The survey got off to a good start on Friday morning with the first leg from Ipswich to Southend during which we had both visual and acoustic detections of porpoises. On Saturday the team surveyed from Southend up to Hermitage Community Moorings, in Wapping close to Tower Bridge. Early Sunday morning saw SOTW heading down the river as far as the Thames Barrier and back by 4am for a few hours sleep before holding a public open day. Due to the high level of traffic it is only practical to tow the hydrophone array in the early hours of the morning when this section of the river is quiet.
Tuesday marked the mid-point of our spring survey for harbour porpoises in the tidal Thames. As these small, discrete marine mammals show little of themselves at the surface, spotting them at sea typically requires calm conditions. Fortunately, the weather has been favourable so far in our survey and we have seen nine separate groups of harbour porpoises. All of these have been in the outer estuary, with none seen in the main body of the river. However, as we have been able to tow our hydrophone at most points of this survey, it is possible that a more thorough review of the acoustic data back in the office will reveal more acoustic encounters with porpoises that went unnoticed in the field. Our survey also been enlivened by numerous sightings of grey seals, and as they lift their heads quizzically at the surface, it is clear they are monitoring us with a similar degree of interest.
The choppy waters and light fog shrouding the London Array prevented us from seeing any marine mammals during the morning survey effort. As the wind and sea state decreased in the afternoon, the sightings of porpoises and seals started to roll in. Checking the acoustic data at anchor in the evening , we found several additional porpoises had been detected on our hydrophone array. This brought the daily tally to 10 encounters with groups of harbour porpoises.
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