Effects of river flow on larval growth and survival of Japanese seaperch Lateolabrax japonicus (Pisces) in the Chikugo River estuary, upper Ariake Bay

Abstract

The abundance and growth history of larval and juvenile Japanese seaperch Lateolabrax japonicus were investigated in the Chikugo River estuary, upper Ariake Bay, from 1990 to 2000. Growth during the larval period (up to 15 mm standard length, L S , the size at recruitment into the estuary) was backcalculated using sagittal otolith microstructures by the biological intercept method. Growth rates in length declined at body sizes >14 mm L S . High freshwater discharge through the Chikugo River was associated with high temperatures of the upper Ariake Bay where the larvae spend their planktonic life. Mean larval stage duration (days) from hatch to 15 mm (D 15 ) varied between 48Á8 and 76Á2 days and was inversely correlated with the estimated mean temperature history [mean daily temperature (°C) experienced by the larvae during the period from hatch to 15 mm, T 15 ]. Mean abundance (number m À2 ) of larvae and juveniles was highest in years when T 15 , D 15 and freshwater discharge were at intermediate levels.Although the abundance was not correlated with either of these variables, an exponential relationship between abundance and D 15 was found when data collected during the highest river discharge years (1990, 1991 and 1998) were excluded. The increase in freshwater discharge through the Chikugo River probably had the potential to enhance or diminish Japanese seaperch recruitment in two ways: 1) it could increase recruitment probability by increasing temperature and larval growth and 2) high river flow also had the potential to decrease the probability of immigration into the river by increasing larval seaward dispersion, predation due to decreased turbidity and starvation due to decreased zooplankton prey abundance in the estuary.

Influence of spring river flow on the recruitment of Japanese seaperch <em>Lateolabrax japonicus</em> into the Chikugo estuary, Japan

“…Recent surveys have demonstrated that the biological and physical properties of the ETM, such as turbidity (Shoji et al, 2006a) and spatial and temporal distribution of chlorophyll and copepods (Okazaki et al, 2005;Ueda et al, 2004), fluctuate with the variability of freshwater discharge of the Chikugo River. Growth analyses using larval otolith microstructure have shown that temperature in the northern part of Ariake Bay and larval growth were high but the recruitment was poor in the years of high winter flow (Shoji et al, 2006b). This suggests that an increase in river flow may decrease Japanese seaperch recruitment in the Chikugo River estuary through a density-independent process, as reported in other estuarine dependent fishes (Turner and Chadwick, 1972;Hayman and Tyler, 1980;Crecco and Savoy, 1984;Rulifson and Manooch III, 1990;Strydom et al, 2002;Whitefield, 2005;Shoji et al, 2006b).…”

“…flow has been reported to be associated with high temperature (Shoji et al, 2006b). In addition, production of copepods-major prey organisms of the larval Japanese seaperch-in the upper Ariake Bay increased when the river flow increased (Okazaki et al, 2005).…”

“…These observations seem to indicate that environmental conditions are more favourable for feeding and growth of Japanese seaperch larvae and juveniles in high flow years. However, analysis on the larval growth (Shoji et al, 2006b) and recruitment abundance of the Japanese seaperch from 1990 to 2000 (present study) indicated that recruit was poor in years of high winter river flow even though the temperature experienced by the larvae and the back-calculated larval growth was high in the high flow years (Shoji et al, 2006b). A more direct, density-independent mechanism affected by the physical properties of the habitat is suggested to control Japanese seaperch recruitment and lead to its high variability, as found in other estuaries (Whitfield, 2005).…”

Highly variable recruitment in an estuarine fish is determined by salinity stratification and freshwater flow: implications of a changing climate

“…Recruitment variability indicated by age structure for king threadfin in a drytropical estuary was also shown to be positively related to freshwater flow (Halliday et al 2008). Not all studies, however, show positive linear effects of flow on (Deegan 1990, Rulifson & Manooch 1990, Sarre & Potter 2000, Shoji et al 2006. Flow is thought to have a positive influence on Japanese sea perch recruitment, except in years of very high flow (Shoji et al 2006), suggesting a domed relationship.…”

“…A number of studies have demonstrated a positive relationship between freshwater flow and recruitment variability of estuarine-dependent fish (Kimmerer et al 2001, North & Houde 2003, StauntonSmith et al 2004, Robins et al 2005 and invertebrates (Robins et al 2005). In other cases, however, high freshwater flows can have a detrimental effect on recruitment (Deegan 1990, Rulifson & Manooch 1990, Sarre & Potter 2000, Shoji et al 2006, with intermediate flows resulting in the highest recruitment success (Rulifson & Manooch 1990, Shoji et al 2006.…”