DISTRIBUTION AND ECOLOGY OF PELAGIC FISHES 



STUDIED FROM EGGS AND LARVAE IN 



AN UPWELLING AREA OFF SPANISH SAHARA 



Maurice Blackburn^ and Walter Nellen- 



ABSTRACT 



Fish eggs and larvae were taken in vertical zooplankton hauls in a small upwelling area off Spanish 

 Sahara. Series of hauls were made repetitively from March to May 1974, sometimes with accompanying 

 hydrocasts. About 58% of the eggs and 72% of the larvae belonged to the following pelagic species: 

 Sardina pilchardus, Engraulis encrasicholus, Trachurus spp., and Maurolicus sp. It was estimated 

 from contemporaneous current meter data and other information that the eggs of those species were 

 spawned very close in time and space to where they were collected. Thus adult Sardina and Engraulis 

 appeared to occur typically on the continental shelf, adult Trachurus at the edge of the shelf, and adult 

 Maurolicus over the continental slope. These distributions were verified for Sardina and Trachurus 

 from fishing results of Polish vessels. Acoustically detected concentrations of fish were identified by 

 species according to those results. 



The area of abundance of Sardina was characterized by ma.xima of phytoplankton and small 

 zooplankton. Abundance of Sardina eggs changed with time, because of variations in the size of the 

 adult population in the area (acoustically estimated) and in its production of eggs. The major change in 

 population size coincided with a similar change in the amount of food, especially phytoplankton, 

 available. Variations in egg production may have been associated with the mean temperature in the 

 water column, since eggs were scarce when the mean was below 16.5°C even when adults were 

 abundant. 



A multidisciplinary group of U.S. scientists made 

 an oceanographic study off Spanish Sahara from 

 March through May 1974. The program is called 

 Coastal Upwelling Ecosystems Analysis (CUEA) 

 and is part of the International Decade of Ocean 

 Exploration (IDOE). The operation off Spanish 

 Sahara (Figure 1) was called JOINT-I. It made 

 observations of many kinds over an upwelling area 

 which was small enough to be studied synoptically 

 in great detail repetitively under various condi- 

 tions such as changes in the wind field. Most of the 

 work was done from the coast to long. 18°00'W, 

 between lat. 21°30' and 21°50'N. The continental 

 shelf in this area is bounded by the 100-m isobath, 

 beyond which there is a steep slope (Figures 2-4). 

 Pelagic fish are a major component of the animal 

 biomass in the area. They support large fisheries 

 conducted by several nations. It was the task of a 

 small group of CUEA investigators to estimate 

 biomass of pelagic fishes by species and, if possi- 

 ble, by trophic levels during JOINT-I; to show the 

 distributions of these biomasses in space and time; 



'Institute of Marine Resources, University of California, La 

 Jolla, CA 92093. 



-Institut fiir Meereskunde, Universitat Kiel, Kiel, West 

 Germany. 



Figure 1. 



20" 



-Part of northwest Africa showing the principal area 

 of JOINT-I work. 



Manuscript accepted April 1976. 



FISHERY BULLETIN: VOL. 74, NO. 4, 1976. 



885 



