The impact of fishing on individual fish is complex, depending on factors like the fishing method, species, and how the fish is handled. This article explores the various ways fish can be affected, from immediate physical trauma to physiological changes and long-term behavioral alterations.
Immediate Physical Injuries
Fish can sustain direct, visible harm during the fishing process. Hooking is a primary cause of such injuries, with the severity depending on the hook’s location. Hooks embedded in the mouth, particularly the lip or jaw, generally result in higher survival rates compared to those that penetrate deeper.
Injuries to sensitive areas like the gills, eyes, or stomach are more severe and can be fatal. A gill-hooked fish may experience hemorrhage or suffocation. Deep hooking into the throat or gut can cause major internal organ damage and may impair feeding ability.
Beyond hooks, other aspects of capture also inflict physical harm. Fishing lines can cause abrasions, while nets may lead to fin tears or scale loss. Scales provide a protective barrier against pathogens and physical damage, so their loss makes fish vulnerable to infection and disease. Rough handling can remove a fish’s protective slime coat, which is a crucial defense against bacteria and fungi. Squeezing a fish or allowing it to thrash can result in internal organ damage, even if no external wounds are visible.
Stress Responses and Their Effects
Beyond physical injuries, fish experience significant physiological stress during capture, handling, and release. When caught, fish undergo a fight-or-flight response, increasing stress hormones like adrenaline and cortisol. This response causes metabolic changes. One significant internal effect is the buildup of lactic acid in the muscles due to anaerobic activity during the struggle.
The accumulation of lactic acid leads to a decrease in blood pH, a condition known as acidosis. This disruption in blood chemistry can impair metabolic functions and the fish’s ability to recover. While some blood parameters, like glucose and lactate, may return to baseline levels within hours, others, such as cortisol, can remain elevated for longer periods, indicating prolonged stress. This internal biological reaction weakens the fish, making it more susceptible to disease, infection, or predation, even if it appears outwardly unharmed.
Post-Release Mortality
Fish that are released after being caught may not always survive, even if they swim away initially. This phenomenon, known as post-release mortality, can be delayed, occurring hours or even days after the fish is returned to the water. This delayed mortality often results from a combination of the physical injuries and the physiological stress experienced during capture and handling.
Several factors influence the likelihood of a released fish dying. Water temperature plays a significant role; higher temperatures, especially above 18°C, can increase mortality rates, particularly for cold-water species, as warm water reduces dissolved oxygen and exacerbates the effects of exhaustive exercise. The duration of the fight also impacts survival; longer struggles lead to greater lactic acid buildup and higher mortality. Air exposure is another factor, as it limits oxygen exchange across the gills and can cause physical damage, increasing physiological stress and recovery time. Proper handling techniques, such as minimizing time out of water and using wet hands, are important to improve survival chances.
Long-Term Behavioral and Health Impacts
Beyond immediate and delayed mortality, fishing experiences can lead to less apparent but still significant long-term behavioral and health impacts on individual fish. A traumatic capture event might alter a fish’s normal feeding patterns, potentially reducing its foraging efficiency or causing it to avoid certain areas where it was caught. Changes in feeding behavior could affect the fish’s growth and overall energy reserves. Repeated capture or a highly stressful fishing encounter may also influence a fish’s migratory behavior, potentially disrupting its natural movements and patterns.
Some studies suggest that the stress of angling, particularly during spawning periods, can negatively affect reproductive success, such as nest abandonment in species that provide parental care. For instance, male largemouth bass that are highly vulnerable to angling may also exhibit more intensive parental care, and their capture could impact brood survival. Angling nesting bass has been shown to reduce nest success rates and can cause fish to avoid previously used nest sites in future reproductive seasons.
Furthermore, the physiological stress induced by fishing can compromise a fish’s immune system, making it more susceptible to diseases and parasites over time. Elevated cortisol levels, a stress indicator, can suppress immune function, increasing vulnerability to infections that the fish might otherwise resist. This chronic effect on an individual fish’s well-being can impact its ability to thrive and contribute to the population in the long run.