Extensive larval dispersal and restricted movement of juveniles on the nursery grounds of sole in the Southern North Sea

Abstract

Connectivity between spawning and nursery grounds influences the colonization, replenishment and resilience of populations of marine organisms. Connectivity rate, measured as the exchange of individuals between spawning and nursery grounds, is therefore a crucial determinant of stock size. However, connectivity of early-life stages is hard to explore due to sampling limitations and insufficient knowledge on potential larval sources. Here we present new insights into pre-and post-settlement dispersal of the common sole (Solea solea L.) at a spatial scale of 5-500 km in the Southern North Sea. Patterns at a scale of <100 km were considered local, whereas patterns further than 100 km were considered regional. Multi-elemental signatures of the otolith edge of 213 juvenile sole were used to discriminate at 79% of overall accuracy three main nursery grounds in the Southern North Sea, namely UK coast, Belgian coast and Dutch Wadden Sea. Interregional differences in otolith composition (especially for Mg, Mn and Ba) suggest that sole migration following settlement is limited in the Southern North Sea. Elemental signatures of the same fish indicated mixing during larval dispersal. Each nursery ground recruited an important mix of juveniles from three of the four chemically distinct natal sources identified from the larval otolith signatures. However the percentage of correct regional re-assignment varied from 67 to 80% with a maximum in the Wadden Sea. The results contributed to the validation of biophysical models of larval drift. Our findings support decision making for both fisheries management and marine spatial planning at the national and European level. Highlights ► In the North Sea, juvenile otolith signatures differ at the regional scale (100 km). ► Movement appears to be limited once the juveniles have reached a nursery ground. ► Local nursery areas receive larvae from four chemically distinct natal sources. ► Mixed larval contributions to nurseries point to an extensive larval dispersal.

Validating a biophysical dispersal model with the early life-history traits of common sole (Solea solea L.)

“…Juvenile sole were collected between August and October in 2013 and 2014 in Belgian coastal waters, with the exception of one sample collected in May 2014, from the Netherlands in September 2014, and from the UK in March 2016 ( Fig 1 , Table 1 ). These coastal areas were chosen as they represent three major sole nursery grounds in the Southern North Sea, which are known to be reached by larvae coming from different spawning grounds [ 5 , 16 ]. The spatio-temporal differences in sampling locations and periods were largely driven by the opportunistic design of the study, with sole juveniles collected from different sampling surveys in the frame of different projects.…”

“…Over all samples, 402 juvenile sole were collected, measured and weighed, and immediately immersed in ice to be sacrificed by hypothermia. In total, 154 juvenile sole were selected for otolith extraction (on average 45% of the juveniles sampled at each sampling location or moment), of which the left otoliths have been used for elemental footprint and shape analysis, published in parallel studies [ 5 , 20 ], while the right-side otoliths were used in this study for daily growth ring analyses. The standard length of the selected individuals was representative for the overall sampled sole cohort per location (average standard length and standard deviation per location highly comparable with the overall averaged standard length and standard deviation (84.76 ± 14.46 mm) of the total fish sampled).…”

“…This variability is induced by an interaction of biological traits with hydrodynamics and other biotic and abiotic factors [ 3 , 4 ]. Movements of larvae and juveniles from the spawning to the nursery grounds are key to the survival of species with a planktonic larval phase and non-migratory adult populations, as connectivity between these grounds determines the distribution of the species and the existence of metapopulations [ 5 ]. Efficient management strategies rely on the understanding of early life dynamics and conditions [ 5 , 6 ].…”

“…The Larvae&Co model, which combines local hydrodynamics and larval active behaviour, predicts larval dispersal of sole from six main spawning grounds towards the associated nursery grounds within the southern North Sea and English Channel [ 3 , 13 , 14 ]. Delerue-Ricard et al [ 5 ] confirmed four natal sources for juvenile sole, based on otolith microchemistry, testifying a certain level of connectivity between spawning and nursery grounds. Chemical signatures associated with the juvenile nursery phase suggest limited movement after settlement and high residency in each nursery along the North Sea coast [ 5 , 20 , 21 ].…”

“…Delerue-Ricard et al [ 5 ] confirmed four natal sources for juvenile sole, based on otolith microchemistry, testifying a certain level of connectivity between spawning and nursery grounds. Chemical signatures associated with the juvenile nursery phase suggest limited movement after settlement and high residency in each nursery along the North Sea coast [ 5 , 20 , 21 ].…”