Impacts of a novel shellfishing gear on macrobenthos in a marine protected area: pump-scoop dredging in Poole Harbour, UK

Abstract

-Understanding the impact of bottom-fishing gears at various scales and intensities on habitats and species is necessary to inform management. In Poole Harbour, UK, a multiple use marine protected area, fishermen utilise a unique "pump-scoop" dredge to harvest the introduced Manila clam Ruditapes philippinarum. Managers need to balance the socio-economic benefits of the fishery with ecological concerns across the region, which has required a revision of by-laws that include both spatial and temporal measures. Within an operational fishery, we used a Before-After-Control-Impact sampling design to assess the impacts of pump-scoop dredging on benthic physical characteristics and community structure in an area where there was no dredging, an area newly opened to dredging and an area subject to high levels of historic dredging. A sampling grid was used in each area to best capture any fishing effort in the newly opened area. Core samples were taken to a depth of 30 cm within intertidal mudflats. A significant loss of fine sediments was observed in the site subject to high intensity dredging and a significant change in community structure also occurred in both dredged sites throughout the study period. In the newly opened site this was characterised by a relative increase in species richness, including increased abundance of annelid worms, notably Hediste diversicolor and Aphelochaeta marioni and a decline in the abundance of the bivalve mollusc Abra tenuis. These changes, albeit relatively small, are attributed to physical disturbance as a direct result of pump-scoop dredging, although no difference in the classification of the biotope of the site was observed. This is of particular interest to managers monitoring site condition within areas under the new bylaws as the Manila clam is spreading to other protected estuaries in the region.

Detecting ecological thresholds and tipping points in the natural capital assets of a protected coastal ecosystem

“…number of licenced clam boats) was used as a proxy for fishing pressure (Piet et al, 2006). As fishermen in Poole Harbour utilise a unique "pump-scoop" dredge to harvest the Manila clam (95% of catch is typically clam landings; Clarke et al, 2017) fleet capacity is likely an effective pressure indicator that describes the impact induced by fishing activities on the system. Annual stock surveys for Manila clam were obtained for three sites in the harbour: Arne Bay, Seagull Island and Round Island.…”

“…Nonetheless, such financial benefits must be balanced against the potential problems of removing commercial quantities of Manila clams from Poole Harbour. For example, there is evidence that the use of pump-scoop dredges can have significant impacts on the benthic community by reducing fine sediment and some prey species available to wintering birds (Clarke et al, 2017). Managing fisheries and aquaculture development in a way that does not lead to deleterious ecosystem change is considered as a serious governance challenge not just in Poole Harbour but in many marine protected areas around the world (Edgar et al, 2014).…”

Temporal and Spatial Trends in Benthic Infauna and Potential Drivers, in a Highly Tidal Estuary in Atlantic Canada

“…Since coastal waters can be a focus for human activities, infaunal communities are affected by a range of anthropogenic stressors, including fishing (Clarke et al 2018 ); dredging and dumping of dredged material (Cooper et al 2011 ; Donázar-Aramendía et al 2018 ); organic enrichment due to discharge of domestic sewage and agricultural run-off (Zeldis et al 2020 ); and sediment contamination with heavy metals, polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and other organic and inorganic substances (Birch 2000 ; Sprovieri et al 2007 ; Ozcan et al 2013 ). This is especially true near ports and harbours, where intense human activity can lead to highly contaminated sediments (Martínez-Lladó et al 2007 ; Gibert et al 2009 ).…”

Population dynamics of a commercially harvested, non-native bivalve in an area protected for shorebirds: Ruditapes philippinarum in Poole Harbour, UK

“…The geographic range of the Manila clam Ruditapes philippinarum (Adams and Reeve, 1850) has 33 been expanding since the early 20 th century, facilitated by aquaculture and fishing activities due to 34 its high food value (Humphreys et al, 2015;de Montaudouin et al, 2016a). In many European 35 estuaries and lagoons the Manila clam has replaced the native clam Ruditapes decussatus (Bidegain 36 and Juanes 2013) and represents a key target species for both recreational and commercial fishers 37 (Bidegain and Juanes, 2013; Robert et al, 2013;Beck et al, 2015;Clarke et al, 2018). The species is 38 now one of the most commercially valuable bivalves globally (Astorga 2014).…”

“…There is therefore little evidence that the introduction and naturalisation 75 of R. philippinarum has displaced native bivalve species within the harbour, rather the species 76 comprises a newly exploitable food item for molluscivorous bird predators (Hulscher, 1996;Caldow 77 et al, 2007). The species now supports a significant local fishery, harvested along with the common 78 cockle Cerastoderma edule from intertidal and shallow subtidal areas by a novel 'pump-scoop' 79 dredge (Clarke et al, 2018), and provides an additional food source for the oystercatchers, reducing 80 5 overwinter mortality within the harbour (Caldow et al, 2007), which is a protected area under the 81…”