Exploring Reef Fish Abundance, Mobile Predator Presence, and Unexplored Mesophotic Habitats around Guam using Baited Remote Underwater Video Stations (BRUVs)

Submitted by Louise Giuseffi, Joe O’Malley and Jake Asher

NOAA Scientists Jake Asher, Jamie Barlow, and Louise Giuseffi conducted 160 baited remote underwater video stations (BRUVs) deployments from the NOAA research vessel Oscar Elton Sette during the Guam Insular Fish Research Project (SE-14-05).  These stereo-camera deployments extended from shallow reefs (0-30m) to deep mesophotic regions (30-100m) surrounding Guam’s perimeter.  The primary objectives were to 1) increase the depth range of reef fish surveys previously limited to diver depths, and provide preliminary assessments of mesophotic reef fish populations and benthic habitats 2) provide information on the habitat range of mobile, roving predators (primarily sharks and jacks).  BRUVs work by using sets of pre-calibrated off the shelf handycams (Sony CX7s or CX12s) in a stereo-video configuration on one frame, which allows researchers to estimate overall assemblage and species-specific populations, obtain accurate size measurements of target reef fish species and biomass, and better understand the dynamic of the benthic habitat and their associated assemblages.

NOAA Scientists, from left to right, Jamie Barlow, Louise Giuseffi and Jake Asher pose with a stereo-BRUVs

NOAA Scientists, from left to right, Jamie Barlow, Louise Giuseffi and Jake Asher pose with a stereo-BRUVs

Image of a stereo-BRUVs recovery.

Image of a stereo-BRUVs recovery.

To our knowledge, there has never been extensive reef fish or benthic research conducted in mesophotic regions around Guam and we are excited to review the stereo-video footage in the subsequent months to discover what lives at these great depths.  In brief nightly reviews of the footage, we found areas with flourishing mesophotic reef systems, including areas abundant in soft coral species rich in fish biomass, and additional areas hosting extensive algal fields.  We were surprised at the light transmission and water clarity in several of the deeper (100m) drops.  Finally, one could visibly discern the thermocline (cold water mixing with warm water) in a few of the video surveys, which looked like little underwater distortion waves.

Fish feeding assemblage on the bait bag on a slope.

Fish feeding assemblage on the bait bag on a slope.

Deep mesophotic feeding assemblage.

Deep mesophotic feeding assemblage.

Some of the videos documented sharks that were attracted to the BRUVs.  Most were curious and spent a few moments swimming back and forth around the bait.  Many other species of fish fed on the contents of the bait bag, including species that are not considered classic piscivores (fish eaters).  In one BRUVs deployment, an octopus completely enveloped the bait bag and fed on its contents through the wire mesh.

A tiger shark approaches the bait bag from a distance.

A tiger shark approaches the bait bag from a distance.

A silver tip reef shark gets up close and personal with the bait bag.

A silver tip reef shark gets up close and personal with the bait bag.

Despite periods of torrential rain and strong sun/high humidity, favorable weather during the cruise allowed for deployments in areas (e.g. windward coast) that are typically too rough for small boat operations.  The BRUVs team also worked in extremely powerful currents while around Guam, which rank among the most powerful they have ever experienced.  These created a challenging work environment; however, the future results from these videos may prove to be the biggest reward!

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