Fish behaviour from fishers’ knowledge: the case study of tropical tuna around drifting fish aggregating devices (DFADs)

Abstract

Purse seining for tropical tuna is one of the most technologically advanced fisheries in the world. The purpose of this study was to apply Local Ecological Knowledge (LEK) to assist in the planning of future in situ studies of fish behaviour around Drifting Fish Aggregating Devices (DFADs) by prioritizing research topics, thereby reducing the number of potential hypotheses to explore. Interviews of fishing masters of the purse seine fleets working in the Western Indian Ocean (WIO) provided an alternate, independent and previously unexplored source of behavioural information: specifically on the attraction, retention and departure behaviours of tuna schools in relation to DFADs. Most fishing masters agreed that the maximum attraction distance of a DFAD is approximately 10 km and generally agreed to the following statements: Tuna form distinct schools under FADs, commonly segregated by species and size. The main reasons for the departure of tuna aggregations from FADs are changes in currents or FAD movements and location in relation to physical or oceanographic features. The number of actively monitored DFADs at sea in the WIO was estimated at approximately 2100 drifting objects. Incorporating fishermen into the planning and design stages of future research projects will facilitate collaborative and integrated approaches.

Visual censuses around drifting fish aggregating devices (FADs): a new approach for assessing the diversity of fish in open-ocean waters

“…Worm et al 2003), where the spatial strategy of sampling is dictated by fishermen and not scientists. Moreno et al (2007) have shown from empirical knowledge of fishermen that non-tuna species (i.e. the species sampled in the present study, see below) seem to begin aggregating to drifting FADs a short time after deployment (within 1 to 3 wk).…”

A method for assessing fishers’ ecological knowledge as a practical tool for ecosystem-based fisheries management: Seeking consensus in Southeastern Brazil

“…In order to access reliable and valid data from FEK, it is essential to identify the most qualified and experienced fishers to be responding to the questionnaires (Moreno et al, 2007). Thus, between April and September 2009 two fieldtrips were made, and a pilot phase was conducted in order to select key fishers.…”

A critique of the ecosystem impacts of drifting and anchored FADs use by purse-seine tuna fisheries in the Western and Central Pacific Ocean

“…The attraction of tuna to FADs appears to be an active process (Brill et al 1999), although this may only occur once fish have already encountered the assemblage through chance. Tuna appear capable of sensing and orienting movement towards FADs from around 10 km away, based on both detailed analysis of individual movement patterns (Girard 2004), and anecdotal fisher evidence (Moreno et al 2007). The sensory mechanism used by pelagic fish to locate and orientate towards FADs is unknown, but is unlikely to be chemotaxic (Dempster and Kingsford 2003).…”

“…As both anchored and drifting FADs appear to have a similar area of influence on fish, however, noises from both the floating device itself and the aggregation of other species are plausible explanations. When associated with FADs, tuna appear to form distinct schools (Josse et al 1998;Schaefer and Fuller 2005;Leroy et al 2009) that can be segregated by species, size or time of arrival (Doray et al 2006;Moreno et al 2007). These schools are distributed at different depths and distances from the assemblage.…”

“…Anecdotal support for this hypothesis comes from commercial fishers, for whom large scale changes in oceanic conditions were associated with tuna aggregations abandoning FADs (Moreno et al 2007). However, an analysis of specific environmental variables did not find correlations with the end of FAD residence (Ohta and Kakuma 2005).…”