Abstract
There is widespread evidence that small-scale fisheries (SSF) bycatch threatens many populations of small cetaceans, yet conservation efforts are often limited by a lack of basic knowledge regarding their abundance, distribution and habitat use. Here, we used passive acoustic monitoring from an SSF platform-of-opportunity to better characterize the distribution and habitat use of small cetaceans in northern Peru, focussing on the little known Burmeister’s porpoise Phocoena spinipinnis. From 2009 to 2012, acoustic click detectors (C-PODs) were attached to fishing nets for the duration of 116 fishing sets (30 fishing trips). Dolphins (unspecified delphinids) and porpoises were recorded around 71% and 22% of fishing sets, respectively. The probability of occurrence and buzzing activity (a proxy of foraging), and time spent were linked to both static and dynamic environmental variables to examine the drivers of habitat use. Dolphin activity was spread evenly throughout the fishing area and was not linked to any habitat variables. In contrast, porpoises were detected in neritic waters and habitat models performed well, identifying preferences for shallow (< 200 m depth) and cooler (17-18 °C) waters, close (< 50 km) to shore. The high bycatch rate of small cetaceans in the Peruvian SSF gave us the unique opportunity to investigate the link between bycatch and cetacean acoustic activity. We found a positive relationship between the likelihood of a bycatch event and acoustic presence for both dolphins and porpoises, however as we did not know the timing of entanglement, we could not link vocalization rates to mortality events. Nonetheless, as small cetaceans (particularly dolphins) frequently encounter fishing boats, the likelihood of entanglements may be reduced through effective efforts to alert animals to the presence of the net, either acoustically (through acoustic alarms) or visually. This study demonstrates that passive acoustic monitoring from a fisheries platform can provide insights into the distribution and habitat use of small cetaceans at relatively low cost, and is likely to be suitable in regions with low monitoring effort and high fishing pressure.
Highlights
Artisanal or small-scale fisheries play a vital role in global food production and employment, in developing countries (Berkes et al, 2001; Chuenpagdee et al, 2006; Pauly, 2006)
The data were modeled in a two-step process using hurdle generalized linear mixed models (GLMMs) in the R package glmmADMB (Fournier et al, 2012): for the first part, we estimated the probability of presence using a binomial error structure and logit link function; and for the second part we modeled DPM as the response variable using only positive values, and specifying a zero-truncated negative binomial error distribution and log link function (Zuur et al, 2009)
Knowledge of the distribution and habitat use of small cetaceans is crucial for informing conservation efforts, in regions where they overlap or interact with human activities such as fisheries
Summary
Artisanal or small-scale fisheries (hereafter SSF) play a vital role in global food production and employment, in developing countries (Berkes et al, 2001; Chuenpagdee et al, 2006; Pauly, 2006). Small-scale fisheries have traditionally received relatively little attention from fisheries managers, while conservation measures are often not implemented due to lack of political will or viable fishing alternatives (Read, 2008; Mangel et al, 2010; Reeves et al, 2013). Research on the abundance and distribution of captured species is often lacking, so the impacts of SSF on cetacean populations are generally poorly understood (Reeves et al, 2005; Read, 2008)
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