NOTE Macchi et al.: Effect of the spawning pattern of Merluccius hubbsi on recruitment 



451 



from samples collected two months later (March) than 

 those during 1996-2001. These authors suggested that 

 the spatial distribution or catchability of juvenile hake 

 could have changed from January to March, resulting in 

 a greater abundance index during 2002. 



The higher recruitment levels observed for Patago- 

 nian hake during 2001 and 2002 were coincident with 

 higher indices of egg production estimated offshore in 

 January during the two previous years (2000 and 2001). 

 Therefore, in principle we concluded that the change in 

 spatial location of spawners in the Patagonian stock did 

 not appear to negatively affect the recruitment of this 

 species. The next question to be answered is: "Why were 

 recruitment indices in the early 2000s higher than in 

 previous years?" 



Several authors have analyzed the spawner-recruit 

 relationship in different species and have concluded 

 that recruitment is often positively correlated with 

 spawner biomass estimated from virtual population 

 analysis (VPA) (Myers and Barrowman, 1996). In the 

 case of Patagonian hake, the increase in abundance at 

 age 1 observed in 2001 and 2002 was not associated 

 with higher values of the VPA-based spawner biomass 

 in previous years (GEM, unpubl. data 2 ). Thus, envi- 

 ronmental and ecological factors affecting prerecruit 

 mortality should be considered, mainly in association 

 with a no-fishing area implemented in 1997. Moreover, 

 the demographic composition and the nutritional state 

 of spawning females (maternal effect) are other factors 

 that have been related to recruitment levels (Trippel et 

 al., 1997; Kjesbu et al., 1998; Cardinale and Arrhenius, 

 2000). 



Analysis of hydrographic characteristics from the 

 north-Patagonian waters in the 1980s and 1990s indi- 

 cated that the Patagonian shelf, including the Isla Es- 

 condida area, is a relatively stable environment (Erhlich 

 et al. 2 ). On the other hand, analysis of temperature 

 and salinity data collected from 1995 to 2002 in the 

 nursery area of the Patagonian stock (San Jorge Gulf), 

 showed that higher values of salinity and temperature 

 during the time of hatching were associated with higher 

 indices of abundance at age 1, one year later (Santos 

 et al. 3 ). 



The high proportion of larger females in the offshore 

 area mainly in 2000 and 2001 may have affected the 

 quality as well as the quantity of hake progeny. In gen- 

 eral, older females produce larger eggs and larger lar- 

 vae with higher rates of survival, in combination with 

 more egg batches over a longer spawning season (Kjesbu 

 et al., 1996; Trippel, 1998). Previous reports showed 

 that M. hubbsi older than 5-years have a longer spawn- 

 ing season (Macchi et al., 2004) and produce heavier 

 eggs than young females do (Pajaro et al. 4 ). Thus, an 

 increase in the proportion of older spawning females in 



4 Pajaro, M, E. Louge, G. J. Macchi, N. Radovani, and L. 

 Rivas. 2002. Calidad de los ovocitos de la poblacion 

 patagonica de merluza {Merluccius hubbsi) durante la epoca 

 de puesta estival. Tech. Rep. 55/02, 13 p. INIDEP, CC. 

 175, Mar del Plata (7600), Argentina. 



the stock may result in improved recruitment, as has 

 been reported for other species (Mairteinsdottir and 

 Thorarinsson, 1998). 



The fishing regulation for Patagonian hake imple- 

 mented in the late 1990s mainly affected bottom trawl- 

 ers and the factory freezer fleet, which applied greater 

 fishing effort in the north Patagonian area during the 

 1990s. It is possible that this decline in harvesting 

 pressure by trawlers on Patagonian hake after 1997 in- 

 fluenced the reproductive success of this species. Stress 

 can have a negative impact on fish reproduction (Camp- 

 bell et al, 1994; Clearwater and Pankhurst, 1997). The 

 potential effects of trawl avoidance can affect the repro- 

 ductive physiology and behavior during spawning, which 

 could lead to the production of fewer viable juveniles 

 (Morgan et al., 1999). 



Finally, other factors, such as predation and feeding 

 conditions within the new spawning ground of Patago- 

 nian hake, can affect survival of the early life stages. 

 In addition, future studies should include a comparison 

 between the inshore and offshore waters of the north- 

 Patagonian area with respect to the abundance of jel- 

 lyfish (i.e., Medusae and Ctenophora), which are known 

 to be major predators of fish eggs and larvae (Bailey, 

 1984; Fancett, 1988). 



Acknowledgments 



We thank Jorge Hansen for assistance with the method 

 used to estimate fish abundance. We would also like to 

 thank Hector Cordo for reading and making suggestions 

 to improve the manuscript. 



Literature cited 



Aubone, A., S. Bezzi, R. Castrucci, C. Dato, P. Ibanez, G. Irusta, 

 M. Perez, M. Renzi, B. Santos, N. Scarlato, M. Simonazzi, 

 L. Tringali, and F. Villarino. 



2000. Merluza {Merluccius hubbsi). In Sintesis del estado 

 de las pesquerias maritimas argentinas y de la Cuenca 

 del Plata. Anos 1997-1998, con una actualizacion de 

 1999 (S. Bezzi, R. Akselman and E. Boschi, eds.), p. 

 29-40. INIDEP, Mar del Plata, Argentina. 

 Bailey. K. M. 



1984. Comparison of laboratory rates of predation on five 

 species of marine fish larvae by three planktonic inver- 

 tebrates. Effects of larval size on vulnerability. Mar. 

 Biol. 79:303-309 

 Campbell, P. M„ T. G. Pottinger, and J. P. Sumpter. 



1994. Preliminary evidence that chronic confinement 

 stress reduces the quality of gametes produced by brown 

 and rainbow trout. Aquaculture 120:151-169. 

 Cardinale, M., and F. Arrhenius. 



2000. The influence of stock structure and environmen- 

 tal conditions on the recruitment process of Baltic cod 

 estimated using a generalized additive model. Can. J. 

 Fish. Aquat. Sci. 57: 2402-2409. 

 Ciechomski, J. D„ R. P. Sanchez, C. A. Lasta, and M. D. 

 Ehrlich. 



1983. Distribucion de huevos y larvas de anchoita (En- 



