So you know that I am out helping Steve with his PhD work looking at the effects of fishing pressure around Guam and Saipan. But what does the work were doing specifically involve?

Currently Steve is examining the potential depth refuge from fishing pressure. The theory is that deeper waters, inaccessible to certain fishing practices can form a refuge (like a marine protected area) where fish can grow and reproduce. The Marina Islands are a perfect case study for examining this theory, where freedive spearfishing is prevalent across all islands but remarkably SCUBA spearfishing is legal practice in Guam (while banned in the other islands). These SCUBA spearfisherman in Guam are pretty crazy and apparently pushing the limits to depths of over 80m in search of fish that were once prevalent in shallower waters. So he is sampling inside and outside of the marine protected areas of Guam and comparing to other islands including Saipan.

The main survey technique Steve is employing is the non-destructive sampling method of Baited Remote Underwater Video Stations (BRUVS). These video stations are effective for sampling across a broad range of depths and habitats. Steve is using stereo-video systems on his BRUVS, designed by Dr. Euan Harvey (Steve’s supervisor) from the University of Western Australia. Stereo-video allows accurate measurements of fish length and the size of the sampling area. The video stations are relatively simplistic in design, consisting of two forward facing video cameras mounted to a steel frame attached to a rope and buoy.  Each unit is baited with 1kg of oily fish, which is placed in a plastic mesh basket suspended in front of the two cameras. We have been fortunate enough to have fantastic weather while surveying, but when a swell picks up baiting the cameras can make for a stomach churning experience.

The simplistic nature of the video units allows for rapid deployment and easy retrieval. Just to give you an idea of how efficient the sampling method can be, Steve are I are using five stereo-BRUVS units whilst in Saipan, we can drop and pick up each unit at least 3 times throughout a day giving Steve over 15 hours footage to analyse. Compare that to diver surveys of fish populations and you would be lucky to get a quarter of that data (not to mention the depth limitations). The stations are dropped down onto the seafloor at pre-determined GPS locations and left to ‘soak’ for at least 1hr, we then come along and winch them back and repeat the process. Quite simply, rinse and repeat.

The principle behind stereo-video is that the two cameras are positioned in a slightly converged angle and their frame rate can be synced using a LED diode that is attached to the bait pole. Once the cameras are calibrated by spinning a large cube in front of the cameras it works in a very similar way to 3D television, allowing for a depth of field to be measured. This allows for distances of fish from the cameras, fish length, total fish area, fish abundance and diversity all to be measured. Stereo video is the most accurate way to size fish without catching them, giving some of the most useful data in terms of assessing fishing pressure on fish populations.

Steve also has access to habitat maps showing the bathymetry of the ocean floor, he uses this to select his sampling locations targeting deepwater coral reefs. Here is a video of some of his earlier sampling aboard the NOAA ship Oscar Elton Sette on an offshore bank south of Guam.

http://vimeo.com/11831197

We have been dropping these BRUVS all along the Northern and Southern coasts of Guam and Saipan. Unfortunately our research vessel is not as spacious as the NOAA ship in the previous video…… Nestled into our overly packed 6m boat, it can be a cramped ride out to the field sites. But once the initial cameras are dropped and we have some room to breath the operation goes very smoothly.

It’s not all work and no play out on the boat dropping cameras we often make time for some freediving. Sampling in some of the most remote and inaccessible locations around Guam and Saipan, swimming amongst the shallow coral reefs, deepwater drop-offs and exploring sea caves makes for the best working break I can think of!

I have learned so much about the techniques used to assess fish populations since my time with Steve. Calibrating the BRUVS cameras, learning the software and data analysis, and of course getting my hands dirty out in the field have made me appreciate fieldwork in the marine sciences even more than before, fuelling my love for marine ecology.

Images from left to right: 1. Steve and I with our BRUVS boat in Saipan 2-3. Steve with his winch and installing it (I’m so thankful for this winch!) 4. The BRUVS 5.  Docked and ready to go 6. Pulling up a BRUVS off the coast of Saipan 7,10. BRUVS stacked and ready in Guam 8.All of Steve’s 16 video cameras! 9. Preparing the video cameras 11-13 Some screen shots of BRUVS footage (the tigershark was taken on Steve’s NOAA trip in Saipan) 14. Calibrating the cameras in the pool.