Invasion by saffron cod Eleginus gracilis into nearshore habitats of Prince William Sound, Alaska, USA

We recently identified saffron cod Eleginus gracilis as a dominant fish species in near-shore habitats (<5 m deep, <20 m offshore) of western Prince William Sound (PWS), Alaska, USA. Saffron cod have not been previously reported in PWS, and their capture suggests that fish community structure has changed in nearshore habitats. Nearly 16 000 saffron cod were captured in 49 of 95 beach seine hauls at 8 locations in western PWS in 2006 and 2007. Saffron cod accounted for 32% of the total fish catch (49 060 fish, 45 species). Abundance of saffron cod differed by season and habitat type; catch was greater in summer and fall than in spring, and fish were captured almost exclusively in eelgrass Zostera marina habitat. Most saffron cod captured were Age-0; based on age from otoliths, mean size of Age-0 fish increased from 70 mm total length (TL) (n = 8) in July to 108 mm TL (n = 21) in September. Age-0 saffron cod consumed predominantly pelagic fauna (oikopleurans), whereas fish aged >= 1 targeted predominantly epibenthic fauna (polychaetes and crustaceans). Most saffron cod left the nearshore area by late summer; of 1002 fish that were fin-clipped and released at 1 sampling location (eelgrass) in July 2007, only 2 were recaptured in late August 2007. Reasons for the sudden and dramatic increase in the abundance of saffron cod in western PWS are unclear; possible ecological implications, however, include competition for food and space and increased predation risk to commercially important and forage fish species.