of Santa Monica Bay, California

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Whales and dolphins are long-lived, warm-blooded creatures that reproduce slowly and spend most of their lives hidden beneath the water's surface in the oceans and seas around the world.

For thousands of years, humans have been fascinated with the origins of these elusive animals and their mysterious existence. Human attention toward cetaceans has been mostly a commercial one and until lately, what we knew about them came from whalers and dolphin trainers. In the last several decades, scientists have taken a great interest in the lives of marine mammals, and have made significant efforts toward understanding more about their behavior and their "intelligence", both in marine ecosystems and aquaria.

Persistent efforts and sophisticated technologies (e.g., telemetry, molecular analyses, electron microscopy, geographic information systems) provided new insights. These new scientific studies have been paralleled by developments in legislation, conservation, and public awareness concerns. Over the last years, scientists engaged in improving marine mammal populations, heavily impacted by habitat degradation and unsustainable fisheries, have increasingly become occupied in the development of numerous recovery plans.

Despite the whirlwind of scientific advances, dissemination of policy and increases in public interest, more research is still needed to better understand these creatures in their environment. Additional work is necessary to create a link between science, public awareness, education, and resource management.

Why is a long-term marine mammal study in the Santa Monica Bay important?

Although there are many excellent papers on cetaceans (whales, dolphins, and porpoises) and pinnipeds (sea lions and seals), the purpose of my Ph.D. work was to fill the need for information on these animals in an heavily impacted area heretofore not investigated, and in which various marine mammal species occur year-round.

My dissertation is divided into three parts. The first part presents an overview of the field research on dolphins and whales observed in the Santa Monica Bay, California, over the past five years. Little is known about the cetaceans of the Los Angeles waters even though the county is inhabited by millions of people and these waters are highly frequented by marine mammals. This work represents the first long-term longitudinal study on cetaceans and pinnipeds ever conducted in the Santa Monica Bay. Beginning with a general framework on the composition, distribution, and relative abundance of different species of cetaceans in the years 1997-2001, it illustrates the changes in the distribution and relative abundance of these marine mammals before, during, and after the strong 1997-1998 El Niño event and following La Niña. Scientific data collected throughout these years of elevated surface water temperature, represents a valuable opportunity to investigate likely indirect changes in cetacean spatial and temporal distribution, seasonality, relative abundance and species composition.

The high presence of three species of cetaceans in the Bay, bottlenose dolphins and two species of common dolphins, offered also the opportunity to investigate and compare their ecology. The bottlenose dolphin, found widely in temperate and tropical coastal waters, is the most commonly studied cetacean along shore. The offshore pelagic populations, however, are still unknown due mostly to the difficulties of locating and following offshore dolphins that are unpredictably distributed, and the logistical problems of surveying the pelagic environment. Through a long-term photo-identification study of inshore and offshore populations in the study area, the author attempted to assess population dynamics and ascertain whether there are two distinct populations of inshore and offshore bottlenose dolphins in Southern California waters, as reported by other authors or, on the contrary, if the same dolphins inhabit the entire research area. The data collection on bottlenose dolphins and other species of marine mammals constitutes an important bridge between the information on these animals collected in Southern California (mostly San Diego coastline) and Northern California (mostly Monterey Bay area).

Common dolphins are also widespread in the Santa Monica Bay. Characterized by a wide distribution in tropical and warm temperate waters, these marine mammals tend to inhabit offshore waters in which they aggregate in large schools. In the Eastern North Pacific, two distinct species of common dolphins, the short-beaked common dolphin and the long-beaked common dolphin, are believed to occur. Data and descriptions on these animals for the study area have yet to be attempted. The Santa Monica Bay offers an excellent platform to investigate the presence and frequency of the two species in separated or mixed schools.

Following the overview on the marine mammals present in the study area, the second part begins to explore the behavioral patterns of the most familiar species. Generally, field research on cetacean behavior has appeared with escalating frequency although a large number of these studies are still concentrated on animals maintained in captivity. Dolphins and whales are not only difficult to study in the field for logistical reasons, but also because they can be elusive, fast-moving, and wide-ranging. Various species are also characterized by complex societies that usually require long-term studies and a great amount of perseverance and patience. Bottlenose dolphins, for instance, live in fission-fusion societies. These societies are evocative of those of chimpanzees and spider monkeys, in which individuals travel in small groups that frequently change in composition. Long-term longitudinal behavioral studies seem to be the only key to a deeper understanding of the nature of cetacean ecology. The second part of my dissertation focuses on the three most observed species, bottlenose and the two species of common dolphins, although attention is also given to other cetaceans present in the Bay. The purpose is to comprehend their behavioral patterns, potential differences among populations of the same species, and associations between diverse species in mixed-schools in the study area.

Studying cetacean populations and understanding their behavior and interaction with other animals is unquestionably critical. In addition, dolphins represent apex predators in a coastal ecosystem exceptionally sensitive to fluctuations of temperature, with corresponding changes in the populations of zooplankton and fish. Gathering data on dolphins, known as reliable bio-indicators of the status of the environment, and monitoring trends in their populations, is an excellent way of protecting all marine organisms living in the local ecosystem, as well as the ecosystem itself. A better understanding of marine mammal and their habitat use is important in planning effective conservation strategies for animals inhabiting highly impacted waters. The second part of my dissertation also looks at bottlenose dolphins' behavior in inshore populations in the presence of human activities and the disturbance of the author's research boat during surveys conducted along the Santa Monica Bay shoreline. Anthropogenic effects on dolphins - through factors such as disturbance, pollution, etc.- have not been investigated in the study area, although bottlenose dolphins tend to travel very close to shore where a high presence of swimmers, surfers, and kayakers is reported year-round, predominantly during the summer. In these highly frequented waters, dolphins must be considered as a key species of the marine environment. Due to the enormous popularity of human interaction with free-ranging dolphins, various authors report identification of stress-related behaviors by cetaceans in the last decade. The identification of these behaviors appears to be a beneficial tool in determining impacts to the animals as well as in minimizing effects when included in conservation management programs of marine resources. The long-term, quantitative study of bottlenose dolphins' behavior in the study area, offers a great opportunity for a "precautionary approach" that may prevent the disappearance of this and other species of cetaceans from the Bay.

The Santa Monica Bay is not solely an exceptional area to investigate diverse species of cetaceans and collect data on their behavior and interaction with human activities; it also represents an excellent platform for the study of local association and interaction between dolphins and sea lions, and their respective or combined foraging behavior. Aggregations between pinnipeds and cetaceans have been mentioned by various authors in the literature, and different hypotheses regarding this "associative" behavior have been proposed. However, comprehensive and detailed descriptions of dolphin and sea lion aggregations at sea are still lacking due to the complexity of following and recording the behavior of these fast-moving and widespread animals from the surface. The overlapping of prey and habitat for pinnipeds and cetaceans in the study area, offers a great opportunity to closely observe these species in their own environment. In addition, feeding ecology can have a significant role in conservation of marine mammals, helping to define a species habitat and the resources necessary for their sustenance. Multi-species aggregations and multi-species foraging strategies are mentioned in literature, but again, the phenomena have not yet been explained in detail, particularly for mixed-schools of cetaceans and pinnipeds.

The expectation of this long-term longitudinal study is to build a framework for future conservation and research, giving a contribution to the knowledge on marine mammals in the Santa Monica Bay with new insights about the lives of wild dolphins, whales and pinnipeds, their interactions, and the environment in which these magnificent animals conduct at least part of their existence.

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