Abstract
The Galveston Ship Channel (GSC) is a narrow, congested waterway that supports large-scale shipping, commercial fishing, dolphin tourism, and recreation. Human activity and common bottlenose dolphins (Tursiops truncatus) converge in the GSC with potentially negative consequences on the dolphins. Elevated land-based tracking and behavioral observation of dolphins and vessels were conducted along the GSC in June-August 2013 using a digital theodolite. Positional information was used to calculate dolphin movement patterns and proximity to vessels. Log-likelihood ratio and Chi-square contingency tests were used to assess behavioral states, and generalized additive models were used to analyze movement patterns (i.e., swimming speed, reorientation rate, and linearity) relative to endogenous and exogenous factors and vessel presence. Dolphins regularly use the GSC to forage (57% of observed behavioral states) and socialize (27%), and it is not a travel corridor for accessing other favorable sites (traveling = 5%). Dolphin behavior varied significantly based on time of day, group size, calf presence, and general boat presence. When boats were present, the proportion of time dolphins spent socializing and foraging was significantly less than expected by chance. Swimming speeds increased significantly in the presence of small recreational boats, dolphin-watching tour boats, shrimp trawlers, and when tour boats and shrimp trawlers were both present. Reorientation rate increased significantly in the presence of tour boats and trawlers. Dolphin behavioral responses to vessel presence may result in decreased energy consumption due to disrupted foraging activity. Without proper management, the observed behavioral changes may be detrimental to individuals within this population in the short term, with potential long-term consequences to health and survivorship.
Highlights
Marine mammals that inhabit near-shore waters are exposed to recreational and commercial activities [1, 2] where habitats and resources, such as prey items, are exploited by humans [3]
Post-feeding socializing has been observed in other cetacean species that include Guiana dolphins, Sotalia guianensis, [78] and dusky dolphins (Lagenorhynchus obscurus) off Argentina [79]
This study shows that dolphin-watching tourism in the Galveston Ship Channel (GSC) can lead to behavioral harassment
Summary
Marine mammals that inhabit near-shore waters are exposed to recreational and commercial activities [1, 2] where habitats and resources, such as prey items, are exploited by humans [3]. Disruption to marine mammal habitat-use and behavior have been documented in coastal. Coastal-living marine mammal species are often found in or near natural and artificially-dredged channels where fish prey are abundant or aggregated [10,11,12,13]. The ability of dolphins to exploit features of channels, such as steep slopes, may increase their efficiency of prey detection and acquisition by providing barriers with which to herd prey [14]. Dredged channels created for large vessel passage may increase feeding opportunities for dolphins. Exposure to vessels is intensified in narrow shipping channels (
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