Importance of scale to the relationship between abundance of sardine larvae, stability, and food

Abstract

We used a spatially explicit regression model to relate sardine (Sardinops sagax) larval abundance to water column stability, phytoplankton, and zooplankton off South Australia. The distribution of sardine larvae was significantly associated with stability (p , 0.05) and phytoplankton fluorescence or zooplankton displacement volume (p , 0.001) at broad scales. In contrast there was no relationship between sardine larvae, stability, phytoplankton, or zooplankton at medium or fine scales. The relationships are shown to be scale-dependent. Although the results generally support Lasker's (1978) ''stable ocean'' hypothesis, mid-range rather than high stability appears to be favored, in accord with theoretical expectations at both large and small scales.Many studies have attempted to relate recruitment success in clupeoids to environmental and ecological factors. No single factor explains the observed variability in clupeoid recruitment but the role of water column stability is considered to be critical for survival of the early larval stages. Lasker's original idea (Lasker 1978) now referred to as the ''stable ocean'' hypothesis, suggested that survival of first-feeding anchovy larvae and subsequent recruitment would be improved when food of a suitable size and concentration aggregated in layers, associated with a stable water column, in the absence of intense upwelling advecting the larvae into possibly unfavorable food environments. However, evidence for the correlation of stability with larval survival is variable and has seldom been shown to agree with theoretical expectations (Peterman and Bradford 1987;Cury and Roy 1989;Butler 1991). The survival of newly hatched larvae is most likely determined by a combination of physical and biological characteristics, rather than by feeding conditions alone (Muelbert et al. 1994). However, sardine recruitment appears to be determined by the mortality experienced by post-larvae to juvenile (age 0) fish (Watanabe et al. 1996), rather than by the first feeding stage.Stability exerts an effect at a range of scales by altering the prey environment experienced by larval clupeoids as they lose their yolk sacs and begin feeding. In the case of anchovies, the prey are often dinoflagellates (Lasker 1975), whereas first feeding sardine consume copepod nauplii (Watanabe et al. 1998). First feeding larvae must encounter prey of suitable size at sufficient densities to meet their metabolic requirements for growth (Lasker 1975). Aggregation of the prey in layers provides a sufficiently concentrated food source for the larvae to be able to meet their metabolic requirements for growth and to grow rapidly enough to minimize predation mortality. Some species of early stage larval fish can swim well enough to locate the layers of prey and to successfully capture food particles if the stability conditions are favorable (MacKenzie and Kiorboe 2000). Although there is little swimming speed data for sardine larvae, it is thought that postflexion larval stages are likely to be able to move ...

Spatial analysis of egg distribution and geographic changes in the spawning habitat of the Brazilian sardine Sardinella brasiliensis

“…Agglomerations of zooplankton during summer preying upon large phytoplankton aggregates are also related to low‐temperature CW and patches occurring on the intermediate shelf and shelf break. This contrasts with results from south‐eastern Australia where thermocline is not critical to the survival of fish larvae in shallow coastal regions characterized by frequent perturbations in the position and intensity of thermocline (Gray & Kingsford, 2003; McClatchie et al , 2007). If vertical distribution of mesozooplankton is homogeneous or if it is prevalent above the thermocline, then fish larvae may not find it necessary to aggregate in thermoclines.…”

Abundance patterns of early stages of the Pacific sardine (<i>Sardinops sagax</i>) during a cooling period in a coastal lagoon south of the California Current

“…However, the evidence of a correlation between water column stability and larval survival varies (Cury andRoy 1989, Planque et al 2007). In Sardina pilchardus from the Bay of Biscay, egg abundance drops as water stratification increases (Planque et al 2007), while the egg abundance of S. sagax in South Australia is significantly related to water column stability (McClatchie et al 2007). In this study, sardine eggs and larvae were more abundant in non-stratified waters, although this was not statistically significant, probably because larvae occurred at stations both close to the bay entrance and in stable and shallow waters inside the bay.…”

“…In this case, food production determines survival and reproductive success of small pelagic larvae (Lasker 1978, Lynn 2003, Logerwell and Smith 2001, McClatchie et al 2007, Planque et al 2007, Aceves-Medina et al 2009). Survival of first-feeding larvae improves when there is food of an adequate size and layered concentrations associated with a stable water column (Lasker 1978).…”

“…The spatial range and location of spawning can be critical for eggs and larvae due to interan-nual changes in population structure and geographic variations in environmental conditions (Planque et al 2007, Smith and Moser 2003, Emmett et al 2005, Ibaibarriaga et al 2007, Coombs et al 2006. However, few comprehensive surveys of eggs and larvae are available to determine preferred spawning locations and little is known of the stock structures of various important species (Agostini and Bakun 2002), which are influenced by physical processes that provide favourable habitat requirements for larval growth and survival (Lasker 1978, Parrish et al 1981, Bakun 1996, Logerwell and Smith 2001, Lynn 2003, McClatchie et al 2007, Planque et al 2007, Aceves-Medina et al 2009). …”

Influence of hydrographic conditions on larval fish assemblage structure in the northern Gulf of California

“…Larvae are vulnerable to different mortality sources, with their specific requirements and the characteristics of spawning grounds as important components in the development and survival. Processes that promote the enrichment and concentration of particles (e.g., convergence, water column stability, mixing), along with retention processes, often result in favorable spawning conditions and good larval survival (Lasker 1978, Bakun 1996, Logerwell & Smith 2001, Agostini & Bakun 2002, Lynn 2003, McClatchie et al 2007). …”