DOI: 10.5061/dryad.jv5f8
title: Data from: How to capture fish in a school? Effect of successive predator attacks on seabird feeding success

description: 1. Prey aggregations, such as fish schools, attract numerous predators.
 This typically leads to the formation of multi-specific groups of
 predators. These aggregations can be seen both as a place of increased
 competition and as a place of possible facilitation between predators.
 Consequently, the functional role of such predator-prey aggregation is
 uncertain, and its effect on individual feeding success is virtually
 unknown. 2. Using underwater film footages of different predators feeding
 on fish schools during the sardine run in South Africa, we directly
 measured the in-situ feeding success of individual Cape gannets Morus
 capensis in different foraging situations. 3. We determined the types of
 Cape gannet attacks (direct plunge dive or plunge dive followed by
 underwater pursuit) and we measured the occurrences and timing of attacks
 from the different species (mostly Cape gannets and long-beaked common
 dolphins Delphinus capensis). We also estimated the size of the targeted
 fish schools. These observations were complemented with a simulation model
 to evaluate the cumulative effect of successive predator attacks on the
 prey aggregation structure. 4. The probability to capture a fish in one
 feeding attempt by Cape gannets averaged 0.28. It was lower when gannets
 engaged in underwater prey pursuit after the plunge compared to direct
 plunge (0.13 vs. 0.36). We found no effect of the number of prey on
 gannets’ feeding success. However, the timing and frequency of attacks
 influenced strongly and positively the feeding success of individuals. The
 probability to capture a fish was the lowest (0.16) when no attack
 occurred in the few seconds (1-15 s) prior to a dive, and the highest
 (~0.4, i.e. more than twice) when one or two attacks occurred during this
 time window. The simulation model showed that a prey aggregation
 disorganized just after an attack, and that the maximum of disturbance was
 obtained a few seconds after the initiation of the successive attacks. 5.
 Our study suggests that, in multi-species predator assemblages, the
 cumulative effect (through disorganisation of school cohesiveness) of the
 multiple species attacking a prey aggregation may increase the feeding
 success of each individual. Therefore, facilitation between predators is
 likely to overcome competition in these multi-specific assemblages.
description: PredationBehavioursData based on in situ underwater footage of marine predators feeding on fish schools, initially shot for the film OCEANS by J. Perrin and J. Cluzaud (Galatée Films Production). Predation behaviours recorded from the observation of footage.Data per sceneData based on in situ underwater footage of marine predators feeding on fish schools, initially shot for the film OCEANS by J. Perrin and J. Cluzaud (Galatée Films Production). Observations aggregated per scene.PerSceneData per attackData based on in situ underwater footage of marine predators feeding on fish schools, initially shot for the film OCEANS by J. Perrin and J. Cluzaud (Galatée Films Production). Observations per Cape gannet attack.PerAttack