Vertical distribution and feeding of larval blue whiting in turbulent waters above Porcupine Bank

Abstract

In April 1995 a patch of blue whiting larvae Micromesistius poutassou was found at low illumination levels below 20 m depth near Porcupine Bank, west of Ireland, together with high densities of copepod nauplii and reduced turbulence rates, suggesting that larval blue whiting vertical distribution was determined by prey concentration, illumination and turbulence. Most (83·8%) larvae (2·0-7·5 mm L s ) had food in their guts. Feeding incidence and feeding intensities increased with increasing larval length. Only larvae >5·5 mm reduced numerical in favour of weight-based feeding intensity, indicating a shift in dietary composition. Maxima of the diel rhythms of feeding incidence and intensities occurred at 1800 and 2100 hours and minima at dawn (0600 hours). Proportionately, more nauplii were eaten by day but more copepod eggs and tintinnids at night. The distinct diel pattern in larval blue whiting feeding suggests that any analysis of factors mediating feeding must take into account diel feeding cycles. Larval feeding was significantly affected by wind speed. The larvae ate more and larger items at low than at higher turbulence levels. The data suggest that the maximum level of turbulence was not beneficial for larval blue whiting, but more moderate wind speeds could have had an enhancing effect on larval feeding success.2000 The Fisheries Society of the British Isles

Small-scale patterns in distribution and feeding of Atlantic mackerel ( Scomber scombrus L.) larvae in the Celtic Sea with special regard to intra-cohort cannibalism

“…Youngest fish larvae are often less aggregated and occur at greater depths than larger fish larvae, particularly under high turbulent energy dissipation rates. With improving swimming ability during growth, larger larvae become more able to compensate for turbulent dispersion and tend to be more aggregated (Heath et al 1988;Heath 1992;Hillgruber and Kloppmann 2000). The results of our study were the opposite of the aforementioned scenario, i.e., mackerel larvae <5.0 mm were highly aggregated near the thermocline and showed distinct diel vertical migration patterns, while mackerel larvae ≥5.0 mm were more dispersed with only slight diurnal movement patterns discernible.…”

“…Fiksen et al (1998) performed a modeling study and observed that both turbulence and light could have a strong impact on larval ingestion rates. While turbulence in the present study was at a level that proved not to be beneficial for larval blue whiting foraging success (Hillgruber and Kloppmann 2000), it did not change over time, so that changes in the composition of the diet should be solely due to light. However, mackerel larvae of both size classes ingested proportionately more smaller prey at lower light levels.…”

“…2a). Wind generated turbulent energy dissipation at the depth of maximum mackerel larvae density was always ε>10 -3 cm 2 s -3 , values that proved to be suboptimal for larval blue whiting feeding (Hillgruber and Kloppmann 2000;Fig. 2b).…”

“…Feeding success in marine fish larvae is largely dependent on light (Paul 1983;Blaxter 1986) and larval feeding activity often follows a diel pattern as to quantity and composition of prey in the gut (Conway et al 1998;MacKenzie et al 1999;Hillgruber and Kloppmann 2000). While sufficient illumination is of primary importance, other factors have been suggested to affect larval feeding success, e.g., small-scale turbulence (Rothschild and Osborn 1988;Dower et al 1997), temporal and spatial overlap between predator and prey (Lasker 1975;Cushing 1990), length-specific changes in predator prey capture success and preference, and prey visibility and escape capability (Buskey et al 1993).…”

Individual-based simulations of larval fish feeding in turbulent environments

“…These behaviours are important mechanisms which differ among larval fish species and which nonetheless lead to the dominance of larval diets by a relatively few species (Munk 1995, Hillgruber et al 1997, Heath & Lough 2007. Our modelling approach can potentially enable us to investigate how larval diets in the field change depending on prey characteristics and turbulence conditions (Dower et al 1998, Hillgruber & Kloppmann 2000, Fiksen & MacKenzie 2002. Future climate change will affect not only the spatial and temporal pattern of exposure of larvae to wind and tidally induced turbulence, but will also affect the relative timing of production of individual species of zooplankton (Edwards & Richardson 2004) and larval fish (Greve et al 2005).…”