Fig 1.
Spatial positions of mackerel and herring slipping events for Vessel A and Vessel B. Triangles denote slipping events not included in the analysis due to no behaviour being recorded; circles denote slipping events included in the analysis. Note that some points overlap.
Fig 2.
Illustration of the discharge opening and camera positioning.
The discharge opening was formed in the bunt end of the purse seine to allow fish escape. The positioning of cameras (and approximate filming orientation in green) for observation of behaviour is indicated: a) bridge camera to observe net hauling and discharge opening from the surface; b) horizontally orientated discharge camera; c) vertically orientated discharge camera and d) vertically orientated drop camera. See main text for further description of camera set up and slipping methodology. Adapted from [7], with permission IMR.
Fig 3.
Examples of behavioural units.
Behavioural units were used to classify collective fish behaviour during escape from purse seines: a) “No escape”; b) “Single fish”; c) “Small group”; d) “Orderly”; e) “Disorderly”; f) “Return”, with a fish re-entering the net indicated by the arrow. See Table 1 for full definition of behavioural units.
Table 1.
Ethogram of collective fish behaviour during escape from purse seines.
Table 2.
Candidate Dirichlet regression models.
Candidate models and associated hypotheses to explain the behavioural composition of fish whilst being slipped from purse seines.
Table 3.
Number of observed slipping events of mackerel and herring from purse seines.
Fig 4.
The behavioural time budget of mackerel and herring whilst escaping from purse seines, from different slipping events (casts) from two different vessels.
Fig 5.
Probability of escape as a function of time.
Estimated probability (with 95% confidence intervals) of a purse seine escape of any kind over time, for mackerel and herring. The lower panel shows the number of observed escape events per tenth-part of elapsed time. The dataset includes observations from both Vessel A and Vessel B.
Fig 6.
Probability of disorderly escape as a function of time.
Estimated probability (with 95% confidence intervals) of a disorderly purse seine exit over time for mackerel and herring from Vessel A and Vessel B. The lower panels show the number of observed escape events per tenth-part of elapsed time.
Table 4.
Ranking of candidate Dirichlet regression models to explain the behavioural composition of fish whilst slipping from purse seines.
Table 5.
Dirichlet regression results of the most parsimonious model.
Parameters of the best selected model to explain the behavioural composition (comprised of small, orderly and disorderly behaviours) of fish slipped from purse seines, fitted by Dirichlet regression.
Fig 7.
Behavioural composition as a function of slipped amount.
The relationship between slipped amount and the composition of slipping behaviour (comprised of the behavioural units of disorderly, orderly and small) for herring and mackerel released by two different purse seine vessels. For Vessel B, note that the regression lines for “Disorderly” and “Small” overlap.
Fig 8.
Tail beat frequency during and after escape.
Model predicted mean (with 95% confidence intervals) tail beat frequency of mackerel and herring during and after slipping from purse seines.