MEASURING INTERACTIONS BETWEEN COMMON BOTTLENOSE DOLPHIN (TURSIOPS TRUNCATUS) AND ARTISANAL FISHERIES IN THE LIGURIAN SEA: 1) PASSIVE ACOUSTIC MONITORING ON BOTTOM SET NETS MISURANDO LE INTERAZIONI DEL TURSIOPE (TURSIOPS TRUNCATUS) CON LA PESCA ARTIGIANALE IN MAR LIGURE: 1) MONITORAGGIO ACUSTICO PASSIVO DI RETI DA POSTA

Interactions between common bottlenose dolphins (Tursiops truncatus) and artisanal fisheries were studied a) monitoring dolphin presence at night by means of an Ecological Acoustic Recorder (ad hoc modified EAR) and b) identifying depredation by specific net damage. Dolphin presence was recorded during 21 of 34 fishing operations; only in 3 cases did dolphin presence in proximity of the net coincide with specific net damage. Introduction - Despite the fact that possible interactions between common bottlenose dolphin (Tursiops truncatus Montagu, 1821) feeding strategies and artisanal fisheries are widely reported, it is not entirely clear what "interaction" really means and which damage is definitely due to dolphin depredation. First observations carried out for an on-going study in the Ligurian Sea are described here: the study includes on board monitoring of net conditions before and after each fishing operation and the collection of acoustic data during the night. While a Mod EAR replaces cetacean observation from the boat, depredation is documented by specific damage observed on the net. In this note passive acoustic monitoring results are presented. Materials and methods - An ecological acoustic recorder (EAR) prototype (Lammers et al., 2008), adapted to be easily located and removed on a set net, was applied first on a trammel net and later on a gill net, following a fisherman fishing schedule. Fishing operations occurred between April and September 2010 in an inshore area in the proximity of Chiavari harbour. The acoustic device, named Mod EAR, was programmed to record 30 seconds every 3 minutes at 50 kHz sample rate for 12 hours, from 7 pm to 7 am, based on a previous study carried out with EAR in front of La Spezia (Fossa et al., 2010). Data were analyzed with Adobe Audition™ 1.5. Details of the catch composition and damage to the nets can be found in Fossa et al., 2011. Results - 4217 different sounds were recorded and classified in four classes: sounds produced by vessel engines (64% of the total amount); sound produced by marine organisms other than cetaceans (28%); dolphin sounds, including all vocalization types produced by dolphins (5%) and other (3%). Among dolphins sounds, "click trains" were the most frequent category (64%), followed by "whistles" (19%) and "whistles and clicks" (17%). Dividing the whole time recorded per night into 3 hour intervals, dolphins seem to be more present in the first two fractions: 7.00 pm - 10.00 pm and 10.00 pm - 1.00 am, a result similar to previous observations derived from a 24 hour acoustic monitoring (Fossa et al., 2010) (Fig. 1). Dolphins resulted in proximity of the nets during 21 of 34 fishing operations (Fig. 2) with a 37.5 minutes