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Habitat Selection Response of Small Pelagic Fish in

Different Environments. Two Examples from the

Oligotrophic Mediterranean Sea

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Angelo Bonanno *, Marianna Giannoulaki , Marco Barra , Gualtiero Basilone , Athanassios Machias ,
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Simona Genovese , Sergey Goncharov , Sergey Popov , Paola Rumolo , Massimiliano Di Bitetto ,
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Salvatore Aronica , Bernardo Patti , Ignazio Fontana , Giovanni Giacalone , Rosalia Ferreri ,
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Giuseppa Buscaino , Stylianos Somarakis , Maria-Myrto Pyrounaki , Stavroula Tsoukali ,
Salvatore Mazzola 1
1 Consiglio Nazionale delle Ricerche, Institute for Coastal and Marine Environment (IAMC), Detached Units of Capo Granitola (TP), Mazara del Vallo (TP) and Naples, Italy,
2 Hellenic Centre for Marine Research, Institute of Marine Biological Resources, Iraklion, Greece, 3 Russian Federal Research Institute of Fisheries and Oceanography
(VNIRO), Moscow, Russia, 4 Consiglio Nazionale delle Ricerche (CNR), Roma, Italy
Abstract
A number of scientific papers in the last few years singled out the influence of environmental conditions on the spatial
distribution of fish species, highlighting the need for the fisheries scientific community to investigate, besides biomass
estimates, also the habitat selection of commercially important fish species. The Mediterranean Sea, although generally
oligotrophic, is characterized by high habitat variability and represents an ideal study area to investigate the adaptive
behavior of small pelagics under different environmental conditions. In this study the habitat selection of European anchovy
Engraulis encrasicolus and European sardine Sardina pilchardus is analyzed in two areas of the Mediterranean Sea that largely
differentiate in terms of environmental regimes: the Strait of Sicily and the North Aegean Sea. A number of environmental
parameters were used to investigate factors influencing anchovy and sardine habitat selection. Acoustic surveys data,
collected during the summer period 2002–2010, were used for this purpose. The quotient analysis was used to identify the
association between high density values and environmental variables; it was applied to the entire dataset in each area in
order to identify similarities or differences in the ‘‘mean’’ spatial behavioral pattern for each species. Principal component
analysis was applied to selected environmental variables in order to identify those environmental regimes which drive each
of the two ecosystems. The analysis revealed the effect of food availability along with bottom depth selection on the spatial
distribution of both species. Furthermore PCA results highlighted that observed selectivity for shallower waters is mainly
associated to specific environmental processes that locally increase productivity. The common trends in habitat selection of
the two species, as observed in the two regions although they present marked differences in hydrodynamics, seem to be
driven by the oligotrophic character of the study areas, highlighting the role of areas where the local environmental regimes
meet ‘the ocean triad hypothesis’.
Citation: Bonanno A, Giannoulaki M, Barra M, Basilone G, Machias A, et al. (2014) Habitat Selection Response of Small Pelagic Fish in Different Environments. Two
Examples from the Oligotrophic Mediterranean Sea. PLoS ONE 9(7): e101498. doi:10.1371/journal.pone.0101498
Editor: Brian R. MacKenzie, Technical University of Denmark, Denmark
Received December 5, 2013; Accepted June 6, 2014; Published July 3, 2014
Copyright: ß 2014 Bonanno et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits
unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funding: This study was supported by the Commission of the European Union through the MEDIAS Project, Italian Data Collection Program, and Greece Data
Collection Program. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing Interests: The authors have declared that no competing interests exist.
* Email: angelo.bonanno@cnr.it

Introduction preferences are species specific and largely depend on local area
conditions. Moreover, even when the same environmental variable
During the last few years the identification of suitable habitat for are found influential among different areas, the preferred ranges
pelagic fish species represented one of the prominent challenges in
may vary considerably. The Mediterranean Sea is generally
fishery research community [e.g. 1–4]. Even though it is widely considered an oligotrophic area, being at the same time highly
accepted that the habitat selection by fish species follows the ‘‘ideal
heterogeneous in terms of hydrography, bathymetry and produc-
and free distribution’’ theory [5], a large number of factors can tivity. Anchovy (Engraulis encrasicolus) and sardine (Sardina pilchardus)
modulate this tendency, making it difficult to interpret the way fish
population dynamics and distribution patterns are known to be
species select their own ‘‘favorable’’ habitat in different sea areas. strongly dependent on the environment [4,15], representing an
Several studies have been focused recently on small pelagic fish
important amount of the total small pelagic fish catches in the
(mainly sardine and anchovy) habitat selection by means of Mediterranean [16].
different methodologies: generalized additive modeling [e.g.
In the current work, a large environmental dataset, composed
1,3,4,6,7], quotient analysis [e.g. 8–11], randomization tests [e.g, by in situ measurements and satellite data, is used to study and
12,13] and geostatistical analysis [e.g. 14]. Environmental
PLOS ONE | www.plosone.org 1 July 2014 | Volume 9 | Issue 7 | e101498