Understanding the Interactions Between Cetaceans and Other Megafauna With the Albacore Tuna Fishery: A Case Study From the Cyprus’ Pelagic Longline Fishery

Abstract

Depredation by cetaceans on fisheries is a major issue globally, both in terms of conservation and fisheries economics. The present study conducted in Cyprus, Eastern Mediterranean Sea, aimed to understand the extent, level, and type of cetacean depredation on the albacore tuna pelagic longline fishery, and in particular to quantify and evaluate the economic consequences of depredation and identify potential dolphin-longline conflict areas and mitigation practices for management. The data were obtained from fisher’s logbooks, interviews and onboard observations between June and August 2018. A novel and simple approach was applied to estimate the depredation rate and economic loss by using simple calculations including the number and weight of depredated fish, landings and fishing effort. The results revealed that there is an estimated economic loss per fishing trip of 313.07± 486.19 EUR and an estimated annual economic loss for the entire fleet of 259,272 EUR from depredation caused by cetaceans. The study also estimated that 16,639 albacore tunas were depredated in 2018 and the depredation rate ranged between 0% to 100% with a mean depredation rate of 17% per fishing trip. Depredation by the common bottlenose dolphin and striped dolphin was reported in more than 50% of their fishing trips. Other species that were found to be involved in depredation were the neon flying squid, the shortfin mako shark and the Risso’s dolphin. This is the first official record worldwide of depredation from the common bottlenose dolphin, the striped dolphin and the neon flying squid on the pelagic longline albacore tuna fishery. A total bycatch of 62 individuals of common bottlenose dolphins and one individual of stripped dolphin were reported in interviews as a result of depredation on bait and catch. The study also identified depredation hotspots and possible depredation mitigation measures. Such information could support the development of management action plans and measures to minimise interactions between cetaceans and pelagic longlines.

Understanding the Interactions between Small-Scale Fisheries and the Mediterranean Monk Seal Using Fishermen’s Ecological Knowledge

“…These were important steps to gain the trust of the interviewees as there were sensitive questions such as reporting monk seal bycatch that could have affected their responses. Furthermore, the researcher/interviewer was already known and trusted among many fishermen from previous studies and projects [ 39 , 41 ] which supported the process of recommending the researcher to other fellow fishermen. These steps were followed in order to minimise withholding of information and helped with the clarity and somehow the validity of their responses.…”

“…Standardised interview methodologies and best practices previously used in fisheries studies were followed during all interviews to maximise the clarity and consistency of the responses, e.g., [ 13 , 39 , 43 , 44 , 45 ]. The interviews were conducted in-person and private with the participant to avoid the influence of other fellow fishermen.…”

“…It is likely that interactions between fisheries and marine mammals will continue to grow as the competition for the same biological resources is increasing and prey availability for marine megafauna is decreasing [ 37 ]. Interactions between fisheries and marine mammals in Cyprus have been previously reported for small-scale [ 38 ] and pelagic longline fisheries [ 39 ], with reports of incidental capture and mortality. Improving our understanding of these interactions could lead to better management and conservation actions which have the potential to eventually reduce the conflicts between fisheries and marine megafauna, with mutual benefits.…”

Acoustic deterrence to facilitate the conservation of pantropical spotted dolphins (Stenella attenuata) in the Western Pacific Ocean

“…Harbor porpoises (Phocoena phocoena) were unable to detect monofilament nets from distances greater than 3 to 6 m. This limitation in their biosonar system might mislead the animals to deliberately remove fish captured in gear and become entangled (Rabearisoa et al, 2015;Machernis et al, 2021). The fishery bycatch of marine mammals, imposed by the growing need for seafood consumption, has become a serious issue widely in the South Pacific, Indian, North Pacific, and Atlantic Oceans, involving dozens of cetaceans (Werner et al, 2015;Papageorgiou et al, 2022). Reeves et al (2013) pointed out that the past two decades has witnessed a gillnet bycatch on at least 75% of odontocetes, 64% of mysticetes, 66% of pinnipeds, and all species of sirenians and marine mustelids.…”

“…However, these means cannot force the animals to actively swim away from fishing sites. Using sounds sensitive to the potential bycatch victims was useful to exclude marine mammals, e.g., odontocetes from fishery regions by increasing their minimum distance to the threat, mitigating bycatch situations (Au, 1993;Barlow and Cameron, 2003;Kastelein et al, 2006;Nachtigall and Supin, 2008;Graham et al, 2009;Mooney et al, 2009;Schakner and Blumstein, 2013), as has been demonstrated in studies previously conducted on porpoises and beaked whales (Culik et al, 2001;Koschinski et al, 2006;Carretta et al, 2008;Carlström et al, 2009;Papageorgiou et al, 2022). Porpoises were excluded hundreds of meters away from the fishing sites, and bycatch cases of beaked whales dropped to zero after the acoustic deterrent device was deployed to work.…”