Do man‐made structures and water depth affect the diel rhythms in click recordings of harbor porpoises (Phocoena phocoena)?

Abstract

The construction of industrial offshore structures may lead to colonization by a variety of marine organisms resulting in locally enhanced biodiversity and biomass, which may then affect the habitat use and behavior of marine predators. For harbor porpoises high nocturnal echolocation activity was demonstrated near industrial structures and it was hypothesized that this was caused by increased feeding opportunities at night. Here we tested the hypothesis that bridge pillars will lead to more nocturnal echolocation activity by porpoises near them than at positions further away. The daily rhythms in porpoise detections near bridge pillars tended to be slightly more pronounced and a greater proportion of clicks occurred during the night. However, water depth had a greater impact on these rhythms, with more nocturnal porpoise echolocation activity and more pronounced daily rhythms in deeper waters. This may be related to different feeding techniques and prey choice by porpoises in deep and shallow water. In deeper water porpoises may be feeding pelagically on herring and cod, which show more activity and are easier to catch at night. In shallow water they may be targeting mainly gobies using a bottom feeding technique and this may not be more efficient at night.

Fine‐scale habitat use in Indo‐Pacific humpback dolphins, Sousa chinensis, may be more influenced by fish rather than vessels in the Pearl River Estuary, China

“…Significant diurnal variation within both dolphin detections and vessel presence was observed within the current study, with more dolphin occurrences during the night and a higher vessel presence during the day. This diel pattern in dolphin activity has also been seen in a wide range of odontocetes (Goold 2000, Carlstr€ om 2005, Todd et al 2009, Soldevilla et al 2010, Leeney et al 2011, Hodge et al 2013, Linnenschmidt et al 2013, Mikkelsen et al 2013, Brandt et al 2014, Baumann-Pickering et al 2015, Lin et al 2015, Yamamoto et al 2016, including the Indo-Pacific humpback dolphin (Wang et al 2015b). Indo-Pacific humpback dolphins have also shown increases in the acoustic activity associated with feeding during nights compared to day periods (Wang et al 2015b).…”

Acoustic monitoring reveals the times and tides of harbor porpoise (Phocoena phocoena) distribution off central Oregon, U.S.A.

“…Furthermore, water depth has a significant impact on porpoise diel rhythms, with more nocturnal porpoise echolocation activity occurring in deeper waters (Brandt et al . , Wisniewska et al . ).…”

“…This is concurrent with other PAM studies that reported porpoises appear to shift their distribution to different depths and/or habitats at night, perhaps to take advantage of changing prey availability (Carlström 2005, Todd et al 2009, Mikkelsen et al 2013). Furthermore, water depth has a significant impact on porpoise diel rhythms, with more nocturnal porpoise echolocation activity occurring in deeper waters (Brandt et al 2014, Wisniewska et al 2016. In deeper waters, porpoises may be feeding pelagically on prey species that vertically migrate up into the water column at night, such as herring (Cardinale et al 2003).…”

Marine mammal sightings around oil and gas installations in the central North Sea

“…), which are all known prey species for the marine mammal species observed during this reporting programme (Thompson et al, 1996;Abend & Smith, 1997;Pauly et al, 1998;Olsen & Holst, 2001;Sveegaard et al, 2012). Similarly, increased availability of prey items are associated with presence of top predators around a wide range of marine structures such as a reconstructed stony reef (Mikkelsen et al, 2013), a large bridge (Brandt et al, 2014), O&G facilities (Todd et al, 2009Arnould et al, 2015), and wind farms (Russell et al, 2014).…”