Growth and condition of larval rockfish in a Patagonian fjord-type inlet: role of hydrographic conditions and food availability

A field experiment was conducted for 4 consecutive days in December 2010 in Hornopirén inlet, a fjord from Chilean Patagonia, in order to determine the impact of marked environmental differences on fish larval distribution and growth (i.e., otolith microstructure) of the rockfish Sebastes oculatus . Two layers were noticeable: a surface one (0–10 m depth), characterized by warmer temperature and lower salinity, separated by a strong thermo- and halocline from the deep layer (>10 m depth), with lower temperature and saltier waters. As a prey field, nauplii showed similar abundances between strata, but calanoid copepodites were more abundant below the thermocline. Larval S. oculatus were more abundant in the deep stratum. Temperature was negatively correlated with calanoid copepodites as well as with S. oculatus abundances. Larval density was positively correlated with copepodites but not with nauplii abundance. S. oculatus larvae from the surface layer grew faster (0.137 ± 0.006 mm day −1 ) than those collected below the thermocline (0.103 ± 0.012 mm day −1 ). Otolith size (radius) as well as the recent otolith growth index was similar in individuals collected from both water parcels; however, linear mixed-effects models indicate that microincrement widths were slightly wider in older larvae occurring above the thermocline. Conclusions are that water temperature was more important than food availability for larval fish growth and recent hydrographic conditions are affecting the growth trajectories of larval rockfish in a Chilean fjord.