Little Evidence of Benthic Community Resilience to Bottom Trawling on Seamounts After 15 Years

Abstract

The resilience and recovery dynamics of deep-sea habitats impacted by bottom trawling are poorly known. This paper reports on a fishing impact recovery comparison based on four towed camera surveys over a 15-year period (2001-2015) on a group of small seamounts on the Chatham Rise, east of New Zealand, on which pre-disturbance benthic communities are dominated by thicket-forming scleractinian corals. The six seamounts studied encompass a range of trawl histories, including one with high and persistent levels of trawling throughout the survey period, two with intermittent and intermediate levels of trawling, two which were low/untrawled, and one, 'Morgue', which was closed to trawling in 2001, having been heavily trawled up to that point. Still photographs from all surveys were analyzed for the identification and abundance of all visible benthic fauna with effort made to ensure consistency of data among surveys. Because increases in image resolution and quality over time resulted in a persistent trend of increasing abundances, analyses were concentrated on comparisons among seamounts within surveys and how these relationships changed with time. The abundance, species richness, and diversity of benthic communities were higher on low/untrawled seamounts than on those that had been trawled. Multivariate community structure showed similar patterns at each survey point, the low/untrawled seamounts being strongly dissimilar to the persistently trawled seamount, with the others ranged between these extremes, broadly in accordance with their cumulative trawl histories. Community structure on the persistently trawled seamount was less variable than on the other seamounts throughout the study period, possibly because of regular 're-setting' of the community by disturbance from trawling. Although there was some variability in results between whole seamount and summit sector analyses, in general communities on Morgue remained similar to those on the persistently trawled seamount, showing little indication of steps toward recovery to its pre-disturbance state following its closure. These results indicate low resilience of benthic communities on the seamounts to the effects of bottom trawling.

Cold-Water Corals and Other Vulnerable Biological Structures on a North Pacific Seamount After Half a Century of Fishing

“…Even after recolonization, the rate of ecosystem recovery is likely to be on the order of decades to centuries for many of the slow-growing biological structures we observed on Cobb Seamount (Roberts and Hirshfield, 2004;Murillo et al, 2011;Clark et al, 2019). Some scallops and crinoids are estimated to live decades (MacDonald et al, 1991;Murillo et al, 2011), glass sponges can live hundreds of years (Samadi et al, 2007), and sea fans can grow as little as a centimeter or two per year (Andrews et al, 2002(Andrews et al, , 2009 and live thousands of years (Roark et al, 2006;Rogers et al, 2007).…”

Habitat Features and Their Influence on the Restoration Potential of Marine Habitats in Europe

“…Cold-water coral habitats are sensitive to a range of human activities, including commercial bottom fisheries, hydrocarbon exploration and extraction, and if developed, deep-sea mining (Ramirez-Llodra et al, 2011;Ragnarsson et al, 2017). The bottom fisheries are considered to be the major pressure, often resulting in the removal of entire communities, with little evidence of recovery (Clark et al, 2019). An important challenge in the restoration of deep-sea coral habitats is the remoteness of these habitats, which makes restoration actions highly dependent on technological means (e.g., large ships and ROVs), being costly in comparison with shallow-water habitats (van Dover et al, 2014;Da Ros et al, 2019).…”

Sustainability in Deep Water: The Challenges of Climate Change, Human Pressures, and Biodiversity Conservation

“…The orange roughy fisheries have been depleted, seamount after seamount, although apparently sustainable populations have been identified (Doonan et al, 2015). Additionally, and perhaps more importantly, the harvest methods of bottom trawling and even longlining can destroy the three-dimensional structure created by habitat-forming species such as corals, sponges, and bryozoans (Clark et al, 2015(Clark et al, , 2019. Growing energy demands have led to increasingly deeper discovery and extraction of oil and gas, with wells now present to 3,500 m water depth (Merrie et al, 2014).…”