Podest^: Migratory pattern of Merluccius hubbsi 



71 



8 ' 



6 



2 



S' 



12 



66* 64- 62- 60- 58° 56° 54'W 



34* 



36' 



38° 



40 



42S 



12 



10 

 11 2 



12 1 



66' 64* 62* 60- 



58" 56- 5?V\r 



se- 



as- 



42 S 



Figure 5 



Monthly weighted latitude and longitude means of (a) fishing effort 

 and Oj) Argentine hake CPUE in southwestern Atlantic Ocean, com- 

 puted from 1978 commercial fishery statistics. Numbers indicate 

 months. 



latter value was only slightly higher than that com- 

 puted for the active northward migration, 9.2 km/day 

 (February-March). If a significant difference in south- 

 ward vs. northward migrating speed exists, it probably 

 cannot be detected using coarse fishery statistics. 



The migration speeds estimated above must be con- 

 sidered only as a first approximation, but they general- 

 ly agree with values reported for a similar species. 

 Francis (1983) estimated swimming speeds for Pacific 

 hake Merluccius productus of different ages based on 

 timing of sequential appearance at different latitudes. 

 His estimated speeds for the age classes 4-7, those 

 predominant in Argentine hake catches, range from 9 

 to 12 km/day. Ermakov (1974; cited in Bailey et al. 

 1982) concluded from direct observation of a school that 

 the northward migration of Pacific hake is at speeds 

 of 5-11 km/day. 



respectively, to speeds of 6-11 km/day and 1-4 km/day 

 (Table 1). Higher speeds, obviously, are associated with 

 periods of active migration. 



The estimated speeds of the northward and south- 

 ward (i.e., feeding and spawning) migrations were sim- 

 ilar. Estimated speeds during the most active periods 

 of southward displacement were 11.7 km/day (August- 

 September) and 9.5 km/day (September-October). The 



Interannual variability in the migratory 

 pattern of hake 



Cumulative time density of fishing effort is shown in 

 Figin-e 6 for three regions: Buenos Aires slope north 

 (region 1), Patagonian slope north (region 4), and south- 

 ern spawning grounds (region 8). The values shown in 

 the figures for each month represent the proportion 

 of yearly regional effort accumulated up to the end of 



