Abstract
The 6.5 billion humans alive today are stressing the earth on an unprecedented scale with landscape and seascape modifications, overconsumption of natural resources, pollution, and global trade and travel—all of which are increasingly impacting natural ecosystems. Today over 60% of the human population lives in coastal areas, and the coastal human population is increasing at twice the rate of inland populations.7 The negative impacts that humans have on the health of oceans are immense. Oceans have been our sinks for disposal and discharge. Humans have harvested protein from the oceans for thousands of years, although this harvesting has reached unsustainable levels only in the last 100 years. The impacts of pollution and over-exploitation are being noted in all the world’s oceans with devastating effects in some regions.
In the Gulf of Guinea (GoG) of West and Central Africa, oil and gas development has historically been onshore and in shallow water. In recent years, changes have begun focusing on deep water exploitation using ultra-deep extraction technology. The United States and Europe will invest $30–40 billion (possibly up to $360 billion) in the next decade for oil and gas from the region.1 In addition to these natural resources, the GoG remains one of the richest marine environments on earth, containing locally and globally important fish stocks in a marine ecosystem that is mostly intact.4
Resource extraction and trade has led to large-scale coastal development and increased vessel activity in the GoG. Industrial trawlers routinely flout fishing zone restrictions along the Gabonese coast. Although there is a seasonal ban on shrimp fishing, other methods that would reduce by-catch and decrease the negative impact of fishing, such as harvest control and turtle excluder devices, are not practiced. Oil extraction processes are often associated with some degree of leakage with environmental contamination from spills. The seismic activity required for oil reserve discoveries may potentially have negative impacts on animals in the marine environment.3 Marine debris (human garbage) is common on many of the beaches and in the inshore water courses along the coast (Deem, unpublished data); this contamination is most likely a source of morbidity and mortality for marine species in the region.
The GoG has also been identified as a globally important site for a variety of marine mammals, including humpback whales (Megaptera novaeangliae), Atlantic humpback dolphins (Sousa teuszii), West African manatee (Trichechus senegalensis), common dolphins (Delphinus capensis), bottlenose dolphins (Tursiops truncatus), killer whales (Orcinus orca), rough-toothed dolphins (Steno bredanensis), and sperm whales (Physeter macrocephalus). In addition to the marine mammal diversity, the GoG is also home to a variety of sea turtles, including green (Chelonia mydas), hawksbill (Eretmochelys imbricata), and olive Ridley (Lepidochelys olivacea) turtles; it has some of the most important nesting sites in the world for the highly endangered leatherback turtle (Dermochelys coriacea).2
Currently, we know little about the health of the GoG ecosystem. Assessing the health of an ecosystem is often approached by one of three methods: (1) ecosystem distress syndrome, (2) counteractive capacity, and (3) risk analysis.6 With each of these methods, various indicators of stress and/or ecosystem responses are measured. Assessing wildlife health can serve as an indicator of ecosystem health. The marine ecosystem health program in Gabon, Central Africa focuses on sentinel wildlife species as one means of assessing the health of this ecosystem. Through the collection of baseline data and long-term monitoring, the health of the GoG will be assessed in conjunction with monitoring of the increasing anthropogenic pressures in the region.
The marine ecosystem health program is currently divided into three projects: 1) nesting female and hatchling leatherback turtle health studies, 2) determination of causes of sea turtle mortality, and 3) development of a marine mammal stranding network.
For the first project, standardized physical examinations are being performed and baseline blood health indices are being determined in conjunction with leatherback tagging and monitoring programs. Additionally, a hatchling orientation study is ongoing, with a specific aim of determining the influence of artificial lights on hatchling survival.
For the second project, a standardized approach of assessing sea turtle carcasses has been developed in order to determine the causes of mortality. A workshop is scheduled for October 2006 to train regional biologists in sea turtle necropsy and data collection techniques. To date, assessments have been performed on 102 olive Ridley, four green, and three leatherback turtle carcasses found washed ashore in the southern 380-km region of Gabon from September–November 2005.5 Although standardized sampling and data collection are still being implemented, it appeared that most of these mortalities were fisheries-related, based on physical findings (i.e., flipper amputations from machetes, monofilament lesions).
For the third project, a proposal to establish a marine mammal stranding network along the coast of Gabon, and ultimately throughout the GoG region, has been written and submitted to various funding agencies. Once funded, this network will ensure proper sample and specimen collection for natural history and health data. These data will be used for the documentation of marine mammal species found in the region and the determination of the causes of mortality. The need for a marine mammal stranding network is clear. In 2002, a rough-toothed dolphin stranded at Sette Cama (Collins, unpublished data), providing the first direct evidence of the species presence in Central Africa. In 2004, two stranded dolphins (unidentified) were reported by ecoguides on beaches of Loango National Park; in 2005, a neonatal sperm whale washed ashore in the same region. This latter animal was freshly dead, and although tissues were collected for DNA analysis, no other samples were collected, as there was no veterinary involvement at that time. During 2005, we also learned of five humpback whales that stranded in Gabon and Congo. Unfortunately, again no samples were collected, as our stranding network had yet to be developed and a veterinarian was not yet incorporated into the marine mammal conservation program in the region.
Stranded sea turtles and marine mammals serve as highly visible environmental indicators of ocean health. Although there are a few biases with using stranded marine animals as sentinels, these animals do provide invaluable data to assess both the health status of species examined and the marine ecosystem where they live. Many marine conservation programs in the GoG have been established for a number of years. The integration of a veterinary health component into some of these programs will allow us to gain a better understanding of the health of marine wildlife in the GoG as one indicator of the health of this ecosystem.
Literature Cited
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