Anthropogenic food patches and association patterns of Tursiops truncatus at Lampedusa island, Italy

Abstract

Anthropogenic food patches in the marine environment, such as aquaculture farms and active trawlers, may impact on the behavior of marine mammals through modification of habitats, changes in predation pressure, or alterations in food distribution, availability, and predictability, affecting related social interactions and population demographics. This study examined patterns of association of a population of common bottlenose dolphins (Tursiops truncatus) around Lampedusa Island (Italy) during 1996-2006 and tested the hypothesis that the trawl fishery and the presence of an aquaculture farm could affect such patterns. Here, we used measures of association between pairs of individuals to assess this impact on social unit composition/cohesion and some analytical techniques to describe the structure of dolphin social networks and temporal stability of associations. Association information for 71 regularly sighted individuals was obtained from photo-identification surveys within groups observed or not at ''feeding stations.'' We found association patterns between dolphins were nonrandom. The Lampedusa population seems to be arranged into 6 clusters and organized in communities composed of animals that were either never seen in association with feeding stations (N individuals) or those that are (Y individuals), although mixed assemblages were also recorded. Both communities showed long-term preferred companions, with different degrees of social cohesion-as resulted by network measures and temporal analysis. Delineating community structure at Lampedusa Island has offered basic information for further investigations in the area, also providing novel evidences on how disparities in association patterns between bottlenose dolphin individuals may have resulted from a combination of ecological and anthropogenic factors.

An integrated approach for cetacean knowledge and conservation in the central Mediterranean Sea using research and social media data sources

“…Areas with higher relative abundance estimates and identified as suitable habitat for bottlenose dolphins are likely to be influenced by other anthropogenic factors as well. In particular, bottlenose dolphins were observed both by citizens and researchers to regularly follow trawlers or move near different fishing gears, resulting in the overlap between recreational, artisanal, and professional fishing operations and the species; this well‐known interaction behaviour, already reported in numerous coastal areas in the Mediterranean Sea and worldwide, where animals are attracted towards easily accessible and concentrated food sources (Bonizzoni et al, ; Fertl & Leatherwood, ; Gonzalvo, Giovos, & Moutopoulos, ; Lauriano, Fortuna, Moltedo, & Notarbartolo di Sciara, ; Pace, Pulcini, & Triossi, , ; Pennino, Rotta, Pierce, & Bellido, ; Pulcini et al, ), was then documented for the first time in the study area, conferring further support to the reliability of the approach applied.…”

Marine Mammal Behavior: A Review of Conservation Implications

“…In addition to prey preferences, cultural conformism may also inhibit an individual's adaptive use of space, through dispersal or migration. For example, it has been suggested that killer whales may continue to use traditional areas despite increases in chemical and noise pollution (Osborne, 1999).…”

“…Interactions with human activities, such as co-operative fishing (Daura-Jorge et al, 2012), trawling (Chilvers et al, 2001;Pace et al, 2011;Ansmann et al, 2012), depredation (i.e., taking fish from fishing gear; Esteban et al, 2016b), provisioning, or begging (Mann and Kemps, 2003;Donaldson et al, 2012), can provide a novel foraging niche, which marine mammals can learn to utilize through social transmission. As a result there is a risk of social groups becoming dependent on these human activities, in what has been termed "anthropo-dependence" (CMS, 2014).…”

Long-term acoustic monitoring of bottlenose dolphins, Tursiops truncatus, in marine protected areas in the Spanish Mediterranean Sea

“…Food availability is one of the main drivers of bottlenose dolphin distribution (Hastie et al, 2004). Bottlenose dolphins have commonly been reported to follow trawling boats to take advantage of discarded fish or seize fish from the net in different areas of the Mediterranean Sea (Bearzi et al, 1999;Gonzalvo et al, 2008;Fortuna et al, 2010;Pace et al, 2012). As such, the presence of a trawler fishery fleet of 11 vessels in the nearby ports of Ibiza, San Antonio (also in the island of Ibiza), and Formentera, that transit near or through Freus, might have an important influence in diel bottlenose dolphin presence in this MPA.…”