1. Possible recruitment of jack mackerel (Trachurus murphyi) from oceanic waters off Chile to the stock in Peruvian and Ecuadorian waters in 2010 Ad Corten Netherlands Ministry of Economic Affairs / Pelagic Freezertrawler Association

2. Distribution of catches of juvenile jack mackerel < 25 cm (yellow squares) by the PFA fleet during the 2010 fishing season compared to catches of larger jack mackerel (red squares)

3. Length distribution of PFA catches from 2007 – 2013

4. Catches of jack mackerel by country

5. Peru Ecuador 0° 10° 20° 30° 40° 50° 80°90° 70° 100°110°60° South Pacific Current Humboldt Current Chile Presumed pathway of juvenile jack mackerel from June to December 2010

6. length distribution of commercial catches in Peru in November 2010 – April 2012

7. length distribution of jack mackerel catches in Ecuador in February 2011

8. Time axis with modal length of juvenile jack mackerel in central Pacific (June 2010) and modal length in Peruvian catches (November 2010 – April 2012). All measurements in total length

9. Peru Ecuador 0° 10° 20° 30° 40° 50° 80°90° 70° 100°110°60° South Pacific Current Humboldt Current Chile Presumed pathway of juvenile jack mackerel from June to December 2010

10. Positive SST anomalies in eastern Pacific in April 2010 illustrate the existence of an El Niño in the first half of 2010

11. Strong negative SST anomalies in the eastern Pacific in September 2010 illustrate the existence of a La Niña in the second half of the year

12. Suitable habitats for jack mackerel in the south-eastern Pacific

13. Classical scheme of juvenile jack mackerel migrations off Chile. From Arcos et al. 2001

14. Recent model for migrations of juvenile jack mackerel in the south-eastern Pacific. From Gretchina et al. 2007

15. Distribution of juveniles (red cloud) off Chile in a normal year (left) and in an El Niño year (right). From Gretchina et al. 2007.

16. Chilean juveniles may be adopted by the Peruvian population “Adopted Migrant” hypothesis (McQuinn 1997) Pelagic fish develop an attachment to the area where they happen to be at the time they turn into adults In this way, juveniles from Chilean origin may turn into “Peruvian” jack mackerel with biological characteristics similar to the Peruvian population

17. Conclusions Immigration of juveniles from Chile into Peru are likely to happen during La Niña periods A strong La Niña occurred in the second half of 2010 This may have resulted in a transport of juveniles of year- class 2008 from Chile to Peru at this time The Chilean juveniles may have been “adopted” by the Peruvian population The occasional immigration of juveniles from Chile into Peru would explain the lack of genetic difference between the population in both areas