The effects of aquaculture on bottlenose dolphin (Tursiops sp.) ranging in Shark Bay, Western Australia
Introduction
Aquaculture, the farming of finfish or shellfish, has grown 11% in the last decade, becoming the fastest growing industry in the world food economy (Newton, 2000). Aquaculture has the potential to reduce the amount of fish and shellfish taken from the ocean and to bring substantial income to an area; it produced 37.8 million metric tons of fish and shellfish and $55.7 billion USD in 2002 (Food and Agriculture Organization of the United Nations, 2003). However, farming of carnivorous fish that require food from the ocean still results in a net take of wild stocks (Naylor et al., 2000). Furthermore, if finfish or shellfish are farmed in a natural marine environment, concern arises over the effects of increased biodeposition from fecal and pseudofecal matter, introduction of new species, genetic mingling of wild and captive stock, antibiotics and medicines, as well as competition with, displacement of and interaction with other fauna (Fleming, 1994, Buschmann et al., 1996, Würsig and Gailey, 2002). The described impacts of shellfish farming primarily involve competition with local bivalves, deposition of organic matter, altered benthic communities, and introduction of exotic species (Mirto et al., 2000, Naylor et al., 2000, Naylor et al., 2001, Henderson et al., 2001, La Rosa et al., 2001).
Potential impacts on marine mammals as a result of aquaculture interaction include death or injury through entanglement in gear, displacement, altered food chain, disruption of migration pathways (for large cetaceans), and human intervention (marine mammals killed or relocated). Most of the literature to date has focused on otters and pinnipeds that prey on finfish and some shellfish, but there is a paucity of information on cetaceans and aquaculture (reviewed in Würsig and Gailey, 2002, Kemper et al., 2003). Unlike pinnipeds, cetaceans have not been reported to consume fish or shellfish out of farms, but have been known to get entangled in equipment, resulting in the damage of gear, release of fish, and self injury (Dans et al., 1997, Kemper and Gibbs, 2001, Crespo and Hall, 2002, Hall and Donovan, 2002). Displacement of cetaceans by aquaculture may also occur because they frequently share the same coastal habitat (Crespo and Hall, 2002, Würsig and Gailey, 2002, Markowitz et al., 2004).
Unlike finfish farms that are netted at the periphery, shellfish farms typically have open areas that are large enough to allow small cetaceans to swim through the farm. Nevertheless, cetaceans may still avoid shellfish farms because of ropes, equipment, human activities, water clarity, prey availability, or other habitat factors. In the last few years, several reports to management agencies (Mann and Janik, in litt.; Slooten et al., in litt.; Paton et al., in litt.) have highlighted the potential displacement of dolphins by oyster and mussel farming operations. For example, dusky dolphins (Lagenorhynchus obscurus) use a green-lipped mussel (Perna canaliculus) farm area less than nearby areas in Marlborough Sounds, New Zealand (Markowitz et al., 2004).
Bottlenose dolphins (Tursiops spp.) are appropriate and useful study animals in this case because of their world-wide distribution in tropical and temperate coastal waters. Because of their cosmopolitan distribution, the information gained in our study can be applied to management of shellfish farms world-wide and, because they share valuable coastal habitat with humans, bottlenose dolphins may be particularly affected by aquaculture. Variable coastal habitats may provide niches important for dolphin foraging or as a refuge from predators. For example, dolphins that specialize in habitat-specific foraging strategies (Mann and Sargeant, 2003) may be seriously affected if they are displaced from that area. Resident communities of dolphins are likely to be most affected and displacement could result in a population decline. Furthermore, the pressures of aquaculture on the dolphin population may add to existing anthropogenic pressures, such as boat traffic (see Chilvers et al., 2005 for an example of human impacts on marine mammals in Moreton Bay, Australia).
Even though these data are from only one bottlenose dolphin study site, it is appropriate to extrapolate to other areas. Shark Bay represents one of the longest running and extensive studies on small cetaceans; it is the only site where ranging information prior to a pearl oyster farm is available. Comparisons of Shark Bay to other sites show similar bottlenose dolphin social structure and behavior (Connor et al., 2000). Therefore, our study offers the best available test to date of the effects of an oyster farm on small cetacean ranging.
Marine mammals, including cetaceans, not only attract public interest, but are also protected in Australia under the Environmental Protection and Biological Conservation Act 1999. To manage a growing industry, more information on the effects of aquaculture on cetaceans is needed.
The aim of this paper is to determine if ranging patterns of bottlenose dolphins have been altered by an oyster farm in Shark Bay, Western Australia. To do this we analyzed their movements near the farm before and during its operation. We addressed the following questions: (1) do bottlenose dolphins change their use of an area once farming begins there; (2) do they move away from the farm; and (3) do they move around (but not through) the farm? We also make recommendations for future research and management. The analytical techniques discussed apply broadly to aquatic and terrestrial animals.
Shark Bay was designated in 1991 as a World Heritage Area for its extensive seagrass beds and dugong (Dugong dugon) population (United Nations Educational, Scientific, and Cultural Organization, 1991). Although Shark Bay is not a World Heritage Area because of the dolphins that inhabit it, the dolphins are a significant tourist draw to the area; currently four dolphins are hand fed daily and attract more than 100,000 tourists per year (Mann and Kemps, 2003). Feeding is regulated by the Western Australian Department of Conservation and Land Management. These four, and hundreds of other dolphins, have been part of a long-term research project since 1982 and have been continuously studied since 1984 (Connor and Smolker, 1985, Connor et al., 2000).
Section snippets
Study site
Mann has been researching mother and calf behavioral ecology since 1988, collecting data on 99 calves born to 67 females. Eleven females that regularly used the bay (Red Cliff Bay) where the oyster farm is located were the focus of this analysis. The study area is located off the campground and resort of Monkey Mia (25°47′S, 113°43′E) on the eastern side of Peron Peninsula, which bisects Shark Bay. Red Cliff Bay is adjacent to Monkey Mia, with Whale Bight (also called Hell’s Gate) to the north.
Change in use of an area
Sighting frequency within the reported use area did not differ between before and after full-scale farming occurred (n = 10 females, one-tailed, p = 0.70; Fig. 2). However there was a significant decrease in sighting frequency in the extension area when oyster lines were put into place compared to before (n = 11, one-tailed, p = 0.04), and then no change after the lines were removed (n = 11, two-tailed, p = 0.25; Fig. 2).
Movement away from the oyster farm
Using a general estimating equation to model the variation between points on the same
Discussion
The adult female bottlenose dolphins studied here appeared to have been displaced by aquaculture. They showed a significant decrease in use of the extension area when the pearl oyster farming was introduced. The fact that this same pattern was not seen for the reported use area could be attributed to the possibility that oyster farming never actually occurred there. Because of decreased GPS accuracy or human error when the lease was established, and the shallow depth of most of the reported use
Acknowledgments
We thank all field assistants, our colleagues in Shark Bay, Western Australian Department of Fisheries, Western Australian Conservation and Land Management, Dr. Barry Wilson, and Monkey Mia Dolphin Resort. Funding was provided to J.M. by NSF #9753044, Eppley Foundation for Research, and the Brach Foundation, the National Geographic Society to J.M. and J.J.W., Georgetown University Graduate Student Research Award to J.J.W. Thanks to Magellan of Australia for providing us with GPS units. Thanks
References (30)
- et al.
A review of the environmental effects and alternative production strategies of marine aquaculture in Chile
Aquacultural Engineering
(1996) - et al.
Moreton Bay, Queensland, Australia: an example of the co-existence of significant marine mammal populations and large-scale coastal development
Biological Conservation
(2005) - et al.
Heterotrophic bacteria community and pollution indicators of mussel-farm impact in the Gulf of Gaeta (Tyrrhenian Sea)
Marine Environmental Research
(2001) - et al.
Microbial and meiofaunal response to intensive mussel-farm biodeposition in coastal sediments of the western Mediterranean
Marine Pollution Bulletin
(2000) - et al.
Habituated dolphins (Tursiops sp.) in Western Australia
Journal of Mammalogy
(1985) - et al.
The bottlenose dolphin: social relationships in a fission–fusion society
- et al.
Interactions between aquatic mammals and humans in the context of ecosystem management
- et al.
Incidental mortality of Patagonian dusky dolphins in mid-water trawling: retrospective effects from the early 1980s
Report of the International Whaling Commission
(1997) - Food and Agriculture Organization of the United Nations, 2003. Review of the State of World Aquaculture. Food and...
Captive breeding and the conservation of wild salmon populations
Conservation Biology
(1994)
Environmentalists, fisherman, cetaceans, and fish: is there a balance and can science help to find it?
Use of hydrodynamic and benthic models for managing environmental impacts of marine aquaculture
Journal of Applied Ichthyology
Behaviour of harbour porpoises (Phocoena phocoena) in response to ropes
Dolphin interactions with tuna feedlots at Port Lincoln, South Australia and recommendations for minimising entanglements
Journal of Cetacean Resource Management
Cited by (61)
Life Cycle Assessment of a large commercial kelp farm in Shandong, China
2023, Science of the Total EnvironmentUsing local ecological knowledge to determine ecological status and threats of the East Asian finless porpoise, Neophocaena asiaeorientalis sunameri, in south Bohai Sea, China
2021, Ocean and Coastal ManagementCitation Excerpt :Furthermore, long term overfishing has heavily changed the fishery ecosystem structure and function (Jin et al., 2013), as well as aquaculture (particularly shellfish farming) (Du et al., 2015). These industries cause habitat loss, leading to habitat exclusion in cetaceans and causing potentially negative effects (Markowitz et al., 2004; Watson-Capps and Mann, 2005; Ribeiro et al., 2007; Pearson et al., 2012). Historically, more than 20 cetacean species have been observed within the Bohai Sea (Wang, 2012; Jefferson et al., 2015) but today, the East Asian finless porpoise (EAFP, Neophocaena asiaeorientalis sunameri Pilleri and Gihr, 1975) is the exclusive species that is still frequently sighted2.
Far-field and near-field effects of marine aquaculture
2018, World Seas: An Environmental Evaluation Volume III: Ecological Issues and Environmental ImpactsThe North-Western margin of Australia
2018, World Seas: An Environmental Evaluation Volume II: The Indian Ocean to the PacificDusky dolphin (Lagenorhynchus obscurus) habitat use in a mussel farming region and changes over time
2024, New Zealand Journal of Marine and Freshwater ResearchAn ecological-economic fishery model: Maximizing the societal benefit through an integrated approach of fishing and ecotourism
2023, Mathematical Methods in the Applied Sciences