Preliminary estimates of the abundance and fidelity of dolphins associating with a demersal trawl fishery

Abstract

The incidental capture of wildlife in fishing gear presents a global conservation challenge. As a baseline to inform assessments of the impact of bycatch on bottlenose dolphins (Tursiops truncatus) interacting with an Australian trawl fishery, we conducted an aerial survey to estimate dolphin abundance across the fishery. Concurrently, we carried out boat-based dolphin photo-identification to assess short-term fidelity to foraging around trawlers, and used photographic and genetic data to infer longer-term fidelity to the fishery. We estimated abundance at ≈ 2,300 dolphins (95% CI = 1,247–4,214) over the ≈ 25,880-km2 fishery. Mark-recapture estimates yielded 226 (SE = 38.5) dolphins associating with one trawler and some individuals photographed up to seven times over 12 capture periods. Moreover, photographic and genetic re-sampling over three years confirmed that some individuals show long-term fidelity to trawler-associated foraging. Our study presents the first abundance estimate for any Australian pelagic dolphin community and documents individuals associating with trawlers over days, months and years. Without trend data or correction factors for dolphin availability, the impact of bycatch on this dolphin population’s conservation status remains unknown. These results should be taken into account by management agencies assessing the impact of fisheries-related mortality on this protected species.

Bottlenose dolphins (Tursiops truncatus) in the north‐western Adriatic Sea: Spatial distribution and effects of trawling

“…This opportunistic behaviour exposes the animals to a greater risk of getting incidentally caught or hooked, especially when dolphins deliberately and regularly engage in high‐risk depredation to increase their foraging options (Bearzi, Piwetz & Reeves, 2019). Common bottlenose dolphins Tursiops truncatus (hereafter bottlenose dolphins) have been documented to forage behind trawlers in several areas around the world (Leatherwood, 1975; Fertl & Leatherwood, 1997; Allen et al, 2017; Kovacs, Perrtree & Cox, 2017; Piwetz, 2019). In the northern Adriatic, this species has been long known to follow midwater pair trawlers and otter trawlers (Bearzi, Politi & Notarbartolo di Sciara, 1999; Genov et al, 2008; 2019; Rako‐Gospić et al, 2017; Ribarič, 2018).…”

Small Scale Fisheries, Dolphins and Societal Challenges: A Case Study in the City of Volos, Greece

“…Bottlenose dolphins have a catholic diet and a coastal distribution, and thus their encounters with fisheries are more common. Although common dolphins prefer more open waters to hunt, their depth distribution at around 250 feet may trouble fisheries [49][50][51]. Dolphins live in groups most often of the same kind; the group moves together and its members cooperate for a number of tasks [52,53].…”

Multidimensional Evaluation of Brown Shrimp Trawling Fisheries on the Amazon Continental Shelf

“…The industrial exploitation of the brown-shrimp stock in the Amazon coast is considered one of the least sustainable practices among the fisheries conducted in this region (Isaac et al, 2009), especially due to the impact of trawling on by-catch fauna, which is captured incidentally and is mostly discarded (Hall et al, 2000;Allen et al, 2017;Bomfim et al, 2019).…”

“…Figure 5 shows that the FPI results of the industrial fishery in the northern Brazilian coast are lower regarding ecological and economic indicators, compared to the average of fisheries conducted in developing countries and to the top 10 fisheries with the best FPI performance. It is worth emphasizing that the ecological indicator obtained the worst indicators, owing to the conditions under which the fishery occurs in the trawling modality, which is considered to have low selectivity (Allen et al, 2017;Bomfim et al, 2019). The community indicators (4.00) obtained a higher score compared to the performance observed in developing countries, yet still lower than the average of the top 10 fisheries with the best performance, with higher structure provided for the fishery.…”