Estimating consumption rate of Atlantic salmon smolts (Salmo salar) by striped bass (Morone saxatilis) in the Miramichi River estuary using acoustic telemetry

Abstract

9Differentiating detections of a telemetered fish from those of predators which may have 10 consumed that telemetered fish presents problems and opportunities. Previous efforts to quantitatively 11 classify predation events have had to rely on data from unknown states of fish (i.e. unsupervised 12 learning techniques) with the consequence that model performance cannot be refined or compared to 13 alternate models. We circumvent this limitation by analysing acoustic telemetry track data to 14 differentiate movement patterns of tagged Striped Bass (Morone saxitilis) from those of Atlantic Salmon 15 (Salmo salar) smolts which were known to not have been predated by Striped Bass over a three year 16 period in the Miramichi River estuary. A random forests classification model (i.e. supervised learning 17 technique) was used to differentiate the movement patterns of these two species and the model was 18 applied to Atlantic Salmon smolt movement characteristics to provide an index of Striped Bass 19 predation-derived mortality. The optimized random forests model inferred that predation rates by 20 Striped Bass were highly variable between years for two smolt stocks, ranging from 1.9% to 17.5%. 21Spatial and temporal overlap of the two species is a likely factor defining the between stock and annual 22 variation of predation rate estimates. 23 For personal use only. This Just-IN manuscript is the accepted manuscript prior to copy editing and page composition. It may differ from the final official version of record. Introduction 24Telemetry studies often assume that detections are from the individual tagged. This assumption is 25 violated when a tagged fish is consumed by a predator or scavenger and the tag continues to be 26 detected by acoustic receivers (Gibson et al. 2015). Miniaturization of acoustic transmitters is permitting 27 researchers to make inferences on survival and movement behaviour of increasingly smaller fish (Welch 28 et al., 2009), exasperating the issue of predation in telemetry studies. Biases in movement behaviour 29 and survival can be introduced if no attempt is made to differentiate between the detections of targeted 30 species of interest and those of possible predators. As acoustic telemetry became a more widely 31 adopted tracking method, classification of movement behaviours of presumed predated and presumed 32 unpredated fish evolved from observations (Beland et al. 2001), subjective and qualitative analyses 33 (Melnychuk et al. 2013) and, more recently, to quantitative approaches (Gibson et al. 2015; Romine et 34 al. 2014). Efforts to quantify predation events, however, have had to rely on data from unknown states 35 of fish otherwise termed unsupervised classification methodologies. This has primarily been due to the 36 absence of known states of the tagged individuals as either having been predated or not. 37In the absence of data of known states of tagged individuals, model classification error cannot be 38 evaluated. Furthering the development of quantitative models, e...

Estimates of Red Drum Mortality via Acoustic Telemetry

“…; Daniels et al. ). If an aquatic predator consumed a tagged Red Drum and remained in the river, then the Red Drum would be assumed alive initially after predation; however, tag movement would have likely ceased within 1 month given tag expulsion from the predator (Friedl et al.…”

“…Therefore, movement of carcasses and tags outside of Red Drum likely did not bias the alive fate classification. Tag movement within the stomach of an aquatic predator is another potential source of bias in the alive fate classification (Romine et al 2014;Gibson et al 2015;Daniels et al 2018). If an aquatic predator consumed a tagged Red Drum and remained in the river, then the Red Drum would be assumed alive initially after predation; however, tag movement would have likely ceased within 1 month given tag expulsion from the predator (Friedl et al 2013;Schultz et al 2015).…”

Atlantic Salmon Recovery Informing and Informed by Ecosystem‐Based Fisheries Management

“…Saunders et al (2006) summarized Maine's diadromous fish community and discussed links to Atlantic Salmon recovery. Predator and prey dynamics are also important; as an example, the rebuilding of the Striped Bass Morone saxatilis population increases predation pressure on Atlantic Salmon smolts and potentially restricts recovery (e.g., Daniels et al 2018). Predator and prey dynamics are also important; as an example, the rebuilding of the Striped Bass Morone saxatilis population increases predation pressure on Atlantic Salmon smolts and potentially restricts recovery (e.g., Daniels et al 2018).…”

“…The health of the diadromous fish community is considered a primary element for recovery in the ESA Critical Habitat designation. Predator and prey dynamics are also important; as an example, the rebuilding of the Striped Bass Morone saxatilis population increases predation pressure on Atlantic Salmon smolts and potentially restricts recovery (e.g., Daniels et al 2018). Prey buffering, whereby abundant river herring provide alternative prey for predators of salmon, may also be an important component of predator-prey dynamics related to recovery (Saunders et al 2006).…”

Fisheries Volume 44 Number 9 September 2019

“…The health of the diadromous fi sh community is considered a primary element for recovery in the ESA Critical Habitat designation. Predator and prey dynamics are also important; as an example, the rebuilding of the Striped Bass Morone saxatilis population increases predation pressure on Atlantic Salmon smolts and potentially restricts recovery (e.g., Daniels et al 2018 ). Prey buffering, whereby abundant river herring provide alternative prey for predators of salmon, may also be an important component of predator-prey dynamics related to recovery (Saunders et al 2006 ).…”