Dietary Comparison of Two Hawaiian Monk Seal Populations: The Role of Diet as a Driver of Divergent Population Trends

April 23, 2013

Monk seals in the Northwestern Hawaiian Islands and main Hawaiian Islands eat a similar diet, but seals in the main Hawaiian Islands may experience less competition for food. In addition, prey that may be more bountiful and better quality, allowing the main Hawaiian Islands population to increase while the Northwestern Hawaiian Islands population continues to decrease.

Divergent trends in population abundance of Endangered Hawaiian monk seals (Monachus schauinslandi) are apparent between the Northwestern Hawaiian Islands and the main Hawaiian Islands. The smaller, recently established main Hawaiian Islands seal population is increasing, exhibits higher juvenile survival, and seals appear to be in better condition overall relative to seals in the Northwestern Hawaiian Islands. Using traditional dietary analysis we characterize the diet of main Hawaiian Islands monk seals for the first time and examine the hypothesis that diet and prey availability may be driving these regional trends. Prey remains from feces and regurgitates (n = 120) were identified to the lowest possible taxonomic level and compared with results from Northwestern Hawaiian Islands historical data. The most common prey taxa, by percent frequency of occurrence, were Balistidae (48.3%), Crustacea (37.5%), Acanthuridae (32.5%), Muraenidae (30.8%), Serranidae (20.8%), Cephalopoda (18.3%), Holocentridae (17.5%), Labridae (16.7%), and Scaridae (10.8%). Results indicate that main Hawaiian Islands and Northwestern Hawaiian Islands seals eat similar diets; however, an incongruity in body conditions of seals between regions indicates a possible difference in intra- or inter-specific competition, prey availability, and quality. Further research assessing foraging behavior and habitat use would aid in identifying the regional differences observed.

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Cahoon MK, Littnan CL , Longenecker K, Carpenter JRDietary Comparison of Two Hawaiian Monk Seal Populations: The Role of Diet as a Driver of Divergent Population Trends. Published in Endangered Species Research.

Last updated by Pacific Islands Fisheries Science Center on 03/05/2019

Hawaiian Monk Seal Northwestern Hawaiian Islands