Graz. Schloßberg.

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A new approach to estimate fecundity rate from inter-birth intervals

Accurate estimates of fecundity rate are key to population assessments and effectively direct conservation efforts. We present a new approach to estimate fecundity rate based on the probability of a female giving birth, conditional on a previous birth t years ago, from which an expected inter-birth interval (IBI) can be estimated. We use generalized linear mixed-effects models to account for individual and temporal variability and apply the approach to individual reproductive histories of bottlenose dolphins (Tursiops truncatus) from the east coast of Scotland. We estimate a fecundity rate of 0.222 (95% CI = 0.218–0.253) and an expected IBI of 4.49 yr (95% CI = 3.94–4.93 yr). We use simulated data samples to show that the approach produces estimates with a minimum bias of <3%. Simulations are also used to investigate the effect of the most common data-driven biases in the estimates of birth intervals and fecundity rate; we recommend longitudinal studies of at least 10 yr and capture probabilities of at least 0.3 when using this methodology. The approach may be modified to incorporate other parameters of interest and should be applicable to any population with comprehensive data on birth intervals

Improving understanding of bottlenose dolphin movements along the east coast of Scotland. Final report.:Report number SMRUC-VAT-2020-10 provided to European Offshore Wind Deployment Centre (EOWDC), March 2021 (unpublished).

This report provides a summary of the photo-identification surveys conducted by the Sea Mammal Research Unit (SMRU) in the summers of 2017 to 2019 in the Tay estuary and adjacent waters, supported by the European Offshore Wind Development Centre. The survey data were used to estimate the abundance of animals using this area since 2009, and compared to the total east coast of Scotland population, estimated using part of the long-term photo-identification dataset collected by the University of Aberdeen and SMRU (2009-2019). In addition, this collaborative long-term dataset (1989 - 2019) was used to provide estimates of survival and fecundity rate, as well as analyse the movement of animals between the Tay estuary and adjacent waters and the Moray Firth Special Area of Conservation (SAC). A total of 63 boat-based photo-identification surveys were conducted in the Tay estuary and adjacent waters across the three-year study period between May and September each year. These resulted in 54 encounters with bottlenose dolphin groups, and a total of 154 different individuals from all age classes identified from high quality photographs. The estimated abundance of animals in the Tay estuary and adjacent waters ranged between 84 dolphins (95% CI 77 - 93) in 2011 to 138 dolphins (95% CI 110 - 173) in 2016. On average, the number of animals using this area between 2009 and 2019 represented 53.8% of the estimated total population using the main range between the Moray Firth SAC and the Firth of Forth. A total of 230 identified juvenile or adult bottlenose dolphins were included in the analysis to estimate survival rate between 1989 and 2019. A total of 105 females gave birth at least once during that time period and were used to estimate birth rate, defined here as the annual probability of a reproductive female having a calf. The estimated apparent survival probability for juveniles/adults was 0.944 (95% CI 0.933 - 0.953) based on the most supported model. The expected inter-birth interval for the population was estimated at 3.95 years (95% CI 3.63 - 4.20), resulting in an estimated birth rate of 0.253 (95% CI 0.238 - 0.275). A continuous time hidden Markov model was used to assess movement patterns of male and female bottlenose dolphins between the Moray Firth SAC and the Tay estuary and adjacent waters. Between 2017 and 2019, 112 individuals were only seen in the Moray Firth SAC, 103 were only seen in the Tay estuary and adjacent waters and 51 were seen in both areas. Of the 51 seen in both areas, 40 were seen in both areas within the same year. Model results for the period 1990 - 2019 indicated that movement between the two sites is infrequent but that, despite the clear individual heterogeneity, there is a seasonal movement pattern that is directional and consistent over years. The transition intensities (movement rates) were highest from the Tay estuary and adjacent waters towards the Moray Firth SAC in early summer and from the Moray Firth SAC to the Tay estuary and adjacent waters in late summer. This pattern was consistent across individuals of both sexes, but male dolphins had higher transition intensities than females leading to differences in estimated mean sojourn times spent in one area or the other. It is unclear what drives different individuals to move between these two locations

Data from: Variations in age- and sex-specific survival rates help explain population trend in a discrete marine mammal population

1. Understanding the drivers underlying fluctuations in the size of animal populations is central to ecology, conservation biology and wildlife management. Reliable estimates of survival probabilities are key to population viability assessments, and patterns of variation in survival can help inferring the causal factors behind detected changes in population size. 2. We investigated whether variation in age and sex-specific survival probabilities could help explain the increasing trend in population size detected in a small, discrete population of bottlenose dolphins Tursiops truncatus off the east coast of Scotland. 3. To estimate annual survival probabilities we applied capture-recapture models to photo-identification data collected from 1989 to 2015. We used robust design models accounting for temporary emigration to estimate juvenile and adult survival, multi-state models to estimate sex-specific survival, and age-models to estimate calf survival. 4. We found strong support for an increase in juvenile/adult annual survival from 93.1% to 96.0% over the study period, most likely caused by a change in juvenile survival. Examination of sex-specific variation showed weaker support for this trend being a result of increasing female survival, which was overall higher than for males and animals of unknown sex. Calf survival was lower in the first than second year; a bias in estimating third-year survival will likely exist in similar studies. There was some support first-born calf survival being lower than for calves born subsequently. 5. Coastal marine mammal populations are subject to the impacts of environmental change, increasing anthropogenic disturbance and the effects of management measures. Survival estimates are essential to improve our understanding of population dynamics and help predict how future pressures may impact populations, but obtaining robust information on the life history of long-lived species is challenging. Our study illustrates how knowledge of survival can be increased by applying a robust analytical framework to photo-identification data

Reproductive parameters of the Amazon river dolphin or boto, Inia geoffrensis (Cetacea Iniidae); an evolutionary outlier bucks no trends

Reproductive parameters of the Amazon river dolphin, or boto Inia geoffrensis, were estimated from a population of individually recognizable animals in the Brazilian Amazon throughout 24 years. Gestation lasts 12.3-13 months, and calves are nursed for 1.5-5.8 years. The mean inter-birth interval is 4.6 years, and there is no evidence of reproductive senescence. Females first give birth at a mean age of 9.7 years and become sexually mature at body lengths of 180-200 cm. Body length at birth averages 84 cm. The annual pregnancy rate was ~0.4, but the annual birth rate was 0.22; therefore, almost half of pregnancies do not result in a calf seen by our research team. Entanglement of neonates in monofilament gillnets might account, at least in part, for these losses. Births can occur year round, but peak at low water, when botos and their newborn calves are concentrated on river margins. Despite profound physical and behavioural adaptations over millions of years to a life in shallow, fresh waters and complex habitats, the boto has remarkably similar reproductive characteristics to those of its marine counterparts, dolphins of the family Delphinidae. The fundamental reproductive characteristics of small odontocetes have apparently been robust to change over a very considerable evolutionary timespan. © 2018 The Linnean Society of London, Biological Journal of the Linnean Society