Post-release Survival Research Articles

Challenges of estimating post-release mortality of istiophorid billfishes caught in the recreational fishery: A review

Istiophorid billfishes are targeted in recreational fisheries throughout the tropical and subtropical waters of the world's oceans. Over the past thirty years, changes in management regulations and increased angler conservation awareness have resulted in an increasing proportion of the billfish catch being released alive, and in many areas the fishery is principally catch-and-release. However, the fate of released fish, and thus the fishing mortality associated with the recreational fishery, is not well understood. Some insights into post-release mortality of billfishes caught in the recreational fishery have been gained from analyses of conventional tag data, hooking location information, and acoustic tracking data. Over the past 10 years pop-up satellite archival tags (PSATs) have been used to specifically estimate post-release mortality for a limited number billfish species. Extrapolation of the results of these limited studies throughout the various recreational billfish fisheries is not prudent due to potential influences of different species, areas, seasons, fishing styles, and hook types. The current high cost of PSATs presents a significant obstacle to evaluating the effect of these variables on rates of post-release survival. Nonetheless, the results of the few studies to date have had an important impact on fisheries management and the behavior of recreational anglers.

Bycatch mortality of endangered coho salmon: impacts, solutions, and aboriginal perspectives.

We used biotelemetry and human dimensions surveys to explore potential solutions to migration mortality of an endangered population of coho salmon caught as bycatch in an aboriginal beach seine fishery. From 2009 to 2011, 182 wild coho salmon caught as bycatch in the lower Fraser River (Canada) were radio-tagged and tracked as they attempted to complete their migrations to natal spawning areas over 300 km upstream. Failure to survive to reach terminal radio receiving stations averaged 39% over three years. This mortality estimate is low compared to those obtained from telemetry studies on other salmon fisheries in the Fraser River. However, this value is markedly higher than the mortality estimate currently used to manage the fishery's impact. It is also in contrast to the perceptions of the majority of aboriginal fishers, who did not think survival of coho salmon is affected by capture and release from their fishery. Increased probability of survival was associated with lower reflex impairment, which is consistent with previous findings. Reflex impairment was positively correlated with entanglement time, suggesting that greater efforts by the fishers to release bycatch from their nets quickly would minimize post-release mortality. Survey responses by aboriginal fishers also suggested that they are receptive to employing new bycatch handling methods if they are shown to increase post-release survival. However, attempts to facilitate revival of a subset of captured fish using cylindrical in-river recovery bags did not improve migration success. Fisheries managers could use the new information from this study to better quantify impacts and evaluate different harvest options. Since aboriginal fishers were receptive to using alternate handling methods, efforts to improve knowledge on minimizing reflex impairment through reductions in handling time could help increase bycatch survival. Such a direct integration of social science and applied ecology is a novel approach to understanding conservation issues that can better inform meaningful actions to promote species recovery.

Effects of hatchery rearing on Florida largemouth bass Micropterus floridanus resource allocation and performance under semi-natural conditions.

This study examined the growth, activity, metabolism and post-release survival of three groups of Florida largemouth bass Micropterus floridanus: wild-caught fish, hatchery fish reared according to standard practice (hatchery standard) and hatchery fish reared under reduced and unpredictable food provisioning (hatchery manipulated). Hatchery-standard fish differed from wild-caught fish in all measured variables, including survival in semi-natural ponds. Hatchery-standard and hatchery-manipulated fish showed higher activity levels, faster growth and lower standard metabolic rates than wild-caught fish in the hatchery. Fish reared under the manipulated feeding regime showed increased metabolic rates and increased post-release growth, similar to wild-caught fish. Their activity levels and post-release survival, however, remained similar to those of hatchery-standard fish. Activity was negatively correlated with post-release survival and failure of the feed manipulation to reduce activity may have contributed to its failure to improve post-release survival. Activity and post-release survival may be influenced by characteristics of the rearing environment other than the feeding regime, such as stock density or water flow rates.

Sterile Male Peach Fruit Flies,Bactrocera zonata(Saunders) (Diptera: Tephritidae), as a Potential Vector of the EntomopathogenBeauveria bassiana(Balsamo) Vuillemin in a SIT Programme

Tephritid fruit flies are serious pests in Mauritius, of which Bactrocera zonata (Saunders) (Diptera: Tephritidae) is one. One of the pathogens of fruit flies is Beauveria bassiana (Balsamo) Vuillemin; the introduction of this entomopathogen into the wild fly population would be beneficial for suppression of fruit fly populations. Five releases were made to study the dispersal behaviour and survival of sterile B. zonata males either treated or untreated with dry conidia of B. bassiana, in vegetable plantations bordered with papaya and mango trees in northern Mauritius from April 2010 to December 2012. The flies used were reared for ≈172 generations in the laboratory. Results showed that the dispersal behaviour and post-release survival were different for the two types of sterile males. Recapture rates of B. bassiana-treated sterile males (2.0 ± 1.4 %) were significantly lower than those of untreated flies (6.2 ± 5.5 %). However, the recapture rates for both types of males were within acceptable limits for release—recapture studies with mass-reared and irradiated fruit flies. Up to day 4 after release the percentage recovery of sterile B. zonata males untreated and treated with B. bassiana was 76 % and 81 %, respectively; 90 % of the recovered sterile flies from both groups were recovered up to 100 m from the release point, and only 4 % at a distance between 150 m and 200 m from the release point. Our results suggest that sterile B. zonata males could potentially be used as vectors of B. bassiana to supplement suppression of this pest in a sterile insect release programme.

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.

Food unpredictability in early life increases survival of captive grey partridges ( Perdix perdix ) after release into the wild

Abstract Reintroducing locally extinct species is an increasingly used conservation tool. However, many reintroductions fail to establish self-sustaining populations. The quality of the individuals released may crucially affect reintroduction success, but it is largely unknown which quality traits are important and how they might be improved, especially in captive-reared animals. We aimed at increasing survival of captive-bred grey partridges (Perdix perdix) after release. We experimentally tested the effects of prenatal and postnatal unpredictable food supply on post-release survival of two captive strains (two or >30 generations in captivity). 691 Full-grown birds representing all eight strain × prenatal × postnatal treatment combinations were released in autumn in 28 social groups (coveys) and followed in the field for six months by radio tracking and visual observations. Data were analysed with multistate capture-recapture models including several random effects. Post-release survival was higher in birds having encountered postnatal unpredictable food supply and decreased drastically with later release dates. Also, coveys strongly affected an individual’s survival prospects. Our results suggest that post-release survival of captive-bred grey partridges can be increased significantly through simple, inexpensive pre-release measures in captivity, i.e. exposing them to an unpredictable environment. Similar measures might be successful in other species and could ultimately enhance reintroduction success.

Dispersal, migration, and predation of juvenile crucian carps after release from rice fields

The crucian carp (Carassius spp.) fishery in Lake Biwa, Shiga Prefecture, Japan, is economically and culturally important. Annual fishery catch, however, has been decimated allegedly due to predation by largemouth bass (Micropterus salmoides) and bluegill (Lepomis macrochirus). This prompted the local government to restore natural stocks by rearing juvenile crucian carps in rice fields, but to little avail. Little is known about the post-release fate of aquacultured fish in this system. Hence, we conducted the present study to address the following questions: 1) How quickly do carp juveniles disperse from rice fields into Lake Biwa?, 2) Are carp juveniles preyed upon by largemouth bass and bluegill en route to Lake Biwa?, 3) Are there any differences in dispersal patterns or predation loss among different species or different size classes of crucian carps? Results showed that the approximately 1 km movement from rice fields into Lake Biwa via the Ezura River was completed within about 2 weeks of release. Largemouth bass consume carp juveniles, whereas bluegill consume few juveniles. Largemouth bass selected to consume larger juveniles, and C. grandoculis over C. cuvieri. These results suggest that: 1) carp juveniles should be released at smaller sizes (<30 mm), 2) C. cuvieri may withstand predation pressure better than C. grandoculis, and 3) the presence of larger alternative prey may help reduce predation on juveniles. Rice fields are ideal nursery grounds for growing larval fish at low cost and effort. Increasing the post-release survival will effectively restore fishery resources in inland waters.

Recruitment of juvenile, captive-reared eastern loggerhead shrikes Lanius ludovicianus migrans into the wild population in Canada

AbstractHigh post-release survival, low dispersal and the recruitment of captive-reared individuals into the wild population are critical to the success of any reintroduction programme. Reintroducing a migratory species poses an additional challenge as success also depends on the return of captive-reared individuals to breeding grounds in subsequent years. We investigated the effects of seven husbandry and management factors on the return rate of captive-reared eastern loggerhead shrikes Lanius ludovicianus migrans and documented the recruitment of returning individuals. During 2004–2010, 564 juveniles were released in Ontario, Canada, as part of a field propagation and release programme and there were 27 confirmed sightings of returning birds during 2005–2011. Returning birds were significantly more likely to have been released in large groups of juveniles (9–10 birds) at 5.5 weeks post-fledging from the Carden field propagation site. Comparisons of the number of young fledged and survival to 2 weeks post-fledging revealed similar results for pairs comprising one captive-reared and one wild-reared individual and pairs comprising two wild individuals. These results highlight the contribution of captive-reared shrikes to the recovery of the wild population and the importance of monitoring outcomes and evaluating techniques.

Factors influencing immediate post-release survival of spectacled eiders following surgical implantation of transmitters with percutaneous antennae

Surgically implanted transmitters are a common method for tracking animal movements. Immediately following surgical implantation, animals pass through a critical recovery phase when behaviors may deviate from normal and the likelihood of individual survival may be reduced. Therefore, data collected during this period may be censored to minimize bias introduced by surgery-related behaviors or mortality. However, immediate post-release mortalities negate a sampling effort and reduce the amount of data potentially collected after the censoring period. Wildlife biologists should employ methods to support an animal's survival through this period, but factors contributing to immediate post-release survival have not been formally assessed. We evaluated factors that potentially influenced the immediate post-release survival of 56 spectacled eiders (Somateria fischeri) marked with coelomically implanted satellite transmitters with percutaneous antennae in northern Alaska in 2010 and 2011. We modeled survival through the first 14 days following release and assessed the relative importance and effect of 15 covariates hypothesized to influence survival during this immediate post-release period. Estimated daily survival rate increased over the duration of the immediate post-release period; the probability of mortality was greatest within the first 5 days following release. Our top-ranking model included the effect of 2 blood analytes, pH and hematocrit, measured prior to surgical implantation of a transmitter. We found a positive response to pH; eiders exhibiting acidemia (low pH) prior to surgery were less likely to survive the immediate post-release period. We found a curvilinear response to hematocrit; eiders exhibiting extremely low or high pre-surgery hematocrit were also less likely to survive the immediate post-release period. In the interest of maximizing the survival of marked birds following release, hematological data obtained prior to surgical implantation of telemetry equipment may be useful when screening for optimal surgical candidates or informing appropriate response to mitigate potentially deleterious disorders such as acidemia. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.

Post-release survival and behavior and exposure to fisheries in juvenile tiger sharks, Galeocerdo cuvier, from the South Atlantic

General declines in the abundance of sharks due to intense exploitation rates have been increasing the pressure for mitigating bycatch mortality in longline fisheries. Understanding post-release mortality and behavior of sharks is required to ensure the adequacy of management strategies focusing on the release of live animals. Also, such information is crucial for addressing shark attack mitigation strategies focusing on mechanisms other than shark culling. This study used a combination of conventional tags with acoustic and satellite transmitters to assess both post-release survival and behavior and exposure to fisheries in tiger sharks caught in a longline survey off Recife, Brazil. Although none of the sharks experienced post-release mortality, one episode of presumable natural mortality occurred after 45days at-liberty. The exposure of tiger sharks to fishing pressure in this region seems to be high since at least 23% of the tiger sharks tagged and released off Recife were caught by coastal and oceanic fisheries, most (83%) of which after only 69 (±42)days at-liberty. Upon release, all satellite-tracked sharks moved offshore to deeper waters, usually in the oceanic realm, within an average of 17.72 (±10.99)h, corresponding to a minimum cross-shelf swimming speed of 0.40 (±0.22)m·s−1. The archival data of 3 recovered satellite tags depicted post-release behaviors with exceptional detail, with all such sharks exhibiting a yo-yo movement pattern with increasing depths until the shelf break was reached. Some sharks consistently spent a period of 12 (±2)days in deep-diving before returning to shallower waters, presumably from the continental shelf, which could correspond to a species-specific behavioral response to hooking stress. Tagged sharks did not return to the area where they were caught and it would be unlikely that they would return before several months because most of them traveled through great distances to northward latitudes. Altogether, tiger sharks caught alive in longline gear seem to experience negligible post-release mortality if they are adequately released, thus an eventual mandatory release of live animals could be effective to improve the conservation of the species. Also, recently-released tiger sharks should not be expected to further interact with the same fishing gear that caught them for some time, or to further pose any threat to beach users in Recife, where an abnormally high shark attack rate is verified since 1992.

Hatchery Steelhead Smolt Release Size Effects on Adult Production and Straying

Studies have demonstrated higher postrelease survival for larger hatchery steelhead Oncorhynchus mykiss smolts than for smaller ones. However, the ideal release size should also maximize adult returns and minimize interactions of hatchery fish with wild fish. We conducted a study over five release years with paired groups of anadromous hatchery steelhead smolts reared to target sizes of either 90 g (small size) or 113 g (large size). After stream release, we monitored out-migration travel times and survival to a downstream dam using freeze-brand marks in a subsample of each release group. Steelhead smolts that out-migrate quickly may interact less with wild fish. Across all release groups, travel time was about 3 d slower for small-sized smolts than for large ones, but this difference was not statistically significant, and there was no significant difference in the percentage of brands detected at the dam between the two smolt sizes. Coded wire tag recovery was used to compare smolt-to-adult survival (SAS), the number of adults produced per 100 kg of smolts released, and the percentage of adults that strayed. Across all years, large-sized smolts had an average SAS of 1.31% compared with 0.92% for small-sized smolts, a statistically significant difference of 42.0%. The average number of adult steelhead produced per 100 kg of smolts released also was higher for the large-sized group (11.4 adults/100 kg of smolts) over the small-sized group (10.1 adults/100 kg of smolts), though the 12.8% difference was not statistically significant. Adults originating from large-sized smolt releases strayed at a rate of 13.1% compared with a 7.9% rate for the small-sized smolt groups, a difference that was statistically significant. In this study, larger hatchery steelhead smolts had a higher survival after release; however, we found tradeoffs between management objectives associated with maximizing adult production and those aimed at minimizing ecological risks.

Boldness towards novelty and translocation success in captive‐raised, orphaned Tasmanian devils

Translocation of endangered animals is common, but success is often variable and/or poor. Despite its intuitive appeal, little is known with regards to how individual differences amongst translocated animals influence their post-release survival, growth, and reproduction. We measured consistent pre-release responses to novelty in a familiar environment (boldness; repeatability=0.55) and cortisol response in a group of captive-reared Tasmanian devils, currently listed as "Endangered" by the IUCN. The devils were then released at either a hard- or soft-release site within their mothers' population of origin, and individual growth, movement, reproduction (females only), and survival across 2-8 months post-release was measured. Sex, release method, cohort, behavior, and cortisol response did not affect post-release growth, nor did these factors influence the home range size of orphan devils. Final linear distances moved from the release site were impacted heavily by the release cohort, but translocated devils' movement overall was not different from that in the same-age wild devils. All orphan females of reproductive age were subsequently captured with offspring. Overall survival rates in translocated devils were moderate (∼42%), and were not affected by devil sex, release method, cohort, release weight, or pre-release cortisol response. Devils that survived during the study period were, however, 3.5 times more bold than those that did not (effect size r=0.76). Our results suggest that conservation managers may need to provide developmental conditions in captivity that promote a wide range of behaviors across individuals slated for wild release.

Short-term survival of discarded pearl perch (Glaucosoma scapulare Ramsay, 1881) caught by hook-and-line in Queensland, Australia

Post-release survival of line-caught pearl perch (Glaucosoma scapulare) was assessed via field experiments where fish were angled using methods similar to those used by commercial, recreational and charter fishers. One hundred and eighty-three individuals were caught during four experiments, of which >91% survived up to three days post-capture. Hook location was found to be the best predictor of survival, with the survival of throat- or stomach-hooked pearl perch significantly (P<0.05) lower than those hooked in either the mouth or lip. Post-release survival was similar for both legal (≥35cm) and sub-legal (<35cm) pearl perch, while those individuals showing no signs of barotrauma were more likely to survive in the short term. Examination of the swim bladders in the laboratory, combined with observations in the field, revealed that swim bladders rupture during ascent from depth allowing swim bladder gases to escape into the gut cavity. As angled fish approach the surface, the alimentary tract ruptures near the anus allowing swim bladder gases to escape the gut cavity. As a result, very few pearl perch exhibit barotrauma symptoms and no barotrauma mitigation strategies were recommended. The results of this study show that pearl perch are relatively resilient to catch-and-release suggesting that post-release mortality would not contribute significantly to total fishing mortality. We recommend the use of circle hooks, fished actively on tight lines, combined with minimal handling in order to maximise the post-release survival of pearl perch.

Hematological, biochemical, and morphological parameters as prognostic indicators for stranded common dolphins (Delphinus delphis) from Cape Cod, Massachusetts, U.S.A.

AbstractThe current paucity of published blood values and other clinically relevant data for short‐beaked common dolphins, Delphinus delphis, hinders the ability of veterinarians and responders to make well‐informed diagnoses and disposition decisions regarding live strandings of this species. This study examined hematologic, clinical chemistry, and physical parameters from 26 stranded common dolphins on Cape Cod, Massachusetts, in light of their postrelease survival data to evaluate each parameter's efficacy as a prognostic indicator. Statistically and clinically significant differences were found between failed and survived dolphins, including lower hematocrit, hemoglobin, TCO2, and bicarbonate and higher blood urea nitrogen, uric acid, and length‐to‐girth ratios in animals that failed. In general when compared to survivors, failed dolphins exhibited acidosis, dehydration, lower PCVs, and decreased body condition. Additionally, failed dolphins had the highest ALT, AST, CK, LDH, GGT, and lactate values. These blood values combined with necropsy findings indicate that there are likely a variety of factors affecting postrelease survival, including both preexisting illness and stranding‐induced conditions such as capture myopathy. Closer evaluation of these parameters for stranded common dolphins on point of care analyzers in the field may allow stranding personnel to make better disposition decisions in the future.

Comparing the effects of release methods on survival of the Eurasian black vultureAegypius monachusreintroduced in France

AbstractThe Near Threatened Eurasian black vultureAegypius monachusis considered highly threatened in Europe, and the species was reintroduced in France between 1992 and 2004. A total of 53 individuals were released, using two methods: immatures were released from large aviaries at the reintroduction site after a stay of several months (the aviary method), whereas juveniles were placed on artificial nests until fledging (the hacking method). The survival rates of released birds were compared to the survival of wild-born offspring through a multi-event capture–recapture analysis accounting for tag loss. Survival rates were higher in adults than in juveniles and immatures (0.98 ± SE 0.02 vs 0.85 ± SE 0.03) and were constant over time. Overall there were no differences in post-release survival between the two release methods: immatures released by the aviary method had a similar survival to juveniles released by the hacking method or born in the wild. Immatures can breed before juveniles, so releasing immatures by the aviary method could accelerate reintroduction settlement and increase population viability. Accurate estimates of post-release survival are essential to improve the reliability of viability analysis of reintroduced populations and the management of such populations.

Birds introduced in new areas show rest disorders

All colonizing individuals have to settle in a novel, conspecific-free environment. The introduction process should be poorly compatible with a good rest. We compared the resting behaviour of radio-tagged house sparrows (Passer domesticus) experimentally translocated into new, conspecific-free areas (introduced individuals, n = 10), with that of translocated sparrows that settled in naturally established populations (controls, n = 5). Resting habits of introduced sparrows markedly differed from those of control birds: they did not vocalize before going to roost, they changed their roosting habitat and they roosted 24 ± 7 min later and departed 13 ± 4 min earlier from the roost, resulting in a 5% rest debt. Because colonizing a new environment is expected to require heightened cognitive and physical activities, which in turn are constrained by the quality and duration of rest, we hypothesize that rest disorders and resulting cognitive impairments of newly released individuals could functionally contribute to the low post-release survival observed in (re)introduction attempts.

Assessing reintroduction success in long-lived primates through population viability analysis: western lowland gorillas Gorilla gorilla gorilla in Central Africa

AbstractThe use of population modelling has become an increasingly common tool in reintroduction planning and assessment. Although initial reintroduction success is often measured by quantifying post-release survival and reproduction, longer-term success is best assessed through measurements of population viability. Here we develop a population model capable of providing useful results for influencing management of a reintroduction programme for a long-lived and slow-reproducing primate, the western lowland gorilla Gorilla gorilla gorilla. We used post-release monitoring data from two reintroduced populations in the Batéké Plateau region of Congo and Gabon, complemented with published data on wild and captive populations, to develop a population model using Vortex. Sensitivity testing illustrated that the model was highly sensitive to changes in the input parameters for annual birth rates, the number of lethal equivalents, and for female annual mortality rates, especially for adults. The results of the population viability analysis suggested that the reintroduced gorilla populations have a reasonable chance of persistence (&gt; 90% over 200 years) but illustrated that reinforcement of the populations could significantly improve probabilities of population persistence and retention of genetic diversity. Equally, catastrophic events could have significant negative impacts. Continued monitoring of the populations should allow refinement of the model, improving confidence in its predictions and its relevance to decision-making.

Environmental enrichment promotes neural plasticity and cognitive ability in fish

Different kinds of experience during early life can play a significant role in the development of an animal's behavioural phenotype. In natural contexts, this influences behaviours from anti-predator responses to navigation abilities. By contrast, for animals reared in captive environments, the homogeneous nature of their experience tends to reduce behavioural flexibility. Studies with cage-reared rodents indicate that captivity often compromises neural development and neural plasticity. Such neural and behavioural deficits can be problematic if captive-bred animals are being reared with the intention of releasing them as part of a conservation strategy. Over the last decade, there has been growing interest in the use of environmental enrichment to promote behavioural flexibility in animals that are bred for release. Here, we describe the positive effects of environmental enrichment on neural plasticity and cognition in juvenile Atlantic salmon (Salmo salar). Exposing fish to enriched conditions upregulated the forebrain expression of NeuroD1 mRNA and improved learning ability assessed in a spatial task. The addition of enrichment to the captive environment thus promotes neural and behavioural changes that are likely to promote behavioural flexibility and improve post-release survival.

The degree and result of gillnet fishery interactions with juvenile white sharks in southern California assessed by fishery-independent and -dependent methods

Previous reports have documented juvenile white shark interactions with gillnet fisheries in southern California; however, there has been no quantification of the degree of this interaction using fishery-independent methods. We compared geopositioning data from juvenile white sharks fitted with acoustic (n=11) or satellite transmitters (n=13) to fisheries data to determine the degree and effect of white shark interactions with the gillnet fisheries in southern California. Between 2006 and 2008, set gillnet effort comprised a majority of the total gillnet effort (88%) and both set gillnet and inshore drift gillnet effort were significantly and positively correlated with incidence of white shark capture (p<0.0001, τ=0.34 and 0.32) and number of satellite detections (p<0.0001, τ=0.34 and 0.33). However, spatial and temporal overlap of white sharks with gillnet fisheries was limited. Approximately 18% of CDFW fishing blocks where white sharks were detected overlapped with blocks that were also heavily utilized by gillnet fisheries. Total gillnet effort tended to peak in the month of July before declining substantially whereas SPOT detections of tagged sharks were the most numerous in fall months. Although juvenile white sharks were shown to overlap with gillnet fisheries in their vertical, horizontal and temporal distributions, post-release survival of sharks retrieved live in gillnets was high (92.9%). Sharks were more often found live in gillnets when net soak times were low. Therefore, continued research is needed to further evaluate the potential benefit of reducing soak times to improve incidental capture survival of white sharks at this age class.

Consequences of Incidental Otter Trawl Capture on Survival and Physiological Condition of Threatened Atlantic Sturgeon

AbstractAtlantic Sturgeon Acipenser oxyrinchus aggregate in Minas Basin in the inner Bay of Fundy, Nova Scotia, during summer, presumably to feed on abundant intertidal invertebrates. The Atlantic Sturgeon aggregation is composed of multiple stocks from Canada and the USA. Government agencies from both nations have recently recognized Atlantic Sturgeon as threatened or endangered due to overfishing and habitat degradation. Little is known about the fate of Atlantic Sturgeon that are captured as bycatch in fisheries targeting other species, making it difficult to determine the extent to which bycatch is contributing to the Atlantic Sturgeon population's decline. To characterize the effects of otter trawl capture and release on Atlantic Sturgeon, we calculated a minimum survival rate for fish after catch and release by using acoustic telemetry, and we examined physiological indicators of stress. The minimum postrelease survival rate from otter trawl capture events was high (94% survival). Results also demonstrated that the magnitude of blood lactate in trawl‐captured fish relative to experimental control fish increased with longer handling times. Trawl capture and handling did not cause significantly elevated levels of blood glucose or cortisol relative to those of controls. Minimization of handling time (i.e., time on deck) should be a priority in trawl fisheries that capture Atlantic Sturgeon as bycatch. Future studies should attempt to quantify the postcapture behavior of these fish to better understand whole‐organism condition after fisheries encounters.