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Growth rates of round herring Etrumeus teres, Japanese anchovy Engraulis japonicus, and Japanese sardine Sardinops melanostictus larvae respond differently to seasonal temperature variations in Sagami Bay on the Pacific coast of central Japan. Larvae of these three clupeoid species were collected from small seine net catches between February 2008 and April 2009. Correlations between otolith growth increment widths and ambient temperatures were examined at five body sizes and indexed to otolith radii of 50-175 μm, which corresponded to notochord lengths of 15-24 mm. Round herring larvae showed positive correlations between growth rate and habitat temperature at all five body sizes. In contrast, Japanese sardine larvae did not show significant correlations between growth rate and ambient temperature at any of the five body sizes. Japanese anchovy larvae showed significant but weaker correlations between growth rate and temperature than round herring. Although these three species share habitats with some differences in seasonal occurrence in the bay, they showed different species-specific responses to seasonal habitat temperature variations. These differences in response to temperature variations may constitute an ecological basis for different migration patterns among the three species. [ABSTRACT FROM AUTHOR]

We examined the effects of process and observation errors on the selection of the stock-recruitment relationship (SRR) curve using simulations. When the process and observation errors were added to both spawning stock biomass and recruitment, the results were as follows: (1) When the proportional model was set as the true SRR model, there was a high probability that the Ricker or Beverton and Holt model was selected in response to the errors; (2) When the Ricker or Beverton and Holt model was set as the true SRR model, the proportional model was seldom selected in response to the errors; (3) The proportional SRR model should be accepted as the optimum SRR model for the Pacific stock of Japanese sardine; (4) We should use an SRR model that is constructed from more than two independent variables (spawning stock biomass, environmental factors, etc.) when we discuss management of fisheries resources. [ABSTRACT FROM AUTHOR]

The diet of juvenile (predominantly age 1) southern bluefin tuna Thunnus maccoyii (SBT, N = 720), caught over 11 years of the recruitment monitoring survey off southern Western Australia during summer, consisted overwhelmingly of teleosts (97.4% by volume). Pilchard Sardinops sagax (27.4% V), blue mackerel Scomber australasicus (16.7% V), and jack mackerel Trachurus declivis (14.2% V) were the major taxa, with pilchard more abundant in coastal waters and jack mackerel more frequently encountered in fish caught closer to the shelf-edge. Prey size varied from 5 to 240 mm, with 67% of ingested items measuring between 30 and 50 mm. Pilchard dominated the prey size category 130-190 mm (84% by number), but the overall contribution of this species to the diet of juvenile SBT was much lower than previously reported. Future research in relation to the feeding ecology of juvenile SBT should focus on the biology and ecology of the young lifestages of the main prey species in this area and on prey distribution and dynamics as a key factor linking environmental change and SBT distribution. [ABSTRACT FROM AUTHOR]

This study assessed the stock-recruitment relationship (SRR) for the Japanese sardine Sardinops melanostictus in the North-western Pacific. Of the 20 SRR models investigated, the Akaike information criterion (AIC) was the minimum (AIC = 551.2) when the data were separated into two groups (A and B) and the log-normal distribution was applied as the error term. Group A was constructed with SRR data from 1976–1987 and 1992–2004. Group B consisted of data from 1988–1991. The AIC minimum model was R = 22.8 S × e ε for Group A, where R, S, and ε denote the recruitment of sardine (individual number of 0-year old fish), spawning stock biomass (SSB), and error term, respectively. This model indicated that recruitment was proportional to the SSB and that no density-dependent effect operated over the range of SSB investigated (51 000–11.3 million t). Recruitment was markedly higher (lower) when the sea surface temperature (SST) of the Kuroshio Extension area in February was low (high). The essential SRR can simply be expressed as R = 22.8 S × e ε with the level of recruitment deviating from the model to a greater or lesser degree depending on the environmental conditions. [ABSTRACT FROM AUTHOR]

Changes in the growth of the Japanese sardine Sardinops melanostictus during a period of declining stock size was examined by using sardines sampled from 1990 to 1996 in Tosa Bay, south-western Japan, one of the main spawning grounds on the Pacific coast of Japan during February and March. The growth parameter k -values of the von Bertalanffy growth equation of female sardines were small in the 1987–1990 years classes, while the values for the 1991–1992 years classes were larger, which corresponded closely with the decrease in catch of the sardines in south-western Japan, suggesting that there are density-dependent effects on the growth of sardines in Tosa Bay. In contrast, the body length decreased since the 1993 years class, but the fatness of female sardines improved after 1993. Since 1994, many I year females with transparent eggs in the ovaries have been collected from Tosa Bay. It is speculated that good nutritional conditions of the 1993 year class led to maturation at an earlier age, and that the decrease of growth from the 1993 year class occurred due to the reduction of resources channeled to growth as a result of the maturation at I year. [ABSTRACT FROM AUTHOR]

ABSTRACT: The developmental processes of the olfactory organ, taste buds, lateral line system, and inner ear in the Japanese sardine Sardinops melanostictus were examined in reared and wild specimens. Both the ciliated and microvillous receptor cells in the olfactory organ were found shortly after hatching. Formation of the olfactory nostrils and lamellae began at about 20 mm standard length (SL). The calculated inflection points in the relationship between the number of olfactory lamellae and standard length were at 30.3 and 62.7 mm SL. Taste buds first appeared in a 16.1-day-old larva of 11.2 mm notochord length. Newly hatched larvae were equipped with 12 pairs of neuromasts on the head and trunk. The formation of the lateral line canal commenced at about 20 mm SL and the four canals had ossified by 32.5 mm SL. At hatching, the inner ear was an oval-shaped auditory vesicle with two otoliths. Three semicircular canals formed by the first-feeding stage, and larvae assumed an upright position. The pro-otic bulla was gas-filled and formation of the lagena pocket began at about 20 mm SL. The saccular sac was entirely formed by about 32 mm SL. From the present results, the basic structure of the sense organs was almost completed by 32 mm SL, and the adult condition might be attained at 60–70 mm SL, as suggested by the second inflection point in the relationship between the number of olfactory lamellae and SL. [ABSTRACT FROM AUTHOR]

We determined the complete nucleotide sequence of the mitochondrial genome for a Japanese sardine, Sardinops melanostictus (Teleostei: Clupeiformes). The entire genome was purified by gene amplification using long polymerase chain reactions (PCR), and the products were subsequently used as templates for PCR with 30 sets of fish-versatile primers (including three species-specific primers) that amplify contiguous, overlapping segments of the entire genome. Direct sequencing of the PCR products demonstrated that the genome [16 881 base pairs (bp)] contained the same 37 mitochondrial structural genes (two ribosomal RNA, 22 transfer RNA, and 13 protein-coding genes) as found in other vertebrates, with the gene order identical to that in typical verte-brates. A major non-coding region between the tRNA Pro and tRNA Phe genes (1200 bp) was considered as the control (D-loop) region, as it has several conservative blocks characteristic to this region. [ABSTRACT FROM AUTHOR]