Post-release Survival Research Articles

The costs and healing rates of minor injuries in neonatal reef sharks.

Elasmobranch fishes (i.e., sharks, skates, and rays) exhibit remarkable wound-healing capabilities and consistently maintain a high capacity for tissue regeneration throughout their lives. This high capacity for wound healing may be particularly important for neonatal elasmobranchs that are still developing their immune system. However, little is known about the costs associated with wound healing and the potential influence of environmental variables or life history. In this study, we explore (1) the impact of minor, external injuries on the growth and body condition of neonatal blacktip reef (Carcharhinus melanopterus) and sicklefin lemon (Negaprion acutidens) sharks using a long-term fisheries-independent dataset from Moorea, French Polynesia, (2) the influence of ambient temperature on healing rates in neonatal blacktip reef sharks at two experimental temperatures (25°C and 29°C), and (3) variations in umbilical wound-healing rates between blacktip reef and sicklefin lemon sharks using an additional long-term dataset from St. Joseph Atoll, Seychelles. We found no impact of minor, external injuries on growth and body condition in neonatal blacktip reef and sicklefin lemon sharks, accelerated umbilical wound healing in neonatal blacktip reef sharks exposed to elevated ambient temperatures, and distinct umbilical wound-healing rates between neonatal blacktip reef and sicklefin lemon sharks. Enhancing our understanding of sharks' healing capabilities and the influence of environmental factors on this process is crucial for informing handling practices aimed at improving post-release survival rates of captured sharks under current and future oceanic conditions.

Population structure and sub-legal catch in a California spiny lobster (Panulirus interruptus) fishery in Baja California, Mexico

Promoting sustainable fisheries is a global challenge. Growing numbers of initiatives identify sustainable fishing practices through certification programs. One of the most widespread and impactful is the Marine Stewardship Council, which, in 2004, certified the California spiny lobster ( Panulirus interruptus, Palinuridae) trap fishery of Baja California, Mexico as the first certified small-scale fishery in a developing nation. Despite this success, questions about the possible impact of high bycatch of sub-legal lobster, and the efficacy of current management practices under scenarios of increasing future stressors, remain. This study quantifies (1) catch structure and sub-legal bycatch rate of a fishing cooperative of Baja California, Mexico; and (2) rate of sub-legal recaptures. We found high rates of sub-legal bycatch (82.0%) consistent with previous studies. Multiple recaptures occurred in ∼12% of tagged sub-legal individuals, raising questions about the potential impact of multiple recaptures. Results support previous assumptions of high post-release survival of sub-legal individuals but highlight a need for research on potential impacts of multiple recaptures to increase fishery sustainability and resilience, especially under potential future stressful conditions.

Successful treatment of megaesophagus with sildenafil in juvenile Pacific harbor seals (Phoca vitulina richardii) undergoing rehabilitation.

To describe the outcome of megaesophagus in harbor seal pups undergoing rehabilitation from January 2021 to December 2023. 5 harbor seal (Phoca vitulina richardii) pups, 2 males and 3 females, were included in the study. All 5 cases had no clinical signs associated with megaesophagus on initial presentation to the rehabilitation facility. Case 1 presented with regurgitation, diarrhea, bloating, and poor gain of body mass starting 24 days into rehabilitation. Case 2 presented with regurgitation and bloating on day 12. Case 3 presented with hyporexia, bloating, poor gain of body mass, and regurgitation between days 55 and 60. Case 4 presented with lethargy, diarrhea, and regurgitation starting on day 12 of rehabilitation. Case 5 presented with difficulty gavage feeding 14 days into rehabilitation and regurgitation starting day 28. Radiographs in all 3 cases revealed dilation of the esophagus and gas distention of the stomach and intestines, consistent with megaesophagus. Cases 1, 2, and 3 were treated with 1 mg/kg sildenafil by mouth every 12 hours for 14 days at the time of diagnosis. Cases 1 and 2 showed improvement in radiographic lesions and resolution of clinical signs after treatment and were released after 1 and 3 months of posttreatment monitoring respectively. None of the clinical signs returned after medications were discontinued. Postrelease survival was monitored in case 2 via a satellite-linked transmitter for 39 days. Case 3 was euthanized due to worsening lethargy, difficulty tube feeding, and continued loss of body mass after 6 days of treatment. Case 4 was euthanized at the time of diagnosis of megaesophagus on radiographs due to dull mentation and declining clinical status, and case 5 died a few hours after diagnosis of megaesophagus on radiographs before sildenafil treatment could be initiated. Sildenafil successfully managed megaesophagus in 2 of 3 P vitulina richardii juveniles. This case series highlights that sildenafil may be a potential treatment option for megaesophagus in P vitulina richardii pups undergoing rehabilitation. Based on the results of these cases, it is hypothesized that megaesophagus in rehabilitated harbor seals is not always a congenital defect but possibly an iatrogenic condition.

Postrelease survival of undersized swordfish (Xiphias gladius) caught on pelagic longline gear in a U.S. commercial fishery in the western North Atlantic Ocean: Suppl. Fig. 3

Postrelease survival of undersized swordfish (Xiphias gladius) caught on pelagic longline gear in a U.S. commercial fishery in the western North Atlantic Ocean: Suppl. Fig. 3

Postrelease survival of undersized swordfish (Xiphias gladius) caught on pelagic longline gear in a U.S. commercial fishery in the western North Atlantic Ocean: Suppl. Fig. 2

Postrelease survival of undersized swordfish (Xiphias gladius) caught on pelagic longline gear in a U.S. commercial fishery in the western North Atlantic Ocean: Suppl. Fig. 2

Postrelease survival of undersized swordfish (Xiphias gladius) caught on pelagic longline gear in a U.S. commercial fishery in the western North Atlantic Ocean

Postrelease survival of undersized swordfish (Xiphias gladius) caught on pelagic longline gear in a U.S. commercial fishery in the western North Atlantic Ocean

Postrelease survival of undersized swordfish (Xiphias gladius) caught on pelagic longline gear in a U.S. commercial fishery in the western North Atlantic Ocean: Suppl. Fig. 1

Postrelease survival of undersized swordfish (Xiphias gladius) caught on pelagic longline gear in a U.S. commercial fishery in the western North Atlantic Ocean: Suppl. Fig. 1

The effect of downstream translocation on Atlantic salmon Salmo salar smolt outmigration success.

Trap and transport, the capture and subsequent translocation of fish during the freshwater phase of their migration, is becoming more common as a management intervention. Although the technique can be successful, it is costly and can have unintended effects on the fish being transported. This study investigates whether trap and transport can be used to increase the migration success of Atlantic salmon, Salmo salar, smolts in naturally flowing rivers. Seaward-migrating S. salar (n = 294) from two UK rivers were tracked using acoustic telemetric techniques. Outmigration success and timing were compared between non-transported (released at the original in-river capture site) and transported (released ca. 23 km downstream of the capture site) individuals. Downstream translocation increased the proportion of fish that successfully migrated to marine waters, and there was no indication that transport reduced post-release survival. The post-release migration speed of transported fish was slower than expected but this was likely a function of their advanced migration timing rather than an inhibition of their capacity to migrate. These results suggest that trap and transport can increase the outmigration success of S. salar smolts, but the earlier river exit dates of transported fish could negatively affect their survival at sea.

Starting From Scratch: Husbandry Techniques to Establish the First Population of 'Akikiki (Oreomystis bairdi) in Human Care Using Wild-Collected Eggs.

Conservation breeding programs can save species from extinction by establishing assurance populations that provide individuals for achieving species recovery goals in the wild. However, keeping animals in human care can result in the selection of phenotypes that may be suboptimal for post-release survival and reproduction. It is therefore essential that conservation breeding programs provide animals with naturalistic conditions that facilitate the performance of species-typical behaviors, an endeavor that is also a vital aspect of animal welfare. Here, we describe how we established a conservation breeding program for the 'Akikiki (Oreomystis bairdi), a Hawaiian honeycreeper that is facing imminent extinction in the wild. We share how we utilized the species' native habitat as a template for developing husbandry practices with a primary focus on how we simulate wild environmental conditions in enclosures, mimic naturalistic foraging experiences, and facilitate pair bonding and parental breeding behaviors.

Post-release survival of loggerhead sea turtles (Caretta caretta) incidentally hooked in a North Atlantic pelagic longline fishery

Estimating mortality of sea turtles incidentally captured in fishing gear is essential to understanding fishery impacts on sea turtle populations. Loggerhead turtles (Caretta caretta) are a component of bycatch in pelagic longline fisheries, including those operating in Atlantic Canada. In this study, we used pop-up satellite archival tags (PSATs) attached to 62 loggerhead turtles incidentally hooked in Atlantic Canadian shallow-set pelagic longline gear (2012–2018) to estimate associated post-release survival. Consistent with conventional fishing practices, hooks were not removed from turtles prior to release. Analysis of diving behaviour, ocean temperature, and ambient light level was used to assign fates to turtles. Post-release survival was calculated using the Kaplan-Meier estimator with right censoring. Based on this method, the annual survival probability of an individual loggerhead post-release is 0.877 ± SE 0.052. While it is commonly assumed that hook location is an important variable in predicting fates of turtles after release, there was no difference in survival of deep-hooked (swallowed hook) versus shallow-hooked turtles. These results indicate higher survivorship among hooked loggerheads captured in shallow-set pelagic longline gear than prevailing wisdom and suggest that at least some of the population impacts on loggerhead turtles conventionally attributed to pelagic longline interactions may be linked to other threats.

Appendage damage effects on Southern Rock Lobster growth and mortality

Handling of crustaceans can result in injuries such as limb damage, reducing post-release survival and subsequent growth. Quantifying the impact of handling damage can provide insight into the effects of increased handling, which can occur when undersized animals are released by fishers or during translocations of animals between areas. We investigated the impact of handling on the Southern Rock Lobster (Jasus edwardsii) using three decades of scientific tag-recapture data from a no-fishing reserve. We used a Bayesian modeling approach with a modified Von Bertalanffy growth model which is robust to measurement error and Cormack-Jolly-Seber capture-recapture model to estimate growth and survival probability parameters. We found that even low levels of damage (1–4 appendages) can decrease growth by ∼ 10 % in the subsequent moult. Male lobsters suffered greater effects of handling-induced damage than did females, potentially due to the additional energy reserves available to brooding females.

Free Flight Training as a Tool for Psittacine Reintroductions

As habitat loss and other threats accelerate, ecological restoration and reintroduction science are becoming progressively more important. The psittacines are among the most endangered bird groups and are prime candidates for restoration through reintroduction. Unfortunately, post-release survival of captive-raised animals is often quite low because, in part, of high predation rates, low site fidelity, poor flight ability, and low flock cohesion. Current best practices in parrot release hold the birds in captivity for a year or more and include distinct methods to address each of these challenges. Here, we conduct a small-scale, proof-of-concept study using free flight methods and human-socialized trained adult birds to hand raise and release a group of six fledgling Blue-and-yellow Macaws in their historical range in southeastern Brazil. All six released birds showed strong flock cohesion and fidelity to the release site, avoided predation, and survived without supplemental feeding for over one year. One bird was captured by local people but was recovered and rereleased and it has reintegrated into the group and is still alive and doing well. The human-socialized trained adult birds modeled both desirable behaviors (flocking, foraging, reacting to predators) and undesirable behaviors and they were returned to captivity before the conclusion of this study. Our study suggests that free flight training has great potential to help captive-raised young attain a broad array of vital skills needed for survival post-release.

Identifying Potential Critical Angel Shark Areas in Türkiye, Eastern Mediterranean Based on New Records of Squatina spp. Identified through Fisher Engagement

This study presents new records of three Critically Endangered angel shark species (Family: Squatinidae) occurring in the Eastern Mediterranean—Smoothback Angelshark S. oculata Bonaye, 1840, Sawback Angelshark S. aculeata Cuvier, 1829, and Angelshark S. squatina (Linnaeus, 1758). The supporting data serves to highlight three potential Critical Angel Shark Areas (CASAs) in Türkiye: Fethiye Bay, Çanakkale Strait (i.e., Dardanelles), and Antalya Bay. These data also demonstrate that female S. oculata may mature at a smaller size than prior published estimates of length at first maturity. This new dataset provides details of 23 S. squatina specimens, 52 S. oculata specimens, and 5 S. aculeata specimens, totalling 80 recent angel shark specimens found in Turkish waters mostly sent to us from small-scale fishers who had incidentally caught angel sharks. Also presented are four capture-induced parturition events in Turkish waters onboard fishing vessels, thus providing details on internal yolk sacs, reproductive habitats, and indications of spawning season. Our dataset presented here spans from 2018 to 2023 and suggests that mature adults of S. squatina and S. oculata still occur in Turkish waters, in Fethiye Bay and Çanakkale, respectively. Due to elevated chances of fishers encountering Critically Endangered angel sharks in Türkiye, we suggest that fishers are trained in handling and safe-release methods, to ensure reduced incidents of capture-induced parturition, and improved post-release survival. This study demonstrates that bottom set nets set by small-scale fishers pose less risk to mortality for angel sharks as they are almost always encountered alive after a usual 12 h soak time, suggesting that bottom trawling in critical habitats should be better regulated (or phased out) to help improve national angel shark conservation initiatives.

Post-release survival of Whiteleg skate (Amblyraja taaf) caught as bycatch on demersal longlines in deep waters of the Southern Ocean (Crozet Archipelago)

Abstract Whiteleg skate (Amblyraja taaf) is a bycatch species commonly discarded in demersal longline fisheries targeting Patagonian toothfish around the Crozet archipelago (Southern Ocean). While there are global conservation issues on elasmobranchs, the post-release survival of this deep-sea species remains unknown. This study is the first tagging programme conducted on Whiteleg skates to investigate their fate after being released at sea. Almost 3000 skates were captured, double-tagged with conventional tags and released between 2020 and 2022 to assess survival using capture–mark–recapture (CMR) models. Our primary result was an estimated annual apparent survival rate higher than 92% for skates released in good condition (with 185 skates recaptured after up to 944 days at liberty). Low detection rate highlighted methodological challenges for CMR models. However, skate size and depth of capture had an effect on apparent survival probability with smaller individuals having lower values (<65 cm; 0.84 ± 0.04) as well as skates caught at shallower depths (<1200 m; 0.83 ± 0.04). Overall, this study suggests that the mandated release of skates in good condition is effective to limit fishing impact on skates in this fishery. To further limit this impact, we recommended changes in fishing practices (hauling speed and soak time).

First long-term trajectory of an ocean sunfish (Mola mola L.) from the northwestern Mediterranean.

The ocean sunfish is a large fish for which many aspects of its ecology and biology are still poorly known. Electronic tagging was used to provide the first information on the movements of an ocean sunfish from the northwestern Mediterranean. The sunfish moved towards the Gibraltar strait over the year and displayed substantial movements in the water column. The potential of the tagging technique employed for studying its behavior and long-term migratory dynamics, and assessing the post-release survival of ocean sunfish is highlighted.

A Systematic Review of Global Marine Mammal Rehabilitation and Refloating, 2000–2023

Rehabilitation of marine mammals is performed throughout the world, yet the impact of rehabilitation on individuals and populations is questionable given the lack of robust information on the rehabilitation process and post-release monitoring in most cases. The goals of this study were to perform a systematic review of existing literature on marine mammal rehabilitation between 2000–2023 to determine the current state of rehabilitation and to evaluate the rehabilitation and conservation factors that could be used to build a framework to assess the health of rehabilitation programs worldwide. A total of 418 publications encompassing 52 species of marine mammal were included in the systematic review. Rehabilitation efforts focused mostly on pinnipeds, and North America was the most represented region. Data are scarce for both short- and long-term post-release survival across species. Reports about species threatened with extinction were significantly more likely to include information about conservation parameters than those species of least concern. A meta-analysis demonstrated a fairly strong fit of the dimensions of the proposed framework for a rehabilitation health index. Further refinement would strengthen the utility of this tool for both rehabilitation and conservation programs.

Anatomical hooking location and bleeding occurrence in northern pike (Esox lucius) caught in recreational catch-and-release angling in a lake with reduced prey fish availability

Catch-and-release (C&R) is a common practice in recreational angling for northern pike (Esox lucius), whereby the angler releases the fish back into the water after capture with the expectation that it will survive with negligible stress and physical injuries. This may not always be the case, as hooking in critical anatomical locations, such as gills, esophagus, and stomach, increases the frequency of bleeding at the hook wound and has been recognized as a key determinant of post-release mortality in pike. Several factors (e.g. bait type and size, hook characteristics, and fish length) can influence the risk of hooking in critical locations, and the fish’s willingness to strike the fishing lure/bait may largely depend on previous feeding history and associated motivation to feed. In this respect, food deprivation and greater feeding motivation can be expected to result in an intensified response and more forceful attacks on fishing lures/baits, which could increase the risk of hooking injuries in sensitive tissues, as the fish may ingest the hook more deeply. Here, we assess the hooking location and bleeding occurrence in pike caught on soft plastic shads and baitfish in a shallow eutrophic lake. The prey fish density of this lake, primarily common roach (Rutilus rutilus), has been substantially reduced by seining as part of a lake restoration project. Experimental angling sessions took place at the end of 2020 and 2022, approximately 1–2 months and 25–26 months after the initial reduction in prey fish density, respectively. Removal of roach from the lake was also done regularly by seining after the angling sessions in 2020. Pike angled in 2022 had significantly lower body condition than individuals caught in 2020, indicating that mass removal of roach from the lake resulted in food shortage. The risk of hooking in critical locations (herein defined as hooking in gills and back of mouth) was not associated to angling year, body condition, or length of the pike. However, across the two angling years, the incidence of hooking in critical locations was higher for soft plastic shads compared to baitfish (24.2% versus 7.4%). Pike caught on soft plastic shads also bled more frequently than individuals caught on baitfish (19.7% versus 6.2%), most likely due to the fact that hooking in the gills almost exclusively occurred with soft plastic shads. Bleeding propensity was also not related to angling year, body condition, or fish length. Hence, the present study found no evidence that long-term reductions in food availability and resulting declines in body condition influence how pike strike and ingest fishing lures/baits, at least not in a manner that increases the risk of hooking injuries in sensitive locations. Instead, bait type seems to play the largest role for the observed bleeding patterns. We recommend that future studies investigate the potential effects of C&R angling on the post-release survival of pike with reduced body condition due to limited food availability.

Water temperature at the time of the catch-and-release event is a better predictor of survival in Atlantic salmon (Salmo salar) than acute water temperature changes before and after.

Despite studies on the effect of catch-and-release on the survival of Atlantic salmon (Salmo salar) being widespread in the literature, studies to date have failed to evaluate the potential role of thermal history. Herein, we show that despite cooler conditions post-release, 4/18 (22%) salmon died when caught-and-released at water temperatures ≥20°C, whereas 1/13 (8%) salmon caught-and-released at water temperatures ≤20°C, but who encountered mean water temperatures ≥20°C post-release, died. We conclude water temperature at time of the catch-and-release event remains the most suitable predictor of post-release survival.

The role of temperature in vitality and survival assessments of beam-trawled and discarded European plaice (Pleuronectes platessa).

Thermal stress can influence the recovery of fish released after capture. Vitality assessments using reflex and behavioural responses require that responses can be observed reliably, independent of temperature. Here, we tested whether reflex and behavioural impairment and survival of beam-trawled and discarded European plaice (Pleuronectes platessa) are independent from seasonal air and water temperature deviations. In total, 324 beam-trawled plaice (n = 196 in summer and n = 128 in winter) were exposed to two air temperature treatments and two water treatments (i.e. modified and ambient temperatures for both). The modified treatments (i.e. cooled in summer, warmed in winter) represent the thermal shock a fish may experience when being returned to the water. All reflexes and tested behaviours were affected by ambient temperature, with high impairment noted in summer. None of the reflexes were affected by temperature shocks alone, only body flex was. Body flex was highly impaired under every exposure combination. Fish size and duration of air exposure further influenced impairment of reflexes such as head complex and tail grab. More generally, post-release survival was assessed as 21% [95% CI: 16-28%] in summer and 99% [97-100%] in winter. Beam trawling in summer is likely to induce high reflex impairment and mortality in discarded plaice, and therefore spatial-temporal mitigation approaches should be prioritized over control of on-board temperatures.

Postrelease survival of undersized swordfish (Xiphias gladius) caught on pelagic longline gear in a U.S. commercial fishery in the western North Atlantic Ocean

Postrelease survival of undersized swordfish (Xiphias gladius) caught on pelagic longline gear in a U.S. commercial fishery in the western North Atlantic Ocean