Dundavin Sponge Reef: Methods and Results from ROV Survey PAC2017-094

Le résumé fourni par la source

In 2017, a scientific survey (PAC2017-094) was led by Fisheries and Oceans Canada (DFO) to map and assess the ecological status and character of the 48km² glass sponge reef in Chatham Sound and to survey a smaller unmapped sponge reef, referred to as Dundavin Reef, in Seaforth Channel, northwest of Bella Bella. The focus of this report is to summarize the methods and results from the survey of Dundavin Reef. Six remotely operated vehicle (ROV) transects, totaling 2.45 km in length and spanning depths of 74–276 m, were conducted, and a sound recording device was deployed. Video and still imagery were collected using the ROV and annotated for species presence and reef-building glass sponge cover. A total of 1,947 species annotations were recorded from video and 7,510 from still images (differing due to image quality, camera angle, and species lists), including sponges, corals, anemones, echinoderms, crustaceans, and fishes. Only one anthropogenic object (e.g., debris or equipment) was observed across the six transects. Live and dead reef-building glass sponge cover annotations were used to categorize reef habitat in video segments. All transects had more than 45% (up to 75%) of their area covered by living visible sponge reef cover, categorized as mixed, live, or dense live habitat. Small amounts (<4% of the transect area) of dense live reef habitat were observed on four out of six transects. Sound was recorded on the reef for 62 days and analyzed for boat and fish sounds. Boat noise was most frequent during daylight hours, and fish noise during the night, the latter perhaps in part due to masking by boat noise. This survey is the first assessment of the status, extent, and sponge coverage of Dundavin Reef: a small glass sponge reef possibly interspersed with glass sponge gardens on bedrock. The imagery and sound data collected have shown that the reef supports a diversity of reef-associated fishes, invertebrates, and emergent corals; the reef appears to be relatively intact compared to available survey data for other glass sponge reefs. Complete mapping of Dundavin Reef requires further data collection, including high-resolution multibeam echosounder data.

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