Predation costs of impaired chemosensory risk assessment on acid-impacted juvenile Atlantic salmon (Salmo salar)

Abstract

Weak levels of acidification (pH < 6.6) inhibit the ability of fishes to assess predation risk via interference with damage-released chemical alarm cues. While survival benefits associated with behavioural responses to alarm cues have been demonstrated under laboratory conditions, it remains largely unknown whether fishes under natural conditions experience similar benefits. Using hatchery-reared juvenile Atlantic salmon (Salmo salar) as a model organism, we conducted a tethering experiment in reaches of neutral (pH ≥ 6.6) and acidic (pH < 6.6) salmon nursery streams, plus one additional stream that varied between pH classes. Despite exposure to fewer predatory fish species, similar availability of physical refugia, and similar threat from terrestrial predators, tethered fish in acidic streams were significantly more likely to be predated over the course of a trial than their counterparts in neutral streams. These results suggest that (i) in the absence of compensatory mechanisms, juvenile Atlantic salmon under acidic conditions may experience greater rates of predation as a result of impaired chemosensory risk assessment, and (ii) brook trout (Salvelinus fontinalis) appear to play the greatest role in limiting the survival of young-of-theyear (0+) salmon. Résumé :De faibles niveaux d'acidification (pH < 6,6) inhibent la capacité des poissons d'évaluer le risque de prédation en entravant les signaux chimiques d'alarme libérés en cas de lésions. Si des avantages pour la survie associés aux réactions comportementales à des signaux d'alarme ont été démontrés en laboratoire, de tels avantages pour les poissons en situation naturelle restent généralement à démontrer. En utilisant le saumon atlantique (Salmo salar) juvénile issu d'alevinière comme organisme modèle, nous avons mené une expérience avec des individus attachés dans des tronçons neutres (pH ≥ 6,6) et acides (pH < 6,6) de cours d'eau natals, en plus d'un cours d'eau qui oscillait entre les deux catégories de pH. Bien qu'ils aient été exposés à moins d'espèces de poissons prédateurs, à une disponibilité semblable de refuges physiques et à une menace similaire de prédateurs terrestres, les poissons attachés dans les cours d'eau acides présentaient une probabilité de prédation significativement plus grande que leurs congénères en rivières neutres durant la période de l'essai. Ces résultats donnent à penser que (i) en l'absence de mécanismes compensatoires, les saumons atlantiques juvéniles en conditions acides pourraient présenter des taux de prédation plus élevés en raison de leur plus faible capacité d'évaluation chimiosensorielle des risques et (ii) les ombles de fontaine (Salvelinus fontinalis) constitueraient le facteur limitatif le plus important en ce qui concerne la survie des saumons de l'année 0+. [Traduit par la Rédaction]

Rising pCO2 in Freshwater Ecosystems Has the Potential to Negatively Affect Predator-Induced Defenses in Daphnia

“…Moreover, changes of behavioral responses showing significant alterations in olfactory abilities with mal-adaptive anti-predator strategies and increased anxiety were observed [12,[27][28][29]. In this context, field experiments have shown that juvenile Atlantic salmon (Salamo salar) experiences greater predation rates [30]. Also, invertebrate taxa have recently been found to be susceptible to elevated pCO 2 , which affected valve movement in three North American freshwater mussels [31].…”

Cortisol does not increase risk of mortality to predation in juvenile bluegill sunfish: A manipulative experimental field study

“…We acknowledge in addition that tethering, as an experimental methodology, can limit natural predator‐avoidance tactics as well as making organisms more conspicuous to predation, which may act to mask treatment‐level effects (reviewed in Lawrence et al, ). Nevertheless, tethering serves as an important tool in estimating relative rates of predation in wild fish in ecologically‐relevant settings (Elvidge & Brown, ; Lawrence et al, ; Rypel et al, ). Further study is needed to address how cortisol influences fine‐scale risk‐taking and antipredator behaviors.…”

“…Tethering has been used effectively to assess the risk of predation on teleost fish in natural aquatic environments (see Elvidge & Brown, ; Lawrence et al, ; Rypel, Layman, & Arrington, ). As in previous work (Lawrence et al, ; Rypel et al, ), tethers consisted of a single piece of monofilament fishing line (1.5‐m in length; 2.72 kg test monofilament) attached to the lower jaw of the fish.…”

Nonconsumptive Effects of Predation and Impaired Chemosensory Risk Assessment on an Aquatic Prey Species

“…These streams have served as the setting for several earlier studies on the chemically-mediated antipredator behaviours of juvenile salmon that reliably demonstrate differences attributable to the loss of alarm cue function [15,25,27]. The salmon used were exclusively young-of-year (0 + ), hereafter referred to as "fry.…”

“…Consequently, waterbodies can be divided into functional categories of acidic or neutral around a boundary of pH 6.6 based on the different behavioural patterns demonstrated by resident fish. Acid-impacted juvenile Atlantic salmon (Salmo salar) have demonstrated both increased predator mortality in acidic streams relative to neutral ones when they were physically 2 International Journal of Ecology constrained in a tethering experiment [27] and responses of greater strength to remaining visual threat cues [15] when they are free-swimming. However, visual cues are often unavailable and may be unreliable in aquatic habitats, so additional compensatory mechanisms are necessary to explain the persistence of prey populations in acidic streams given their apparent greater vulnerability to predation.…”