Use of otolith-shape analysis for stock discrimination of Boops boops along the Algerian coast (southwestern Mediterranean Sea)

Abstract

Otolith-shape analysis was examined to determine its utility for biological stock identification of the bogue Boops boops along the Algerian coast of the Mediterranean Sea. The outlines of 179 sagittal otolith pairs from fish collected at three locations (Oran, Bejaia and Annaba) between 2013 and 2016 were digitised and analysed for shape variation by elliptical Fourier analysis. Potential confounding sources of variation (fish length, age and sex, and left or right otolith position) were examined and accounted for in the analyses before interpretation of spatial differences in distribution of the stock. Redundancy analysis showed a significant difference between the left and right otoliths. No difference was correlated with sex and age, but fish length and sampling location had a significant effect on otolith shape. Differences in otolith shape between fish from the three locations (a span of approximately 1 000 km) were not large enough to support the concept of separate biological stocks of B. boops along the Algerian coast, as illustrated by the scatterplot of discriminant scores. This study emphasises the need to carefully evaluate the confounding effects of the otolith side (left or right) on the Fourier descriptors of otoliths before drawing conclusions about stock structure of the bogue on the basis of otolith-shape differences among samples of fish from different stocks or areas.

Stock discrimination of the bogue, Boops boops (Actinopterygii: Perciformes: Sparidae), from two Tunisian marine stations using the otolith shape

“…Elliptic Fourier analysis of the otolith contour shape revealed a clear asymmetry between the left and right sides within and between the fish samples in the two localities. These results are consistent with those previously cited on the sparid Oblada melanura (Linnaeus, 1758) (see Barhoumi et al 2018), Diplodus annularis (see Trojette et al 2015), and Pagellus erythrinus (see Mejri et al 2018Mejri et al , 2020, which are cohabiting different habitats in Tunisian waters, as well as on the B. boops sampled from three locations along the Algerian coast (Ider et al 2017) and from the Gulf of Tunis (Mahé et al 2019). Similarly, the asymmetry of the otolith shape has also been found in other species that live elsewhere outside of Tunisian waters, such as Gadus morhua Linnaeus, 1758 (see Campana andCasselman 1993, Hüssy et al 2016) Khemiri et al 2018).…”

“…In addition, this species is demersal, as well as semi-pelagic, gregarious, and lives on all types of the bottom substrata, including mud, rock, sand, and seagrass beds (Simsek et al 2018). However, it is commonly found at depths between 50 and 350 m and in coastal waters, it sometimes moves in aggregations, ascending mainly to the surface at night (Ider et al 2017). Pollard et al (2014) mentioned that B. boops grows rapidly in length during the first year of life, where it reaches 53.49% of its final length of growth and can live up to seven years.…”

“…Jawad (2003) analyzed the asymmetry in some bilateral characters of samples collected from coastal waters near Benghazi City, Libya, and found the highest level of asymmetry in the postorbital length character, while he observed the lowest level in the eye lens diameter and weight. Also, Ider et al (2017) analyzed the variability of otolith shape in three populations of B. boops collected from the Algerian coast and observed a significant difference between the left and right otoliths and added that the shape is influenced by the fish length and the sampling location, but it is not related to sex and age. In addition, Ferri et al (2018) studied the variability of the otolith morphology and morphometry in six juvenile specimens collected from the eastern coastal Adriatic region and recorded variations in the sagittae shape, margins, and anterior region among the studied juveniles.…”

Directional bilateral asymmetry in otolith morphology may affect fish stock discrimination based on otolith shape analysis

“…This stock structure is similar to that observed for other species in the same areas such as sardine or cephalopods (see Jemaa et al, 2015;Keller et al, 2017). Ider et al (2017) analyzing only the data from the Algerian coasts, identified only one stock for this area just as the present study conducted at much larger geographic scale, which indicates consistency of otolith shape-based stock discrimination across multiple geographic scales. Factors structuring bogue stocks at the level of the Mediterranean region seem to be linked to environmental features, notably physical oceanographic characteristics of the studied area.…”

Otolith fluctuating asymmetry inBoops boops(Actinopterygii, Sparidae) from two marine stations (Bizerte and Kelibia) in Tunisian waters

“…In addition, this is a demersal species, as well as semi-pelagic, gregarious, and lives on all types of the bottom substrata, including mud, rock, sand and seagrass beds (Ceyhan et al, 2018;Şimşek et al, 2018). It is commonly found at depths between 50-350 m and in coastal waters, it sometimes moves in aggregations, ascending mainly to the surface at night (Rachid et al, 2014;Ider et al, 2017). Pollard et al (2014) reported that B. boops grows rapidly in length during the first year of life, where it reaches 53.49% of its final growth length and can live up to 7 years.…”