Reducing the impacts of deep-sea bottom fishing in the high seas on non-target and associated and dependent species, including vulnerable marine ecosystems (VMEs) is an important element of an ecosystem-based approach to fisheries management. This approach is an evolution of fisheries management, which incorporates biodiversity protection and is underpinned by legal frameworks including the United Nations Convention on the Law of the Sea (UNCLOS), United Nations Fish Stocks Agreement (UNFSA)1, the Compliance Agreement2, and the Convention on Biological Diversity (CBD). Soft law mechanisms including the Code of Conduct for Responsible Fisheries, the United Nations General Assembly (UNGA) Sustainable Fisheries Resolutions, and the International Guidelines for the Management of Deep-sea Fisheries in the High Seas (FAO DSF Guidelines; FAO, 2009) provide further guidance to reduce impacts from fishing activities. Most recently, the Aichi Biodiversity Targets under the Convention on Biological Diversity (CBD), and the targets through the Sustainable Development Goal framework, specifically SDG 14 strengthen the framework within which States can take actions to reduce biodiversity loss in marine ecosystems. Deep-sea sponges are important contributors to some VMEs and may be considered VMEs on an individual species basis, either through forming dense single and multi-species patches on the seafloor or as part of diverse deep-sea coral/sponge communities. Deep-sea sponges tend to be long lived and slow growing, and perform a variety of ecosystem functions including habitat provision for associated species in both hard and soft substrates, benthic-pelagic coupling, carbon, nitrogen and silica uptake and cycling, particle deposition, water filtration and removal of bacteria as well as current baffling, and alteration of the surrounding microenvironment. While comparatively less well studied than species in shallow water and on coral reefs, deep-sea sponges play similar roles in the ecosystem. However, much less is known about their growth rates, reproduction and recovery than in shallow water systems.

In response to commitments by States to implement the “calls” included within the UNGA Sustainable Fisheries Resolutions and adhere to guidance provided by the FAO DSF Guidelines, RFMOs have implemented a variety of measures to avoid and mitigate impacts of deep-sea bottom fishing on sponges, including identification of sponges as a potential VME indicator, development of encounter thresholds for sponges that trigger move-on rules for fishing vessels, inclusion of sponges in assessments of significant adverse impacts (SAI) of fishing on seafloor ecosystems, area closures and development of exploratory fishing protocols. In some cases, ecological modelling has been used to predict locations of high concentrations of deep-sea sponges, however the majority of information on locations of sponges has been gathered from bycatch assessment of fishing activities and identification in research trawl surveys, with some information derived from in situ sampling with still cameras and video. The comprehensiveness of management measures varies by RFMO and advice on deep-sea sponges may differ depending on the type of ecosystems, type of fishing and fishing gear used, the level of scientific knowledge and taxonomic expertise, as well as the type of fishing that is occurring.

Methods for ecological risk assessment have been established by some States and RFMOs and the FAO DSF Guidelines provide specific elements to be considered in assessing SAI on VMEs. In a fisheries context, the EAF framework as promoted by FAO also includes a risk assessment procedure as one of the key steps in fisheries management planning (FAO 2003, 2005, 2012). In addition, there are multiple risk assessment frameworks that could be applied to the mitigation and avoidance of deep- sea bottom fishing impacts on sponge ecosystems.

Specific information to inform these risk assessments has been generated by the SponGES project, funded by the European Union Horizons 2020 Blue Growth initiative between 2015 and 2019. SponGES spurred unprecedented research on deep sea sponges in the North Atlantic, resulting in improved knowledge and understanding of sponge distribution, ecological function, impacts of human activities and climate change, role in the deep sea ecosystem and their potential economic contributions through biotechnological components. The scientific information generated allows integration into policy and governance frameworks for deep sea ecosystems.