Predation by signal crayfish Pacifastacus leniusculus on fish eggs and its consequences for coregonid recruitment

Abstract

The character and magnitude of predation by the invasive, ectothermic Pacifastacus leniusculus, a crayfish widely introduced to Europe and Japan from North America, on the eggs of coregonid fishes, vendace Coregonus albula and whitefish Coregonus lavaretus were examined by experimentation, modelling and field data. The present results showed that P. leniusculus has the potential to be very efficient predator of fish eggs under winter conditions, but the predation by P. leniusculus did not significantly decrease production of coregonid larvae during the years with a high P. leniusculus population in the study lake. Hence, the mortality caused by the novel invertebrate predator appeared to compensate for other yet unexplored mortality factors instead of having an additive effect on the present salmonids.

Predation by invasive signal crayfish on early life stages of European barbel may be limited

“…Indeed, signal crayfish have been shown to prey on the eggs and/or juveniles of at least two non‐benthic (i.e. roach Rutilus rutilus , common bream Abramis brama ; Rosewarne et al, ) and benthic‐dwelling fishes: Atlantic salmon (Edmonds et al , ; Gladman, Adams, Bean, Long, & Yeomans, ; Holdich et al, ), brown trout Salmo trutta (Findlay, ) and burbot (Karjalainen et al, ), with a predictive model indicating a likely signal predation on European bullhead (Findlay, ). However, the present study is the first to demonstrate this for newly‐emerged European barbel larvae.…”

“…Atlantic salmon Salmo salar (Holdich, James, Jackson, & Peay, ; Peay, Guthrie, Spees, Nilsson, & Bradley, ) and brown trout Salmo trutta (Findlay, ), but not others (e.g. stone loach Barbatula barbatula : Ruokonen, Karjalainen, Kiljunen, Pursiainen, & Hämäläinen, ; burbot Lota lota : Karjalainen et al, ), with conflicting reports of various deleterious effects (Bubb, O'Malley, Gooderham, & Lucas, ; Findlay, ) and no impacts (Ruokonen et al , ) on European bullhead Cottus gobio , which has protected status in parts of its native range (Findlay, ). Indeed, a review of crayfish impacts emphasizes these divergent results (Degerman, Anders Nilsson, Nyström, Nilsson, & Olsson, : p. 231), that ‘crayfish effects on fish may be highly dependent on specific species and methods used, and that the effects of crayfish on fish populations deserve further attention to enable reliable predictions of community processes in streams’.…”

Communal pair spawning behaviour of vendace (Coregonus albula) in the dark

“…Similarly, the density of eggs in the spawning ground is low: the mean density of eggs in four Finnish lakes was 8 eggs m −2 (SD = 10, n = 29, min = 0.1, max = 35; recalculated from reports by Huuskonen, 2005;Väisänen, Karjalainen, & Viljanen, 1994;Valkeajärvi et al, 2001). Due to the long egg incubation time (up to 6 months from October to May) without protection, the dispersal of eggs seems to be a strategy to decrease the mortality by predators with the type III functional response (Holling 1959) preying visually, but also by vertebrate predators which can also be active at night (Karjalainen et al, 2015). If spawning shoals in lakes move around the spawning ground, the eggs of an individual female may spread around a broad bottom area during the spawning period which can last several days.…”

“…Direct observations of spawning shoal movements in lakes are needed to verify this assumption. Due to the long egg incubation time (up to 6 months from October to May) without protection, the dispersal of eggs seems to be a strategy to decrease the mortality by predators with the type III functional response (Holling 1959) preying visually, but also by vertebrate predators which can also be active at night (Karjalainen et al, 2015). On the other hand, the strategy of spawning in darkness may serve to protect against visually feeding fishes (most of the fishes in boreal lakes) that would potentially feed on the spawning vendace themselves (e.g.…”

“…As the fish were not individually marked, we cannot rule out the possibility of permanent pairing between certain male and female individuals, but according to video recordings, it appears more likely F I G U R E 3 Mean number of spawn rises (black bar) and eggs laid per a spawn rise (open bar) for the 30-min observation periods during one dark period (from 31 October at 20:04:00 to 1 November at 07:45:00) in the spawning period. The fertilisation rate of eggs in our experiment (68%) corresponds to the proportion of fertilized eggs pumped from the spawning areas of vendace in four Finnish lakes (from 37% to 87%,Karjalainen et al, 2015). All events have been counted from the field of vision of the top-side camera F I G U R E 4 Cumulative relative mortality (%) of mature vendace individuals before, during and after the spawning period.…”