Spiral valve parasites of blue and common thresher sharks as indicators of shark feeding behavior and ecology.

This study documented the parasite faunas of the spiral valves of blue sharksPrionace glauca(L. 1758) and common thresher sharksAlopias vulpinus(Bonnaterre, 1788) caught in the California Current Large Marine Ecosystem (CCLME) north of the Mexican border. The spiral valves of 18 blue and 19 thresher sharks caught in the CCLME from 2009 to 2013 were examined for parasites. Seven parasite taxa were found in blue sharks and nine in threshers. The tetraphyllidean cestodeAnthobothriumsp. (78% prevalence) was the most common parasite in blue sharks, and the phyllobothriid cestodeParaorygmatobothriumsp. (90% prevalence) was the most common in threshers. An adult nematode of the genusPiscicapillariawas found in threshers for the first time and may be a new species. Adult individuals ofHysterothylaciumsp. were found in both shark species. The adult acanthocephalanRhadinorhynchus cololabisand remains of the parasitic copepodPennellasp. - both parasites of Pacific saury,Cololabis saira- were found in the intestines of threshers, indicating recent feeding on saury. This study paves the way for a more comprehensive examination, including more samples and a wider variety of shark species, to provide a greater understanding of shark feeding behaviour and possibly provide information on shark population biology.