Why do fish die after severe exercise?

Trout fitted with dorsal aortic cannulae were subjected to 6 min of intensive exercise and monitored over the following 12 h recovery period. Delayed mortality was 40%; the majority of deaths occurred 4–8 h post‐exercise. Surviving fish exhibited a short‐lived haemoconcentration reflected in increased haematocrit, haemoglobin, plasma protein, Na+ and Ch‐ levels; an extended rise in plasma [K+]; a quickly corrected respiratory acidosis; and a more prolonged metabolic acidosis in concert with a rise in blood lactate. Dying fish exhibited very similar trends except for a significantly greater metabolic acidosis, lower plasma [Cl‐], and the apparent accumulation of an unknown anion in the blood prior to death. Cardiac failure did not occur. Blood metabolic acid levels, while elevated, were only ∼ 50% of peak lactate anion levels and well within the normal range of tolerance, as were all other changes observed in the blood of non‐survivors. The hypothesis that post‐exercise mortality is due to excessive ‘lactic acid’ accumulation in the blood is discounted. It is suggested that intracellular acidosis may be the proximate cause of death.

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

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.

The design and analysis of field studies to estimate catch-and-release mortality

The practice of catch and release (CR) as a fisheries management tool to reduce fishing mortality is widely applied in both freshwater and marine fisheries, whether from shifts in angler attitudes related to harvest or from the increasing use of harvest restrictions such as closed seasons or length limits. This approach assumes that for CR fishing policies to benefit the stock, CR will result in much lower mortality than would otherwise occur. There are many challenges in the design of CR studies to assess mortality, and in many practical settings it is difficult to obtain accurate and precise estimates. The focus of this article is on the design and quantitative aspects of estimating CR mortality, the need for a comprehensive approach that explicitly states all components of CR mortality, and the assumptions behind these methods. A general conceptual model for CR mortality that is applicable to containment and tagging‐based studies with a slight modification is presented. This article reviews the design and analysis of containment and tagging studies to estimate CR mortality over both the short and long term and then compares these two approaches. Additionally, the potential population‐level impacts of CR mortality are discussed. A recurring theme is the difficulty of designing studies to estimate CR mortality comprehensively and the need for additional research into both statistical model development and field study design.

Capture efficiencies of two hook types and associated injury and mortality of juvenile muskellunge angled with live baitfish

Strict harvest regulations and a strong catch‐and‐release ethic among recreational anglers of muskellunge Esox masquinongy have led to interest in developing strategies for reducing injury and mortality of released fish. With many anglers using live baitfish to capture muskellunge, the use of circle hooks may reduce deep hooking and hence mortality. We contrasted the performance of circle hooks and J‐style aberdeen hooks when capturing juvenile muskellunge with actively fished live baitfish. The J hooks performed better than circle hooks in terms of capture efficiency. The J hooks were more efficient at hooking muskellunge than were circle hooks, but landing efficiency was similar between the two types. Interestingly, injury was judged to be low regardless of hook type. Neither anatomical hooking location nor hooking depth differed significantly between fish captured on J and circle hooks. No fish were hooked in potentially lethal locations (e.g., gullet or eye) during the use of either hook type. Ease of hook removal did not differ between hook types, and hooks were generally categorized as easy to remove. Bleeding was considered minor and did not differ between hooks. We observed no initial or delayed mortality for fish captured on J or circle hooks. Given that J hooks have a higher muskellunge capture efficiency and that the use of circle hooks did not provide any compelling conservation benefits, anglers will probably continue to use J hooks and avoid circle hooks. Nonetheless, use of circle hooks could be advantageous for other fishing styles (e.g., still fishing, where baitfish are often swallowed), other species, or different sizes of muskellunge.

Using tag return models to estimate the number of times fish are captured in fisheries with hightcatch-and-release rates

Exploitation rates are often estimated using tag‐return studies. However, in fisheries with a catch‐and‐release component, exploitation rate or fishing mortality may not be the most important metric of interest. Instead, angler catch rates (e.g., fish caught per hour), total catch (including fish that are harvested or released), or the average number of times an individual fish is caught may be a better measure of fishery performance. However, if anglers remove tags from fish before release, then catch estimates will be negatively biased because tag removal will not be accounted for. In this study, maximum likelihood estimation methods were used to estimate catch in fisheries with high rates of catch and release. Right‐censored models were used to accommodate tags that may or may not be removed by anglers. Model‐derived maximum likelihood estimates of mean catch were relatively unbiased under two simulated fishery scenarios. There was a nonlinear, positive relationship between the percentage of tags that were removed from fish before release and the standard error of estimated mean catch. Although the models performed well at estimating catch in the simulations, more study is needed to evaluate how possible violation of model assumptions can affect catch estimates.

Effects of angling with a single hook and live bait on muskellunge survival

Use of live bait for angling of muskellunge, Esox masquinongy, is popular in Wisconsin. A traditional method utilizes a large hook through the bait fish’s snout, which requires the muskellunge to swallow the bait prior to hook set. Adult muskellunge (>76 cm; 30 in) were held in lined hatchery ponds and caught while fishing with live bait on 10/0 size single hooks. The leader was cut and the muskellunge was released when hooked in the stomach. Survival was monitored for up to 1 year. No immediate ( <24 h) mortality occurred. However, 22% of hooked muskellunge died within 50 days and 83% died within 1 year. Necropsies revealed extensive trauma to the stomach and other organs from hooks, along with systemic bacterial infections. Highest mortality on both hooked and control fish occurred over winter through spring. This peak mortality may be associated with natural stressors that occur during the spring spawning period. Mortality rates observed in this study are considered unacceptable for trophy management of muskellunge. Although use of live bait for muskellunge is traditional in Wisconsin, terminal tackle such as quick-strike rigs that hook fish in the mouth or buccal cavity should enhance the chances a released muskellunge will survive.

My, my, how far we’ve come: An examination of the impacts of catch-and-release angling for muskies

Muskellunge (Esox masquinongy) angling has undergone enormous change since the mid 1900s when catch-and-kill regined supreme. When the angling organizations of Muskies Canada Inc. and Muskies Inc. were found in the later 1960s-early 1970s, a paradigm shift occurred and the implementation of catch-and-release practices became increasingly prevelant. Changes to angling equipment, landing devices, angler knowledge (e.g., the impacts of air exposure and water temperature) and attitudes led to the development of today’s handling methods. In 2009, a research project began to test the impact of current prac5ticies and compared them against a gentler alternative procedure. Over two years, 77 muskellunge, up to 132 cm, were angled and blood sampled to examine the physiological changes associated with the two angling treatments. A subsample of 30 fish were radio-tagged to determine the short term behavioural impacts of the catch-and-release process and to determine survival rates. Little physiological change or short term behavioural impacts were noted between ntreatments. All radio-tagged fish survived. The results indicate that today’s handling practices greatly reduced the impacts associated with catch-and-release angling on muskellunge. Furthermore, our research illustrates how angling groups can effectively co-manage resources by ensuring as many fish stay within a population as possible and to ultimately improve the fisheries they use.

Catch-and-release of muskellunge: Philosophy and methods

Organized fishing clubs, such as Muskies Canada and Muskies Inc., feel very strongly that the future of the muskellunge is in doubt. Serious muskellunge anglers feel an obligation to help protect and study this valuable predators, so they are concerned with environmental changes that affects its biology and habits. The dedicated muskellunge angler is also concerned that trophy fish remain available. Since it is the largest freshwater predator, it is hoped there wiol be a new world record. Current conditions indicated that, if trophies of more than 35 pounds are to be expected, most of the smaller fish must be released. Voluntary live release is the most direct and unselfish act an angler can practice to aid this species.

Muskellunge fishing clubs practice and promote live release extensively. Annual records of release and related statistics are share with resource management authorities who in turn share their biological expertise with anglers. Anglers are being taught the sensitivity of the muskellunge and the need to handle it correctly. The fishing public is being made aware of the release concept and proper methods of live release through the media, sports shows and direct demonstration. Achievements by fishermen in this program are publicly acknowledged.

At the present time, anglers have shown a willingness to practice “catch-and-release” and to use one of more of the general release methods which are best described by the handling technique or equipment employed in each. The ten categories are: net, stretchers, hand, lip lock, pistol grip, vice grips, tailing, stunning and two gaff methods. Each technique requires special care, consideration and practice. To ensure future survival of the muskellunge it is the hope of Muskies Canada that fishery agencies in Canada and the U.S. undertake studies to document the best release-handling methods.

The role of temperature in the capture-and-release of fish

We searched major electronic databases to identify peer‐reviewed literature investigating the role of temperature on the stress response and mortality of captured and released fish. We identified 83 studies that fit these criteria, the majority of which were conducted in North America (81%) on freshwater fish (76%) in the orders Perciformes (52%) and Salmoniformes (28%). We found that hook‐and‐line fisheries (65% of all studies) were more commonly studied than all net fisheries combined (24%). Despite the wide recognition for many species that high water temperatures exacerbate the effects of capture on released fish, this review is the first to quantitatively investigate this problem, finding that warming contributed to both mortality and indices of stress in 70% of articles that measured each of those endpoints. However, more than half (58%) of the articles failed to place the experimental temperatures into a biological context, therefore limiting their broad applicability to management. Integration of survival and sublethal effects to investigate mechanisms of fish mortality was relatively rare (28%). Collectively, the results suggest that capture–release mortality increases at temperatures within, rather than above, species‐specific thermal preferenda. We illustrate how knowledge of ecologically relevant high temperatures in the capture and release of fish can be incorporated into management, which will become increasingly important as climate change exerts additional pressure on fish and fisheries.

Catch-and-release rates of sport fishes in northern Wisconsin from an angler diary survey

Recreational freshwater fisheries are key components of local economies in many regions. The quality of these fisheries can be affected not only by harvest but also by catch‐and‐release practices. Documenting catch and release among sport fish taxa is, therefore, important to fisheries researchers studying sport fishes and managers regulating these fisheries. We used an angler diary survey to assess taxon‐specific effort, catch, harvest, release, and reason for release during the 2011 open‐water season. Our study included information on 5,007 fishing trips taken by 652 anglers. These anglers visited 279 lakes spanning 11,761.5 km2 of northern Wisconsin. Muskellunge Esox masquinongy , black bass (i.e., Smallmouth Bass Micropterus dolomieu and Largemouth Bass M. salmoides ), Northern Pike E. lucius , Walleye Sander vitreus , and panfish were released at rates of 99, 97, 86, 67, and 67%, respectively, when targeted by anglers. This study is the first to document black bass catch‐and‐release rates in the region and corroborates previous findings of Muskellunge and Walleye catch‐and‐release rates based on creel surveys. Voluntary catch and release was the most common reason for release. Our findings suggest that regulations may be much more generous than the harvest rates practiced by anglers and that catch‐and‐release angling practices may be an important factor affecting these sport fish populations.