Suffering at the hands of anglers often continues after fish are unhooked.
Anglers were deployed to catch 1,087 trout on 45 fishing trips, from the Bois Brule River in Wisconsin, United States. 3.5% of the fish died. Of these, 85% died immediately, more than 90% within 24 hours (Dubois, 2004).
In the Bahamas, bonefish were tracked using ultrasonic transmitters and small visual floats. When anglers returned the fish back into waters with a high number of sharks, 39% of the traumatised fish were eaten within half an hour (Cooke, 2004).
An independent panel of experts, who reported in the Medway Report in 1980 for The Royal Society for the Protection of Animals, said that the delicate outer skin and mucus layer of fish can be damaged by anglers when they handle the fish. Normally it provides a barrier to disease-causing micro organisms, found in water. If the harm done is severe, there could be infection of the skin, or circulatory failure, both of which could kill the fish.
Induced stress can lead a weakened immune system, which makes the fish less resistant to disease. Stress can also result in retarded growth. Stress from hooking can also restrict the fish in their reproductive development and success (Muoneke, 1994).
BASS GROW LESS AFTER THEY ARE HOOKED
The species of fish that make nests for their offspring can be threatened by anglers. Scientists in Canada (Kieffer, 1995) found that smallmouth bass, which were exhausted by anglers playing them on a line, took four times longer to return to their nests, exposing their young to predators.
Scientists in America and Canada (Cooke, 2000), while studying largemouth and smallmouth bass, found that males, even when removed by anglers for a short time, lost young to predators. Studies indicate that the behavioral and physiological effects of exhaustive exercise, caused by angling during the spawning period, may be stressful enough to cause abandonment of broods.
Blue sharks off the north-east coast of the USA are frequent victims of anglers. In a single two-day shark fishing tournament off Massachusetts, over 2000 blue sharks were caught. Scientists (Borucinska, 2002) in a study found that 3% of the sharks still had hooks inside their bodies. It is not known how many had died after release. Hooks were found in the oesophagus and gastric wall. Accompanying lesions included oesophagitis, gastritis, hepatitis and proliferative peritonitis. Mechanical trauma and persistent irritation by corroding hooks and bacterial infection causing severe, chronic peritonitis. Sharks can be left seriously weakened and dying.
Also targeted by anglers off the east coast of America, are tunas and marlin. Researchers (Skomal, 2002) found extreme metabolic disruption to the extent of causing the fish to be unable to function properly, or survive at all. After ten minutes of being hooked, tunas had significantly high levels of the stress hormone, cortisol in their blood. The scientists measured cortisol in marlin and discovered that it was among the highest ever measured. A single bluefin tuna, angled for 42 minutes, died immediately after release. This fish had a depressed blood pH and high blood lactate levels, indicative of a severe acidemia (high levels of acid in the blood).
Barotrauma results from a process called decompression, where fish are brought from depth to the surface quickly, leading to rapid changes in ambient pressure. The higher pressure inside the fish can cause horrendous injuries to the fish. Canadian scientists (Gravel, 2008) studied smallmouth bass as they suffered this fate. The harm done to the fish included:
Three-quarters of fish studied had at least one sign of barotrauma (either hemorrhaging or swim bladder distension), a third had severe barotrauma, two-thirds had showed signs of haemorrhage, and nearly half showed signs of extreme bloating.
At the end of the monitoring period, a fifth of fish with severe barotrauma had died; a further fifth that were still at the release site were on the point of death.
Some fish with barotrauma floundered at the surface when released, and one of these fish was subsequently hit and killed by a boat. The researchers found many fish unable, or struggling, to return from the surface. They then faced possible predators, burning from the sun, impacts from boats, or being carried ashore or to hostile environments.
CAUGHT AT DEPTH - HORRIFIC INJURY
A brochure, Bring That Rockfish Down (pdf), produced by the University of Southern California and the California Department of Fish and Game, says that when a Rockfish is caught at depth, its swim bladder rapidly inflates as it is dragged to the surface, even when reeled in slowly. This can cause its stomach to be forced out of its mouth. Eyes may bulge, and there can be injury to other organs. The fish may die from the damage, from temperature shock, or from predators. The longer at the surface, the greater the chance there is of the fish dying, with the odds doubling for every ten-minute increase in time at the surface.
When an angler punctures a fish's swim bladder with a needle or tube they can cause serious injury, and another organ can be damaged and infection can be introduced.
The stress of being caught by anglers reduces the fish's ability to reproduce and can affect its growth. For example, the growth of smallmouth bass was inversely related to the number of times hooked.