Sunday, August 4, 2013

Safely back on land

The ocean is a tough place to work. It can be dangerous even under the best conditions. Weather can be unpredictable. But even if the weather is good, the marine environment can still be a challenge to work in. Salt water is extremely corrosive, marine organisms grow on what may seem to us as eminently inhospitable (such as our data collection instruments), and all of this can impact our data collection efforts. As a result, any instrument that we deploy for extended periods of time needs to be able to withstand all of these pressures.

Prior to returning to the US Virgin Islands, we were particularly concerned that our acoustic recorders developed at WHOI – the DMON – would get damaged or lost by storms, degraded by an extended deployment in saltwater, or fouled by marine organisms, impairing their function.

Our three study sites on St John, USVI
But, despite our concerns, we got lucky. Sort of. None of the instruments were lost – in fact, they were exactly where we expected them to be, much to our relief. Back in April, we deployed two instruments on each of three reefs to record the acoustic activity of the animals living at each of those reefs. Our reasoning for using two instruments was that if both worked we would be able to look at spatial variability within the reef over long periods of time. If only one worked, we could at least get a good time series of acoustic activity at that site. And, in case neither worked, we deployed a third acoustic recording instrument – the DSG, built by Loggerhead Instruments – as our real backup.

Four slightly fouled DMONs offloading their four months
of data (Photo: M. Kaplan)

On Friday we recovered the instruments from two of our sites – Rams Head and Yawzi – and we were thrilled to see that all of the instruments had recorded correctly and were still intact. Feeling confident, we retrieved the remaining instruments on Saturday. But our success was short-lived. While both DMONs that we deployed at our Tektite site were still functional, neither had recorded for more than a day. The fact that the only two DMONs to fail were at the same site is just bad luck. Yet, although this will impact our analysis, we still have recordings from the third backup instrument and it will still be possible to make comparisons between sites.

For the remainder of the trip we will continue carrying out visual surveys of the benthic environment and the fish diversity in addition to deploying more DMONs for short time periods – 24 hours at a time at our various sites.

Tom carrying out a benthic survey (Photo: M. Kaplan)

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