445 



Can a change in the spawning pattern of 

 Argentine hake (Merluccius hubbsi) 

 affect its recruitment?* 



recruitment of this stock in different 

 years between 1988 and 2001. 



Materials and methods 



Gustavo J. Macchi 



Conseio Nacional de Investigaciones Cientificas y Tecnicas (CONICET) 



Rivadavia 1917 



1033 Buenos Aires. Argentina 



Present address: Instituto Nacional de Investigacion y Desarrollo Pesquero (INIDEP) 



Paseo Victoria Ocampo N° 1. CC. 175 



Mar del Plata, 7600, Argentina 

 E-mail address gmacchnaHnidepeduar 



Marcelo Pajaro 



Adrian Madirolas 



Instituto Nacional de Investigacion y Desarrollo Pesquero (INIDEP) 

 Paseo Victoria Ocampo N° 1 CC. 175 

 Mar del Plata, 7600, Argentina 



Argentine hake (Merluccius hubbsi) 

 inhabit waters of the Southwest 

 Atlantic Ocean between 22° and 55°S, 

 at depths ranging from 50 to 500 m 

 (Cousseau and Perrota, 1998). This 

 species has historically been among 

 the more abundant fish resources in 

 the Argentine Sea, where its biomass 

 has ranged between one and two 

 million metric tons annually since 

 1986 (Aubone et al., 2000). In this 

 area, there are two identified fish- 

 ing stocks, limited by the 41°S paral- 

 lel. The southern group (Patagonian 

 stock) is the more important with an 

 abundance of about 85% of the total 

 biomass estimated for this species in 

 1999 (Aubone et al., 2000). During 

 the late 1990s, the spawning biomass 

 of both stocks and their recruitment 

 indices declined drastically, both of 

 which were attributed to an increase 

 in exploitation (Aubone et al., 2000). 

 The Patagonian stock of Argentine 

 hake spawns from November through 

 March and peak spawning occurs in 

 January (Macchi et al., 2004). This 

 species is a batch spawner and has 

 indeterminate annual fecundity, 

 which is to say that unyolked oocytes 

 continuously mature and are spawned 

 throughout the reproductive season 

 (Macchi and Pajaro, 2003). Thus, to 

 estimate total fecundity, it is neces- 

 sary to determinate the number of 



eggs released at one spawning (batch 

 fecundity) and to estimate the num- 

 ber of batches spawned in a repro- 

 ductive season (spawning frequency). 

 Macchi et al. (2004) estimated these 

 parameters for the southern stock of 

 M. hubbsi. They analyzed total egg 

 production during the reproductive 

 season and determined that the size 

 composition of the spawning fraction 

 influences the reproductive potential 

 of the stock. 



Reproductive activity of the Pata- 

 gonian hake historically has taken 

 place mainly in coastal waters off the 

 Chubut province at depths near 50 

 m, in the area known as Isla Escon- 

 dida (43°30-44°S) (Ciechomski et al., 

 1983). Since 1997-98, a movement of 

 reproductive hake to deeper waters 

 and a decrease in fish density have 

 been observed (Ehrlich et al. 1 ). These 

 changes, mainly in the location of the 

 spawning area, may have affected 

 the reproductive potential of this spe- 

 cies, reducing the survival of eggs 

 and larvae. If so, we would expect a 

 negative effect on the number of juve- 

 niles recruited after this period. 



In this note, we hypothesize that a 

 change in spawning site for Patago- 

 nian hake can affect species recruit- 

 ment. We studied temporal changes 

 in the location and density of spawn- 

 ing aggregations, egg production, and 



Samples of M. hubbsi were collected 

 from the area where the Patagonian 

 stock is known to reproduce during 

 four acoustic surveys in December 

 1988, 1993, 1996, and 2000 and 

 during six trawl cruises carried out 

 in January between the years 1996 

 and 2001. 



Acoustic surveys covered the Isla 

 Escondida area between 43° and 

 45°S (Fig. 1). A SIMRAD EK400/QD 

 echointegrator was used for the 1988 

 survey and a SIMRAD EK500 echo- 

 sounder and BI500 postprocessing 

 program were employed for subse- 

 quent surveys. To avoid possible bi- 

 ases due to the presence of fish in the 

 near-bottom, acoustic transects were 

 carried out at night when hake as- 

 sume a more pelagic behavior. Trawl 

 catches were carried out during the 

 day, when fish are concentrated close 

 to the bottom, and immediately af- 

 ter each acoustic transect. Because 

 trawls were intentionally biased to 

 those areas of higher fish density, 

 their positions were different be- 

 tween 1988 and 2000. Nevertheless, 

 the study area, transect design, and 

 sampling effort were similar for all 

 cruises covering the main spawning 

 shoals. 



In January, information was col- 

 lected from trawl surveys to assess 

 the Patagonian stock of juvenile 

 hake between 1996 and 2001. These 

 cruises covered a wide area between 

 43° and 47°S that included a section 



' Contribution 1357 from the Instituto 

 Nacional de Investigacion y Desarrollo 

 Pesquero, Mar del Plata, Argentina. 

 Ehrlich, M. D., P. Martos, A. Madirolas, 

 and R. P. Sanchez. 2000. Causes of 

 spawning pattern variability of anchovy 

 and hake on the Patagonian shelf. ICES 

 CM 2000/N:06. 



Manuscript submitted 2 July 200.3 

 to the Scientific Editor's Office. 



Manuscript approved for publication 



20 December 2004 by the Scientific Editor. 



Fish. Bull. 103:445-452 (2005). 



