Fraser River Sockeye Fisheries and Fisheries Management - Cohen ...

equirements have been applied to several gear types (e.g., gillnetting, seine nets, fishwheels, dip nets, angling). Releasing fish (a.k.a. “discarding” in some literature) hasbecome used increasingly in management but is predicated on the assumption that truerelease mortality estimates are known. Unfortunately, there is almost no scientificallydefensible information on post-release mortality associated with any freshwater gear typeand across all three fishing sectors for Pacific salmon. That stress and injury associatedwith capture can cause mortality after release (both short-term and delayed) in salmonand has been well recognized for over 50 years and therefore efforts have already beenmade to develop effective recovery methods for ocean commercial fisheries (Farrell et al.2001). However, there has been little research to quantify levels of mortality or tounderstand the mechanism underlying mortality in order to better mitigate or preventmortality. Without this type of information, especially in an era of warming riverswherein we expect higher stress-related mortality (Dempson et al. 2002), it is difficult toensure sustainability of salmon fisheries and conservation of stocks.In virtually all types of fisheries, some proportion of individuals die shortly after releaseas a result of acute physical injury (e.g., hooked in the heart, gills tangled in a net).Fitness (i.e., the ability to survive or reproduce) of escapees can also be reduced becauseof minor injury, physiological disturbance, or behavioural alterations (Cooke and Wilde2007). Most research that examines mortality of released fish does so holding them inpens, tanks, or cages (reviewed in Davis 2002, and Cooke and Schramm 2007).Biotelemetry is being used increasingly to study mortality of released fish, eliminatingissues associated with holding fish in captivity (crowding, water quality, abrasion, lack ofpredators) (reviewed in Donaldson et al. 2008). When fish are captured by angling,release mortality can range from 90% depending on specific gear, species,fisher’s skill/intentions, and many environmental factors (reviewed in Arlinghaus et al.2007).A fish’s response to capture is physiologically similar to burst swimming and results in asuite of hormonal, energetic and ionic changes (Wood 1991; Farrell et al. 2000; Kieffer2000). Specifically, it causes anaerobic consumption of endogenous fuels, lactic acidaccumulation, changes in cellular structure and enzyme function, and shifts of water outof the plasma into muscle, ultimately disrupting ionic/osmotic balance (Wood 1991;Kieffer 2000). Capture also causes production of ‘stress hormones’ such as cortisol(Barton et al. 2002), which help fish maintain biochemical homeostasis during stressfulevents but results in the shift of energy from anabolic processes (i.e., growth andreproduction) to catabolic ones (i.e., energy mobilization and restoration of homeostasis)(Wendelaar Bonga 1997). Hypoxia can be associated with capture and release dependingon how fish are captured (e.g., a gill net that restricts ventilation in a fish) and handled57