204 



Fishery Bulletin 103(1) 



The low number of positive stations in spite of the 

 intense sampling conducted within the area of distribu- 

 tion of P. semifasciata suggests a reduced spawning site. 

 Both the area off Peninsula Valdes and the one near 

 Isla Escondida have rocky bottoms, which complicates 

 trawling operations. A few experienced captains were 

 able to target P. se?nifasciata by trawling along sandy 

 corridors between rocky outcrops off Peninsula Valdes 

 during the reproductive season (Elias 4 ). Likewise, where 

 running Argentine sandperches were observed near Isla 

 Escondida, trawling is possible only in one orientation 

 (Ehrlich, personal observ. ). This could indicate that 

 spawning grounds are associated with rocky outcrops. 

 Spawning associated with rocky reefs and the existence 

 of chromatic sexual dimorphism is compatible with Mac- 

 chi et al.'s (1995) and Gonzalez's (1998) suggestions of a 

 complex mating system involving sexual courtship. 



Spawning activity of P. semifasciata in northern 

 Patagonia (42-44°S) peaks in November and Decem- 

 ber (Elias and Burgos, 1988; Macchi et al., 1995), and 

 in October within San Matias Gulf (Gonzalez, 1998). 

 Maximum densities of larvae (>20 larvae/10 m 2 of sea 

 surface) were found in December 1986, 1996, and 1999. 



The temperature at 10 m depth at positive ichthyo- 

 plankton stations varied between 12.3°C and 18.7°C. 

 Such a wide range of temperature reflects the wide 

 latitudinal range in the distribution of P. se?nifasciata 

 and the extended time period (November-March) in 

 which larvae were collected. 



Posttransition pinguipedid juveniles were mainly col- 

 lected at depths between 60 and 65 m, in both sea- 

 sons sampled (summer and fall). A total of seven P. 

 semifasciata juveniles ranging in total length from 

 66 to 82 mm were collected in fall (June), near the 

 northern coast of San Matias Gulf (40°58'S-41°00'S; 

 64°18'W-64 24'W), at 29-54 m depth, associated with 

 rib mussel beds (Aulacomya ater) (Gonzalez 5 ). Our dis- 

 tributional data indicate that settlement and nursery 

 grounds could be located near shore. The absence of 

 posttransition juveniles off northeast of Camarones 

 Bay during summer and their presence in the fall could 

 be a consequence of a delayed spawning pulse in the 

 southern stocks. Some independent observations sup- 

 port this hypothesis: 1) back-calculations of hatching 

 date based on daily growth increments from 19 post- 



4 Elias, I. 2004. Personal commun. Centra Nacional Pata- 

 gonico, Puerto Madryn, Chubut, Argentina. 



5 Gonzalez, R. A. C. 2004. Personal commun. Instituto 

 de Biologia Marina y Pesquera "Alte. Storni," San Antonio 

 Oeste, Rio Negro, Argentina. 



