Who killed big pike?

A few weeks ago, Fern and I took an early morning walk by the river and found an otter. The photos can be seen on the blog of the time. However, that wasn’t the end of the walk. On the way back, Fern became obsessed with something buried in the vegetation by the bank. She emerged triumphantly carrying the biggest fish-head I’ve ever seen. It was old, stained, mostly bone covered with parchment skin, and I almost had to wrestle her to the ground to get my hands on it.
It was a pike’s skull. After cleaning, bleaching and varnishing, it smelled sweeter and was easier to examine. It measured 22.9 cm (9 inches) from the point of the jaw to the back of the skull, giving an overall fish length in excess of 1.14 meters (45 inches). That’s about the height of a kitchen unit.
pike skulls
So how did it come to be there? I am no pike expert so a lot of what follows is conjecture. Like most living things, death in pikes will occur as a result of natural causes, disease, or injury.
The natural lifespan of a pike seldom exceeds fifteen years. On dying, it will presumably float – like goldfish do – upside down. Assuming it doesn’t become caught in weed or supermarket trollies, it will rise to the surface, whereupon any scavenger could take advantage of a free meal. The skull, being short on meat and long on teeth, would be left to rot. The skull Fern found had splintered bone on one side corresponding to the upper jaw in the dog or cat. Perhaps something had had a gnaw and decided against the rest.
There are a number of parasites – worms and flukes – that can infest pikes; a variety of fatal viral diseases, and surprisingly to me, a tendency to succumb to cancer. Mainly lymphoma (a type of leukaemia) that may be caused by a virus. These can weaken the fish and ultimately, kill it.
Top of the list for inflicting injury to pikes is people. The pike is a sought-after catch and the Broads in particular are a popular area for pike fishing. Anglers come for miles around. Expeditions are mounted. Sometimes the equipment used is crude and damage-causing. Individuals may be caught repeatedly. They are, according to various websites, being fished to the limits of sustainability. An exhausted or injured fish is more likely to become prey rather than predator.
As the pike is pretty well top predator in its own environment, there are not many animals apart from man that can kill it.
Last year an osprey made a regular appearance in our area, and ospreys will catch and eat pike. As I understand it, though, pike are ambush predators, hiding in the weed and pouncing on passing prey. Ospreys catch fish on or near the surface, so pike-eating may be a bit of a rarity.
Then there are otters. They have very catholic diet which includes frogs, small birds and mammals, eggs, and, of course, fish. They have been known to take small pike. A full grown male otter can reach 1.8 m in length, including the tail, or 1.2 m nose to start-of-tail. About the same length as the pike our skull belonged to.
Unless otters hunt in packs, it would have been an almighty battle for a single animal to overcome a pike equal to its size. But then, of course the fish could have been weakened through old age, disease or injury …