Jeffrey A. Buckel

Vulnerability of marine forage fishes to piscivory: effects of prey behavior on susceptibility to attack and capture

We conducted a series of size-structured laboratory experiments to quantify and compare the susceptibility of several estuarine and marine forage fishes to attack and capture by piscivorous predators. Size-dependent estimates of capture success, handling time, and prey profitability were generated from single-species experiments offering bay anchovy, Atlantic menhaden, Atlantic silverside, and age-0 striped bass to piscivores. Bay anchovy and Atlantic menhaden were most susceptible to capture and yielded high profitability compared to Atlantic silverside and age-0 striped bass prey. Variation in capture success among forage species was particularly influential in generating disparate profitability functions. Although morphological differences among forage species contributed to variation in susceptibility to predation, behavioral analyses indicated that variable reaction distances to approaching predators and activity levels of prey may explain a large fraction of the observed differences in susceptibility. When several forage species were offered to predators simultaneously in larger enclosures, mortality was highest and occurred earlier for bay anchovy and Atlantic menhaden compared to other prey, which points to the strong influence of predator capture success on overall forage fish vulnerability. Our results demonstrate species-specific differences among forage fishes in the ability to avoid attack and capture by piscivores, and we conclude that the

Estimating piscine prey size from partial remains: testing for shifts in foraging mode by juvenile bluefish

Knowledge of prey sizes consumed by a predator aids in the estimation of predation impact. Young-of-the-year bluefish, Pomatomus saltatrix, attack their prey tail-first and often bite their prey in half; this poses a unique problem in determining prey sizes from stomach content analysis. We developed a series of linear regressions to estimate original prey lengths from measurements of eye diameter and caudal peduncle depth for striped bass, Morone saxatilis, bay anchovy, Anchoa mitchilli, American shad, Alosa sapidissima, blueback herring, Alosa aestivalis, Atlantic silverside, Menidia menidia, and white perch, Morone americana. We then used these regressions to estimate original prey sizes from pieces of prey found in stomachs of bluefish collected in the Hudson River estuary from 1990–1993. Lengths of prey that were swallowed whole were compared to estimated lengths of prey that were consumed in pieces. Lengths of prey that were consumed in pieces were larger than prey that were consumed whole. We determined the prey length/predator length ratio at which bluefish began shifting from swallowing their prey whole to partial consumption. Shifting occurred at a ratio of approximately 0.35 irrespective of prey species, suggesting that prey length plays an important role in predator foraging decisions and may contribute to gape limitations. Shifts in foraging mode effectively reduce gape limitation and allow bluefish to consume larger prey sizes which may increase their effect on prey populations.

A combined telemetry - tag return approach to estimate fishing and natural mortality rates of an estuarine fish

A joint analysis of tag return and telemetry data should improve estimates of mortality rates for exploited fishes; however, the combined approach has thus far only been tested in terrestrial systems. We tagged subadult red drum (Sciae- nops ocellatus) with conventional tags and ultrasonic transmitters over 3 years in coastal North Carolina, USA, to test the efficacy of the combined telemetry - tag return approach. There was a strong seasonal pattern to monthly fishing mortality rate (F) estimates from both conventional and telemetry tags; highest F values occurred in fall months and lowest levels occurred during winter. Although monthly F values were similar in pattern and magnitude between conventional tagging and telemetry, information on F in the combined model came primarily from conventional tags. The estimated natural mortality rate (M) in the combined model was low (estimated annual rate ± standard error: 0.04 ± 0.04) and was based pri- marily upon the telemetry approach. Using high-reward tagging, we estimated different tag reporting rates for state agency and university tagging programs. The combined telemetry - tag return approach can be an effective approach for estimat- ing F and M as long as several key assumptions of the model are met.

Functional response and switching behavior of young-of-the-year piscivorous bluefish

Young-of-the-year (YOY) bluefish, Pomatomus saltatrix (L.) impose significant mortality on recently metamorphosed striped bass, Morone saxatilis (W.) in the Hudson River estuary. Field observations indicate that bluefish selectivity on striped bass increases with increasing striped bass density suggesting a density-dependent feeding response. Functional response and switching experiments were conducted to aid in determining the mechanism for this response. The type of functional response exhibited by bluefish under several prey treatments was examined. These were striped bass alone, Atlantic silversides, Menidia menidia (L.) alone, striped bass with a background density of alternative prey, and striped bass in the presence of eelgrass Zostera marina (L.). The functional response of bluefish to increasing prey density was more similar to a type I or II model than a type III model under all treatments. Switching was examined by providing bluefish both striped bass and silversides at five different ratios with and without a prey refuge, eelgrass. Bluefish did not exhibit a type III functional response or switching behavior suggesting that these mechanisms do not explain the observed density-dependent selectivity pattern in the field. Switching experiments did suggest that the presence of prey refuge can determine selectivity by YOY bluefish in the field. The abundance of submerged aquatic vegetation and other prey refuge may be important in controlling the predatory impact of bluefish on striped bass in the Hudson River.

Effects of a Delayed Onset of Piscivory on the Size of Age-0 Bluefish

Abstract Variation in advection or other physical forces may accelerate or delay arrival of young marine fishes into productive nearshore habitats, thereby affecting the length of the available growing season. The bluefish Pomatomus saltatrix is an oceanic spawner whose juvenile stages, upon entry into estuarine waters, become piscivorous and thereby experience greatly increased growth. Size attained during the growing season may therefore be determined by time of arrival into estuarine habitats. We exposed bluefish recently recruited to an estuary to three diet shift treatments in which test fish were fed adult brine shrimp Artemia sp. for 0, 10, or 20 d before they were switched to piscine prey. Bluefish that had a delayed onset of piscivory were smaller after 40 d of growth, indicating that they did not fully compensate for prior periods of slow growth. These bluefish did exhibit immediate moderate growth compensation (about 6% over 10 d) resulting from increased consumption rates, but relatively low g...

Prey Selectivity and Diet of Striped Bass in Western Albemarle Sound, North Carolina

Abstract We collected 1,399 striped bass Morone saxatilis from western Albemarle Sound, North Carolina, during May through October of 2002 and 2003 to characterize diet, prey type selectivity, and prey size selectivity. Herrings Alosa spp., Atlantic menhaden Brevoortia tyrannus, bay anchovy Anchoa mitchilli, silversides Menidia spp., and yellow perch Perca flavescens dominated the diets of age-1 striped bass, while Atlantic menhaden dominated the diets of older striped bass. Selectivity was calculated for three categories of striped bass (ages 1, 2, and 3+ [3–7]) based on fish prey collections from a 61-m beach seine and a 76-m purse seine. Striped bass of all ages primarily consumed fish prey regardless of the month or year. Each age category of striped bass selected for one or more species of prey from the suborder Clupeoidei. Age-1 striped bass selectivity of Alosa spp. generally increased with the progression of each sampling season, whereas selectivity for Atlantic menhaden, Menidia spp., and yellow ...

Movements and Mortality Rates of Striped Mullet in North Carolina

Abstract Striped mullet Mugil cephalus is an economically important species to commercial and recreational fishermen, as well as an ecologically significant detritivore linking lower trophic levels with a wide variety of estuarine and marine fish and birds. Despite this importance, striped mullet migration patterns and mortality rates are poorly understood. Approximately 15,000 striped mullet were tagged in North Carolina between 1997 and 2001, and monthly movement information was collected on recovered individuals (n = 384) from commercial and recreational fishermen and state agency personnel. A tag return model was used to estimate an instantaneous total mortality rate, and this rate was partitioned into natural and fishing components by means of life history methods. Nearly all (98.2%) striped mullet were recovered in North Carolina, the remaining few being recovered in nearby states. Striped mullet moved southward of their tagging locations and had the highest daily movement rate between the months of...

Recruitment of Juvenile Red Drum in North Carolina: Spatiotemporal Patterns of Year‐Class Strength and Validation of a Seine Survey

Abstract Sixteen years of data from a North Carolina Division of Marine Fisheries seining survey were analyzed to assess the validity of the survey, describe spatial and temporal patterns in recruitment of red drum Sciaenops ocellatus, and evaluate factors that potentially contribute to recruitment variation. Overall, 11,817 age-0 red drum (total length = 11–104 mm) were collected in the survey during 1991–2006. Annual estimates of red drum recruitment were variable over time and showed no long-term trend. The dome-shaped catch-per-unit-effort (CPUE) pattern of all annual cohorts indicated that the seine survey captured peak abundance levels each year; the spatial coverage of the survey also appeared to be adequate. Regional correlations within North Carolina were strongest for areas that were adjacent to one another, and the North Carolina statewide index was not correlated with indices from Florida or Texas, suggesting that factors controlling recruitment of red drum operate at a scale of tens to hundre...

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

Abstract 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.

Recruitment Patterns and Habitat Use of Young-of-the-Year Bluefish along the United States East Coast: Insights from Coordinated Coastwide Sampling

Protracted spawning and pulsed juvenile production are common in coastal spawning fishes, the phenology of which determines potential environmental effects on recruitment. This article examines bluefish (Pomatomus saltatrix), a cosmopolitan coastal spawning species that produces multiple cohorts of juveniles utilizing both estuarine and coastal habitats as nurseries along the U.S. east coast. To determine recruitment on a coastwide basis, ocean (bottom, neuston, and surfzone) and estuarine habitats were sampled in Florida and North Carolina south of Cape Hatteras in the South Atlantic Bight, and Maryland, New Jersey, and New York in the Middle Atlantic Bight. This coordinated sampling effort across multiple habitats with multiple gears on a coastwide basis allowed the resolution of the occurrence, growth, and movement of cohorts along the coast. Production of the spring-spawned cohort occurred in both South Atlantic Bight and Middle Atlantic Bight habitats, while summer-spawned cohort production was limited to the Middle Atlantic Bight. Information from the present study is synthesized with prior research to develop a conceptual model of the seasonal patterns of YOY bluefish habitat use and to emphasize the value of coordinated sampling at a large spatial scale in understanding recruitment processes in this and potentially other important marine species.