Background and issues addressed

Rapidly increasing angler use of the Alagnak River rainbow trout fishery since the early 1990’s led to concerns about the health of the population(s) and resulted in regulatory changes to catch-and-release fishing only beginning in 1996. Determined by the number of angler days per year, the Alagnak River is one of the most heavily used trout sport fisheries in the southwest Alaska wild trout management area. Alagnak River rainbow trout are subjected to stresses including exhaustion during the landing process, handling and air exposure during hook removal, and a high probability of hook injury with heavy catch-and-release fishing pressure.

Map of the Alagnak River Drainage

The effects of high incidences of catch-and-release captures on the physiological response by trout to acute stress and any sublethal effects resulting from hooking injuries remain unknown. Mortality and sublethal effects such as changes in reproductive behavior, resistance to disease, and growth suppression or a decrease in appetite have been an observed response by fish subjected to different types of acute stress. Fish with sublethal injuries may be at risk to opportunistic organisms, disease, or fungal infection, and certain injuries, such as eye injuries, may influence the feeding habits of fish. In 1997 and 1998, USGS biologists captured approximately 2100 rainbow trout, the majority of which were caught by hook and line. The number of obvious previous hooking scars was recorded for 1900 individual captured Alagnak River rainbow trout and over 30% of those captured had at least one distinctive mutilation most likely due to previous hooking. Numerous cases of angler dissatisfaction due to trout deformities or injuries purportedly resulting from repeated hooking by anglers have been reported to USGS biologists. The detrimental aesthetics of injured trout have reduced the overall appreciation of the Alagnak River by many anglers traveling to Alaska to fish pristine waters. Research on the various factors that influence hooking injury and the duration of the angling process may provide supplemental information essential in evaluating ways to reduce the severity of hooking injuries, angling mortality, and associated sublethal effects of Alagnak River rainbow trout.

Objectives

The goals of this study were to assess the incidence of hooking injury and measure the immediate physiological stress response to the duration of angling and handling during hook removal. We will address the issues of whether different tackle, methods of fishing (fly vs. spin), time fish are played and landed, experience level of anglers, and water temperature influence the physiological stress levels (cortisol, glucose, lactate, and ions) and hooking injuries in rainbow trout.

Methods

Physiology - Fish greater than 254 mm FL were sampled for blood chemistry during the summers of 2000-2002. Rainbow trout were anesthetized using a clove oil solution and blood was withdrawn from the caudal vessels. Fish recovered in a tub of freshwater and were released near their capture when equilibrium was reached and normal swimming activity resumed. Using a field camp “lab” that was set up on the boat, blood samples were centrifuged and plasma was extracted. Plasma samples were stored in liquid nitrogen tanks and eventually transported to a freezer for analysis at the USGS Conte Anadromous Fish Research Center (http://www.lsc.usgs.gov/caflindex.asp). Different portions of each capture and sampling procedure were timed for fish that were to be sampled for blood chemistry. The timed events included: from the point a fish was hooked until it was landed, time to remove hook, time in clove oil, time fish was sampled for blood, and recovery time. Upon release, fish were followed by foot until out of sight and behavior was recorded (also a timed event).

Drawing blood from the caudal vessels of rainbow trout following catch-and-release fishing.

Hooking injury - Rainbow trout were caught by hook and line using different types of terminal gear in the Alagnak River and at outlets of Nonvianuk and Kukaklek lakes. Method of fishing (fly or spin) and hook type (circle hook barbed and barbless, J hook barbed and barbless) each angler used were randomized twice daily. All captured fish were weighed (g), fork length (mm) measured, and examined for present or past hooking injuries. Angler experience was classified as novice (fished < 10 days over their lifetime) and experienced (fished > 10 days per year) based on the fishing experience of anglers participating in this study. Anglers consisted of USGS and NPS biologists and volunteers, and volunteers from other governmental agencies or the general public.

Fish were not held after capture to monitor mortality rates or the duration of the physiological response to avoid any associated stress or injury resulting from confinement.

Collecting measurement and hooking injury data from captured rainbow trout

Results

Physiology – The levels of plasma cortisol and lactate were evaluated in fish landed and handled for less than 2 minutes (rapid capture) and greater than 2 minutes (extended capture). Plasma cortisol and lactate increased significantly as the duration of the angling process (landing and handling combined) increased. Levels of plasma glucose and ions (sodium, chloride, potassium) did not differ significantly in relation to the duration of the angling process, water temperature, or length. The duration of the angling process was significantly related to fish size, i.e. larger fish took longer to land and handle than smaller fish. Water temperature varied significantly among years, and the levels of plasma cortisol and lactate were significantly higher in years with higher temperatures. Plasma cortisol and lactate concentrations increased with the amount of time fish were angled regardless of the temperature range, however, the magnitude and range of the response was higher in when temperatures were warmer. 

Hooking injury: Hooking injury results were similar in all years and methods remained consistent, thus the data were combined. Hooking injuries were defined as present if there was sufficient tissue damage to external areas that would lead to a permanent scar or if the injuries occurred in sensitive areas (e.g. tongue, gills), and past injuries were old injuries thought to have resulted from previous capture by angling. The majority of fish captured were hooked in the upper or lower external jaw (71%), with the eye or eye and jaw (10%) being the next most common hook locations. About 30% of fish captured had at least one previous hooking scar (mean fork length 410 mm) indicating a substantial portion of the population is subjected to multiple captures.

An example of an Alagnak River trout with no obvious hooking scars

Rainbow trout with a torn maxillary from being previously caught and released

Rainbow trout with missing maxillary and 2 scars on the chin (gular region)

Rainbow trout with missing maxillary

Rainbow trout with inverted maxillary from being previously caught and released

Rainbow trout with missing eye from being previously caught and released

Fifty-eight (n=386/666) percent of fish captured by hook and line experienced at least one new hooking injury (which would lead to a scar or was in a sensitive area). There was no significant difference in the proportion of newly injured fish caught with J hooks by fly fishing (57% injury rate) or spin fishing (62% injury rate), or fish injured while fly fishing with circle hooks (46% injury rate) compared to J hooks (56% injury rate). However, when examining internal injuries only, internal injuries (e.g. tongue, gills, eye, and esophagus) were more frequent in fish caught using J hooks compared to circle hooks, and internally hooked fish bled more frequently than fish hooked externally. Bleeding from new hooking injuries occurred in 25% of fish captured. Of fish injured using fly and spin fishing gear with J hooks (n = 355), significantly more fish were injured when caught using barbed hooks (67% injury rate) than with barbless hooks (50% injury rate). Barbed J hooks were more efficient at landing fish than barbless hooks, with fewer fish lost using barbed hooks, and J hooks were more efficient at landing fish than circle hooks. Barbed J hooks also took significantly longer to remove than barbless hooks. Novice anglers injured proportionally more fish than experienced anglers (70% and 56% injury rate, respectively). Experienced anglers took significantly longer to land fish than novice anglers. There was little variation in the size of fish injured in this study that were caught fly or spin fishing, or caught with barbed or barbless hooks. The degree of injury, as indicated by medium to heavy blood flow, was slightly higher in fish captured with barbed hooks (15%) as compared with barbless hooks (10%) for both fishing methods. Immediate mortality was observed in 8 fish (1.2%), the majority of which were hooked internally and experienced moderate to heavy bleeding from the hook wound or gills.

Management Implications

The results of this study will have direct application for management decisions regarding catch-and-release fishing throughout cold-water regions, and will provide specific recommendations for management tools to restore the naturally occurring rainbow trout population in the Alagnak Wild River to a more pristine state.

Barbed J hooks caused significantly more new hooking injuries, took longer to remove, and were more efficient at catching fish than barbless hooks in this study. A restriction on barbed J hooks would reduce the frequency of injuries and associated bleeding rates, and reduce the amount of time fish are handled when removing hooks. Although circle hooks were not as efficient at landing fish as J hooks, and the overall injury rates were similar between circle and J hooks, the frequency of internal injuries were much less using circle hooks. Numerous studies on the effects of hooking injuries on mortality indicate that fish hooked in sensitive internal areas suffer the highest initial mortality rates. The use of circle hooks could provide benefits to minimize mortality by lessening the frequency of internally hooked fish, yet the poor catch efficiency of circle hooks may make them undesirable for use by anglers.

Initiating angler education programs focusing on proper hook removal techniques and the importance of quick landing times to minimize the physiological response could potentially reduce injury rates and sublethal effects associated with landing and handling times. Minimizing the duration of the angling process will ultimately reduce the peak physiological response and duration of recovery of angled fish, particularly at warmer water temperatures. As the popularity of angling for wild rainbow trout continues to rise in Alaska, resulting in heavier angling pressure and catch-and-release regulations, managers will need to consider the physiological impacts of multiple recaptures on the response of wild fish and the sublethal effects resulting from hooking injuries and the duration of angling on individual rainbow trout, and trout populations.

Manuscripts in preparation.

Contact Information

Julie Meka
Fishery Biologist
USGS, Alaska Science Center
Biological Science Office
1011 E. Tudor Rd., MS 701
Anchorage, AK  99503
(907) 786-3917
(907) 786-3636 FAX
email: julie_meka@usgs.gov

USGS Crew #1 of 2002 - From left to right, Brian Byrne (volunteer), Julie Meka (USGS), Dan Parker (volunteer), Jim Pikul (volunteer), and Elliot Aguillor (NPS). Not pictured, Brad Hanson (volunteer) and Steve McCormick (USGS).
USGS and SCA Alagnak Crew of 2001 left to right - Duncan Oswald (USGS), Bob Frampton (SCA), Julie Meka (USGS), Ryan Gray (SCA), and Phil Richards (USGS)	USGS, NPS, and SCA Alagnak Crew of 2000 left to right - Derek Wilson (USGS), Julie Meka (USGS), Chris Wall (NPS), and Ryan Beatty (SCA)