Abundance and Occurrence of Common Bottlenose Dolphins (Tursiops truncatus) in Three Estuaries of the Northwestern Gulf of Mexico

Abstract

IntroductIon Common bottlenose dolphins (Tursiops truncatus, Montagu, 1821) are globally distributed between the 60 th parallels in temperate to tropical oceanic and coastal waters, and estuarine populations have been documented throughout their range (Jefferson et al. 2008, Wells and Scott 2018). In the Gulf of Mexico (GOM), common bottlenose dolphins (hereafter referred to as "bottlenose dolphins") are widely distributed in bays, sounds, estuaries, and coastal waters, including the waters of Texas (

Salinity and Water Temperature as Predictors of Bottlenose Dolphin (Tursiops truncatus) Encounter Rates in Upper Galveston Bay, Texas

“…Travel between Texas bays has been documented in other studies for some individuals (Blaylock and Hoggard, 1994;Maze and Würsig, 1999;Lynn and Würsig, 2002;Ronje et al, 2020). Previous studies have identified changes in abundance aligning with annual temperature fluctuation in studies in Galveston and other Texas estuaries (Shane, 1980;Henningsen and Würsig, 1991;Fertl, 1994;Wilson et al, 1997;Ronje et al, 2020). As in UGB, dolphin abundance peaks during the summer in other northern Texas coastal locations and decreases with cooler temperatures (Fertl, 1994;Wilson et al, 1997;Ronje et al, 2020), while in central and south Texas the opposite pattern has been documented (Shane, 1980;McHugh, 1989).…”

“…However, it is unknown if most remain in the lower Bay or if they leave the estuary to utilize nearby coastal waters, or travel to other estuaries. Travel between Texas bays has been documented in other studies for some individuals (Blaylock and Hoggard, 1994;Maze and Würsig, 1999;Lynn and Würsig, 2002;Ronje et al, 2020). Previous studies have identified changes in abundance aligning with annual temperature fluctuation in studies in Galveston and other Texas estuaries (Shane, 1980;Henningsen and Würsig, 1991;Fertl, 1994;Wilson et al, 1997;Ronje et al, 2020).…”

“…Previous studies have identified changes in abundance aligning with annual temperature fluctuation in studies in Galveston and other Texas estuaries (Shane, 1980;Henningsen and Würsig, 1991;Fertl, 1994;Wilson et al, 1997;Ronje et al, 2020). As in UGB, dolphin abundance peaks during the summer in other northern Texas coastal locations and decreases with cooler temperatures (Fertl, 1994;Wilson et al, 1997;Ronje et al, 2020), while in central and south Texas the opposite pattern has been documented (Shane, 1980;McHugh, 1989). Telemetry studies will be required to map detailed range patterns, but future winter observational studies focused on lower Galveston Bay could help determine if most UGB dolphins remain in the estuary during the cooler months and could identify calving hotspots.…”

“…In Galveston Bay, Moreno (2005) observed dolphins further north of Bolivar Roads only June through August, the months with the warmest annual water temperatures. Ronje et al (2020) indicated a summer increase in overall abundance for Galveston Bay, encountering more dolphin groups in UGB and shallow waters of the estuary during these months, and noting a density shift to deeper channel and Gulf pass habitats during the winter. Anecdotal data gathered from Bay-users also indicated a perceived increase in the number of dolphins present in UGB during summer months (Fazioli et al, 2016).…”

“…Prior to this study, most research on common coastal bottlenose dolphins (herein referred to as "dolphins") in Galveston Bay focused on describing dolphin activity in the southern portion of Galveston Bay, primarily in or adjacent to "Bolivar Roads" (the inlet that connects the Bay to the Gulf of Mexico) (e.g., Henningsen and Würsig, 1991;Bräger et al, 1994;Fertl, 1994;Moreno and Mathews, 2018). This area has been consistently described as having a high concentration of dolphins (Henningsen and Würsig, 1991;Moreno and Mathews, 2018;Ronje et al, 2020). On the other hand, few studies focused on waters of the inner estuary and upper portions of the Bay, and observational surveys conducted in the 1980s-1990s resulted in few or no dolphin sightings in UGB (Jones, 1988;Henningsen and Würsig, 1991;Blaylock and Hoggard, 1994).…”