No more detectable fishing effect on Northern Gulf of St Lawrence benthic invertebrates

Abstract

Trawling has been reported worldwide to alter seabed structure, and thus benthic habitats and ecosystems. Usually, a decrease in species richness and biomass is observed, and community structure is modified towards more opportunistic species. The Gulf of St Lawrence (Canada) has been intensely exploited since the 17th century, including net, longline, dredge and trawl fishing activities. Recently, the collapse of groundfish stocks induced a shift in fishing practices toward shrimp trawling, which is currently considered a sustainable fishing activity in the region. However, no long-term study has evaluated the potential effects of trawling disturbances on benthic mega-invertebrates. We investigated whether shrimp trawling had long- (ca. 20 years), mid- (ca. 10 years), and short-term (ca. 4 years) impacts on benthic mega-invertebrate taxa richness, biomass, and community structure. Scientific and fishery trawling data analyses showed that no significant long-, mid-, or short-term effect was detected on taxa richness. Significant but weak effects on biomass and community structure were detected at the mesoscale, i.e. at the scale of fishing grounds. In this long-exploited ecosystem, we suggest that a critical level of disturbance was attained by the first gear passages, which occurred decades ago and had irreversible impacts on the seabed by removing vulnerable taxa and structures that provided three-dimensional habitats. It is likely that benthic communities have subsequently reached a disturbed state of equilibrium on which current trawling disturbance has limited or no further impacts.

Signatures of the collapse and incipient recovery of an overexploited marine ecosystem

“…However, it is uncertain whether the Newfoundland shelf ecosystem will ever fully return to its previous state. Warming temperatures, species interactions and selection for smaller bodied individuals driven by centuries of fishing pressure may direct the community towards a new dynamical regime [ 15 , 35 , 62 , 63 ]. The nearby Grand Banks groundfish community has also shown a similar pattern of rapid compositional rearrangement and return from 1990 until present [ 24 ], but as that study did not extend to the time period prior to the collapse it is difficult to judge the extent to which that community has returned to its prior state.…”

Comparing environmental metabarcoding and trawling survey of demersal fish communities in the Gulf of St. Lawrence, Canada

“…Trawling is the most common fishing technique in deep‐sea waters, but it is known to damage the seabed and benthic communities (Clark et al., 2016; Kaiser, Collie, Hall, Jennings, & Poiner, 2002; Thurstan, Brockington, & Roberts, 2010; Tillin, Hiddink, Jennings, & Kaiser, 2006; Trenkel et al., 2019; Yesson et al, 2017). However, recent shifts in shrimp trawling with higher gear selectivity have decreased certain impacts on benthic communities (Moritz et al., 2015). Spatial analysis of trawling effects in Canadian waters of the Atlantic and Pacific Oceans has demonstrated benthos disturbances due to the interaction of fishing gears with the bottom, and its impact on groundfish bycatch (Kulka & Pitcher, 2001).…”

Detection of Ecological Thresholds and Selection of Indicator Taxa for Epibenthic Communities Exposed to Multiple Pressures

“…Several studies have examined the impacts of environmental pressures on the distribution of benthic communities in the EGSL (Bourget et al, 2003;Lévesque, 2009;Belley et al, 2010;Moritz et al, 2013Moritz et al, , 2015. Current trawl fisheries in the EGSL appear to have very little impact on epibenthic communities (Moritz et al, 2015). Depth, bottom current, temperature, and oxygen saturation have been shown to influence the distribution of benthic communities.…”