Northern pike

Appearance

Northern pike are most often olive green, shading from yellow to white along the belly. The flank is marked with short, light bar-like spots and there are a few to many dark spots on the fins. Sometimes the fins are reddish. Younger pike have yellow stripes along a green body, later the stripes divide into light spots and the body turns from green to olive green. The lower half of the gill cover lacks scales and they have large sensory pores on their head and on the underside of the lower jaw which are part of the lateral line system. Unlike the similar-looking and closely related muskellunge, the northern pike has light markings on a dark body background and fewer than six sensory pores on the underside of each side of the lower jaw.

A hybrid between northern pike and muskellunge is known as a Tiger Muskellunge. In the hybrids, the males are invariably sterile, while females are often fertile, and may back-cross with the parent species. Another form of northern pike, the silver pike, is not a subspecies but rather a mutation that occurs in scattered populations. Silver pike, sometimes called silver muskellunge, lack the rows of spots and appear silver, white, or silvery-blue in color. When ill, Silver pike have been known to display a somewhat purplish hue; long illness is also the most common cause of male sterility.

In Italy, the newly discovered species ''Esox flaviae'' was long thought to be a color variation of the northern pike, but was in 2011 announced to be a species of its own.

Naming

The northern pike gets its name from its resemblance to the pole-weapon known as the pike . The genus name, ''Esox'', comes from the Greek and Celtic for "big fish" and "salmon". Various other unofficial trivial names are: American pike, common pike, great northern pike, Great Lakes pike, grass pike, snot rocket, slough shark, snake, slimer, slough snake, northern, gators , jack, jackfish, Sharptooth McGraw, Mr. Toothy and other such names as Long head and Pointy nose.

Distribution

''Esox lucius'' is found in freshwater throughout the northern hemisphere, including Russia, Europe and North America. It has also been introduced to lakes in Morocco and is even found in brackish water of the Baltic Sea. However pike are confined to the low salinity water at the surface of the Baltic sea, and are seldom seen in brackish water elsewhere.

Within North America, there are northern pike populations in Illinois, North Dakota, South Dakota, Minnesota, Michigan, Montana, Maryland, West Virginia, Wisconsin, Indiana, Connecticut, Rhode Island, New Hampshire, Maine, New Jersey, Massachusetts, Vermont, Iowa, Utah, Northern New Mexico and Arizona, Colorado, New York, Idaho, Alberta, Saskatchewan, Manitoba, Ontario and Québec , Alaska, the Ohio Valley, the upper Mississippi River and its tributaries, the Great Lakes Basin and surrounding states, Missouri, Kansas, Nebraska, Colorado and parts of Oklahoma. They are also stocked in, or have been introduced to, some western lakes and reservoirs for angling purposes, although some fisheries managers believe this practice often threatens other species of fish such as bass, trout and salmon, causing government agencies to attempt to exterminate the pike by poisoning lakes.

Behavior

Pikes are capable of “fast start” movements, which are sudden high energy-bursts of unsteady swimming. Many other aquatic fish exhibit this movement as well. The reason that most fish utilize this mechanism is to avoid life-threatening situations for most fish, similar to an adrenaline rush. For the pike however, it is a tool used in order to capture prey from their sedentary position. They flash out in such bursts and capture their prey. These fast starts terminate when the pike has reached terminal velocity. During such motions, pikes make S conformations while swimming at high rates. To decelerate, they, simply make a C conformation, exponentially slowing down their speed so that they can “stop”. An interesting behavioral trait that pikes have is that they have short digestion times and long feeding periods. It makes sense in the fact that they can undergo many of these fast-bursts in order to collect as much prey as they can. For pikes, their time of least activity is during the night. Naturally, the larger the pike, the faster it can swim.

Habitat

Pike are found in sluggish streams and shallow, weedy places in lakes, as well as in cold, clear, rocky waters. Pike are typical ambush predators; they lie in wait for prey, holding perfectly still for long periods and then exhibit remarkable acceleration as they strike. In short, they will inhabit any water body that contains fish, but suitable places for spawning are essential for their numbers. Because of their cannibalistic nature, young pike need places where they can take shelter between plants so they are not eaten. In both cases it comes down to a rich submersible vegetation nearby. Pikes are seldom found in brackish water, except for the Baltic Sea area. Pike are known to prefer water with less turbidity but that is probably related to their dependence on the presence of submersible vegetation and not to their being a sight hunter.

Reproduction

Pike are known to spawn in spring when the water temperature first reaches 9 °C . The males are first at the spawning grounds preceding the females for a few weeks. The larger females tend to be earlier than the smaller ones. Mostly a female is followed by several smaller males. When a pair starts slowing down the male will put his tail under the female's body and release it's sperm that is mixed with the eggs due to the tail movement. The spawning consists of a great number of these moves several times a minute and going on for a few hours a day. Every move between 5 and 60 eggs are laid. A female can continue the mating for three days in a row. After the mating the males tend to stay in the area for a few extra weeks.

The color of the sticky eggs is yellow to orange, the diameter is 2.5 to 3 mm. The embryos are 7.5 to 10 mm in length and able to swim after hatching but stay on the bottom for some time. The embryonic stage is 5 to 16 days, dependent on water temperature . Under natural circumstances the survival from free swimming larva to 75 mm pike is around 5 percent.
Pike can reach the reproductive stage in a year, females being 30 cm, males 19 cm. Pike normally live 5 to 15 years, but can be as old as 30. Life expectancy and growth are dependent on circumstances. Some Canadian populations have many old slender pikes, Baltic pike grow to great lengths in a short time while eating nutrient rich herring.

Food

The young free swimming pike feed on small invertebrates starting with daphnia, and quickly moving on to bigger prey like isopods like asellus or gammarus. When the body length is 4 to 8 cm they start feeding on small fish.

The pike have a very typical hunting behavior; they are able to remain stationary in the water by moving the last fin rays of the dorsal fins and the breast fins. Before striking they bend their body and dart out to the prey using the large surface of tail fin, dorsal fin and anal fin to propel themselves. The fish has a distinctive habit of catching its prey sideways in the mouth, immobilising it with its sharp backward pointing teeth, and then turning the prey headfirst to swallow it. It eats mainly fish, but also small mammals and birds fall prey to pike. Young pike have been found dead from choking on a pike of a similar size, an observation referred to by the renowned English poet Ted Hughes in his famous poem 'Pike'. Northern pike also feed on frogs, insects and leeches. They are not very particular and eat spiny fish like perch and will even take sticklebacks if that is the only available prey.

The northern pike is a largely solitary predator. It migrates during a spawning season, and it follows prey fish like Roach to their deeper winter quarters. Sometimes divers observe groups of similar sized pike that might have some cooperation and it is known to anglers pike tend to start hunting at the same time, so there are some "wolfpack" theories about that. Large pike can be caught on dead immobile fish so it is thought that these pike move about in a rather large territory to find the food to sustain them. Large pike are also known to cruise large water bodies at a few metres depth, probably pursuing schools of prey fish.
Smaller pike are more of an ambush predator, probably because of their vulnerability to cannibalism. Pikes are often found near the exit of culverts, which can be attributed to the presence of schools of prey fish and the opportunity for ambush. Being potamodromous, all esocids tend to display limited migration, although some local movement may be of key significance for population dynamics. In the Baltic they are known to follow herring schools, and therefore have some seasonal migration.