| Abstract |
The main objective of the present project was to characterize the spawning habitat
of the European anchovy, Engraulis encrasicolus, in the North Aegean Sea and how this
is affected by seasonal changes in the biotic and abiotic environment. Ichthyoplanktonic
and acoustic sampling was carried out in late spring (May) and mid summer (July) 2010,
i.e. during the beginning and peak of the spawning period of anchovy. Differences were
observed between the two periods concerning the productivity and major hydrographic
features (intensity of Black Sea Water [BSW] inflow). The spawning intensity was
remarkably low in May, and this could be explained in terms of low mesozooplankton
biomass in spite of increased phytoplankton concentration during the same period. In
July, eggs and larvae were observed over the entire study area, and higher abundances
seemed to be related to the presence of BSW.
In order to develop robust statistical models of the spawning habitat, apart from the 2010
cruises, a series of past datasets were also used concerning the North Aegean Sea and the
period of June-July (2003-2006, 2008). Two types of parameters were used as
explanatory variables: (a) in situ data collected during the sampling cruises (CTD,
mesozooplankton biomass), and (b) output parameters of the biogeochemical model
POM-ERSEM, operating within the POSEIDON Operational System
(www.poseidon.hcmr.gr). Generalized Additive Models (GAMs) were used to model
anchovy spawning habitats. Models were built based on ichthyoplankton as well as
acoustic (adult) presence/absence data and were developed separately for each month and
for the eastern (Stratum I) and western (Stratum II) part of the study area. Differences
were observed between the two Strata and among different months concerning the
explanatory variables that were most important in characterizing the anchovy spawning
habitat. Both types of explanatory variables performed well in describing the association
between the environment and the presence/absence of eggs and adults, and in predicting
the probability of anchovy presence.
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Χαρακτηρισμός του αναπαρωγικού ενδιαιτήματος του ευρωπαϊκού γαύρου Engraulis encrasicolus στο Β. Αιγαίο με τη χρήση στατιστικών μοντέλων
