New Publication on the rescue effect in Scopoli's Shearwaters !

Sanz-Aguilar, A.; Igual, J.M.; Tavecchia, G.; Genovart, M; Oro, D. 2016. When immigration mask threats: The rescue effect of a Scopoli’s shearwater colony in the Western Mediterranean as a case study. Biological Conservation, 198, 33–36. doi:10.1016/j.biocon.2016.03.034

Photo: M. Gomila

Abstract: Populations of long-lived species are highly sensitive to increases in mortality, but a loss of breeders can be compensated for by recruitment of local individuals or immigrants. Populations maintained through immigration can be sinks, jeopardizing the viability of the metapopulation in the long term when additive mortality from anthropogenic impacts occurs. Thus, the correct identification of whether a breeding population is maintained by local recruitment or by immigration is of special importance for conservation purposes. We developed robust population models to disentangle the importance of local recruitment and immigration in the dynamics of a Western Mediterranean population of Scopoli's shearwater Calonectris diomedea showing low adult survival but stable breeding numbers. Our results show that the shearwater population is not self-maintained but rescued by immigration: yearly immigrants recruiting in the population represents ~ 10–12% of total population size. We believe that this situation may be common to other Western Mediterranean populations, currently acting as sinks. We recommend urgent demographic studies at large core colonies to evaluate the global conservation status of the species.

 
A press release of the publication has just appeared. You can read the spanish version here

Stage at the G.E.P.

Julia Bos joined the GEP for her Erasmus+  stage.  She will be investigating the within-colony differences in egg volume, clutch size, movements and spatial structure of the Yellow Legged Gull at Dragonera Island. Welcome Julia.

New Publication on Indo-Pacific bottlenose dolphins !

Pérez-Jorge, S., Gomes, I., Hayes, K., Corti, G., Louzao, M., Genovart, M. and Oro, D. 2016 : Effects of nature-based tourism and environmental drivers on the demography of a small dolphin population Biological Conservation: doi:10.1016/j.biocon.2016.03.006

Abstract: Many marine top predators are experiencing significant declines due to anthropogenic impacts, and therefore reliable monitoring is essential to understand their population dynamics. We used Pollock's robust design capture–recapture modelling to assess the influence of oceanographic variables, artisanal fisheries and human disturbance on several demographic parameters (abundance, temporary emigration and survival) of the Indo-Pacific bottlenose dolphin (Tursiops aduncus), using long-term data on marked individuals from East Africa.

Photo-identification data was collected over 551 boat-based surveys between 2006 and 2009, with 137 individuals identified. Our best fitting model indicated that exposure to tourism (represented by the number of tourist boats) increased the probability of dolphins seasonally emigrating from the study area. The return rate of temporary emigrants was negatively linked to the seasonal sea surface temperature, probably associated with food availability. That model supported the existence of heterogeneity in annual local survival estimates, with transient dolphins showing a lower value than resident individuals (0.78 and 0.98, respectively). Furthermore, abundance estimates showed a small population size ranging from 19 individuals (95% CI: 11–33) to a maximum of 104 dolphins (95% CI: 78–139). This small population, together with their high site fidelity and coastal distribution, might be particularly vulnerable to human disturbances. This study highlights the influence of environmental and anthropogenic factors on dolphin demography and population dynamics and the need to integrate these drivers to provide robust evidences for conservation stakeholders in an adaptive management framework.