Sailfish hunt, but is cooperation evolving?
Sailfish are sportsman's fish, fish-lovers fish and most definitely an animal to be admired for their fantastic adaptations to pelagic hunting. The bill and the sail add to its basic perch geometry to give it an almost mythical look. If it didn't exist, we would have to invent a fictional alternative. This paper makes the point that their hunting technique with sardines shows the bare beginnings of cooperative hunting.
Individual fish benefit from group hunting although they have no defined roles or social organisation. Each one may gain less prey in its personal
catch but they are guaranteed more sardines per unit time when they hunt in groups.
This is because the micro-toothed bill injures more and more prey, as each predator sallies into the schooling sardines. As the injuries to the shoal members increase, more are liable to be caught by later sailfish. An obvious solution for the lazy would be to wait till your group has begun the attack and then join in at the end when more sardines will be available. The authors compute the possible advantage of this, with interesting results:
the prediction was that benefit from a delayed attack would result if the
cost of attacking were 10X higher than remaining in the group;
if the waiting time is not very short, the benefit wanes;
sitting it out and waiting to attack would be an individual strategy;
overall, it seems the fish may not have to cooperate deliberately - they may simply all join in, with an evolution of cooperative hunting as they alternate their attacks.
James E Herbert-Read of Uppsala and Stockholm Universities (Sweden) and many mathematically and ecologically-minded colleagues from, among others, Princeton, New Jersey, US, the Leibnitz Institute of Freshwater Ecology and Inland Fisheries in Berlin, Germany, the Université Pierre et Marie Curie, Paris,(France) the University of Copenhagen (Denmark) and the Universities of Sydney and Deakin in Australia presents this paper in Proc. Roy. Soc. B, entitled
Proto-cooperation: group hunting sailfish improve hunting success by alternating attacks on grouping prey.
The researchers believe more work on individual sailfish will reveal just how likely cheating might be, while Istiophorus platypterus continues with a 24% success rate in its individual catch-rate. Up to 70 sailfish can cooperate, according to the mathematical model, with the results so far indicating that this could be the precursor or
protocooperation phase in evolution for many animals. Our mammalian, bird fish and insect examples often use a much more complex set of behaviours which have evolved into true group-hunting strategies. You could even take human children as an example, as hunting develops in tribal peoples as a vital part of everyday life. Perhaps I'm pushing that argument too far!