Otolith shape analysis of the European sardine Sardina pilchardus from Atlantic and Mediterranean waters: connectivity and population density
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1
Portuguese Institute of Ocean and Atmosphere (IPMA), Portugal
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2
Centro de Investigação em Biodiversidade e Recursos Genéticos, Universidade de Évora, Portugal
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3
Faculty of Sciences, University of Porto, Portugal
The European sardine - Sardina pilchardus (Walbaum, 1792) - is a small pelagic fish that occurs from the Northeast Atlantic to the south of Cape Verde. In Portugal, sardines are of high cultural importance and constitute the largest national fishing resource in terms of landed biomass per year and overall commercial value. Recent data on landings statistics and recruitment estimates, indicates that the Atlanto-Iberian sardine stock is declining, reflecting the strong reduction in total biomass, estimated to be 75% below the historical average. Like other species of the Clupeidae family, sardines suffer large population fluctuations due to natural causes, the effects of fishing and environmental drivers such as climate change and pollution should be investigated. Currently, for management purposes, a single stock is considered in the Atlanto-Iberian Peninsula. If there is evidence of population structure at the geographical level in this area, is critical to assess the connectivity between stocks (i.e. the rate of exchange of individuals between stocks as measured by genetic flux). The objective of this work is to contribute to the knowledge of population structure of sardines using otolith morphometry. Otoliths from historical IPMA collections were analyzed, during contrasting years of population biomass to study if connectivity is dependent of density. The methods used to evaluate the shape of the otoliths included multivariate statistical analyzes of descriptive otolith information. Each sample digitized image was analyzed and general shape parameters were extracted, as area, perimeter, maximum length, and maximum width, as well as shape indices including circularity, eccentricity, area, perimeter, shape factor, and annual growth increments.
This work is part of the project (SARDINOMICS, Mar2020) which intends to evaluate the genetic structure of the populations and their connectivity, allowing the identification of sardine stocks and, using historical samples, estimate the temporal variability of the sardine populations in the national territory, comparing the results derived from molecular and genetic techniques, with the information obtained by traditional techniques using otolith morphometry. This will allow to evaluate the degree of correspondence between methodologies and allowing to evaluate the spatial and temporal consistency of the stocks. This project is based on the experience of a multidisciplinary team, with research evidence, both in research on the important resource that is sardine, fish genomics, but also in advanced joint training. The results of this project, especially the methodologies that support it, will be integrated into the implementation of Directive 2008/56/EC of the European Parliament and of the Council of 17 June 2008 establishing a framework for community action in the field of marine environmental policy (Marine Strategy Framework Directive), which relates to one of the qualitative descriptors for the definition of good environmental status, in particular "The populations of all commercially exploited fish and molluscs are within safe biological limits, presenting a population distribution by age and size indicative of a good state of existences".
The expected final results are geographic structuring at the geographical level (stocks genetically distinct), corroborated by analyzes of the structure and shape of otoliths; and occurrence of reproductive isolation of stocks (connectivity). If these results are confirmed, it will be important to analyze and interpret sardine stocks at a local/population level, rather than a single sardine stock in the Iberian Peninsula, as at present.
References
Campana, Steven E., and John M. Casselman. "Stock discrimination using otolith shape analysis." Canadian Journal of Fisheries and Aquatic Sciences 50.5 (1993): 1062-1083.
ICES (2013) Report of the Working Group on Southern Horse Mackerel, Anchovy, and Sardine (WGHANSA), 21–26 June 2013, Bilbao, Spain. ICES CM 2013/ACOM:16, 544 pp.
Jemaa, S., Bacha, M., Khalaf, G., Dessailly, D., Rabhi, K. and Amara, R. (2015) What can otolith shape analysis tell us about population structure of the European sardine, Sardina pilchardus, from Atlantic and Mediterranean waters? Journal of Sea Research, 96: 11–17.
Mapp J., E. Hunter, J. van Der Kooij, S. Songer and M. Fisher (2017) Otolith shape and size: The importance of age when determining indices for fish-stock separation. Fisheries Research 190: 43–52.
Keywords:
Sardina pilchardus,
Population connectivity,
Otolith morphometrics,
North east atlantic,
Mediterraenan sea,
Shape Analysis
Conference:
XVI European Congress of Ichthyology, Lausanne, Switzerland, 2 Sep - 6 Sep, 2019.
Presentation Type:
Oral
Topic:
OTOLITHS AS A TOOL TO STUDY FISH LIFE CYCLES
Citation:
Neves
JB,
Silva
AA,
Moreno
A,
Veríssimo
A,
Santos
AM and
Garrido
S
(2019). Otolith shape analysis of the European sardine Sardina pilchardus from Atlantic and Mediterranean waters: connectivity and population density.
Front. Mar. Sci.
Conference Abstract:
XVI European Congress of Ichthyology.
doi: 10.3389/conf.fmars.2019.07.00092
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Received:
21 Jun 2019;
Published Online:
14 Aug 2019.
*
Correspondence:
Mr. João B Neves, Portuguese Institute of Ocean and Atmosphere (IPMA), Lisbon, Portugal, jfbneves@gmail.com