Entanglement and count data for Steller sea lions and California sea lions in northwest Washington
Steller and California sea lions in northwest Washington were counted and monitored for entanglements from 2010 through 2018 to determine population trends and temporal and spatial patterns of entanglement rates for the two species. The collection of count data and the majority of monitoring of entanglements occurred at four major sea lion haulout complexes: Tatoosh Island, Bodelteh Islands, Carroll Island, and Sea Lion Rock. We conducted counts with the aid of 8x40 and 7x50 binoculars. We photographed each sea lion with evidence of entanglement using a digital SLR camera with powerful zoom lens of either 70-300 mm or 100-400 mm. Some entanglements were observed and recorded at minor haulouts outside of the four complexes and were recorded for purposes of characterizing the temporal patterns of what type of debris causes entanglements. After surveys, we processed photographs to determine characteristics of each entanglement event. Our first step was to evaluate if our photographs were of sufficient quality for subsequent analyses. If the photos were not, we often relied on field notes to record details on the entanglement. For each suitable photograph of an entanglement, we recorded the species of sea lion entangled and whether the entanglement was active or was a scar from a previous entanglement. For active entanglements, we recorded what type of debris caused the entanglement into twelve categories: fishing lure, flasher, gillnet, longline, monofilament, net, packing band, rope, rubber band, scar, trawl net, unknown. Last, we determined the sex and age of each entangled individual to allow analyses to determine if there were patterns in the type of marine debris that affected sea lions of different age, sex, and species.