The abundance of common bottlenose dolphins (Tursiops truncatus) in the former special marine reserve of the Cres‐Lošinj Archipelago, Croatia

Abstract

There is a resident common bottlenose dolphin population inhabiting the Kvarnerić area of the northern Adriatic Sea, Croatia. The observed decline in population size between 1995 and 2003 led to the declaration of a part of the Kvarnerić as the Cres‐Lošinj Special Marine Reserve (CLSMR) in 2006. Protection lasted 3 years, before lapsing. A boat based photo‐identification study was conducted between 2004 and 2011 with the aim to estimate the number of bottlenose dolphins inhabiting the CLSMR area, investigate the factors influencing their habitat use and explore the possibility that this area is representative of the population for the whole Kvarnerić. Standard mark–recapture methods and the Mth estimator of Chao for closed populations were applied. The lowest value was estimated in 2008 (N = 112; 95% CI = 94–150) and the highest in 2006 (N = 310; 95% CI = 265–392). The statistically significant inter‐annual variability is likely to reflect natural and anthropogenic driven shifts in habitat use rather than real changes in population size. The average monthly sighting rate was lower in the tourist season (Jun–Aug) than in the pre‐ and post tourist‐season, suggesting that developed nautical tourism may influence shifts in habitat use. Other potential causes are distribution of prey and fishing effort. Inclusion of data from the rest of the Kvarnerić for the years of 2005 and 2011 did not reveal a significant increase in estimated abundance (2005: z = −0.413, P = 0.3398; 2011: z = −1.749, P = 0.0401). This indicates that the CLSMR area is representative of the whole Kvarnerić. The number of bottlenose dolphins using the CLSMR area seems to have increased compared with the previous study (1995–2003). This could be due to a shift in habitat use or an increase in population size. However, yearly variations indicate processes causing displacements within the dolphin population home range. Conservation measures aiming at reducing the displacements are proposed. Copyright © 2013 John Wiley & Sons, Ltd.

Population genetic structure of common bottlenose dolphins (Tursiops truncatus) in the Adriatic Sea and contiguous regions: implications for international conservation

“…These studies and our data imply a broader, worldwide pattern of small‐scale differentiation for this genus. Photo‐identification data have suggested that common bottlenose dolphins of the Adriatic Sea are structured in putative local populations (Fortuna, ; Genov et al ., , ; Holcer, ; Pleslić et al ., in press), corroborating the results of this study. For instance, in the North Adriatic, no matches were found between individuals from the Gulf of Trieste (Italy, Slovenia and Croatia) and the Kvarnerić archipelago, Croatia, only 120–150 km apart (Genov et al ., , ).…”

“…The absence of a clear assignment of individual multilocus genotypes to distinct genetic clusters, despite the Bayesian clustering approach distinguishing five partitions, may be due to limitations of the software in detecting genetic differentiation when F ST values are low (Latch et al ., ). The existence of both resident and visiting individuals, as indicated by photo‐identification studies (Genov et al ., ; Pleslić et al ., ) may be an additional or concomitant cause of why consistent assignment to distinct clusters could not be detected. In particular, a significant proportion of either migrants or individuals of mixed ancestry may result in a degree of gene flow that potentially obscures population structure.…”

A Robust Design Capture-Recapture Analysis of Abundance, Survival and Temporary Emigration of Three Odontocete Species in the Gulf of Corinth, Greece

“…[38, 40, 77, 78]. However, the uncertainty associated to the proportion of unmarked animals is taken into account in the total population estimate because the lower is the mark rate, the higher is the variance [34].…”

“…Given bottlenose dolphin movement patterns in and out of the Gulf, our yearly estimates should be interpreted strictly as the number of individuals using the area during the primary occasions and inter-annual variability is unlikely to reflect fluctuations in population size [39]. In other areas, seasonal variations in the abundance of bottlenose dolphins have been related to temporal shift in habitat use, due to factors including reproduction [52], disturbance, and prey availability [23, 40]. Comparisons with photo-identification catalogs from other areas in the Ionian Sea (and beyond) as well as genetic analyses would be needed to investigate population structure [88].…”

“…Here, we contribute robust estimates of abundance and survival that can be used to inform conservation action in the Gulf of Corinth. To do so, we apply capture-recapture (CR) methods [30, 31, 32] that have been used extensively on several taxa (reviewed by [33]) including marine mammals [34, 35, 36, 37, 38, 39, 40, 41]. Several cetacean species can be individually photo-identified based on long-term natural markings, allowing for the application of non-invasive CR methods [42].…”