Size-effect, asymmetry, and small-scale spatial variation in otolith shape of juvenile sole in the Southern North Sea

Abstract

While otolith shape analysis can provide a valuable tool for discriminating between fish populations, factors which may influence otolith shape, such as the effect of size, directional asymmetry in growth, and local environmental conditions, are often unknown. Here, we analyzed differences in otolith shape across three size classes of age-0 common sole Solea solea L. from nursery grounds off the Belgian coast and in the Wadden Sea. Across size classes, form-factor decreased and roundness remained consistently high in both nursery grounds, while ellipticity increased in the Belgian nursery. Directional asymmetry between left and right otoliths measured by Fourier coefficients accounted for 0.96 and 7.2% of the variance when comparing otoliths overall, and for each size class, respectively. Within the Belgian nursery, results were consistent across sampling years and locations. In addition, otolith shape was marginally different between nursery grounds, but highly variable within nursery grounds. A small divergent group, which seems partly related to fish size, was noted at both spatial and temporal scales. Based on these results and before embarking on a study of population structure using otolith shape in age-0 common sole, we recommend testing for directional asymmetry and fish size effects across the entire region of interest.

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

“…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).…”

“…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 ].…”

Complementarity and discriminatory power of genotype and otolith shape in describing the fine-scale population structure of an exploited fish, the common sole of the Eastern English Channel

“…Moreover, compared to other natural tracers, otolith shape is relatively cheap and easy to use in routine with a dedicated software. Consequently, otolith shape may suitably complement genetic analyses to capture the various scales at which dispersal processes happen [ 49 , 50 ]. Comparing tracers that integrate information at the ecological and evolutionary time scales may allow to detect spatial population structure and its stability over time [ 51 ].…”