Sport fishing is a form of recreational fishing where the primary reward is the challenge of finding and catching the fish rather than the culinary or financial value of the fish's flesh. The distinction is not completely rigid - in many cases, sport fishers will also eat their catch. The philosophies and tactics used for sport fishing, however, are usually sufficiently different from "food fishing" to make the distinction clear enough. Sport fishing methods vary according to the area being fished, the species being targeted, the personal strategies of the angler, and the resources available, ranging from the aristocratic art of fly fishing, ostensibly invented in Great Britain, to the high-tech, incredibly expensive methods used to chase marlin and tuna. In virtually every case, however, the fishing is done with hook, rod and reel rather than with nets or other aids. In the past, sport fishers, even if they did not eat their catch, almost always killed them to bring them to shore to be weighed or for preservation as trophies. External pressure from conservationists, combined with a genuine concern about fish stocks, have caused many sport fishers to begin releasing their catch alive, sometimes after fitting them with identifying tags and recording their details so as to aid fisheries research (known as tag and release). Sport fishing competitions give competitors (individuals if the fishing occurs from land, usually teams where conducted from boats) a specified time and area from which they are to catch fish. Scores are awarded for each fish caught, the points depending on the fish's weight and species, and then, sometimes, divided by the strength of the fishing line used (so catching fish on thinner, weaker line scores additional points). In tag and release competitions, a flat score per fish, divided by the line strength, is awarded for each species caught.