ESR 15:29-37 (2011)  -  DOI: https://doi.org/10.3354/esr00364

ABSTRACT: Food limitation and poor body condition are significant factors affecting the survival of juvenile Hawaiian monk seals Monachus schauinslandi in the Northwestern Hawaiian Islands. Previous research has indicated that juvenile monk seals infected with cestodes are in worse body condition than those that are uninfected. To test whether individual growth and survivorship are boosted by intermittently reducing parasites, we initiated a deworming study on juvenile seals at Laysan Island. Forty-three unique juvenile seals were captured, weighed, measured, feces-sampled, and either given an injectable antihelminthic (praziquantel) or used as untreated controls up to 4 times at 8 to 16 wk intervals across a 7 month period. The effect of treatment on survival, egg shedding, and gain in mass was evaluated. Survival of the subset of the 3 cohorts included in the study was 100% for the 2007 and 2008 cohorts and 85.2% for the 2009 cohorts. Egg prevalence did not differ significantly between control and treated seals. Percent daily mass gain was greatest in the March to May period. Older juveniles gained more mass than young-of-the-year (treated and control), which lost mass between the first 2 treatments. Percent mass gain was significantly greater for treated than control seals during March to May, but not during December to March or over the entire treatment period (December to May). The questionable efficacy of injectable praziquantel indicates that a different route of administration or dosage of praziquantel or a different antihelminthic may be more suitable for treatment of cestodes in this species.

KEY WORDS: Hawaiian monk seal · Monachus schauinslandi · Antihelminthic · Praziquantel · Cestodes