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Linking Demersal Fish to Habitat: Scales, Patterns, Future Directions

03 June 2012

Adoption of the ecosystem approach to fisheries management relies on recognition of the link between fish and other components of the ecosystem, namely their physical and biological habitat. However, identifying the habitat requirements of marine fishes and hence determining their distribution in space and time is scientifically complex, writes Andrew Johnson, Bangor University.

Through analysing the methodologies and findings of research on temperate, demersal fish habitat requirements to highlight the main developments in this field and to identify potential shortfalls.

Many studies were undertaken over large spatial scales (‡100s km2) and these generally correlated abundances of fish to abiotic variables. Biological variables were accounted for less often.

Small spatial scale (£m2), experimental studies were comparatively sparse and commonly focused on biotic variables. Whilst the number of studies focusing on abiotic variables increased with increasing spatial scale, the proportion of studies finding significant relationships between habitat and fish distribution remained constant. This mismatch indicates there is no justification for the tendency to analyse abiotic habitat variables at large spatial scales.

Conclusion

Determining the habitat requirements of demersal fish species is inherently difficult because of the complex nature of marine ecosystems, the multiple factors affecting fish–habitat associations, the range of scales over which they act and the general difficulties of sampling marine habitats. Defining fish–habitat relationships will, however, be one of the necessary steps towards the advocated ecosystem-based approach to fisheries management and the sustainable exploitation of demersal fish stocks.

Many developments in techniques and technologies show promise in elucidating the complex interactions between demersal fishes and their habitat. The successful application of such developments will, however, strongly rely on the quality of the data used combined with understanding of the fundamental ecology of the systems and species under study (Austin 2007). Where possible, it will therefore be advantageous to test habitat variables under controlled experimental conditions (i.e. small-medium spatial scales), building results from such studies into larger scale models.

Our analysis highlights some important trends in the field of demersal fish habitat determination. The reasons behind the focus on larger scales are no doubt a result of a combination of factors. It is, however, clear that to advance the field, there should be a move towards the investigation of abiotic variables at smaller spatial scales as well as increased attention to the analysis of biotic habitat variables over all spatial scales of study.

This will help describe distributions determined by abiotic habitat variables that may act over small spatial scales not previously considered and allow biotic-based causal relationships to be better explained. It will therefore be necessary to invest in the implementation of more, smaller spatial scale data collections or alternatively increase the resolution of larger spatial scale data sets. Work investigating the power of monitoring surveys to detect trends in abundance (e.g. Blanchard et al. 2008) will therefore prove invaluable in the design of future studies and surveys.

Defining temporal aspects of habitat will also prove valuable in advancing ecological understanding of the species under study. The inclusion of longer time scales and the consideration of temporal differences in habitat use may also provide important information on the cumulative effects of human-induced impacts, the overall status and recovery of impacted systems and increase capabilities to predict future change of the species or system under study (Hewitt et al. 2001). We argue that through attention to the areas highlighted herein, along with more holistic definitions of habitat, researchers are likely to be better equipped to inform management at a range of spatial and temporal scales.

Further Reading

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June 2012

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