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Report, 2015

Coastal fish community indicators in Sweden - variation along environmental gradients

Bergström, Lena; Olsson, Jens

Abstract

Coastal fish communities have a central role in both environmental and fisheries management. The following report summarizes the current state (2014) of indicator-based approaches in Sweden, to assess the status of coastal fish communities in relation to internationally agreed directives. Coastal fish is not included as a biological quality element in the European Water Framework Directive (WFD), with the exception of transitional waters, but they are included in the European Marine Strategy Framework Directive (MSFD). The report is particularly focused on potential connection points between the MSFD and WFD, in order to facilitate the harmonisation of assessments of different ecosystem components and geographical areas. One important aspect would be to develop geographically based assessment methods, to make better use of data from inventory studies. Key aspects for this development are explored in an example case study, which is based on data with wide geographical coverage. The study addresses general patterns in the distribution of species and indicators among geographical areas in the Baltic Sea, and explores the relationship between indicators and environmental variables. Changes in the indicators were to a large extent attributed to gradients in natural environmental variables, such as temperature, salinity and wave exposure. The results indicate that all these variables should be included in a geographically based assessment. Variables attributed to eutrophication were important for five of the eight studied indicators. This was mainly coupled to a gradient in water transparency. Variables attributed to the mortality of fish were less influential. Possibly, the indicators assessed were not sensitive enough, or the studied gradient was not strong enough for evaluating this pressure. Potentially, also, the explanatory variables that were used were not quantified in an adequate way. A need was seen to update information on the geographical distribution of recreational fisheries and top predators (cormorants, seals), in order to support the assessment of pressure-state relationship, and identify connection points to management measures. All these aspects need to be considered further in the continued indicator development. The environmental variables explained a reasonable part of the observed variation in the data set, although a relatively large part of the variation was left unexplained. The unexplained variability may potentially be reduced by more refined quantitative analyses, which can also explain variation at different geographical scales. The study was also limited by available environmental data. In terms of additional explanatory variables, habitat quality is often expected to have high influence on species abundances, and hence on indicators. However, this variable could not be included, due to a lack of data with sufficient geographical coverage.

Keywords

status assessment, WFD, MSFD, coastal fish, indicators, environment

Published in

WATERS Report
2015, number: 2015:1
Publisher: Havsmiljöinstitutet

Authors' information

Swedish University of Agricultural Sciences, Department of Aquatic Resources
Swedish University of Agricultural Sciences, Department of Aquatic Resources

Associated SLU-program

Coastal and sea areas

UKÄ Subject classification

Ecology
Zoology

URI (permanent link to this page)

https://res.slu.se/id/publ/73772