Daryl C. Parkyn

Distribution of Gulf of Mexico Sturgeon in Relation to Benthic Invertebrate Prey Resources and Environmental Parameters in the Suwannee River Estuary, Florida

Abstract The distribution of threatened Gulf of Mexico sturgeon Acipenser oxyrinchus desotoi (hereafter referred to as Gulf sturgeon) in the Suwannee River estuary, Florida, was examined relative to the distribution of benthic invertebrate prey and environmental variables (salinity, temperature, dissolved oxygen, and sediment type) to determine potential foraging areas within the estuary. Eighteen Gulf sturgeon (1,279–2,010 mm total length, 15.25–53.25 kg) were netted at the mouth of the Suwannee River during their spring upriver migration in 2001 and surgically implanted with ultrasonic tags. These sturgeon were subsequently tracked as they migrated seaward out of the Suwannee River and into the estuary in fall 2001 and as they returned to the estuary in spring 2002 to migrate upriver again. Invertebrates and sediment type were identified in diver-collected cores from the Suwannee River estuary during spring 2002. Thirteen of the 18 tagged Gulf sturgeon were relocated in the Suwannee River estuary. Eight...

Use of Human-Altered Habitats by Bull Sharks in a Florida Nursery Area

Abstract Bull Sharks Carcharhinus leucas in the Indian River Lagoon, Florida, have been documented to frequently occur in humanaltered habitats, including dredged creeks and channels, boat marinas, and power plant outfalls. The purpose of this study was to examine the short-term movements of age-0 and juvenile Bull Sharks to quantify the extent to which those movements occur in altered habitats. A total of 16 short-term active acoustic tracks (2–26 h) were carried out with 9 individuals, and a 10th individual was fitted with a long-term coded transmitter for passive monitoring by fixed listening stations. Movement and activity space statistics indicated high levels of area reuse over the span of tracking (hours to days). All but one shark used altered habitat at some point during tracking, such that 51% of all tracking positions occurred in some type of altered habitat. Of the sharks that used altered habitat, the mean ( ± 1 SD) percent of positions within altered habitat was 66 ( ± 40) %. Furthermore, tracks for 3 individuals indicated selection for altered habitats. The single passively monitored Bull Shark was detected in power plant outfalls almost daily over a 5-month period, providing the first indication of longer-term fidelity to thermal effluents. Use of one dredged creek was influenced by local salinity, the tracked sharks dispersing from the altered habitat when salinity declined. The affinity of young Bull Sharks to altered habitats in this system could help explain their reported accumulation of a variety of harmful contaminants, which could negatively affect their health and survival.

Augmentation of French grunt diet description using combined visual and DNA-based analyses

Trophic linkages within a coral-reef ecosystem may be difficult to discern in fish species that reside on, but do not forage on, coral reefs. Furthermore, dietary analysis of fish can be difficult in situations where prey is thoroughly macerated, resulting in many visually unrecognisable food items. The present study examined whether the inclusion of a DNA-based method could improve the identification of prey consumed by French grunt, Haemulon flavolineatum, a reef fish that possesses pharyngeal teeth and forages on soft-bodied prey items. Visual analysis indicated that crustaceans were most abundant numerically (38.9%), followed by sipunculans (31.0%) and polychaete worms (5.2%), with a substantial number of unidentified prey (12.7%). For the subset of prey with both visual and molecular data, there was a marked reduction in the number of unidentified sipunculans (visual – 31.1%, combined – 4.4%), unidentified crustaceans (visual – 15.6%, combined – 6.7%), and unidentified taxa (visual – 11.1%, combined – 0.0%). Utilising results from both methodologies resulted in an increased number of prey placed at the family level (visual – 6, combined – 33) and species level (visual – 0, combined – 4). Although more costly than visual analysis alone, our study demonstrated the feasibility of DNA-based identification of visually unidentifiable prey in the stomach contents of fish.

Postrelease Rate of Loss of Juvenile Red Drum Stocked out of Season in the Chassahowitzka National Wildlife Refuge, Florida

Abstract Rates of loss of juvenile red drum Sciaenops ocellatus (∼85 mm total length) stocked out of season were estimated using hatchery releases and ultrasonically tagged fish in Pumpkin and May creeks in the Chassahowitzka National Wildlife Refuge on the Gulf coast of Florida. In Pumpkin Creek, approximately 7,000 of the 10,000 fish released on 27 June 2000 survived combined transport mortality (2%) and 24-h acute mortality (28 ± 8.7% [mean ± SE] n = 6). In May Creek, approximately 5,100 of the 10,000 fish released on 29 June 2000 survived combined transport (7.5–10%) and 24-h acute (44 ± 0%, n = 2) mortality. Catch curve estimates of the instantaneous “rate of loss” (mortality or emigration) within 5 d were 0.46/d and 0.50/d for Pumpkin and May creeks, respectively. Red drum with ultrasonic transmitters (n = 12) also rapidly “disappeared” from the creeks within 4 d after release. These are the first estimates of postrelease rate of loss for juvenile red drum released out of season on the west coast of...

Nonlethal Sex Determination of the Greater Amberjack, with Direct Application to Sex Ratio Analysis of the Gulf of Mexico Stock

Abstract Stock assessments for the Gulf of Mexico (Gulf) Greater Amberjack Seriola dumerili continue to designate the stock as overfished and undergoing overfishing, despite increasing regulatory measures. Knowledge of sex-specific spatial distribution and fishing mortality may contribute to our understanding of the stocks overexploitation, especially since Greater Amberjacks may be subject to sex-specific mortality resulting from minimum size regulations. Currently, the sex ratio of the stock is assumed to be 1:1. An average and range of sex ratios were estimated for the Gulf stock based on sampling of fish landed in the recreational and commercial fisheries and based on released fish that were nonlethally sexed during a tagging study of sex-specific movement patterns and release mortality. The nonlethal method of sex determination was developed based on external features of the urogenital region; urogenital catheterization was used to validate the external sexing and to collect oocyte samples for determining maturity stages of females during the spawning season. Of the 238 fish (108 males and 130 females) for which sex was verified, only one smaller female was incorrectly sexed. Urogenital catheterization identified females that were spawning or that would likely spawn in the upcoming spawning season, but no differentiation could be made between immature and resting females. Analysis of published data sets suggested that the Gulf stock has an overall female-skewed sex ratio, with estimates ranging from 1:1.7 to 1:2.5 (male : female), while the nonlethal sexing data from the current study suggest that the overall sex ratio is slightly male skewed (1:0.8) in some regions. All studies report a female-skewed sex ratio of 1:2.3, on average, for 1,000-mm FL and larger fish in the Gulf. Sex ratios that deviate from the assumed 1:1 ratio should be incorporated into future assessments of the Gulf Greater Amberjack stock to investigate potential consequences for stock status and management.

Salinity Preference in Hatchery-Reared Juvenile Red Drum

Juvenile red drum (Sciaenops ocellatus), reared in either 15- or 30-ppt salinity seawater, were tested to determine whether they develop preference for the salinity of the water in which they were cultured. In a two-choice test, large- and small-sized juvenile red drum chose the raceway that matched the seawater in which they were cultured over the other salinity. Additional large and small fish reared in either 15- or 30-ppt salinity water were also tested following a 4-h acclimation period that simulated the duration of transport time from the hatchery to a release site. These fish also showed preference for their original culture salinity. This observed salinity preference in juvenile red drum has implications with respect to movement or residency of hatchery-reared juvenile red drum out-planted into natural coastal systems.

Comparison of Total Mortality of White Grunt from the Headboat Fishery on the Gulf Coast of Florida during Spawning and Postspawning Seasons

Abstract White grunts Haemulon plumieri were sampled from catches of the headboat fishery operating on the Gulf Coast of Florida to determine sex-specific total mortality by using catch curve analyses. Sampling was conducted during the peak of the spawning season (April–June) and in a postspawning season (July–October). In total, 1,051 white grunts were sampled in the spawning season, and 1,141 were sampled in the postspawning season. Recruitment to the fishery occurred at age 2, and the majority of males and females landed in the fishery during both the spawning and postspawning seasons were ages 2–4. The maximum age of females sampled was 18 years; for males, the maximum was 15 years. Instantaneous total mortality (Z) estimates from the catch curves did not differ significantly between spawning females, spawning males, postspawning females, and postspawning males; the pooled Z was estimated to be 0.357 (95% confidence interval, 0.284–0.430). Total annual mortality (A) was therefore estimated to be 30% (...