Relative predation vulnerability of three juvenile (Age-0) North Pacific flatfish species: possible influence of nursery-specific predation pressures

Abstract

Pleuronectid flatfish are generally thought to utilize stereotypical anti-predator behavior to reduce encounters with potential predators. In this study, we tested the relative vulnerability of 3 juvenile (Age-0) flatfish species to predation under controlled laboratory conditions. Predators consumed significantly more English sole Parophrys vetulus than either Pacific halibut Hippoglossus stenolepis or northern rock sole Lepidopsetta polyxystra in clear water (0 nephelometric turbidity units, NTU), suggesting differing anti-predator strategies and/or capabilities. In contrast to halibut and rock sole, which remained buried and inactive, English sole were often observed actively moving about. As a result, English sole were encountered more frequently by predators than the other 2 species, suggesting that they were more conspicuous to the predators. This was further evidenced by a higher frequency of stalk encounters for English sole, whereby the predators detected and approached them prior to prey flushing. However, as an estuarine-dependent species, English sole are generally exposed to lower densities of predators in an environment that tends to be highly turbid. When similar trials were conducted at higher turbidity (18 NTU), predation rates on English sole decreased to rates comparable to that for halibut and rock sole in clear water (0 NTU). Although English sole appeared more vulnerable to predation, their behavior may have evolved in response to, and be mitigated by, the turbid nature of the estuarine nursery environments to which they recruit, where predation pressure is significantly reduced in comparison to open coastal habitats.

A review of flatfish behavior relative to trawls

“…When lying flat on the sediment, their low body profile and ability to cryptically match the color and texture of sediments, as well as bury in it (Ramachandran et al, 1996;Ellis et al, 1997;Healey, 1999), renders them nearly invisible to approaching predators and/or prey. Upon detecting an approaching predator, flatfish cease movement (Burrows and Gibson, 1995;Burrows et al, 1994;Lemke and Ryer, 2006a) and are reticent to flee unless the predator gets very close (Ryer et al, 2004b;Lemke and Ryer, 2006b). In contrast, many of the roundfish that are targeted by trawl fisheries (e.g.…”

Negative effect of turbidity on prey capture for both visual and non‐visual aquatic predators

“…Increased turbidity is often a result of increased concentration of suspended particles (Davies‐Colley & Nagels, 2008; Nieman, Oppliger, McElwain, & Gray, 2018). Increased turbidity decreases the ability of visually oriented predators to see their prey (Higham, Stewart, & Wainwright, 2015; Ranåker, Nilsson, & Brönmark, 2012; Sweka & Hartman, 2003; Turesson & Brönmark, 2007), which negatively influences their prey consumption (Figueiredo et al., 2019; Sweka & Hartman, 2003). The reduced efficiency in capturing prey in turbid waters of visually oriented predators may even result in their low abundance and local extinction (dos Santos et al., 2017; Manning, Mayer, Bossenbroek, & Tyson, 2013; Tejerina‐Garro, Fortin, & Rodríguez, 1998).…”

Growth and distributional correlates of behavior in three co-occurring juvenile flatfishes

“…When faced with predation risk, they behave more like rock sole. Standardized predation trials indicated that English sole were the most vulnerable to predation, rock sole the least, and halibut were intermediate between the other 2 species (Lemke & Ryer 2006b.…”