The use of GIS to cartography the variation of the abundance of eggs and larvae of sardine in the Moroccan Atlantic area

Rachida Houssa, Omar Ettahiri, Amina Berraho, Ahmed Makaoui, Karim Hilmi

Institut National de Recherche Halieutique (INRH), Casablanca (MA)

Abstract

In this work linked to NATFISH program, the Geographical information System (GIS) and the geostatistical techniques are used to analyze and cartography the spatio-temporal variation of the distribution of eggs and larvae of sardine (Sardina pilchardus) in the Moroccan Atlantic region.

The spatio-temporal variation of eggs and larvae distribution was studied according to two cases :

- the seasonal variation where the distinction between the season of winter and summer permits to define the different phases of the biology of sardine. The change of eggs and larvae behavior from one season to the other is susceptible to be accompanied by habitat change, hence of the geographical distribution.
- the interannual variation that can be the reflection of environmental parameters modification.

Data of 4 years of scientific prospecting surveys (1994-1997) have been used. The area of study is spreading from Safi (32°18 ' North) to cap blanc (21° North), and from the shore to 1000m depth.

The following steps are used to cartography area of distribution of eggs and larvae of sardine:

- spatio-temporal exploration: the analysis of data of eggs and larvae densities by station of every survey permits to verify the spatio-temporal resolution;
- spatio-temporal modelisation: the interpolation on a grid of 0.016 degree followed by a classification in 4 classes of densities facilitates the identification of zones corresponding to various level of eggs and larvae concentrations;
- the spatial combination of data of eggs and larvae densities with environmental parameters permit to identify the influence of climatic condition variations on the distribution and the abundance of eggs and larvae of sardine.