The relationship between Sardinella aurita landings and the environmental factors in Moroccan waters (21°-26°N)

2019·2.2 MB·English

by  Baali, A

Scientific paper
The relationship between Sardinella aurita landings and
the environmental factors in Moroccan waters (21°-26°N)
by
Ayoub BAAli* (1), Najib ChArouki (2), khalid MANChih (2), ismail BessA (3), ikram elqorAyChy (1),
Mouna elqeNdouCi (1), khadija AMeNzoui (2) & Ahmed yAhyAoui (1)
Abstract. – The objective of this study is to assess the effects of environmental variations on the abundance of
the round sardinella (Sardinella aurita, Valenciennes, 1847) in Moroccan waters (21°-26°N) using generalized
additive models. The monthly variability of Sardinella aurita abundance in the south of Morocco is investigated
using sea surface temperature (ssT), upwelling index (ui) and chlorophyll-a (Chl-a) concentration from Global
ArMor3d l4 product, esA ocean Colour CCi and AquaModis satellite data between 2009 and 2016. The
results show that there is a significant correlation between fish landings, ssT and Chl-a, especially at latitude
22°N. Concerning the UI, the correlation is positive and not significant at latitudes 21 and 22°N. The relationship
between the environmental parameters indicate that there is a high and significant correlation between the SST
and Chl-a at latitude 22°N. using generalized additive models, it was found that environmental parameters (ssT,
Chl-a, and ui) in the latitude 22°N played a major role in explaining differences in monthly landings for S. aurita
(65.1% deviance explained). The high abundance of S. aurita, observed in autumn, is due to the adequate envi-
© SFI
Submitted: 1 May 2018 ronmental condition in the south of Morocco, which leads to the migration of this species from Mauritanian to
Accepted: 18 Jan. 2019 Moroccan waters.
Editor: O. Otero
résumé. – la relation entre les débarquements de Sardinella aurita et les facteurs environnementaux dans les
eaux marocaines (21°-26°N).
Key words
l’objectif de cette étude est d’évaluer les effets des variations environnementales sur l’abondance de la sar-
Chlorophyll-a
dinelle ronde (Sardinella aurita, Valenciennes, 1847) dans les eaux marocaines (21°-26°N) à l’aide du modèle
Fish landings
additif généralisé. la variabilité mensuelle de l’abondance de Sardinella aurita dans le sud du Maroc est étudiée
Moroccan waters
en utilisant la température de la surface de la mer (ssT), l’indice d’upwelling (ui) et la concentration en chloro-
Sardinella aurita
phylle-a (Chl-a) du produit Global ArMor3d l4, esA ocean Colour CCi et les données satellitaires d’Aqua-
sea surface temperature
MODIS, durant la période 2009-2016. Les résultats montrent qu’il existe une corrélation significative entre les
upwelling index
débarquements de la sardinelle ronde, la ssT et la Chl-a, surtout au niveau de la latitude 22°N. Concernant l’ui,
la corrélation est positive et non significative aux latitudes 21 et 22°N. La relation entre les paramètres environ-
nementaux indique qu’il existe une corrélation significativement élevée entre la SST et la Chl-a au niveau de la
latitude 22°N. À l’aide du modèle additif généralisé, nous avons constaté que les paramètres environnementaux
(ssT, Chl-a et ui) au niveau de la latitude 22°N jouent un rôle majeur dans l’explication des variabilités men-
suelles des débarquements de S. aurita (65,1% de déviance expliquée). la forte abondance de S. aurita, obser-
vée en automne, est due aux conditions environnementales adéquates dans le sud du Maroc, ce qui conduit à la
migration de cette espèce des eaux mauritaniennes vers les eaux marocaines.
INTroducTIoN nops sagax (Jenyns, 1842) and Sardina pilchardus (Wal-
baum, 1792)] and sardinella [Sardinella aurita Valenciennes,
Climate change is impacting the marine fish and fisheries 1847 and Sardinella maderensis (lowe, 1838)] (klyashtorin,
and will continue to do so in the future (roessig et al., 2004). 1998; yanez et al., 2002; loukos et al., 2003; Beare et al.,
Most of the investigations concerning the impact of climate 2004; Guisande et al., 2004; lloret et al., 2004; zeeberg et
change on fish stocks have been on pelagic fish species such al., 2008; diankha et al., 2015; Thiaw et al., 2017; Brochier
as tuna [particularly Thunnus albacores (Bonnaterre, 1788), et al., 2018). More particularly, small pelagic fishes are sub-
T. thynnus (linnaeus, 1758) and Katsuwonus pelamis (lin- ject to pressure factors related to human population growth,
naeus, 1758)], mackerel [Trachurus declivis (Jenyns, 1841) overfishing, global climate change, pollution, and habitat
and T. novaezelandiae richardson, 1843], sardines [Sardi- degradation (klemas, 2012) and global warming affects all
(1) Biodiversity, ecology and Genome laboratory, Faculty of science, Mohammed V university in rabat, Morocco.
[[email protected]] [[email protected]] [[email protected]] [[email protected]]
(2) institut National de recherche halieutique, Casablanca, Morocco. [[email protected]] [[email protected]]
[[email protected]]
(3) laboratory of engineering and Materials, department of physics, Faculty of sciences Ben M’sik, university hassan ii, Casablanca,
Morocco. [[email protected]]
* Corresponding author
Cybium 2019, 43(1): 51-59. doi: 10.26028/cybium/2019-431-005
Environmental influences on sardinella aurita Baali et al.
major marine ecosystems except California and humboldt and Koranteng, 1995). Its biomass has fluctuated during the
Current (Belkin, 2009; sherman et al., 2009). in general, sea last years (Baali et al., 2015) and between 1990 and 2016,
surface temperature (ssT) has increased by 0.6°C over the the catches varied from year to year (Fig. 1) in relation with
past 100 years (iPCC, 2007). According to klemas (2012), its migratory nature. S. aurita is one of the dominant species
the ocean productivity began to decline about 40 years ago, in our study area, i.e. the south of Atlantic Morocco (iNrh,
reaching maximum sustainable yield. This suggests that the 2015), where it represents the second pelagic species caught
relationship between climate change and the primary pro- after the sardine (Sardina pilchardus) with a percentage of
duction of the oceans is critical for future fisheries produc- 14% of small pelagic catch (Baali et al., 2015). The average
tion (Cushing, 1975). indeed, phytoplankton production yet catch during the last five years was about 51,735 tons per
impacts fish landings (Ware and Thomson, 2005; Chassot et year and the south of Cape Boujdour area contains 90% of
al., 2007); Moreover, the temperature affects fish during the the average catch in Morocco (iNrh, 2015). S. aurita makes
different phases of their life; during egg-laying, development extensive seasonal migrations from senegal and Gambia
and survival of eggs and larvae, the distribution, aggregation, to Mauritania and Morocco (zeeberg et al., 2008) with the
migration, and behaviour of juveniles and adults (Gordoa et presence of a sedentary stock in Morocco between 22° and
al., 2000). 30°N (FAo, 2001). This means that this stock is exploited in
The south of Atlantic Moroccan coast is characterise all these countries but without any joint management. This
by the presence of the canary upwelling system, one of the may entail that each country tries to maximize the exploi-
four major eastern boundary upwelling systems (Fréon et tation of the resource when the fish is present in its waters,
al., 2009), it is situated along the northwest African coast. under national jurisdiction, which is an additional risk to
The dynamics of an eastern boundary current interacting increase the current overexploitation (FAo, 2011).
with trade wind-driven upwelling control a marine ecosys- understanding how climate controls the abundance of
tem with exceptionally high biological productivity (Cury S. aurita in the Moroccan waters is the aim of this paper,
and roy, 1989; Binet, 1997; demarcq and Faure, 2000). within the objective of proposing a sustainable fisheries
This productivity sustains a large variety of pelagic species, management plan. Three environmental parameters are used
including commercial fish species, e.g. Sardinella aurita. because they explain most of the relationship between envi-
The round sardinella (Sardinella aurita Valenciennes, ronmental change and fish abundance (Diankha et al., 2013):
1847) are small pelagic fish and mostly feed on phytoplank- the sea surface temperature (ssT), the upwelling index (ui),
ton like any small pelagic species (zainuddin et al., 2004) that reflects the productivity of the area by entraining nutri-
and seems to be an excellent tool for studying the effects of ents above mixed layer depth and in turn, allowing phyto-
climate change on marine ecosystems. its life span is short; plankton to sustain food-web with the help of photosynthe-
its food relies on plankton food chain; and its recruitment sis, and the chlorophyll-a concentration (Chl-a) that reflects
is largely controlled by egg and larval survival, the latter the phytoplankton biomass available. in this work we will
depending on the prevalence of appropriate oceanographic study the correlation between Sardinella aurita landings and
and atmospheric conditions (Cury and roy, 1989; Bernal, the environmental factors in order to evaluate the effect of
1991; hunter and Alheit, 1995; Bakun, 1996). ssT, ui and Chl-a on S. aurita abundance using a General-
Sardinella aurita is a key species inhabiting the ecosys- ized Additive Model (GAM).
tem of the upwelling region of north-western Africa (Bard
Figure 1. – Total S. aurita catch in
Morocco during the period from 1990
to 2016.
52 Cybium 2019, 43(1)
Baali et al. Environmental influences on sardinella aurita
MATErIAL ANd METHodS same latitude that is 5° to the west. Therefore, an increase
(decrease) in the upwelling index is equivalent to a decrease
Fish landed data (increase) in the intensity of the upwelling.
We use the monthly landed catch data from 2009-2016 The correlations between the three parameters (ssT,
to study the variability of Sardinella aurita abundance in Chl-a and ui) and S. aurita landings were tested for each
Moroccan waters. The landing data were obtained from degree of latitude of the south of Morocco (21°N-26°N)
the statistical section of the National institute of Fisheries
(Fig. 2) considering all possible lag. only the latitude with
research in Casablanca (iNrh) and constitutes the total
high and significant correlation was considered further.
landings in Morocco. in the Atlantic Moroccan coast, sar-
dinella is exploited by a fleet of Moroccan purse seiners and
Statistical analyses between S. aurita landings and the
by refrigerated seawater (rsW) trawlers. it is also exploited
environmental data (SST, uI, chl-a)
by industrial trawlers from the russian Federation, and the
The monthly climatology was calculated to analyse the
european union.
seasonal abundance of S. aurita relative to the variation of
ssT, ui and Chl-a.
Environmental data
The relationships between ssT, ui, Chl-a and S. aurita
The ssT data is from the seasonally mean Global
landings were evaluated using the Pearson correlation coef-
ArMor3d l4 product with a resolution of a 1/4-degree
ficient. The later was also used for testing the correlation
regular grid. The product is obtained by combining satellite
between environmental parameters in the different degrees
and in situ (temperature profiles) observations through sta-
tistical methods. detailed description of quality/Accuracy/ of latitude. The correlation coefficient was checked against
Calibration and further information can be found in the offi- the assumption that it was zero with a 95% confidence level.
cial CMeMs website, with the validation reports and quality relationships between the landings of S. aurita and envi-
documentations (www.marine.copernicus.eu). ronmental conditions were explored using generalized addi-
ocean colour technique exploits the emerging electro- tive modeling (GAM) to define the set of parameters that best
magnetic radiation from the sea surface in different wave- describes the conditions associated with the round sardinella
lengths. The spectral variability of this signal defines the landings. GAM is a form of non-parametric multiple regres-
so-called ocean colour, which is affected by the presence of sion that models a response (dependent) variable as a func-
phytoplankton. By comparing reflectance at different wave- tion of one or more predictor (independent) variables (hastie
lengths and calibrating the result against in-situ measure- and Tibshirani, 1990; Wood, 2000). GAMs in this study
ments, an estimate of chlorophyll content can be derived. are given by: y = β(X) + ε, where y is the value of the
i i i i
The upwelling index (UI) is defined as the difference in
response variable (landings), β(X) the predictor function,
i
ssT between the ssT-coast and the ssT-ocean (reynolds et
and ε the residual. The predictor function β(X) is given by:
i i
al., 2007). Where ssT-coast is the ssT of the grid closest to
β(X) = α + s(X), where X is the explanatory variable (envi-
i i i
the coast and ssT-ocean is the ssT of the grid box along the
ronmental variable), α the intercept, and s(X) the smoothing
i
function. The “mgcv” packages (Wood, 2013) in r software
(version 3.5.1) were used. The Gaussian distribution with the
identity-link relating the dependent variable to the predictors
(ssT, Chl-a, and ui) and tensor product smoothers (“ti” in
mgcv) were applied.
rESuLTS
Spatial distribution of Sardinella aurita landings
The distribution of total landings of Sardinella aurita
from the different landing ports in Morocco is shown in the
figure 3. The Dakhla port represent 97% of S. aurita land-
ings, followed by laâyoune port (2%) and the rest of the
ports represent a very low percentage of landings (> 1%).
The data from the dakhla port (23°N) are used in the next
Figure 2. – location of sampling areas of ssT, Chl-a and ui data. analyses.
Cybium 2019, 43(1) 53
Environmental influences on sardinella aurita Baali et al.
Figure 5. – seasonal variability of Sardinella aurita landings in
Figure 3. – Total landing distribution of round sardinella by region dakhla port (2009-2016).
in Morocco during the period (2009-2016).
Figure 4. – inter-annual variability of
Sardinella aurita landings in dakhla
port (2009-2016).
Annual variability of Sardinella aurita landings, SST and (Fig. 6). The low sea surface temperature and concentration
chl-a of chlorophyll-a observed these last years coincide with the
Sardinella aurita landings reveal inter-annual variability decrease of S. aurita landings (Figs 4, 6).
with a downward trend in recent years (Fig. 4). The maxi-
mum value of S. aurita landings was reported in 2012 with relationship between environmental parameters and
a mean of 101,373 t. Concerning the lowest value, it was Sardinella aurita landings
found in 2016 with a mean of 8,230 t. The seasonal variabil- The correlation between the environmental parameters
ity of landings between 2009 and 2016 are shown in figures showed a significant relationship between the ssT and
4 and 5. The maximum average landing of S. aurita was Chl-a at latitude 22 and 23°N. For the ssT and ui the results
observed in autumn (5,738 t) (Fig. 5). The lowest S. aurita reveal a positive and significant relationship between the two
landing occurred in summer (3,388 t) (Fig. 5). parameters at latitude 21°N. however, for the Chl-a and ui,
The inter-annual variability of the environmental param- we observed that there is no correlation (Tab. i).
eters (ssT, Chl-a) has two patterns. Maximum values of ssT The correlation between the S. aurita landings and the
were observed in summer and autumn (warming season) environmental parameters (ssT, ui, and Chl-a) was tested
(> 20°C) and lowest values in winter and spring (cold sea- monthly, with all possible offsets and for each degree of
son) (< 20°C) (Fig. 6A). For the Chl-a, the figure 6 showed latitude. The results showed that the correlation between
a period of high Chl-a concentration in the warming sea- ssT, Chl-a and S. aurita landings was high and significant
son (> 1.5 mg.m–3) and a period of low Chl-a concentration especially at latitude 22°N (P < 0.05). While the correlation
in the cold season (< 1.5 mg.m–3) (Fig. 6B). The intensity between the ui and S. aurita landings showed a positive
of ssT and Chl-a concentration differs between altitudes relationship at latitude 21 and 22°N. This correlation was not
54 Cybium 2019, 43(1)
Baali et al. Environmental influences on sardinella aurita
Figure 6. – interannual trends of the ssT (a) and Chl-a (b).
Table i. – Correlation between environmental parameters for each degree of latitude in southern significant (P > 0.05) (Tab. ii).
Morocco.
in the univariate GAMs
latitude 21°N 22°N 23°N 24°N 25°N 26°N proposed, the three explana-
ssT (°C)/Chl-a (mg.m–3) 0.56 0.86 0.83 0.69 –0.56 –0.04 tory variables chosen were
(P = 0.06) (P = 0.00) (P = 0.00) (P = 0.01) (P = 0.04) (P = 0.89) highly significant (P < 0.001)
ssT (°C)/ui 0.70 0.33 –0.28 –0.24 –0.60 0.17 (Tab. iii). The deviance of the
(P = 0.01) (P = 0.29) (P = 0.38) (P = 0.45) (P = 0.04) (P = 0.61) monthly landings explained
Chl-a (mg.m–3)/ui –0.13 0.18 0.09 0.22 –0.2 –0.44 by the sea surface temperature,
(P = 0.68) (P = 0.58) (P = 0.79) (P = 0.49) (P = 0.53) (P = 0.17)
Chl-a, and ui in the differ-
ent latitudes is presented in
Table ii. – Correlation between ssT, Chl-a, ui and landings in tons for Sardinella aurita for each degree
table iii. The most impor-
of latitude in southern Morocco.
tant explanatory variable
latitude 21°N 22°N 23°N 24°N 25°N 26°N
with 65.1% of deviance
ssT (°C)/landings (t) 0.74 0.76 0.67 0.66 0.54 0.52
explained was found at the
(P = 0.006) (P = 0.005) (P = 0.02) (P = 0.02) (P = 0.07) (P = 0.09)
latitude 22°N.
Chl-a (mg.m–3)/landings (t) 0.64 0.68 0.40 0.65 –0.11 –0.04
We used the data from
(P = 0.03) (P = 0.02) (P = 0.19) (P = 0.02) (P = 0.74) (P = 0.91)
the ssT, Chl-a and ui at
ui/ landings (t) 0.54 0.31 –0.03 0.002 –0.37 –0.17
latitude 22°N as a repre-
(P = 0.07) (P = 0.34) (P = 0.91) (P = 0.99) (P = 0.24) (P = 0.59)
sentative latitude to assess
the impact of these param-
Table iii. – The p-values and percent of explained deviance by each
latitude tested for explaining variations in the monthly landing of eters on S. aurita landings in the south of Morocco.
Sardinella aurita in southern Morocco. The GAM results showed a linear relationship between
latitude p-value % deviance explained landings of S. aurita and environmental parameters (Fig. 7).
21°N 3.24e-07 55.8 in the south of Morocco, positive relationships were found
22°N 1.30e-07 65.1 for ssT, Chl-a and ui with landings (Fig. 7). The results
23°N 2.64e-07 58.3 allowed the identification of the most favourable SST and
Chl-a range for S. aurita. The landings of the round sar-
24°N 6.65e-07 46.8
dinella were highest at higher ssT (> 19°C) and Chl a
25°N 4.28e-07 29.2
(> 2.5 mg.m-3). The relationship between the ui and S. auri-
26°N 1.46e-06 34.6
ta landings was not significant (Fig. 7).
Cybium 2019, 43(1) 55
Environmental influences on sardinella aurita Baali et al.
Figure 7. – GAM smoothing curves fit-
ted to effects of ssT, Chl-a, and ui on
S. aurita landings at latitude 22°N. The
solid lines are the estimated smoother
and the dashed lines represent 95%
confidence intervals around the main
effects. The black lines at the bottom of
each plot indicate where the data values
lie.
The monthly variation of fish landings showed that the tration from december-April (Fig. 8).
maximum of S. aurita landings were observed in october our results show that from the year 2010, the landings
(6,698 t) with a minimum in June (2,493 t) (Fig. 8). since of S. aurita start to increase, the maximum values were
June, the ssT and ui began to increase until they reached observed during the period ranging from 2011-2013 (Fig. 8).
their maximum value in summer, then the two parameters in this period, the concentration of Chl-a (2.28 mg.m–3), ui
decreased reaching their minimum values in winter (Fig. 8). (0.72) and ssT (18.74°C) was high (Fig. 8). After that, the
The values of the ssT and Chl-a ranged from 15.98 to 20.8°C S. aurita landings began to decrease, reaching their mini-
and 0.72 to 6.18 mg.m–3, respectively. The monthly Chl-a mum values in 2016. This decrease was observed also for
average shown below exhibited two patterns. it showed a the concentration of Chl-a (1.90 mg.m–3), ui (0.45) and ssT
period of high Chl-a concentration from May-November (18.58°C) during the last years (Fig. 8).
with a peak in september and a period of low Chl-a concen-
Figure 8. – interannual trends of Sardinella aurita landings, ssT, ui and Chl-a at latitude 22°N.
56 Cybium 2019, 43(1)
Baali et al. Environmental influences on sardinella aurita
dIScuSSIoN ssT, ui, and Chl-a also increase during this period. it seems
that this situation, the warming trend of ssT, is favourable
Landings from commercial fishery can provide indica- to the abundance of S. aurita, because of its preference for
tions of changes in population composition and abundance warm water (zeeberg et al., 2008). The upwelling inten-
(Pauly et al., 1998, 2002; Maunder and Punt, 2004; sun- sity is a source of inter-annual fluctuations observed in the
dermeyer et al. 2005; quirijns et al., 2008; Pitchaikani and coastal abundance of S. aurita (demarcq and Faure, 2000;
lipton, 2012; ho et al., 2013; Teixeira et al., 2014). how- Braham et al., 2014; diankha et al., 2015; Mbaye et al.,
ever, fishery landings have some limitations, because many 2015; Thiaw et al., 2017). The increase in S. aurita landings
factors can affect recruitment, and consequently abundance during this period (July-october) is due to the migratory
(Pauly et al., 1998). These include environmental factors, nature of this species (zeeberg et al., 2008). on the Maurita-
fishing techniques, fishing equipment, fishermen behaviour, nian coasts, temperatures are below 21°C during the winter
changing markets, discarding, management and economic (January-March) (zeeberg et al., 2008). Although primary
factors (Anderson, 1994; daan, 1997; horwood and Mill- production is the highest in these months, wind mixing is
ner, 1998; Marchal et al., 2002). Another source of bias was
high and the “upwelling filaments” (Nykjær and Van Camp,
the use of landings, instead of catches. For fishes with a high
1994; Barton, 1998) carry water away from the coast to the
commercial value, the fraction of the catches that is not land-
unproductive ocean (rodrigues et al., 1999; demarcq and
ed, but sold directly in markets, can be high; conversely, for
Faure, 2000; Bécognée et al., 2006). These conditions are
low-value species, there is probably a lot of discarding, con-
unfavourable for S. aurita because fish growth is limited by
tributing to differences between what was actually caught
temperature and spawning will be less successful (Cole and
and what was landed (Teixeira et al., 2014). Thus, landings
McGlade, 1998). At this time of the year, most S. aurita are
are really underestimates of the catches for these resources.
found in senegalese waters where the temperature remains
despite these limitations, data from commercial fishery
above 21°C (zeeberg et al., 2008). Around May, the condi-
landings can provide useful information on the dynam-
tions become less favourable, with ssT increasing to around
ics of marine populations (Teixeira et al., 2014). The fish-
25°C, stratifying surface water and reducing food availabil-
ing effort of the fleets targeting small pelagic species in the
ity. As the strength of the trade winds decline in April/May,
south Morocco is expressed in sea fishing days. This effort
tropical water rush north with strong surface geostrophic
is available on a monthly scale and is used in assessments of
currents. Most of S. aurita population then moves to Mau-
the targeted small pelagic fish; at the South Moroccan region
ritania, looking for more appropriate spawning habitat. dur-
level (iNrh, 2017) and at the North West Africa level in the
ing May-July, fish benefit from high productivity in the Mau-
framework of CeCAF (FAo, 2018). however, sardinella is
ritanian zone by feeding and breeding at the same time. in
not among the targeted species by the small pelagic fisheries
August/September, high water temperatures indicate stratifi-
in this area. sardinella is usually caught as by catch when it
cation of surface water and reduce the productivity (zeeberg
is encountered by the fishing units in their quest for sardines
et al., 2008). When food production is further reduced, fish
and mackerel. Therefore, the effort, expressed in fishing
leave Mauritania and migrate north into Moroccan waters.
days, can’t reflect the fishing pressure exerted specifically on
here, the upwelling continues throughout the year, and food
sardinella. Thus we consider that sardinella catches are more
remains abundant in autumn (zeeberg et al., 2008).
relevant to represent the fish abundance than catches per
The decline of the stock apparent from total landing
fishing days (CPUE), since this species is caught only when
(Fig. 4) indicates that sardinella is presently overexploited
it’s available without dedicating a specific effort to it.
(iNrh, 2015). The concentration of Chl-a was strongly cor-
The results of this study showed that there is a signifi-
cant relationship between environmental variables (ssT and related with S. aurita landings. The decline of Chl-a concen-
Chl-a) at 22° N and S. aurita landings in dakhla. This can tration during the period from 2013-2016, seems to be unfa-
be summarized by the variability of the ssT and Chl-a. The vourable for this species. low S. aurita abundance probably
fact that monthly landings of S. aurita are strongly related to signifies low productivity in the studied area during these
the effect of ssT and Chl-a, may be a consequence of their last years. The close association of S. aurita abundance with
effects on S. aurita larval survival, growth rates, and peak the ocean climate warrants strict management measures,
of spawning (diankha et al., 2013). Numerous studies have because the effects of climate may aggravate the effects of
suggested that the abundance of small pelagic resources is fisheries and vice versa.
related to the spatial and temporal variability of environmen- overall, this study showed that there is a strong link
tal factors such as ssT, Chl-a, wind stress, and sea-surface between the abundance of S. aurita, the sea surface tempera-
height (Cury and roy, 1989; Fréon, 1991; Bakun, 1996; ture and the concentration of chlorophyll-a in the south of
zagaglia et al., 2004; diankha et al., 2013). S. aurita land- the Atlantic Moroccan waters. The monthly abundance of
ings increase during the period from July to october. The S. aurita is strongly governed by the effect of ssT and Chl-a
Cybium 2019, 43(1) 57
Environmental influences on sardinella aurita Baali et al.
whereby an increase in these parameters leads to an increase BroChier T., AuGer P.A., PeCquerie l., MAChu e.,
CAPET X., THIAW M., MBAYE B.C., BRAHAM C.B.,
in S. aurita abundance.
eTTAhiri o., ChArouki N., seNe o.N., WerNer F. &
The environmental parameters (ssT, ui and Chl-a) BREHMER P., 2018. – Complex small pelagic fish population
at latitude 22°N seem to be a good indices that govern the patterns arising from individual behavioral responses to their
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