A model study of the large-scale transport of fish eggs in the Kattegat in relation to egg density

Abstract

Pacariz, S., Björk, G., Jonsson, P., Börjesson, P., and Svedäng, H. 2014. A model study of the large-scale transport of fish eggs in the Kattegat in relation to egg density. – ICES Journal of Marine Science, 71: 345–355. A process-oriented model, with high vertical resolution, has been used to investigate variation in the transport of fish eggs and early larvae in relation to egg density. The main focus is on gadoid eggs from the spawning grounds in the southern Kattegat. Additionally, transport from the neighbouring areas, the central Kattegat and Öresund, is presented. The model results clearly indicate that transport is dependent on the egg density; lighter eggs are transported northwards whereas heavier eggs are to a larger extent retained or transported southwards. This study suggests that optimum densities in order to promote retention in the southern Kattegat are in the range of 1023–1026 kg m−3. Observations from 2005 and 2006 of the vertical distribution of gadoid eggs combined with hydrographical data indicated high concentrations of eggs at the upper part of the pycnocline at densities of 1017–1022 kg m−3. Combining the observations and modelling results on amount of dispersal and retention, suggests that gadoid eggs are mainly retained in the southern Kattegat (although shifted from maximum retention density) and simultaneously dispersed northwards. Even though the results of the study are described in the context of gadoid eggs, the results are applicable for other marine species with pelagic stages and buoyant particles within the tested density range.

Recent decline in cod stocks in the North Sea–Skagerrak–Kattegat shifts the sources of larval supply

“…High egg retention in Kattegat was also suggested by a box model in Pacariz et al (2014). The present study differs from most previous model studies of dispersal in cod (e.g., Pacariz et al, 2014) as it, in addition to egg drift, also includes the 3-4 times longer larval phase and, therefore, better predicts the connectivity and Figure 7. Relationship between winter North Atlantic Oscillation index (Hurrell NAO index, based on principal components) and the connectivity between central North Sea and the Norwegian Skagerrak for the modelled 6 yrs (correlation coefficient = 0.97, P = 0.01).…”

“…High egg retention in Kattegat was also suggested by a box model in Pacariz et al . (). The present study differs from most previous model studies of dispersal in cod (e.g., Pacariz et al ., ) as it, in addition to egg drift, also includes the 3–4 times longer larval phase and, therefore, better predicts the connectivity and retention of the whole dispersal phase.…”

“…(). The present study differs from most previous model studies of dispersal in cod (e.g., Pacariz et al ., ) as it, in addition to egg drift, also includes the 3–4 times longer larval phase and, therefore, better predicts the connectivity and retention of the whole dispersal phase. Local retention in Kattegat was surprisingly stable across years and relatively insensitive to drift depth, although surface drifters resulted in lower local retention reflecting the export to Skagerrak in the Baltic surface current.…”

“…Larval traits such as drift depth and pelagic larval duration (PLD) can have a large effect on dispersal and connectivity, in particular in areas where the water column is strongly stratified, such as in the Kattegat/ Skagerrak region, resulting in depth-specific dispersal trajectories (Corell et al, 2012;Moksnes et al, 2014;Myksvoll et al, 2014;Pacariz et al, 2014). In the present study, we used the literature and monitoring data of temperature and salinity to select spawning period, drift depth and pelagic duration of cod eggs and larvae for the model study (S3 in Appendix S1 for details).…”

The influence of discharge, current speed, and development on the downstream dispersal of larval nase (Chondrostoma nasus) in the River Danube

“…The movement (or dispersal) of early life history stages of fishes (i.e., eggs, free embryos, larvae) from spawning sites to appropriate rearing habitats affects the survival and fitness of the individual and, consequently, year-class strength, probability of completion of the life cycle, and population health (Daewel et al 2011;Hinrichsen et al 2012). The dispersal of eggs can generally be described using passively drifting particles (Dudley and Platania 2007) or 3D hydrodynamic models (Peck et al 2009;Pacariz et al 2014). For a long time, the same was also assumed for larvae, because of their presumed poorly developed behavioural, physical, and sensory capabilities (Brown and Armstrong 1985;Roberts 1997).…”