Temporal and spatial variability in growth and condition of dab (Limanda limanda) and sprat (Sprattus sprattus) larvae in the Irish Sea

Abstract

Variability in the high mortality rate during early life stages is considered to be one of the principal determinants of year-class variability in fish stocks. The influence of water column stability on the spatial distribution of fish larvae and their prey is widely acknowledged. Water column stability may also impact growth through the early life history of fishes, and consequently alter the probability of survival to maturity by limiting susceptibility to predation and starvation. As a test of this concept, the variability in condition and growth of dab (Limanda limanda) and sprat (Sprattus sprattus) larvae was investigated in relation to seasonal stratification of the water column in the north-western Irish Sea. RNA/DNA ratios and otolith microincrement analysis were used to estimate nutritional status and recent growth rates of larvae captured on four cruises in May and June of 1998 and 1999. Dab and sprat larvae were less abundant in 1999 and were in poorer condition with lower growth rates than in 1998. Dab larvae of <13 mm also exhibited spatial variability with higher RNA/DNA ratios at the seasonal tidal-mixing front compared with stratified and mixed water masses. However, the growth and nutritional status of sprat larvae was uncorrelated to water column stability, meaning the more favourable feeding conditions generally associated with the stratified pool and tidal-mixing front in the Irish Sea were not reflected in the growth and condition of these larvae. This suggests that the link between stability, production and larval growth is more complicated than inferred by some previous studies. The existence of spatio-temporal heterogeneity in the growth and condition of these larvae has implications for larval survival and the recruitment success of these species in the Irish Sea.

Larval Transport and Dispersal in the Coastal Ocean and Consequences for Population Connectivity

“…Encounter with oceanographic features such as fronts or mesoscale eddies can also influence food supply and exposure to predators (Grimes and Kingsford, 1996;Sponaugle and Pinkard, 2004). Thus, a complex oceanographic environment coupled with variable egg quality at spawning results in a pool of larvae with variable traits (Jarrett, 2003;Lee et al, 2006;). …”

“…The coarsest measures of condition often use size as a proxy (e.g., many invertebrates), while others measure organic (Jarrett, 2003) or lipid content (Hentschel and Emlet, 2000), RNA/DNA ratios (Suthers et al, 1996;Lee et al, 2006) refereNCe s…”

Multi-species larval fish growth model based on temperature and fluorometrically derived RNA/DNA ratios: results from a meta-analysis

“…Canino et al 1991, Canino 1997, Rooker et al 1997, Kimura et al 2000, Chícharo et al 2003, Catalan et al 2006, Garcia et al 2006, Lee et al 2006, Malzahn et al 2007). When fish size and water temperature between sites are similar, interpretation of results is straightforward: the group with the higher RD is in better condition since it contains more machinery (potential) for protein synthesis.…”

A novel length back-calculation approach accounting for ontogenetic changes in the fish length – otolith size relationship during the early life of sprat (Sprattus sprattus)

“…However, the use of a backcalculation model assuming a steady FL-OL relationship is often limited to the larval stage, as the shape of the FL-OL relationship may change between life stages (e.g., Takahashi et al 2008). For instance, in our case study on sprat, the larval stage is described by an allometric FL-OL relationship (Lee et al 2006), whereas a linear form is assumed for the juvenile stage (Baumann et al 2006a). Only a few approaches consider ontogenetic changes in the FL-OL relationship (Butler 1989;Laidig et al 1991;Hobbs et al 2007), allowing length reconstruction over different life stages.…”