Colour-ring wear and loss effects in citizen science mark-resighting studies

Background: Ring wear and loss may have important consequences for mark-recapture studies that aim to estimate survival trends. Our study quantifies the rates of wear and loss from a long-running colour-ringing project of the Eurasian Oystercatcher (Haematopus ostralegus) in the Netherlands. Methods: Our analysis included 8909 colour-ringed oystercatchers with 118,071 resightings, predominantly ringed and observed by citizen scientists. We quantified how ring wear and loss may vary with ring colour and age, and how this may impact resighting probabilities. We then determined how ring loss may impact survival estimates and resighting probabilities of mark-recapture models by simulating four scenarios of how citizen scientists may resight and report birds with lost colour rings. Results: Annual rates of colour ring loss averaged 2.5% compared with 1% for ring wear, but lost rings also had a higher reporting probability (31.2%) than worn rings (10.3%). Lost rings may not directly impact survival estimates since 50% of oystercatchers with lost rings could still be uniquely identified. Ring wear and loss rapidly increased between 10 and 15 years after ringing. Rates of ring loss were comparable amongst ring colours, but the wear rate appeared higher for red and white rings compared to other colours. Rates of ring wear and loss varied significantly amongst different regions in our study, which were characterised as having different habitat features. Differential rates of ring wear may have important implications for studies conducted over large geographical scales or of multiple species. Conclusions: Based on simulations of ring loss in our population, estimates of apparent survival may be 0.3–1.2% lower whilst the impact of ring wear was deemed even lower. We developed a table of recommendations containing advice for ring fitting, data collection, study design, and mark-recapture analyses, so that future colour-ringing studies can benefit from our experiences in collecting and analysing data of ring wear and loss through citizen science.

An examination of the population dynamics of syngnathid fishes within Tampa Bay,Florida,USA

Seagrass ecosystems worldwide have been declining, leading to a decrease in associated fish populations, especially those with low mobility such as syngnathids （pipefish and seahorses）. This two-year pilot study investigated seasonal patterns in density, growth, site fidelity, and population dynamics of Tampa Bay （FL） syngnathid fishes at a site adjacent to two marinas under construction. Using a modified mark-recapture technique, fish were collected periodically from three closely located sites that varied in seagrass species （Thalassia spp., Syringodium spp., and mixed-grass sites） and their distance from open water, but had consistent physical/chemical environmental characteristics. Fish were marked, photographed for body size and gender measurements, and released the same day at the capture site. Of the 5695 individuals surveyed, 49 individuals were recaptured, indicating a large, flexible population. Population density peaks were observed in July of both years, with low densities in late winter and late summer. Spatially, syngnathid densities were highest closest to the mouth of the bay and lowest near the shoreline. Seven species of syngnathid fishes were observed, and species-specific patterns of seagrass use emerged during the study. However, only two species, Syngnathus scovelli and Hippoeampus zosterae, were observed at high frequencies. For these two species, body size decreased across the study period, but while S. scovelli＇s population density decreased, H. zosterae＇s increased. Across six of the seven species, population size declined over the course of this preliminary study; however, seasonal shifts were impossible to distinguish from potential anthropogenic effects of construction [Current Zoology 56 （1）： 118-133, 2010].

Sex Ratio and Sexual Size Dimorphism in a Toad-headed Lizard, Phrynocephalus guinanensis

Phrynocephalus guinanensis has sexual dimorphism in abdominal coloration, but its ontogenetic development of sexual size dimorphism （SSD） is unknown. Using mark-recapture data during four days each year from August from 2014 to 2016, we investigated the development of sex ratios, SSD, sex-specific survivorship and growth rates in a population of P guinanensis. Our results indicated that the sex ratio of males to females was 1：2.8. Males had a lower survival rate （6%） than females （14%） across the age range from hatchling to adult, which supported the discovered female-biased sex ratio potentially associated with the low survival rate of males between hatchlings and juveniles. Male-biased SSD in tail length and head width existed in adults rather than in hatchling or juvenile lizards. The growth rates in body dimensions were undistinguishable between the sexes during the age from hatchling to juvenile, but the growth rate in head length from juvenile to adult was significantly larger in males than females. Average growth rate of all morphological measurements from hatchling to juvenile were larger compared with corresponding measurements from juvenile to adult, but only being significant in tail length, head width, abdomen length in females and snout-vent length in males. We provided a case study to strengthen our understanding of the important life history traits on how a viviparous lizard population can survive and develop their morphology in cold climates.

Photo-Identification Methods Reveal Seasonal and Long-Term Site-Fidelity of Risso’s Dolphins (<i>Grampus griseus</i>) in Shallow Waters (Cardigan Bay, Wales)

A photo-identification study on Risso’s dolphins was carried out off BardseyIslandinWales(July to September, 1997-2007). Their local abundance was estimated using two different analytical techniques: (1) mark-recapture of well-marked dolphins using a ‘closed-population’ model;and (2) a census technique based on the total number of identified individual dolphins sighted over the study period. The mark-recapture estimates of 121 (left sides;64 - 178 95% CI;CV 0.24) and 145 dolphins (right sides;78 - 213 95% CI;CV 0.24) closely matched the census technique estimates (population size of 90 - 151). It was found that the dolphins showed a degree of long-term and seasonal site-fidelity. A first long-distance match was made for Risso’s dolphins (319 km) betweenBardseyIslandandCornwall, confirming they can be wide-ranging animals. This study demonstrates that the combination of systematic and opportunistic photo-ID studies has complementary value as a population assessment tool in generating the first local abundance estimate for Risso’s dolphins inUKwaters. From the conservation perspective, these studies confirm the regular presence of Risso’s dolphins in these waters and the presence of calves shows breeding.BardseyIslandmay be part of a network of localities that are important habitats to this species where it may take advantage of prey abundance in shallow waters. As such, results of this study may provide assistance to include the Risso’s dolphin in future regional conservation strategies including the envisaged marine protected areas.

Rostrum abnormalities in the endangered Indian Ocean humpback dolphin(Sousa plumbea)in South Africa

Morphological abnormalities in wild animals can be indicators of the underlying health of a population and may be determined through routine photographic surveys.Here,we assess unusual rostrum conditions in Indian Ocean humpback dolphins(Sousa plumbea)inhabiting South African coastal waters to understand the rate of prevalence of abnormal rostrums and formulate hypotheses on potential causes.Photographic data were collated from sys-tematic boat surveys and opportunistic sightings,obtained between April 1998 and March 2021 in various regions along the South African coast.Overall,31 unique individuals were found with abnormal rostrum conditions,vary-ing from slight misalignments to severe wounds and/or aberrant morphologies.In most cases,injuries were likely caused by natural events during the animal’s life history such as interactions with sharks and/or reef-associated hunting strategies.Mark–recapture data indicated that individuals had survived with these injuries for up to 10 years.This study reports the highest incidence of rostrum abnormalities in the species.As numbers reflect only those that have survived their injuries,they are considered a minimum estimate.A better understanding of the cause(s)of these injuries is important given the endangered status of this species.

Spatiotemporal variation in the adult sex ratio,male aggregation,and movement of two tropical cloud forest dung beetles

While theory suggests that at conception the sex ratio should be balanced(1:1),this can be variable across space and time in wild populations.Currently,studies of the environmental factors that regulate adult sex ratio(ASR)in species with different life history traits are scarce.Using capture–recapture over a year,we analyzed the influence of habitat type(forest and nonforest)and season(rainy and dry)on variation in ASR,male aggregation and the trajectory movement of 2 dung beetle species with different life history traits:Deltochilum mexicanum(a hornless roller species)and Dichotomius satanas(a tunneler species with horns on its head and thorax).We found opposite tendencies.The D.mexicanum population tends to be female-biased,but the population of D.satanas tends to be predominantly male,and observed values were not related to habitat type or season.However,the 95%confidence intervals estimated were highly variable between seasons depending on habitat.On examining the monthly variation in ASR for both habitats,we found that it depends on the species.In addition,male aggregation differed between species depending on habitat type and season,and species movement patterns were closely related to their habitat preferences.Based on our results,we argue that comparative population studies of species with different life history traits are necessary to understand the variation in demographic parameters as well as its ecological and evolutionary implications in the face of spatial and climatic environmental variation.

Combining spawn egg counts,individual photo-ID and genetic fingerprinting to estimate the population size and sex ratio of an endangered amphibian

According to the International Union for Conservation of Nature Red List,41%of the world’s amphibian species are threatened with extinction,making them more threatened than any other vertebrate group nowadays.Given the global amphibian crisis,comprehensive understanding of demographics and population trends of declining and threatened species is essential for effective management and conservation strategies.Counting egg spawns is widely used to assess population abundance in pond breeding anurans.However,it is unknown how such counts translate into robust population size estimations.We monitored the breeding activity of the Natterjack toad(Epidalea calamita),combining egg string counts and individual photo-identification with Capture-Mark-Recapture population size and operational sex ratio estimation.Male Natterjack toads were identified by the pattern of natural markings with repeated ID of the same individual confirmed for 10%of the samples using genetic fingerprinting.We identified 647 unique individuals within a closed study population at Caherdaniel,Co Kerry.Population estimates derived from egg string counts estimated a breeding population of 368 females(95%CI 353–384)and Capture-Mark-Recapture estimated a breeding population of 1698 males(95%CI 1000–2397).The female:male sex ratio was conservatively estimated at 1:5(95%CI 1:3–1:6)where 62%±6%of females were assumed to spawn.These substantially departed from any priori assumption of 1:1 which could have underestimated the breeding population by up to 72%.Where amphibian absolute population size estimation is necessary,methods should include empirical survey data on operational sex ratios and not rely on assumptions or those derived from the literature which may be highly population and/or context-dependent.

Ancient fish weir technology for modern stewardship: lessons from community-based salmon monitoring

Introduction:The UN Declaration on the Rights of Indigenous Peoples states that indigenous people have a fundamental right to contribute to the management of the resources that support their livelihoods.Salmon are vital to the economy and culture of First Nations in coastal British Columbia,Canada.In this region,traditional systems of management including weirs-fences built across rivers to selectively harvest salmon-supported sustainable fisheries for millennia.In the late-19th century traditional fishing practices were banned as colonial goverments consolidated control over salmon.Outcomes:In collaboration with the Hei ltsuk First Nation we revived the practice of weir building in the Koeye River.Over the first four years of the project we tagged 1,226 sockeye,and counted 8,036 fish during fall stream walks.We used a mark-recapture model which accounted for both pre-spawn mortality due to variation in temperature,and tag loss,to produce the first mark-resight estimates of sockeye abundance in the watershed(4,600-15,000 escapement).Discussion:High river temperatures are associated with increased en route morality in migrating adult sockeye.We estimated pre-spawn mortality ranged from 8-72%across the four years of study,highlighting the degree to which climate conditions may dictate future viability in sockeye salmon populations.These results demonstrate the power of fusing traditional knowledge and management systems with contemporary scientific approaches in developing local monitoring.