• Fobert, Emily
  • Meining, Patrick
  • Colotelo, Alison H.
  • O‘Connor, Constance M.
  • Cooke, Steven J.


Research on a wide range of fish species has revealed that deep hooking is perhaps the single most important determinant of injury and post-release mortality in recreational fisheries. However, there is little information on the best option for dealing with deeply hooked fish that are to be released; should the line be cut or should the hook be removed? Using bluegill sunfish (Lepomis macrochirus) as a model we investigated sublethal (e.g., swimming performance, physiological condition, injury levels) and lethal consequences associated with removal of deeply ingested hooks versus cutting the line and leaving the hook embedded in the esophagus, relative to shallowly hooked controls. Neither hook retention nor deep hook-removal altered the swimming performance of the fish in this study relative to controls. However, there was evidence of short-term physiological disturbance. For example, hematocrit was reduced for fish that had hooks removed, consistent with visual observations of bleeding. In addition, blood glucose levels tended to be higher and plasma Na+ levels tended to be lower in deeply hooked fish that had hooks removed indicating stress and ionic imbalance even 24 h after capture. During holding experiments we noted the highest mortality levels in fish for which the hook was removed (33% after 48 h and 44% after 10 days). Mortality rates were lowest for the controls (0% after 48 h and 4% after 10 days) and intermediate for the line-cut treatment (8% after 48 h and 12.5% after 10 days). After 48 h, 45.5% of the fish from the line-cut treatment group were able to expel the hook originally embedded in their esophagus, and at the end of the 10 day study, 71.4% had expelled the hook. Even with the hook left in the esophagus, fish were able to feed although at lower rates than controls during the first 48 h of holding. By 10 days post-capture, there were no differences in feeding rates as evidenced by growth patterns among the treatment groups, nor were there differences in the hepasomatic index. Collectively, the findings from this study demonstrate that cutting the line is a more effective release method than removing the hook when fish are deeply hooked. As such, angler education efforts should focus on disseminating this message to anglers as well as encouraging the use of gear and techniques that minimize incidences of deep hooking (e.g., circle hooks, non-organic bait).


Field site and fish capture

All experiments were conducted at Queen's University Biological Station on Opinicon Lake, Ontario. Opinicon Lake is a mesotrophic natural lake with abundant populations of rock bass Ambloplites rupestris, largemouth bass Micropterus salmoides, smallmouth bass M. dolomieu, pumpkinseed Lepomis gibbosus and, in particular, bluegill sunfish L. macrochirus. Experiments were conducted between May 8 and July 5, 2008. Water temperatures during this time ranged from 12 °C to 23 °C. Cooke et al. (2003) and Gingerich et al. (2007) reported that mortality rates for angled bluegill were uniformly low for bluegills at various temperatures below 26 °C in Opinicon Lake provided that there were not prolonged periods of air exposure. Therefore, water temperature was not considered to be a factor in bluegill mortality rates in this study. Individual study components (e.g., the swimming performance assessment, physiological assays) were conducted across a narrow (1 or 2 °C) thermal range because of the influence of temperature on swimming ability. Other study components (e.g., growth evaluations) involved exposing treatment and control fish to the same thermal environment simultaneously so temperature variation across a study period was not relevant.

All fish were angled using rod and reels and all angling was conducted either from a fishing boat or from docks that extend out into the lake to a depth of at least 1 m. Commercially available barbed J-hooks (Jeros Brand, Rahway, NJ; model K5BH10, snelled baitholder style, bronze material, thin wire, size 10 with a 6 mm gape) were used for angling. These hooks were appropriate to target bluegill (Cooke et al., 2005) and are routinely used by anglers. Organic bait – small worm pieces measuring approximately 5 mm × 5 mm – were used by all anglers. Air exposure duration for all fish caught, whether deep or shallow (controls) was standardized at 60 s, including removal of hook and enumeration, to control for the negative impacts of air exposure and to eliminate differential handling times and air exposure durations as a factor in the analysis. Previous research on bluegill in Opinicon Lake revealed that there was negligible mortality as a result of air exposure of this duration at the temperatures observed in this study (Gingerich et al., 2007). Angler expertise ranged from novice to expert, however, all handling (e.g., once the angler had landed the fish) was conducted by experienced research staff to eliminate the influence of angler expertise on fish handling. Our intention was not to characterize deep hooking rates. Instead, we intentionally let fish “nibble” for sufficiently long periods to ensure that some fish were deeply hooked. Experiments focused on fish that were >130 mm in total length and were carefully balanced across all treatment groups and experiments such that there were no significant (P < 0.05) differences in size (overall mean total length ± SEM = 167 ± 3 cm). All experiments were conducted in accordance with the guidelines of the Canadian Council on Animal Care as administered by the Carleton University and Queen's University Animal Care Committees and with scientific collection permits provided by the Ontario Ministry of Natural Resources.Experimental treatments

Experimental treatments

For all experiments, fish were classified upon capture as either shallowly hooked (hooked in the lip), deeply hooked (hooked in the gullet), or hooked in other locations (e.g., roof of mouth, gills, eye). Fish in the shallow and deeply hooked groups were individually marked with small numbered anchor tags (Floy Manufacturing, WA) while fish hooked in other locations had the hook removed and were released. The shallowly hooked fish were designated the control group, and the hook was carefully removed. The deeply hooked fish were randomly assigned to one of two treatment groups; one in which the hook was removed with surgical hemostats using a steady pull on the line or hook (the hook-removal treatment group), and one in which the line was cut about 1 cm from mouth of the fish and the hook was left in place (the line-cut treatment group). Following hook removal or line cutting, the fish was examined for injury in the mouth and presence of blood was determined to be “none,” “moderate” (less than 0.1 ml), or “severe” (more than 0.1 ml). All fish were then placed into a 1 m3 round tank holding approximately 700 l of water and held for further experimentation (see below).