Defining thresholds of sustainable impact on benthic communities in relation to fishing disturbance

Abstract

While the direct physical impact on seabed biota is well understood, no studies have defined thresholds to inform an ecosystem-based approach to managing fishing impacts. We addressed this knowledge gap using a large-scale experiment that created a controlled gradient of fishing intensity and assessed the immediate impacts and short-term recovery. We observed a mosaic of taxon-specific responses at various thresholds. The lowest threshold of significant lasting impact occurred between 1 and 3 times fished and elicited a decrease in abundance of 39 to 70% for some sessile epifaunal organisms (cnidarians, bryozoans). This contrasted with significant increases in abundance and/or biomass of scavenging species (epifaunal echinoderms, infaunal crustaceans) by two to four-fold in areas fished twice and more. In spite of these significant specific responses, the benthic community structure, biomass and abundance at the population level appeared resilient to fishing. Overall, natural temporal variation in community metrics exceeded the effects of fishing in this highly dynamic study site, suggesting that an acute level of disturbance (fished over six times) would match the level of natural variation. We discuss the implications of our findings for natural resources management with respect to context-specific human disturbance and provide guidance for best fishing practices.

Capturing threshold responses of marine benthos along gradients of natural and anthropogenic change

“…Individual studies often fail to detect trawling‐specific community changes in areas exposed to high levels of natural hydrodynamic disturbance. This has led to the conclusion that natural and trawling‐induced physical disturbance affect benthic communities in comparable ways and that trawling disturbance in hydrodynamically active environments causes limited additional changes in benthic communities (Lambert et al, 2017; Lengkeek & Bouma, 2010; Van Denderen et al, 2015). Attempts to determine how consistent and applicable these study‐specific conclusions are at larger spatio‐temporal scales have been hampered by the lack of reliable estimates of the historic trawling effort and therefore relied on meta‐analyses of existing studies (e.g.…”

Estimating sensitivity of seabed habitats to disturbance by bottom trawling based on the longevity of benthic fauna

“…Lambert et al. () showed the seabed biota in the shallow waters of the Cardigan Bay, on the west coast of Wales, to be resilient to scallop dredging. This area has a relative low tidal shear stress but is exposed to strong wave disturbance.…”

“…This implies that in areas where wave-induced shear stress is important, such as the Dogger Bank in the North Sea, habitat sensitivity is overestimated. Lambert et al (2017) showed the seabed biota in the shallow waters of the Cardigan Bay, on the west coast of Wales, to be resilient to scallop dredging. This area has a relative low tidal shear stress but is exposed to strong wave disturbance.…”

Effects of Benthic Protection Extent on Recovery Dynamics of a Conceptual Seafloor Community

“…In addition, recovery can be highly dependent on habitat type, for example, commercially important fish species such as the common dentex (Dentex dentex), striped red mullet (Mullus surmuletus), forkbeard (Phycis phycis), brown meager (Sciaena umbra) and black scorpionfish (Scorpaena porcus) were only found to increase in abundance and spillover to areas adjacent to protected areas when seagrass (Posidonia oceanica) meadows were present in a study of three Mediterranean MPAs (Forcada et al, 2009). Further, species and functional groups have been shown to have differing sensitivities to a variety of disturbances (Lambert et al, 2017;Lundquist et al, 2018). Here, the type of disturbance was not specified, and it was assumed that in the locations subject to disturbance the functional groups were removed.…”

“…Although the soft sediment bryozoan reef community is a common habitat on the continental shelfs in some parts of the world, e.g., New Zealand (Cranfield et al, 2003), this does not encompass all possible functional groups or benthic subtidal habitat types. The effects of disturbance and subsequent recovery of communities, for example from the physical damage of the fishing gear on the seafloor, vary with habitat type (Kaiser et al, 2006;Lambert et al, 2014Lambert et al, , 2017. In addition, recovery can be highly dependent on habitat type, for example, commercially important fish species such as the common dentex (Dentex dentex), striped red mullet (Mullus surmuletus), forkbeard (Phycis phycis), brown meager (Sciaena umbra) and black scorpionfish (Scorpaena porcus) were only found to increase in abundance and spillover to areas adjacent to protected areas when seagrass (Posidonia oceanica) meadows were present in a study of three Mediterranean MPAs (Forcada et al, 2009).…”