Warp strike observations

This report contains an analysis of data on seabird trawl-warp strike collected by fisheries observers. The survey was carried out in the southern squid trawl fishery (SQU6T/1T) over the summer of 2004 – 2005. The aim of the work was to test a new protocol for quantifying warp-strikes and to assess the factors (fishery, environmental, and behavioural, temporal) that appeared to influence the probability of warp strikes occurring for small and large birds. The protocol was designed for use by non-specialist observers, to provide a robust and objective assessment of warp strike occurrence. The key results are listed below.
• 904 good observations were made from 526 separate tows, on 19 different vessels
• 789 large bird heavy contacts were observed, at an average rate of 3.5 heavy contacts per hour (c. v. 9%)
• The number of small bird heavy contacts was lower, with 306 contacts over the entire survey. This corresponds to an average rate of 1.4 per hour (c. v. 12%)
• Offal discharge was the most significant factor associated with large bird strikes
• Discharging offal increased the large-bird strike rate by an estimated factor of 6, compared with no offal discharge
• The strike-rate for large-birds decreased by an estimated factor of 2 when bird bafflers were used
• Higher small-bird strikes were observed at higher discharge rates, and the small-bird strike rates were not strongly dependent on discharge type
• 106 dead or injured birds were recovered from the tows, a rate of 0.2 birds per tow (c. v. 13%)
• The discharge of offal was the factor most significantly associated with the recovery of dead and injured birds from the warps and the recovery of dead or injured birds from the warp was significantly associated with the warp strike rate