Effects of experimental otter trawling on the macrofauna of a sandy bottom ecosystem on the Grand Banks of Newfoundland

) than at disturbed sites (30 to 52 kcal m -2 yr -1 ). The soft-bodied tube-building polychaete Thelepus cincinnatus dominated production at the undisturbed site, while hard-shelled bivalve molluscs Astarte spp. and P. magellanicus were prevalent at the disturbed site. Mobile fishing gear disturbance has a conspicuous effect on benthic megafaunal production in this hard-bottom habitat. Cessation of mobile fishing has resulted in a marked increase in benthic megafaunal production. These findings should help fishery managers to gauge the costs and benefits of management tools such as area closures and low-impact fishing gears.

Section: Discussionsupporting

confidence: 60%

Section: Discussionsupporting

confidence: 58%

Mobile fishing gear reduces benthic megafaunal production on Georges Bank

Hermsen¹,

Collie²,

Valentine³

2003

“…Veale et al 2000, Jennings et al 2001b, Kenchington et al 2001, Thrush et al 2001, Hermsen et al 2003. Here, we found a significant negative relationship between trawling and production of the whole infaunal community.…”

Section: Discussionsupporting

confidence: 53%

Effects of fishing disturbance on benthic communities and secondary production within an intensively fished area

Reiss¹,

Greenstreet²,

Sieben³

et al. 2009

Demersal fishing alters seabed habitats and affects the structure and functioning of benthic invertebrate communities. At a critical level of disturbance, such communities may approach an equilibrium disturbed state in which a further increase in disturbance has little additional impact. Such arguments have been used to suggest that an ecosystem approach to fisheries management (EAFM) should protect lightly fished areas and deflect fishing activity into areas that are already intensively fished. In this study, the effects of variation in fishing disturbance on the secondary production, species diversity, abundance, biomass, and community structure of benthic infauna were examined in a region of the German Bight (North Sea) that has been intensively trawled for decades. Variation in fishing disturbance across the study area was determined using automated position registration and vessel monitoring through satellite. Even in such a heavily fished area, linear regression analyses revealed that biomass, species richness, and production decreased significantly with increasing fishing intensity. Although redundancy analyses (RDA) showed that sediment characteristics were influential in determining the structure of the infauna community, partial RDA revealed that fishing continued to have an impact on community structure in terms of biomass. These results suggest that, in implementing an EAFM, managers will need to consider the possibility that, even in areas with high chronic fishing disturbance, further increases in fishing activity may still cause additional damage to benthic invertebrate communities.

“…In practice, high fishing intensities can reduce colonial epifaunal richness and biomass (Veale et al 2000), and can be correlated with shifts in assemblages from those dominated by large, erect, rigid colonies to those with more flexible, runner-like, or encrusting growth forms (Pitcher et al 2000, Bradshaw et al 2001, Bremner et al 2003, Henry & Kenchington 2004b. Bottom fishing can also alter seabed physical characteristics, such as sediment properties , Kenchington et al 2001, microtopography (Caddy 1973, Thrush et al 1995, Currie & Parry 1996) and substrate stability (Caddy 1973, Black & Parry 1994, Freese et al 1999, while resuspending sediments (Churchill 1989, Jennings & Kaiser 1998. These physical characteristics affect recruitment and community structure of colonial epifauna (e.g.…”

Section: Introductionmentioning

confidence: 99%

Impacts of otter trawling on colonial epifaunal assemblages on a cobble bottom ecosystem on Western Bank (northwest Atlantic)

Henry¹,

Kenchington²,

Kenchington³

et al. 2006

Colonial epifauna are an important component of benthic communities, providing structural complexity at scales of millimetres to metres. Many are sessile, emergent and fragilecharacteristics which render them vulnerable to disturbances associated with bottom fishing. Many also have impressive abilities to rapidly regenerate both sexually and asexually and, consequently, the ultimate results of impacts of physical disturbance are difficult to predict. We analysed the effects of 3 yr of pulsed experimental otter trawling, following an asymmetrical before-after-control-impact design, on grab-sampled colonial epifauna. Our study site was on a cobble seabed on the Scotian Shelf in a formerly important fishing ground which had seen no disturbance by mobile fishing gears for 10 yr. The number of taxa, total biomass, the biomass of component major taxa (hydroids, bryozoans, sponges, tunicates, soft corals) and the community composition were analysed for single-year and cumulative effects. The study site had a rich colonial fauna containing at least 53 taxa, the majority of which were hydroids. The small vase sponge Scypha ciliata, the leafy bryozoans Dendrobeania spp. and the hydroids Symplectoscyphus spp. were the most frequent, occurring in > 70% of the samples. Significant inter-annual differences at control sites were observed. The number of taxa, total biomass and hydroid biomass increased over the study period, with associated changes in community composition. Short-term effects of trawling were detected as decreases in the number of taxa per sample, total biomass and total hydroid biomass across the trawling events, although these trends were non-significant after Bonferroni adjustment. No cumulative effects from the pulsed trawling were detected, and colonial species assemblages on control and impacted lines were similar at the end of the experiment. While some of the tests for trawling effects were statistically weak, it is certain that any effects were small relative to natural inter-annual change.