Defining winter trophic habitat of juvenile Gulf Sturgeon in the Suwannee and Apalachicola rivermouth estuaries, acoustic telemetry investigations

Abstract

Summary Three automated listening post‐telemetry studies were undertaken in the Suwannee and Apalachicola estuaries to gain knowledge of habitats use by juvenile Gulf Sturgeons (Acipenser oxyrinchus desotoi) on winter feeding grounds. A simple and reliable method for external attachment of small acoustic tags to the dorsal fin base was developed using shrink‐tubing. Suspending receivers on masts below anchored buoys improved reception and facilitated downloading; a detection range of 500–2500 m was realized. In the Apalachicola estuary, juvenile GS stayed in shallow water (< 2 m) within the estuarine transition zone all winter in the vicinity of the Apalachicola River mouth. Juvenile GS high‐use areas did not coincide with high density benthic macrofauna areas from the most recent (1999) benthos survey. In the Suwannee estuary, juveniles ranged widely and individually throughout oligohaline to mesohaline subareas of the estuary, preferentially using mesohaline subareas seaward of Suwannee Reef (52% of acoustic detections). The river mouth subarea was important only in early and late winter, during the times of adult Gulf Sturgeon migrations (41% of detections). Preferred winter feeding subareas coincided spatially with known areas of dense macrofaunal benthos concentrations. Following a dramatic drop in air and water temperatures, juvenile GS left the river mouth and estuary, subsequently being detected 8 km offshore in polyhaline open Gulf of Mexico waters, before returning to the estuary. Cold‐event offshore excursions demonstrate that they can tolerate full‐salinity polyhaline waters in the open Gulf of Mexico, for at least several days at a time. For juvenile sturgeons, the stress and metabolic cost of enduring high salinity (Jarvis et al., 2001; McKenzie et al., 2001; Singer and Ballantyne, 2002) for short periods in deep offshore waters seems adaptively advantageous relative to the risk of cold‐event mortality in shallow inshore waters of lower salinity. Thus, while juveniles can tolerate high salinities for days to weeks to escape cold events, they appear to make only infrequent use of open polyhaline waters. Throughout the winter foraging period, juvenile GS stayed primarily within the core area of Suwannee River mouth influence, extending about 12 km north and south of the river mouth, and somewhat seaward of Suwannee Reef (< 5 km offshore). None were detected departing the core area past either of the northern or southern acoustic gates, located 66 and 52 km distant from the river mouth, respectively.

Macrobenthic prey and physical habitat characteristics in a western Gulf sturgeon population: differential estuarine habitat use patterns

“…Our data on the reduced macrobenthic density assemblages indicates comparatively high mean values of 16 801 m −2 by station across the study area (see Table S1 for details by zone and season). Harris et al (2005) and Sulak et al (2009) indicated that areas with high benthic density serve as a proxy for detecting critical Gulf sturgeon feeding habitat, and our data support this assertion. However, macrobenthic density patterns were spatially variable even within a single coastal system like the Pascagoula River estuary, as ranked group macrobenthic similarity patterns and associated HMD indices indicated that west zone assemblages were more similar and less dispersed compared to east zones.…”

“…New captures were tagged with T-bar and PIT tags as described by Heise et al (2004). Juvenile and subadult fish were tagged externally at the base of the dorsal fin (Sulak et al 2009, Havrylkoff et al 2012) with uniquely coded low-powered acoustic tags (either Model V9-2L or V13-1L; 69 kHz; 90 s mean random delay; VEMCO). Adult fish were tagged internally (USFWS 1993, Moser et al 2000 with high-powered uniquely coded and coated (clear Platinum Silicone Elastomer) V16-6H acoustic tags (69 kHz; 90 s mean random delay).…”

“…Receivers were attached to an aluminum buoy pipe and were allowed to pivot with any buoy movements. Receiver bottoms were positioned about 1 m below the surface in a top-down orientation with an assumed maximum detection radius of 750 m (Sulak et al 2009, Havrylkoff et al 2012 to maximize coverage and minimize duplicate detections. The overall array was deployed on 5 October 2010 as part of a 3 yr study, but for the present study, acoustically tagged Gulf sturgeon detections were only analyzed for 45 d before or after the middle day of each seasonal benthic sampling date (see below).…”

“…Gulf sturgeon occur in drainages from the Suwannee River, Florida, to the Pearl River, Louisiana (Wooley 1985, Rogillio et al 2007), where they spawn in upriver reaches during the early spring (Sulak & Clugston 1998, Heise et al 2004, and young-of-the-year spend 6 to 10 mo feeding in-river as they migrate down river before they appear in the estuary in December to February (Sulak & Clugston 1998, Havryl koff et al 2012). Juveniles (< 6 yr, except young-of-the-year) are believed to overwinter in the estuary (Sulak & Clugston 1998, 1999, Sulak et al 2009). In Mississippi, large sub-adult and adult Gulf sturgeon overwinter in the Mississippi Sound, congregating near the passes between barrier islands (Rogillio et al 2007, Ross et al 2009).…”

Downstream migration patterns of one-year-old hatchery-reared European sturgeon (Acipenser sturio)

“…Studies on juvenile in the field have mainly concerned large juveniles (above 60 cm long or greater than 2 years of age) such as the Gulf sturgeon (Acipenser oxyrinchus desotoi) (Harris et al, 2005;Sulak et al, 2009), the green sturgeon (Acipenser medirostris) (Lindley et al, 2011) or the white sturgeon (Acipenser transmontanus) (Parsley et al, 2008). Knowledge is poorly developed in our understanding of habitat use and migration tactics in juveniles, and telemetry studies on released fish could improve our understanding of sturgeon life histories and stocking program sustainability (Gessner et al, 2006).…”