The big (Raja binoculata), California (R. inornata), longnose (R. rhina), and sandpaper (Bathyraja kincaidii), skates are commonly found on soft-bottom regions of the central California continental shelf and upper slope. The feeding ecology of this assemblage was compared to evaluate the degree of trophic separation among species, based on the results of previous speciesspecific diet studies. Specimens were collected from fishery independent trawl surveys conducted during September 2002-March 2003 at depths of 9-536 m. Using single and compound measures, diet composition of small (£60 cm TL) and large (>60 cm TL) individuals were compared within continental shelf (£200 m) and slope (>200 m) regions using traditional, multivariate, and novel techniques. Diet compositions within size classes were similar in both regions. Diet compositions between size classes generally differed, however, with fishes more important and crustaceans (especially shrimps and euphausiids) less important in the diets of large individuals. Crabs contributed substantially to skate diet compositions on the shelf, but were uncommon prey items at deeper depths, probably because of their relative scarcity in slope waters. Conversely, cephalopods were common prey items at slope depths, but were rarely ingested at shelf depths. The studied skate assemblage appears to consist primarily of generalist crustacean and fish predators that exhibit high dietary overlap at similar sizes. It is possible that resource competition among skates and groundfish species has been reduced because of considerable recent declines in the biomass of upper trophic level groundfishes. Skates may therefore play important roles in contemporary benthic food web dynamics off central California.

Erroneous standard error values of the percentage index of relative importance (%IRI) were presented in the above article (see Figure 3); leading to the unsubstantiated conclusion that %IRI calculations were much less precise than those of the percentage geometric index of importance (%GII). When corrected, standard error estimates of %IRI were actually only slightly less precise than those of %GII. For example, %IRI and %GII values (mean ± SE) corresponding to the most important prey taxa of the sandpaper skate (Bathyraja kincaidii) were: shrimplike crustaceans (%IRI=65.7±4.1; %GII=50.2±2.5); polychaetes (%IRI=13.4±2.2; %GII=16.9±2.2); and cephalopods (%IRI=9.9±1.9; %GII=13.8±1.8). Although precision of %GII calculations was always greater than that of %IRI for our data set, measures of occurrence differ between indices and this result may not be typical. Environ Biol Fish (2009) 84:241 DOI 10.1007 The online version of the original article can be found at http:// dx

The stomachs of 130 sandpaper skates, Bathyraja kincaidii (Garman, 1908), were sampled from off central California to determine their diet composition. The overall diet was dominated by euphausiids, but shrimps, polychaetes and squids were also important secondary prey. A three-factor MANOVA demonstrated significant differences in the diet by sex, maturity status and oceanographic season using numeric and gravimetric measures of importance for the major prey categories. These three main factors explained more variation in diet than interactions between the factors, and season explained the most variance overall. A detailed analysis of the seasonal variation among the prey categories indicated that abundance changes in the most important prey, euphausiids, were coupled with seasonal changes in the importance of other prey. When upwelling occurred and productivity was great (Upwelling and Oceanic seasons), euphausiids were likely highly abundant in the study area and were the most important prey for B. kincaidii. As productivity declined (Davidson Current season), euphausiids appeared to decrease in abundance and B. kincaidii switched to secondary prey. At that time, gammarid amphipods and shrimps became the most important prey items and polychaetes, mysids and euphausiids were secondary.

The stomachs of 130 sandpaper skates, Bathyraja kincaidii (Garman, 1908), were sampled from off central California to determine their diet composition. The overall diet was dominated by euphausiids, but shrimps, polychaetes and squids were also important secondary prey. A three-factor MANOVA demonstrated significant differences in the diet by sex, maturity status and oceanographic season using numeric and gravimetric measures of importance for the major prey categories. These three main factors explained more variation in diet than interactions between the factors, and season explained the most variance overall. A detailed analysis of the seasonal variation among the prey categories indicated that abundance changes in the most important prey, euphausiids, were coupled with seasonal changes in the importance of other prey. When upwelling occurred and productivity was great (Upwelling and Oceanic seasons), euphausiids were likely highly abundant in the study area and were the most important prey for B. kincaidii. As productivity declined (Davidson Current season), euphausiids appeared to decrease in abundance and B. kincaidii switched to secondary prey. At that time, gammarid amphipods and shrimps became the most important prey items and polychaetes, mysids and euphausiids were secondary.

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