realm, showed relatively higher PLD’s (ranging from 16 to 58 days) than the other
species considered. This result can be reliably extended to the Mediterranean
anchovy and sardine, species that were not referred to in the study. Other
benthopelagic species as the European hake have PLD of around 40 days, according
to otolith studies (Hidalgo et al. 2009, 2019).
The chances of surviving passive drift are related to the temporal duration of the
PLD, which on the other hand exhibits seasonal differences in the sense that larvae
originating during spring-summer show shorter PLDs than species developing in
autumn-winter (MacPherson and Raventos 2006). Consequently, the PLD conditions the spatial scale of a distribution which may comprise several subpopulations
(Cowen and Sponaugle 2009), although other factors are also influential. Among
them, the vital habitat (benthic versus pelagic species), or location of the spawning
grounds (inshore versus offshore) and depth of the spawning (see next section) are
noteworthy.
12.5.3 Depth Distribution and Vertical Migration
Depth of spawning and nychthemeral vertical migrations of ELHS influence the
dispersion course depending on the life cycle habitats of the species concerned.
Benthopelagic species as spotted seabream (Pagellus bogaraveo) or hake
(Merluccius merluccius), both inhabiting the Alboran Sea/Strait of Gibraltar region
and considered priority species by the General Fisheries Commission for the Mediterranean, occupy deeper layers during their life cycle. They can be exposed to two
different hydrodynamic patterns depending on the depth concerned, namely the
surface Atlantic current or the underneath Mediterranean flow, which flow in
opposite directions. If the ELHS reside at depths influenced by the surface circulation, their drift is basically to the east, whereas if they are found deeper, they would
be transported to the west and, eventually, to the Atlantic Ocean if they are advected
a long enough way/time. In contrast, epipelagic species such as sardine or anchovy
are only influenced by the surface circulation (Catalan et al. 2013; Ruiz et al. 2013)
and their ELHS have no chances to drift west through the Strait of Gibraltar into the
Atlantic, unless the coeval of the very unusual circumstances already mentioned are
exceptionally met.
Therefore, the horizontal distribution pattern of ELHS is affected by their distribution in the water column. The above-mentioned species lack specific studies on
their vertical distribution in the Alboran Sea. Nevertheless, the diel behavior of
ELHS for hake and small pelagic species inhabiting other regions of the Mediterranean may serve to exemplify their vertical distribution. Studies carried out in the NW
Mediterranean (Olivar et al. 2001; Sabates 2004) found maximum concentration of
anchovy eggs and larvae above 20 m, whereas sardine ELHS were spread over
10–40 m depth range. Despite geographic and seasonal variability differences
between both spawning ecosystems, the main features of the vertical depth distribution are very likely still representative of the Alboran Sea sardine and anchovy.
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J. Garcia-Lafuente et al.
species considered. This result can be reliably extended to the Mediterranean
anchovy and sardine, species that were not referred to in the study. Other
benthopelagic species as the European hake have PLD of around 40 days, according
to otolith studies (Hidalgo et al. 2009, 2019).
The chances of surviving passive drift are related to the temporal duration of the
PLD, which on the other hand exhibits seasonal differences in the sense that larvae
originating during spring-summer show shorter PLDs than species developing in
autumn-winter (MacPherson and Raventos 2006). Consequently, the PLD conditions the spatial scale of a distribution which may comprise several subpopulations
(Cowen and Sponaugle 2009), although other factors are also influential. Among
them, the vital habitat (benthic versus pelagic species), or location of the spawning
grounds (inshore versus offshore) and depth of the spawning (see next section) are
noteworthy.
12.5.3 Depth Distribution and Vertical Migration
Depth of spawning and nychthemeral vertical migrations of ELHS influence the
dispersion course depending on the life cycle habitats of the species concerned.
Benthopelagic species as spotted seabream (Pagellus bogaraveo) or hake
(Merluccius merluccius), both inhabiting the Alboran Sea/Strait of Gibraltar region
and considered priority species by the General Fisheries Commission for the Mediterranean, occupy deeper layers during their life cycle. They can be exposed to two
different hydrodynamic patterns depending on the depth concerned, namely the
surface Atlantic current or the underneath Mediterranean flow, which flow in
opposite directions. If the ELHS reside at depths influenced by the surface circulation, their drift is basically to the east, whereas if they are found deeper, they would
be transported to the west and, eventually, to the Atlantic Ocean if they are advected
a long enough way/time. In contrast, epipelagic species such as sardine or anchovy
are only influenced by the surface circulation (Catalan et al. 2013; Ruiz et al. 2013)
and their ELHS have no chances to drift west through the Strait of Gibraltar into the
Atlantic, unless the coeval of the very unusual circumstances already mentioned are
exceptionally met.
Therefore, the horizontal distribution pattern of ELHS is affected by their distribution in the water column. The above-mentioned species lack specific studies on
their vertical distribution in the Alboran Sea. Nevertheless, the diel behavior of
ELHS for hake and small pelagic species inhabiting other regions of the Mediterranean may serve to exemplify their vertical distribution. Studies carried out in the NW
Mediterranean (Olivar et al. 2001; Sabates 2004) found maximum concentration of
anchovy eggs and larvae above 20 m, whereas sardine ELHS were spread over
10–40 m depth range. Despite geographic and seasonal variability differences
between both spawning ecosystems, the main features of the vertical depth distribution are very likely still representative of the Alboran Sea sardine and anchovy.
476
J. Garcia-Lafuente et al.