Science Advisory Report 2021/041

Identification of Representative Seamount Areas in the Offshore Pacific Bioregion, Canada

Summary

• Seamounts are Ecologically and Biologically Significant Areas (EBSAs) and Vulnerable Marine Ecosystems (VMEs) that are unique within Canada to the Offshore Pacific Bioregion (OPB).
• Compared to the surrounding deep seafloor, the relatively shallow habitat provided by all seamounts supports diverse and distinct species assemblages including habitat-forming cold-water corals, sponges, and hundreds of other benthic and pelagic species.
• There are 62 seamounts known or predicted to occur in the OPB, of which 43 were newly identified (not currently reported in the Canada Gazetteer; 29 from DFO 2019 and 14 from this process). The location and depth of 21 of these new seamounts have been ground-truthed. DFO Science is working in partnership with several First Nations to name these new seamounts.
• The Area of Interest (AOI) for the Offshore Pacific Marine Protected Area (MPA) contains the majority (47) of OPB seamounts. Three seamounts are in SG̲áan K̲ínghlas-Bowie Seamount (SK̲-B) MPA, and 12 are in the OPB outside conservation areas.
• Newly delineated seamount boundaries can be used for future spatial planning.
• The density of seamounts within the AOI and the OPB is notable (approximately 5 and 3 times the global average, respectively).
• A regional assessment of geography and oceanography (major currents), supported by biological observations, revealed no evidence of biogeographic boundaries (i.e., barriers to dispersal) among the OPB seamounts. Additional research, such as genetic analyses, is needed to assess connectivity among the seamounts.
• Depth zones on the OPB seamounts are delineated by light availability and oxygen concentration, and align with depths of documented biological community transition zones.
• The information for the global seamount classification system previously used to classify the OPB seamounts was updated to include new seamounts, improved depth data, and an additional criterion.
• OPB seamounts were assigned to one of seven biophysical classes using quantitative thresholds of export productivity (new to this iteration), summit depth, and dissolved oxygen concentration at the summit. Two additional criteria, biogeographic province and distance to nearest seamount, do not vary within the OPB and so do not differentiate any seamounts.
• Assemblages of cold-water corals, sponges, and other benthic species vary across seamount classes and depth zones, supporting the classifications as biologically relevant. Seamounts with shallower summits span multiple depth zones and support higher species richness. SK̲-B Seamount, the shallowest in the OPB, supports unique benthic assemblages not represented elsewhere in the OPB (e.g., shallow subtidal communities).
• The seamount classification system is regionally relevant, as its criterion thresholds align with oxygen concentrations and depth boundaries observed in the OPB, and it can be applied to undiscovered OPB seamounts or those outside of Canadian waters.
• Representativity of the seamount classes within the OPB was assessed. Five of the OPB seamounts are rare or unique (occurring in only a few locations or the only one of its kind): Dellwood, Hodgkins, Explorer, Union, and SK̲-B seamounts.
• OPB conservation areas cover at least one representative seamount of each class. Six of the seven classes occur in the AOI, and the only Class H5 seamount, SK̲-B, occurs in SK̲-B MPA.
• It is recommended that the methods presented here be used to update/reassess the seamount classifications (classes and zones) as new data becomes available (e.g., improved bathymetry, seamount morphology, substrate, pelagic data).
• Future applications of the classification could consider new non-depth related metrics. For example, differences in summit morphology may affect local currents, which in turn may influence the community structure of cold-water coral and sponge assemblages.
• Seamounts provide ecosystem functions that enhance regional productivity, biological diversity, resilience, and connectivity. In general, shallower seamounts are thought to provide more ecosystem functions than deeper ones.
• All OPB seamounts are anticipated to experience changes, now or in the near future, as a result human activities and changing ocean conditions. Shallower seamounts such as SK̲-B and Union seamounts are anticipated to experience more changes.
• The amount of existing baseline data by which to detect change varies among OPB seamounts. In general, more is known about shallow seamounts and those closer to shore.
• Information on the anticipated environmental changes and existing ecological data for the 62 seamounts are presented in a single “portfolio” summary, illustrating a degree of likelihood associated with detecting change if the seamount is monitored in the future. Representative seamount areas with a high degree of likelihood (i.e., reference sites) are identified for each seamount class and for each conservation area.
• To support the scoping stage of the Ecological Risk Assessment Framework (ERAF), an inventory of species known to occur on OPB seamounts was compiled and potential Significant Ecosystem Components were provided. Since the last assessment in 2015, the number of known taxa on OPB seamounts has quadrupled. With increased sampling and examination of voucher specimens, more species are likely to be identified.
• There is no evidence of endemism (i.e., species unique to any one seamount).
• The remote nature, vast size, and range of habitats in the OPB make gathering comprehensive and/or representative data a challenge. The analyses presented here are limited to discrete or static (“snapshot”) information, but the OPB is a dynamic system with multi-scale spatial and temporal variability.
• It is recommended that this information is suitable for a range of potential applications, such as the ERAF and the development of an MPA management plan, conservation objectives, a monitoring framework and plan, and future survey design and research development.

This Science Advisory Report is from the November 25-26, 2020 regional peer review on the Identification of Important Seamount Areas in the Offshore Pacific Bioregion, Canada. Additional publications from this meeting will be posted on the Fisheries and Oceans Canada (DFO) Science Advisory Schedule as they become available.

Science Advisory Report 2021/041 (PDF, 1,302 KB)

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