Forage Fish Size, Age, and Energy Density Data from Prince William Sound, Alaska

All Pacific sand lance and capelin were captured in July to sample age composition, size,and body condition. Forage fish were collected using a variety of methods, including a purse seine, beach seine, herring jig, cast net, dip net, and gill net. The purse seine was deployed from a skiff, and was 46.9 m long and 6.1 m deep, with a mesh size of 32 mm and 3.2 mm. The beach seine was set parallel to shore from a skiff and retrieved from the beach and was 37 m long with diminishing mesh size from 28 mm at the wings to 5 mm at the center. Herring jigs (hook size 4, 6, 8 and 10), cast nets (mesh size 6.4 mm and 19.1 mm), long-handled dip nets (mesh size 5 mm) and gill nets (18.2 m x 4.9 m with variable mesh panels of 6.4 mm, 7.9 mm, and 9.5 mm square mesh) were used infrequently to sample small, shallow schools.

Fish length was measured to the nearest mm from either freshly captured individuals at sea (Field_length _mm) or thawed individuals in the laboratory (Lab_length_mm). Age was assigned by counting translucent annular rings on sagittal otoliths by two independent, blind readers. In the event of disagreement in age assignment, readers re-examined an otolith jointly and assigned a consensus age for analysis. Otoliths were extracted, dried, and examined under reflected light using a Leica M60 dissection microscope. Digital images of each otolith were captured using a Leica DFC425 digital camera. Energy density and whole body energy were estimated using bomb calorimetry on a subset of samples following otolith removal and age assignment. Ten individuals were randomly selected within each primary age class (age-0, age-1) and collection year for energy density analysis. Whole fish were freeze-dried until weight stabilized and no moisture was apparent (approximately 48 hours). Dry mass was recorded to the nearest 0.0001 g. Dried fish were homogenized using a mortar and pestle and a pellet was pressed from a subsample and weighed immediately. A semimicro Parr 6725 calorimeter was used to measure energy density. Benzoic acid standards and duplicate tissue samples were used to evaluate precision. Energy density was reported per unit dry mass (kJ g-1 dry mass) as wet mass measurements likely introduce a desiccation bias that can mask the true biological relationships (Montevecchi and Piatt 1987, Hislop et al. 1991, Van Pelt et al. 1997, Ball et al. 2007). Whole body energy (kJ fish -1) was estimated by multiplying energy density (kJ g-1 dry mass) by dry mass (g).