Effects of physical factors on the vertical distribution of larval walleye pollock Theragra chalcogramma under controlled laboratory conditions

Abstract

Larval fish possess behavioral mechanisms which enable them to alter position in the water column to deal with vertical environmental gradients and select favorable conditions or avoid unfavorable ones. This study examined, under controlled laboratory conditions, behavioral responses of larval walleye pollock (4 to 8 mm) to various physical factors that may potentially play a role in vertical movements and distribution. Die1 periodicity in vertical distribution was evident and appeared to be under exogenous control. During the day, with light intensity at 70 FE m-' S-', larvae moved downward from the surface. As light intensity decreased during simulated evening twilight, larvae moved upward. At night, with no available light, larvae continued to swim upward, apparently the result of negative geotaxis. They remained near the surface until morning when they then began moving downward. Changes in vertical distribution occurred concomitantly with changes In activity, orientation and behavior. Formation of a vertical thermal gradient caused larvae to move upward and away from cold water. Turbulence at the surface, induced by an airstream, elicited an avoidance response and resulted in larvae moving downward. Findings are compared with information from field studies and suggest how behavioral responses to a number of integrated factors can determine the vertical movement and distribution of larval walleye pollock.

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

“…This relationship has been hypothesized to be dome-shaped rather than linear (MacKenzie et al 1994); according to this model, maximum feeding rates occur at intermediate levels of turbulence, while highly turbulent conditions will reduce the rate of successful larval prey capture, which will lead to an overall decrease in ingestion rates. Our model predicted higher feeding rates under high turbulence levels; it did not show a decrease over the range of values observed (the maximum wind speed measured in our study was approximately 20 m s -1 (a speed estimated to reduce ingestion in Atlantic cod Gadus morhua larvae; MacKenzie et al 1994), possibly because walleye pollock larvae avoid high turbulence situations by moving deeper down the water column (Olla & Davis 1990, Kendall et al 1994). However, marine fish larvae are visual predators, and must rely on sufficient illumination to detect and successfully ingest prey (Paul 1983, Blaxter 1986.…”

“…First-feeding walleye pollock Theragra chalcogramma larvae initiate exogenous feeding on copepod eggs and small naupliar stages (Canino et al 1991, Hillgruber et al 1995, but quickly expand their prey field to include copepodite stages and adult copepods (Nishiyama & Hirano 1985, Kendall et al 1987, Grover 1990). In addition, their ability to respond to physical variables, such as light and turbulence, equally increases as swimming performance improves with increasing size (Olla & Davis 1990, Davis & Olla 1995.…”

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

“…Effect of physical variables in the fish larvae vertical distribution Larval fish have behavioural mechanisms that allow them to alter their position at the water column to address environmental gradients, selecting the most favourable (i.e., turbulence avoidance, vertical migration; Olla & Davis, 1990). The vertical distribution of fish larvae has often been linked to the thermal stratification of the water column (Roepke et al, 1993;Boehlert & Mundy, 1994;Moser & Pommeranz, 1999).…”

“…The vertical distribution of fish larvae has often been linked to the thermal stratification of the water column (Roepke et al, 1993;Boehlert & Mundy, 1994;Moser & Pommeranz, 1999). The thermocline is considered important as a barrier (Smith & Suthers, 1999) or as an indirect measurement of the offshore Ekman layer, that acts above or below in the vertical distribution of some fish larvae (Coombs et al, 1981;Davis et al, 1990;Olla & Davis, 1990;Rojas, 2014). The significant correlations found between the depth values of physical variables with the vertical position of some fish larvae having bathy-mesopelagic (V. lucetia) and epimesopelagic (T. oculeus) habits, suggest that location of the thermocline and oxygen minimum zone may have a large influence on the vertical distribution of these species.…”

Underwater infrared video system for behavioral studies in lakes

“…This may both raise an issue in conservation and alter the quality of the results. Infrared light sources and infrared sensitive cameras have been largely used in the laboratory (Batty 1983;Olla and Davis 1990;Widder 1992;Janssen et al 1995;Link and Edsall 1996;Olla et al 1998;Roberts and Anderson 2002;Fisher and Bellwood 2003), but not in the field. Widder et al (2005) have successfully used red light for in situ observations in clear ocean waters.…”