450 



Fishery Bulletin 103(2) 



change was characterized by a decrease in density on 

 shoals and a movement of spawning females to deeper 

 water, withand a more scattered distribution than in the 

 early 1990s. Our results confirm previous observations 

 reported by Ehrlich et al. 1 , who analyzed ichtyoplankton 

 samples collected from 1973 to 1999, in the traditional 

 spawning area of Isla Escondida. These authors did not 

 observe significant environmental anomalies that might 

 have affected the spawning of hake and associated the 

 change with the high levels in fishing exploitation in the 

 1990s. These shifts in the pattern of reproduction led to 

 the following question: "How does the movement of the 

 center of spawning affect the recruitment of Patagonian 

 hake?" — given that different environmental conditions 

 could be present in the new spawning area. 



Our analyses show that the abundance of active fe- 

 males offshore of the north Patagonian area increased 

 from 1998 to 2001, coinciding with a significant de- 

 crease in hake biomass in the shallow waters of Isla 

 Escondida. During these years, demographic changes 

 in the offshore area were characterized by an increase 

 of larger females (>50 cm TL) compared to previous 

 years. The increase in proportion of older individuals 

 in spawning condition may result in a greater contribu- 

 tion to egg production because of the higher fecundity 

 produced by larger females (Mairteinsdottir and Thora- 

 rinsson, 1998). In fact, egg production estimated for the 

 offshore Patagonian hake during January showed an in- 

 crease since 1998, with the highest values in 2000 and 

 2001 (400% more than those estimated in 1996-97). A 

 high proportion (70%) of these eggs were spawned by 

 females larger than 50 cm TL (s5-year old, Otero et al., 

 1986), whereas in January 1996 and 1997 eggs were 

 mainly produced by young females. 



Because of the displacement of active females to deep 

 water, the offshore north Patagonian area from 43°30' 

 to 45°S and between 50 m and 100 m depths was con- 

 sidered an important section of the spawning ground for 

 Patagonian hake after 1998. The comparison between 

 the January 1996 and 2001 surveys, in which inshore 



1996 

 1997 

 1998 



-1999 

 -2000 

 -2001 



40 50 60 70 80 



Total length (cm) 



90 



100 



Figure 6 



Relative egg production (%) by length class estimated 

 for Argentine hake (Merluccius hubbsi) in January from 

 1996 to 2001. 



and offshore samples of the north Patagonian area were 

 collected, demonstrated this change. In January 1996, 

 spawning of Patagonian hake was concentrated inshore 

 (Isla Escondida), whereas in January 2001 reproduction 

 of this stock took place mainly offshore (Fig. 2). For 

 this reason, the offshore egg production value obtained 

 after 1998 was considered a representative index of the 

 spawning area. 



Relative abundance of hake at age 1 (number of indi- 

 viduals/hour) in the north-Patagonian area, showed a 

 decline from 1996 to 2000 and an increase in 2001 and 

 2002, reaching the highest values of the study period. The 

 recruitment index obtained for 2002 (2444 individuals/h) 

 was about twice that estimated for 2001 (1367 individu- 

 als/h). According to Santos et al., 3 it is possible that this 

 value has been overestimated, because it was determined 



3 Santos, B. A., E. B. Louge, and R. Castrucci. 2003. Estu- 

 dio de las variaciones conjuntas de la temperatura y de la 

 salinidad del area de cria de la merluza con los indices de 

 abundancia de los grupos de edad 0. 1 y 2. (enero 1995-enero 



2002). Tech. Rep. 10/03. 6 p. INIDEP, CC. 

 Plata (7600), Argentina. 



175. Mar del 



