Conflict between Fishermen and Giant Otters Pteronura brasiliensis in Western Brazilian Amazon

Abstract

The recovery of giant otter populations after the hunting prohibition and restriction of the pelt trade resulted in more frequent conflicts with fishermen. In this study, fisherman–giant otter conflicts were analyzed in the Uacari Sustainable Development Reserve, where giant otters are accused of interfering with fisheries by eating the fish (predation), frightening the fish away (local interference), and damaging fishing equipment (direct interference). Interference by predation was analyzed by evaluating overlap in fish species consumption between humans (measured by subsistence and commercial catches) and giant otters. The giant otter diet was assessed from fecal samples, and the human diet through questionnaires. Local and direct interferences were analyzed through fish samples using gillnets and comparing capture efficiency with and without giant otters’ presence. The overlap between human and giant otter diets was low (0.37), varied seasonally, and was smaller in the low water (0.24) than in the high water period (0.60), when both species tend to be more generalists. Overlap between fish species consumed by giant otters and those exploited by commercial fisheries was small (0.34). Giant otter presence during the experimental fishing was low (9.5%), restricted to the high water period, and did not significantly reduce the captures (U = 13, P = 0.61). The low overlap in diet may be a result of differences in preferences and fishing strategies. The conflict between giant otters and fishermen is greater in the high water period, when the income of the fisheries decreases; however, the conflict seems to be mainly motivated by the resident's prejudice against giant otters.

Advances in the study of giant otter (Pteronura brasiliensis): ecology, behavior, and conservation: a review

“…The family Erythrinidae (represented by trahiras, Hoplias malabaricus) is frequently found in the giant otters diet in small rivers and creeks (Duplaix, 1980;Rosas et al, 1999;Davenport, 2008;Cabral et al, 2010;Rosas-Ribeiro et al, 2012). Cabral et al (2010) mention that in Balbina reservoir the presence of piranhas occurred at twice the level reported in other studies, even though the subfamily Serrasalminae is relatively frequently identified in scats from different regions Cabral et al, 2010;Rosas-Ribeiro et al, 2012). On the other hand, scat analysis in Peru found that two species in particular are preferred -Prochilodus nigricans (Prochilodontidae) and Satanoperca jurupari (Cichlidae) -although the precise reason for this preference over other species such as the abundant piranha is not clear 6,8 .…”

“…The fish families most frequently found in giant otters diet include Cichlidae, Erythrinidae, Characidae and Anostomidae followed by Prochilodontidae, Auchenipteridae, Doradidae, Loricariidae, Pimelodidae, Gymnotidae and Sciaenidae (Duplaix, 1980;Rosas et al, 1999;Davenport, 2008;Cabral et al, 2010;Rosas-Ribeiro et al, 2012). The family Erythrinidae (represented by trahiras, Hoplias malabaricus) is frequently found in the giant otters diet in small rivers and creeks (Duplaix, 1980;Rosas et al, 1999;Davenport, 2008;Cabral et al, 2010;Rosas-Ribeiro et al, 2012).…”

“…The emerging conflict with fisheries has motivated the killing of giant otters in Brazil (Rosas-Ribeiro et al, 2012), Guyana 3 and French Guiana 8 . There are no official records for these killings or for the dependent cubs killed with the death of their parents.…”

“…Preferred fish are from the orders Characiformes, Perciformes and Siluriformes (Duplaix, 1980;Rosas et al, 1999;Staib, 2005;Cabral et al, 2010). Although fish comprise the main prey item, other prey such as crustaceans, mollusks, birds, reptiles, amphibians and small mammals are mentioned in the literature 6 (Duplaix, 1980;Schweizer, 1992;Rosas et al, 1999;Staib, 2005;Cabral et al, 2010;Rosas-Ribeiro et al, 2012), including small anacondas, turtles and caimans (Kruuk, 2006;Ribas et al, 2012). Captive giant otters eat on average 10% of their body weight per day and wild adults may consume around 3-4kg of fish per day (Duplaix, 1980;Staib and Schenck, 1994;Cabral et al, 2010).…”

“…The fish families most frequently found in giant otters diet include Cichlidae, Erythrinidae, Characidae and Anostomidae followed by Prochilodontidae, Auchenipteridae, Doradidae, Loricariidae, Pimelodidae, Gymnotidae and Sciaenidae (Duplaix, 1980;Rosas et al, 1999;Davenport, 2008;Cabral et al, 2010;Rosas-Ribeiro et al, 2012). The family Erythrinidae (represented by trahiras, Hoplias malabaricus) is frequently found in the giant otters diet in small rivers and creeks (Duplaix, 1980;Rosas et al, 1999;Davenport, 2008;Cabral et al, 2010;Rosas-Ribeiro et al, 2012). Cabral et al (2010) mention that in Balbina reservoir the presence of piranhas occurred at twice the level reported in other studies, even though the subfamily Serrasalminae is relatively frequently identified in scats from different regions Cabral et al, 2010;Rosas-Ribeiro et al, 2012).…”