Stephen T. Szedlmayer

A Life History Review for Red Snapper in the Gulf of Mexico with an Evaluation of the Importance of Offshore Petroleum Platforms and Other Artificial Reefs

Red snapper mature as early as age 2, have high fecundity (a 10-year-old female produces 60 million eggs per year), and may live for over 50 years. Eggs, larvae, and post-settlement juveniles typically show high rates of natural mortality. For example, of the 60 million eggs produced annually by a 10-year-old female, only about 450 would survive to 5 cm, the size at which they enter the shrimp fishery. Changes in abundance by size and age appear to be consistent with density dependence in survival rate from ages 0 to 1 and likely ages 0 to 2. Red snapper are attracted to structure or reef habitat at all ages, but larger, older fish also occur over open habitat once they have reached a size that renders them largely invulnerable to predation. Artificial reefs comprise a small fraction of the overall high-relief reef habitat, but harbor a large fraction of the present-day age 2 red snapper populations. Prior to the proliferation of artificial reefs in the northern Gulf, age 2 red snapper may have historically occurred mainly over open-bottom, sand-mud benthic habitat where natural and shrimp trawl bycatch mortality was high. Age 2 fish dominate red snapper populations at artificial reefs, whereas the age composition of red snapper at natural reefs usually show older ages are dominant. The present day red snapper fishery is heavily dependent on catches at artificial reefs. Evidence is presented that suggests red snapper production in the northern Gulf likely has been increased by the establishment of significant numbers of artificial reefs.

Patterns of Seasonal Availability and Habitat Use by Fishes and Decapod Crustaceans in a Southern New Jersey Estuary

We examined the community structure of fish and selected decapod crustaceans and tested for within estuary differences among habitats at depths of 0.6 m to 7.9 m, in Great Bay and Little Egg Harbor in southern New Jersey. Several habitat types were identified a priori (e.g., eelgrass, sea lettuce, and marsh creeks) and sampled by trawl (4.9 m headrope, 19-mm mesh wings, 6.3-mm mesh liner), monthly, from June 1988 through October 1989. Repetitive (n=4) 2-min trawl tows were taken at each habitat type from 13 locations. The fishes and decapod crustaceans collected were typical of other Mid-Atlantic Bight estuaries but varied greatly inseasonal abundance and species. In the years sampled, bay anchovy (Anchoa mitchilli) was the dominant species (50.5% of the total number), followed by spot (Leiostomus xanthurus) (10.7%), Atlantic silverside (Menidia menidia) (9.7%), fourspine stickleback (Apeltes quadracus) (5.9%), blue crab (Callinectes sapidus) (4.6%), and northern pipefish (Syngnathus fuscus) (4.2%). The biota were examined by multi-dimensional scaling (MDS) for habitat associations and “best abiotic predictor” of community structure. Percent silt combined with salinity was the most important abiotic determinant of the faunal distributions among habitats. Temperature was a major factor influencing seasonal occurrence of the biota but had less effect on habitat comparisons. The analysis confirmed the distinct nature of the assemblages associated with the habitats, that is, eelgrass, upper estuary subtidal creeks, channels, and open bay areas. Several species were associated with specific habitats: for example,A. quadracus andS. fuscus with eelgrass, clupeids with subtidal creek stations,L. xanthurus with marsh channels, and black sea bass (Centropristis striata) and spotted hake (Urophycis regia) with sponge-peat habitat. Species richness appeared to be positively related to habitat structural heterogeneity. Thus, the best predictors for these estuarine fish and decapod crustacean assemblages were seasonal temperature, percent silt and salinity combined, and the physical heterogeneity of the habitat.

Long-Term Residence of Red Snapper on Artificial Reefs in the Northeastern Gulf of Mexico

Abstract Red snapper Lutjanus campechanus (N = 54) were tagged and tracked on 12 artificial reefs in the northeastern Gulf of Mexico. Fish were surgically implanted with ultrasonic transmitters and monitored with Vemco remote receivers and Sonotronics surface receivers from August 2000 to 2004. Four fish were manually tracked from the surface overnight, and their positions were recorded every hour for either 9 or 16 h. The total length of fish tagged was 589 ± 14 mm (mean ± SE). The number of detections by the remote receivers was 290,340 ± 44,696. By the end of this study, 5 fish were still being tracked, 8 fish had been lost immediately after tagging, 15 fish had been caught by fishers, and 26 fish had been lost after extended tracking. Red snapper were resident on artificial reefs for 218 ± 28 d, and residence time ranged from 1 to 595 d. We estimated that most (67%) of the tagged red snapper showed long-term residence (117–595 d), 13% were resident for 8–91 d, and 20% left the tagging site soon after ...

Diel Feeding Patterns of Red Snapper on Artificial Reefs in the North-Central Gulf of Mexico

Abstract Diets of red snapper Lutjanus campechanus were compared among four diel feeding periods (dawn, day, dusk, and night) and among three standard length size-classes: small (200–299 mm), medium (300–399 mm), and large (400–499 mm). Fish were collected from August through October 2000 in the north-central Gulf of Mexico. A total of 432 stomachs were examined, of which 164 (37%) contained prey. Size-class influenced diets; diets of small red snapper were dominated by fish, those of medium red snapper by fish and tunicates, and those of large red snapper by crabs and fish. Red snapper fed on prey from several different habitats. Small red snapper fed mostly on reef and sand prey types; medium red snapper fed on similar portions of reef, sand, and mixed prey types; and large red snapper fed on mixed prey types. Adjusting for fish size, mean gut fullness was significantly lower for the dusk than for the day period. Fish were the most important prey for all periods. The second most important prey group cha...

Substrate preference in age-0 red snapper, Lutjanus campechanus

We tested age-0 red snapper, Lutjanus campechanus, for sand or shell substrate preference in a circular tank (1.5 m diameter × 0.6 m deep). The test tank was divided into two equal areas of whole oyster shell or sand substrates. All trials were video taped for 20 to 25 min. Tapes were viewed on a monitor and locations of all fish recorded and timed with respect to substrate. Mean ± SE time on shell was 11.6 ± 0.5 sec (4 fish trial−1) and 13.8 ± 1.1 sec (1 fish trial−1). Mean ± SE time on sand was 9.7 ± 0.4 sec (4 fish trial−1) and 8.9 ± 0.5 sec (1 fish trial−1). Fish spent significantly more time on shell compared to sand substrate in four-fish trials (paired t-test, p < 0.10) and also in single-fish trials (paired t-test, p < 0.05). Shell substrate may offer increased food and shelter for age-0 red snapper compared to sand substrate. However, a preference for shell substrate in the natural habitat may occur only during the nursery period, because as fish grow (> 100 mm TL) in the late fall they probably outgrow the shell habitat.

Population dynamics of spot,leiostomus xanthurus, in polyhaline tidal creeks of the York River estuary, Virginia

Most populations of estuarine-dependent, early life stages of marine fishes are open. As a result, it has been difficult to apply conventional population models to most systems. In this study, a marked population of young-of-year spot (Leiostomus xanthurus) was released into a polyhaline tidal creek within the Guinea Marshes of the York River estuary, Virginia. Over a 90-day study period, 221 marked fishes were recaptured. Plots of the ratio of marked to unmarked individuals (mi/ni) in subsequent samples indicated that the population was resident in the creek for up to 162 days with the average individual present for 81 days. When this population turnover rate was compared to the total population decay rate (marked plus unmarked fish), it was determined that exchange between habitats (immigration/emigration) accounted for about 36.4% of the total decay rate, with the remainder attributed to natural mortality. By correcting the overall disappearance rate for population turnover due to emigration and using this adjusted value as a measure of instantaneous mortality (z), the estimated production (over 90 days) in this population was 23,630 cal (98,870 J) per m2. This figure agrees with a previously derived estimate for spot in the Guinea marshes and is nearly two orders of magnitude higher than other reported values for this species for all size classes over the entire growing season.

Proximity Effects of Larger Resident Fishes on Recruitment of Age-0 Red Snapper in the Northern Gulf of Mexico

Abstract Small artificial reefs (1.2 × 1.02 × 1.1 m) were placed near to (15 m; n = 20) and distant from (500 m; n = 20) larger artificial reefs (1.2 × 2.4 × 2.4 m; n = 20) in July 2008 and 2009, and each set of reefs (two small and one large) was placed 1.7 km apart at a site 28 km south of Dauphin Island, Alabama, in the northern Gulf of Mexico. Divers used visual surveys to identify and count all fish present on the small reefs and estimated fish lengths in 25-mm categories during August 2008, August 2009, and September 2009. Significantly higher numbers of age-0 red snapper Lutjanus campechanus were detected on the small distant reefs (500 m) than on the small nearby (15 m) reefs in all surveys. In addition, significantly higher densities of rock sea bass Centropristis philadelphica and pygmy filefish Stephanolepis setifer were observed on the small distant reefs compared with the small nearby reefs in both August and September 2009. Mean species richness was significantly higher on the small distant ...

The use of otolith shape analysis for ageing juvenile red snapper, Lutjanus campechanus

Morphological changes in otolith shape with age, of young (<age 3) red snapper were examined through shape analysis and tested as an objective method for age determination. Otoliths from two collections of juvenile fish (hatchery and wild) were used in the study. First, shape analysis was applied to a series of known-age otoliths from hatchery-reared age 0, 1 and 2 fish. Multidimensional scaling and non-parametric analysis of similarities showed significant shape differences among the three age classes of fish. Discriminant function analysis and cross-validation classification showed 65.6% correct age classification based on shape variables alone, and 86.7% correct age classification with inclusion of otolith weight in the discriminant function (n = 90). Subsequently, the method was applied to otoliths from a series of age 0, 1 and 2 wild caught red snapper. Otoliths from wild fish showed a similar age classification success rate of 68.9% based on shape variables alone and 86.7% correct age classification with the inclusion of otolith weight in the discriminant function (n = 90). Ageing of juvenile red snapper through otolith increment counts has been difficult in past studies and this study provides an alternative, objective method of otolith shape analysis for ageing young fish of this species.

Recruitment of Age-0 Gray Triggerfish to Benthic Structured Habitat in the Northern Gulf of Mexico

Abstract Recruitment of age-0 gray triggerfish Balistes capriscus to benthic artificial reefs was documented by diver surveys from 2003 to 2007. Divers counted and estimated the sizes of all gray triggerfish that recruited to three types of artificial reefs (all in 20-m depths) ranging from 1.2 to 4.0 m2 in area. Reefs were located in the Gulf of Mexico 28 km south of Dauphin Island, Alabama. Forty artificial reefs built in June 2003 were surveyed in October–December 2003 and May 2004; 20 artificial reefs built in October 2005 were surveyed in October and December 2005 and May, August, and December 2006; 40 artificial reefs built in July 2006 were surveyed in June 2007; and 30 artificial reefs built in August 2007 were surveyed in September, October, and December 2007. Recruitment patterns were similar in the fall and winter of 2003 and 2007. In 2005 significantly lower numbers of recruits were detected than in other years, which may have been caused by a major hurricane. Peak recruitment of age-0 gray tr...

Vertical distribution, size structure, and habitat associations of four Blenniidae species on gas platforms in the northcentral Gulf of Mexico

We counted individuals of the family Blenniidae and estimated their sizes on gas platforms southeast of Dauphin Island, Alabama. We observed species abundance decreasing as depth increased. Fish sizes also decreased with depth. The most abundant species was molly miller, Scartella cristata, followed by plumed blenny, Hypleurochilus multifilis, tessellated blenny, Hypsoblennius invemar, and seaweed blenny, Parablennius marmoreus. Total blenny abundance was positively related to the barnacle, Megabalanus antillensis, and dissolved oxygen concentrations, and inversely related to Anthozoa. Individually, S. cristata was correlated with M. antillensis, and inversely related to salinity, while the other blenny species showed more complex correlations to invertebrates. As a community, blennies showed a clear separation based on depth independent of offshore/inshore sites and sample date based on multidimensional scaling analyses. Our study suggests that attached invertebrates, particularly M. antillensis, provided a predation refuge, allowing these blenny species to exist in an otherwise unsuitable habitat, i.e. open shallow waters of the northern Gulf of Mexico.