Distribution and Growth of Juvenile Pink Salmon in the Coastal Waters of Eastern Hokkaido Determined with Otolith-Marking

In Hokkaido, northern Japan, although relatively constant numbers (approximately 140 million fish) of hatchery pink salmon juveniles have been released annually since the 1990s, even and odd year catches of pink salmon in coastal fisheries consistently differ. The reason(s) for this interannual pattern is unknown. There is little consistently gathered information on the ecology and status of pink salmon in Hokkaido although Morita et al. (2005) documented their population structure. It has been suggested that ocean conditions can limit salmon production and high mortality occurs during their early sea life (Parker, 1968; Mortensen et al. 2000). Consequently, we wished to improve our understanding of the early marine ecology of juvenile pink salmon with respect to their offshore movement and growth. We monitored the distribution and growth of juvenile pink salmon and environmental conditions off the Abashiri coast of the Okhotsk Sea beginning in 2002 (Ando et al. 2005). Four transects were established (A–D; Fig. 1), each with three sampling sites 1 km, 4 km, and 7 km from the shore. Sampling occurred every ten days from late April to early July, 2002–2005. In coastal waters, we captured juvenile pink salmon using a surface trawl net pulled by two boats. We also beach seined littoral waters (St. E; Fig. 1) starting in 2003. Because juvenile pink salmon captured in the coastal or littoral waters of the Abashiri coast might include hatchery-origin fish released from several sites as well as naturally spawned fish, we designed an otolith-marking experiment in 2005 to survey the distribution and growth of juveniles of known origin. Of the 17.