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Table 1.

Parameters analysed during trials in two tasks (fish and no fish) for the two harbour porpoises, Eigil and Freja, as well as for Freja blindfolded(Freja bf)

Fish
No fish
ParameterEigilFrejaFreja bfEigilFrejaFreja bf
Mean time per trial (s) 6.0±0.6 5.6±0.8 12.2±2.0 5.8±1.0 4.5±0.7 9.9±0.6 
Mean distance per trial (m) 22.8±0.8 25.2±1.7 25.4±0.6 23.8±1.4 21.5±2.1 24.3±1.0 
Mean number of clicks recorded per trial 339.4±44.8 328.2±119.5 630.8±64.4 89.0±12.8 71.2±14.7 195.0±12.0 
Mean distance to fish at transition point (m) 4.4±2.6 1.9±0.8 3.9±1.7 n.a. n.a. n.a. 
Mean click interval at transition point (ms) 57.5±14.4 48.3±16.0 41.5±14.4 n.a. n.a. n.a. 
Minimum click interval in near stage (ms) 1.4±0.2 1.6±0.1 1.6±0.1 n.a. n.a. n.a. 
Mean click interval in far stage (ms)* 47.0±6.3 54.7±4.8 47.1±4.0 n.a. n.a. n.a. 
Mean lag timeF in far stage (ms)* 34.8±5.0 42.8±4.8 35.0±3.0 n.a. n.a. n.a. 
Mean lag timeR (ms)* n.a. n.a. n.a. 40.2±2.8 34.8±1.7 31.7±0.7 
Mean click density (clicks m–1)* (excl. near stage) 4.1±1.0 3.2±0.2 7.4±0.7 2.7±0.2 3.1±0.3 6.2±0.8 
Mean speed (m s–15.4±0.5 5.9±0.5 3.0±0.4 6.3±0.4 5.9±0.5 3.3±0.4 
Slope (±95% CI) (ms m–1) before splash for DR≤26 m 0.23±1.45 2.34±1.59 0.96±0.63 – – – 
Slope (±95% CI) (ms m–1) after splash* –0.50±0.96 –0.17±0.93 0.02±0.94 1.80±0.37 1.41±0.55 1.71±0.90 
Slope (±95% CI) (ms m–1) for DF(far stage)* 0.19±1.24 –0.03±0.62 0.59±0.76 n.a. n.a. n.a. 
Slope (±95% CI) (ms m–1) for DF(near stage) 10.91±3.90 – 9.72±7.15 n.a. n.a. n.a. 
Fish
No fish
ParameterEigilFrejaFreja bfEigilFrejaFreja bf
Mean time per trial (s) 6.0±0.6 5.6±0.8 12.2±2.0 5.8±1.0 4.5±0.7 9.9±0.6 
Mean distance per trial (m) 22.8±0.8 25.2±1.7 25.4±0.6 23.8±1.4 21.5±2.1 24.3±1.0 
Mean number of clicks recorded per trial 339.4±44.8 328.2±119.5 630.8±64.4 89.0±12.8 71.2±14.7 195.0±12.0 
Mean distance to fish at transition point (m) 4.4±2.6 1.9±0.8 3.9±1.7 n.a. n.a. n.a. 
Mean click interval at transition point (ms) 57.5±14.4 48.3±16.0 41.5±14.4 n.a. n.a. n.a. 
Minimum click interval in near stage (ms) 1.4±0.2 1.6±0.1 1.6±0.1 n.a. n.a. n.a. 
Mean click interval in far stage (ms)* 47.0±6.3 54.7±4.8 47.1±4.0 n.a. n.a. n.a. 
Mean lag timeF in far stage (ms)* 34.8±5.0 42.8±4.8 35.0±3.0 n.a. n.a. n.a. 
Mean lag timeR (ms)* n.a. n.a. n.a. 40.2±2.8 34.8±1.7 31.7±0.7 
Mean click density (clicks m–1)* (excl. near stage) 4.1±1.0 3.2±0.2 7.4±0.7 2.7±0.2 3.1±0.3 6.2±0.8 
Mean speed (m s–15.4±0.5 5.9±0.5 3.0±0.4 6.3±0.4 5.9±0.5 3.3±0.4 
Slope (±95% CI) (ms m–1) before splash for DR≤26 m 0.23±1.45 2.34±1.59 0.96±0.63 – – – 
Slope (±95% CI) (ms m–1) after splash* –0.50±0.96 –0.17±0.93 0.02±0.94 1.80±0.37 1.41±0.55 1.71±0.90 
Slope (±95% CI) (ms m–1) for DF(far stage)* 0.19±1.24 –0.03±0.62 0.59±0.76 n.a. n.a. n.a. 
Slope (±95% CI) (ms m–1) for DF(near stage) 10.91±3.90 – 9.72±7.15 n.a. n.a. n.a. 

The duration of a trial was determined by the first and last click analysed from an echolocation sequence (see Materials and methods). The values for regression slopes (±95% confidence interval, CI) for mean click intervals are shown over distance to reference (DR; before splash DR<=26 m; after splash DR=18–12m excluding the near stage in fish), and over the distance to fish (DF) in the far stage as well as in the near stage. Regression slope values with a ±95% confidence range that include the value 1.3 are not significantly different from the slope of the two-way transit time. Those ranges including zeros do not show a significant regression, those excluding zero are slopes significantly different from zero. Significant positive regression slopes (marked in bold)show a positive correlation between click interval and distance to reference or distance to fish, respectively. The dashes indicate insufficient data. n.a., not applicable/not available. Number of trials included for Eigil/Freja/Freja bf are: fish=5/5/5, no fish=5/5/4. *Calculated for DR=18–12 m

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