Can underwater refuges protect fish populations against cormorant predation? Evidence from a large‐scale multiple pond experiment

Abstract

Artificial structures can protect fish against predation by cormorants (Phalacocorax spp.). However, their effectiveness in larger water bodies with different fish communities in the presence of natural vegetation still needs to be explored. Using a large‐scale field experiment with 24 ponds stocked with differently composed fish communities, the present study investigates the extent to which the effect of artificial refuges on fish is species‐specific and determined by the characteristics of the fish community. This study provides strong experimental evidence for artificial refuges protecting fish against predation from cormorants, even in the presence of submerged vegetation. The effect of refuges was, however, highly species‐specific and depended on the composition of the fish community. Strong positive effects of refuges on rudd, Scardinius erythrophthalmus (L.), and roach, Rutilus rutilus (L.), populations were observed, especially in ponds where these species dominated. Overall, the total biomass of young‐of‐the‐year, 1‐year‐old and adult rudd and roach was on average 500, 7 and 15 times lower in ponds without than in ponds with refuges, respectively. No effect of artificial refuges on other fish species was found. This study indicates that artificial refuges can facilitate the coexistence of predation vulnerable fish populations with cormorants in lakes and ponds.

Cormorant predation effects on fish populations: A global meta‐analysis

“…The “refuge” studies were based on the methodology of totally covering a body of water (Glahn & Dorr, 2002) or underwater refuges in the form of cages (Lemmens et al., 2016; McKay et al., 2003; Russell et al., 2008). Positive effects of predation on fish populations were identified in Glahn and Dorr (2002), but these represent individual fish being larger, in mass, in depredated versus control ponds.…”

“…Lemmens et al. (2016), however, conclude that effects are highly species specific with large positive effects on common rudd ( Scardinius erythrophthalmus , Cyprinidae) and common roach (both as Cyprinidae/cyprinids in analyses) but smaller effects on European perch, ide, common carp, and European pike. The study by Wright (2003) investigated the effects on fish populations by “shooting” cormorants.…”

Understanding the Temporal Dynamics of a Lowland River Fish Community at a Hazardous Intake and Floodgate to Inform Safe Operation

“…Anthropogenic structures, like the hazardous intake studied here, can also provide refuge for prey fish (e.g., Russell et al, 2008) as vegetation in the main-river dies off during winter. Furthermore, avian predators are deterred by the associated human activity (Lemmens et al, 2016). Accordingly, the stochastic diel fish count data here may have been influenced by temporally variable predator-prey interactions (Brodersen et al, 2008).…”

The impact of extreme flood‐relief pump operations on resident fish in an artificial drain and the potential for artificial habitat introduction

“…Elsewhere, artificial habitats have been introduced to supplement degraded natural habitats (Allen et al, 2014) and increase local abundance of fish (Frehse et al, 2021). Thus, introducing artificial habitats in artificial drains could provide fish with refuge from resident aquatic and avian predators when pumps do not operate and provide flow refuge during pump operation (Lemmens et al, 2016). Structural design of artificial habitats may affect fish occupancy.…”

“…Thus, introducing artificial habitats in artificial drains could provide fish with refuge from resident aquatic and avian predators when pumps do not operate and provide flow refuge during pump operation (Lemmens et al, 2016). Structural design of artificial habitats may affect fish occupancy.…”