Severe Karenia brevis red tides influence juvenile bottlenose dolphin (Tursiops truncatus) behavior in Sarasota Bay, Florida

Abstract

Harmful algal blooms (HABs) are natural stressors in the coastal environment that may be increasing in frequency and severity. This study investigates whether severe red tide blooms, caused by Karenia brevis, affect the behavior of resident coastal bottlenose dolphins in Sarasota Bay, Florida through changes to juvenile dolphin activity budgets, ranging patterns, and social associations. Behavioral observations were conducted on free‐ranging juvenile dolphins during the summer months of 2005–2007, and behavior during red tide blooms was compared to periods of background K. brevis abundance. We also utilized dolphin group sighting data from 2004 to 2007 to obtain comparison information from before the most severe recent red tide of 2005 and incorporate social association information from adults in the study area. We found that coastal dolphins displayed a suite of behavioral changes associated with red tide blooms, including significantly altered activity budgets, increased sociality, and expanded ranging behavior. At present, we do not fully understand the mechanism behind these red tide‐associated behavioral effects, but they are most likely linked to underlying changes in resource availability and distribution. These behavioral changes have implications for more widespread population impacts, including increased susceptibility to disease outbreaks, which may contribute to unusual mortality events during HABs.

Evaluation of Potential Protective Factors Against Metabolic Syndrome in Bottlenose Dolphins: Feeding and Activity Patterns of Dolphins in Sarasota Bay, Florida

“…Although observations were limited to the period 10:00–17:00, feeding was noted during all available observation periods. Peaks in foraging behavior were observed during morning through mid-day, each dolphin with a different hourly peak from 10:00 to 12:59 (Figure 5), comparable to the timing reported by McHugh (24). …”

“…Using similar methods to Waples (23), McHugh (24) focused on juvenile Sarasota Bay dolphins and found no significant differences in overall activity budgets by time of day during daylight hours with all activities occurring across all time periods. Activity patterns varied seasonally, however, with less time overall spent foraging in winter and significant diurnal variation in foraging patterns in summer, but not winter.…”

“…At each sample point, the activity of the focal animal was recorded. The key activities recorded by Waples and most other researchers working with Sarasota Bay dolphins [e.g., (24)] included: Travel – directed movement either in a straight line or zig zag.Mill – non-directed movement.Probable feed – strong indication of feeding without positive confirmation of the presence of a captured prey item; includes sub-surface swirling, fish leaping, and dolphins chasing fish.Feed – direct evidence of feeding, i.e., a fish in the mouth of the focal animal.Socialize – tactile or active interaction with at least one other dolphin.Rest – slow quiescent activity or remaining motionless at the water surface.Play – interaction with an object, i.e., algae, stingrays, or boats.…”

Food provisioning increases the risk of injury in a long-lived marine top predator

“…A reduction in natural prey could force dolphins to interact more with humans in order to obtain supplemental feeding from such interactions. The rapid increase in conditioning beginning in 2005–2006 may have resulted at least in part from an especially severe red tide event in 2005 which decimated overall fish abundance, including many key dolphin prey species, made significant changes to estuarine fish community structure, and shifted resident dolphin behaviour and association patterns temporarily [44,48]. We were not able to find a statistically significant relationship between dolphin prey density and the number of conditioned dolphins, but that could be due to the small sample size ( n  = 10 years).…”

Marine Mammals of the Gulf of Mexico

“…These behavioral changes may result in more widespread population impacts and increased susceptibility to disease outbreaks. While the mechanisms behind red tide-associated behavioral effects are not well understood, they are most likely linked to changes in resource availability and distribution (McHugh et al 2010). …”