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Science Response 2020/026

Ground-truthing the latest set of suspected glass sponge reefs in Howe Sound: Reef delineation and status assessment


Fisheries and Oceans Canada (DFO) has been working to identify and mitigate the impacts of bottom-contact fishing on glass sponge reefs in the Strait of Georgia and Howe Sound through the Strait of Georgia and Howe Sound Glass Sponge Reef Conservation Initiative (DFO 2019). Glass sponge reefs are unique biogenic habitats found along the Pacific coast of Canada and the United States with historic, ecological, and economic value. The reefs play important roles in carbon and nitrogen processing, act as silica sinks, and support diverse communities of invertebrates and fish (Cook et al. 2008, Chu and Leys 2010, Tréguer and De La Rocha 2013, Kahn et al. 2015, DFO 2018, Dunham et al. 2015, 2018b).

Over the past 16 years, a number of glass sponge reefs have been discovered and mapped in the Strait of Georgia and Howe Sound using remote sensing (Conway et al. 2004, 2005, 2007) and standardized visual surveys (Dunham et al. 2018b). Two recent DFO Science initiatives carried out in collaboration with Natural Resources Canada and conservation organizations delineated 19 glass sponge reef complexes, assessed their condition, and recommended assessment and monitoring methods. The resulting science advice (subsequently published as DFO 2018; Dunham et al. 2018a) formed the scientific basis for nine bottom-contact fishing area closures implemented in June 2015, followed by eight closures implemented in April 2019. These closures are considered Other Effective Area-Based Conservation Measures (DFO 2016), contributing to Canada's Marine Conservation Target commitment to protect 10% of Canada's coast by 2020.

When the latest set of closures was implemented in April 2019, nine additional areas in Howe Sound were identified as possible sponge reefs based on SCUBA divers’ observations, drop camera footage, or geological records. Data available at the time were deemed insufficient for reef status confirmation; these areas required ground-truthing before their status could be determined (DFO 2018, see Appendix 7).

DFO Sustainable Fisheries Framework Unit has requested advice from the Science Branch assessing the status of these nine suspected reefs, to serve as the final component of science support and advice for the above-mentioned Conservation Initiative (DFO 2019).

The primary goals of the present assessment are to (1) gather all available ecological and geological data for the nine areas in Howe Sound suspected to be glass sponge reefs; (2) ground-truth seven visual-data-deficient areas by surveying them with a Remotely Operated Vehicle (ROV); and (3) determine reef status and quantitatively describe the condition of each reef.

Specific objectives of this assessment include:

  1. For each of the nine areas:
    • Map geological signature indicative of glass sponge reefs, if present, using available multibeam and backscatter data layers;
    • Map the presence of live reef-building glass sponges and reef structure based on ROV video and still images;
    • Determine whether the area is a living glass sponge reef based on criteria outlined in DFO (2018).
  2. For each area determined to be a glass sponge reef:
    • Characterize reef condition (sponge cover, habitat categories) using quantitative metrics developed in Dunham et al. (2018a) and applied in DFO (2018);
    • Create 1-page summaries of reef extent and status similar to DFO (2018);
    • Provide advice on potential benefits of protection;
    • Identify any uncertainties in the data.

For consistency, this assessment follows the terminology, methods, content order, and layout of DFO (2018), with minor adjustments described in the text.

The assessment and advice arising from this Canadian Science Advisory Secretariat (CSAS) Science Response will be used to inform management and monitoring of the sponge reefs in Howe Sound and to respond to stakeholder requests for scientific information. It is expected to support DFO Sustainable Fisheries Framework Unit and Oceans in advancing Canada’s commitments around Other Effective Area-Based Conservation Measures. This report is not intended to explicitly recommend areas for spatial protection, but rather to gather and summarize all available geological and ecological information for each of the nine areas to facilitate management decisions.

This Science Response results from the Science Response Process of February 19, 2020 on Ground-truthing the final set of suspected sponge reef complexes in Howe Sound: Reef delineation and status assessment.

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