Podest.3: Migratory pattern of Merluccius hubbsi 



169 



- 9- 



45 S 



Figure 2 



Schematic description of the annual migratory pattern of Argentine 

 hake in southwestern Atlantic Ocean. Approximate locations of some 

 oceanic features mentioned in the text are also shown. 



Figure 3 



[A) Temperature section (°C) along the northern Argentine shelf 

 break, July 1978. (B) Log of Argentine hake CPUE at fishing sta- 

 tions occupied at the same latitude as the hydrographic stations, but 

 slightly shoreward. Date from the RV Wnlthcr Henvig. 



does not require between-year consistency in the mea- 

 sure of effort. The technique is based on the fluctua- 

 tions in fish abundance as a function of time in a fixed 

 geographic reference frame and originally employed 

 catch or CPUE data (Mundy 1982). However, the 

 regions considered showed no fishing effort during 

 some months and CPUE was undefined; the zero ef- 

 fort value, in contrast, was meaningful. Therefore, I 

 used effort values (hours trawled per month) to con- 

 struct the cumulative time density series in the man- 

 ner described by Mundy (1982). 



Results 



Migratory pattern of hai<e 



Figure 2 shows a schematic description of the migra- 

 tory pattern of Argentine hake, derived from catch- 

 and-effort statistics of the commercial fleet for 1978 

 and 1979 and complemented by literature reports. 

 Hake show a cyclic northward-southward migration 

 accompanied, respectively, by offshore-inshore 

 movements. 



The northernmost area reached by concentrations of 

 hake exploited by the Argentine fleet is off Rio de la 

 Plata, between 34°S and 38°S. Hake arrive around 

 May and stay through August, so this area can be con- 

 sidered the wintering grounds. During these months, 

 hake concentrate along the outer shelf and continen- 

 tal slope. 



Figure 3a shows a temperature section from hydro- 

 graphic stations occupied along the shelf break, approx- 

 imately between 35.5°S and 38°S, by the RV WaWier 

 Herwig in July 1978. The tightening of the isotherms 

 in the northern part of the section (at about 36°S) in- 

 dicates the confluence of the Malvinas Current, which 

 flows northward carrying nutrient-rich subantarctic 

 waters, and the subtropical waters of the southward- 

 flowing Brazil Current (Olson et al. 1988). Figure 3b 

 shows hake CPUEs in fishing stations occupied at the 

 same latitudes as the hydrographic stations, but slightly 

 shoreward. The highest densities of hake occurred near 

 the Brazil-Malvinas confluence. 



By the end of winter (September), a southward move- 

 ment begins, accompanied by a corresponding inshore 

 migration to shallower waters (Christiansen and Cous- 

 seau 1971, Bellisio et al. 1978). During the southward 

 migration, fishing effort is widely scattered and CPUE 

 values are relatively homogeneous throughout the 

 shelf. This suggests a spatial dispersion of hake, which 

 is not observed during the northward leg of the migra- 

 tion (Otero 1986). 



The southward migration is associated with a move- 

 ment towards spawning grounds. Mature female hake 

 can be found year-round (Christiansen and Cousseau 

 1971), but most of the reproductive activity takes place 

 in spring and summer (Ciechomski et al. 1979b). Octo- 

 ber and November are months of active spawning for 

 at least some part of the stock(s). Commercial fishery 

 statistics do not allow any conclusions on reproductive 

 status, as only the weight of fish caught is reported. 



