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Estimation of Discard Mortality Rates for Pacific Halibut Bycatch in Groundfish Longline Fisheries
Abstract
Mandatory release to the sea of Pacific halibut Hippoglossus stenolepis incidentally harvested in Alaskan and Canadian groundfish fisheries has the potential to close fisheries or to close fishing to individual fishermen or vessels that reach Pacific halibut bycatch mortality limits. Tagging experiments of Pacific halibut from longline gear demonstrated that Pacific halibut with similar types of injuries experienced lower mortality following release from small (13/0) circle or autoline hooks than from large (16/0) circle hooks. As a result, the current viability criteria for individual Pacific halibut overestimate discard mortality rates. Proposed, simplified four-category viability criteria based on injury codes increased accuracy of bycatch mortality calculations over the present three-category criteria. The new criteria may reduce calculated discard mortality of Pacific halibut released from longlines by 20%. Use of the new criteria would result in more accurate estimates, which in turn could lower the probability of bycatch-induced fishery closures, increase the Pacific halibut available for a directed fishery, or both.
... First, a gag reflex test was conducted by holding the head with one hand for stability and inserting a finger into the buccal cavity and touching the throat. A positive response was flaring of the operculum and opening of the mouth more widely [10,17]. Second, an operculum flare reflex was tested by opening the mouth wide and releasing, with the expectation of a flare and then a return to an unflared, closed mouth [10,17]. ...
... A positive response was flaring of the operculum and opening of the mouth more widely [10,17]. Second, an operculum flare reflex was tested by opening the mouth wide and releasing, with the expectation of a flare and then a return to an unflared, closed mouth [10,17]. Third, the vestibular-ocular response was tested by holding the fish above the surface of the water with two hands with minimal pressure and rotating the fish 90 degrees to the right and the left around the long body axis. ...
... Third, the vestibular-ocular response was tested by holding the fish above the surface of the water with two hands with minimal pressure and rotating the fish 90 degrees to the right and the left around the long body axis. A positive reflex was when the eyes tracked the tester or another object [10,17]. Fourth, a reflex to vibration was tested by tapping on the side of the holding tank and watching for a startled movement, sideways or forward [9]. ...
Shortspine thornyhead (Sebastolobus alaskanus) are a benthic, deepwater species in the family Scorpaenidae. They have been tagged annually in Alaska since 1992, but have a low tag return rate of 1.6%. This may be at least partially attributed to post-release mortality related to capture. In this study, 21 shortspine thornyhead were caught on bottom hook-and-line longline gear and immediately given reflex tests. Eighteen were transported to the laboratory and held for 10–42 days, given reflex tests again, and then given postmortem examinations, including histopathology of tissues; three were given postmortem examinations after reflex tests on the vessel. There were no histological findings that could be directly linked to capture and holding; however, there were occurrences of myxozoan (protozoa) and metazoan (nematode) parasites, sometimes associated with minor inflammation. The vibration response reflex was found in only 24% of fish on deck and in 56% of fish after holding in the laboratory. The vestibular-ocular response was present in 47% of fish on deck and 89% of fish in the laboratory. A fish’s ability to right itself was successful on deck in 43% of fish (an additional 19% responded slowly) and 100% in the laboratory. Some reflex impairments may be permanent or may take more than days or weeks to improve. Reflex responses to other tests, the tail grab, gag, and operculum flare, were 95–100% successful on deck and later in the laboratory. A lack of reflexes may increase the risk of predation after release and may affect other behaviors related to survival and productivity.
... Coastwide harvests are distributed among International Pacific Halibut Commission (IPHC) regulatory areas, with a requirement that all commercially captured Pacific Halibut smaller than 81.3 cm FL must be returned to the sea with a minimum of injury. Still, injuries and stress associated with the capture and handling of these fish result in mortality for a portion of released individuals (Kaimmer and Trumble 1998;Trumble et al. 2000;Davis and Olla 2001). Pacific Halibut lack a swim bladder but have been observed to inhabit depths greater than 800 m (Seitz et al. 2011) and may therefore be subject to barotrauma affecting other organ systems (Carlson 2012). ...
... Total discard mortality is subsequently estimated by applying a mean discard mortality rate (DMR) of 16% to the estimated volume of discards. For Pacific Halibut that are directly observed prior to release, individual viability assessments can be conducted that allow these fish to be assigned to one of four injury categories (minor, moderate, severe, or dead) that are associated with category-specific mortality rates (Trumble et al. 2000). During 2020, mandatory discard of sublegalsized Pacific Halibut in the directed commercial fishery was estimated to represent 2.2% of total fishery-induced mortality (Stewart and Webster 2021). ...
... severe = 66.2%; dead = 100%) and the mean fishery-wide DMR (16%) are derived. Injury-specific and mean fisherywide values represent the results of tag recovery analyses (Hoag 1975;Clark et al. 1993;Trumble et al. 2000), based predominantly upon trawl-caught fish, in which Pacific Halibut were assigned to injury categories, tagged, and released. Relative recovery rates by category have been inferred to represent the effects of differential discard mortality, assuming 3.5% capture-induced mortality of Pacific Halibut released with only minor injuries. ...
Pacific Halibut Hippoglossus stenolepis captured in directed commercial longline fisheries in Canada and the USA that are below the legal minimum size for retention must be returned to the sea without incurring additional injury. Estimates of mortality caused by discarding sublegal‐sized fish are included in annual estimates of total mortality from all sources and affect the results of stock assessment and the yield available to fisheries. Currently, an average discard mortality rate (DMR) of 16% is applied to all sublegal‐sized longline discards. These discards consist of fish that suffer injuries ranging from minor to severe. The 16% DMR that is currently applied was derived by averaging injury‐specific DMRs that in turn assume 3.5% mortality of Pacific Halibut that are released to the sea with only minor injuries. The latter has been derived experimentally but only in captivity. Here, we used acceleration‐logging pop‐up archival transmitting tags to infer individual survival outcomes for Pacific Halibut that were released in situ following capture on longline gear. Postrelease behavioral data were evaluated for 75 fish that were at liberty for 2–96 d. Three fish were confidently inferred to have died after periods at liberty of 41–80 d, and another three fish may have died 96 d after release, resulting in minimum and maximum estimated 96‐d postrelease DMRs of 4.2% (range = 0.0–8.7%) and 8.4% (range = 1.7–14.6%), respectively. These ranges are consistent with the currently applied value of 3.5%. However, the observation that no mortalities occurred until after 40 d postrelease departs from the findings of captive studies, in which the majority of capture‐induced mortality occurred within 20 d of release.
... thin each variable were calculated by dividing the number of recaptured fish by the number of tagged fish for each category. Absolute survival rates were calculated for each level of hook severity on the basis of observed recapture rates and the survival rate of a Pacific halibut with minor hooking injuries (Kaimmer, 1994;Kaimmer and Trumble, 1998;Trumble et. al., 2000). Previous studies have determined that the expected survival of a properly handled Pacific halibut is in the 95-98% range; a released fish with minor injuries has an estimated 96.5% survival rate (Trumble et al., 2000). We used the Pacific halibut estimate of survival rate as a proxy for that of sablefish for the following reasons: thes ...
... al., 2000). Previous studies have determined that the expected survival of a properly handled Pacific halibut is in the 95-98% range; a released fish with minor injuries has an estimated 96.5% survival rate (Trumble et al., 2000). We used the Pacific halibut estimate of survival rate as a proxy for that of sablefish for the following reasons: these species do not experience barotrauma as a result of rapid decompression; they co-occur in the same water temperatures, areas, and depths; they are caught with nearly identical gear types; and they are commonly fished by the same fishing vessels and crew. ...
... Like Pacific halibut, sablefish are hardy and, when handled appropriately, have high survival rates after capture and discard. Long-term tagging programs for both species provide evidence of their hardiness (Kaimmer, 2000;Maloney 2 ). The hardiness of sablefish is also supported by previous research in a laboratory setting where there was 100% survival after 60 days (Davis et al., 2001). ...
Sablefish (Anoplopoma fimbria) are often caught incidentally in longline fisheries and discarded, but the extent of mortality after release is unknown, which creates uncertainty for estimates of total mortality. We analyzed data from 10,427 fish that were tagged in research surveys and recovered in surveys and commercial fisheries up to 19 years later and found a decrease in recapture rates for fish originally captured at shallower depths (210-319 m) during the study, sustaining severe hooking injuries, and sustaining amphipod predation injuries. The overall estimated discard mortality rate was 11.71%. This estimate is based on an assumed survival rate of 96.5% for fish with minor hooking injuries and the observed recapture rates for sablefish at each level of severity of hook injury. This estimate may be lower than what actually occurs in commercial fisheries because fish are likely not handled as carefully as those in our study. Comparing our results with data on the relative occurrence of the severity of hooking injuries in longline fisheries may lead to more accurate accounting of total mortality attributable to fishing and to improved management of this species.
... For most applications, the characteristics used to categorize the degree of injury, fish activity, and reflex impairment can be generic to a range of species caught in a range of fisheries (e.g., Benoît et al., 2010; Table 4.1). Alternatively, they can be tailored to a specific situation if there are particular characteristics of discarded individuals for which mortality consequences are known or suspected (e.g., Trumble et al., 2000). For example, there may be specific injuries of hook-caught fish related to tearing of mouthparts or the alimentary canal with differential impacts on mortality, or there may be species-specific responses that can discriminate different degrees of vitality impairment. ...
... In turn, conditional estimates of survival with respect to vitality level obtained from captive observation or tagging can be combined with the vitality observations to produce a weighted estimate of survival that is representative for that fishery (e.g., Richards et al., 1995;Hueter et al., 2006;Benoît et al., 2012)(see Section 4.6). In a unique example, Pacific halibut SQA vitality scoring and prediction of discard mortality has been validated with tagging studies and is used in active fisheries observer programs to estimate mortality rates in assessment models and stock management (Richards et al., 1995;Trumble et al., 2000;NOAA Fisheries 2014). This presents a particularly effective method for representative discard survival estimation. ...
... Different types of injury can be simply quantified as present or absent. Commonly observed injury types include barotrauma (Hannah et al., 2008) and wounding from hooking, abrasion, and predation (Trumble et al., 2000). ...
... Sand fleas (amphipods) may "attack" fish that are recovering after discard from fishing vessels . These scavengers may also attack seemingly healthy fish that are confined within pots or on longlines, especially gears that prevent fish from swimming off the bottom (Trumble et al. 2000). In addition, large predators such as sharks may bite fish that are caught and restricted by longlines and gill nets. ...
... Tag and Recapture Methodology. The tag and recapture methodology has been used to estimate the survival of discarded and released fish (e.g., Pacific halibut; Trumble et al. 2000). This method may provide an indication of long-term survival, but it does not explain much about those fish that have died (when, where, and why). ...
... This method may provide an indication of long-term survival, but it does not explain much about those fish that have died (when, where, and why). In addition, the mark-recapture method used by Trumble et al. (2000) required a host of assumptions that make their survival estimates suspect. ...
Introduction Mortality of Discards and Escapees Assessment of Mortality Factors Causing Stress, Injury, and Mortality Measures to Improve Survival Concluding Remarks References
... Hooking mortality is variable and is affected by many factors, for example, the size and shape of the hook. Trumble, Kaimmer and Williams (2000) conducted a large-scale tagging experiment on Pacific halibut released from longline gear; halibut experienced lower mortality following release from small circle or autoline hooks than from large circle hooks. Neilson, Waiwood and Smith (1989) studied the survival of Atlantic halibut (< 81 cm in size) caught by longline (16/0 circle hooks, at 210 to 300 m). ...
... The tag and recapture methodology has been used mainly to estimate the survival of discarded and released fish (e.g. Pacific halibut; Trumble, Kaimmer and Williams, 2000). This method may provide an accurate indication of long-term survival, but it does not explain much about those fish that have died (when, where and why). ...
... These methods have only been applied in a limited number of fisheries because of the inherent logistical difficulties in holding fish in the field and using tagging studies to estimate bycatch mortality. The most extensive tag and recapture studies of discard mortality have been made on Pacific halibut, with the results being used in management to predict discard mortality rates based on halibut wounding observed in various fisheries (Kaimmer and Trumble 1998;Trumble et al. 2000). Although tag and recapture studies may be an accurate way to assess discard mortality, the results from these studies suffer from being obtained under a limited range of fishing, environmental, and biological (e.g., mixtures of sizes and species of animals) conditions and their interactions. ...
... Delayed mortality resulting from capture has been measured in situ with tag and recapture studies in which all resulting mortality was assumed to result from capture stress. The most extensive studies developed a condition index for delayed mortality in Pacific halibut caught by trawl and hook and line, with fish being recaptured up to several years after tagging ( Richards et al. 1995;Kaimmer and Trumble 1998;Trumble et al. 2000). The fish condition index, based on shipboard visual observations of wounding, has been widely used to estimate Pacific halibut discard mortality rates for management. ...
The mortality of discarded fish bycatch is an important issue in fisheries management and, because it is generally unmeasured, represents a large source of uncertainty in estimates of fishing mortality worldwide. Development of accurate measures of discard mortality requires fundamental knowledge, based on principles of bycatch stressor action, of why discarded fish die. To date, discard mortality studies in the field have focused on capture stressors. Recent laboratory discard experiments have demonstrated the significant role of environmental factors, size- and species-related sensitivity to stressors, and interactions of stressors, which increase mortality. In addition, delayed mortality was an important consideration in experimental design. The discard mortality problem is best addressed through a combination of laboratory investigation of classes of bycatch stressors to develop knowledge of key principles of bycatch stressor action and field experiments under realistic fishing conditions to verify our understanding and make predictions of discard mortality. This article makes the case for a broader ecological perspective on discard mortality that includes a suite of environmental and biological factors that may interact with capture stressors to increase stress and mortality.La mortalité des prises accessoires rejetées à l'eau est une question d'importance dans la gestion des pêches; parce qu'elle est rarement mesurée, elle représente une source considérable d'incertitude dans les estimations de la mortalité due à la pêche à l'échelle mondiale. L'élaboration de mesures précises de la mortalité des prises accessoires nécessite des connaissances fondamentales sur les causes de cette mortalité basées sur les modes d'action des facteurs de stress. À ce jour, les études se sont concentrées sur les stress reliés à la capture. Des études récentes en laboratoire ont souligné le rôle significatif des facteurs de l'environnement, de la sensibilité au stress spécifique à la taille et à l'espèce et des interactions entre les facteurs de stress, qui accroissent tous la mortalité. De plus, la mortalité retardée est un élément important du plan d'expériences. La meilleure façon d'aborder le problème de la mortalité des prises accessoires est par une combinaison d'études de laboratoire des différentes classes de facteurs de stress pour obtenir des connaissances sur les principes fondamentaux de leur mode d'action et par des expériences sur le terrain dans des conditions de pêche réalistes pour vérifier ces connaissances et faire des prédictions sur la moralité. Il faut donc utiliser dans l'étude de la mortalité des prises accessoires une perspective écologique élargie qui considère une série de facteurs environnementaux et biologiques qui peuvent interagir avec les facteurs de stress lors de la capture pour accroître le stress et la mortalité.[Traduit par la Rédaction]
... Previous studies show that RAMP scores are positively correlated with intensity of capture stressors (e.g., Davis 2005Davis , 2007Davis and Ottmar 2006;Humborstad et al. 2009;Raby et al. 2012), but none considered the potential linkage between RAMP and physical injury. Nonetheless, wounds inflicted in fish during capture, which can be highly variable, are a major source of mortality for discards and escapees (Trumble et al. 2000;Suuronen et al. 2005). In the interim, quantitative indexes for physical injuries in fishes have been developed and used in field settings such as visual assessments (e.g., Trumble et al. 2000;Davis 2005;Baker and Schindler 2009) or use of forensic techniques (e.g., fluorescein) to detect nonmacroscopic injuries (Noga and Udomkusonsri 2002;Davis and Ottmar 2006;Colotelo et al. 2009) and might be useful to include when predicting mortality. ...
... Nonetheless, wounds inflicted in fish during capture, which can be highly variable, are a major source of mortality for discards and escapees (Trumble et al. 2000;Suuronen et al. 2005). In the interim, quantitative indexes for physical injuries in fishes have been developed and used in field settings such as visual assessments (e.g., Trumble et al. 2000;Davis 2005;Baker and Schindler 2009) or use of forensic techniques (e.g., fluorescein) to detect nonmacroscopic injuries (Noga and Udomkusonsri 2002;Davis and Ottmar 2006;Colotelo et al. 2009) and might be useful to include when predicting mortality. ...
We sought to improve the understanding of delayed mortality in migrating sockeye salmon (Oncorhynchus nerka) captured and released in freshwater fisheries. Using biotelemetry, blood physiology, and reflex assessments, we evaluated the relative roles of gill net injury and air exposure and investigated whether using a recovery box improved survival. Fish ( ), captured by beach seine, were allocated to four treatment groups: captured only, air exposed, injured, and injured and air exposed. Only half of the fish in each group were provided with a 15-min facilitated recovery. After treatment, fish were radio-tagged and released to resume their migration. Blood status was assessed in 36 additional untagged fish sampled after the four treatments. Compared with fish sampled immediately on capture, all treatments resulted in elevated plasma lactate and cortisol concentrations. After air exposure, plasma osmolality was elevated and reflexes were significantly impaired relative to the control and injured treatments. Injured fish exhibited reduced short-term migration speed by 3.2 km/d and had a 14.5% reduced survival to subnatal watersheds compared to controls. The 15-min facilitated recovery improved reflex assessment relative to fish released immediately but did not affect survival. We suggest that in sockeye salmon migrating in cool water temperatures (∼13°–16°C), delayed mortality can result from injury and air exposure, perhaps through sublethal stress, and that injury created additive delayed mortality likely via secondary infections.
... The authors concluded that the term "dead" was a misnomer. In response to those issues, the IPHC has developed a more elaborate scheme for grading condition, which was considered to be more objective than the previous approach (Table 4; Trumble et al. 2000). ...
... On the other hand, the IPHC has relied extensively on this methodology to validate the condition grades described in the previous section. The different perspectives might be due to the fact that the IPHC were able to tag a large (14,872) number of individuals over three studies conducted during the 1990s, while obtaining an overall 5% recapture rate (Trumble et al. 2000). Such a reporting rate is considerably higher than that experienced in Atlantic tagging studies involving large pelagic species. ...
... Sample sizes would be too small to provide such studies with sufficient statistical power. Conventional tagging has been effectively employed to estimate finfish post-release mortality rates when extremely large sample sizes and high recapture rates were achieved (Trumble et al., 2000). Typically low rates of tag recapture, and confounding by tag shedding and low reporting of recaptured tags, however, generally preclude estimating post-release mortality rates using conventional tagging methods (Neilson et al., 2012). ...
... As with sea turtles, finfish post-release mortality may also be accurately predicted by observing fish condition and vitality. For example, condition indices have been developed for Pacific halibut Hippoglossus stenolepis Schmidt 1904 based on wounding, and for sharks based on revival time following release (Trumble et al., 2000;Hueter et al., 2006). Reflex impairment (Davis & Ottmar, 2006) is a quantitative measure of fish condition that is correlated with stress and may be rapidly evaluated in experiments. ...
Cryptic, not readily detectable, components of fishing mortality are not routinely accounted for in fisheries management because of a lack of adequate data, and for some components, a lack of accurate estimation methods. Cryptic fishing mortalities can cause adverse ecological effects, are a source of wastage, reduce the sustainability of fishery resources and, when unaccounted for, can cause errors in stock assessments and population models. Sources of cryptic fishing mortality are (1) pre-catch losses, where catch dies from the fishing operation but is not brought onboard when the gear is retrieved, (2) ghost-fishing mortality by fishing gear that was abandoned, lost or discarded, (3) post-release mortality of catch that is retrieved and then released alive but later dies as a result of stress and injury sustained from the fishing interaction, (4) collateral mortalities indirectly caused by various ecological effects of fishing and (5) losses due to synergistic effects of multiple interacting sources of stress and injury from fishing operations, or from cumulative stress and injury caused by repeated sub-lethal interactions with fishing operations. To fill a gap in international guidance on best practices, causes and methods for estimating each component of cryptic fishing mortality are described, and considerations for their effective application are identified. Research priorities to fill gaps in understanding the causes and estimating cryptic mortality are highlighted.
... These methods have only been applied in a limited number of fisheries because of the inherent logistical difficulties in holding fish in the field and using tagging studies to estimate bycatch mortality. The most extensive tag and recapture studies of discard mortality have been made on Pacific halibut, with the results being used in management to predict discard mortality rates based on halibut wounding observed in various fisheries (Kaimmer and Trumble 1998;Trumble et al. 2000). Although tag and recapture studies may be an accurate way to assess discard mortality, the results from these studies suffer from being obtained under a limited range of fishing, environmental, and biological (e.g., mixtures of sizes and species of animals) conditions and their interactions. ...
... Delayed mortality resulting from capture has been measured in situ with tag and recapture studies in which all resulting mortality was assumed to result from capture stress. The most extensive studies developed a condition index for delayed mortality in Pacific halibut caught by trawl and hook and line, with fish being recaptured up to several years after tagging (Richards et al. 1995;Kaimmer and Trumble 1998;Trumble et al. 2000). The fish condition index, based on shipboard visual observations of wounding, has been widely used to estimate Pacific halibut discard mortality rates for management. ...
The mortality of discarded fish bycatch is an important issue in fisheries management and, because it is generally unmeasured, represents a large source of uncertainty in estimates of fishing mortality worldwide. Development of accurate measures of discard mortality requires fundamental knowledge, based on principles of bycatch stressor action, of why discarded fish die. To date, discard mortality studies in the field have focused on capture stressors. Recent laboratory discard experiments have demonstrated the significant role of environmental factors, size- and species-related sensitivity to stressors, and interactions of stressors, which increase mortality. In addition, delayed mortality was an important consideration in experimental design. The discard mortality problem is best addressed through a combination of laboratory investigation of classes of bycatch stressors to develop knowledge of key principles of bycatch stressor action and field experiments under realistic fishing conditions to verify our understanding and make predictions of discard mortality. This article makes the case for a broader ecological perspective on discard mortality that includes a suite of environmental and biological factors that may interact with capture stressors to increase stress and mortality.
... Numerous studies have detailed the amounts of fishes discarded from specific fisheries but few studies have documented possible delayed mortality of these discards (Ross & Hokenson, 1997). An obvious exception is in the management of Pacific halibut Hippoglossus stenolepis Schmidt where observations of fish injury are routinely used as substitute measures to calculate mortality rates for fish that are discarded from trawl and fixed gear fisheries (Kaimmer & Trumble, 1998;Trumble et al., 2000). Pacific halibut discard mortality calculations are based on relationships between physical injury and delayed mortality that were Although these substitute indices are widely used, further testing is needed to expand the range of fishing conditions that were included in their formulation. ...
... In light of the observed relationships between physical injury, behavioural impairment and delayed mortality a more accurate substitute measure should include measurement of behaviour impairment and the degree of physical injury (Davis, 2002). Quantitative indices for physical injury in fishes have been developed and used in field settings (Adams et al., 1993;Trumble et al., 2000;Noga & Udomkusonsri, 2002;Parker et al., 2003). ...
Sablefish Anoplopoma fimbria aged 1+ and 2+ years were towed for 4 h in a net, transferred to air for either 15 or 30 min, and then held in tanks for up to 35 days for observation of physical injury, immediate mortality, behaviour impairment, delayed mortality and total mortality. Behaviour was impaired for at least 3 h and returned to normal levels by 24 h after stress induction. Behaviour impairment was correlated with delayed mortality in 2+ year fish but not in 1+ year fish which showed greater variation in stress responses. The results of this study and a review of past discard and escapee studies showed that substitute measures for delayed mortality in the field should include physical injury and behaviour impairment. These two measures integrate the effects of capture-related stressors which can produce and magnify physical and physiological injury, resulting in changes in fish condition and delayed mortality.
... over a range of fisheries (Chopin and Arimoto, 1995). Condition indexes for discards have been developed for Pacific halibut Hippoglossus stenolepis based on wounding and for sharks based on revival time after discarding (Clark et al., 1992;Trumble et al., 2000;Hueter et al., 2006). Plasma constituents have also been tested for possible prediction of fish condition in fishing experiments (ICES, 2000). ...
... A potential problem with the fluorescein technique is that punctures, internal hemorrhaging, or depth of wounds will not be discerned. Types of wounds inflicted in fish during capture are highly variable and can be a major source of mortality for discards and escapees (Neilson et al., 1989;ICES, 2000;Trumble et al., 2000;Suuronen, 2005). Fish injury can be caused by interactions with net structure, other spiny animals in the net, and crushing by biomass or debris in the net; while hooking and unhooking can cause obvious wounding to the mouth, gills, or gut, but little abrasion or crushing. ...
The goal of this study was to test the hypothesis that wounding and reflex impairment, measures of fish condition, could be used to predict mortality in flatfish and roundfish that had been towed in a net in the laboratory. The extent of fish wounding resulting from net abrasion was measured with computer analysis of green fluorescence that occurred when fluorescein was retained in wounds and illuminated with ultraviolet light. Reflex impairment was measured in free swimming fish 5 min after towing by observing orientation, and startle responses to visual and mechanical stimuli. Wounding was related to mortality in walleye pollock, a species that was sensitive to net abrasion, but not in other less sensitive species. Wounding may not predict mortality associated with environmental factors and combinations of stressors in fishing, as the effects of these factors can change without corresponding changes in the extent of wounding. Reflex impairment in walleye pollock, sablefish, northern rock sole, and Pacific halibut was significantly related to mortality in biphasic relationships described by sigmoid curves (y=a/(1+e−(x−x0/b))). Measurement of reflex impairment may be a powerful tool for expanding the scope and replication of fishing experiments in the field and for comparing bycatch mortality among various fishing practices and fisheries.
... Fish condition has been discussed as a general predictor for delayed mortality, but no guidance about how this would be accomplished over a range of fisheries has been given (Chopin and Arimoto, 1995). Condition indices for discard mortality have been developed for Pacific halibut, Hippoglossus stenolepis, based on wounding, and for sharks, based on revival time after discarding (Clark et al., 1992;Trumble et al., 2000;Hueter et al., 2006). To be a comprehensive predictor of bycatch mortality, fish condition must be correlated with discard and escapee mortality over a wide range of fishing conditions including but not limited to catch amount, wounding, environmental factors, and fish size. ...
... These condition measures show inconsistent responses to different types of fishing conditions, including capture, environmental factors, fish size, and combinations of stressors ICES, 2000;Davis, 2002Davis, , 2005Parker et al., 2003;Davis and Schreck, 2005;Lupes et al., 2006). Types of fish wounds that occur during capture are highly variable and can be a major source of mortality in bycatch discards and escapees (ICES, 2000;Trumble et al., 2000;Suuronen, 2005). However, wounding may not predict bycatch mortality when other lethal stressors are present, which act without altering the extent of wounding (ICES, 2000;Davis, 2002;Suuronen, 2005). ...
Davis, M. W. 2007. Simulated fishing experiments for predicting delayed mortality rates using reflex impairment in restrained fish. – ICES Journal of Marine Science, 64: 1535–1542.
Development of efficient methods to predict discard and escapee mortality in fishing operations is essential to the conservation of sensitive fish stocks. For a few fisheries, mortality data are available from fishing experiments in the field; these require long-term holding or monitoring of fish in tanks, cages, or tag and recapture experiments to detect delayed mortality. A different approach to predicting discard and escapee mortality is to use reflex action mortality predictors (RAMP) consisting of relationships between mortality and reflex impairment for species of interest. Fish were towed in a net in the laboratory and then either restrained in foam-lined holders and rapidly tested for reflex impairment five minutes after towing, or held for up to 60 days to determine delayed mortality. Delayed mortality occurred up to 20 days after towing. RAMP was related to mortality with biphasic sigmoid functions. As fishing stressors increased in intensity, the first phase showed an increase in RAMP with no concomitant mortality. In the second phase, RAMP continued to increase, while mortality became apparent and increased. The measurement of RAMP in restrained fish on board fishing vessels during experiments to predict discard mortality and in caged free swimming fish to predict escapee mortality is feasible and advisable.
... Untapped "blue" resources for various uses are abundant in marine environments. Greenland halibut may be a new alternative to provide collagen for conventional cosmetic applications because skins from halibut species are a very abundant by-product in fisheries due to its high volume of fishing [37,38].In this study, the collagen isolated from the skin of the Greenland halibut was used as a raw material for a cosmetic formulation. Our work intends to fully recycle wastes from the fish plant industry and reconvert them in high added value. ...
The industrial processing of fish for food purposes also generates a considerable number of by-products such as viscera, bones, scales, and skin. From a value-added perspective, fish by-products can act also as raw materials, especially because of their collagen content (particularly in fish skin). Interestingly, the potential of marine collagen for cosmetic applications is enormous and, remarkably, the extraction of this protein from fish skins has been established for different species. Using this approach, we investigated the integration of marine collagen (COLRp_I) extracted from the skin of the Greenland halibut as an active ingredient in a cosmetic hydrogel formulation. In this study, extracts of marine collagen at concentrations up to 10 mg/mL showed a non-cytotoxic effect when cultured with fibroblast cells for 3 days. In addition, marine collagen extract, when incorporated into a cosmetic hydrogel formulation, met criterion A of ISO 11930:2019 regarding the efficacy of the preservative system (challenge test). In addition, the cosmetic formulations based on marine collagen at dosages of 0.1, 0.25 and 0.5% were tested in a clinical study on the skin of the forearms of 23 healthy volunteers, showing a sightly hydration effect, suggesting its potential for beauty applications. Moreover, this work illustrates that the circular economy concept applied to the fish processing industry can represent important benefits, at innovation, environmental and economic levels.
... High-grading and discarding of undersized or smaller fish is not considered an important issue in the halibut fishery because of the high survival rate of released halibut (because halibut do not have swim bladders) (Kaimmer & Trumble, 1998;Trumble, Kaimmer, & Williams, 2011). In addition, discarding is not common because baiting and setting hooks on longline gear is time-intensive and bait is expensive; fishermen generally prefer to change their location if they are catching undesired sizes of halibut or non-target species, rather than discarding these. ...
Many fisheries managers and neoliberal fisheries economists promote Individual Transferable Quotas (ITQs) as a solution to the race for fish which can cause rent dissipation under competitive quota or open access fisheries. These actors consider the Canadian Pacific halibut ITQ fishery an example of successful achievement of these objectives. However, critics note the weak performance of this management model in distribution of benefits, increased capital costs to fishermen, deteriorating safety conditions, reductions in crew income and barriers to entry. They point to the layup system which successfully managed effort in the Pacific halibut fishery for four decades prior to the introduction of ITQs. A system similar to the layup has been used for Atlantic halibut since 2013, initiated by the Fish Food and Allied Workers (FFAW) representing owner‐operator license holders in the halibut fishery off the coast of western Newfoundland and southern Labrador. The FFAW rejected the two halibut management plan options presented to them by Fisheries and Oceans Canada: the status quo (a competitive 12‐hr “derby” fishery) or IQs, likely leading to ITQs. Instead, the FFAW worked with license holders to develop a management plan that required harvesters to choose between different fishing periods that spread fishing opportunities over time. This approach improved conservation results, delivered strong economic returns, distributed benefits widely to active fishermen, and allowed an even flow into the market. The authors consider the advantages of these Canadian east and west coast halibut co‐management systems and their broader application.
... Single-species management can be quite successful [6], but often ignores important ecosystem considerations such as species interactions, bycatch, changes in ecosystem structure, and gear impacts on habitat [7]. For example, large bycatch of Pacific halibut in the Bering Sea and Aleutian Islands Groundfish fishery have reduced the catch in the commercial Bering Sea halibut fishery [8,9]. Additionally, the use of single-species reference points, such as harvesting each species at its maximum sustainable yield (MSY), could cause severe deterioration in trophic levels and ecosystem structure by removing top predators with unpredicted consequences at bottom trophic levels [10]. ...
Ecosystem-based fisheries management (EBFM) was developed to move beyond single species management by incorporating ecosystem considerations for the sustainable utilization of marine resources. Due to the wide range of fishery characteristics, including different goals of fisheries management across regions and species, theoretical best practices for EBFM vary greatly. Here we highlight the lack of consensus in the interpretation of EBFM amongst professionals in marine science and its implementation. Fisheries policy-makers and managers, stock assessment scientists, conservationists, and ecologists had very different opinions on the degree to which certain management strategies would be considered EBFM. We then assess the variability of the implementation of EBFM, where we created a checklist of characteristics typifying EBFM and scored fisheries across different regions, species, ecosystems, and fishery size and capacity. Our assessments show fisheries are unlikely to meet all the criteria on the EBFM checklist. Consequentially, it is unnecessary for management to practice all the traits of EBFM, as some may be disparate from the ecosystem attributes or fishery goals. Instead, incorporating some ecosystem-based considerations to fisheries management that are context-specific is a more realistic and useful way for EBFM to occur in practice.
... To evaluate the mortality of discarded animals (henceforth termed "delayed discard mortality"), a variety of methods have been employed. These include the following: 1) captive-holding methods (Kennelly et al., 1990;Bergmann et al., 2001;Parker et al., 2003); 2) mark-recapture methods (Kruse et al., 1994; Watson and Pengilly 1 ; Trumble et al., 2000); and 1 Watson, L. J., and D. Pengilly. 1994 . ...
The delayed mortality rate of crab discarded during fishing operations can be under- or overestimated in laboratory holding experiments, given the unnatural conditions and the short-term duration of these experiments. To evaluate the extent to which a method affects accuracy in these estimations, we compared mortality rates established through laboratory holding with mortality inferred from a year-and-a-half long tag-return study of Dungeness crab (Cancer magister) discarded in Oregon crab fisheries. The reflex action mortality predictor (RAMP) approach, which relates reflex impairment to probability of mortality, was applied in both studies. Similar patterns in mortality-and tag return- rates with respect to fishery, sex, reflex impairment, shell hardness, and injury from the 2 studies lends support to the reliability of the laboratory-generated mortality rates. However, results suggest that mortality rates determined in captivity are likely underestimated when crab are dropped a distance of greater than 6 m (and potentially less) back to water. This underscores the importance of determining the contribution to mortality of variables in the capture, handling, and discard process that are not incorporated in a study to estimate mortality of discarded animals. Both studies also highlighted the significance of sample size when applying the RAMP approach to a fishery with low rates of discard mortality. © 2018, National Marine Fisheries Service. All rights reserved.
... Neilson et al. (1989) estimated that 77% of the Atlantic halibut caught on longline gear would survive. Studies of Pacific halibut survival indicate that survival rates may be as low as 26% and as high as 97% depending on hook removal method, hook removal injury, condition code, and hook size (Kaimmer and Trumble, 1998;Trumble et al., 2000). Most fish caught are in good condition, so a mean population-level survival rate of Pacific halibut caught and released was estimated at 94% (Webster et al., 2013). ...
Atlantic halibut (Hippoglossus hippoglossus) have a long history of exploitation in the Northwest Atlantic and have gone through several periods of high biomass followed
by a population crash. An assessment model using data collected on the Scotian Shelf and southern Grand Banks shows that the
population peaked in 1984, then decreased sharply to a low in 1993. Several management measures were taken during the decline,
including reductions in total allowable catch and a minimum size limit. Concurrently, removals by the otter trawl fishery
were drastically reduced following the collapse of the cod (Gadus morhua) fishery. In 2003, recruitment increased and continued to be high for 6 years. Fishing mortality rates were moderate in the
late 1990s and 2000s and the population increased. By 2009, the Atlantic halibut population was highly productive with both
high biomass and high levels of recruitment. The coincidence in the timing of population recovery and management actions indicates
that effective management contributed to the recovery of Atlantic halibut.
... Numerous studies on a variety of species have shown that, in general, deep-hooking rates are reduced with circle hooks compared to conventional bait hooks, especially in marine settings (reviewed in Cooke and Suski 2004). This has fostered wide acceptance for circle hook use in commercial and recreational marine fisheries, but use in freshwater sport fisheries is also growing in popularity (Kaimmer and Trumble 1997, Trumble et al. 2000, Meka 2004, Cooke and Suski 2004, despite the fact that freshwater research has not demonstrated the benefits of circle hooks as consistently as marine studies (Cooke et al. 2003). Because hooking mortality rates for circle hooks relative to J hooks have been inconsistent across species and settings, Cooke and Suski (2004) suggest that management agencies should not universally adopt the use of circle hooks as a means of reducing deep-hooking in bait fisheries unless compelling comparative species-specific data exist. ...
We estimated hooking and landing success and relative hooking mortality for stream-dwelling trout caught with baited circle and J hooks, J hook dry flies, and treble hook spinners (all hooks barbed). Trout were caught, individually marked, and released for 69 days. Deep-hooking rate was higher for trout captured with baited J hooks (21%) than for spinners (5%), baited circle hooks (4%), and dry flies (1%). Relative mortality rate was higher for trout captured with baited J hooks (25%) and spinners (29%) than for trout captured with baited circle hooks (7%) and dry flies (4%). Deep-hooking was two and six times higher for baited J hooks than baited circle hooks for fish caught actively and passively , respectively. For baited circle hooks, deep-hooking was over three times greater when using an active fishing method (i.e., an active hookset) compared to passive fishing method (no hookset), which conflicts with manufacturer&s recommendations on how circle hooks should be fished. Hooking success (ratio of hook-ups to number of fish strikes) was about one-third lower for baited circle hooks fished both passively and actively compared to other hook types and fishing methods, except for passively-fished baited J hooks. Once hooked, landing success (ratio of fish landed to number of hook-ups) was relatively high for all hook types and fishing methods (range 68–87%). Our results suggest that when bait fishing for trout in streams, circle hook use may reduce deep-hooking and hooking mortality (but also catch rate) regardless of whether anglers fish passively or actively.
... Caging studies have been used to estimate discard mortality but may bias mortality estimates because of unmeasured interaction of fish in cages, elimination of predation, pressure effects from raising and lowering cages on multiple occasions, and questions about whether a fish's caged environment approximates that outside of it (Davis 2002;Pollock and Pine 2007). Tagging methods can be used to estimate rates of mortality for released fish (Trumble et al. 2000) but care must be given to having a control group (Hueter et al. 2006;Pollock and Pine 2007); additionally, the various tagging treatments need to be distributed evenly in space if there will be spatial heterogeneity in tag-recapture effort. ...
We estimated survival rates of discarded black sea bass (Centropristis striata) in various release conditions using tag–recapture data. Fish were captured with traps and hook and line from waters 29–34 m deep off coastal North Carolina, USA, marked with internal anchor tags, and observed for release condition. Fish tagged on the bottom using SCUBA served as a control group. Relative return rates for trap-caught fish released at the surface versus bottom provided an estimated survival rate of 0.87 (95% credible interval 0.67–1.18) for surface-released fish. Adjusted for results from the underwater tagging experiment, fish with evidence of external barotrauma had a median survival rate of 0.91 (0.69–1.26) compared with 0.36 (0.17–0.67) for fish with hook trauma and 0.16 (0.08–0.30) for floating or presumably dead fish. Applying these condition-specific estimates of survival to non-tagging fishery data, we estimated a discard survival rate of 0.81 (0.62–1.11) for 11 hook and line data sets from waters 20–35 m deep and 0.86 (0.67–1.17) for 10 trap data sets from waters 11–29 m deep. The tag-return approach using a control group with no fishery-associated trauma represents a method to accurately estimate absolute discard survival of physoclistous reef species.
... Killer whale presence can be difficult to confirm visually if sea surface conditions are rough or the whales are depredating far off the vessel, resulting in an underestimate of the number of affected skates. In contrast, it is possible that some damaged fish brought on board were damaged by sharks, other fish or sand fleas (High, 1980; Trumble et al., 2000; Dalla Rosa and Secchi, 2007; Stahl and Holum, 2008), possibly resulting in an overestimate of affected skates. Despite the challenges inherent in confirming killing whale depredation, we are confident these results represent a reasonable, if not slightly conservative, estimate of the proportion of skates affected by killer whales on the longline survey and associated catch reductions of depredated groundfish species. ...
Killer whale (Orcinus orca) depredation (whales removing or damaging fish caught on fishing gear) adversely impacts demersal longline fisheries in western Alaska. These interactions increase operating costs and reduce the profitability of longline fishing. This study synthesizes National Marine Fisheries Service observer data, sablefish longline survey and fishermen-collected depredation data to: 1) estimate the frequency of killer whale depredation; 2) estimate depredation-related catch per unit effort reductions; and 3) assess direct costs and opportunity costs incurred by longliners as a result of whale interactions. Average catch per unit effort reductions on depredated sets ranged from 35.1-69.3% for the observed longline fleet in all three management areas from 1998-2012. To compensate for depredation, fishermen set additional gear to catch the same amount of fish, and this increased fuel costs by an additional 82% per depredated set (average 494 per depredated vessel-day for fuel and crew food. This assessment of killer whale depredation costs will help longline fishermen and managers consider the costs and benefits of depredation avoidance and alternative policy solutions.
... There are a variety of tools that have been utilized to estimate rates of bycatch mortality. These tools include direct observation: mark-recapture (Kruse et al., 1994;Trumble et al., 2000;Watson and Pengilly, 1994), acoustic telemetry (Pepperell and Davis, 1999), and captive holding studies Kennelly et al., 1990;Parker et al., 2003). Researchers have also quantified impairment attributed to fishing stressors based on physiological parameters, including metabolic, biochemical, and immune responses (Aparicio-Simón et al., 2010;Broadhurst et al., 2009;Leland et al., 2013;Mercier et al., 2006; http://dx.doi.org/10.1016/j.fishres.2014.07.012 0165-7836/© 2014 The Authors. ...
The fate of incidentally captured snow crab (Chionecetes opilio) and Tanner crab (C. bairdi) in Alaskan groundfish bottom trawl fisheries is not expressly understood. The uncertainty in predicting fatality restricts assessments of the crab populations and depiction of trawl fleet impacts. To predict the fate of discarded crab we used an adapted reflex action mortality predictor, which uses the absence of several reflexes to predict delayed mortality. Crabs caught in the trawl were assessed using this predictor, then samples with the different reflex states were observed over time and mortality was noted. Previous research evaluated the potential to use this method to predict delayed mortality of crabs that interact with the gear, but are not captured. This study aims to validate the use of this prediction method on captured crabs, to compare its application to crabs that encounter the trawl but are not landed to those that are, and to evaluate the influence of variables such as haul time, time on deck, and catch volume.
This project is being conducted as part of the Collaborative Fisheries Research Graduate Fellowship Program, which provides opportunities for scientists to conduct research jointly with fishermen, combining the unique knowledge and experience of each to enhance research. This work will benefit from the support of the Program community as well as from previously developed partnerships in Alaska.
... There are a variety of tools that have been utilized to estimate rates of bycatch mortality. These tools include direct observation: mark-recapture (Kruse et al., 1994;Trumble et al., 2000;Watson and Pengilly, 1994), acoustic telemetry (Pepperell and Davis, 1999), and captive holding studies Kennelly et al., 1990;Parker et al., 2003). Researchers have also quantified impairment attributed to fishing stressors based on physiological parameters, including metabolic, biochemical, and immune responses (Aparicio-Simón et al., 2010;Broadhurst et al., 2009;Leland et al., 2013;Mercier et al., 2006; http://dx.doi.org/10.1016/j.fishres.2014.07.012 0165-7836/© 2014 The Authors. ...
To quantify total fishing mortality it is necessary to incorporate mortality rates attributed to bycatch, including animals that are discarded and that interact with the gear without being caught. The Reflex Action Mortality Predictor (RAMP) approach has been increasingly used to determine bycatch mortality rates in fisheries. This methodology creates a RAMP that relates reflex impairment to probability of mortality. As the RAMP approach becomes more prevalent it becomes important to evaluate the efficacy of its application. We evaluated the flexibility of this methodology by creating a RAMP for Tanner crab (Chionoecetes bairdi) discarded from the groundfish bottom trawl fishery in the Gulf of Alaska and comparing it to a previously established RAMP for unobserved Tanner crab bycatch (encountered gear and remained on the seafloor) from the bottom trawl fishery in the Bering Sea. The two RAMPs and the overall mortality rates calculated using these predictors were comparable. However, we detected significant differences between RAMPs. While probabilities of mortality were similar between the two studies for crab with all or no reflexes missing, discarded crab with intermediate reflex impairment had lower mortality probabilities than those from the unobserved-bycatch study. Our results indicate that a RAMP may produce more accurate mortality estimates when applied to animals experiencing similar stressors as those evaluated to create the RAMP, through similar methodology.
... If mortality is a function of the severity of injury, then this would explain at least a small part of why Area 4B had lower recovery rates than other areas. Trumble et al. (2000) estimated survival rates of captured fish by injury class for longline gear (used on the IPHC surveys), and based on these rates and the values in Table 1, 94% of fish would survive the tagging process in a typical regulatory area, while 91% would survive in Area 4B. ...
Results of a coastwide tagging study show that ontogenetic migration of Pacific halibut (Hippoglossus stenolepis) continues for larger fish, whereas in recent years the assumption had been that only smaller, younger fish migrated. In 2003–2004, a total of 67 000 Pacific halibut tagged with passive integrated transponder tags were released by the International Pacific Halibut Commission (IPHC) from Oregon to the Bering Sea. Portside scanning recovered over 3000 of these tags. Models were fitted that allowed commercial fishing mortality to be a function of fish length, year, and IPHC regulatory area, while migration probability was a function of area and length. Estimates from the models support the view that exploitation rates were much higher in eastern than western areas prior to the reduction of quotas following new results from a coastwide stock assessment in 2007. We explore possible explanations for differences between tagging and IPHC stock assessment results and note that this research provides confirmation of historical inferences regarding patterns of halibut migration based on conventional tagging.
... Flatfish are one of the important components in several demersal communities around the world [25,26]. They are also an important commercial catch species [11]. ...
The seasonal dynamics of flatfish assemblage in the coastal waters off northeastern Taiwan was examined based on samples collected between March 2004 and March 2005 taken by bottom trawlers and landed at Da-Shi fishing port, Yilan county. A total of 28 species from 5 families and 18 genera were found. The Bothidae was the most dominant family, accounting for 81% of the total catch, while the most dominant species was the Pseudorhombus pentophthalmus. Species richness and diversity were high between the end of fall and the end of spring, but low in summer. Multivariate analyses based on cluster and nonparametric multi-dimensional scaling identified three seasonal assemblages as follows: late-spring to summer, fall to mid-winter, and late-winter to mid-spring. The two dominant species in each assemblage were the same, namely P. pentophthalmus and Cynoglossus kopsii. Rare or less abundant species were found to account for most of the differences among seasonal assemblages. The overwhelming dominance of one or two species suggests that monitoring of ecosystem change may be possible using these species. In addition, in this region a striking increase has been observed in both flatfish catch (3.5 folds from 2001 to 2007) and catch percentage (2.5 folds from 2002 to 2008), during the period when total landings of trawl fisheries either remained stable (2002-2007), or declined (after 2007). These findings may be due to the increase of fishing pressure andmay reflect changes in the community structure of demersal fish in the region.
... When predators are the proximate cause of mortality for fishes released from fishing gears, the ultimate cause of the predation event is anthropogenic imposition of stress and injury. A fish's encounter with fishing gear always includes both physical injury (Trumble et al. 2000;Baker and Schindler 2009) and physiological stress (Wood et al. 1983); indeed, it is not possible to capture a fish, at least on a hook, without causing both (Cooke and Sneddon 2007). Examples of common physical injuries are hooking wounds, loss of protective mucous, scale loss, skin loss or loss of appendages (e.g. ...
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.
... Killer whale presence can be difficult to confirm visually if sea surface conditions are rough or the whales are depredating far off the vessel, resulting in an underestimate of the number of affected skates. In contrast, it is possible that some damaged fish brought on board were damaged by sharks, other fish or sand fleas (High, 1980;Trumble et al., 2000;Dalla Rosa and Secchi, 2007;Stahl and Holum, 2008), possibly resulting in an overestimate of affected skates. Despite the challenges inherent in confirming killing whale depredation, we are confident these results represent a reasonable, if not slightly conservative, estimate of the proportion of skates affected by killer whales on the longline survey and associated catch reductions of depredated groundfish species. ...
Peterson, M. J., Mueter, F., Hanselman, D., Lunsford, C., Matkin, C., and Fearnbach, H. 2013. Killer whale (Orcinus orca) depredation effects on catch rates of six groundfish species: implications for commercial longline fisheries in Alaska.
– ICES Journal of Marine Science, 70: 1220–1232.
Killer whale (Orcinus orca) depredation occurs when whales damage or remove fish caught on longline gear. This study uses National Marine Fisheries
Service longline survey data from 1998–2011 to explore spatial and temporal trends in killer whale depredation and to quantify
the effect of killer whale depredation on catches of six groundfish species within three management areas in Alaska: the Bering
Sea, Aleutian Islands and Western Gulf of Alaska. When killer whales were present during survey gear retrieval, whales removed
an estimated 54–72% of sablefish (Anoplopoma fimbria), 41–84% of arrowtooth flounder (Atheresthes stomias) and 73% (Bering Sea only) of Greenland turbot (Reinhardtius hippoglossoides). Effects on Pacific halibut (Hippoglossus stenolepis) and Pacific cod (Gadus macrocephalus) were significant in the Western Gulf only with 51% and 46% reductions, respectively. Overall catches (depredated and non-depredated
sets) for all groundfish species significantly impacted by killer whale depredation were lower by 9–28% (p < 0.05). Effects on shortspine thornyhead (Sebastolobus alascanus) catches were not significant in any management area (p > 0.05). These results provide insight into the potential impacts of killer whale depredation on fish stock abundance indices
and commercially important fisheries in Alaska and will inform future research on apex predator–fisheries interactions.
... Furthermore, as conditions in the fishery change between years (e.g., different seasons or areas fished), so can the resulting discard mortality rates. However, the problem of estimating relevant discard mortality rates remains tractable if it can be decomposed into conditionally linked steps (e.g., Hueter and Manire, 1994;Richards et al., 1995;Trumble et al., 2000). In doing so, research efforts can be focussed on the step(s) where the contribution to variance in survival estimates is greatest, and where changes in fishery conditions are most likely to effect changes in mortality. ...
Obtaining a representative estimate of discard mortality for population and ecosystem assessments is very challenging. This can only rarely be done directly by recovering tagged discarded individuals. Instead, semi-quantitative measures of individual fish vitality or physical condition, obtained by onboard observers prior to discarding, can be used. Such vitality measures can be a good indicator of discard mortality, and by virtue of the data collection method, should also reflect the condition of discards throughout the fishery. Furthermore, vitality can be predicted using covariates known to affect discard mortality, allowing for a more general assessment. We argue that a representative mortality rate can be estimated using the product of at least two probabilities: that of belonging to a particular vitality class, conditional on the factors experienced during capture and catch handling; and the probability of surviving the event, conditional on pre-release vitality. Here we estimate mortalities for five fish taxa captured in southern Gulf of St. Lawrence fisheries. The conditional survival probabilities were obtained using survival analysis of data from experiments in which fish were captured using commercial fishing methods and held to assess short-term mortality (2–3 days). The analysis included a mixture model with a fraction of unaffected individuals, which appears appropriate for data from bycatch mortality studies. Based on this study and the mechanistic interpretation of the mixture model, short-term monitoring of discard mortality may be sufficient to characterize longer term impacts in a number of taxa.
... Research undertaken on a variety of fish species in India, South Africa, Canada, and United States indicates factors that can affect bycatch rates, including seasonal fluctuations in fish abundance, area fished, depths fished, type of equipment used, size of catch, and presence of an independent observer (Howell & Langan 1987;Wallace et al. 1998;Trumble et al. 2000;De Silva et al. 2001;Helser et al. 2002;Milessi & Defeo 2002). Many of these factors are of little importance in the New Zealand ling BLL fishery. ...
Reports by commercial fishers in New Zealand's ling (Genypterus blacodes) bottom longline fishery were analysed to identify the influence of official fishery observers on reported weights of bycatch. Observer data show that on every day ling were taken by bottom longline, both individual transferable quota (ITQ) and nonquota (non‐ITQ) bycatch were reported. However, commercial fishers reported ITQ bycatch on 82% of days fished, and non‐ITQ bycatch on only 50% of days fished. Frequencies of reported bycatch were compared for fishers’ data with and without an observer aboard for the Chatham Rise, Campbell Plateau, and Bounty Plateau areas. Significant underreporting of bycatch was indicated for some bycatch fish species in several areas in the absence of an observer. A sample selection model of reported spiny dogfish (Squalus acanthias) bycatch was used to model the effects of observers on whether spiny dogfish bycatch was reported at all, and the effects of observer presence and other independent variables on the quantity of spiny dogfish bycatch reported. The evidence reported here illustrates that misreporting of bycatch is common and can introduce significant errors into total catch estimation that can have serious implications for fishery sustainability.
... Increasing the survival of undersized fish will contribute to an increase in spawning stock biomass. There is considerable evidence that large discard quantities represent forgone production and yield, leading to future economic losses for the fishery (Trumble et al. 2000;Davis 2002). A recent stock assessment of red porgy suggested that effective monitoring of the stock's recovery, especially under further fishing mortality reduction, would require more detailed information on discards (SAFMC 2002). ...
Red porgy Pagrus pagrus, scamps Mycteroperca phenax, and gags M. microlepis support valuable recreational and commercial fisheries in North Carolina. Fish in the snapper–grouper complex are managed to prevent overfishing and maintain a stable spawning stock. We investigated postrelease mortality of 263 undersized red porgy, scamps, and gags that were captured by angling and subjected to short-term (2 h) and long-term (48 h) holding experiments. Fish were caught at depths ranging from 15 to 45 m using traditional bottom-fishing hook-and-line gear. Catch per unit effort ranged from 0.11 to 1.80 fish/rod-hour (FRH) for sublegal-sized fish and from 0.06 to 0.50 FRH for legal-sized fish. Nontarget species predominated in the catch (N = 1,135), but the red porgy was the most frequently caught individual species (N = 196). The effects of short-term (2-h) holding within species were similar between fish held in different locations (oxygenated live well or cage anchored to the seafloor); mortality did not differ between the two holding location groups. Mortality of fish subjected to short-term holding in the live well was 6.1%; mortality of fish in the submerged cage was 10.5% for the 2-h holding period and 12.3% for the 48-h holding period. There was no significant effect of anatomical hook location on mortality of gags or scamps. However, hook location significantly affected survival of red porgy; individuals hooked in the lip were 11.34 times more likely to survive than fish hooked in other locations. The results of this study suggest that short-term holding is appropriate for assessing mortality of undersized fish caught offshore in a hook-and-line fishery.
... There are few methods for estimating mortality rates after fish are discarded. Correlating observed wounding and delayed mortality in discarded Pacific halibut with tag and recapture methods has been used under a limited set of fishing conditions by the International Pacific Halibut Commission (IPHC) to model and calculate discard mortality rates (Williams et al. 1989;Trumble et al. 2000). Measurement of plasma constituents in fish stressed by capture or handling has been suggested as a method for estimating delayed mortality (Schreck 1981;Schreck et al. 1989;Olla et al. 1998). ...
Age-1 and age-2 Pacific halibut Hippoglossus stenolepis were exposed to a range of times in air (0–60 min) and air temperatures (10°C or 16°C) that simulated conditions on deck after capture to test for correspondence among responses in plasma constituents and mortality. Pacific halibut mortality generally did not correspond with cortisol, glucose, sodium, and potassium since the maximum observed plasma concentrations were reached after exposure to 30 min in air, while significant mortality occurred only after exposure to 40 min in air for age-1 fish and 60 min in air for age-2 fish. Predicting mortality in discarded Pacific halibut using these plasma constituents does not appear to be feasible. Lactate concentrations corresponded with mortality in age-1 fish exposed to 16°C and may be useful predictors of discard mortality under a limited set of fishing conditions.
... In other studies off northeastern America, Caddy (1973) and Meyer et al. (1981) employed scuba divers to directly observe the damage and unaccounted fishing mortality (caused by escape, drop out and predation) of deep-sea scallops and Atlantic surf clams, respectively, after dredging. While such methods have not been extensively applied to other towed gears (Richards et al. 1995), mark-recapture studies have been used to estimate the mortality of fish released from capture by hook and line (Trumble et al. 2000) and could have some utility in future work with trawls, provided there is sufficient effort and cooperation among fishers to guarantee an adequate rate of tag returns. ...
More than 50% of the world's total marine catch (approximately 81 million tonnes) is harvested using towed fishing gears (i.e. Danish seines, dredges and otter and beam trawls). As for all methods, the total fishing mortality of these gears comprises the reported (landed) and unreported catch and other unaccounted, collateral deaths due to (i) avoiding, (ii) escaping, (iii) dropping out of the gear during fishing, (iv) discarding from the vessel, (v) ghost fishing of lost gear, (vi) habitat destruction or subsequent (vii) predation and (viii) infection from any of the above. The inherent poor selectivity of many towed gears, combined with their broad spatial deployment, means that there is considerable potential for cumulative effects of (i)–(viii) listed above on total fishing mortality, and subsequent wide-scale negative impacts on stocks of important species. In this paper, we develop a strategy for minimizing this unwanted exploitation by reviewing all the primary literature studies that have estimated collateral, unaccounted fishing mortalities and identifying the key causal factors. We located more than 80 relevant published studies (between 1890 and early 2006) that quantified the mortalities of more than 120 species of escaping (26 papers) or discarded (62 papers) bivalves, cephalopods, crustaceans, echinoderms, elasmobranches, reptiles, teleosts and miscellaneous organisms. Seven of these studies also included the estimates of mortalities caused by dropping out of gears, predation and infection [(iii), (vii) and (viii) listed above]. Owing to several key biological (physiology, size and catch volume and composition), environmental (temperature, hypoxia, sea state and availability of light) and technical (gear design, tow duration and speed) factors, catch-and-escape or catch-and-discarding mechanisms were identified to evoke cumulative negative effects on the health of most organisms. We propose that because the mortalities of discards typically are much greater than escapees, the primary focus of efforts to mitigate unaccounted fishing mortalities should concentrate on the rapid, passive, size and species selection of non-target organisms from the anterior sections of towed gears during fishing. Once maximum selection has been achieved and demonstrated to cause few mortalities, efforts should be made to modify other operational and/or post-capture handling procedures that address the key causal factors listed above.
... Conditional survival rates have been successfully estimated for Pacific halibut (Hippoglossus stenolepis; Hoag, 1975;Trumble et al., 2000) and sharks (Hueter and Manire, 1994), based on tagging. Preliminary analyses in the present study, suggest that this is possible for a broader suite of species, based on laboratory holding. ...
Understanding the factors affecting the likelihood that discarded fish will die can contribute to better management of resources by enhancing the potential for successful live release and by improving the estimation of otherwise unaccounted fishing mortality. Semi-quantitative measures of individual fish vitality or physical condition, obtained by at-sea observers aboard commercial fishing vessels, are often used as an indicator of survival potential for discarded fish. The present study and previous ones have shown that these measures relate well to eventual survival. However, observer subjectivity in fish vitality scoring can affect the precision and accuracy of inferences drawn from an analysis of the observations. Here we propose the use of a mixed-effects multinomial proportional-odds model, which is appropriate for modelling ordinal vitality data and is a useful approach for addressing observer scoring subjectivity. This model was used to analyse data collected for eleven fish taxa captured by four gear types. The effect of eight factors previously shown to affect discard survival was evaluated. The gear type used and amount of time that fish spent on deck prior to discarding most strongly and consistently affected the distribution of fish among vitality levels. Sea surface and air temperatures, and fish body size, were also important factors for a number of taxa, while other factors such as the depth fished, catch size and fishing activity duration were important only for certain taxa. A random effect in the model, used to account for observer subjectivity, was significant for most taxa and fisheries. Failure to account for this effect could affect both the precision and accuracy of inferences on the survival potential of discarded fish.
... Aguilar et al. (2002) found similar results for adult red drum angled in North Carolina waters. Other studies have also shown that circle hooks increase CPUE while decreasing deep hooking in a longline setting (Trumble et al. 2000; Woll et al. 2001). We found that overall 48-h mortality percentages of deep-hooked adults were similar between J-hooks and nonoffset circle hooks. ...
Saltwater anglers along the entire coast of the southeastern United States target red drum Sciaenops ocellatus more frequently than any other recreational fish species. The frequency of catch-and-release angling has increased dramatically for this species in the past two decades, but little is known about the survival of released fish. This study demonstrates that catch-and-release mortality rates for subadult and adult red drum differed significantly among the most popular types of fish hooks in each fishery. To investigate the effect of hook type on anatomical hooking location and short-term (48-h) mortality, we captured subadults (339-825 mm total length [TL]) by use of 2/0 J-hooks (n = 57 fish), 4/0 nonoffset circle hooks (n = 58 fish), and 4/0 offset circle hooks (n = 57 fish). Nonoffset circle hooks penetrated shallow regions of the body (jaw, tongue, or inside of mouth) significantly more frequently (90%) than did J-hooks (60%) or offset circle hooks (80%). Nonoffset circle hooks also resulted in the lowest rate of subadult mortality (2%). Adults (660-1,138 mm TL) were captured on bottom longline gear with 7/0 J-hooks (n = 60) and 9/0 nonoffset circle hooks (n = 107). The frequency of deep hooking in adults was significantly higher for J-hooks (30%) than nonoffset circle hooks (3%). Only deep hooked fish were monitored for 48-h survival. Adult mortality after 48 h was lower for nonoffset circle hooks (1.9%) than for J-hooks (3.3%). These mortality rates should be considered in future red drum stock assessments.
... flexes the body when the throat is stimulated and the vestibular-ocular response (VOR) shown by eye rolls when the body is rotated around the long axis (Trumble et al. 2000;Davis 2007). Other studies of reflexes in free swimming fish have included atonic immobility, dorsal light reaction, and optomotor and optikinetic responses (Douglas and Hawryshyn 1990;McCormack and McDonnell 1994;Wells et al. 2005;Hasegawa 2006). ...
Fish stress and mortality can be significant problems in both capture and culture operations. In addition to inexpensive and real-time metrics, ones that are simple to use are also desirable for measuring fish stress and predicting mortality. Current methods to define stress rely on expensive, laboratory-based measurements of changes in fish pathology such as disease, necropsy and histology, in physiology such as plasma cortisol, lactate, glucose and ions and in complex behaviour determined from swimming, feeding and predator evasion. All of these methods are often not rigorously linked to fitness outcomes. An alternative is to observe reflex impairment as a direct sign of stress which can be easily and rapidly measured in free swimming or restrained fish responding to peripheral stimuli such as gravity, light, sound and touch. Reflex impairment is correlated with stress and mortality outcomes, eliminating the need for prolonged holding or monitoring of fish. A few examples of reflexes that may be impaired include orientation, startle responses, fin erection, body flex upon restraint, operculum and mouth clamping or gaping, gag response and vestibular–ocular response. Reflex impairment combines the effects of stressors and their interactions and is not dependent on fish size, motivation states and acclimation which make it a consistent sign of stress across a wide range of stressor types and fish ages. Use of reflex impairment to measure stress and predict mortality would significantly improve monitoring of fish health and welfare in many types of field operations such as commercial and recreational fishing, aquaculture, live transport, stock enhancement and tagging.
... Although this has been changing in recent years, the change has not been significant enough to precipitate high-grading. Unlike many other groundfish, halibut has low discard mortality so that when juvenile or under-sized halibut are hooked and discarded, greater than 80% are expected to survive [14]. Highgrading and discard mortality of the target species are, therefore, two problems widely appearing in ITQ systems [15] which are absent or minimal in the halibut fishery. 2 Because of the contentious nature of the halibut ITQ system, twice voted down by a majority of fishermen, a rule was created capping the holding of more than 1% of the TAC as quota on a single halibut license. ...
Despite the increasingly positive reviews of individual transferable quotas (ITQs), few studies have considered how quota leasing activities can reduce the economic benefits to society and to fishermen operating under the ITQ fisheries system. This analysis reveals negative economic impacts of ITQs previously overlooked by examining the extent of quota leasing and the relationship between the catch value, the cost of fishing, and the quota lease price in the BC halibut fishery, long considered a poster child for ITQs. Findings challenge assumptions of economic theory used to promote the benefits of ITQs.
... There are relatively few reports on discard rates or the fates of dis-carded fish from commercial longline fisheries (Rudershausen et al., 2007;Trumble et al., 2000;Welch et al., 2008;Willis and Millar, 2001). ...
Conservation of ecologically related species and understanding the discard composition of fisheries are major concerns for marine ecosystem conservation. However, high sea longline fisheries data are insufficient because of difficulties in deploying observers for data collection. Observer data collected from 77 trips on Taiwanese large-scale longline fishing vessels in the Indian Ocean from June 2004 to March 2008 were used to estimate the scale of the bycatch. At least 40 species were recorded. Albacore, bigeye, yellowfin, and southern bluefin tuna were the major species recorded and comprised over 73.30% of the total retained catch. Major bycatch species were swordfish, blue shark, sailfish, pomfret, and escolar. The average discard rate was 14.09%, ranging from 3.20% for the yellowfin tuna fleet to 18.09% for the bigeye tuna fleet. In total, 0.80% of the catch of the albacore, 4.74% of the bigeye, and 2.32% of the yellowfin tuna were discarded. There were significant differences among seasons and areas for the discard rates of the bigeye and yellowfin tuna. The discard rates of the bigeye and southern bluefin tuna were positively correlated to the catch per unit effort. The depredation percentage of tuna by cetaceans was from 0.7% to 12.3% of total discards for the different fleets. The high discard and cetacean depredation rates showed that major possible reasons for discards are depredation by cetaceans, economic factors, and quota limitations. Regarding other species, 61 seabirds and 84 sea turtles were a part of the bycatch. The major species were Indian Yellow-nosed Albatross in the southern Indian Ocean and Olive Ridley turtles in tropical areas. The estimated annual incidental catch numbers were 715 to 311 seabirds and 1856 to 1127 sea turtles from 2004 to 2007. For conservation, this discard information could be used to assess tuna stocks. Mitigation measures, including the live release of small-sized fish, and the use of bird-scaring lines and circle hooks, are required to minimize the bycatch.
Identification of variables that can be used to predict discard mortality is an important step towards improving estimates of total fishery removals. I explored the utility of capture depth, six external signs of barotrauma, two behavioral responses, and an impairment index that summed the physical and behavioral impairment associated with rapid decompression at predicting the submergence success of hook-and-line captured yelloweye (n = 95) and quillback (n = 65) rockfish that were released at the water's surface. Random forests classification models were used to identify the relative importance of predictor variables (n = 11) for each species and to explore the ability of these variables to accurately predict individual submergence success. Capture depth was identified as the most important variable in predicting yelloweye rockfish submergence but provided little improvement to the quillback rockfish model. The impairment index and the barotrauma sign associated with maximal gas retention were identified as important predictor variables for both yelloweye and quillback rockfish. These findings suggest that the impairment index, unlike capture depth, was able to account for individual variability in submergence success or failure of quillback rockfish.
The fishery for snow crabs Chionoecetes opilio in Alaska occurs during the winter, and handling mortality may be high due to cold-air exposure. Heat budget models that include convection, evaporation, long-wave radiation, and solar radiation were developed for snow crabs. Model performance was evaluated by comparing observed and predicted temperatures of live crabs exposed to cold air. The model performed well, predicting temperatures of the body, legs, and eyes within 1.5°C. Legs and eyes cooled faster than the body and may be more susceptible to cold-air exposure. Weather variables were ranked in the following order of importance: (1) air temperature, (2) solar radiation, (3) wind speed, (4) humidity, and (5) cloud cover. Clear, cold, breezy nights are the most detrimental conditions for crabs. Hourly weather records from a site near the fishing grounds were used in conjunction with the thermal model to estimate cooling rates for crabs every hour during actual and hypothetical seasons. The probability of damage for various cooling rates was estimated based on previously published laboratory data. Discard handling damage rates were highly variable, ranging from 0% to 30% over 21 actual fishing seasons. Damage rates for hypothetical seasons that varied in length, start day, and daily fishing hours were calculated. Damage rates were reduced by delaying the start day (15 January) until 1 March as well as by limiting fishing time to daylight hours. Combining a later starting day with limited fishing hours resulted in 90% of the hypothetical seasons having damage rates of 10% or less. Generally, longer seasons had lower damage rates, especially when fishing hours were limited. Although developed for cold-weather Alaska fisheries, this approach can easily be adapted to other fisheries where handling mortality due to temperature changes during capture is a concern.
Since the 1970s, the recreational fishery for Pacific halibut Hippoglossus stenolepis off the West Coast of the United States (Washington, Oregon, and California) has grown substantially, thereby reducing the amount of halibut available to other users. A catch sharing plan (CSP) was developed in 1988 to allocate the available yield among recreational fishers, commercial fishers, and treaty Indian tribes. The CSP defines the share of the total available catch allocated to each group and further subdivisions within the groups. The most complex allocation is that for the recreational fishery, which is managed by the agencies of the three coastal states, the federal fisheries agency, and an international commission that has overall responsibility for the preservation of the species. Management tools for the recreational fishery include seasons, bag limits, closed areas, vessel licensing and registration, minimum length limits, and various levels of catch monitoring. Although the recreational fishery has been managed conservatively, catches often exceed catch limits, though not substantially. Further refinements to management will probably need to pursue new directions, as current management practices are performing as well as can be expected.
Discarding in commercially exploited fisheries has received considerable attention in the last decade, though only more recently in Australia. The Reef Line fishery (RLF) of the Great Barrier Reef (GBR) in Australia is a large-scale multi-sector, multi-species, highly regulated hook and line fishery with the potential for high levels of discarding. We used a range of data sources to estimate discard rates and discard quantities for the two main target groups of the RLF, the coral trout, Plectropomus spp, and the red throat emperor, Lethrinus miniatus, and investigated possible effects on discarding of recent changes in management of the fishery. Fleet-wide estimates of total annual quantities discarded from 1989 to 2003 were 292–622 t and 33–95 t for coral trout and red throat emperor, respectively. Hypothetical scenarios of high-grading after the introduction of a total allowable commercial catch for coral trout resulted in increases in discard quantities up to 3895 t, while no high-grading still meant 421 t were discarded. Increasing the minimum size limit of red throat emperor from 35 to 38 cm also increased discards to an estimated 103 t. We provide spatially and temporally explicit estimates of discarding for the two most important species in the GBR RLF of Australia to demonstrate the importance of accounting for regional variation in quantification of discarding. Effects of management changes on discarding are also highlighted. This study provides a template for exploring discarding levels for other species in the RLF and elsewhere.
Since the 1960s, fisheries for groundfish other than Pacific halibut Hippoglossus stenolepis have caused an average of about 9,000 metric tons (mt, round weight) of halibut bycatch mortality every year, whereas annual directed catches of Pacific halibut have varied from 13,000 to almost 50,000 mt. About half of the bycatch consists of juvenile Pacific halibut caught in Alaska, some of which would otherwise migrate south and contribute to the fishery in British Columbia. These interceptions have long been a difficult issue for the United States and Canada. At recent levels of high juvenile abundance, the juvenile bycatch reduces coastwide recruitment by about 10%. The resulting yield loss, plus bycatch of adult fish, reduces yield to the directed fishery by about 11,000 mt per year. Migration modeling indicates that the yield loss due to bycatch occurs almost entirely in the area where the bycatch is taken. In particular, bycatch in Alaska reduces Pacific halibut yields in British Columbia by, at most, a few percent. During the 1980s and early 1990s, annual quotas in the directed Pacific halibut fishery were reduced by an amount equal to, or sometimes greater than, the total Pacific halibut bycatch mortality, and the quota reduction was distributed among regulatory areas in proportion to Pacific halibut exploitable biomass. At present, the Pacific halibut quota in each regulatory area is reduced by the amount of adult Pacific halibut bycatch mortality in that area, and the target exploitation rate is adjusted downward (slightly) to offset the bycatch mortality of juveniles.
Setline vessels in the North Pacific have recently begun using automated gear retrieval systems incorporating hook strippers to remove unused bait and caught fish from the hooks during gear retrieval. Pacific halibut removed by these automated systems suffer a handling mortality which is as much as nine times that experienced by fish removed carefully by the more traditional manual method of rolling the hook out of the mouth using a gaff. This increased mortality results from more severe injuries in the mouth area associated with the automated removal. Fish receiving sublethal injuries as a result of automated removal experience a significantly reduced growth rate in subsequent years.
Pacific halibut caught as bycatch or intended for discard by longline vessels in US and Canadian waters of the north Pacific must be removed from the hook using careful release techniques required by regulation. In many fisheries, trained observers subsample the released halibut for fish condition. These condition codes are used to track cumulative bycatch mortality in these fisheries. Tag return rates of halibut released from longline gear near Kodiak Island, Alaska, are used to estimate relative and absolute mortalities of fish by release method, hook removal injury, and condition code. Generally, the proper application of the careful release techniques results in only minor hook removal injuries. Survival rates of moderately and severely injured halibut are 1.5–2 times higher than previously assumed. One result of our study is the finding that not all fish judged at tagging as likely to die actually die. We recommend a reworking of the condition code methodology.