Accounting for a nonlinear functional response when estimating prey dynamics using predator diet data

Abstract

In marine ecosystems, intermediate trophic-level species (i.e. forage fishes) play a key role in regulating the energy flow from primary and secondary producers to top predators (Pikitch et al., 2014), and understanding their population dynamics is crucial for food web studies and ecosystem-based fisheries management (Link et al., 2020;Tam et al., 2017). However, reliably estimating the abundance of forage fishes is challenging; these species are often data limited because they are not directly targeted and/or poorly

Assessing small pelagic fish trends in space and time using piscivore stomach contents

“…Including more information on the process of fish predation (which we somewhat controlled for as catchability covariates for number of predators, predator size, and temperature) may help to refine aggregate forage indices. For example, in this initial model, we have not accounted for functional responses of predators, but new research may allow us to do so in future iterations (Smith and Smith 2020;Robertson et al 2022;Thorson et al 2022). Predator behavior/thinning rates information could potentially supply information on "area swept" for the forage index, allowing more direct comparisons with survey sampling gear.…”

Testing models of increasing complexity to develop ecosystem‐informed fisheries advice

“…We considered including the role of (1) climatic variability on habitat availability and predator–prey overlap using the Newfoundland and Labrador (NL) climate index (NLCI; Cyr & Galbraith, 2021), mean normalized anomalies of the spring bottom‐water temperature derived from multiple data sources (Cyr et al., 2021), and the mean normalized anomalies of the summer cold‐intermediate layer (CIL) area over hydrographic sections on the NL shelf (Cyr & Galbraith, 2021), (2) prey availability using a time series of capelin biomass (Koen‐Alonso et al., 2021) and northern sand lance abundance (Robertson, Koen‐Alonso, et al., 2022) and (3) a potential competitor for food and habitat, thorny skate using a survey time series of estimated biomass for this species (Simpson et al., 2018).…”

“…Meanwhile, M for both species was tested against climate time series without a moving average, because M was most likely affected by the direct impacts of climate within a given year. The northern sand lance index was extended back to 1984 by combining estimates from separate nonlinear functional response models (Robertson, Koen‐Alonso, et al., 2022) for Engels and Campelen research survey data. Every covariate was standardized using the standard score equation () prior to inclusion to improve model convergence and to determine whether longer time series could serve as proxies for correlated shorter time series (see Appendix S3).…”

“…(2) prey availability using a time series of capelin biomass (Koen-Alonso et al, 2021) and northern sand lance abundance (Robertson, Koen-Alonso, et al, 2022) and (3) a potential competitor for food and habitat, thorny skate using a survey time series of estimated biomass for this species (Simpson et al, 2018).…”

“…These flounder species consume similar benthic (e.g., amphipods and crustaceans) and forage fish prey (e.g., sand lance [ Ammodytes dubius , Ammodytidae] and capelin [ Mallotus villosus , Osmeridae]) on the Grand Banks, although forage fish provide a larger contribution to the diet of plaice (Bruno et al., 2000; Gonzalez et al., 2006). The capelin population collapsed in the 1990s (DFO, 2019), and although pre‐1990s estimates of sand lance population size do not exist, recent estimates indicate that their population has followed similar fluctuations to capelin in recent years (Robertson, Koen‐Alonso, et al., 2022), indicating a potentially limited forage fish prey base.…”