The understudied and underappreciated role of predation in the mortality of fish released from fishing gears

Abstract

The assumption that animals released from fishing gears survive has frequently been scrutinized by researchers in recent years. Mortality estimates from these research efforts can be incorporated into management models to ensure the sustainability of fisheries and the conservation of threatened species. Post‐release mortality estimates are typically made by holding the catch in a tank, pen or cage for short‐term monitoring (e.g. 48 h). These estimates may be inaccurate in some cases because they fail to integrate the challenges of the wild environment. Most obvious among these challenges is predator evasion. Stress and injury from a capture experience can temporarily impair physiological capacity and alter behaviour in released animals, a period during which predation risk is likely elevated. In large‐scale commercial fisheries, predators have adapted their behaviour to capitalize on impaired fishes being discarded, while in recreational catch‐and‐release fisheries, exercise and air exposure can similarly impede the capacity for released fish to evade opportunistic predators. Owing to the indirect and often cryptic nature of this source of mortality, very few studies have attempted to document it. A survey of the literature demonstrated that <2% of the papers in the combined realms of bycatch and catch‐and‐release have directly addressed or considered post‐release predation. Future research should combine field telemetry and laboratory studies using both natural and simulated predation encounters and incorporate physiological and behavioural endpoints. Quite simply, predation is an understudied and underappreciated contributor to the mortality of animals released from fishing gears.

Estimating and mitigating the discard mortality of Atlantic cod (Gadus morhua) in the Gulf of Maine recreational rod-and-reel fishery

“…Lack of a depth effect was also observed in the Baltic Sea's recreational cod fishery, yet in that study fishing was limited to depths ,20 m . It is important to note, however, that the lack of depth effect in the current study pertains only to the capture of cod at 45 -83 m (Table 5) and does not suggest that depth would (Raby et al, 2014), only 5.2% (n ¼ 31) of all cod initially floated at the surface upon release in the current study, which is comparable with other studies where cod were released with no to minimal injury (2.2%, Ferter et al, 2015b). Based on the presence of intraperitoneal gas bubbles and ability to re-submerge in the current study, it is possible that the majority of cod suffered swimbladder ruptures before handling (Humborstad and Mangor-Jensen, 2013).…”

Shark recreational fisheries: Status, challenges, and research needs

“…Often sharks are fingered as the culprit for post-release predation on teleost fish (see Raby et al 2014), but they may also predate upon released sharks (con-specifics or other shark species). The extent to which this occurs is unknown but is certainly worthy of study given that sharks sometimes occur in predator-rich environments.…”

The physiological stress response, postrelease behavior, and mortality of blacktip sharks (Carcharhinus limbatus) caught on circle and J-hooks in the Florida recreational fishery

“…Although the catch-and-release method is advocated and broadly mandated to minimize impacts on fisheries stocks, postrelease mortality may still occur owing to stress, injuries, and an increased susceptibility to natural predation (Bartholomew and Bohnsack, 2005;Cooke and Schramm, 2007;Raby et al, 2014). In efforts to reduce mortality, management practices are enacted to reduce capture stress and physical trauma and thus, ultimately increase the sustainability of fisheries (Davis, 2002;Cooke and Schramm, 2007).…”