Page 8 - Habitat_Selection_2014

Habitat Selection Response of Anchovy and Sardine

Figure 4. Sardine distribution maps in the North Aegean Sea (upper part) and in the Strait of Sicily (lower part). Symbols size is
proportional to the abundance of strictly positive values, while zero values are omitted.
doi:10.1371/journal.pone.0101498.g004
Similar behavior is evidenced in terms of the UML thickness, North Aegean Sea sardine does not seem to be influenced by this
BL temperatures and PED by both species in the two study areas, parameter, whereas anchovy avoids lower values and selects the
despite selection/avoidance ranges slightly varies (Fig. 6). Partic- ones in the range 6–7 cm.
ularly, in both areas lower UML thickness values are selected and In order to highlight the presence of structure in the
higher ones are avoided, as well as higher BL temperatures are environmental dataset, PCA analysis has been used. PCA results
selected a lower avoided. Concerning the PED parameter, all cases show that in both study areas the first two factors account
show a preference for lower values, reflecting the selection of less approximately for 50% of the total variability and can be related
stratified waters, as well as an active (i.e. significant) avoidance of to specific processes. Particularly, in the Strait of Sicily (Table 5a)
th
high stratified ones. Notably sardine in both areas shows similar lower values on the 1 PC (hereafter PC1), explaining 37% of the
selection behavior, selecting PED values lower than 150 kg variance, correspond to lower PED, UML thickness, bathymetry
s
m 22 22 . and MADT as well as to higher CDOM, CHL sat and POC, and
The analysis of quotient curves obtained for satellite parameters could be linked to areas influenced by weak coastal upwelling.
(Fig. 7) highlights similar behavior for both species concerning the Conversely, the second PCA axis (PC2), accounting for an
CDOM index, POC and Chl sat in both areas, despite selection/ additional 15% of the variance, is mostly related to water masses
tolerance/avoidance ranges varies according to the environmental dynamics and specifically to variables like KE, salinity (both UML
differences characterizing the two study areas. Anchovy and and BL) and MADT. Differently from Sicily waters, in North
sardine select higher CDOM index, POC and Chl sat values and Aegean Sea PCA analysis (Table 5b) highlights two different
avoid lower ones (Fig. 7). Quotient curves for KE (Fig. 7) highlight processes driving food availability. Higher values on the first PCA
in the North Aegean Sea a clear selective behavior for lower KE axis (explaining 29% of the variance) coincide with higher food
values by both species, indicating a preference for less intense availability (higher CDOM, CHL sat and POC), UML temperature
water movements. In the Strait of Sicily, mainly due to the and MADT, as well as lower column water salinity and UML
occurrence of high water masses dynamics, sardine clearly shows thickness, and could be related to the presence of BSW.
an avoidance behavior for high KE values, while anchovy seems to Furthermore, lower values on the second PCA axis (explaining
2
2
select an intermediate range of KE (130–210 cm /s ). As regards 19% of the variance) are linked to higher CHL sat , POC and BL
PAR, in the Strait of Sicily both species do not show any clear temperature as well as to lower PED and depth, thus identifying
selection behavior. In North Aegean Sea waters low PAR values coastal enriched areas that could be affected by the formation of a
(,55 Einsteins m 22 day 21 ) are actively selected, while higher PAR weak coastal upwelling.
values are avoided. In a further step, and in order to demonstrate the association
The selectivity curves related to MADT clearly show a different between identified processes and habitat suitability of anchovy and
situation between the two areas. In the Strait of Sicily both species sardine, a QI analysis (Fig. 8) has been performed on the PCA
avoid MADT values higher than 6 cm, while a selection is shown factor coordinates (i.e. the observation values on each PCA axis
for waters presenting MADT between 22 cm and 0 cm. In the obtained after the system was rotated and centered). The results

PLOS ONE | www.plosone.org 8 July 2014 | Volume 9 | Issue 7 | e101498