Category: Home Slider, ANMN, SA-IMOS
Chance spotting leads to recovery of broken IMOS mooring on the Yorke Peninsula
A member of the public last month found a large orange buoy, with instrumentation attached, washed up on a remote beach on the Yorke Peninsula, South Australia.
He contacted the South Australian Research and Development Institute (SARDI), a division of Primary Industries and Regions SA (PIRSA), to report his find and sent a photo of the ID tag attached to the structure. The buoy was identified as part of ‘SAM8SG’, the Southern Australian Integrated Marine Observing System (SAIMOS) Spencer Gulf mooring, which broke loose and was swept away.
The Spencer Gulf mooring is part of the South Australian regional array located in the path of the gulf/shelf water exchange. It monitors outflows from the Spencer Gulf that are expected for winter and the upwelling expected for summer. In addition to monitoring physical variables (temperature, salinity and currents), the mooring samples chlorophyll fluorescence (indicator of phytoplankton concentrations) and measures dissolved oxygen.
Given the remote location of the beached buoy, recovery was always going to be a challenge. The mooring was lodged between rocks at the south end of a beach north of West Cape (West Bay), between West Cape headland and Pondalowie Bay to the north. Access to this part of the beach, roughly 1km south of the carpark, is by foot only and the road is elevated from the beach.
SARDI’s Paul Malthouse and Mark Doubell packed for an overnight trip and set off with ropes and tools to recover the mooring on foot. On 20 July, after a 50 minute walk through deep sand and over rocks, they reached the mooring.
Surprisingly, the float pack, current profiler, ‘Conductivity, Temperature & Depth’ (CTD) and acoustic release unit (CART) pack appeared to be relatively undamaged. The Novatech strobe light and the satellite tracker both suffered obvious damage.
Malthouse and Doubell dismantled the components and, over the course of a few hours, carried them back to their car. The float was too large to haul all the way along the beach, given the rising tide and amount of daylight remaining, so they anchored it to a safe place in the dunes for later recovery.
Breaking loose - a mystery
Data logs showed that the instruments surfaced at roughly 4:00 pm on 13 July, the day after a vigorous southwestly front pushed through the region. The SABLE satellite tracker wasn’t functioning properly and didn’t notify SARDI of the surfacing mooring. Nor did it track the mooring whilst drifting, so its release went undetected.
The reason for the release of the mooring is unclear. The acoustic release unit was still engaged and not damaged. The metal lifting ring that joins the mooring gear to the anchor pack (via a nylon snatch strap) was also still attached. This suggests that either the nylon snatch strap had been torn, bitten or worn to breaking point and released or the shackle to the anchor pack has failed.
SARDI intends to deploy a replacement mooring at the SAM8SG location in early September 2016.