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

Abstract

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 commu- nity 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 oto- liths, 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; pos- sible ecological implications, however, include competition for food and space and increased preda- tion risk to commercially important and forage fish species.