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Depredation of Demersal Reef Fishes Released with Descender Devices Is Uncommon off North Carolina, USA
Abstract
Descender devices are increasingly recognized as a leading means of barotrauma mitigation for released reef fishes. Yet, some resource users oppose regulations requiring or encouraging descender device use, arguing that predators frequently eat fish during release (depredation), sometimes causing device loss. We synthesized data for over 1,200 descended releases (both videoed and non‐videoed) of 16 species of reef fish off North Carolina, USA. Of 114 videos, we observed possible predators on seven, none of which showed actual depredation. Of 1,176 non‐videoed releases, we lost zero descender devices, indicating that, although cryptic depredation may have occurred, equipment loss was nonexistent. The lack of any evidence of depredation in ocean waters off North Carolina provides information to managers that they can use to reinforce education and outreach to encourage descender use.
The effectiveness of venting and recompression for increasing postrelease survival for fish that experience barotrauma has rarely been tested across a range of depths. We conducted a field tag–recapture experiment to test how well venting and recompression each increased postrelease survival of Black Sea Bass Centropristis striata relative to untreated controls at three different depth ranges on the U.S. South Atlantic continental shelf: 24–26, 29–32, and 35–38 m. Venting and recompression were applied by researchers alongside untreated controls at all three depths, and venting by anglers who were inexperienced with this technique was an additional treatment at the intermediate depth. Tests of independence were used to evaluate the association between treatment type (venting versus controls) and postrelease submergence at each depth. Cox proportional hazards models were fit to the tag–recapture data that were collected at each depth to determine whether the experimental treatment influenced postrelease survival. Postrelease submergence was significantly higher in vented fish at the intermediate and deep depths but not at the shallow depth. The hazards rates were not significant for venting and recompression at the shallow and intermediate depths but were at the deepest depth, demonstrating that these techniques practiced at >35 m increased postrelease survival relative to untreated controls. Mean increases in absolute survival at the 35–38 m depth were calculated to be 6.8% and 8.1% relative to controls when using venting and recompression, respectively. The results further suggest that anglers who are unfamiliar with venting do not reduce postrelease survival compared with venting by experienced personnel. These results provide guidance to fishery managers who are tasked with seeking methods to reduce catch‐and‐release mortality for an important reef species. Taken together, the findings from submergence success and survival models suggest that both venting and recompression should be encouraged to increase the postrelease survival of Black Sea Bass that are caught from depths >29 m.
Barotrauma—injury induced by changes in pressure—is a widespread challenge for successfully releasing fishes following capture. We used acoustic telemetry to examine the long-term post-release survival and behaviour of four rockfish species (genus Sebastes) suffering from barotrauma following capture using recreational fishing techniques. We placed particular emphasis on examining Cowcod (Sebastes levis) and Bocaccio (Sebastes paucispinis), two historically overfished species along the United States West Coast that serve as good model species representing different ecological lifestyles. We show that fish survival was species specific and that 40% of observed mortality occurred more than 48 h post release—a typical time period used in many short-term survivorship studies. Cowcod survival was correlated with fish length, sea surface temperature, and dissolved oxygen concentration at the mean depth of capture. Generalized additive mixed models of Cowcod and Bocaccio behaviour showed that surviving individuals were negatively affected by capture and barotrauma for at least 30 d post-release. Our findings demonstrate the need for extended observations to accurately quantify the mortality of fishes suffering from barotrauma and show how such data can be successfully implemented into fisheries management through engagement between managers, scientists, and the fishing community.
Fishery regulations mandate the release of many caught fish, elevating the importance of having accurate estimates of discard mortality. Red Snapper Lutjanus campechanus are overfished and undergoing overfishing in the southeast U.S. Atlantic, in part due to the high number of releases that die from discard mortality. We used acoustic telemetry to track the fine-scale movements of hook-and-line-caught Red Snapper released with descender devices at a hard-bottom site off North Carolina, USA. Movement characteristics of known-fate (live and dead) Red Snapper were used to infer fates of other individuals, from which we generated a proportional mortality estimate of 0.08 (95% CI = 0.00–0.17) for successfully descended Red Snapper with no hook trauma. This best-case mortality estimate was then used in a simulation to estimate overall Red Snapper discard mortality for the recreational fishery in the southeast U.S. Atlantic based on hooking location and a depth of approximately 37 m. For this fishery, we estimated the median proportional rate of discard mortality to be 0.13 (2.5% and 97.5% percentiles = 0.10, 0.17) if all released individuals were descended. This estimate is lower than the discard mortality values (˜0.2–0.3 for the recreational fishery) used in the current Red Snapper stock assessment, but it is likely not reflective of the current reality given that descender use is not 100% in this region; this estimate is also depth specific. Increased use of descender devices will reduce discard mortality for Red Snapper, enhancing efforts to rebuild this stock.
False killer whales (Pseudorca crassidens) depredate bait and catch in the Hawai‘i‐based deep‐set longline fishery, and as a result, this species is hooked or entangled more than any other cetacean in this fishery. We analyzed data collected by fisheries observers and from satellite‐linked transmitters deployed on false killer whales to identify patterns of odontocete depredation that could help fishermen avoid overlap with whales. Odontocete depredation was observed on ˜6% of deep‐set hauls across the fleet from 2004 to 2018. Model outcomes from binomial GAMMs suggested coarse patterns, for example, higher rates of depredation in winter, at lower latitudes, and with higher fishing effort. However, explanatory power was low, and no covariates were identified that could be used in a predictive context. The best indicator of depredation was the occurrence of depredation on a previous set of the same vessel. We identified spatiotemporal scales of this repeat depredation to provide guidance to fishermen on how far to move or how long to wait to reduce the probability of repeated interactions. The risk of depredation decreased with both space and time from a previous occurrence, with the greatest benefits achieved by moving ˜400 km or waiting ˜9 d, which reduced the occurrence of depredation from 18% to 9% (a 50% reduction). Fishermen moved a median 46 km and waited 4.7 h following an observed depredation interaction, which our analysis suggests is unlikely to lead to large reductions in risk. Satellite‐tagged pelagic false killer whales moved up to 75 km in 4 h and 335 km in 24 h, suggesting that they can likely keep pace with longline vessels for at least four hours and likely longer. We recommend fishermen avoid areas of known depredation or bycatch by moving as far and as quickly as practical, especially within a day or two of the depredation or bycatch event. We also encourage captains to communicate depredation and bycatch occurrence to enable other vessels to similarly avoid high‐risk areas.
Reducing discard mortality in recreational fisheries remains an important component of stock rebuilding for many reef fish species. Discard mortality for these species can be high due in part to barotrauma injury sustained during capture coupled with high catch rates, but recent advances in fish descending devices can mitigate some of these declines. Despite high survival rates with rapid recompression strategies, recreational angler opinions and perceived effectiveness of the devices are relatively unknown. This study surveyed the perceptions, opinions, and attitudes of 538 recreational anglers regarding the use of descending devices in the reef fish fisheries of the Gulf of Mexico and U.S. South Atlantic, with particular emphasis on Red Snapper Lutjanus campechanus. In total, 1,074 descending devices were distributed to marine recreational anglers from North Carolina to Texas. After using the device for an average of 8 months and 15 fishing trips, recipients completed a questionnaire assessing their perceptions on the efficacy of the device. While 72% of respondents had little to no knowledge of descending devices prior to the study, 70% indicated that they preferred this release method over venting after the study. Survey respondents released over 7,000 Red Snapper and 4,000 other reef fish species with their descending devices, and 76% were likely to continue employing the device on their vessel. Eighty‐nine percent of respondents believed descending Red Snapper would significantly reduce discard mortality in the recreational fishery. We discovered that recreational anglers perceive the devices to be highly useful in reducing discard mortality and are willing to employ them when releasing reef fish experiencing barotrauma. Other studies have demonstrated that these descending devices do reduce discard mortality of reef fishes, and this study indicates that recreational anglers are very willing to use them as a conservation tool.
Geopositioning underwater acoustic telemetry was used to test whether rapid recompression with weighted return-to-depth (descender) devices reduced discard mortality of red snapper (n = 141) and gray triggerfish (n = 26) captured and released at 30-60 m depths at two 15 km 2 study sites in the northern Gulf of Mexico. Cox proportional hazards modelling indicated red snapper released with descender devices had significantly lower discard mortality within the first 2 d (95% CI ¼ 18.8-41.8% for descender-released vs. 44.0-72.4% for surface-released, unvented fish), while there was no significant effect of descender devices on discard mortality of gray triggerfish. Predation by large pelagic predators was estimated to account 83% of red snapper and 100% of gray triggerfish discard mortality. Discard mortality due to predation has likely been overlooked in previous mark-recapture, laboratory, and enclosure studies, suggesting cryptic population losses due to predation on discards may be underestimated for red snapper and gray triggerfish. Large-area three-dimensional positioning acoustic telemetry arrays combined with collaboration and data sharing among acoustic telemetry researchers have the potential to advance our knowledge of the processes affecting discard mortality in reef fishes and other taxa.
Geopositioning underwater acoustic telemetry was used to test whether rapid recompression with weighted return-to-depth (descender)
devices reduced discard mortality of red snapper (n = 141) and gray triggerfish (n = 26) captured and released at 30–60m depths at two
15 km2 study sites in the northern Gulf of Mexico. Cox proportional hazards modelling indicated red snapper released with descender devices had significantly lower discard mortality within the first 2 d (95% CI = 18.8–41.8% for descender-released vs. 44.0–72.4% for surface-released, unvented fish), while there was no significant effect of descender devices on discard mortality of gray triggerfish. Predation by large pelagic predators was estimated to account 83% of red snapper and 100% of gray triggerfish discard mortality. Discard mortality due to predation has likely been overlooked in previous mark-recapture, laboratory, and enclosure studies, suggesting cryptic population losses due to predation on discards may be underestimated for red snapper and gray triggerfish. Large-area three-dimensional positioning acoustic telemetry arrays combined with collaboration and data sharing among acoustic telemetry researchers have the potential to advance our knowledge of the processes affecting discard mortality in reef fishes and other taxa.
Discard survival of deepwater (>60 m) groupers (Serranidae; Epinephelinae) is often assumed to be 0% given the severity of barotrauma and the inability of fish to submerge. We used acoustic telemetry to study the activity of 19 deepwater grouper after a recompressed release with a descender device, achieved by rapidly returning fish to a depth where expanded gases can contract. The species tested were the Scamp Mycteroperca phenax (n = 8), Snowy Grouper Hyporthodus niveatus (n = 7), and Speckled Hind Epinephelus drummondhayi (n = 4). Individuals of all three species showed post‐recompression variation in water depth and acceleration indicative of survival, whereas information from other tags indicated discard mortality. Nonparametric Kaplan–Meier survivorship procedures yielded a 14‐d survival estimate of 0.50 (95% confidence interval = 0.10–0.91); although low, this estimate is higher than the currently assumed 0% survival. Additionally, our estimate of discard survival is likely biased low because we assumed that no individuals shed their tag, which is unlikely for our attachment method. A technique to increase discard survival of deepwater groupers may lead to better‐constructed regulations for reef fishes in the southeastern USA and in other areas where these species are caught and released.
Descending fish to depths of neutral buoyancy is a promising, less-invasive alternative to swim bladder venting for relieving barotrauma and reducing mortality in sport fish. However, we lack a broad perspective on the relative benefits of these two approaches. We reviewed the most up-to-date literature to evaluate the effectiveness of venting compared to descending treatments. Mean relative risk (RR) based on 76 published comparisons (51 marine, 25 freshwater; 18 genera, 28 species) showed that venting (2.0 ± 4.7 [mean ± SD]) and descending (1.6 ± 1.4) both had positive effects on survival (RR ≥ 1.1). However, RR was generally small and statistically indistinguishable between treatments, providing no strong support for the use of one method over the other. Modeling of factors affecting RR showed that the study design variable “assessment method” was the only important factor affecting RR, having a larger influence on survival than habitat, capture depth, or treatment type (venting versus descending). Biotelemetry and ex situ methods produced significantly higher estimates of RR than other assessments. Our review suggests that the two major approaches to barotrauma relief do not differentially influence survival outcomes and that study design may be an important source of bias. Consequently, we recommend that managers consider barotrauma relief options carefully on a case-by-case basis, and we encourage additional research on sublethal endpoints in addition to mortality.
Received November 29, 2016; accepted March 9, 2017
Fishery collapses cause substantial economic and ecological harm, but common management actions often fail to prevent overfishing. Minimum length limits are perhaps the most common fishing regulation used in both commercial and recreational fisheries, but their conservation benefits can be influenced by discard mortality of fish caught and released below the legal length. We constructed a computer model to evaluate how discard mortality could influence the conservation utility of minimum length regulations. We evaluated policy performance across two disparate fish life-history types: short-lived high-productivity (SLHP) and long-lived low-productivity (LLLP) species. For the life-history types, fishing mortality rates and minimum length limits that we examined, length limits alone generally failed to achieve sustainability when discard mortality rate exceeded about 0.2 for SLHP species and 0.05 for LLLP species. At these levels of discard mortality, reductions in overall fishing mortality (e.g. lower fishing effort) were required to prevent recruitment overfishing if fishing mortality was high. Similarly, relatively low discard mortality rates (>0.05) rendered maximum yield unobtainable and caused a substantial shift in the shape of the yield response surfaces. An analysis of fishery efficiency showed that length limits caused the simulated fisheries to be much less efficient, potentially exposing the target species and ecosystem to increased negative effects of the fishing process. Our findings suggest that for overexploited fisheries with moderate-to-high discard mortality rates, reductions in fishing mortality will be required to meet management goals. Resource managers should carefully consider impacts of cryptic mortality sources (e.g. discard mortality) on fishery sustainability, especially in recreational fisheries where release rates are high and effort is increasing in many areas of the world.
Barotrauma is increasingly being recognized as a serious conservation and management issue in catch-and-release fisheries. Barotrauma results from decompression that can cause physiological alterations and physical injuries. During the summers of 2007 and 2008, we angled for fish in the St. Lawrence River to determine the incidence of barotrauma injuries and the related mortality rates. An angler survey was also conducted in 2008. A total of 212 fish were caught at depths ranging from 1 to 21 m. Sixty-three fish (30%) showed signs of barotrauma, 99% of these being smallmouth bass Micropterus dolomieu, walleyes Sander vitreus, and yellow perch Perca flavescens. These three species represented 77% of all the fish caught and, excluding round goby Neogobius melanostomus, represented 94% of the fish caught at depths greater than 6 m. Signs of barotrauma were bloating (89%), loss of equilibrium (66%), stomach eversion (62%), bulging eyes (18%), hemorrhaging in the eyes and fins (12%), and anal eversion (5%). Most fish had multiple signs, approximately 50% showing loss of equilibrium, bloating, and stomach eversion. The incidence of barotrauma increased with depth, first appearing at 6.1 m. There was a threshold at approximately 10 m, from which the incidence rapidly increased to 100% at 21 m. Mortality occurred in 67% of the fish with barotrauma, even in those with less severe signs (e.g., mild bloating and slight loss of equilibrium only when stationary) and showed a similar rate of increase starting at 9 m. There were interspecific differences in the susceptibility to barotrauma that may be related to habitat preferences and physiological and physical differences that should be considered when targeting different species and depths.
Much research on the fish physiological consequences of tournaments has been conducted to date and has provided anglers and tournament organizers with strategies for reducing stress and mortality. However, one aspect of tournaments that has received little attention is barotrauma. At a fall competitive angling event on Rainy Lake in northwestern Ontario, we evaluated the incidence of barotrauma among tournament-caught smallmouth bass Micropterus dolomieu; we then tagged and released a subset of fish that had severe barotrauma indicators and compared physiology, postrelease behavior, and fate between these fish and those with negligible signs of barotrauma. Overall, 76% of fish had at least one sign of barotrauma (either hemorrhaging or swim bladder distention), but only 32% of fish had two or more indicators and were thus deemed to have severe barotrauma. When telemetered fish were released at a common site, we determined that fish with negligible signs of barotrauma evacuated the release site more rapidly than fish with severe barotrauma did. Some fish with barotrauma floundered at the surface when released, and one of these fish was subsequently hit and killed by a boat. At the end of the monitoring period, 20% of fish with severe barotrauma had died; two additional individuals (20%) that were still at the release site were moribund (failed to respond to diver stimuli). Conversely, we failed to observe any mortality in fish with negligible signs of barotrauma. All tournament fish had elevated levels of blood glucose and lactate. However, stress indices were higher in fish with barotrauma and tended to be highest among fish with barotrauma that died after release. This study revealed that the incidence of barotrauma in tournaments can be high; moreover, outside of a laboratory environment, a significant proportion of fish with severe barotrauma may die after release. Additional research is needed to determine the seasonal variation in incidence and consequences of barotrauma as well as the effectiveness of different depressurization techniques in the field that could be used during fishing tournaments.
Two experiments were used to assess the effects of barotrauma on initial capture survival and short-term postrecompression survival of line-caught (range 18–225 m) southern California rockfish (Sebastes spp.). Occurrence of external and internal signs of barotrauma was characterized across all species. Despite species-specific differences in the extent of barotrauma observed, initial capture survival of rockfish held in a live well for a 10-min period following capture was 68% overall (19 species, n = 168). Overall 2-day survival of rockfish following recompression in cages was also 68% (17 species, n = 257). Short-term survival varied across species (range 36% to 82%), as did the occurrence of external signs of barotrauma. The degree of external signs of barotrauma was not a significant predictor of initial capture survival or short-term survival. The most significant predictor of short-term survival was surface holding time, with short-term survival increasing with decreasing surface holding time. These results suggest that rapid recompression of rockfish can significantly decrease discard mortality and could potentially enhance rockfish conservation.
In some fisheries, releases are a high percentage of total catch. Recent tagging data of marine fishes have revealed that recapture of the same individual multiple times occurs frequently. We investigated the magnitude of this phenomenon and its effect on survival using previously collected mark-recapture data of four reef-associated species. We used Cox proportional hazard regression models to examine whether survival varied with release number. For three of four species, survival was significantly higher after the second, third, and/or fourth release as compared to the first release, perhaps resulting from selection for robust individuals. Repetitive recapture implies that the estimated number of unique released fish is biased. Increased survival following later releases as compared to the initial release suggests that the number of dead discards may be similarly overestimated. We analysed the sensitivity of stock assessment results to reduced estimates of dead discards using two of our species that had recently been assessed. We found that reduced estimates of dead discards had a modest effect on assessment results but could nonetheless affect the perception of fishery status. Our findings highlight the need to revise current practices for estimating live and dead discards, either internal or external to stock assessment models.
Fate assignment is crucial to the results of survival studies, particularly those that utilize acoustic tagging. Most current methodologies are at least partially subjective, thus having a means of objectively assigning fates would improve precision, accuracy, and utility of such studies. We released 57 acoustically tagged deepwater groupers of six species off North Carolina, USA, via surface release and recompressed release with descender devices. We applied a three‐state hidden Markov model (HMM) in a novel way, to distinguish movement patterns between alive and dead fish (which might have been eaten by predators). We assigned fates using two approaches that differed in their reliance on HMMs. When HMMs were the predominant source of fate assignment, we estimated survival of 40 deepwater groupers released with descender devices at the continental shelf break (66‐120 m depth) to be 0.46 (95% confidence interval 0.33, 0.65). When a combination of HMMs and prior information was utilized, we estimated survival of the same 40 groupers to be 0.61 (0.47, 0.80). Both estimates represent a substantial improvement over survival of surface released grouper (~zero). Furthermore, HMMs estimated zero survival for an additional five descended groupers at a wreck site in 240 m depth, though one analysis using prior information suggests survival may be possible in that depth. These estimates were aided by the objectivity of HMMs and we recommend future survival studies involving acoustic tagging employ similar methodologies. The improved survival of groupers after descending is an important finding for management, as this taxon contains several species of impaired stock status or fishery status.
Increasing post‐release survival of discarded fishes is a critical challenge to the development of effective conservation and management strategies for a multitude of commercial and recreational fisheries. Among reef fishes, this challenge is further complicated by pressure‐related injuries collectively known as barotrauma. Left alone, these injuries are often fatal. Tactics to mitigate the adverse effects of barotrauma, including piercing an expanded swim bladder to release trapped gas (venting) and using a specially designed device to return a fish to the depth of capture (descending), have been well‐described and readily adopted by regulatory agencies as best practices. Recently, the South Atlantic Fishery Management Council enacted a rule requiring anglers targeting species in the snapper grouper fishery management unit to be equipped with descender devices (SAFMC 2020), and similar regulations are anticipated for the Gulf of Mexico (GoM; AFS 2020). However, since enforcement is unfeasible, simply requiring possession of descender devices does not guarantee their use. Consequently, any potential benefits resulting from these rules rely completely on anglers embracing the use of descender devices, which will only happen if anglers truly believe that these devices increase post‐release survival. A recent study suggests that anglers in the southern Atlantic who routinely use descender devices are willing to formally adopt them as a conservation strategy (Curtis et al. 2019); however, additional factors like predation influence the actual and perceived survival of descended fishes, yet remain poorly understood.
We tested the ability of venting and descender (recompression) devices to increase the relative survival of released Black Sea Bass Centropristis striata, a physoclistous reef species with high discard rates in hook‐and‐line fisheries that operate in the U.S. Atlantic Ocean and Gulf of Mexico. We caught fish via hook and line from waters that were 38 m deep, a depth where Black Sea Bass often exhibit signs of barotrauma and may be unable to submerge after release. Fish were conventionally tagged and vented with either an 11‐gauge cannula or a 16‐gauge needle, descended using a descender (recompression) device, or released as tagged controls (no venting or recompression). Tests of independence were used to determine the relationship between submergence and treatment (excluding recompressed fish) as well as between submergence and tag return rate. Tag‐recapture data were used to inform a Cox proportional hazards model that evaluated the survival of fish treated with each experimental device relative to the control group. A significantly greater proportion of fish submerged when treated with either venting device relative to the controls, and the fish that submerged had a greater proportion of tag returns relative to those that did not submerge. Venting and recompression increased postrelease survival compared with the controls. The results provide guidance to managers who seek methods to reduce discard mortality rates in hook‐and‐line fisheries for this important species. Future studies should examine the use of these devices at a range of depths to determine their effectiveness.
Recreational fishing is increasingly recognised as an important source of mortality for marine fish populations. In the United States, estimates of marine recreational catch and effort were recently revised for the time period 1981 and beyond, and for many species, the revised estimates were substantially higher than the original values. Here, the proportion of total landings that came from the recreational sector in the Southeast US Atlantic was quantified. The proportions for 22 oceanic species and for all species combined were computed, using a full time series of landings (1981–2016) and a more recent time series (1999–2016). For the full and recent time series, landings of most species (15/22 and 17/22, respectively) were dominated by the recreational sector. For all species combined, 71% of landings in the full time series were from the recreational sector, and 76% in the recent time series. Trend analysis indicated that most species had a stable or increasing proportion of landings from the recreational sector. In addition, stock assessments were conducted on four species, and the catch revisions increased the estimated scale of abundance and, in some cases, affected stock or fishery status. This work underscores the importance of recreational fishing for marine resource management.
We estimated condition-specific survival rates of gray triggerfish (Balistes capriscus) using a tag-recapture approach and extrapolated these values to produce an overall discard survival estimate for the US South Atlantic recreational hook-and-line fishery. Tag return rates of fish tagged at the seafloor using SCUBA served as a reference for return rates of fish tagged at the surface. We examined the validity of gross necropsy as a proxy for survival by identifying likely causes of discard mortality. Best-condition surface-released fish (no external trauma) had an estimated mean proportional survival of 0.39 (95% confidence interval 0.28, 0.55). For gray triggerfish exhibiting visible trauma, estimated survival was 0.24 (0.10, 0.60). Floating fish had a survival rate of zero. The necropsy-based estimate of gray triggerfish lacking organ displacement closely matched the tag-based estimate of survival. Mean estimated discard survival across all depths for North Carolina was 0.35 (0.10, 0.59) and for Florida was 0.34 (0.08, 0.59). These results have implications for gray triggerfish management because our estimate of discard survival is substantially lower than previously assumed and for future discard survival research given our findings with gross necropsies.
Fishes caught from depth often suffer from barotrauma, which can result in high mortality rates (close to 100% for some species) when released at the surface. To mitigate for this, the recreational fishing community pro-actively developed several different types of descending devices designed to assist unwanted or prohibited fish back toward the bottom for release. Post-release survival using recompression techniques has been documented for some species, which has allowed fisheries managers to begin revising estimates of total fishing mortality in some cases, but the effectiveness of the different commercially-available descending device types has not been quantified. We conducted 24 Commercial Passenger Fishing Vessel charters at 11 sites along the coast of California, and invited volunteer recreational anglers aboard the charters to test the effectiveness of five different commercially available device types, and respond to a survey of their device preferences. During release, all fish were descended either to 46 m (150 ft) depth or directly to the bottom, whichever depth was shallower. While there were some significant differences between device types, all devices were effective for releasing rockfishes back to depth. Initial post-release mortality (defined as all mortality events observable from the vessel while fishing) across all devices was relatively low (7.5%) in capture depths less than 100 m, but increased significantly to 16.4% at capture depths from 100 to 135 m. Our results suggest that rockfishes should be released at least halfway to the bottom (preferably directly to the bottom) for the device to be effective in minimizing post-release mortality. The time required to use the devices averaged under three minutes regardless of device type, meaning that all device types could be used efficiently on deck, but anglers showed a clear preference for the SeaQualizer ™. This device produced some of the lowest release error rates and lowest initial post-release mortality of rockfishes aboard the charters, so angler preference coincided with device effectiveness. Collaborating with the recreational fishing community was an extremely important aspect to this study, provided more robust results, and fostered working relationships that can be built upon in future research projects.
It is easy for graduate students and other fisheries scientists to forget the most important species we are trying to manage: humans. In the column below, I outline my recent re‐energizing experience meeting with stakeholders about a challenging issue in marine reef fisheries. Keys to success in interacting with the stakeholders of your fish include losing the usual jargon, identifying common ground between at‐odds groups, and collaborating with stakeholders when doing research. This article is protected by copyright. All rights reserved.
Gear performance is often assumed to be constant over various conditions encountered during sampling; however, this assumption is rarely verified and has the potential to introduce bias. We used fishery-independent vertical line surveys to evaluate whether gear efficiency and selectivity is similar while assessing reef fish populations at oil and gas platforms, artificial reefs, and natural banks in the western Gulf of Mexico. We conducted 192 vertical line sets with cameras placed on a subset of these deployments to validate any differences in efficiency among habitat types. Red snapper (Lutjanus campechanus) accounted for 93% of the catch. No difference in red snapper CPUE among habitats was detected. When evaluating fish size, 8/0 and 11/0 hooks sampled significantly larger red snapper at natural banks than at artificial habitats. While CPUE was similar among all hooks at artificial habitats, CPUE at natural banks was lower for shallower hooks and increased towards the bottom hooks along the backbone. At all habitats, red snapper TL decreased from shallow to deep hook positions. Simultaneous camera deployments revealed other processes affecting efficiency such as bait removal and depredation. Vermilion snapper (Rhomboplites aurorubens) were effective at removing bait while avoiding capture. Perhaps related to this observation, Red snapper CPUE was negatively correlated with the vermilion snapper video index of abundance. Video confirmed gear saturation was prevalent (70% of deployments), occurring more frequently on artificial habitats. Furthermore, the time fished was effectively "shorter" at artificial habitats as the number of available baited hooks declined rapidly. These results point towards higher relative abundance at artificial habitats; however, the prevalence of saturation indicates vertical line CPUE may not always be proportional to true abundance, hindering our ability to detect differences at the scale examined in this study. Vertical line surveys should evaluate the prevalence of saturation as inferences regarding relative abundance may be compromised when this information is unknown.
Red Snapper Lutjanus campechanus is the most economically important reef fish in the Gulf of Mexico, and despite being intensively managed, the stock remains overfished. These fish are susceptible to pressure-related injuries (i.e., barotrauma) during fishing that compromise survival after catch and release. Barotrauma-afflicted fish may not only experience immediate mortality but also delayed mortality after returning to depth. This variability and unknown fate leads to uncertainty in stock assessment models and rebuilding plans. To generate better estimates of immediate and delayed mortality and postrelease behavior, Red Snapper were tagged with ultrasonic acoustic transmitters fitted with acceleration and depth sensors. Unique behavior profiles were generated for each fish using these sensor data that allowed the classification of survival and delayed mortality events. Using this information, we compared the survival of Red Snapper released using venting, nonventing, and descending treatments over three seasons and two depths. Red Snapper survival was highest at cooler temperatures and shallower depths. Fish released using venting and descender tools had similar survival, and both these groups of fish had higher survival than nonvented surface-released fish. Overall, Red Snapper had 72% survival, 15% immediate mortality, and 13% delayed mortality, and all fish suffering from delayed mortality perished within a 72-h period after release. Results from these field studies enhance the understanding of the delayed mortality and postrelease fate of Red Snapper regulatory discards. Moreover, these data support the practice of using venting or descender devices to increase the survival of discarded Red Snapper in the recreational fishery and show that acoustic telemetry can be a valuable tool in estimating delayed mortality.
Received March 6, 2015; accepted July 15, 2015
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 29-34mdeep 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 20-35m 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.
Operational interactions between odontocetes ( i.e. , toothed whales) and longline gear are a global phenomenon that may threaten the conservation of odontocete populations and the economic viability of longline fisheries. This review attempts to define the issue, summarize the trends and geographical extent of its occurrence over the last half century, explore the potential impact on odontocetes and on fisheries, and describe potential acoustic and physical mitigation solutions.
Reports of odontocete bycatch rates are highly variable (between 0.002 and 0.231 individuals killed per set) and at least 20 species may be involved. Information about marine mammal population size, migration patterns and life history characteristics are scarce, although at least one population may be in decline due to losses attributable to longline bycatch. Information about the financial impact of depredation on pelagic longline fisheries is also scarce, although estimates of daily fleet‐wide losses range between US$1,034 and US$8,495 (overall fleet income was not reported). Such biological and financial losses may be unsustainable.
Recent developments in acoustic and physical mitigation technologies have yielded mixed results. Acoustic mitigation technologies have no moving parts, although require complex electronics. To date, they are insufficiently developed and their efficacy has been difficult to assess. Physical mitigation technologies generally require complex moving parts, although they are relatively simple to develop and assess. Further development and testing remains necessary before widespread implementation would be possible. Development of these approaches should be prioritized and a “toolbox” of various strategies and solutions should be compiled, because a single panacea to the problem is unlikely to emerge.
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]
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.
Commercial fishing has repeatedly been identified as a major causal factor for global declines in fish stocks. Recently, recreational fisheries have also been considered as having the potential to contribute to fisheries declines. Here, we take a global focus, contrasting the characteristics of commercial and recreational fisheries relevant to conservation and sustainability of exploited fishes in both marine and freshwater environments. We provide evidence to support our assertion that the same issues that have led to global fisheries concerns regarding commercial fishing can have equivalent, and in some cases, magnified effects in recreational fisheries. Contrasts revealed that the issues of bycatch and catch-and-release, fisheries-induced selection, trophic changes, habitat degradation, gear technology, fishing effort, and production regimes are remarkably similar among fishery sectors. In recognition of this conclusion, we present a new vision for recreational fishing that positions it on the same scale and urgency as commercial fisheries. Efforts to manage and conserve fisheries must recognise that issues and threats are similar in these fundamentally and philosophically different fisheries, as may be the solutions. Failure to recognise the similarities will further polarise these sectors and retard efforts to conserve aquatic resources. Fishing activity of any kind, whether commercial or recreational, has the potential to affect negatively fish and fisheries, as well as aquatic environments.
In general terms, barotrauma is defined as an injury or disorder resulting from the establishment of a pressure difference across the wall of an anatomical structure or an injury of a body part or organ as a result of changes in pressure. In fish, barotrauma is physiological damage to nonauditory tissue. Barotrauma may be expressed as physical injury or changes in behavior and may result in immediate or delayed direct or indirect mortality.
Promotion of better procedures for releasing undersize fish, advocacy of catch-and-release angling, and changing minimum legal sizes are increasingly being used as tools for sustainable management of fish stocks. However without knowing the proportion of released fish that survive, the conservation value of any of these measures is uncertain. We developed a floating vertical enclosure to estimate short-term survival of released line-caught tropical and subtropical reef-associated species, and used it to compare the effectiveness of two barotrauma-relief procedures (venting and shotline releasing) on red emperor (Lutjanus sebae). Barotrauma signs varied with capture depth, but not with the size of the fish. Fish from the greatest depths (40-52 m) exhibited extreme signs less frequently than did those from intermediate depths (30-40 m), possibly as a result of swim bladder gas being vented externally through a rupture in the body wall. All but two fish survived the experiment, and as neither release technique significantly improved short-term survival of the red emperor over non-treatment we see little benefit in promoting either venting or shotline releasing for this comparatively resilient species. Floating vertical enclosures can improve short-term post-release mortality estimates as they overcome many problems encountered when constraining fish in submerged cages.
In an operant-conditioning study, a bull shark responded to signals at frequencies between 100 and 1500 cy/sec. In its band of greatest sensitivity (400 to 600 cy/sec), it discriminated, from high-level ambient noise, signals of amplitudes which the apparatus could not measure.
Sharks, skates and rays: the biology of elasmobranchs
- H. Bleckmann
- M. H. Hofmann
The effects of noise on aquatic life
- T. J. Carlson
Release methods for rockfish
- S. Theberge
- S. J. Parker
Occurrence of depredation by common bottlenose dolphins (Tursiops truncatus) on reef fish captured and released by rod and reel fisheries in the northeastern Gulf of Mexico
- C. E. Grewal
Utility and usage of descender devices in the Red Snapper recreational fishery in the South Atlantic
- J. Vecchio
- D. Lazarre
- B. Sauls