You are what you eat, even if you’re a sea lion! Did you know that sea lion poop could be used to determine diet?
Seal and sea lion researchers often travel to remote locations to collect scats from haul-out areas and rookeries. The scats are labeled with an ID number and location, and then brought back to the lab, where they are sieved repeatedly to sift out ‘hard parts’ such as otoliths (inner ear bones) and squid beaks. These hard parts are then counted and measured to estimate the number and size of prey species ingested. This can sometimes take hundreds of hours!
FUN FACT: The best way to accomplish this is to put the scat in a small mesh bag and run it through the washing machine!
Accurate dietary information is an important component of marine mammal population monitoring and for developing recovery plans for at risk populations. Diet and diet diversity are also central to assessing hypotheses regarding the interactions of pinnipeds with fisheries and to determine if nutritional stress has contributed to declining populations. Wildlife and fisheries managers use diet information to design appropriate mitigation strategies.
Dr. Dom Tollit undertook a three-year diet study in collaboration with UBC’s Marine Mammal Research Unit to determine the diet composition of Steller sea lions (Eumetopias jubatus) from 2001 to 2004 in Frederick Sound, Alaska. Using hard parts from 1,693 scats (think of how long these took to collect!), the team highlighted that Steller sea lions in this region switched from adult pollock to juvenile pollock, and took advantage of spawning concentrations of salmon in autumn and herring in late-spring and summer, as well as a climate-driven increase in hake availability. Together with Arrowtooth flounder and skate these six species accounted for 80-90% of the diet. Overall, 80% of fish were 14 – 42 cm long and mainly pelagic, and 40% of scats contained benthic-associated prey. These temporal and spatial shifts in diet point to the need for robust scat sampling protocols to capture temporal (and spatial) variability in prey selection.
This project was funded to the North Pacific Universities Marine Mammal Research Consortium by the National Oceanographic Atmospheric Administration and the North Pacific Marine Science Foundation.
The full paper, ‘Diet composition of Steller sea lions (Eumetopias jubatus) in Frederick Sound, Southeast Alaska: a comparison of quantification methods using scats to describe temporal and spatial variability’ can be read here.