(Sardina pilchardus) and sardinella (Sardinella aurita ...

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research vessel FRS 'Dr Fridtjof Nansen'. These surveys were undertaken hydro-acoustically and were designed to estimate annual biomass of five.
GIS/Spatial Analyses in Fishery and Aquatic Sciences (Vol.5) Houssa et al - Spatial dynamics of sardine (Sardina pilchardus) and sardinella (Sardinella aurita), two small pelagic fishes in the Canary Current System (119-132) ⒸInternational Fishery GIS Society, 2013

Spatial dynamics of sardine (Sardina pilchardus) and sardinella (Sardinella aurita), two small pelagic fishes in the Canary Current System Rachida HOUSSA Institut National de Recherche Halieutique (INRH), 2 rue de Tiznit, Casablanca (20270) Morocco Phone: 212 (Morocco) 522220 249 Fax: 212 (Morocco) 522266 967 E-mail:[email protected]

Souad KIFANI Institut National de Recherche Halieutique, INRH, Morocco

Naoki TOJO Institut National de Recherche Halieutique, INRH, Morocco

Aziza LAKHNIGUE Institut National de Recherche Halieutique, INRH, Morocco

Najib CHAROUKI Institut National de Recherche Halieutique, INRH, Morocco

Abstract Geographic information system tools are used to examine geographical variations of distribution of sardine (Sardina pilchardus) and round sardinella (Sardinella aurita) in the eastern central Atlantic area. For this we used geo-referenced data of historical series (1962–2005) of commercial fish landings and acoustic surveys of small-pelagic resources. Results suggest inverse changes over time in positions of the centres of distribution of these two species—that sardine and sardinella alternate their ranges latitudinally, with sardine moving from north to south and sardinella moving from south to north. These shifts in the geographical 119

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distribution of sardine and sardinella are most likely due to climate regime changes in the area of the Canary Current System as determined in 2005 by Freon, Cury, Shannon and Roy. The evolving progression of climate change and the variability at a multi-decadal time scale should both be taken into consideration for ecological interpretation of the distribution of these species.

Keywords Canary Current area, GIS, pelagic fish distribution, sardine, sardinella, SST.

1. Introduction As part of the ecosystem of the Canary Islands, the eastern central Atlantic (CECAF) region is characterized by the importance of small – pelagic resources, including sardine Sardina pilchardus and round sardinella Sardinella aurita. These small-pelagic species have great economic importance since they constitute the bulk of the catch in the maritime countries of the CECAF region and provide the raw material for industry transformation (Tacon, 2004; Brochier, 2009). The management of this living resource is particularly difficult due to the high variability in stocks of small-pelagic species (Fréon et al., 2005; Brochier, 2009). The evolution of small-pelagic catches in the CECAF region over the last decade was marked by significant fluctuations that can be explained partly by the natural variability in the system and partly by the high level of fishing effort. The eastern central Atlantic area is notable for its intense upwelling. This natural variability amplifies the vulnerability of small-pelagic stocks, short-life-cycle species whose recruitment is closely related to changes in the environment (Belvèze, 1991; Cury and Roy, 1998a, cited by Weigel, 1999; Zizahet al., 2001). Between 1990 and 1994, the temporary and partial withdrawal of the Russian industrial fleet from the CECAF region had a positive effect on catches, which highlighted the impact of fishing effort (Weigel, 1999).In the late 1990s, the overall catch indicated a pronounced geographical imbalance in favour of the CECAF region (especially in the Mauritanian EEZ) to the detriment of the southeast Atlantic; twenty years prior, catches were approximately equal in both areas (Weigel, 1999). This scenario is also observed in other ecosystems in the world that are characterized by strong upwelling (California, Humboldt and Benguela systems) and most of the recent research (MacCall, 1990; 120

Houssa et al - Spatial dynamics of sardine (Sardina pilchardus) and sardinella (Sardinella aurita), two small pelagic fishes in the Canary Current System (119-132)

Samb and Pauly, 2000; Rodríguez-Sánchez et al., 2002) has used a unidimensional approach (simple correlation between species variability and climate change over time scales) to focus on understanding the influence of climate on pelagic-stock variations. This approach does not take account adequately of the complexity of the species interactions and their relation to their environment. There is a need to include dynamic geography for understanding the structure of fish populations and their relationship to their environment (Rodríguez-Sánchez et al., 2002). Currently in the CECAF region, sardine ranks first in production (800,000–1,000,000 ty-1) followed by round sardinella (300,000–400,000 ty-1) (FAO, 2008). In this study, we use GIS tools to analyse the spatial variability and interactions of the coupled sardine–round sardinella populations and the effect of climate change in the marine environment.

2. Materials and methods 2.1 Study area The study area corresponds to the continental shelf of CECAF‘s northern coastal area belonging to Atlantic geographical sub areas (GSA) 34.1 (from 36° to 19°North) and the shelf of CECAF’s southern coastal area belonging to GSA 34.3(from 19° to 12°North), the GSAs defined by the General Fisheries Commission for the Mediterranean (GFCM) (FAO/GFCM, 2001) (Map 1). Map 1 . Geographic location of the area studied and spatial distribution of the data used.

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2.2 Density maps Two main sources of data were used to map the distributions of sardine and round sardinella, namely scientific surveys and commercial-fisheries landings. For surveys data we used a dataset of eight surveys that were conducted between 1999 and 2005 in autumn or winter by the Norwegian research vessel FRS ‘Dr Fridtjof Nansen’. These surveys were undertaken hydro-acoustically and were designed to estimate annual biomass of five small pelagic species, namely sardine, anchovy, horse mackerel, mackerel and round sardinella. The investigations with this scientific vessel covered the entire continental shelf of the CECAF coastal area. Course tracks of the vessel did not follow a fixed strategy. The same area could be covered several times to check if biomass remained constant or not. The strong point of this research vessel was the number of fishing operations made—5 to 7 per day. The objective was to identify (or confirm) the echo-traces recorded by sonar (Marchal, 1989; Jolly and Hampton, 1990). Additionally, we used commercial-catch data from the Russian fishing vessels that operated in Atlantic GSA 34.1, from 1962 to 1999. These vessels used pelagic trawls to complete 64 surveys over a six-month period each, and making a total of 36 735 trawling operations. To map spatial distribution of density, all data were displayed on a 10´x10´-cell grid. For each cell, the mean of the data located in it was aggregated for annual collected data. Decadal averages were estimated for each cell grid from the annual densities for the years from 1969 to 1999 (with the exception of the 2000s, where the average was estimated for six years only—from1999 to 2005). The GIS software ArcGIS9.2 was used to build these maps.

2.3 SST maps Time series of sea surface temperature (SST) for the same period (1962– 2005) were obtained from the Russian and FRS ‘Dr Fridtjof Nansen’ surveys carried out in the Moroccan Atlantic area, from Cape Spartel (35° North) to Cape Blanc (20°North). Available SST data are representatives of 5-mile squares. The means of data displayed on 1°x1°cell grid were calculated with ‘Surfer’ software and used to identify spatial and temporal variability of SST.

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2.4 GIS tools To follow the spatial dynamics of the populations, we calculated their weighted centres (wc).The concept of the weighted centre in spatial analysis is based on the famous gravitation theory of Newton. In gravity spatial analysis, the weighted centre (or gravity centre) of a distribution is the position where the maximum accessibility can be reached (Liu and Coleman, 1996).This position, which is not inevitably located among all the individual points, provides a representation of the variability of a population’s distribution in space (Ebdon, 2004). The calculation of this parameter is done according to the following equations (Jenness, 2004):

(1)

X

wc

=

∑f x ∑f i

i

i

(2)

y

wc

=

∑f y ∑f i

i

,

i

, where X is latitude; Y is longitude; wc is the weighted centre; and

f

the frequency (or weighting factor).

3. Results Maps 2 and 3show how the areas of abundance of sardine and round sardinella, respectively, change by latitude and decade. There is an area to the south of Cape Blanc where data are missing during the 1970s and 1980s; however, sardine shows an abundance-zone extension south of 21°N during the 1989s and 1990s. Sardinella patches were not observed to the north of Dakhla in the 1980’s data, but began to be detected there from the beginning of the 1990s. During these last years, abundance areas of round sardinella were observed near latitude 30°N. The weighted centres calculated from the annual densities of sardine and round sardinella show inter-annual variability of distribution of these two species, with a general trend for the northern species (sardine) to move to the south and for the southern species (round sardinella) to move to the north (Figure 1). 123

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A ○

B ○

Map 2.

Pattern of sardine distribution using commercial data (A) and surveys data (B). The left-hand map in A shows overall distribution area between 1962 and 1999. The remaining maps in A and those in B show areas of sardine abundance for the time periods indicated.

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Houssa et al - Spatial dynamics of sardine (Sardina pilchardus) and sardinella (Sardinella aurita), two small pelagic fishes in the Canary Current System (119-132)

A ○

B ○

Map 3.

Pattern of round sardinella distribution using commercial data (A) and surveys data (B). The left-hand maps in A and B show overall distribution area between 1962 and 1999. The remaining maps show areas of round sardinella abundance for the time periods indicated.

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Figure1. Inter-annual variability between 1972 and 1999 in the location of weighted centres of sardine and round sardinella distribution.

The weighted centre calculated per decade confirm the previous result, namely geographical variation in the position of the centres of distribution of sardine to the south and of round sardinella to the north (Map 4). The distribution map of SST between 1960 and 2005 (Figure 2) shows a general warming trend from south to north with the exception of the period between 1970 and 1975 when a shift for cooling was recorded. 126

Houssa et al - Spatial dynamics of sardine (Sardina pilchardus) and sardinella (Sardinella aurita), two small pelagic fishes in the Canary Current System (119-132)

Spatio-temporal variations in weighted-centre locations of sardine and round sardinella distribution in 1969–1978, 1979–1987 and 1988–1999.

Latitude

Map 4.

Figure 2.

Sea surface temperature variation in the eastern central Atlantic between 20°North and 35°North from 1960 to 2007.

4. Discussions and conclusions Pelagic fishes migrate seasonally according to strong seasonal environmental patterns (Cury and Roy, 1988b; Fréon, 1988). Inter-annual environmental variability also affects fish abundance and distribution. Using time series of pelagic fish catch (mainly sardine) in the eastern Atlantic since 1950, some authors shows that environmental changes can 127

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modify fish-population abundance and force ecological systems to spread or retract in space (FAO 1997; Binet et al., 1998). It is noteworthy that the high abundance of sardinella at the beginning of the 1990s is associated with a period of higher temperatures, which in turn means that the habitat range for the southern fish species could potentially extend further north as the biomass increases. During the last several decades, the Canary Current was marked by important changes in the fish community, which in turn strongly affected fisheries patterns. Species that experienced drastic changes occupy different habitats and have very different ecological requirements and life history traits (Longhurst and Pauly, 1987). The same results, such as the alternation between sardine and anchovy, were observed in most upwelling ecosystems, in the Humboldt, Benguela and California (Rodriguez-Sanchez, 2002; Freonet al., 2005). In the pan-Pacific area including California and the eastern coast of Japan, the alternation of the small-pelagic fish species has been actively studied and discussed in relation to climate change and regime shift (Takasuka et al., 2007; Takasuka et al., 2004; Chavez et al., 2003). Vulnerability of small-pelagic fish in their early life stage and response to environment has been regarded as the causal mechanism in these Pacific studies. The different growth patterns of the species in their larvae phase generate differences in survival ("optimal growth temperature hypothesis"; Takasuka et al., 2007).Variability in the interaction with predators depending on size was suggested as one of the processes causing the changes in early-life survival of the Japanese sardine (Sardinops melanostics) and Japanese anchovy (Engraulis japonicus) (Takasuka et al., 2003; Takasuka et al., 2007). The hypothesis was tested by age analyses of larvae in the stomach contents of predators and the results supported growth-rate-dependent predation on the larvae of these two species ("growth-selective predation"; Takasuka et al., 2004;Takasuka et al., 2007).Since these two Pacific species have different optimal temperatures for their growth, the difference in growth that results from climate variability and climate regime-shift will result indifferent survival from predation, based on the tested mechanism. In our case, we cannot evaluate and discuss the condition of population dynamics in terms of early-life survival of our studied species where their distribution is gradually overlapping. As a consequence of migration to the preferred environment for feeding and reproduction, the movement of both species probably began from the 1980s.There would seem to be scope for further research on potential alternation scenarios associated with the identified movements of the centre of adult distribution since the 1980s.The climate regime-shift and movement patterns of fish or 128

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biological regime would bring new consequences for population dynamics of the species and sustainability of the stocks in the area of common distribution.

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