Distribution and Habitat Use of a Cryptic Small Cetacean, the Burmeister's Porpoise, Monitored From a Small-Scale Fishery Platform

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 behavior (a proxy for 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 Peruvian SSF gave us the unique opportunity to investigate the link between bycatch and cetacean activity around vessels. 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 (using 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.

Foraging activity of harbour porpoises around a bottom-gillnet in a coastal fishing ground, under the risk of bycatch

“…No difference in elevation/depression angle was observed between the BB and NB periods, suggesting that porpoises did not become entangled because they had dived deeper than in usual. These observations indicate that harbour porpoises risk entanglement by appearing around a bottom-gillnet, and the risk of bycatch increases with repeated appearances, which is similar to the recent report on Peruvian drift net fishery [46].…”

First record of Burmeister’s porpoise (Phocoena spinipinnis) in the Falkland Islands (Malvinas)

“…If the animal was alive at sea within the Falklands Exclusive Economic Zone (EEZ) prior to the stranding, explanatory possibilities include: (1) the occurrence was an atypical event outside of the species usual distribution range; (2) individuals occasionally enter the Falklands EEZ during longer-range movements from the South American mainland; or (3) Burmeister's porpoises routinely occur in Falklands' waters but have simply remained unrecorded to date. Recent acoustic deployments detected Burmeister's porpoises in neritic habitat up to 200 m depth and over 100 km offshore in Peru (Clay et al 2018). The wide expanse of Patagonian Shelf located between the Falklands and mainland South America is shallow (< 200 m depth) and potentially also provides suitable neritic habitat for the species.…”

“…Corcuera et al 1995;Goodall et al 1995a). They have primarily been reported from nearshore, shallow habitats, including bays, estuaries, channels and fjords (Brownell Jr. and Praderi 1982;Corcuera et al 1994;Goodall et al 1995aGoodall et al , 1995bBrownell Jr. and Clapham 1999), and acoustic data suggest that they preferentially forage in water depths shallower than 50 m and within 30 km of the coast (Clay et al 2018).…”

Marine mammal conservation: over the horizon

“…Pingers have had promising results in deterring several species of cetaceans (e.g. Burmeister's porpoises Phocoena spinipinnis) from small-scale driftnets (Clay et al 2018) but have also been shown to attract some pinnipeds ('dinner bell' effect;Carretta & Barlow 2011). Recently, light-emitting diodes reduced gillnet bycatch of small cetaceans in Peru by 70% (Bielli et al 2020).…”