Spawning habitat and daily egg production of sardine (Sardina pilchardus) in the eastern Mediterranean

Abstract

Spawning habitats of two eastern Mediterranean sardine, Sardina pilchardus (Walbaum, 1792), stocks (coastal waters of central Aegean and Ionian Seas) are characterized from daily egg production method (DEPM) surveys conducted during the peak of the spawning period. The latter occurs earlier in the Aegean Sea (December) than in the less-productive Ionian Sea (February). Single-parameter quotient analysis showed that the preferred bottom depth for spawning was 40-90 m in both areas but sardine selected sites of increased zooplankton in the Aegean Sea during December and increased fluorescence in the Ionian Sea during February. Estimates of daily egg production (P) and spawning stock biomass (B) were about four times lower for the Ionian Sea (P ¼ 7.81 eggs m )2 , B ¼ 3652 tonnes) than the Aegean Sea (P ¼ 27.52 eggs m )2 , B ¼ 16 174 tonnes). We suggest that zooplankton biomass might not be sufficient to support sardine reproduction in the highly oligotrophic Ionian Sea where the very small sardine stock may rely on the late-winter phytoplankton bloom. Actively selecting sites with increased zooplankton or phytoplankton and feeding plasticity (the well-known switching from selective particle feeding to non-selective filter feeding in sardines) are interpreted as adaptations to grow and reproduce optimally at varying prey conditions. Despite differences in temperature and productivity regimes, reproductive performance of sardine in the Ionian Sea was very similar to that in the Aegean Sea during the peak of the spawning period. In comparing adult parameters from DEPM applications to Sardina and Sardinops stocks around the world, a highly significant linear relation emerged between mean batch fecundity (F) and mean weight of mature female (W, g) (F ¼ 0.364W, r 2 ¼ 0.98). The latter implies that, during the peak of the spawning period, mean relative batch fecundity (eggs g )1 ) of sardine is fairly constant in contrasting ecosystems around the world.

Distribution and abundance of fish larvae in the northern Ionian Sea (Eastern Mediterranean)

“…Patterns of larval fish distribution originate from complex spatial and temporal interrelationships that are strongly affected by the seasonality and duration of their meroplanktonic existence (Olivar et al 1998;Koutrakis et al 2004;Palomera et al 2005). Several studies have focused on how biological processes such as high food concentrations, low predator stocks, and certain hydrographic features regulate the distribution and abundance of planktonic organisms, including fish larvae Somarakis et al 2000Somarakis et al , 2006, even if biological-physical interactions are considered to be more important than purely biological forcing mechanisms (Cuttitta et al 2004;Sabates 2004). It has been shown that coastal environments often constitute favourable habitats for the early life stages of fishes living in different marine ecosystems (McGowen 1993), representing nursery areas for species exhibiting distinct spawning habits (e.g.…”

Global-scale distributions of marine surface bacterioplankton groups along gradients of salinity, temperature, and chlorophyll: a meta-analysis of fluorescence in situ hybridization studies

“…The collected data of bacterial group relative abundances and environmental parameters such as chl a concentration, temperature, and salinity were used to estimate the 'preferred' range of environmental parameters for each bacterial group using a quotientrule analysis (QRA, Somarakis et al 2006). Each envi ronmental variable was divided into regular intervals for which the frequencies of occurrence were calculated and expressed in percentages.…”

Poorer breeding by little penguins near Perth, Western Australia is correlated with above average sea surface temperatures and a stronger Leeuwin Current

“…It is no surprise then that peak spawning activity of small pelagic clupeid fish, such as pilchard (Sardinops sagax) and anchovy (Engraulis australis), generally occurs when offshore transport is low and larval food concentrations are high (Somarakis et al 2006;Muhling et al 2008a). These fish species, as well as sandy sprat (Hyperlophus vittatus), blue sprat (Spratelloides robustus) and garfish (Hyporhamphus melanochir), comprise the majority of the diet of the penguins from Penguin Island (Klomp and Wooller 1988a;Wienecke 1989;Wooller et al 1991;Connard 1995;Bradley et al 1997;Murray et al 2011).…”