Impaired detection of chemical alarm cues by juvenile wild Atlantic salmon (Salmo salar) in a weakly acidic environment

Abstract

Many prey fishes rely on damage-released chemical alarm cues to detect and avoid predators. The ability to use these cues has been shown to confer considerable survival benefits to individuals. While several laboratory studies and a single field study have demonstrated that an ambient pH of 6.0 impairs fishes in their ability to detect these alarm cues, no study had yet compared the response to alarm cue exposures across populations residing in multiple streams of a different acidity level. In our study, we conducted live behavioural observations in five nursery streams, ranging in pH from 5.71 to 7.49 on two age classes (young of the year and parr) of wild juvenile Atlantic salmon (Salmo salar). We aimed to assess if the detection of these chemical alarm cues was constantly dependant on the ambient pH or if variations in the detection occurred among populations of the different streams regardless of the ambient acidity level. Our results demonstrated that salmon present in any acidic stream did not respond to alarm cues, while those in neutral streams exhibited typical alarm responses.Résumé : Plusieurs poissons proies utilisent les signaux d'alerte chimiques libérés par les blessures pour détecter et éviter les prédateurs. Il a été démontré que la capacité d'utiliser ces signaux procure aux individus des bénéfices significatifs de survie. Bien que plusieurs études de laboratoire et une seule étude de terrain aient prouvé qu'un pH ambiant de 6,0 compromet la capacité des poissons à percevoir ces signaux d'alerte, aucune recherche n'a encore comparé les réactions à la présence des signaux d'alerte dans une gamme de populations habitant des cours d'eau avec des niveaux différents d'acidité. Dans notre travail, nous avons mené des observations comportementales en nature dans cinq cours d'eau d'élevage dont les pH variaient de 5,71 à 7,49 chez deux classes d'âge (jeunes de l'année et tacons) de jeunes saumons atlantiques (Salmo salar) sauvages. Nous tentons de déterminer si la perception de ces signaux chimiques d'alerte dépend à tout coup du pH ambiant ou s'il existe des variations entre les populations des différents cours d'eau indépendantes des niveaux ambiants d'acidité. Nos résultats démontrent que tous les saumons qui habitent les cours d'eau acides ne réagissent pas aux signaux d'alerte, alors que ceux des cours d'eau neutres montrent des réactions typiques d'alerte.[Traduit par la Rédaction] Leduc et al. 2363

Effects of acidification on olfactory-mediated behaviour in freshwater and marine ecosystems: a synthesis

“…5.0-6.0) in fathead minnows and Atlantic salmon (Salmo salar) [38,46]. Under field conditions, experiments revealed a similar absence of response to chemosensory cues in brook trout (Salvelinus fontinalis) and Atlantic salmon exposed to conspecific alarm cues in acidic streams ( pH range; 5.8 -6.3), whereas avoidance responses were retained in neutral pH streams (pH range; 6.8-7.4) [20,45,47,48]. Likewise, episodic acidifying events may cause short-term loss of chemosensory abilities in freshwater fish.…”

Learning about Danger: Chemical Alarm Cues and Threat‐Sensitive Assessment of Predation Risk by Fishes

“…Elvidge presented wild juvenile Atlantic salmon with realistic model predators (visual cues) in a series of streams varying in ambient pH. Previous studies have shown that weakly acidic conditions inhibit the detection and response to conspecific alarm cues by juvenile salmon (Leduc et al 2006). Presumably, salmon in neutral streams have had previous opportunity to assess risk based on the combined visual plus chemical cues, whereas salmon in the acidic streams would not have prior experience with chemical information.…”

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

“…The occupied sites of twenty individual salmon in each of four streams (neutral: Catamaran Brook and Lower Devil's Brook; acidic: Upper Devil's Brook and Correy Creek; = 40 sites in each stream class), as well as unoccupied nearby control sites ∼1 m directly upstream, were marked with flagged rocks and compared to quantify differences in microhabitat preferences between stream classes. Habitat measurements consisted of pH, temperature ( ∘ C), channel width (m), distance from nearest riverbank (m), shore index (distance from bank/channel width), depth (m), flow rate (m s −1 ) at 50% depth, substrate complexity (described in [15,37]), canopy cover (proportion of the sky directly overhead covered with tree canopy or other vegetation, after [25]), and substrate composition (per cent of area within a 0.5 m radius covered with substrate < 1 cm, 1 cm ≤ < 5 cm, 5 cm ≤ < 15 cm, and ≥15 cm) based on the grain size classes delineated by the Wolman [38] Pebble Count. Physical measures were combined into a multivariate response and analyzed with two-way MANOVA against stream class (neutral or acidic) and fry preference (occupied or unoccupied).…”

“…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.…”

“…In both freshwater and marine systems, weak levels of acidity (pH < 6.6) deprive fishes of an important source of information on risk by rendering damage released chemical alarm cues nonfunctional [25,26]. 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.…”