Resting metabolism, energetics, and seasonal distribution of Pacific white-sided dolphins

• Main Author: Rechsteiner, Erin Ursula
• Language: English
• Published: University of British Columbia 2012
• Online Access: http://hdl.handle.net/2429/42469

Pacific white-sided dolphins (Lagenorhynchus obliquidens) are one of the most abundant cetaceans in British Columbia and throughout the North Pacific Ocean. However, little is known about their seasonal distributions and energy requirements. I analyzed sightings of dolphins attained opportunistically by volunteer observers and from scientific surveys—and found that Pacific white-sided dolphins have been seen with increased frequency along the BC coast over the past 54 years, and seasonally over the past 8 years. The sightings data showed a southward range shift from the 1950s to 2010, and a seasonal movement from offshore to nearshore waters concurrent with the timing of the herring spawn on the BC coast. I deduced whether seasonal movements reflect seasonal shifts in energy requirements by measuring resting metabolic rates and total energy intake for three captive white-sided dolphins twice per month for one year. Open-circuit gas respirometry revealed relatively high resting metabolic rates (~30 MJ day⁻¹ or ~0.3 MJ kg⁻¹day⁻¹) suggesting that white-sided dolphins may need high-energy prey to fuel their energetic requirements. Average resting metabolic rates of the three dolphins were constant throughout the year despite an increase in food consumption in the fall (October to December). I used these average resting metabolic rates and other parameters associated with growth, activity and assimilation efficiency to inform a generalized bioenergetic model and estimate the food requirements of Pacific white-sided dolphins globally, regionally, and locally. My bioenergetic model predicted that wild dolphins require ~30 MJ day⁻¹ for calves, ~60 MJ day⁻¹ for juveniles, ~65 MJ day⁻¹ for adults and pregnant females, and ~90 MJ day⁻¹ for lactating females. These energy requirements are ~50% higher than observed for dolphins fed in captivity, and are generally higher than estimates for other similar sized small cetaceans inhabiting temperate waters. My model predicts that an average sized dolphin (78 kg) in the wild would consume ~10 kg of fish per day, or about 13% of its bodyweight. Pairing information about prey requirements and seasonal distributions of dolphins with fisheries data can be used to assess spatial overlap between dolphins and fisheries, and may assist in reducing entanglement, by-catch, and conflict over prey.