Geology topics

K. J. Sulak

Publications and source records attributed to K. J. Sulak.

22 records · Page 2Linked to original sources

USGS2001

Association of Syscenus infelix (Crustacea: Isopoda: Aegidae) with benthopelagic rattail fishes, Nezumia spp. (Macrouridae), along the western North Atlantic continental slope

During submersible surveys along the continental slope (summers of 1991 and 1992, 184-847 m) between False Cape, Virginia, and Cape Hatteras, North Carolina, USA, we observed the aegid isopod, Syscenus infelix Harger, attached to the macrourid Nezumia bairdii (Goode and Bean). This is the first report of S. infelix attached to fishes in the western North Atlantic. The association of this blind isopod with its host appears species specific. The large, conspicuous isopod always attached to a fish in the same location, the dorsal midline, immediately behind the first dorsal fin. Attachment appears to be long term, with the isopod forming a characteristic scar consisting of a distinct discolored oval depression with seven small, dark impressions that coalesce as the fish grows. Only one S. infelix was found on each host fish. The isopod occurred on 23.7% of N. bairdii observed from submersible on the middle continental slope off Virginia and North Carolina, compared with 16.6% of 1236 museum specimens of the same species (based on inspection for scars) collected at latitudes 26??-64??N. Prevalence of the fish-isopod association was not correlated with depth or latitude. We also found identical scars on preserved specimens of N. aequalis (2.6% of 660 specimens), N. sclerorhynchus (1.2% of 86 specimens), and N. suilla (14.3% of 7 specimens), mostly from areas outside the range of N. bairdii. No scars were found on museum specimens of N. atlantica (n = 27), N. cyrano (n = 57), or N. longebarbata (n = 7). The low incidence of isopod attachment on these species suggests that N. bairdii is the preferred host. Infestation by the isopod appears to result in erosion of host fish scales and tissue. We propose that S. infelix is an obligate associate of its host fish and should be considered parasitic.

Marine Biology↗

USGS1999

Recent advances in life history of Gulf of Mexico sturgeon, Acipenser oxyrinchus desotoi, in the Suwannee River, Florida, USA: A synopsis

Gulf sturgeon spawn on portions of three sites in the upper Suwannee River, which may appropriately be described as spawning reefs. The same areas are utilized from year to year. Habitat factors important in spawning site determination include gravel/cobble substrate, the presence of eddy fields, a neutral to slightly alkaline pH, and an empirically observed range in calcium ion content (6-18 mg/L Ca++, corresponding to a conductivity range of 40-110??S). Eggs are deposited contagiously within a small area (< 10,000 m2) with very little scatter, suggesting little if any current drift. They are not found from samplers on immediately adjacent sand substrate. The broadcast spawner model does not seem to fit the Gulf sturgeon. Spawning begins 4-7 days after the March new moon, with water temperature above 17.0 oC, and extends for 9-23 days as discrete events involving individual females. Spawning may continue, if water temperature remains below 21-22oC. The total annual pool of spawning females in the Suwannee population is estimated at 80 individuals. Young of the year utilize open sand habitat away from shoreline and vegetated habitat. They disperse widely, and occur over freshwater reaches from rkm 10-237; no particular affinity with spring water habitat is evident. Larger Gulf sturgeon tend to congregate in deep holes serving as summer-fall holding areas. They fast and lose weight while remaining in freshwater, but more than compensate this loss during winter feeding in marine waters. The major downriver migration to the estuary takes place in October-November. After a period of river mouth staging, subadults and adults migrate into Gulf of Mexico nearshore mesohaline waters. They move further out and into deeper water (> 3 m) when water temperatures drop in mid-December, but final destinations in mid-winter remain unknown. Age-2 through 6 juveniles remain in the river mouth estuary over winter. In late January through early February YOY migrate downriver for the first time, joining larger juveniles to overwinter and feed. Tag and recapture data yield a Suwannee River population of Gulf sturgeon estimated at 7,650 individuals, with an annual turnover rate of 16%. Based on stability in cumulative recapture rates from 1991-1998, population size is stable with an effective balance between recruitment and mortality. However, population structure is dynamic, controlled by the juxtaposition, conjunction, and summation of successive strong and weak year classes. Length/age frequency distributions for 1995 and 1998 populations censuses are very different. The 1995 distribution is bimodal with a dominant mode of 9-14 year old subadults/adults, and a sub-dominant of mode of 2-4 year old juveniles. The 1998 distribution is trimodal, but overwhelmingly dominated by 6-9 year old subadults. Erosion by 1998 of the major subadult/adult mode from the 1995 census illustrates that large adults encounter the same high mortality as smaller fish. Ultimate adult size in the population has remained constant at 2.2 cm TL over 13 years, indicating a maximum life expectancy of 25 years for Suwannee River Gulf sturgeon.

Conference Paper↗

USGS1998

Early life history stages of Gulf sturgeon in the Suwannee River, Florida

Egg sampling confirmed that Suwannee River Gulf sturgeon Acipenser oxyrinchus desotoi , a subspecies of Atlantic sturgeon A. o. oxyrinchus use the same spawning site at river kilometer (rkm) 215 from the mouth of the river each year. Forty-nine eggs were recorded in 1995, and 368 were recorded in 1996. Spawning began 4–7 d after the March new moon in both years and lasted 10–11 d; in 1996, a second 10-d spawning round began on the April new moon. Developmental synchrony among eggs recovered suggested several discrete spawning events in both years. Total eggs deposited for three 1996 sampling days was estimated as 405,600–711,000/d, approximating the fecundity range of a large female Gulf sturgeon . Eggs were found only in the southern half of the river , an area with surface currents of 0.5–1.5 m/s and numerous eddies producing reverse bottom currents of 0.1–0.5 m/s. Egg substrate consisted of bedrock limestone thinly overlain by fine sand and densely distributed elliptical gravel 2–10 cm in diameter. Eggs were found predominantly in depths of 2–4 m at water temperatures of 17–21°C, conductivities of 50–100 μS, and dissolved oxygen levels exceeding 5.0 mg/L. The Cody Scarp, 15 rkm above the spawning ground, may mark the upstream limit of spawning areas in the river . Three 2–4-month-old riverine juveniles (82–115 mm total length, TL) collected are the smallest yet captured from any river . Data for 18 riverine age-0 juveniles (to 350 mm TL) suggest that this stage lasts 6–10 months, terminating with migration of fish to the river mouth in January–February. Less than 2% of 461 juveniles captured at the estuarine river mouth (1990–1993) were under 350 mm TL. Riverine age-0 fish were collected over long shallow stretches (typically <4 m deep) of relatively barren sand (rkm 12–238).

Florida↗

USGS1996

Metabolic responses to hypoxia of Lycenchelys verrillii (wolf eelpout) and Glyptocephalus cynoglossus (witch flounder): Sedentary bottom fishes of the Hatteras/Virginia middle slope

We collected wolf eelpouts Lycenchelys verrillii and witch flounder Glyptocephalus cynoglossus from Hatteras (North Carolina, USA) and Virginia (USA) Middle Slope sites using a submersible, and made shipboard measurements of their respiration rates and survival in hypoxic (<10% O2 saturation) and anoxic conditions. Both species from the Hatteras site reduced their respiration rates as ambient oxygen decreased, but eelpouts from the Virginia site maintained a constant respiration rate until oxygen saturation dropped below 20%. Moreover, eelpouts from the Hatteras site were significantly more tolerant of hypoxic conditions than fish from the Virginia site and survived anoxia for short periods. These results and our submersible observations of fish behavior support the hypothesis that the Hatteras Middle Slope fauna is exposed to short-term hypoxia events.

Marine Ecology Progress Series↗