Comparison of Processing Pinniped Scat Samples Using a Washing Machine and Nested Sieves

• Published in: Wildlife Society bulletin 2003-04, Vol.31 (1), p.253-257
• Main Authors: Orr, Anthony J., Laake, Jeffrey L., Dhruv, Mark I., Banks, Adria S., DeLong, Robert L., Huber, Harriet R.
• Format: Article
• Language: English
• Subjects: Animals; Beak; Comparative analysis; Diet; Digestive system; Fisheries science; Marine mammals; Ocean fisheries; Otolith organs; Phoca vitulina; Sea lions; Seals; Studies; Technologies and Techniques; Washing; Waste materials; Zalophus californianus
• ISSN: 0091-7648; 1938-5463

Scat (fecal) samples are commonly collected to assess the diet of pinnipeds; however, large sample sizes are required, to account for individual and/or seasonal variation in diet composition. Thus, it is imperative to have an efficient, reliable method to process scats. We tested the reliability and efficiency of processing pinniped scats with a washing machine as compared to nested sieves, which are frequently used. We randomly divided 217 California sea lion (Zalophus californianus) and 218 Pacific harbor seal (Phoca vitulina) scats into 2 nearly equal-sized groups for processing by sieves or washing machine. Hard parts of prey were identified to species, number of prey was enumerated, and length of each otolith was measured. There were no significant differences between the methods in the average number of species or number of individual prey identified. The average length of otoliths processed in the washing machine was 5.1% (SE=1.5%) smaller for sea lion prey but only 2.9% (SE=2.0%) for harbor seal prey than otoliths processed using sieves. To reduce the potential impact of variability among scats, we processed 20 scats using nested sieves, identified the prey, reassembled the remains and waste material, and reprocessed the same scats through the washing machine. As a control for loss during handling, we also processed and reprocessed 20 scats through sieves. Five percent of the individual prey were lost in the reprocessing by washing machine (7 of 131) and sieves (5 of 104). Average otolith length was reduced 1.0% in machine reprocessing and 0.6% in sieve reprocessing. We also compared the time required to process 20 scats via each method. There was a 58.3% reduction in processing time with the washing machine (2.5 hr) compared to the sieves (6.0 hr). Unless scats are collected with substrate material containing rocks or vegetation, washing-machine processing is reliable and significantly faster than sieve processing.