Community structure and abundance of bottlenose dolphins Tursiops truncatus in coastal waters of the northeast Gulf of Mexico

Abstract

We examined bottlenose dolphin Tursiops truncatus community structure and abundance in the northeast Gulf of Mexico coastal waters stretching from St. Vincent Sound to Alligator Harbor, Florida, USA. Photographic-identification surveys were conducted between May 2004 and October 2006 to gain an understanding of dolphin distribution in this region. Dolphins were distributed year-round throughout the region; however, individual sighting records indicate that 2 parapatric dolphin communities exist. We conducted mark-recapture surveys using photographic-identification techniques to estimate the abundance of dolphins inhabiting the 2 areas these communities reside in: St. Vincent Sound/Apalachicola Bay, western; and St. George Sound/ Alligator Harbor, eastern. Sighting records of individual dolphins from 2004 to 2008 support the existence of 2 communities in these areas; only 3.5% of distinctive dolphins photographed were seen in both western and eastern areas. The 2 communities differ in their structure: the eastern area supports a more transient population with 45.7% of distinctive dolphins photo graphed only once compared with 28.3% in the west. Independent estimates of abundance (N, 95% CI = [low, high]) were calculated using the Chapman modification of the Lincoln-Petersen method for June 2007 and for January and February 2008 for the eastern area (242 [141−343], 395 [273−516]) and for the western survey area (197 [130−264], 111 [71−150]), respectively. Our results serve as a baseline that can be used by the US National Marine Fisheries Service to manage bottlenose dolphins in this region.KEY WORDS: Bottlenose dolphin · Photographic identification · Mark-recapture · Community structure · Abundance Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 438: [253][254][255][256][257][258][259][260][261][262][263][264][265] 2011 Bay, Florida ( Photo-identification (photo-ID) methods, which rely on obtaining a photograph of an individual dolphin's natural markings (such as nicks, notches, and/or scars found along the dorsal fin or peduncle), are widely used in the study of bottlenose dolphins. These natural markings are considered to be longlasting, and they have been used successfully to identify individuals and track them over time (Hammond 1990, Wilson et al. 1999. Using photo-ID methods, researchers have found that bottlenose dolphins are distributed relatively continuously in most parts of their range, although within this continuum range boundaries and discrete communities (i.e. resident dolphins that regularly share large portions of their ranges, exhibit similar distinct genetic profiles, and interact with each other to a much greater extent than with dolphins in adjacent waters; Wells et al. 1987) have been defined (Shane 1980, Irvine et al. 1981, Wells 1986, 1991, Wells et al. 1987, Hansen 1990, Shane 1990, Rossbach & Herzing 1999, Chilvers & Corkeron 2003, Lusseau et al. 2005, Fazioli et al. 2006, Balmer et al. 2008, Urian et al. 2009, 2004, and 2005/2...

Niche Differentiation and Prey Selectivity among Common Bottlenose Dolphins (Tursiops truncatus) Sighted in St. George Sound, Gulf of Mexico

“…While relatively stable cohorts of dolphins with long-term site-fidelity, termed resident populations (sighted across multiple seasons and years), have been identified in GoM regions such as Sarasota Bay (Scott et al, 1990;Wells, 2009Wells, , 2014 and St. Joseph Bay (Balmer et al, 2008), variations in dolphin abundances have been attributed to the influx and efflux of individuals that utilize these areas for only a short period of time and may or may not return to a region on a seasonal basis. Recently, similar variations in dolphin abundances have been inferred in St. George Sound, FL from differences in site fidelity observed among dolphins identified using photographicidentification (photo-ID) techniques (described in Tyson et al, 2011). However, in contrast to regions such as Sarasota Bay and St. Joseph Bay that have high rates of site fidelity within enclosed embayments, St. George Sound appears to support a highly transient population of dolphins, with 46% of dolphins sighted by Tyson et al (2011) being seen only once during a photo-ID study conducted in the region from 2004 to 2008.…”

“…Recently, similar variations in dolphin abundances have been inferred in St. George Sound, FL from differences in site fidelity observed among dolphins identified using photographicidentification (photo-ID) techniques (described in Tyson et al, 2011). However, in contrast to regions such as Sarasota Bay and St. Joseph Bay that have high rates of site fidelity within enclosed embayments, St. George Sound appears to support a highly transient population of dolphins, with 46% of dolphins sighted by Tyson et al (2011) being seen only once during a photo-ID study conducted in the region from 2004 to 2008. Tyson et al (2011) suggested this may be the result of St. George Sound offering relatively greater accessibility to the GoM than other bays and estuaries, such as Sarasota Bay and St. Joseph Bay, which are enclosed to a greater degree by barrier islands.…”

“…Seasonal variation in bottlenose dolphin (Tursiops truncatus) abundance has been observed in multiple study regions along the northern Gulf of Mexico (GoM), including St. Joseph Bay, FL (Balmer et al, 2008), Charlotte Harbor, FL (Bassos-Hull et al, 2013), Mississippi Sound, MS (Hubard et al, 2004), Sarasota Bay, FL (Irvine et al, 1981), and St. George Sound, FL (Tyson et al, 2011). These variations have been attributed to prey movements, temperature, and/or potential responses to stressors such as harmful algal blooms (Irvine et al, 1981;Hubard et al, 2004;Balmer et al, 2008).…”

Survival, density, and abundance of common bottlenose dolphins in Barataria Bay (USA) following the Deepwater Horizon oil spill

“…Balmer et al 2008, Speakman et al 2010, Tyson et al 2011. That methodology implements a robust capture-recapture design (Pollock 1982, Kendall et al 1995, 1997 containing secondary sampling occasions nested within primary sampling occasions.…”

Extended Movements of Common Bottlenose Dolphins (Tursiops truncatus) Along the Northern Gulf of Mexico's Central Coast

“…Adjacent to the east-west geographic boundaries of the Northern Coastal Stock, 16 BSE stocks of bottlenose dolphins have also been delineated (Waring et al, 2013). Although extensive research has not been conducted on all 16 of these BSE stocks, several studies (e.g., Conn et al, 2011;Tyson et al, 2011;Bouveroux et al, 2014) have provided valuable information for stock assessment in the nGoMx central coast region (reviewed in Vollmer and Rosel, 2013). For two of these BSE stocks, those of the St. Joseph Bay and Mississippi Sound, photographic-identification (photo-id) surveys have identified long-term (across multiple seasons and years) estuarine residents, in addition to seasonal influxes of dolphins presumed to originate from the Northern Coastal Stock (Hubard et al, 2004;Balmer et al, 2008).…”