Cook R et al. (2013), The substantial first impact of bottom fishing ...

ECB-ART-50088

PLoS One 2013 Jan 01;88:e69904. doi: 10.1371/journal.pone.0069904.

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The substantial first impact of bottom fishing on rare biodiversity hotspots: a dilemma for evidence-based conservation.

Cook R , Fariñas-Franco JM , Gell FR , Holt RH , Holt T , Lindenbaum C , Porter JS , Seed R , Skates LR , Stringell TB , Sanderson WG .

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This study describes the impact of the first passage of two types of bottom-towed fishing gear on rare protected shellfish-reefs formed by the horse mussel Modiolus modiolus (L.). One of the study sites was trawled and the other was scallop-dredged. Divers collected HD video imagery of epifauna from quadrats at the two study sites and directed infaunal samples from one site. The total number of epifaunal organisms was significantly reduced following a single pass of a trawl (90%) or scallop dredge (59%), as was the diversity of the associated community and the total number of M. modiolus at the trawled site. At both sites declines in anthozoans, hydrozoans, bivalves, echinoderms and ascidians accounted for most of the change. A year later, no recovery was evident at the trawled site and significantly fewer infaunal taxa (polychaetes, malacostracans, bivalves and ophuroids) were recorded in the trawl track. The severity of the two types of impact reflected the undisturbed status of the habitats compared to previous studies. As a 'priority habitat' the nature of the impacts described on M. modiolus communities are important to the development of conservation management policy and indicators of condition in Marine Protected Areas (EU Habitats Directive) as well as indicators of 'Good Environmental Status' under the European Union Marine Strategy Framework Directive. Conservation managers are under pressure to support decisions with good quality evidence. Elsewhere, indirect studies have shown declines of M. modiolus biogenic communities in fishing grounds. However, given the protected status of the rare habitat, premeditated demonstration of direct impact is unethical or illegal in Marine Protected Areas. This study therefore provides a unique opportunity to investigate the impact from fishing gear whilst at the same time reflecting on the dilemma of evidence-based conservation management.

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	Figure 1. Study sites.Stars indicate Modiolus modiolus bed study sites north of the Point of Ayre (Isle of Man) and north of the Lleyn Peninsula in Caernarfon Bay (Wales).
	Figure 2. Details of study sites.(A) Map of fixed quadrat locations (dotted squares) on raised ridges (grey polygons) at Point of Ayre study site. Dotted ellipses indicate infaunal sample areas for impacted and control treatments. Two trawl door marks in 2008 are indicated by dashed lines. One trawl door mark in (A) is visible in the video-grab image (B) where the more extreme impact (compared to the net) in the path of the trawl door is also illustrated with dashed lines. The numbers “7” and “3” in (A) are quadrat numbers refered to in Figure 3 and Discussion (respectively). Metal waypoint pins enabled navigation around the site. (C) Side scan sonar image from 2012 at the study site off the north of the Lleyn Peninsula: marks from two gangs of scallop dredges are visible across the surface of the Modiolus modiolus ridges.
	Figure 3. Mosaic quadrat images of quadrats.Quadrat 7 (indicated in Figure 2) from Point of Ayre in 2007 (A) and 2009 (B). (C) Unimpacted quadrat and (D) impacted quadrat from N. Lleyn Peninsula in 2012. Numbers indicate conspicuous epifauna: 1 Alcyonium digitatum, 2 Modiolus modiolus, 3 Echinus esculentus, 4 Ophiothrix fragilis, 5 Antedon bifida.
	Figure 4. MDS plot showing the relationship between impacted and unimpacted epifaunal communities.(A) Point of Ayre. Dummy variable (present everywhere) used to create coherence in low abundance [impacted] data (see (36). (B) North of the Lleyn Peninsula.
	Figure 5. Reductions in epifauna and infauna following bottom-towed fishing gear.Total number of individuals (A), upright emergent epifauna (B) and numbers of M. modiolus (C) recorded on impacted and unimpacted 0.25×0.25 m video quadrats off Point of Ayre(PoA) and North Lleyn Peninsula (nLP). (D) Abundance of infaunal taxa contributing the most to the dissimilarities between impacted and unimpacted treatments at the PoA site (SIMPER). Box plots represent inter-quartile range, median, maximum and minimum values. The effect of physical impact was significant at α of 0.05 for all measures except M. modiolus abundance at nLP (Table 1).

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