Environmental factors influencing larval walleye pollock Theragra chalcogramma feeding in Alaskan waters

Abstract

This study examines potential interactions among the environmental variables likely to affect larval walleye pollock Theragra chalcogramma feeding in the sea. Walleye pollock larvae were sampled from Shelikof Strait, Gulf of Alaska, and from the eastern Bering Sea, with corresponding environmental data. Variables used in our study were time spent feeding, seawater temperature, light, prey density, wind speed and standard length of the larvae. We applied an additivity test to detect the presence of potential interactions among these variables and adopted an expansion of generalized additive models (GAMs) that allowed the inclusion of interaction terms in a non-parametric regression analysis. After testing all possible 2-way interactions among these variables, we found 4 significant terms: (1) time feeding-standard length, (2) temperature-light, (3) light -wind speed and (4) prey density-standard length. The most influential interaction term was the light -wind speed interaction, which caused a decrease of the model-generalized cross-validation (GCV, whereby lower values indicate more parsimonious models) from 0.0402 (for a model with all variables but no interaction term) to 0.0290 (for a model with all variables and this interaction), and an increase of the model explained variance by 7% (R 2 = 0.89 versus 0.82). This result indicates that the effect of wind speed (turbulence) on larval walleye pollock feeding is dependent upon the amount of light available. This may be due to vertical movements in the water column by both walleye pollock larvae and their prey in response to turbulence. KEY WORDS: Larval fish feeding · Walleye pollock larvae · Generalized additive models Resale or republication not permitted without written consent of the publisher

Otolith biochronology reveals factors underlying dynamics in marine fish larvae

“…Instantaneous mortality rates of larvae are decreased in warmer water conditions (Bailey 2000). Strong winds disrupt the survival of larvae due to either the effects of turbulence on feeding rates (Porter et al 2005) or transport of larvae into offshore regions where feeding conditions may be poor (Bailey & Macklin 1994).…”

Individual-based simulations of larval fish feeding in turbulent environments

“…We are aware that in nature all of these factors complicate attempts to model and understand larval fish feeding rates. For example, prey concentrations are strongly affected by storms and other turbulence-generating processes and larvae do alter their vertical distributions depending on wind speed (Heath et al 1988, Porter et al 2005. Larval behaviour which leads to avoidance of strong surface turbulence could be a direct reaction to the high relative velocities associated with strong mixing, or could be a response to a change in the vertical distribution of prey (Franks 2001), whose vertical distributions themselves are sensitive to turbulence intensity , Incze et al 2001.…”

“…Larval behaviour which leads to avoidance of strong surface turbulence could be a direct reaction to the high relative velocities associated with strong mixing, or could be a response to a change in the vertical distribution of prey (Franks 2001), whose vertical distributions themselves are sensitive to turbulence intensity , Incze et al 2001. Moreover, recent statistical analyses of the interaction between larval feeding, vertical distribution, turbulence and light intensity in the sea shows that if a high turbulence event occurs during daylight hours under cloudy conditions, larval feeding rates will decrease (Porter et al 2005). If, instead, the turbulence event occurs during well-lit conditions (e.g.…”

“…All of these processes vary with the intensity of turbulence in highly nonlinear ways and often in opposing directions. These responses of biological and physical processes to ocean turbulence complicate attempts to predict and understand how variations in turbulence affect larval fish ecology-in particular, the feeding success of larvae (Dower et al 1997, MacKenzie 2000, Porter et al 2005.…”

Fish larvae retention linked to abrupt bathymetry at Mejillones Bay (northern Chile) during coastal upwelling events

“…Of the many processes that affect the recruitment, the loss of eggs and larvae by advection seems to be one of the main oceanographic processes which explain the spatial distribution of adult fish (Hutchings, 1992;Bakun, 1996). Thus, upwelling events in the coastal environment may have potential consequences on the ecology of fish larvae, particularly coastal retention and larval feeding success (Dower et al, 1997;MacKenzie, 2000;Porter et al, 2005).…”