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

Abstract

Addressing growing threats of overexploitation to the world's oceans is especially challenging in the High Seas, where limited data and international jurisdiction make it difficult to determine where and when conservation measures are necessary. Of particular concern are vulnerable marine ecosystems (VMEs)-special habitats on the seafloor that are highly sensitive to disturbance and slow to recover. To ensure the long-term conservation and sustainable use of marine resources, regional fisheries management organizations are committed to identifying the locations of VMEs and responding to prevent significant adverse impacts (SAIs). For over 50 years, Cobb Seamount-a shallow underwater volcanic mountain in the Northeast Pacific Oceanhas been commercially fished by multiple nations using various types of gear. Here we have assimilated data from fisheries records and a recent visual survey on the seamount. Our findings show a variety of habitat-forming emergent biological structures widely distributed on Cobb Seamount and generally depth-stratified into high-density assemblages (≥1 m −2). Our spatial analyses show that fishing has also been widely distributed, overlapping the habitat of the biological structures. We found fewer coldwater corals, sponges, and other biological structures in areas with higher recent fishing effort and documented evidence of fishing impacts, such as extensive mats of coral rubble and a high abundance of derelict fishing gear entangled with dead or damaged organisms. Based on the average density of "lost" gear (2,785 ± 1,003 km −2), we can confidently estimate that hundreds of thousands of items of derelict fishing gear are currently entangled with the seafloor of Cobb Seamount and that these pose an ongoing threat to biological structures, the biogenic habitats they create, and the species they support. Such impacts can persist for decades or centuries to come. This study contributes and discusses new information on the condition and distribution of biological structures, VME indicator taxa, physically complex biogenic ecosystems, and human impacts on Cobb Seamount. These data will be necessary to identify the location(s) of potential VMEs and SAIs on this heavily fished seamount in the High Seas.

The Fate of Deep-Sea Coral Reefs on Seamounts in a Fishery-Seascape: What Are the Impacts, What Remains, and What Is Protected?

“…On the Tasmanian continental slope, as has been observed elsewhere in the deep sea (Clark et al, 2016b;Du Preez et al, 2020), the depth distribution of historical bottom trawling strongly overlaps the depth ranges of scleractinian coral reef (Figures 4, 10). At the regional scale, some 300 nm from Sharks tooth to St Helens, our data and extrapolation indicate there is a range of strongly depth-related impacts on individual seamounts: heavy (31 seamounts), moderate (10), light (18) with no impact observed on 62 (mostly inferred on seamounts peaking at >1,500 m), and 70 not assessed.…”

“…Accumulations of coral rubble in the vicinity of deep-sea coral reefs are commonly attributed to trawling. While this is not always substantiated, attribution in many cases is based on compelling images of lost gear or gear marks amongst scleractinian rubble (Fosså et al, 2002;Hall-Spencer et al, 2002;Clark and Dunn, 2012;Baco et al, 2020;Du Preez et al, 2020). In our data, extensive accumulations of coral rubble on shallow seamounts (those peaking in <950 m depths) were interpreted as fragmentation of reef matrix due to recent and repeated trawling.…”

Global Causes, Drivers, and Prevention Measures for Lost Fishing Gear

“…Abandoned, lost or otherwise discarded fishing gear (ALDFG) represents a considerable component of global marine pollution, with adverse impacts to fishers, the seafood industry, coastal communities, and marine wildlife and habitats (Macfadyen et al, 2009;Richardson et al, 2019b). When fishing gear is abandoned, lost or discarded, it can sink to the seafloor where it can damage benthic habitats and organisms through abrasion, dragging, and entanglement (Pham et al, 2014;National Oceanic and Atmospheric Administration Marine Debris and Program, 2016;Du Preez et al, 2020). It may also drift with currents where it has the potential to interact with fish and other marine wildlife (Wilcox et al, 2013;Lebreton et al, 2018;Stelfox et al, 2020), provide habitat for invasive species (Miralles et al, 2018;Rech et al, 2018), and act as a hazard to navigation and safety at sea (Macfadyen et al, 2009;Hong et al, 2017).…”

Rapid deep ocean deoxygenation and acidification threaten life on Northeast Pacific seamounts

“…Episodic human activities could also be harmful. Union and Dellwood (<1,500 m) were both previously fished using bottom‐contact gear (DFO, 2019), which will have reduced densities of vulnerable habitat‐forming taxa by scouring (Du Preez, Swan, & Curtis, 2020), but presumably not to the point of changing their overall depth distributions.…”