Pike Esox lucius; Linnaeus, 1758. Family: Esocidae
The pike ( Esox lucius) is a predator that feeds extensively on fish but includes a range of other animals in its diet, including insect larvae, frogs, water rats and ducks. The pike is usually green and silver in colour with distinct dark striped markings on the flanks to afford good camouflage. Markings vary between individuals and can be used to distinguish among fish.
Life History and Behaviour
The pike is well suited in body form for its predacious habit. The body is elongated and large fins are set near the tail to increase the surface area pushing against the water during the explosive lunges at prey. Much of the routine movement is achieved by sculling motions of the paired fins on the underside of the body. These fins gently manoeuvre the pike into position for attack. The eyes swivel to stay fixed on the prey and the body tenses into an 'S' shape. As the body unwinds and the pike accelerates forward, the mouth opens to engulf the prey fish, which is usually captured sideways on. The pike's large bony mouth is armed with rows of teeth, which point backwards and hinge to allow the prey to slide into the gullet, but mean there is little chance of escape. The prey is usually turned so that it is swallowed head-first.
Pike are sprinters. Their muscles are designed for rapid bursts of activity, but their capacity to swim at moderate speeds for long periods is much reduced as a consequence. They use an energy-conserving approach to life, having a low resting metabolic rate, and even at full stretch do not raise their aerobic metabolism* substantially, compared, for example, with salmon and trout (salmonids). For a young pike, the effort of digesting a large meal is exhausting, and induces maximum heart rates.
Pike are a unique component of Scotland's fish fauna and have a special place in angling folklore. Tales of monster pike abound and fire the imaginations of many anglers. Scottish waters have undoubtedly been capable of producing very large pike, reputedly in excess of 50 lb (22.6 kg). It seems likely that such fish were provided with abundant large prey in the form of runs of sea trout and salmon which put on much of their growth in marine waters and therefore import nutrients into the poorer freshwater systems. At present, mortality of salmonids at sea is high and we may have to wait for a return to the days of high salmon returns and correspondingly large pike in some waters. There is evidence that waters stocked with trout may become the new source of giant pike. Careful management should ensure excellent angling opportunities for both the pike and their prey.
Impact of Pike
There is no doubt that pike have the potential to reduce populations of prey fish, which may include commercially important species such as Atlantic salmon. As a consequence, some managers of salmonid fish have tried to control pike populations. There is a growing awareness that such management must be approached with caution because cannibalistic large pike can regulate numbers of smaller pike. If these large pike are removed, the resulting explosion in numbers of rapidly growing small pike can lead to an increase in damage to prey populations. Each case should be considered individually.
There has been much debate over the origins of Scottish pike. The fish have re-invaded since the last ice age, but it is not clear exactly how this occurred. Undoubtedly there have been introductions by man. Pike were used to 'thin-out' trout that had become too abundant and suffered stunted growth. Monks reputedly introduced pike into their stew ponds to provide weekly food fish. This is a surprising management tactic because pike production would have been low and at a cost of many lost prey fish, which, arguably, could have provided equally good (or poor!) food. Pike spawn in spring and deposit thousands of sticky eggs on water plants. It is possible that these eggs attach to birds and mammals and then are dispersed to new waters. New genetic tools may allow a retrospective assessment of some of the spread of pike.
Pike and People
Regardless of how they arrived, pike are here to stay and they provide fascination and enjoyment to many people, especially those anglers who specialise in catching them. The most important consideration now must be that anglers do not contaminate the very waters that hold the secret to producing large pike by introducing non-native fish species brought along as bait. Introduced animals can destroy the balance of ecosystems, and once that balance is lost, it may never be recovered.
*Aerobic metabolism can be maintained for long periods by continually supplying oxygen to the tissues, and is associated with fast breathing and high heart rates in pike and humans. Anaerobic metabolism occurs during explosive bursts of activity and requires a subsequent period of aerobic activity during recovery.