For the biologist, dolphin research presents challenges and opportunities in trying to understand individual species in their marine ecosystems.
Marine mammals are highly mobile, cover large areas, move in three spatial dimensions, and spend most of their lives under water. So for most species of delphinids, basic aspects of their evolution, physiology, ecology, behavior and population structure are mostly unknown.
Studies in nature mostly rely on visual or photographic recognition of individual specimens. Researchers can describe movement patterns from terrestrial observation points and from vessel expeditions.
Frequent monitoring of individuals may require identifying animals from a distance at each encounter. Some species exhibit individually specific natural markings, other species lack such distinctive markings and require the attachment of artificial marks or tags, when individual identification is the goal.
Research activities are: monitoring the presence of dolphins in the study area, collecting movement data, distribution, abundance, behavior, social structure, habitat use, feeding habits, fishery interactions and effects of tourism.
The purpose of research activities is to provide a scientific basis for the effective protection of dolphins and their habitat through continuous monitoring and identification of major threats to these animals.
Photo-identification
Photo-identification demands obtaining high quality, high resolution images of identifying features. The goal of this method is to keep a photo-id catalog of dolphins for a certain area.
Many of the cetacean features used by researchers for individual identification are visible above the surface briefly during respiratory cycles. Individual identification research involves the collection of permanent records of the distinctive features (i.e. dorsal fins) for detailed analysis.
Biopsy samples
Other kinds of natural markings being used are genetic markers from skin biopsy samples. Molecular analyses of small samples enable determination of sex and individual identification from genotypes provided by microsatellite loci. Such markings can be useful for distinguishing between otherwise unmarked animals within a group.
Genotyping can also be used to reliably identify parent–offspring relationships, although large numbers of microsatellite loci must be examined to provide accurate infromation. It’s worth the effort because thus dispersal can be measured over two generations rather than over the lifetime of single individuals. Determining sex provides a means to examine geographical segregation by sex as it is common with many marine mammal species that females tend to be philopatric, returning yearly to specific feeding or breeding sites.
Mark–recapture analysis
Genetic mark-recapture and monitoring methods are based on genotyping of biopsy sampes. This analysis is widely used in ecology to estimate abundance and survival rates. The basic data required are a set of capture histories of individually identified animals. A capture history is a string of 1s and 0s representing whether an animal was (1) or was not (0) captured in a series of sampling occasions. A sampling occasion is a finite period of time during which data are collected (e.g., a survey day), in studies of marine mammals sampling occasions are often longer – a season.
Research on marine mammals, especially cetaceans, is often expensive and depends on a wide variety of situations, environmental conditions among others, i.e., field work can only be carried out in favorable weather, in abscence of rain, wind and fog.
That’s where modern technology steps in (radio and satellite tags, time-depth recorders, GPS tags, hydrophone arrays, etc.), this has made huge contributions to the knowledge of marine mammals. But such equipment is, as mentioned, expensive.
Terrestrial observation
Terrestrial observation is carried out with hand binoculars on lager static binoculars. Environmental conditions and marine traffic are recorded. Photo-identification can in some cases also be accomplished from shore.
Vessel surveys
Small or medium-sized vessels, including fishing and sail boats are often used for surveys because of reduced cost. On these vessels, searching is conducted with hand-held binoculars or by naked eye, from the highest stable deck or platform. The boat must have a quiet engine which enables monitoring dolphins without disturbing them significantly. During the search, the crew visually inspects the surface of the sea, environmental and navigation data are regularly recorded during the expedition. Dolphins are slowly approached with the vessel, all data is collected as soon as possible. Data being collected: time, GPS position, size and composition of the group, presence of calves, duration of dives and possible interactions with fisheries. Passive acoustic monitoring can also be condicted from such vessels: hydrophones detect and record animals’ calls.
Large oceanographic research vessels, however, are the most versatile and effective platform for at-sea surveys of marine mammals. They can carry more researchers and can remain at sea for weeks, enabling to cover extensive marine areas. Search efficiency is greatest, because observers can search from a greater height above the water and use high-power, deck-mounted binoculars (“big eyes”) when searching for and identifying marine mammals. Large research vessels usually also have equipment for collecting oceanographic data for marine mammal habitat studies, and may be able to tow hydrophones to detect marine mammals acoustically. Studies including photography, biopsy sampling, diving behavior, and prey sampling are also possible during such surveys. A significant disadvantage is a great operating cost: approximately 10.000 $ per day.
Aerial surveys
The main advantages of aerial surveys are the ability to cover large areas quickly and a lower cost compared to large ships. They are useful for rapid assessments and studies to determine relative distribution and abundance of species in a particular region. Using strip or line-transect methods, aerial survey can be used to estimate abundance and monitor trends.
Telemetry
Telemetry allows to hear into the lives of whales, dolphins, sirenians and pinnipeds on their daily activities of feeding, finding mates and avoiding predators.
There are two approaches to collect data with telemetry systems:
1. an archival data logger attached to a marine mammal records data for a set period, then it is recovered, information is downloaded and stored;
2. information is transmitted directly from a marine mammal via radio or acoustic signals.
Simple systems have evolved from the omnidirectional radio or acoustic transmitters that allowed researchers to locate a tagged animal but did not provide information on its behavior or physiology into systems in which large quantities of data can be recorded, compressed, and transmitted via satellite. Data collected by these systems include depth and swim speed. Marine mammals now collect and transmit large quantities of data on physical and biological attributes of their environments, greatly contributing to understanding of their ecology.
Feeding
Early studies relied on stomach content from hunted animals, fecal collections and entrapments in fishing gear to provide information on diving and foraging activity. More recently, major technological advances have provided researchers with satellite transmitters, time-depth recorders, stomach temperature probes and video recorders to study diving and foraging activity.
Age
A large part of the life history data for odontocetes has come from studies of dead animals, as mentioned, from whaling operations, as bycatch to fisheries, or from strandings. Age of odontocetes can be estimated from their teeth. As an individual grows, growth layers are deposited in teeth and bones. In most species, each growth layer group represents an annual increment. So to determine the age, layers are counted. This has yet to be verified in order to use this method for every species. By establishing the ages of animals, it is possible to reveal the age-structure of the population, to estimate ages at which animals mature, reproduce, etimate their lifespan, etc. Long-term studies of odontocete species are now gradually allowing life history parameters to be recorded from living animals. Particularly in establishing lifespan, records show it stretches to a much greater age than wes estimated from catch records. Life histories recorded in this manner show large differences between different odontocete species.
Health
Studies of marine mammal disease and ocean chemical contaminants are increasing in response to an increase in marine mammal strandings and emergence of new marine mammal diseases in recent years. Studies have provided data on the presence of deadly viruses and contaminant levels in tissues of beached and dying marine mammals, but they have provided little insight into immune defense against disease or the biochemical consequences of contaminants. So species-specific biomarkers have been developed to assess the dolphin immune system, such investigations are ongoing.
Field work is followed by reviewing and sorting of the photos and data analysis, which is edited and included in databases.
Often, human intrusions have major effects on animals’ behavior even if they are unintentional. Tracking or stalking animals can lead to changes in their activity patterns so that they spend more time avoiding humans than feeding or giving care. Ethical considerations require that we learn about the effects of research methodologies and attempt to avoid them.
Conservation problems exist for nearly all odontocete species. Since the International Whaling Commission moratorium on catching large whale species, many of the current conservation threats faced by cetaceans are greater for odontocete species than for mysticetes. Their typically smaller size means it’s less possible to free themselves when trapped in nets, leading to high incidence of bycatch. The squid diet of many species makes them prone to plastic ingestion and being higher in the food chain magnify their pollutant load. Additionally, many species are mostly habitat specific so they have poor chances in the face of habitat destruction. Other less direct threats to odontocetes include noise and disturbance, pollution, habitat loss and degradation.
Whale watching for the purposes of research can be traced back to Aristotle, who spent time on boats and with fishermen in Aegean Sea. In “Historia Animalium” he describes the studying of animals by watching them, a key feature of the ethology approach for studying animals. It took longer to attempt such research with cetaceans because of more difficulties of approaching and conducting research at sea.
Many populations and some entire species are facing reductions and even extinction due to human-caused habitat degradation. So it is most important to spread knowledge about the biodiversity. Because by actively and effectvely protecting umbrella species like dolphins, with them we also protect entire ecosystems.
Source: Encyclopedia of marine mammals
Previous part from the dolphin series: Fishery interactions
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