Importance of estuarine nursery areas for the adult population of the temperate seabass Lateolabrax japonicus, as revealed by otolith Sr:Ca ratios

Abstract

Otolith Sr:Ca ratios were used to evaluate the contribution of estuarine nursery areas to the temperate seabass (Lateolabrax japonicus) population in Tango Bay, the Sea of Japan. Otolith Sr:Ca ratios of juveniles collected from freshwater, brackish and coastal areas were analysed to determine a criterion for distinguishing whether individuals used estuarine or coastal areas as nurseries. Otolith Sr:Ca ratios of adult seabass collected around Tango Bay were also analysed to detect the records of salinity that juveniles experienced and to estimate the contribution of each habitat. Sr:Ca ratios of the edges of otoliths of juveniles from freshwater areas were 2.4 9 10 À3 in average, which were significantly lower than those of juveniles collected from a coastal area (4.9 9 10 À3 in average) owing to differences in salinity conditions among these areas. Based on the threshold criterion determined by this difference, 39 out of 107 (36%) adult seabass were estimated to have used the estuary as a nursery during their juvenile stage according to their Sr:Ca chronologies. Despite the small area covered by estuarine nurseries compared with coastal waters, the Yura River estuary contributed considerably to the adult seabass population. This indicates estuaries play an important role as nurseries for seabass juveniles, and it should be noted that the estuaries are important nurseries to conserve the stocks of coastal fishes.

Winter monsoon promotes the transport of Japanese temperate bass Lateolabrax japonicus eggs and larvae toward the innermost part of Tango Bay, the Sea of Japan

“…In contrast to low densities and small sizes of L. japonicus larvae and juveniles occurring outside the bay, developed juveniles occur abundantly in the Yura River estuary as well as sandy beaches and seagrass beds inside the bay (Fuji, ). Among these habitats, estuaries serve as an important nursery for L. japonicus in and around Tango Bay (Fuji et al, ). In this context, transport toward the innermost part of Tango Bay leads to successful settlement in nurseries and therefore assures further survival.…”

“…The two branch bays held in Tango Peninsula and Oura Peninsula are called Miyazu Bay and Maizuru Bay, respectively. Many rivers flowing into Tango Bay provide coastal fish species with estuarine habitats, specifically in the innermost part of the bay including Miyazu Bay and Maizuru Bay (Aoki, Kasai, Fuji, Ueno, & Yamashita, ; Fuji, Kasai, Ueno, & Yamashita, ).…”

“…The coastline is dominated by rocky cliffs outside the bay, whereas inside the bay shallow waters are composed of sandy, gravel, or shelly beaches with patchy seagrass beds (Shiki, 1985;Yatsuya, Nishigaki, Shirafuji, & Takeno, 2007). Bay (Aoki, Kasai, Fuji, Ueno, & Yamashita, 2014;Fuji, Kasai, Ueno, & Yamashita, 2016b).…”

“…Among these habitats, estuaries serve as an important nursery for L. japonicus in and around Tango Bay (Fuji et al, 2016b). In this context, transport toward the innermost part of Tango Bay leads to successful settlement in nurseries and therefore assures further survival.…”

Coastal zone use and migratory behaviour of the southern population of Mugil liza in Brazil

“…() and Fuji et al . () for Sr: Ca . Similarly, the threshold between estuarine and marine water was defined as the mean Ba:Ca ratio measured at the edge for marine fish plus 1 SD of 0.04 + 0.02 = 0.06.…”