Age, growth, and reproduction of dolphinfish (Coryphaena hippurus) caught off the coast of North Carolina

Age, growth, and reproductive data were obtained from dolphinfish (Coryphaena hippurus, size range: 89 to 1451 mm fork length [FL]) collected between May 2002 and May 2004 off North Carolina. Annual increments from scales (n=541) and daily increments from sagittal otoliths (n=107) were examined; estimated von Bertalanffy parameters were L∞ (asymptotic length)=1299 mm FL and k (growth coefficient)=1.08/yr. Daily growth increments reduced much of the residual error in length-at-age estimates for age-0 dolphinfish; the estimated average growth rate was 3.78 mm/day during the first six months. Size at 50% maturity was slightly smaller for female (460 mm FL) than male (475 mm FL) dolphinfish. Based on monthly length-adjusted gonad weights, peak spawning occurs from April through July off North Carolina; back-calculated hatching dates from age-0 dolphinfish and prior reproductive studies on the east coast of Florida indicate that dolphinfish spawning occurs year round off the U.S. east coast and highest levels range from January through June. No major changes in length-at-age or size-at-maturity have occurred since the early 1960s, even after substantial increases in fishery landings

Gastric evacuation rates of piscivorous young-of-the-year bluefish

Abstract.-Estimates of gastric evacuation rates (GER) are needed to calculate consumption rates of fish from field-collected data on stomach contents. The results of 16 GER experiments designed to determine the effects of body size, prey type, and temperature on the GER in youngof-the-year (age-0) bluefish Pomatomus saltatrix are presented. The linear, square-root, and exponential GER models similarly fit the data. Temperature had a highly significant effect on age-0 bluefish GER. However, there was no significant difference in GER between small (5.14 g wet weight) and large (35.99 g wet weight) age-0 bluefish. Among the three different prey types tested (age-0 striped bass Mor one saxatilis, bay anchovy Anchoa mit chilli, and age-0 Atlantic menhaden Brevoortia tyrannus) there was no significant difference in GER. The exponential relation between bluefish GER and temperature can be used in estimating age-0 bluefish consumption rates in the field

Feeding ecology of Atlantic bluefin tuna (Thunnus thynnus) in North Carolina: diet, daily ration, and consumption of Atlantic menhaden (Brevoortia tyrannus)

Diet, gastric evacuation rates, daily ration, and population-level prey demand of bluefin tuna (Thunnus thynnus) were estimated in the continental shelf waters off North Carolina. Bluefin tuna stomachs were collected from commercial fishermen during the late fall and winter months of 2003–04, 2004–05, and 2005–06. Diel patterns in mean gut fullness values were used to estimate gastric evacuation rates. Daily ration determined from mean gut fullness values and gastric evacuation rates was used, along with bluefin tuna population size and residency times, to estimate population-level consumption by bluefin tuna on Atlantic menhaden (Brevoortia tyrannus). Bluefin tuna diet (n= 448) was dominated by Atlantic menhaden; other teleosts, portunid crabs, and squid were of mostly minor importance. The time required to empty the stomach after peak gut fullness was estimated to be ~20 hours. Daily ration estimates were approximately 2% of body weight per day. At current western Atlantic population levels, bluefin tuna predation on Atlantic menhaden is minimal compared to predation by other known predators and the numbers taken in commercial harvest. Bluefin tuna appear to occupy coastal waters in North Carolina during winter to prey upon Atlantic menhaden. Thus, changes in the Atlantic menhaden stock status or distribution would alter the winter foraging locations of bluefi

Environmental Toxicology TESTS OF BIOACCUMULATION MODELS FOR POLYCHLORINATED BIPHENYL COMPOUNDS: A STUDY OF YOUNG-OF-THE-YEAR BLUEFISH IN THE HUDSON RIVER ESTUARY, USA

Abstract-A field-based study regarding uptake of polychlorinated biphenyl compounds (PCBs) by young-of-the-year (YOY) bluefish (Pomatomus saltatrix) was initiated to test a steady-state model of bioaccumulation and trophic transfer in a rapidly growing fish. Determination of prey composition as well as size-dependent growth and specific consumption rates for YOY bluefish from separate field and laboratory studies enabled the input of these species-specific parameters into the model. Furthermore, the time and duration of the exposure of YOY bluefish to dissolved PCBs from a well-characterized system (Hudson River, USA) was well known. Patterns of accumulation of individual PCB congeners differed relative to the accumulation of total PCBs, with the greatest net accumulation occurring for the higher-molecular-weight congeners. Comparison of lipid-normalized bioaccumulation factors (BAFs) with the octanol-water partition coefficients of individual PCB congeners revealed bluefish to be above the BAFs predicted by lipid-based equilibrium partitioning, suggesting that uptake from food is an important source of PCBs in YOY bluefish. Comparison of measured BAFs with values predicted by a steady-state, food-chain model showed good first-order agreement

Relationships between Larval and Juvenile Abundance of Winter-Spawned Fishes in North Carolina, USA

We analyzed the relationships between the larval and juvenile abundances of selected estuarine-dependent fishes that spawn during the winter in continental shelf waters of the U.S. Atlantic coast. Six species were included in the analysis based on their ecological and economic importance and relative abundance in available surveys: spot Leiostomus xanthurus, pinfish Lagodon rhomboides, southern flounder Paralichthys lethostigma, summer flounder Paralichthys dentatus, Atlantic croaker Micropogonias undulatus, and Atlantic menhaden Brevoortia tyrannus. Cross-correlation analysis was used to examine the relationships between the larval and juvenile abundances within species. Tests of synchrony across species were used to find similarities in recruitment dynamics for species with similar winter shelf-spawning life-history strategies. Positive correlations were found between the larval and juvenile abundances for three of the six selected species (spot, pinfish, and southern flounder). These three species have similar geographic ranges that primarily lie south of Cape Hatteras. There were no significant correlations between the larval and juvenile abundances for the other three species (summer flounder, Atlantic croaker, and Atlantic menhaden); we suggest several factors that could account for the lack of a relationship. Synchrony was found among the three southern species within both the larval and juvenile abundance time series. These results provide support for using larval ingress measures as indices of abundance for these and other species with similar geographic ranges and winter shelf-spawning life-history strategies

Variation in movement patterns of red drum (Sciaenops ocellatus) inferred from conventional tagging and ultrasonic telemetry

We used 25 years of conventional tagging data (n= 6173 recoveries) and 3 years of ultrasonic telemetry data (n=105 transmitters deployed) to examine movement rates and directional preferences of four age classes of red drum (Sciaenops ocellatus) in estuarine and coastal waters of North Carolina. Movement rates of conventionally tagged red drum were dependent on the age, region, and season of tagging. Age-1 and age-2 red drum tagged along the coast generally moved along the coast, whereas fish tagged in oligohaline waters far from the coast were primarily recovered in coastal regions in fall months. Adult (age-4+) red drum moved from overwintering grounds on the continental shelf through inlets into Pamlico Sound in spring and summer months and departed in fall. Few tagged red drum were recovered in adjacent states (0.6% of all recoveries); however, some adult red drum migrated seasonally from overwintering grounds in coastal North Carolina northward to Virginia in spring, returning in fall. Age-2 transmitter-tracked red drum displayed seasonal emigration from a small tributary, but upstream and downstream movements within the tributary were correlated with fluctuating salinity regimes and not season. Large-scale conventional tagging and ultrasonic telemetry programs can provide valuable insights into the complex movement patterns of estuarine fish

Spatial extent and isolation of marine artificial structures mediate fish density

Installations of artificial structures in coastal oceans create de facto habitat for marine life. These structures encompass wide varieties of physical characteristics, reflecting their multiple, diverse purposes and creating a need to understand which characteristics maximize fish habitat. Here, we test how physical characteristics – horizontal area, vertical relief, and spatial isolation – relate to fish density from echosounder surveys over artificial structures like concrete pipes, train boxcars, and ships purposely sunk to function as reefs. Echosounder mapping of 31 artificial reef structures and associated fish across a 200 km linear length of the continental shelf of North Carolina, USA, revealed that structures with greater horizontal area and vertical relief host higher fish densities than smaller, shorter structures. Artificial structure spatial arrangement also relates to fish density, as isolated structures are generally associated with greater localized fish densities than structures closer to one another. Patterns in the relationships between fish density and reef characteristics differed for schooling fish, as there was some evidence that reefs of intermediate area exhibited higher schooling fish density. These results suggest that intentional design and spatial arrangement of marine built structures like artificial reefs relates to and can be deliberately incorporated into siting and deployment decisions to enhance their role as fish habitat

Competition between juvenile striped bass and bluefish: resource partitioning and growth rate

ABSTRACT: The potential for competition to influence the population dynamics of bluefish Pomatomus saltatrix and striped bass Morone saxatilis through interactions at the juvenile stage was examined. Habitat and diet utilization were compared between juvenile striped bass and bluefish in 3 New York Bight marine embayments. Juvenile bluefish and striped bass were seldom captured together during the summer and early fall, suggesting low habitat overlap at the scale of a beach seine haul. Diet overlap was also low; age-0 bluefish (spring- and summer-spawned cohorts) had a more piscivorous diet than age-0 and age-1 striped bass. A 60d laboratory growth experiment tested for interference competition between age-0 bluefish (spring-spawned) and age-1 striped bass fed fish prey in mixed- and single-species treatments. In the growth experiment, bluefish grew significantly faster than striped bass; however, within a species, there was no significant difference in growth between the mixed- and single-species treatments. Additionally, long-term field-monitoring data showed that annual estimates of growth rate for bluefish and striped bass were not correlated with annual estimates of their potential competitor’s density. These field and laboratory data provide no evidence for competitive interactions between juvenile striped bass and bluefish

Negative effects of increasing group size on foraging in two estuarine piscivores

Abstract The effect of predator density on per capita ingestion rates in two estuarine predators, age-0 bluefish (Pomatomus saltatrix L.) and age-1 striped bass (Morone saxatilis W.), was examined in a 121,000-l research aquarium. Group size treatments were 3, 6, 12, and 24 predators; each treatment was provided with 100 prey (mummichog killifish, Fundulus heteroclitus L.) during a 22-h feeding trial. The behaviors of predator and prey were recorded. Predator type and group size had a significant effect on per capita ingestion rates. Bluefish had significantly higher per capita ingestion rates compared to striped bass. For bluefish, per capita ingestion rate was highest in the three predator group, while for striped bass, individuals in the six predator treatment had the highest ingestion rates. From these maxima, per capita ingestion rate values declined to their lowest values in the 24 predator treatment for both species. Several factors that may be responsible for lowered per capita ingestion rates at higher group sizes include predator interference, prey depletion, and antipredator behaviors of prey. For juvenile bluefish and striped bass being a member of a relatively large group may lead to decreased individual ingestion rates. Given that large group sizes of these species occur in nature, we conclude that these foraging costs must be outweighed by benefits of group membership.