Bottlenose dolphin body mass index

Body mass index (BMI) is a metric that relates an individual’s height to their weight.

In humans, BMI is often used as an indicator of fitness, fatness, and risk for cardiovascular disease, diabetes, and stroke, based on comparisons to reference intervals.  Reference intervals specify what is expected among individuals in a healthy population given a particular sex and age, and they provide us with a tool to assess health parameters among individuals for which historical data are lacking because they rely on objective, statistical methods.

Recently, BMI reference intervals have been developed for bottlenose dolphins, using data collected during long-term capture-release projects in Sarasota Bay.  Length and weight measurements from 88 males and 72 females collected between 1987 and 2009, and robust statistical methods were used to develop reference intervals for each sex.

In addition to identifying what is ‘normal’ or expected among a healthy population, reference intervals can also be used to detect individuals with abnormal values.  In humans, most health risks are associated with BMI values that are above the reference intervals; however, for dolphins we are mostly concerned about health of animals below reference interval thresholds, which is indicative of poor body condition.

As bottlenose dolphin health assessment projects have increased in number and geographic range in recent years, these reference intervals can be used to detect individuals or stocks with compromised health conditions that may be related to or reflected by changes in body condition.  For example, these bottlenose dolphin BMI reference intervals have recently been used to identify individuals with poor body condition among animals sampled in the Gulf of Mexico as part of the Deepwater Horizon Natural Resources Damage Assessment, since weight loss has been associated with oil exposure in other mammals.

Although these intervals are based on data collected from dolphins in a population on the Gulf of Mexico, they appear to be appropriate for animals sampled along the Atlantic coast, and therefore widely applicable to estuarine bottlenose dolphins across the U.S.

This article was published on page 13 in the January 2014 Nicks n Notches.

2013 Deepwater Horizon oil spill follow-up: Comparative dolphin health assessments in Sarasota Bay, Barataria Bay, and Mississippi Sound

NOAA-led bottlenose dolphin health assessments were performed in 2011 in Barataria Bay, Louisiana, as part of the Deepwater Horizon Natural Resource Damage Assessment conducted by NOAA and other natural resource Trustees in cooperation with BP, to evaluate the potential impacts of the 2010 Deepwater Horizon oil spill.  Barataria Bay was impacted during the spill.  To try to identify health parameters that might have been affected by exposure to oil, comparative health assessments were performed in Sarasota Bay, Florida, in 2011.  Sarasota Bay was identified as a population for comparisons because the oil spill did not reach the bay, and decades of data collected from the long-term, pioneering health assessment activities of the Sarasota Dolphin Research Program (SDRP) enhanced the ability to interpret findings.

As a follow-up to the 2011 work, NOAA conducted additional health assessments in 2013.  Sarasota Bay was again used as a reference site, for comparison to dolphins sampled and examined in Barataria Bay and Mississippi Sound.  During one week in May, 15 dolphins were examined and sampled in Sarasota Bay.  Over two weeks in June, SDRP staff served as part of the NOAA health assessment team, assisting with evaluating 31 dolphins in Barataria Bay.  During two weeks in July-August, 20 dolphins were captured, sampled, examined, and released in Mississippi Sound, again with SDRP staff participation.  Sample and data analyses for 2011 and 2013 are underway.

This article was published on page 5 in the January 2014 Nicks n Notches  .

Study shows Gulf dolphins in poor health following the Deepwater Horizon oil spill

The Sarasota Dolphin Research Program played a major role in ground-breaking dolphin health and oil spill research published on 18 December 2013 in the peer-reviewed scientific journal Environmental Science and Technology.

The health of dolphins in Barataria Bay, Louisiana, an area that received heavy and prolonged oiling from the Deepwater Horizon spill, is compared to the health of long-term resident dolphins in Sarasota Bay, Florida, another shallow-water Gulf site, where oil was not observed, to evaluate potential health effects from the oil spill.

Disease conditions in Barataria Bay dolphins were found to be significantly greater in prevalence and severity than those in Sarasota Bay dolphins, as well as those previously reported in other wild dolphin populations. Many disease conditions observed in Barataria Bay dolphins are uncommon, but consistent with oil and oil byproduct exposure and toxicity.

The unique long-term research of the SDRP was crucial for the 2011 project.  The SDRP provided data and samples from the Sarasota dolphins as key reference values for the comparison, and SDRP staff assisted NOAA with health assessments in Barataria Bay.

A team of more than 50 government, academic, and non-governmental researchers conducted health assessments as part of the Natural Resource Damage Assessment for the oil spill.  Dolphins were temporarily captured, received a veterinary examination, and were then released.

The health exam included measuring each dolphin’s length and weight; doing a physical exam; sampling skin, blood, and blubber; and performing an ultrasound exam to evaluate their internal organs, particularly their lung condition and pregnancy status.

Many of the Barataria Bay dolphins were underweight and their blood tests showed a number of abnormal conditions such as anemia, elevated markers of inflammation, and increased liver enzymes.  Dolphins sampled in Barataria Bay showed evidence of very low levels of some hormones (specifically, cortisol) that are produced by the adrenal gland and are important for a normal stress response, consistent with adrenal toxicity as previously reported for laboratory mammals exposed to oil.

Barataria Bay dolphins were 5 times more likely to have moderate to severe lung disease.  Of 29 dolphins evaluated from Barataria Bay, 48% were given a guarded or worse prognosis, and 17% were considered poor or grave, indicating that they were not expected to survive, as compared to only one dolphin considered to be in guarded condition in Sarasota Bay.  Follow-up research was conducted in Barataria and Sarasota Bays in 2013, and in Mississippi Sound; results are pending.

The research was led by Dr. Lori Schwacke of NOAA’s National Centers for Coastal Ocean Science, and Dr. Teri Rowles, of NOAA’s Marine Mammal Health and Stranding Response Program.  SDRP Director Randy Wells and SDRP Staff Scientist Brian Balmer were co-authors on the research article.  A PDF  of the paper is available from Environmental Science & Technology.

For more information, check out NOAA’s Response and Restoration Blog.


Investigating patterns of bottlenose dolphin growth

The bottlenose dolphin is a long-lived, apex predator that is considered a sentinel of coastal ecosystem health.  The goal of my study is to describe patterns of growth of bottlenose dolphins utilizing two complimentary methods, ontogenetic allometry and body composition.

Ontogenetic allometry describes the rate of growth of a given body component, whereas the body composition technique offers a snapshot of how the developmental rates are manifested in the distribution of body mass over time.  The dataset I will use for this study consists of 175 stranded individuals, and dolphins incidentally killed in fishing operations, collected along the coasts of North Carolina and Virginia from 1990 to the present. All specimens have undergone a systematic mass dissection protocol, which separates the body into discrete anatomical components, including: integument and blubber, functional muscle groups, viscera, and skeleton.

To determine how the body conditions of the specimens in this sample compare to those of wild, free swimming bottlenose dolphins, a body mass index, (total body mass/total body length2 * 1000) will be used to compare the stranded sample to analogous data collected from wild individuals during health assessments in Beaufort, NC and Sarasota Bay, FL.

The Sarasota Bay population provides a unique reference for comparison, as it is one of the few areas where long-term, longitudinal data exist for a free-ranging population of dolphins (> 42 yrs). These dolphins undergo temporary capture-release and health assessments, from which body mass indices have been generated.  I will compare the body mass index from the Sarasota Bay population to the body mass index I generate from the stranded sample.  I will also compare mass/length ratios of a subset of the Sarasota animals (with known age and maturity status), to mass/length ratios of the stranded individuals in the North Carolina and Virginia sample.

I had the unique opportunity to participate in the July 2012 health assessment and observe the dynamics of the process and that of data collection. The opportunity allowed me to participate in this world-renowned research program and observe first-hand how the data I will use as a reference in my research is collected in a wild, free swimming population of bottlenose dolphins.  The product of this study will contribute a comprehensive analysis of growth in bottlenose dolphins and provide a quantitative baseline reference for the distribution of body mass to its components in a sentinel species of ecosystem health.


This article was published on page 18 in the January 2013 Nicks n Notches.

Tests of suction cup temporary tag attachments

 Suction cup testing
Suction cup testing during Sarasota Bay health assessments.

Suction cups are a central part of non-invasive tagging of marine mammals. For short term attachment of technology such as the WHOI Dtag they are the attachment method of choice. They do not penetrate the skin and can be easily dislodged by programming the device to lose suction in the cups at the desired time. However sometimes they come off prematurely.

With support from the National Science Foundation, via the National Ocean Partnership Program, we are exploring the biomechanics of the interface between suction cups and the skin and blubber of dolphins. As the cup sucks, it is deformed, but so is the underlying skin and blubber. The extent to which the latter happens is critical to understand, as if it were infinitely stretchable, the cup would not stick at all. Thus we have been undertaking a series of different low pressure tests using a rigid cup that measures the biomechanical properties of the skin and blubber, without any interference from the cup properties, as we would see with a regular flexible cup. We have also been looking at the behavior of regular cups as their suction fails. We are learning that there are significant differences between the cup skin/blubber interface in different parts of the body.


This article was published on page 18 in the January 2013 Nicks n Notches.