Research About OCS Education Get Involved Gallery
OCS Facebook

L.A. Dolphin Project 1



bottlenose dolphin








Dolphins tell us about the overall health of our oceans

Bottlenose dolphins (Tursiops truncatus) are top predators and, as such, useful bio-indicators of the health and status of the marine environment. Gaining a better understanding of dolphin populations both in coastal and offshore waters – including their ecological comparison and knowledge of their ranging patterns – is crucial to protecting cetacean species and making conservation and management decisions for Marine Protected Areas.

inshore dolphins and surfer
Bottlenose dolphins swimming near surfer off California

Two separate populations of bottlenose dolphins in local California waters - inshore and offshore

Two separate populations of bottlenose dolphins exist in California: coastal and offshore. These two populations exhibit morphological, osteological and molecular differences. In the eastern North Pacific Ocean, the coastal population usually inhabit waters less than 1 km from shore and the offshore population is usually observed in waters more than 1 km from shore.

There are currently approximately 320 coastal bottlenose dolphins and the offshore population is estimated to be about 3000 individuals. Because of the logistical difficulties of following animals offshore, long-term studies have mostly looked at coastal dolphins found near shore.

coastal bottlenose dolphins
Social interaction between coastal bottlenose dolphins

OCS has been studying bottlenose dolphins in the L.A. area since 1996

Since 1996, the OCS research team has studied bottlenose dolphins inhabiting Los Angeles waters, California, focusing primarily on the coastal population (see publications). We have found these animals to be present in the area year-round using the Santa Monica Bay and adjacent coastline mostly for feeding on bottom fish. Our past research shows that this area is an important foraging hotspot for this coastal dolphin population.

Since 1996, our research team has also carried out a long-term study on the offshore population of bottlenose dolphins in California, collecting data on these animals up to 40 miles from shore. This is a challenging task considering the logistical difficulties of recording data on these pelagic and wide-ranging animals!

In 2009, our scientists published a scientific paper entitled "Ecology and comparison of coastal and offshore bottlenose dolphins (Tursiops truncatus) in California". Results from this investigation highlighted the need for more studies on this offshore population. For instance, we discovered that inshore and offshore populations of bottlenose dolphins behave quite differently and we also found, contrary to popular knowledge that these two populations partially overlap. These discoveries opened the door for an all-new set of questions…

How do we collect data on dolphins?

Photo-identification and focal group behavioral descriptions form the key methods of answering our research team questions about these two dolphin populations living in coastal and offshore waters. Photo-identification of individuals is accomplished by taking clear photo records of all individuals' dorsal fins found within a school for comparison, much like the use of a fingerprint. Photos and videos of individuals also help to identify skin diseases and physical deformities on dolphins (see OCS Project on Skin Diseases and Physical Deformities on Bottlenose Dolphins).

dolphin photo identification
LADP researcher photographing bottlenose dolphins
for photo-identification

Behavior and association patterns are observed and comprehensive data recorded into a database that includes – among other information – oceanographic conditions, satellite data, bioacoustic information and digital video providing us with a wide array of information that we may draw upon to enhance our understanding of these complex animals.

For specific information about our methodology, see the OCS peer-reviewed publications on bottlenose dolphins.


dolphin fin dolphin fin outline
dolphin fins

What are the main goals of this research project?

The current project attempts to expand the knowledge of offshore populations and compare that information to a continuing study of coastal groups. Another side goal of this research is also to encourage comparison of our data with other scientists in California and along the entire Pacific coast of United States (Please also refer to the OCS Project - California Dolphin Online Catalog).

Why is this project key for dolphin conservation?

Bottlenose dolphins are regular visitors of California waters and are considered in many locations worldwide to be indicators and sentinels of the status and health of coastal habitats. Systematic monitoring of these free-ranging animals can provide key data for understanding their habitat use as well as tracking the progression of poorly known diseases and emerging and re-emerging pathogens that may impact both dolphin and human health.

Understanding the ecology and dynamics of these coastal and offshore dolphins in California waters – as well as their site fidelity and spatial overlap – is useful not only for decisions affecting new Marine Protected Areas established in California, but these findings also have implications for future genetic and population studies leading to protection of these species.




OCS pioneers the first studies of dolphin diseases & deformities
on the west coast of the United States

Our past studies show that bottlenose dolphins in Santa Monica Bay suffer skin lesions and physical deformities. Ours was the first investigation of this kind on the West Coast of United States! The presence of these diseases is related to environmental factors like sea temperature and salinity, but also to man-made pollutants in our waters. This concerns us because it has potential implications for human health. Our current research aims to continue monitoring of these animals both along the coast and in offshore waters to shed light on the occurrence and frequency of these diseases, and compare data with other studies in California and other areas worldwide.



We are currently searching for funding to continue this study.
Actively support us by making a tax-deductible donation:


Bottlenose dolphins with skin diseases found off Los Angeles

Over 80% of the bottlenose dolphins in our study have skin diseases or malformations

From 1997 to 2007, the OCS research team found a variety of dermal lesions and physical deformities on free-ranging bottlenose dolphins in the Southern California Bight, which raised concerns about the health status of this species and potential negative effects on the entire coastal and offshore populations. As explained in one of our scientific papers, over 80% of bottlenose dolphins found in our study area were discovered carrying skin diseases and/or body malformations (see publications).

Investigations of skin lesions and physical deformities in wild bottlenose dolphins are generally scarce and localized and the majority of investigations have been focused on dead or captive animals. The cause of these lesions is still unknown, but an increasing number of studies on wild bottlenose dolphins suggest that lesions and deformities are anthropogenically induced.

How is this data collected?

Data are collected with laptop computers. When dolphins are spotted, data on the number of animals, behavior, and aggregations with other species are recorded at 5-minute intervals throughout the sighting.

For each sighting of dolphin schools, an attempt is made to photograph all individuals present in the group. Images of dolphin dorsal fins and bodies taken during photo-identification studies offer an excellent tool to assess the presence and prevalence of epidermal diseases because of their visibility. For all distinct individual that have been photo-identified, the best digital images are analyzed for prevalence and extent of skin lesions and the presence of physical deformities using the software ACDSee Pro (each image is enlarged to observe dermal lesions in detail).

OCS research assistant Amber collects data at sea

What are the main goals of this project?

Regular monitoring and photo-identification of coastal and offshore populations of bottlenose dolphins in Santa Monica Bay and adjacent areas, and comparison with other areas along the California coast, are necessary to assess changes in skin lesion presence and extent over time at both the population and individual levels. Stranded and by-caught bottlenose dolphins along the California coast may also provide additional data on skin-lesion presence and changes over time if individuals were photo identified and images compared with already examined individuals.

The current research provides a further step toward assessing the presence and frequency of skin diseases and physical deformities on both already identified animals and new animals present in the area. Further, it offers data for comparison with other study areas in which these types of lesions have been investigated and new ground for discussion on the health of these animals and the impact of anthropogenic activities.

Why is this project important for dolphin conservation and human health?

Bottlenose dolphins are apex predators and vulnerable to indirect threats, such as chemical pollution, acoustic pollution and marine debris. Direct anthropogenic effects on these marine mammals are difficult to assess, but dolphins bioaccumulate toxins and may suffer immunological and reproductive disorders as a consequence. Coastal dolphins are particularly susceptible to harmful threats, as they inhabit regions where pollution is usually abundant. Coastal animals in the Eastern North Pacific are known to have the highest levels of DDT concentration of all marine mammals, which seriously affects reproductive rate.

The presence of skin diseases in bottlenose dolphins is related to environmental factors, but also to man-made pollutants in our waters.
This study aims to provide key data to better understand the extent of this problem and the potential implications for human health.





Over three decades of research have been conducted on coastal bottlenose dolphins (Tursiops truncatus) along the California and Baja California coasts. During this time period, photo-identification images, including related sighting metadata, were collected by several scientists in different locations, including: San Quintin and Ensenada, Baja California, Mexico; San Diego, Orange County, Santa Monica Bay, Santa Barbara, Monterey Bay and San Francisco, in California, USA. Some of these data sets – including our large OCS dataset for the entire Santa Monica Bay and adjacent waters – are now available for online comparisons and analyses.

OCS spearheads a centralized dolphin database that can now be accessed by researches around the globe

In the last years, OCS has spearheaded a statewide effort – conducted in collaboration with other organizations and universities – for the development of a centralized, shared, digital repository for historical and future data that can be openly accessed by researchers around the world. This photo-catalog and online database was named the "California Dolphin Online Catalog" (or CDOC) and was launched online in January 2012.

The CDOC is now hosted by the Duke University OBIS- SEAMAP program and is open access. OBIS-SEAMAP (Ocean Biogeographic Information System Spatial Ecological Analysis of Megavertebrate Populations), is a spatially referenced online database, aggregating marine mammal, seabird and sea turtle observation data from across the globe.

You can now view the OBIS-SEAMAP, browse through species and databases – including our OCS database (login required) – and download data.

The California Dolphin Online Catalog in OBIS-SEAMAP

What are the main goals of this project?

The primary objective of CDOC is to provide an online, open-access, digital database resource and research tool freely available for use by researchers who study coastal bottlenose dolphin populations throughout their geographic range along the entire West Coast of North America. CDOC is primarily intended to be a scientific resource, but it can also serve a key role in facilitating citizen-scientist engagement and public awareness. Our hope is to involve more people in using this great online source for a better understanding of coastal bottlenose dolphin populations.

To date, principal investigators have contributed data identifying 697 individual dolphins collected in areas extending from Ensenada, Baja California, Mexico to Monterey Bay, California, USA during 1981-2001.OCS recently added all the images of our best photo-identified inviduals of coastal bottlenose since 1997 (1997-2015). Our catalog from 1997-2014 included 416 distinct coastal individuals.

Comparison of best photo-ID individuals of bottlenose dolphins

Further Developments and Public Involvement

Further development will be focused on adding more recently collected data from all the areas ranging from Ensenada, Baja California, Mexico to San Francisco, California, USA, refining the online application, and seeking collaboration and input from other interested data holders.

If you are working with coastal bottlenose dolphins along the West Coast of North America – either as a researcher or a citizen scientist – and are interested in collaborating in this effort, please contact OCS Research Director Dr. Maddalena Bearzi.







Studies reveal coastal bottlenose dolphins are highly mobile along the California and northern Baja, Mexico Coast

Past collaborative studies on coastal bottlenose dolphins (Tursiops truncatus) found along the California coastline - including research conducted by OCS researchers – show that these animals display extensive travel and high mobility along the entire California coast and Northern Baja California, Mexico. We'd now like to know more about these movement patterns...

Collaborative analysis of 20 years of research

In the last few years, the OCS research team – in collaboration with other scientists along the California and Mexico coasts – investigated the occurrence and movement data of coastal bottlenose dolphins from boat-based photo-identification surveys over a 20-year period (from 1981 to 2001). The study was carried out in six study areas ranging from Ensenada, Baja California in the south to Monterey Bay, California in the north.

Our primary objective was to determine movements between study areas, movement reversals, travel speed and travel distances. The results of this collaborative effort were recently published in a peer-review scientific paper (Hwang, A., et al. 2013. Range characteristics and movement patterns of common bottlenose dolphins (Tursiops truncatus) off California and Northern Baja California, Mexico).

This paper confirmed that this population of coastal bottlenose dolphins travels regularly and extensively between near shore locations from Ensenada to Monterey Bay. These coastal movements are likely due to the interplay between environmental variables, prey preferences, distributional characteristics, and the behavioral repertoires and distinctive foraging strategies of these animals.

Bottlenose dolphin leaping in California

Paving the way for additional collaborative research among scientists on the west coast of the U.S.

This long-term study on the occurrence and movement of coastal bottlenose dolphins from boat-based photo-identification surveys offers a great foundation for current and future collaborative research among scientists on the West Coast of United States.

For instance, OCS scientists recently worked together with researchers in San Francisco to exchange images and analyze range movement expansion of bottlenose dolphins along the Northern California and Oregon coasts. In addition to the northward range extension, scientists in San Francisco Bay observed bottlenose dolphin predation on Chinook salmon, previously unreported as prey for these coastal dolphins.

OCS will continue to collect and share data with other researchers to better understand range characteristics, foraging hotspots and movement patterns for these animals.

How does this study help protect dolphins?

An issue of concern for our OCS research team, as well as other scientists along the West Coast of United States, is that the wide range movements of bottlenose dolphins may contribute to their feeding success, but they also expose this coastal population to an array of epidemiologic risks (see OCS Project on Skin Diseases and Physical Deformities on Bottlenose Dolphins).

The coastal corridors have many natural and anthropogenic environmental threats and bottlenose dolphins can be at risk by being exposed to localized toxins, toxins that they might otherwise avoid if they were a less mobile species.

For instance, OCS discovered that our study area of Santa Monica Bay is a foraging hotspot for coastal bottlenose dolphins. These animals spend a considerable amount of time along these shores searching for food and feeding (see publications), often in proximity to urban runoff areas. We are currently looking at their occurrence near these polluted areas to better understand the extent of these potential threats.

top of page

© Ocean Conservation Society.
All Rights Reserved.