2.2 Prey sampling
Potential prey items to be collected for macronutrient and energetic analyses were selected based on existing literature on sea otter diets in Southeast Alaska . Five functional prey groups (crabs, clams, sea cucumbers, snails, sea urchins) were identified that were composed of 13 target species for analysis. These five functional groups made up 95% of sea otter diets (in terms of biomass) from visual foraging observations. Five individuals of each target species were collected at two sites (Fig. 1) in May 2018, August 2018, and February 2019. All samples were collected in the intertidal zone. Two collection sites were selected that encompassed the foraging observation sites and had reliable access. Craig (Site 1) and Soda Bay (Site 2) represented differences in sea otter occupation time (> 15 years for Craig, and > 7 years for Soda Bay). Where there were more sea otters present, there were less abundant invertebrate species for collection. Additional samples were opportunistically collected around POW if they were not present or in high enough abundance in the two designated sites. Samples were held in seawater-filled buckets, cleaned of sand and dirt, and then frozen at -18°C.
In the lab, samples were thawed, weighed, measured, and separated into edible and inedible tissues. For bivalves, decapods, gastropods, and sea urchins, all hard parts were removed and discarded, as they were considered inedible as the sea otter excretes these contents . For sea cucumbers, the entire organism was considered edible. Only crabs were processed separately by sex. Remaining edible tissues were weighed and homogenized in a Cuisinart Mini-prep food processor. A maximum of 4 g of tissue was dried in a LECO Thermogravimetric Analyzer 701 (TGA) dryer at 135°C, or in a gravity convection oven (VWR Symphony 414004-552) at 70°C. Standards and duplicates were run with each dryer to confirm consistent moisture values.