Environmental influence on the inter-annual demographic variation of the narrownose smooth-hound shark (Mustelus schmitti, Springer 1939) in the Northern Argentine Coastal System (El Rincón, 38–42°S)

ABSTRACT

Understanding the environmental influence on the demographic structure of a shark population within a specific ecosystem has direct implications for developing effective management and conservation measures. We studied the physical environment influence on the inter-annual demographic variation of the narrownose smooth-hound shark (Mustelus schmitti) in a key coastal ecosystem. The analyses were based on the size assemblage concept of co-occurring length classes that share common traits. We used bottom-trawl datasets (n = 334) collected over 8 spring periods (1994-2012). The analyses indicated that the population was structured in eight size assemblages that represented its main ontogenetic levels. Those corresponding to sub-adult females, young adult males, and juveniles contributed to most of the population similarity. The population structure presented high (>57.7%) inter-annual dissimilarities and showed three main similarity levels with significant differences associated with a higher abundance and similarity contribution of the main assemblages. All size assemblages were more abundant in shallow (<34.5 m), warmer (>14.9 °C), and fresher (<33.24) waters. Although the temperature variations better explained the spatial distribution of abundance, the inter-annual variation in the population similarity matched the spatial coverage of low salinities (<33.5). Overall, the environmental variation explained the variability in the abundance of size assemblages in consecutive years.

KEYWORDS:

• Coastal shark
• population similarity
• population structure
• size assemblages
• Southwest Atlantic Coastal System
• temporal variability

Acknowledgements

Colleagues J. Colonello and F. Cortés, and two anonymous reviewers shared valuable comments on an earlier version of this manuscript. This work was supported by Comisión de Investigaciones Científicas de la Provincia de Buenos Aires (CIC), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), and Instituto Nacional de Investigación y Desarrollo Pesquero (INIDEP).

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

Data cannot be shared because confidentiality agreements are in place.

Additional information

Funding

This work was supported by Comisión de Investigaciones Científicas de la Provincia de Buenos Aires (CIC), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), and Instituto Nacional de Investigación y Desarrollo Pesquero (INIDEP).