Science to Save Monk Seals

monk-seal-01The Hawaiian monk seal is the most endangered pinniped species in the United States with a population estimate of 1,012 individuals remaining (International Union for Conservation of Nature, 2010). Despite their critical status, very little is known about their physiological requirements. This is due in part to the fact that few facilities are able to house Hawaiian monk seals and obtaining permits to perform science with endangered species can be challenging. In addition, their listing status currently dictates field research be as hands-off as possible (National Marine Fisheries Service, 2007).

The Marine Mammal Physiology Project is one of only four facilities in the country permitted to work with these endangered seals and thus, we are contributing vital scientific information to aid conservation efforts by investigating several key physiological aspects of Hawaiian monk seal life. Below are a few of the projects we are currently investigating:

Morphometric Measurements:


Morphometric measurements such as weight, length and girth, are collected on a weekly basis to provide extremely valuable data on growth curves for juvenile and adult Hawaiian monk seals.

Resting Metabolic Rates In-Air:


Seals are asked to rest as motionless as possible while on land. During this resting period, we measure how many calories the seals are expending. This provides us with a baseline of calories required for Hawaiian monk seals resting on beaches or in the surf zone. Additionally, by building strong relationships with our seals, we have been able to measure metabolic rates in-air during and post-molting periods. Hawaiian monk seals experience a catastrophic molt each year where they lose all their fur, top layer of skin, and regenerate both skin and fur within a few week period. This is the first time such measurements have been made for this endangered species, and these data provide great insight to the overall energy budgets for Hawaiian monk seals.

Resting Metabolic Rates In-Water:

monk-seal-04Seals are asked to rest as motionless as possible in their water environment. While animals are resting, we measure how many calories they are expending. This provides us with a baseline of calories required for Hawaiian monk seals resting in the open ocean. Combined with information learned from resting metabolic rates in-air, we are able to compile a complete resting calorie budget for this endangered species.

Thermal Neutral Zone Measurements:

monk-seal-05A thermal neutral zone is defined as the range of temperatures an individual can live in without experiencing a metabolic shift to compensate for additional energy required to either gain or lose heat. In addition to obtaining measurements of resting metabolic rates in the water, we can systematically adjust the temperature of the water in which the animals are resting. As we continue to measure the caloric expenditures of the animals during this process,we were able to determine the thermal neutral zone for Hawaiian monk seals. This is a vital piece of information for conservation of the species as it can help us learn why Hawaiian monk seals are only found around the Hawaiian Islands and if the species possesses the ability to expand beyond Hawaiian waters.

Caloric Cost of Swimming:

monk-seal-06Seals work with their trainers, learning how to swim varying distances for various durations underwater.  We then measure how much energy they expend while completing the requested transit. These transit swims range in duration from less than one minute to four minutes of continuous swimming. The information learned from this project is providing the first estimates of the caloric demands of these critically endangered seals on a per swim stroke basis. This knowledge will lead directly to Hawaiian monk seal conservation by allowing field researchers to determine the energetic expenditures for wild Hawaiian monk seals wearing stroke monitors while they transit to and from breeding and feeding areas. If these seals are expending more energy than they are consuming in these areas, this could be one of many compounding factors leading to the looming extinction of the species.

Why is this Information Important?

monk-seal-07It is important to understand how much energy these animals require because this is the foundation upon which all other behaviors are based. If animals cannot obtain enough food from their environments to meet their energetic demands, they will not successfully reproduce, and as a result the population will continue to decline. This could be one of many challenges the Hawaiian monk seal faces today.

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  • Marine Mammal Physiology Project
    Center for Ocean Health
    Monk Seal | TM Williams
    University of California
  • 100 Shaffer Road
    Santa Cruz, CA 95060