Post-release Survivorship Research Articles

Post-Release Survivorship in a New Population of Blanding's Turtles Established Using Headstarted and Directly Released Turtles

Post-Release Survivorship in a New Population of Blanding's Turtles Established Using Headstarted and Directly Released Turtles

Striped marlin in their Pacific Ocean milieu: Vertical movements and habitats vary with time and place

Striped marlin, Kajikia audax, a top bycatch of the longline fishery, has been designated as being in overfished condition in the Western and Central North Pacific, and overfishing is still occurring. This prompts an urgent need to devise conservation and management measures based on the best, current information on the biology and ecology of this species. Despite decades of conventional tagging around the Hawaiian waters, ecological research on striped marlin in the Central North Pacific has been lacking since 2005, and little is known about striped marlin’s vertical habitat, diving behavior and bycatch vulnerability in this area. To address this knowledge void, 31 popup satellite archival tags (4 X-Tags; Microwave Telemetry, Inc. and 27 MiniPATs; Wildlife Computers Inc.) were deployed on striped marlin (138-192 cm eye fork length) between 2016 and 2019 via the Hawaii-based longline fleet. Transmitted time series records revealed striped marlin spent 38 and 81% of their day and night in the top 5 m, with median daytime and night depths of 44 m and 2 m, respectively. Temperatures experienced were 23.3°C, daytime median, and 24.6°C, nighttime median, to a minimum of 7.6°C at the deepest depth logged, 472 m. Striped marlin exhibited distinct swimming behaviors, including diel depth distributions, excursions around the top of the thermocline, and extended time at the surface, most likely reflecting the dynamic biophysical environment and intrinsic life history of this highly migratory predator. High post-release survivorship (86%) in tagged striped marlin, and their predominant use of the sea surface and mixed layer indicate that live release measures can be a viable bycatch reduction strategy.

Post-release survivorship of 18 years in a hand-reared grey-headed flying-fox (Pteropus poliocephalus) revealed by a metal identification band

An understanding of the factors associated with post-release survivorship in rehabilitated animals is instrumental for evaluating best-practice rehabilitation and release methods to ultimately achieve optimal conservation outcomes. However, there is almost nothing reported in the scientific literature concerning post-release survivorship in hand-reared flying-foxes, with the only published study to date suggesting that hand-reared flying-foxes have significantly reduced mean longevity following release. We report a case of a hand-reared grey-headed flying-fox (Pteropus poliocephalus) that was fitted with a metal identification band when it was released in 2004 and recovered alive in 2022. This information provides clear evidence of this individual having post-release survivorship of 18 years. The distance between the release and recovery locations was approximately 297 km, corresponding with the species’ known nomadism. Based on the current scientific information on longevity in the grey-headed flying-fox, this individual would be considered an old animal.

Post release monitoring of rehabilitated gray seal pups over large temporal and spatial scales

AbstractWildlife rescue and rehabilitation is used globally to aid the conservation and welfare of marine species, however, postrelease monitoring is challenging. Here, long‐term, regional postrelease monitoring provides feedback for rehabilitation centers for gray seals (Halichoerus grypus). Data from 1,094 rehabilitated gray seals over 19 years across the southwest UK were examined to assess postrelease survivorship and the impact of release site on movements and range. Using flipper tags combined with photo identification, 391 rehabilitated seals (35.7%) were resighted, including 188 seals (17.2%) that were traced back to a specific rehabilitated individual with release data. The maximum monitoring duration for a single rehabilitated seal was 17 years, although the majority (151/188; 80%) were sighted for less than 5 years and 80/188 (43%) were resighted for less than a year. Almost all 188 traced rehabilitated seals (n = 176, 93.6%) visited the St Ives Bay Wild Site, yet only half had been released at the adjacent St Ives Bay Release Site. Rehabilitated seals had similar dispersal patterns to their wild conspecifics but over a smaller area. Once released, rehabilitated animals face the same threats as their wild counterparts.

Bigeye thresher shark Alopias superciliosus movements and post-release survivorship following capture on linked buoy gear

Off the US west coast, fishery development efforts have led to the recent recommendation for authorization of deep-set buoy gear (DSBG) and linked buoy gear (LBG), two commercial gear types for targeting swordfish at depth during the day. Because the new deep-set configurations interact with bigeye thresher sharks (Alopias superciliosus), a large pelagic species that is not typically retained for sale, this work has focused on documenting the fate of released catch. Bigeye thresher sharks (BETS) were captured and outfitted with pop-up satellite archival tags (Wildlife Computers sPATs and miniPATs) to assess movement trends and acute (30-d) post-release survival during exempted fishing trials authorized by National Marine Fisheries Service (NMFS) and the Pacific Fisheries Management Council (PFMC). Post-release survivorship was based on 14 BETS (∼157−230 cm LF) caught on LBG between August 2016 and December 2019 following fight times ranging from 17−300 min. Thirteen BETS survived the acute effects of capture, and one immediate mortality was documented following heavy entanglement in the monofilament leader. BETS were resilient to the acute effects of handling stress following capture on LBG, with an observed post-release survival rate of 93 %. Surviving BETS exhibited consistent diurnal dive patterns with sharks remaining well below the thermocline during the daytime (mean = 386 ± 62 m) and within the mixed layer at night (mean = 65 ± 25 m). With the exception of one tag that reported within close proximity of the SCB tagging location, BETS exhibited extensive southward movements (mean = 1235 ± 235 km) towards a potentially relevant migratory corridor for large pelagic sharks.

Influence of early rearing environment on water-borne cortisol and expression of stress-related genes in grass carp (Ctenopharyngodon idella).

Nowadays, lower post-release survivorship of hatchery-reared fish in natural aquatic bodies has attained great attention and research is in progress to determine the reasons for their higher mortality. It is assumed that hatchery rearing environments negatively affect the physiological stress response of the fish. Thus, understanding how rearing environments modulate this is important for the well-being of fish. Here, an attempt has been made to assess the influence of two early rearing environments, i.e., barren (BR), mimic the conventional hatchery rearing environment; without any substrate and enrichment items and structurally enriched (ER), containing multi-colored gravel substrate, cobbles and plants, on the stress regulators i.e., HPI-axis and brain monoaminergic system of fish. Three-day old grass carp (Ctenopharyngodon idella) postlarvae were reared up to the fingerling stage in the aforementioned environments. For the stress assay, fish were subjected to net capture followed by 30min confinement in a small container at a lower water level. The pre- and post-stress responses were compared by evaluating their water-borne cortisol and the mRNA level of corticotropin releasing hormone (CRH), dopamine D1A receptor (DRD1A) and hydroxytryptamine receptor 2B (HTR2B) in the whole brain through qPCR analysis. Results of two-way ANOVA revealed significantly low (p < .001) post-stress concentration and release rate of water-borne cortisol and pre- and post-stress expression of CRH, DRD1A and HTR2B genes in the ER than BR fish. It is concluded that a structurally complex early rearing environment reduces the stress level in fish.

A new animal-borne imaging system for studying the behavioral ecology of small sharks: laboratory and field evaluations

ABSTRACT The use of animal-borne imaging and environmental data collection systems (AVEDs) can provide behavioral and ecological information of animals that many other technologies cannot usually offer. However, many previous AVEDs have been designed for larger sharks, and there is a need for a technology that permits the collection of behavioral and ecological data for small sharks. In this study, we developed and tested the Shark Harness, a novel AVED technology for small to medium size sharks, in both the laboratory and the field. In the laboratory, the swimming behavior of seven dusky smoothhound sharks (Mustelus canis; n = 7) ranging in size from 90.00–114.30 cm total length (TL) was assessed. When compared to unmanipulated individuals, sharks fitted with the Shark Harness exhibited no significant variations in both swimming duration (p = 0.63) and vertical positioning (0.99), whereas a minor, yet statistically significant, increase in tail beat frequency (p = 0.016) was observed. In the field, six dusky smoothhound sharks (90–110.28 cm TL) equipped with the Shark Harness were released in waters near Montauk, New York, USA. Field data suggest that the Shark Harness can be used to assess fine-scale movements, heterospecific interactions, and immediate post-release survivorship of dusky smoothhound sharks and other small sharks (≥80 cm TL) in a wild setting. However, future modifications are required prior to redeployment in a wild setting, including a more cryptic and hydrodynamic design, in order to obtain a more accurate representation of the respective animal’s natural behavior and interactions with con- and hetero-specifics.

Predation and disease limit population recovery following 15 years of headstarting an endangered freshwater turtle

Recovery strategies for endangered species vary in scope and scale, and uncertainties regarding their effectiveness make it necessary to implement evidence-based methods to ensure best management practices and the most efficient use of limited conservation dollars. Assessing recovery actions for species with slow life histories requires decades of study. We quantitatively assessed the putative recovery of two populations (PopA, PopB) of globally endangered Wood Turtles (Glyptemys insculpta) after 30 years of mark-recapture study and 15 years of headstarting implemented in response to a 57% reduction in population size attributed to poaching. We modeled population-specific demographic parameters to evaluate recovery efforts to date, and determine the next phase of management. Both populations showed limited recovery despite the release of 490 headstarted turtles. Recovery has been hindered by lower than expected 1-year post-release survivorship of headstarts (36%, 52% in each population, respectively), and only moderate (for turtles) adult survivorship (89%, 93%). Six headstarted turtles have, however, reproduced suggesting both populations may eventually become self-sustaining. From 2015 to 2018, subsidized predators killed 11 adult turtles, and we detected three diseases (mycotic shell disease, ranavirus, Glyptemys herpesvirus 2) in the headstarts. Our population viability analysis projected that both populations would recover if a predator-management strategy were implemented. Headstarting alone is not enough to save at-risk populations from local extinction when they face multi-faceted problems, including the cascading effects of landscape-scale habitat modification, for which management is challenging.

Post-release survivorship of Pacific bluefin tuna (Thunnus orientalis) captured in the California recreational fishery

In the eastern north Pacific, Pacific bluefin tuna (PBF, Thunnus orientalis) support seasonal fishing operations aboard a diverse fleet of commercial and recreational vessels. Recent PBF stock projections have identified a reduced spawning stock biomass, which has resulted in management restrictions and capacity reduction in all U.S. west-coast fisheries. Although recreational fisheries only account for a minor component of west coast harvest, a bag limit reduction from 10 to 2 fish person−1 day−1 was implemented in 2014. Considering the potential for increased number of PBF released in the fishery, this study assessed post-release disposition using a combination of electronic (Wildlife Computers sPAT) and conventional tags. Additionally, biochemical indices of capture stress were measured in the blood and coupled with tagging data to better understand the physiological response that is mounted as a result of time on the line (fight time). PBF were caught using standardized recreational fishing gear following protocols and techniques currently used by the southern California fleet. Survivorship was based on tagging data from 40 electronically tagged PBF ranging in size from 82 to 148 cm FL (∼11-63 kg) and blood sampling was performed on an additional 49 PBF (80 to 170 cm FL). Tagging results yielded only one immediate mortality for the fish with the longest fight time (280 min; 97.5% survivorship). Additionally, there was also one predation event that occurred seven days after release; if the predation is included as a capture-related mortality, the combined survivorship estimate is 95%. Results from the blood chemistry analyses show a direct correlation between fight time and the levels of blood stress indicators. When compared with the electronic tagging data, it is evident that the physiological impact of the angling event does not appear to be sufficient to impede post release survival, at least when time on the line is less that that examined in this study (<70 min). Collectively, these data show that when handled properly, PBF can tolerate and survive the acute effects of capture and release when using west coast recreational fishing methods.

Amphibian conservation using assisted reproductive technologies: Cryopreserved sperm affects offspring morphology, but not behavior, in a toad

With increasing rates of global biodiversity decline, strategies such as reintroduction or supplementation, have become increasingly important in conserving our remaining biodiversity. To sustain reintroduction programs, insurance colonies are established and bred in captivity. Captive-bred offspring are then released to augment wild populations or establish new populations. A key issue determining the success of reintroduction programs, therefore, is the fitness of captive-bred individuals and their ability to survive once released. Unfortunately, little is known about the quality of captive-bred offspring produced using assisted reproductive technologies, such as gamete cryopreservation. To fill this gap in scientific knowledge and conservation practice, we examined differences in tadpole morphology, tadpole behavior, metamorph morphology, and duration of larval stage between Fowler's toad (Anaxyrus fowleri) offspring produced using cryopreserved sperm (experimental, cryo-derived individuals) and offspring produced by amplectant adults (control individuals). Results indicated cryo-derived individuals were smaller as tadpoles and emerged as smaller metamorphs. However, predator-avoidance behavior was not significantly different between the two treatment groups. Smaller body size in cryo-derived individuals can negatively affect their post-release survivorship and reproductive output, thus limiting the potential success of reintroduction programs. This pioneering study provides insights into the quality and competency of individuals produced using cryopreserved sperm across two distinct life-stages. We show that although cryopreservation has often been proposed as a promising way of contributing to wildlife conservation, more detailed examinations are needed to assess the quality of offspring produced for it to be an effective conservation tool.

Effects of early rearing enrichments on modulation of brain monoamines and hypothalamic-pituitary-interrenal axis (HPI axis) of fish mahseer (Tor putitora).

Enriching rearing environment is the strategy suggested for improving the post release survivorship of captive-reared animals. Here, an attempt has been made to evaluate the impact of early rearing enrichment on the hypothalamic-pituitary-interrenal axis (HPI axis), blood glucose, and brain dopaminergic and serotonergic systems of Tor putitora. Fifteen-day-old hatchlings of T. putitora were reared up to advanced fry stage in barren, semi-natural, and physically enriched environments and compared them with regard to pre-stress and post-stress levels of whole-body cortisol, blood glucose, brain serotonergic activity (5HIAA/5HT ratio), dopaminergic activity (DOPAC/DA and HVA/DA ratios) and norepinephrine (NE) levels. Significantly low basal whole-body cortisol, glucose and brain NE levels were observed in a physically enriched group of fish as compared to the other two groups. However, after acute stress, all rearing groups showed elevated levels of cortisol, blood glucose, brain 5HIAA/5HT, DOPAC/DA and HVA/DA ratios and NE levels but the magnitude of response was different among different rearing groups. The barren reared group showed a higher magnitude of response as compared to semi-natural and physically enriched groups. Similarly, the recovery rate of whole-body cortisol, blood glucose, and whole-brain monoamines were long-lasting in barren-reared mahseer. We illustrate that increased structural complexity (physical enrichment) during the early rearing significantly modulates various physiological and stress-coping mechanisms of mahseer.

Post-release survivorship and movements of bigeye thresher sharks, Alopias superciliosus, following capture on deep-set buoy gear

The bigeye thresher shark (Alopias superciliosus) is a large pelagic predator routinely caught in a new deep-set fishery off California. Deep-set buoy gear (DSBG) was recently developed to selectively target swordfish (Xiphias gladius) at depth during the daytime and is currently being trialed by a limited fleet of vessels operating under an exempted fishing permit (EFP) issued through the National Marine Fishery Service (NMFS) and Pacific Fisheries Management Council (PFMC). Although marketable, bigeye thresher sharks (BETS) are often released or discarded to conserve limited hold space for more valuable catch. This study outfitted BETS with pop-up satellite archival transmitters (PSATs) programmed for 30-day deployments to evaluate acute post-release survival in the DSBG fishery and begin to understand depth and temperature distribution for this poorly known species. Fourteen BETS (43–93 kg) were tagged from 2016 to 2018 with PSATs (Wildlife Computers sPATs and MiniPATs) following fight times that ranged from 15 to 171 min. Out of the 14 deployments, twelve individuals survived the acute effects of capture, one BETS died shortly after release and one individual was preyed upon 6 h after release. Given the lack of information surrounding the predation induced mortality, two survivorship estimates are provided, one that includes the event as a mortality resultant of the capture event (86% survivorship) and one that excludes the event from the analysis (92% survivorship). All surviving BETS exhibited consistent diurnal dive patterns in which the sharks remained below the thermocline during the day and within the mixed layer at night. Mean daytime depths ranged from 250 to 439 m, while mean nighttime depths ranged from 20 to 106 m. Daytime temperatures at depth ranged from 6 to 10 °C with the lowest temperature value (6.0 °C) recorded on the deepest dive (548 m). For all BETS, maximum night temperatures averaged from 22.5 to 25.1 °C. Two tagged individuals remained proximal to the study area (<150 km) with others moving up to >1300 km from the tagging site (mean = 1009 ± 455 km). Mean daily rates of horizontal movement ranged from 3.4 to 41.6 km day−1. The most common movement trend entailed BETS moving in a southerly direction towards a series of offshore seamounts along southern Baja California, Mexico (22°-26 °N and 114°-126 °W), a purported offshore corridor for other large pelagic sharks of the eastern Pacific.

Sea turtles and survivability in demersal trawl fisheries: Do comatose olive ridley sea turtles survive post-release?

Incidental capture of air-breathing species in fishing gear is a major source of mortality for many threatened populations. Even when individuals are discarded alive, they may not survive due to direct injury, or due to more cryptic internal physiological injury such as decompression sickness. Post-release mortality, however, can be difficult to determine. In this pilot study, we deployed survivorship pop-up archival tags (sPAT) (n = 3) for an air-breathing species, the olive ridley sea turtle (Lepidochelys olivacea), one of the first studies to do so. We found that at least two of the three turtles survived after being captured in demersal fish trawl nets and being resuscitated from a comatose state following standard UN Food and Agriculture Organization guidelines. One turtle died; however, the absence of a change in light level but continued diving activity suggested that the turtle was likely predated. Whether capture contributed to the turtle’s susceptibility to predation post-release is unknown, and average tow duration during this fishing trip was similar in duration to that of a turtle that survived (1.5 h). The two surviving turtles displayed normal horizontal and vertical movements based on previous tagging studies. This study suggests that resuscitation techniques may be effective; however, additional study is necessary to increase sample sizes, and to determine the severity of decompression sickness across different levels of activity and in other fishing gears. This will result in better population mortality estimates, as well as highlight techniques to increase post-release survivorship.

Home Range, Body Condition, and Survival of Rehabilitated Raccoons (Procyon lotor) During Their First Winter

The effects of raccoon (Procyon lotor) rehabilitation on postrelease survivorship are unknown. Raccoon rehabilitation success was measured as differences in prewinter body condition, home range size, distance to manmade structures, and during-winter survival between raccoons in the wild and those who have been rehabilitated. Prewinter body condition did not differ between wild and rehabilitated raccoons, but there was a trend for rehabilitated raccoons to have better body conditions. There was no difference between wild and rehabilitated raccoon adaptive kernel (AK) home range for 95% and 90% AK home ranges, or for core (50% AK) use areas. There was no sex difference in distance traveled from the release site within rehabilitated raccoons. However, rehabilitated raccoons were found significantly closer (49.4 ± 4.7 m) to manmade structures than wild raccoons (92.2 ± 14.4 m), and female raccoons were found significantly closer (64.8 ± 4.5 m) to manmade structures than male raccoons (72.3 ± 17.6 m). The results of this study indicate that raccoons can be successfully rehabilitated, but they may occupy habitat closer to manmade structures than wild raccoons.

Post-release survivorship studies on common thresher sharks (Alopias vulpinus) captured in the southern California recreational fishery

The common thresher shark (Alopias vulpinus) is the focus of a popular southern California recreational fishery that targets individuals using multiple fishing gears and techniques. Despite increasing trends in the use of catch and release techniques in the recreational fishery for thresher sharks, a comprehensive estimate of post-release survival is not available for all modes of capture. This study focused on assessing post-release survival in two modes of capture routinely observed in the southern California recreational fishery: (1) sharks that are caught using caudal-based angling techniques and unintentionally released with trailing gear left embedded and (2) sharks that are caught and released using mouth-based angling techniques. Post-release survivorship was assessed using pop-up satellite archival tags programed for 10- and 90-day deployments, with the former used for mouth-caught sharks and the latter for individuals with trailing gear. Post-release survivorship estimates for the trailing gear studies were based on data from nine common thresher sharks (111-175cm FL) while the mouth-based experiments utilized data from an additional seven sharks (125-187cm fork length, FL). For the trailing gear studies, six sharks died within 5days after release, one died after 81days, and two sharks survived the deployment period for an overall survivorship rate of 22%. All seven mouth-hooked common thresher sharks survived the acute (∼10days) effects of capture (100% survivorship). These results suggest that in the southern California recreational thresher shark fishery, caudal-based angling techniques, which often result in trailing gear left embedded in the shark, can negatively affect post-release survivorship. This work also reveals that mouth-based angling techniques can, when performed properly, result in high survivorship of released sharks.

The physiological effects of capture stress, recovery, and post-release survivorship of juvenile sand tigers (Carcharias taurus) caught on rod and reel

Current shark fishery management regulations in the US Atlantic, as well as other regions worldwide, mandate the release of sand tigers (Carcharias taurus) captured in recreational fisheries. To examine the efficacy of this strategy as a conservation tool, the physical and physiological effects of capture stress and post-release survivorship were examined in juvenile sand tigers angled on conventional rod and reel tackle with offset circle hooks. Analysis of blood samples obtained immediately after capture (n=84) indicated that, relative to minimally stressed captive individuals, juvenile sand tiger blood biochemistry is disturbed after brief (<7min) angling events. Serial blood sampling of five captive sharks subjected to a 3min simulated rod and reel angling event revealed rapid and significant disruptions in blood biochemistry with physiological recovery within 12–24h. Post-release monitoring of 65 sharks surgically implanted with acoustic tags demonstrated high degrees of immediate (99%), short- (82%), and long-term post-release survivorship (75%). Physiological disruptions did not appear to reduce immediate survivorship (5 days post capture), however, sharks hooked internally had lower rates of survival 50–100 days following release. Overall, these results suggest that juvenile sand tigers are able to cope with and survive the physiological stress associated with brief rod and reel capture, but physical trauma associated with hook location can impair post-release survival. Regardless, mandatory release appears to be a viable management strategy for juvenile sand tigers captured in rod and reel fisheries.

A review of RSPCA research into wildlife rehabilitation

Wildlife rehabilitation is defined as ‘the treatment and temporary care of injured, diseased, and displaced indigenous animals, and the subsequent release of healthy animals to appropriate habitats in the wild’...

Recovery of visual performance in rosy rockfish ( Sebastes rosaceus) following exophthalmia resulting from barotrauma

Rapid ascent during fishing capture can cause exophthalmia (‘pop eye’) in physoclistic fishes, resulting in stretching of the optic nerves and extraocular muscles, but it is not known whether exophthalmia affects vision temporarily or permanently. We used the optokinetic reflex test to assess changes in visual performance of rosy rockfish ( Sebastes rosaceus) that had experienced exophthalmia. Vision was functional 4 days after recompression and was improved after 1 month of recovery evidenced by individuals being able to track both smaller and faster-moving gratings. Our results suggest that, after recompression, rosy rockfish recover from exophthalmia fairly rapidly and perhaps fast enough to minimize significant adverse impacts on survival. This measured recovery from exophthalmia, in addition to evidence of high short-term, post-release survivorship, shows that recompression of unwanted rosy rockfish may be a viable management technique, and may be appropriate for other rockfish species, some of which are at low population densities due to high fishing pressure.

Plasma catecholamine levels as indicators of the post-release survivorship of juvenile pelagic sharks caught on experimental drift longlines in the Southern California Bight

Between 1983 and 2004, nearly 12 000 shortf in mako (Isurus oxyrinchus), common thresher (Alopias vulpinus) and blue (Prionace glauca) sharks were tagged in the Southern California Bight; however, only 1.97% of these have been returned. One possible reason for this low return rate could be post-release mortality caused by capture stress from the experimental longline. Plasma catecholamine levels were analysed to evaluate stress levels in longline-captured, rod-and-reel-captured and unstressed docile sharks. The mean catecholamine values determined for the three tag–release species ranged from 6539 to 22 079 pg mL–1. The level of adrenaline found in moribund I. oxyrinchus (94 807 pg mL–1) was much higher than in either P. glauca (46 845 pg mL–1) or A. vulpinus (36 890 pg mL–1). In contrast, blood obtained from sharks that were landed within minutes had lower catecholamine values (P. glauca, 889 and 1347 pg mL–1; I. oxyrinchus, 2960 and 3946 pg mL–1, adrenaline and noradrenaline respectively). Among the nine I. oxyrinchus specimens that were recaptured long after their longline capture and release, the highest adrenaline level measured just before release was 33 352 pg mL–1. Because these mako sharks survived sufficiently long to be recaptured, their time-of-release catecholamine levels provide a conservative estimate of ~80% viability on the longline-captured and released population.