Fish farm specialists

Today Silvia is going to make a verbal presentation at the annual conference of the European Cetacean Society. The abstract is copied below.

Bonizzoni S., Eddy L., Würsig B., Bearzi G.  2015.  Fish farm specialists: bottlenose dolphins in the Southern Evoikos Gulf, Greece.  Proceedings of the 29th Annual Conference of the European Cetacean Society.  St. Julians, Malta, 23-25 March 2015.
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Fish farm specialists: bottlenose dolphins in the Southern Evoikos Gulf, Greece

Bonizzoni S.(1,2,3), Eddy L.(1), Würsig B.(3), Bearzi G.(1,2,3)
1) Dolphin Biology and Conservation, 06066 Piegaro PG, Italy; silvia.bonizzoni@gmail.com
2) OceanCare, CH-8820 Wädenswil, Switzerland
3) Texas A&M University at Galveston, Galveston, TX 77553, USA

Finfish farms (FF) are known to aggregate wild fish, primarily because of large quantities of uneaten food lost from the cages.  Complex substrate, increased nutrient levels and provision of fish-feed produce trophic enrichment and can attract dolphin prey.  Common bottlenose dolphins Tursiops truncatus were observed foraging in the proximity of FF in several Mediterranean areas, including in the coastal waters of Greece.  For instance, FF were the main factor influencing dolphin distribution in the Northern Evoikos Gulf.  In October 2014 we conducted boat surveys totalling 771 km throughout the semi-enclosed Southern Evoikos Gulf (surface area 465 km2).  Additionally, we interviewed 52 fishers operating trammel and gill nets.  Photo-identification suggests that a small number of bottlenose dolphins inhabited the Gulf.  Of 14 individuals identified based on 1031 digital photographs, 13 were consistently found near FF cages.  We tracked dolphin movements for 13 h 50 min.  Dolphins spent 7 h 09 min (52% of total time) within 500 m of any of the 15 FF present in the Gulf, and 8 h 44 min (63%) within 1 km.  In one case, 8 dolphins circled around a single FF cage for 1 h 48 min.  While there is no evidence that dolphins depredate or damage FF, depredation of trammel and gill nets was reported by 85% of fishers interviewed during this study.  Some fishers spontaneously stated that dolphins are "always" found near FF or lamented that FF "attract" dolphins (23% of respondents).  This preliminary study contributes further evidence that bottlenose dolphins in the coastal waters of Greece routinely forage in the proximity of FF, wild fish attracted by FF possibly having become the dolphins' primary prey source.  Depredation of trammel and gill nets, a different foraging type, may be increased due to dolphins being attracted to the general area by FF.