Data from: Proto-cooperation: group hunting sailfish improve hunting success by alternating attacks on grouping prey

We present evidence of a novel form of group hunting. Individual sailfish (Istiophorus platypterus) alternate attacks with other group members on their schooling prey (Sardinella aurita). While only 24% of attacks result in prey capture, multiple prey are injured in 95% of attacks, resulting in an increase of injured fish in the school with the number of attacks. How quickly prey are captured is positively correlated with the level of injury of the school, suggesting that hunters can benefit from other conspecifics´ attacks on the prey. To explore this, we built a mathematical model capturing the dynamics of the hunt. We show that group hunting provides major efficiency gains (prey caught per unit time) for individuals in groups of up to 70 members. We also demonstrate that a free riding strategy, where some individuals wait until the prey are sufficiently injured before attacking, is only beneficial if the cost of attacking is high, and only then when waiting times are short. Our findings provide evidence that cooperative benefits can be realised through the facilitative effects of individuals´ hunting actions without spatial coordination of attacks. Such `proto-cooperation´ may be the pre-cursor to more complex group-hunting strategies.本研究提供了一种新型群体狩猎行为的实证证据。个体旗鱼（Istiophorus platypterus）会与群体内其他成员交替对集群的沙丁鱼（Sardinella aurita）发起攻击。尽管仅有24%的攻击能够成功捕获猎物，但95%的攻击会造成多只猎物受伤，随着攻击次数增加，鱼群中受伤个体的数量也随之上升。猎物被捕获的速率与鱼群的受伤程度呈正相关，这表明狩猎者可从其他同种个体对猎物的攻击中获益。为探究这一机制，本研究构建了描述狩猎动态的数学模型。研究表明，在成员数量不超过70的群体中，群体狩猎能显著提升个体的狩猎效率（单位时间内捕获的猎物数量）。本研究同时证实，搭便车策略——即部分个体等待猎物被充分击伤后再发起攻击——仅在攻击成本较高且等待时长较短的情况下才具有收益优势。本研究结果证实，即便攻击行为不存在空间协同，个体的狩猎行为通过协同促进效应也可实现合作收益。这类‘原始合作’或许是更为复杂的群体狩猎策略的雏形。