Estimates Of Apparent Survival Research Articles

Assumptions about survival estimates and dispersal processes can have severe impacts on population viability assessments

Population viability analysis (PVA) is a central tool for conservation decision-making. To ensure the reliability of PVA projections, it is important to identify factors that can introduce biases. This study addresses two general but overlooked related issues in PVAs that can significantly affect the reliability of their projections. First, we examined the effects of using apparent versus true survival estimates on PVA outcomes. Second, we incorporated emigration and immigration into the models to assess their influence on the accuracy of projections based on each type of survival estimate. To evaluate these concerns, we implemented PVAs structured by age, sex, and breeding status using as a study system a threatened raptor population (Bonelli's eagle, Aquila fasciata) from which apparent and true survival were available (2008–2020). The performances of PVA projections based on each survival type and dispersal process were assessed by evaluating their fit to census data. Our findings revealed that using apparent survival underestimated census data, while true survival showed a considerably better fit. However, models including dispersal processes showed that each survival type may only deliver precise projections at very specific levels of emigration and immigration. Given the potentially large differences found when using true and apparent survival, we suggest that the relevance of this issue should be elevated to that of other widely reported PVA limitations. Recently developed, accessible analytical methods may permit an easier estimation of true survival and dispersal processes. Otherwise, calibrating projections against observed data may be fundamental to test the adequacy of survival estimates.

Movement, not survival, differs between wild and hatchery‐reared imperiled desert fishes

AbstractObjectiveStocking streams with hatchery‐produced fishes is an increasingly common practice to restore native populations, but the fate of these fish is uncertain due to low survival or high emigration rates. Monitoring these vital population rates is needed to assess stocking and translocation of rare and endangered fishes to identify approaches that maximize persistence and survival and ultimately result in established populations.MethodsWe quantified survival, emigration, movement directionality, and long‐term (24 months) trends in apparent survival of stocked and wild‐caught fish implanted with passive integrated transponder (PIT) tags. We PIT‐tagged and tracked 1419 individuals, consisting of direct comparisons between two species of hatchery and wild fish, as well as four other wild‐captured species, from 2020 to 2022 in three desert streams in Arizona and New Mexico.ResultWe found that hatchery fish had high (>98%) estimates of survival after being released (<40 days) that was similar to all tagged wild fish. But hatchery fish had a fivefold higher emigration rate than wild conspecifics shortly (<40 days) after being released. Emigrating hatchery fish also tended to move downstream, whereas wild fish were more likely to move upstream. Additionally, apparent survival estimates were about 10 times higher for tagged wild fish than hatchery conspecifics 6 months after release; hatchery fish apparent survival approached zero after about 165 days but did not approach zero for wild fish until 690 days following tagging and release.ConclusionOur results suggest emigration, rather than reduced survival, might limit the success of stocking efforts. Thus, choosing optimal stocking locations and the time of year of the stocking, such as upstream reaches during times near the species reproduction season, might improve retention and establishment of stocked fish.

Are Urban Populations of a Gliding Mammal Vulnerable to Decline?

Small populations are at high risk of extinction, and they are likely to need management intervention. Successful management, however, relies on sufficient long-term demographic data in order to determine whether apparent declines are natural fluctuations or the product of threatening processes. In this study, we monitored a small urban population of squirrel gliders (Petaurus norfolcensis) in Queensland, Australia, over a 16 year period. A reference population in a larger forest patch was also studied in order to investigate whether its demographic trends were similar. Using mark-recapture data to generate estimates of apparent survival and population size, we found evidence of a decline within the small population but not in the reference population over the monitoring period. We suggest that the influence of multiple factors may have led to the decline, but, ultimately, that the genetic condition of the small population may be responsible. Understanding demographic trends is an important context for management interventions of small populations, although causes of decline need to be identified for successful management. The squirrel glider provides a useful case study for small urban populations and particularly for arboreal mammals.

Consistent apparent adult survival and nest‐site fidelity of whimbrel Numenius phaeopus near Churchill, Manitoba, Canada over a 40 year period

Reliable estimates of adult survival for many shorebird species are lacking. We used Cormack–Jolly–Seber (CJS) methods to provide an estimate of apparent, or local, survival (φ) of a population of whimbrels, Numenius phaeopus, breeding in the subarctic Churchill, Manitoba region. We used data collected in two time‐periods: 1973–1976 and 2010–2014. We also quantified nest‐site fidelity in 2010–2014 to provide context to our apparent survival estimates because mark‐recapture analyses cannot distinguish between mortality and permanent emigration. The most parsimonious CJS model did not include effects of sex or time on apparent adult survival in either period (φ = 0.76 ± 0.13 SE; φ = 0.75 ± 0.04 SE, 1973–1976 and 2010–2014, respectively). Additionally, observations of marked whimbrels between 2010 and 2019 (n = 124) showed that 61 of the 105 marked individuals (58.1%) were resighted. These estimates of return rates are, as expected, much lower than estimates of apparent survival. The median year‐to‐year distance between nests (n = 139) in 2010 to 2014 was 198 m ± 88 SE and did not differ significantly (p = 0.84) between females (x̄ = 721.9 m ± 119.8 SE) and males (x̄ = 720.3 m ± 83.1 SE). If our apparent survival estimate is indicative of true survivorship, then adult mortality during the non‐breeding season has remained constant over the last five decades, implying that the recent decline in whimbrel populations may stem largely from reduced fecundity, including egg or juvenile survival, rather than primarily from reduced adult survival.

Long‐term apparent survival of a cold‐stunned subpopulation of juvenile green turtles

AbstractUnderstanding the effects of extreme weather on animal populations is fundamental to ecological and conservation sciences and species management. Climate change has resulted in both warm and cold temperature extremes, including an increased frequency of severe cold snaps at middle latitudes in North America. These unusually cold air masses cause rapid declines in nearshore ocean temperatures in coastal areas, with detrimental effects on marine organisms. Acute cold‐stun events (hereafter cold stuns) occur when hundreds to thousands of resident juvenile sea turtles fail to escape shallow water during cold snaps. Human intervention through rescue and recovery largely mitigates direct juvenile sea turtle mortality, but delayed effects of cold stuns on rescued individuals are not well understood. Our objective was to examine long‐term juvenile green turtle (Chelonia mydas) survival across four cold stuns of varying severity in St. Joseph Bay, Florida, between 2010 and 2018. We used the classic Cormack–Jolly–Seber model in a hierarchical Bayesian framework to estimate apparent survival (i.e., emigration and mortality) of rescued turtles at different time intervals. Our results indicated about half of a cohort rescued during a severe cold stun in January 2010 likely remained in the population 1 year later, with 10%–20% remaining 4 years later, and as few as 5% by 2018. The results also suggested higher apparent survival for cohorts rescued during two subsequent milder cold stuns. Emigration was a more plausible ecological explanation for low apparent survival than delayed mortality. Potential ecological mechanisms underlying emigration include a reduction in food availability and a behavioral response to either the severe weather event or handling during rescue (or both). However, the typical annual turnover of juvenile green turtles, though assumed low, is not well known in St. Joseph Bay. Thus, our apparent survival estimates may be reflective of higher‐than‐expected emigration in the broader population. Our study provides important baseline information about long‐term juvenile sea turtle survival after cold stuns in temperate regions. We also highlight the importance of strategic monitoring between cold stuns to examine additional ecological questions.

Neckband loss and its effect on apparent survival estimates in Greylag Geese (Anser anser): variation with season, sex and age

Mark-recapture studies enable us to estimate population parameters such as survival, if marks do not impact survival and if marks are not lost. Mark loss can result from external wear and damage, but also behavioural factors may be important and could explain differences between seasons or sexes. We studied Greylag Geese (Anser anser) in eastern Netherlands, ringed with neckbands, leg bands and metal rings (912 geese), observed weekly during 1997–2019 (131,625 observations). Given the double marking and high annual resighting probabilities (neckbands: 0.974, leg rings: 0.639), we quantified neckband loss and the effect of neckbands on apparent survival, using multistate mark-recapture models. Annual neckband loss was 0.038, was higher in males (0.056) than females (0.021) and increased with years since marking, up to 0.098 for males more than 8 years after marking. Neckband loss tended to be higher during December–May than June–November, with most losses occurring in March–April. Both the higher loss in males and the peak in spring in both sexes could result from intraspecific fighting (pulling each other’s neck and neckband). Survival was underestimated in Cormack-Jolly-Seber models that did not account for neckband loss, by up to 0.096 for adult males 6–7 years after marking. Thus, ignoring neckband loss may give erroneous survival differences between sexes and seasons, and overestimate the effect of ageing on survival (i.e. senescence). We did not detect an effect of neckbands on mortality, but statistical power for this test was limited. Neckband loss, although lower nowadays than in studies of decades ago, still impacts survival estimates and should be considered in mark-recapture studies.

Emigration effects on estimates of age- and sex-specific survival of two sciurids.

Age‐ and sex‐specific survival estimates are crucial to understanding important life history characteristics, and variation in these estimates can be a key driver of population dynamics. When estimating survival using Cormack–Jolly–Seber (CJS) models, emigration is typically unknown but confounded with apparent survival. Consequently, especially for populations or age classes with high dispersal rates, apparent survival estimates are often biased low and temporal patterns in survival might be masked when site fidelity varies temporally. We used 9 years of annual mark–recapture data to estimate age‐, sex‐, and time‐specific apparent survival of Humboldt's flying squirrels (Glaucomys oregonensis) and Townsend's chipmunks (Neotamias townsendii). For Humboldt's flying squirrels, these estimates support a small body of research investigating potential variation in survival among age and sex classes, but age‐ and sex‐specific survival has not been evaluated for Townsend's chipmunks. We also quantified the effects of age‐ and sex‐specific emigration on confounded estimates of apparent survival. Our estimates of juvenile flying squirrel survival were high relative to other small mammal species and estimates for both species were variable among years. We found survival differed moderately among age and sex classes for Humboldt's flying squirrels, but little among age and sex classes for Townsend's chipmunks, and that the degree to which emigration confounded apparent survival estimates varied substantially among years. Our results demonstrate that emigration can influence commonly used estimates of apparent survival. Unadjusted estimates confounded the interpretation of differences in survival between age and sex classes and masked potential temporal patterns in survival because the magnitude of adjustment varied among years. We conclude that apparent survival estimators are robust during some time periods; however, when emigration rates vary in time, the effects of emigration should be carefully considered and accounted for.

Age-specific, population-level pedigree of wild black bears provides insights into reproduction, paternity, and maternal effects on offspring apparent survival.

Wildlife pedigrees provide insights into ecological and evolutionary processes. DNA obtained from noninvasively collected hair is often used to determine individual identities for pedigrees and other genetic analyses. However, detection rates associated with some noninvasive DNA studies can be relatively low, and genetic data do not provide information on individual birth year. Supplementing hair DNA stations with video cameras should increase the individual detection rate, assuming accurate identification of individuals via video data. Video data can also provide birth year information for individuals captured as young of the year, which can enrich population‐level pedigrees. We placed video cameras at hair stations and combined genetic and video data to reconstruct an age‐specific, population‐level pedigree of wild black bears during 2010–2020. Combining individual birth year with mother–offspring relatedness, we also estimated litter size, interlitter interval, primiparity, and fecundity. We used the Cormack‐Jolly‐Seber model in Program Mark to evaluate the effect of maternal identity on offspring apparent survival. We compared model rankings of apparent survival and parameter estimates based on combined genetic and video data with those based on only genetic data. We observed 42 mother–offspring relationships. Of these, 21 (50%) would not have been detected had we used hair DNA alone. Moreover, video data allowed for the cub and yearling age classes to be determined. Mean annual fecundity was 0.42 (95% CI: 0.27, 0.56). Maternal identity influenced offspring apparent survival, where offspring of one mother experienced significantly lower apparent survival (0.39; SE = 0.15) than that of offspring of four other mothers (0.89–1.00; SE = 0.00–0.06). We video‐documented cub abandonment by the mother whose offspring experienced low apparent survival, indicating individual behaviors (e.g., maternal care) may scale up to affect population‐level parameters (e.g., cub survival). Our findings provide insights into evolutionary processes and are broadly relevant to wildlife ecology and conservation.

Recovery From Reduction: The M’Clintock Channel Polar Bear Subpopulation, Nunavut, Canada

To retain viable polar bear subpopulations, scientific monitoring studies are conducted to inform adaptive management frameworks. Here we report the results of the second structured population study for polar bears in the M’Clintock Channel (MC) subpopulation. Data included biopsy samples collected during a 2014 – 16 subpopulation-wide survey, live mark-recapture data collected during the first subpopulation study from 1998 to 2000, and harvest recovery data from 1998 to 2016. Results of a closed capture-recapture model, implemented in a Bayesian framework for animals over 2 yr., produced a mean abundance estimate of 716 (95% Credible Interval = 545 – 955) for 2014 – 16, indicating an increase from the 1998 – 2000 study estimate (284; our Bayesian-calculated estimate: 325 bears). However, closed model assumptions mean our estimate represents the superpopulation. Mean litter sizes did not differ between study periods, but mean number of yearlings per adult female declined from 0.39 ± 0.10 (SE) to 0.27 ± 0.06 between 1998 – 2000 and 2014 – 16. Apparent survival estimates from observed data were biased low (0.88 ± 0.02) due to unknown immigration and emigration. However, survival calculated using the change in abundance estimates between study periods equaled 0.93, representing a population growth rate of 2%. Body condition improved between study periods. Our findings indicate the MC subpopulation recovered from overharvesting between 1979 and 1999 and may be transiently benefitting from increased biological productivity associated with local sea ice changes. Our demographic analyses were constrained by low density, low harvest, small sample sizes, low recapture probability, and lack of movement information; hence, harvest management decisions should be applied with appropriate caution.

Movement Dynamics and Survival of Stocked Colorado River Cutthroat Trout

AbstractThe ability of native fish to establish self‐sustaining populations when reintroduced to vacant habitats is variable. We evaluated factors that potentially affect the reintroduction success of juvenile Colorado River Cutthroat Trout Oncorhynchus clarkii pleuriticus that were reintroduced to an isolated watershed and were experiencing suboptimal survival and recruitment. We conducted a 3‐year mark–recapture study to model annual apparent survival probability as it related to (1) different ex situ rearing strategies and (2) initial release among different habitat types. The use of PIT tags also enabled the quantification of loss via emigration. Apparent survival was highest for small fish that were minimally exposed to ex situ rearing conditions, stocked in small, headwater stream reaches. However, maximum estimates of apparent survival remained low (≤0.38 ± 0.05 [estimate ± SE]) regardless of rearing treatment, stocking location, or interactive effects between covariates. Emigration of stocked fish (<1%) from the study area did not appear to limit their establishment. Our results suggest that variation in stocking and rearing strategy may have some effect on translocation success and the interaction between rearing and stocking strategy highlights the importance of considering the life history stage of stocked individuals when identifying stocking sites. Consistently low annual survival values may be indicative of a larger issue, requiring in‐depth evaluation of adaptive potential within our brood source and other factors that potentially limit population persistence.

Dancing in the Rain: How Do Abiotic Conditions Influence Sexually Selected Behaviors in the White-Ruffed Manakin?

Tropical animals respond to rainfall in population-specific ways. In extremely wet regions, endotherms experience heavy rains as stressors with consequences for behavior and demography. Ultimately, such stressors can affect the relative strength of abiotic selection, reducing the scope for sexual selection, and other biotic sources of selection. We studied population-level differences in the response to rainfall of White-ruffed manakins (Corapipo altera) on the Caribbean slope of Costa Rica, a species having a lek mating system subject to strong sexual selection. Between 2008 and 2013, we studied reproductive behavior in a population inhabiting an extremely wet site; estimates of apparent survival were low, and the turnover of display courts and dominant males was high. Males also engaged in coordinated display, and sub-adult males practiced in the presence of adults. Over three breeding seasons (2017-2019), we studied a population of the same species at a site only 110 km away, but in a location receiving roughly half as much rain. We tested behavioral predictions of three alternative mechanisms-indirect abiotic effects, direct mortality effects, and direct behavioral effects-linking rainfall to sexual selection in these two populations. Data derived from over 4300 h of observations at 105 display sites revealed high interannual variation in nearly all response variables, including turnover of display sites, retention of alpha status, male display behavior, and time females spent assessing male display. Additionally, we detected spatial differences in drivers of display site turnover. Notably, age distribution of males was skewed toward older individuals at the drier location. Based on these findings, we infer that indirect abiotic effects on forest structure leading to display site transience and direct effects of mortality increasing turnover in the male population likely underlie links between rain and the spatial and temporal differences we documented. Our results are consistent with rain constituting an important source of abiotic selection for tropical endotherms and modulating the scope for sexual selection near the extremes of a species' hygric niche.

Ingestion of PIT Tags by Hatchery‐Reared Juvenile Steelhead and Subsequent Detection at Main‐Stem Dams in the Columbia River Basin

AbstractDuring the past 30 years, millions of hatchery‐reared Pacific salmon Oncorhynchus spp. have been implanted with PIT tags to estimate their survival and track their migration through the extensive system of hydroelectric dams in the Columbia River basin. The mark–recapture models that are used for these analyses assume that the tags are not lost, making it important to understand retention rates for PIT tags and the fate of shed tags. To understand the potential fate of shed PIT tags in a production hatchery, we distributed 12‐mm PIT tags in two traditional cement raceways and the two circular tanks of a partial reuse aquaculture system (PRAS) containing juvenile summer steelhead O. mykiss. We then monitored the detection of these PIT tags at the time that the fish were released as smolts and at main‐stem dams during their migration. The probability that a loose PIT tag was inside a steelhead smolt at release ranged from 0.200 to 0.519 across the raceways and tanks, confirming that the fish consumed tags during hatchery rearing. Detections at six dams—including one located 1,208 km from the release site—and up to 36 d after smolt release confirmed that some ingested tags remained in the steelhead during their migration. The estimates of apparent survival for smolts with ingested and implanted PIT tags suggested that some ingested tags were being excreted during migration through the Columbia River basin. The results highlight the need to reevaluate assumptions about the fate of shed PIT tags in steelhead production hatcheries and ensure that biologists and managers have reliable estimates of tag retention.

Tag Type and Location‐Dependent Retention Impart Varied Levels of Bias on Mark–Recapture Parameter Estimates

AbstractPopulation parameter estimates from mark–recapture studies are dependent on individuals retaining marks or tags. Therefore, tag retention estimates are needed for different tag types and anatomical tagging locations. Few studies have empirically quantified the bias from tag retention on fish population parameters that are derived from mark–recapture studies. We examined differences in retention between T‐bar anchor tags and PIT tags as well as among four anatomical locations for PIT tags in Brown Trout Salmo trutta in a tailwater fishery in Arkansas, USA. We also estimated the relative bias of tag type and PIT tag location on apparent survival estimates from Cormack–Jolly–Seber models. Tag retention for the anchor tags was 15.1% lower than that for the PIT tags after 1 year and 46.1% lower after 4 years. Greater PIT tag retention resulted in less biased estimates of apparent survival for PIT tags (average −7.1%) than for anchor tags (average −37.8%). However, PIT tags that were placed in different anatomical locations had varying retention rates, so the degree of relative bias that was associated with their apparent survival estimates also varied. Inserting the PIT tags in the cheek or dorsal musculature provided the greatest retention for Brown Trout and may provide the least biased apparent survival estimates from future mark–recapture studies.

Flow Conditioning of Hatchery‐Reared Razorback Sucker Increases Apparent Survival in the Wild

AbstractHatchery augmentation of dwindling wild populations has become a common strategy to avoid extinction of endangered fishes. While benign hatchery conditions can lead to low persistence of stocked individuals, experiments have demonstrated that flow conditioning of Razorback Sucker Xyrauchen texanus can increase swimming performance and reduce downstream movements from desired locations after stocking in the Colorado River basin, USA. However, managers have been slow to adopt its use, likely because linking experimental flow conditioning to scales that are relevant to conservation has been difficult. We reared age‐2 Razorback Sucker in two raceways (control: n = 530; flow conditioning: n = 533) for 10 weeks to assess whether flow conditioning could increase apparent survival after stocking into the San Juan River, New Mexico. We used riverwide active sampling and remote PIT tag antennas to resample individuals for 3 years after stocking. Using Cormack–Jolly–Seber mark–recapture models, we assessed the effects of flow conditioning, size at stocking, relative condition (Fulton’s K), and their interactions on apparent survival and downstream movement after stocking. Flow conditioning of fish doubled the mean apparent survival (at a mean size of 325 mm TL) during the first overwinter period (control fish: 0.14, 95% CI = 0.09–0.21; flow‐conditioned fish: 0.28, 95% CI = 0.19–0.38), with both groups having similar mean overwinter apparent survival estimates thereafter (both > 0.75). Size at stocking and K were positively associated with first‐overwinter apparent survival regardless of treatment (mean survival was <0.20 for fish <275 mm TL but was >0.65 for fish >450 mm TL). Downstream movement after stocking was negatively associated with fish size, indicating that emigration likely contributed to higher apparent mortality of smaller fish. Our results suggest that transitioning hatchery practices to include flow conditioning of Razorback Sucker (and potentially other endangered Colorado River fishes) prior to stocking could substantially increase the conservation efficiency of these augmentation programs.

Heterozygosity-Fitness Correlations in a Continental Island Population of Thorn-Tailed Rayadito.

Heterozygosity-fitness correlations (HFCs) have been used to monitor the effects of inbreeding in threatened populations. HFCs can also be useful to investigate the potential effects of inbreeding in isolated relict populations of long-term persistence and to better understand the role of inbreeding and outbreeding as drivers of changes in genetic diversity. We studied a continental island population of thorn-tailed rayadito (Aphrastura spinicauda) inhabiting the relict forest of Fray Jorge National Park, north-central Chile. This population has experienced a long-term, gradual process of isolation since the end of the Tertiary. Using 10 years of field data in combination with molecular techniques, we tested for HFCs to assess the importance of inbreeding depression. If inbreeding depression is important, we predict a positive relationship between individual heterozygosity and fitness-related traits. We genotyped 183 individuals at 12 polymorphic microsatellite loci and used 7 measures of reproductive success and estimates of apparent survival to calculate HFCs. We found weak to moderate statistical support (P-values between 0.05 and 0.01) for a linear effect of female multi-locus heterozygosity (MLH) on clutch size and nonlinear effects on laying date and fledging success. While more heterozygous females laid smaller clutches, nonlinear effects indicated that females with intermediate values of MLH started laying earlier and had higher fledging success. We found no evidence for effects of MLH on annual fecundity or on apparent survival. Our results along with the long-term demographic stability of the study population contradict the hypothesis that inbreeding depression occurs in this population.

Yearling Muskellunge Poststocking Behavior and Survival in Two Central Iowa Reservoirs with Contrasting Habitat Availability

AbstractMuskellunge Esox masquinongy is a prized sport fish throughout much of North America. Due to the species’ popularity among anglers and limited natural recruitment in reservoirs, Muskellunge are commonly stocked to maintain populations. However, little is known about their poststocking behavior and survival in reservoirs. We used radiotelemetry to evaluate behavior and survival of spring‐stocked yearling Muskellunge in two Iowa reservoirs that differed in habitat availability (Big Creek Lake: limited habitat; Brushy Creek Lake: abundant habitat). Hatchery‐reared Muskellunge were implanted with radio transmitters (n = 15–16 fish·lake−1·year−1; 61 fish total) and stocked in both lakes during May 2017 and 2018; fish were tracked daily for 1 week, every other day for the second week, and then weekly until December. Telemetry data were used to evaluate depth and vegetation use, selection of littoral substrate and coarse woody habitat (CWH) complexities, movement, home ranges, and survival. Muskellunge depth use generally increased with time poststocking and was greater in Brushy Creek Lake than in Big Creek Lake. Movement rates were greatest during the first week poststocking and declined thereafter, with greater rates and home ranges in Big Creek Lake. Muskellunge in both systems selected for fine substrates while avoiding coarse substrates. Muskellunge in Brushy Creek Lake were more commonly associated with CWH and aquatic vegetation compared to those in Big Creek Lake. Muskellunge in Big Creek Lake selected for complex CWH, while those in Brushy Creek Lake used CWH classes in proportion to their availability. Cormack–Jolly–Seber daily apparent survival estimates were lowest for the first 4 d poststocking and ranged from 0.59 to 0.99, after which survival increased from May to September before declining in October and November. Results of this study provide a greater understanding of the poststocking success of yearling Muskellunge and suggest that Muskellunge behavior and survival are dependent on habitat complexity, with weaker habitat selection but higher survival in complex systems.

Using Acoustic Telemetry to Estimate Weakfish Survival Rates along the U.S. East Coast

AbstractThe Weakfish Cynoscion regalis, an economically important species, has declined over the last 30 years, corresponding with an increase in total mortality according to the most recent stock assessment. We estimated estuarine‐specific and coastwide apparent survival of Weakfish by using a Cormack–Jolly–Seber model to provide insights into the spatiotemporal component of mortality. Telemetered Weakfish (n = 342) were released across five estuaries ranging from North Carolina to New Jersey between 2006 and 2016. In estuaries from Delaware Bay and northward, egress peaked around the third week of September; in North Carolina, egress peaked by the first week of November. For three estuaries with adequate sample sizes, apparent survival estimates were similar and a joint model including all telemetered Weakfish estimated an extremely low annual apparent survival rate of 0.001 (95% credible interval [CrI] = 0.002–0.0003) or annual apparent instantaneous total mortality of 7.25 (95% CrI = 6.28–8.05). At a minimum, 61% of telemetered Weakfish emigrated in the fall, but only 2 of 149 fish with long‐lived transmitters were detected as returning to estuaries the following year. This is a small proportion for a fish that exhibits spawning site fidelity. We conclude that the disappearance of telemetered Weakfish represents mortality that occurs between emigration and the spring spawning period, potentially during overwinter periods on the continental shelf. Our study provides insights into the magnitude, timing, and location of Weakfish loss and facilitates an improved understanding of Weakfish population dynamics for use in stock rebuilding.

Trends and Effects of a Recreational Lake Sturgeon Fishery in the St. Clair System

AbstractOne frequently desired outcome of Lake Sturgeon Acipenser fulvescens rehabilitation is to create a recreational fishery for the species. However, few waterbodies offer a recreational fishery where anglers can catch Lake Sturgeon regularly. Lake St. Clair and the St. Clair River (hereafter, “St. Clair system”) contain large, stable populations of Lake Sturgeon, and a recreational fishery allowing harvest has been present since 1950. Over the last several decades, the Michigan Department of Natural Resources (MDNR) has monitored the recreational Lake Sturgeon fishery in the St. Clair system by using numerous methods to assess angler participation, harvest rates, and population effects of the fishery. Lake Sturgeon anglers in the St. Clair system are predominantly male (89%) and largely reside in the three nearest counties (72%), although the geographic footprint of Lake Sturgeon anglers appears to be increasing. Estimates of angler abundance, trends in angler recapture of tagged Lake Sturgeon, sturgeon harvest data, and reported capture of MDNR “Master Angler”‐sized Lake Sturgeon by anglers all indicated that angling effort in this Lake Sturgeon fishery has steadily increased since monitoring began. Despite increasing angler participation, the recreational fishery has had no detectable population‐level effect on Lake Sturgeon in the St. Clair system. Harvest rates of tagged Lake Sturgeon are low, with most anglers practicing catch and release. Recapture rates of angler‐caught fish in comparison to MDNR survey‐caught fish suggested that hooking mortality is low. Additionally, apparent survival estimates of Lake Sturgeon have been constant. Information gained from monitoring the recreational Lake Sturgeon fishery in the St. Clair system will be valuable to managers assessing whether to establish a sturgeon fishery in other systems.

Evaluating the effects of red imported fire ants (Solenopsis invicta) on juvenile Houston Toads (Bufo [=Anaxyrus] houstonensis) in Colorado County, TX.

The spread of invasive species is considered a major threat to biodiversity, second only to habitat loss. Red Imported Fire Ants (Solenopsis invicta) are a globally invasive species with negative impacts reported on native invertebrate and vertebrate species. Federally endangered Houston Toads (Bufo [=Anaxyrus] houstonensis), endemic to Texas, are among the vertebrates reportedly negatively impacted by Red Imported Fire Ants (RIFA). Threats posed by RIFA to Houston Toads needed to be explicitly characterized. Large-scale chemical treatments to suppress RIFA and facilitate brood survival in Attwater’s prairie-chickens (Tympanuchus cupido attwateri) at the Attwater Prairie Chicken National Wildlife Refuge (APCNWR) afforded us an opportunity to experimentally examine the influence of RIFA abundance on juvenile Houston Toad growth and survival. We also sought to examine whether juvenile Houston Toads could grow and survive in a vegetation type similar to a historic species locality. We conducted a terrestrial mesocosm experiment to test whether the application of bait-driven suppressant decreased counts of RIFA relative to untreated sites. We examined whether counts of native ant and non-ant native invertebrates were higher in response to potential decreases in RIFA. We compared growth and survival rates in juvenile Houston Toads among treated and untreated sites, expecting juvenile growth and survival to be higher in response to potentially decreased RIFA counts and increased native invertebrate counts. We saw lower counts of RIFA in treated prairies, but we also observed a decrease in native ant counts possibly due to chemical treatment. Therefore, the application of bait-driven suppressant may not affect RIFA alone. We saw no difference in counts of non-ant invertebrates among treated and untreated sites. Juvenile Houston Toads did not differ in growth and survival among treated and untreated sites. We recognize that the lack of a relationship between juvenile growth and survival with a treatment effect, and therefore RIFA abundance, may be limited to APCNWR. We encourage additional experimental studies to elucidate RIFA impacts at other sites. We extrapolated apparent survival estimates from our study to one year. These appear comparable to juvenile survivorship required in simulations for Houston Toad population persistence and on this basis, we recommend that APCNWR be re-evaluated as a reintroduction site for Houston Toads. We also recommend further studies to potentially broaden the regulatory definition of Houston Toad habitat beyond the current restrictive view of canopied forest alone. Such studies would need to examine the utility of native grasslands as dispersal corridors/upland habitat for juvenile Houston Toads. Our findings emphasize the utility of experimental studies in directly examining the influence of perceived threats to imperiled species and the role of such clarifications in adapting recovery efforts.

It's not all black and white: investigating colour polymorphism in manta rays across Indo-Pacific populations.

Intraspecific colour polymorphisms have been the focus of numerous studies, yet processes affecting melanism in the marine environment remain poorly understood. Arguably, the most prominent example of melanism in marine species occurs in manta rays (Mobula birostris and Mobula alfredi). Here, we use long-term photo identification catalogues to document the frequency variation of melanism across Indo-Pacific manta ray populations and test for evidence of selection by predation acting on colour morph variants. We use mark-recapture modelling to compare survivorship of typical and melanistic colour morphs in three M. alfredi populations and assess the relationship between frequency variation and geographical distance. While there were large differences in melanism frequencies among populations of both species (0-40.70%), apparent survival estimates revealed no difference in survivorship between colour morphs. We found a significant association between phenotypic and geographical distance in M. birostris, but not in M. alfredi. Our results suggest that melanism is not under selection by predation in the tested M. alfredi populations, and that frequency differences across populations of both species are a consequence of neutral genetic processes. As genetic colour polymorphisms are often subjected to complex selection mechanisms, our findings only begin to elucidate the underlying evolutionary processes responsible for the maintenance and frequency variation of melanism in manta ray populations.