 UK organisations. Metadata are an enduring resource and contact details are publicly available for a long time. \r\n\t\tPlease contact us (enquiries@medin.org.uk) if you find your contact details on the MEDIN portal and do not consent to this. \r\n\t\tYou can now use our GitHub repository to report issues or access related documents. Metadata records are updated daily and were last updated 2026-04-19. Record deletion takes place weekly and the latest occurred 2026-04-12."
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