Growing up underwater: harbor porpoise muscle development

 Harbor porpoise by Florian Graner. Licensed through  NaturePL.com .

Harbor porpoise by Florian Graner. Licensed through NaturePL.com.

 

Peer-reviewed publication:

Noren, S. R., D. P. Noren, and J. K. Gaydos. 2014. Living in the fast lane: rapid development of the locomotor muscle in immature harbor porpoises (Phocoena phocoena). Journal of Comparative Physiology B. December 2014, Volume 184, Issue 8, pp 1065-1076.

 

This study -- based on harbor porpoise tissue samples collected from strandings, fishery bycatch, or observed killings by killer whales -- looked at muscle development in juvenile harbor porpoises to understand how fast they mature into physically competent adults.

This is important because it shows that immature harbor porpoises can't dive as well as adults and consequently have limitations on the kinds of habitat they can use. It brings attention to the concept that what might be okay for adult harbor porpoise (such as a certain level of boat traffic), might not be something that harbor porpoise calves can deal with as well as adults can.

Growing Up Underwater

Humans aren’t born ready to hunt down game animals — or even order Chinese food. We need mothers to protect and feed us at least until we can read a take-out menu. Life is somewhat similar for baby dolphins and porpoises.Diving ability in marine mammals depends on specialized biochemistry. High concentrations of myoglobin provide oxygen to muscles so divers can remain active while holding their breath. They’re also able to buffer the flush of lactic acid from anaerobic activity after the oxygen is depleted. It takes time, though, for newborn cetaceans to develop these special abilities.

A recent study by SeaDoc and Drs. S. Noren from UC Santa Cruz and D. Noren from National Marine Fisheries Service Northwest Fisheries Science Center (Seattle) used samples collected by the San Juan County Marine Mammal Stranding Network to measure diving capabilities in harbor porpoise, the Salish Sea’s smallest and most bashful cetacean. The results show that harbor porpoise achieve adult myoglobin levels by 9-10 months of age, and increased acid buffering as 2-3 year olds. This is faster than other cetaceans, which tracks with their earlier maturity and shorter lifespan. However, the study also proves that there is a period of time when harbor porpoise calves cannot keep up with the adults. This probably limits the habitat range and foraging of mothers and calves, leaving them vulnerable to habitat degradation.

SeaDoc and collaborators have recently undertaken a study to pinpoint harbor porpoise calving times so that we can further protect them at this delicate stage.

interesting facts about the study

  • This is one of the first studies to document muscle biochemistry development in dolphins and whales. It’s been done before with Fraser’s and bottlenose dolphins, but not with species resident in the Salish Sea.
  • Specimens for this research were collected opportunistically from stranded harbor porpoises, from animals caught accidentally by commercial fishing operations, and from animals killed by killer whales. Collection was performed through the San Juan County Marine Mammal Stranding Network. This program is administered through the Whale Museum and NOAA and is composed of a huge number of very dedicated volunteers.
  • Based on length, specimens were divided into 5 age classes, from fetus to adult.
  • A prior study by Dr. Shawn Noren, et al. (2008) points out that "although cetaceans are born directly into the ocean, the behavior of cetacean calves may mitigate demands that may otherwise drive the maturation of muscle biochemistry. For example, cetacean neonates typically swim in echelon position (calf in close proximity of its mother’s mid-lateral flank), which lowers the effort required by the calf to move at a given swim speed. Cetacean calves are also nutritionally dependent on their mothers’ milk for prolonged periods (8–42 months depending on the species; for review see Evans 1987) so that the calves do not need to dive to meet their nutritional needs. The distinctly different swimming styles and diving requirements of cetacean calves, relative to adults, alleviate the demands of physical activity and exposure to hypoxia early in life.”

Learn more about harbor porpoise in the Salish Sea

Harbor porpoise workshop: On February 7, 2013, the Pacific Biodiversity Institute, Cascadia Research Collective and the SeaDoc Society hosted scientists from Washington and British Columbia to determine the state of knowledge on harbor porpoises and coordinate ongoing research efforts. Read the statement identifying research needs.

Marine Science Lecture on harbor porpoise