Comparing otolith shape descriptors for population structure inferences in a small pelagic fish, the European sardine Sardina pilchardus (Walbaum, 1792)

Abstract

Otolith shape analysis has been one of the most used approaches to study population structure in the past decades. Currently, two sets of shape descriptors are used to perform otolith shape analysis, namely, Elliptic Fourier descriptor (EFd), which focuses on the overall otolith shape differences, and Discrete Wavelet descriptor (DWd), which is sensible to local differences along the otolith contour. Here, the authors conducted a comparative analysis of the performance of both the descriptors in reconstructing the population structure and connectivity patterns in a small pelagic fish species with a wide geographical distribution and fast growth rate, the European sardine Sardina pilchardus (Walbaum, 1792), for the first time. A combination of each otolith shape descriptor and shape indices was explored using multivariate statistical methods. The two otolith shape descriptors showed similar, although limited, overall classification success associated with the population dynamic characteristics of the species. Both descriptors point to migration among adjacent areas, such as northern Atlantic locations, eastern Mediterranean and even across well-defined physical obstacles, such as the Strait of Gibraltar, among Atlantic and western Mediterranean locations. Both descriptors supported the division of the populations of Mediterranean waters into three main groups but slightly differed in the group limits of the Atlantic waters. A comparison of the present results with those from previous otolith shape analysis studies using EFd on a decadal time scale revealed differences in the population structure and connectivity patterns compared to the earlier period.These differences not only may be attributed to changes in environmental variables leading to changes in population dynamics but can also be the result of the sardine biomass sharp decrease that occurred in the past decade.

Population Genomics Reveals the Underlying Structure of the Small Pelagic European Sardine and Suggests Low Connectivity within Macaronesia

“…Interestingly, one of these regions includes genes related to otolit formation. Otolith shapes have been found to divide Atlantic and Mediterranean sardine [27] and support subdivisions within the Mediterranean populations [68]. We observe that the FST values for this genomic region are very high compared to the average genome wide value when including the Aegean population (Figure S3).…”

“…We observed that the F ST values for this genomic region are very high compared to the average genome-wide value when including the Aegean population (Figure S3). This is also valid when comparing with the Adriatic population (Figure 5), which could potentially contribute to the observed regional anatomical divergence within the Mediterranean [68]. Future work, including larger sampling sizes and associated phenotype information, is required to assess how variation in specific regions of the genome affects phenotypes of interest for fisheries and stock assessment.…”

Geographic Variation in Opisthonema oglinum (Lesueur, 1818) in the Southeastern Brazilian Bight Inferred from Otolith Shape and Chemical Signatures

“…This was probably the source of bias in the EFD analyses, which were less accurate in relation to MES and EFD + MES, presenting the most between-areas mixing (HCA), the smallest percentage of reclassification (DFA), and the highest p-value in the MANOVA, even being significant. Notwithstanding, the EFD is an up-to-date approach used to successfully study the spatial discrimination of fish groups, including small pelagic fishes [13,[91][92][93][94].…”

Genomic analysis of NE Atlantic sardine (Sardina pilchardus) reveals reduced variation in a recently established North Sea population and directs reconsideration of management units

“…Here, three stocks are described, a Northern stock (Celtic Sea to English Channel), a Central Stock (Bay of Biscay) and a Southern Stock (spanning the Cantabrian Sea to the Gulf of Cadiz) (ICES, 2019 ). However, the validity of current management boundaries is a matter of debate as there is no consensus as to the species' biological population structure (reviewed in Neves et al., 2021 , 2023 ). The numerous phenotypic based studies (e.g.…”