Daily relative dog abundance, fecal density, and loading rates on intensively and minimally managed dog-friendly beaches in central California
Introduction
Beach advisories in the United States have increased 7–8% each year since 2005, with the number of advisory and beach closure days exceeding 24,000 in recent years (Dorfman and Sinclair Rosselot, 2011). More than two-thirds of these advisories were issued because fecal indicator bacteria (FIB) levels in beach water exceeded public health standards. Because elevated FIB levels have been correlated with an increased risk of illness, culturable FIB, including Escherichia coli and enterococci, are monitored to assess surf zone microbiological water quality and to protect public health at recreational beaches (Wade et al., 2003).
Fecal pollution may be introduced into the aquatic environment from point sources (e.g., wastewater treatment facilities and sewer overflows), and also diffuse nonpoint sources associated with coastal and shoreline development (e.g., leaking septic tanks, urban or agricultural runoff, boat discharges, bathers, and local domestic or wild animal populations) (Halliday and Gast, 2011). Dog waste has been identified as a significant source of fecal pollution in many coastal watersheds (Whitlock et al., 2002, Kitts et al., 2010, Schriewer et al., 2010, Ervin et al., 2014). Furthermore, previous studies that have quantified markers (Silkie and Nelson, 2009) and FIB (Wright et al., 2009) in dog feces demonstrate the impact that even a small number of dogs could have on water quality (Ervin et al., 2014).
California has approximately 60 dog-friendly beaches (Foster, 2006). With few exceptions these beaches receive excellent to very good water quality grades (A or B) during months with low precipitation (Heal the Bay, 2013–2014). However, during wet weather, > 75% of these beaches earn failing grades (Heal the Bay, 2013–2014). With an estimated 85,000 dogs in Monterey County alone (United States Census Bureau, 2010), and < 10 dog-friendly beaches, dog owners and canine advocacy groups are increasingly lobbying for greater access to area beaches to enjoy recreational activities with their companions. However, strong negative feelings are sometimes expressed by communities regarding beach access for canine and park visitors, due to concerns regarding disturbance, fecal deposition, and pollution (Foster, 2006, Wright et al., 2009).
Current water quality standards in most countries focus on control of human fecal contamination and minimally assess risk posed by fecal contamination from animal sources, including pets (WHO, 2012). Although potential for transmission of fecal pathogens from domestic dogs to humans is not well characterized (Ashford and Snowden, 2000), exposure to pet feces can be a significant source of protozoal and bacterial infection for humans (Stehrgreen and Schantz, 1987, Tan, 1997, Robertson et al., 2000). Recent prevalence studies have demonstrated variable shedding of potentially pathogenic parasites (e.g., Cryptosporidium parvum and Giardia duodenalis) and bacteria (e.g., Campylobacter spp., Salmonella enterica) from dogs in Monterey County (Oates et al., 2012a, Oates et al., 2012b). These potential pathogens could impact people, pets, and wildlife populations.
Exposure to fecal contaminated water has been linked with adverse health effects including fever, nausea, gastroenteritis, and cold and flu-like symptoms, such as nasal congestion, sore throat, fever and cough (Curriero et al., 2001). Although the majority of illnesses transmitted through recreational water use are relatively mild and self-limiting, a number of waterborne pathogens (e.g., noroviruses, adenoviruses, C. parvum, G. duodenalis, Campylobactor spp., S. enterica) can cause severe human illness, especially in immunosuppressed individuals (Pond, 2005, Yoder et al., 2008, Wyn-Jones et al., 2011).
Bacterial fecal contamination from dogs has been quantified using microbial source tracking (MST) markers (Ervin et al., 2014, Riedel et al., 2015), and based on census methods, with the assumption that 50–100% of observed dogs defecated at least once while visiting the beach (Wright et al., 2009, Wang et al., 2010). In contrast, no prior studies have estimated canine fecal loading of public beaches based on direct measurement of fecal deposition.
In response to the aforementioned data gaps, this study was designed to 1) estimate daily relative dog abundance at an intensively managed and at a minimally managed dog beach in Monterey County, California; 2) determine daily fecal density rates and estimate fecal loading for both beaches; and 3) assess risk factors that could be used to predict fecal deposition. It was hypothesized that greater canine fecal deposition would be observed on a dog-accessible beach with minimal municipal oversight, when compared to a beach with a formal municipal, dog-friendly management program. It also was thought that defined risk factors, such as distance from the nearest beach entrance and season, would be predictive of fecal deposition. Study findings may help to inform and optimize beach management, ultimately improving beach and water quality at dog-accessible beaches.
Section snippets
Site description
The two study beaches selected are the only marine recreational beaches in Monterey County that offer unrestricted, off-leash access for dogs (Fig. 1). Carmel City Beach (Beach 1; 36.555278, − 121.923333) is an intensively managed beach characterized by an average ambient temperature of 12.8 °C (14.0 °C during summer months and 11.6 °C during winter months) and an average annual rainfall of 444 mm (5.8 mm dry/68.0 mm wet seasons). The beach is approximately 1.6 km long and 100 m wide (160,000 m2) and is
Daily relative dog abundance
Dogs were observed during all surveys at Beach 1 and during 75% of surveys at Beach 2. The number of dogs estimated to use Beach 1 each day ranged between 279 and 504 during the dry season (May–Oct), and 54 to 405 during the wet season (Nov–Apr), with a mean of 402 (SE ± 33.2). At Beach 2, the number of dogs using the beach per day ranged between 0 and 180 dogs each day during the dry season, and 0 to 108 each day during the wet season, with a mean of 62 (SE ± 15.1). After standardizing for beach
Discussion
Based on yearly fecal loading estimates, domestic dogs were a significant contributor to fecal contamination at Beach 1 (1.4 metric tonnes), and Beach 2 (0.2 metric tonnes). These fecal loading estimates are conservative, because sampling was not conducted during holidays when more people would have visited the beaches with their pets (King and McGregor, 2012); and unlike previous studies, loading estimates in this study were based on direct assessment of feces recovered from each beach, not on the
Conclusion
The results from this study provide a means to monitor and track canine fecal deposition, allowing identification of potential risks to waterbodies and human health. These techniques could also facilitate assessment of impacts following implementation of management strategies on dog-friendly recreational beaches. Methodologies outlined in this study can augment current monitoring techniques at coastal beaches throughout California to optimize management, assess visitor compliance, and improve
Acknowledgements
This work was performed under the auspices of the Central Coast Long-term Environmental Assessment Network (CCLEAN), with funding provided by Grant #06-076-553 from the California State Water Board to the City of Watsonville. We thank MWVCRC & UCD staff and volunteers, the Central Coast Regional Quality Control Board, California State Parks, and the City of Carmel for participating in this study.
Conflict of interest statement
The authors declare that they have no competing interests and all have read and approved the final manuscript.
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