Wind-mixing effects on feeding success and condition of blue whiting larvae in the Porcupine Bank area

Abstract

Prey environment, feeding success and condition of blue whiting Micromesistius poutassou larvae were analysed in contrasting meteorological situations west of Ireland in the spring of 2 consecutive years (1994 and 1995). While larval abundance in both years of the study was approximately equal, there were marked differences in the physical and biological environment between the 2 years. 1994 was characterised by strong, unidirectional wind stress, which probably caused the low overall abundance of prey organisms recorded in this year. Abundance of copepod eggs and nauplii was considerably higher in 1995, when wind speeds were lower and wind direction was more variable. Copepod nauplii were also significantly larger than in 1994. Larval feeding success in both years was highly variable, but with considerably higher feeding intensities in 1995 than in 1994. For the determination of larval condition, 3 different condition indices were used, Fulton's K index (FCI) and body height to body length ratio for between-year comparison, and carbon and nitrogen content for estimation of immediate effects of wind stress on larval condition. In 1994, the FCI of blue whiting larvae was significantly lower than in 1995, and 11% of the larvae were significantly lighter at length than their conspecifics, suggesting that a part (11%) of the larval population at any one time fed less successfully at low prey density and high turbulence levels. No differences between the years were observed using the index of body height at the anus versus standard length. Analyses of relative C and N content of blue whiting larvae in relation to varying wind stress showed that while wind stress had a minor negative effect on C content, relative N content was significantly reduced with increasing wind speed, indicating that at periods of high wind-mixing more protein is catabolised in order to satisfy increasing energy demands, thus leaving less material to be assimilated for growth.

Summer larval fish assemblages in the Southern Tyrrhenian Sea (Western Mediterranean Sea)

“…Whereas there is evidence that maximum concentrations of larvae are associated to shelf-break fronts or river plumes (Sabat es 1990;Sabat es & Mas o 1992;Govoni & Pietrafesa 1994), frontal zones appear to be the direct cause of larval retention and enhanced production, therefore contributing to final survival (Kiǿrboe et al 1988). Wind stress can generate highly dynamic conditions that recruit larvae to invest more energy in feeding or maintaining a position in the water column, producing physiologically unfit larvae that have a higher potential mortality (Gallego et al 1996;Kloppmann et al 2002).…”

Combined study of daily growth variability and nitrogen-carbon isotopic signature analysis of schooling Sardina pilchardus larvae

“…On the other hand, the content of C relative to N (C:N) has also been used as an indicator of a condition factor in fish larvae (von Westernhagen et al , 1998; Coombs et al , 1999; Kloppmann et al , 2002) since a decrease of the C:N ratio in starvation experiments with blenniid and Pleuronectes platessa L. 1758 larvae has been reported. The F‐growing larvae had significantly higher C:N ratios, which is indicative of faster metabolic growth rates.…”

“…As a result, the ratio of carbon isotopes ( δ 13 C) can be used to determine the sources of carbon for an organism when the isotopic imprints of these food potential sources are different. Furthermore, the combined use of C and N total content, as well as the C:N ratio, may be used to assess the nutritional status since both elements are primarily responsible for protein synthesis and lipid and fatty acids, respectively (Checkley, 1984; von Westernhagen et al , 1998; Coombs et al , 1999; Kloppmann et al , 2002). The data on C and N content and isotopic composition combined with otolith microstructure analysis to estimate the age of individual larvae allow the examination of differing growth strategies in relation to trophic variations throughout ontogenetic development.…”

Effect of turbulence on feeding intensity and survival of Japanese flounder Paralichthys olivaceus pelagic larvae

“…It is likely that cost of swimming and feeding increases with turbulence level, with the effect that incompetent or weakened larvae would die from feeding failure. It has been suggested that wind‐induced turbulence increases the energy demands on fish larvae since more resources are needed for various behaviours such as feeding (Dower et al , 1997; Kloppmann et al , 2002). The highest survival rate was found under the control condition.…”