Examination of 203 adult bluefish (Pomatomus saltatrix) from Long Island, New York, in 2002 and 2003 and 66 from the Outer Banks, North Carolina, in 2003 revealed the presence of dracunculoid nematodes (Philometra saltatrix) in the ovaries of female fish. Percent prevalence reached 88% in July and then decreased after the peak of the spawning season. Bluefish contained up to 100 parasites per fish. Infection was associated with a range of disorders, including hemorrhage, inflammation, edema, prenecrotic and necrotic changes, and follicular atresia, that may prevent proper development of oocytes and probably affect bluefish fecundity. Historical occurrences, life cycle, and geographical distribution of this nematode remain largely unknown, but may play important roles in recruitment processes of bluefish.

Juvenile growth is submaximal in many species, suggesting that a trade-off with juvenile growth must exist. In support of this, recent studies have demonstrated that rapid growth early in life results in decreased physiological performance. Theory clearly shows that for submaximal growth in juveniles to be optimal, the cost of growth must be nonlinear. However, nearly all of the empirical evidence for costs of growth comes from linear comparisons between fast- and slow-growing groups. It is consequently unclear whether any known cost can account for the evolution of submaximal juvenile growth. To test whether the cost of growth exhibits the logically necessary nonlinearity, we measured critical swimming speed (Ucrit), the maximum speed sustained in incremental velocity trials, in Atlantic silversides, a species for which the costs and benefits of growth are well studied. To increase our ability to detect a nonlinear relationship between Ucrit, a proxy for juvenile fitness, and growth, we manipulated ration levels to produce a broad range of growth rates (0.16 mm/day(-1) to 1.20 mm/day(-1)). Controlling for size and age, we found that Ucrit decreased precipitously as growth approached the physiological maximum. Using Akaike's information criterion, we show that swimming performance decreases with the square of growth rate, providing the first demonstration of a nonlinear cost of growth.

Ecosystem-based fishery management (EBFM) is a new direction for fishery management, essentially reversing the order of management priorities so that management starts with the ecosystem rather than a target species. EBFM aims to sustain healthy marine ecosystems and the fisheries they support. Pikitch et al . describe the potential benefits of implementation of EBFM that, in their view, far outweigh the difficulties of making the transition from a management system based on maximizing individual species.

Survival rates during the first winter of life are strongly size dependent and variable in many temperate fish populations. Starvation is often implicated as the cause of size-dependent first-winter mortality, and interannual variation in energy accumulation and the allocation between growth and storage is a likely source of variability. We examined these processes in young-of-the-year Hudson River striped bass Morone saxatilis, which are known to experience size-selective winter mortality and a winter energy deficit. Neutral-lipid and lean-tissue masses were determined for fish of five consecutive year classes collected through the first year of life. Differences in scaling relationships between body length and neutral-lipid and lean-tissue mass were used to infer patterns of resource allocation. Lipid reserves scaled isometrically with body length in summer but increased at a greater rate than did body length in autumn and winter. Lean-tissue allometries were less variable but followed a similar seasonal cycle. Allometric slopes were homogeneous across years, but significant interannual variation in length-specific lipid content and lean-tissue mass in the later half of the growing season indicated variable allocation patterns. During winter, up to 21% of total energy content and 50% of neutral-lipid stores were depleted. The-results indicate that energy allocation patterns result from interactions among season, ontogenetic stage, and body size. The variation in growth, allocation, and severity of the winter energy deficit likely interact to determine first-winter survival.

Analyses of changes in size distributions over time frequently suggest that mortality rates depend on body size. Such observations, however, are probably confounded with changes in size due to growth. We describe a parametric method by which the size dependence of both mortality and growth may simultaneously be inferred from pairs of size distributions collected at different times. The method is tested in a Monte Carlo study and found to have sampling properties similar to those of other methods that require more data. Survival of the first winter of life appears to be size dependent in a diverse array of taxa, although few prior studies have accounted for growth. Analysis of sizes of Menidia menidia (Atlantic silverside) from three different latitudes revealed that changes in size distributions through winter resulted from growth in southern populations and mortality in the north. Winter mortality was better described by a power function of size than an exponential. Allometric exponents increased with latitude and were greater than predicted from metabolic- or starvation-based models. The steepness of the estimated survivorship curves imply that winter mortality in M. menidia is more consistent with a threshold effect perhaps attributable to offshore migration.

Abstract The existence of temperature-dependent sex determination (TSD) and its latitudinal variability among populations were examined experimentally in Menidia peninsulae. Along the Florida coast, TSD was detected only in a northern population (Apalachee Bay: 29°55′N), wherein the proportion of females declined dramatically with increasing rearing temperature. In lower-latitude populations (New Smyrna Beach: 29°05′N, Vero Beach: 27°46′N, and Grassy Key: 24°45′N), however, offspring sex ratios were temperature-independent and approximated 1:1 at all temperatures examined (17–32 C), indicating genetic sex determination (GSD). The shift from TSD to GSD with decreasing latitude in M. peninsulae occurs coincidentally with a shift from annual to semiannual breeding and life cycle patterns. Combined with the previous studies of the northern congener Menidia menidia (∼32–47°N), the level of TSD in the genus Menidia is generally highest at intermediate latitudes (∼32–38°N), whereas nearly pure GSD is displayed at the northern and southern extremes. This pattern of latitudinal variation across two species confirms that TSD is adaptive in Menidia only in annual life histories wherein temperature during larval development serves as an accurate predictor of length of growing season and hence relative adult body size.

The timing of recruitment for age-0 bluefish Pomatomus saltatrix along the southern and mid Atlantic coast of the USA is bimodal, consisting of spring-spawned and summer-spawned cohorts. We present evidence from surveys of age-0 fish that the recent precipitous decline in the Atlantic bluefish stock over the past decade has been associated with a switch in the relative production of the two cohorts from predominance by spring-spawned fish throughout the 1970s and 1980s to predominance by summer-spawned fish in most years from 1992 to 2002. Given this evidence of a shifting recruitment pattern, we reexamined the contribution of the two cohorts to the adult portion of the population and compared our results with similar earlier assessments. Cohort origin of adults was identified based on back-calculated length at age 1. In four year-classes in which age-0, summer-spawned bluefish predominated, there was little evidence of summer-spawned fish among harvested adults from the same year-classes captured one or more years later. Most adults examined in this study (N = 976) displayed lengths at age I greater than 20 cm, as predicted for spring-spawned bluefish. This contrasts with year-classes of bluefish from the late 1950s, when back-calculated size at age I was clearly bimodal, consisting of both spring-spawned and summer-spawned cohorts. Low numbers of summer-spawned bluefish in our samples did not appear to be an artifact of inaccuracies in aging or back-calculation. The recent decline in the abundance of Atlantic coast bluefish appears to result from poor age-0 recruitment of the spring-spawned cohort and failure of the summer-spawned cohort to contribute substantially to the adult population.

We examined the role of salinity, body size, and energetic state in determining low temperature tolerance of young-of-the-year (YOY) striped bass (Morone saxatilis) and used this information to map optimal overwintering habitat in the Hudson River estuary. A long-term experiment compared survival at 15 ppt and 30 ppt. In additional experiments, winter-acclimated fish were exposed to temperature declines (2.3°C·day–1to 1°C·week–1) at salinities from 0 ppt to 35 ppt. Highest survival at low temperatures was consistently observed at intermediate salinities. These results suggest that the observed distribution of overwintering striped bass is related to physiological constraints on osmo regulatory ability at low temperatures. Low temperature tolerance appeared unrelated to body size and energetic state. Salinity profiles were used to describe the location and extent of optimal wintering habitats under various hydrographic regimes. The location of optimal habitats was displaced by over 27 km along the river axis because of variation in salinity regime. Changes in the availability of optimal habitat may be responsible for variation in recruitment to the Hudson River population. These results demonstrate the need to consider a holistic approach encompassing all seasons of the year in assessing habitat requirements of fishes.

In ectotherms, lower mean temperatures and shorter growing seasons at higher latitudes would be expected to cause a reduction in the annual growth rate of an individual. If slower growth reduces fitness, then organisms at higher latitudes may evolve compensatory responses for these climatic effects. Two such forms of local adaptation with increasing latitude are possible: (1) the capacity for growth may shift to a lower range of temperatures (i.e., temperature adaptation) or (2) maximum growth rate may evolve inversely with length of the growing season (i.e., countergradient variation). A third alternative is a mixed strategy involving both of the above. We hypothesized that the form of local adaptation may be affected by constraints that vary within vs. among species. We used common-environment experiments to compare reaction norms for growth in response to temperature among local populations of two contiguous, closely related fish species, the Atlantic silverside, Menidia menidia (L.), and the tidewater silverside, M. peninsulae (Goode and Bean), which together have a range spanning much of the North American Atlantic coast. The common-environment experiments revealed countergradient variation: maximum growth rate increased with latitude both within and among species. However, growth reaction norms of the northern species were shifted to a lower range of temperatures than those of the southern species, indicating adaptation to temperature at the interspecific level. Hence, adaptation to temperature contributes to the interspecific variation, while countergradient variation contributes to both the intra- and interspecific differences.

We constructed bioenergetic models for locally adapted populations of Atlantic silversides, Menidia menidia, from different latitudes (Nova Scotia and South Carolina) to determine how genetic variation in growth physiology affects model parameters and predicted growth and to test two hypotheses on the evolution of countergradient variation in growth rate. Model parameters were estimated simultaneously for each population through a penalized likelihood approach incorporating laboratory measurements of metabolism, specific dynamic action, consumption, and growth. The resulting population-specific parameters differed by an average of 28%. The models were validated by successful (R-2 > 0.9) prediction of growth in independent experiments under natural light and temperature conditions and by predicting growth in the field (R-2 > 0.95). We then performed virtual reciprocal transplant simulations to test the alternative hypotheses that growth rate along a latitudinal gradient evolves in response to temperature or resource availability. Predictions for each transplanted population deviated significantly from observed growth for each native population, demonstrating the importance of accounting for interpopulation variation in model parameters. Our results indicate that the latitudinal cline in growth rate cannot be explained solely by thermal adaptation but may have arisen owing to the combined effects of temperature and food availability.

The Atlantic silverside (Menidia menidia) exhibits countergradient latitudinal variation in somatic growth rate along the East Coast of North America. Larvae and juveniles from high-latitude populations display higher intrinsic rates of energy consumption and growth than genotypes from low-latitude populations. The existence of submaximal growth in some environments suggests that trade-offs must counter the oft-cited theoretical benefits of energy and growth maximization (e.g., "bigger is better,'' ''faster is better'') in the immature life stages. We hypothesized that energy and growth maximization trades off against investment in defense from predators. We conducted laboratory selection experiments to compare vulnerability to predation of silversides from: (1) fast-growing northern (Nova Scotia, NS) versus slow-growing southern (South Carolina, SC) source populations; (2) phenotypically manipulated fast-growing versus moderately-growing NS fish; and (3) recently fed versus unfed NS and SC fish. Tests involved fish drawn from common-garden environments and were conducted by subjecting mixed-treatment schools of size-matched silversides to natural, common piscine predators. NS silversides suffered significantly higher predation mortality than SC silversides. Parallel results were found in phenotypic manipulation of growth: NS silversides reared on a fast-growth trajectory (approximately 1.0 mm/day) were significantly more vulnerable to predation than those growing at a moderate rate (approximately 0.5 mm/day). Food consumption also affected vulnerability to predators: Silversides with large meals in their stomachs suffered significantly higher predation mortality than unfed silversides. Differences in predation vulnerability were likely due to swimming performance, not attractiveness to predators. Our findings demonstrate that maximization of energy intake and growth rate engenders fitness costs in the form of increased vulnerability to predation.

The importance of activity to overwintering fishes has received little attention. Activity imposes two constraints: maximum swimming speed limits habitats that can be occupied for short periods of time, while the metabolic cost of swimming limits the habitats that are suitable for long-term residence. We measured the energetic consequences of activity and maximum swimming speeds of young-of-the-year striped bass (Morone saxatilis), a species that overwinters in tidal estuaries. The energetic cost of swimming was determined from energy changes in unfed fish forced to swim at various speeds, while energy changes in fed fish provided a measure of their ability to offset swimming costs through feeding. In high-velocity treatments, mortality was size-dependent and appeared to be related to fatigue rather than to depletion of energy reserves. The energetic cost of swimming increased with swimming velocity, but fish increased food consumption and thereby met their metabolic needs. In a second experiment the thermal dependence of swimming capacity in winter-acclimated striped bass was measured. Swimming speeds increased with temperature, from 2.7 body lengths (BL)/s at 2°C to 4.8 BL/s at 8 and 11°C, but were considerably below observed flow velocities in the Hudson River, suggesting a need for behavioral or physical refuge from tidal currents. These results indicate the flexibility of energy budgets of overwintering fishes, allowing energetic stress to be minimized by reducing activity or elevating food-consumption rates when sufficient prey are available.

Latitudinal populations of the Atlantic silverside, Menidia menidia, show substantial genetic variation in rates of energy acquistion and allocation. Reared in common environments, silversides from northern latitudes consume more food, grow faster and more efficiently, store more energy, and produce greater quantities of eggs than their southern conspecifics. The persistence of seemingly inferior southern genotypes in the face of ostensibly superior northern genotypes suggest that there are hidden evolutionary trade-offs associated with these elevated acquisition and allocation rates. We tested the hypothesis that rapid growth and high levels of food consumption trade-off against locomotory performance in M. menidia. We compared both aerobic (prolonged and endurance) and anaerobic (burst) swimming capacities between intrinsically fast-growing fish from the north (Nova Scotia, NS) and intrinsically slow-growing fish from the south (South Carolina, SC) and between growth-manipulated phenotypes within each population. We also compared swimming speeds and endurance between fasted and recently fed fish within populations. Maximum prolonged and burst swimming speeds of NS fish were significantly lower than those of SC fish, and swimming speeds of fast-growing phenotypes were lower than those of slow-growing phenotypes within populations. Fed fish had lower burst speeds and less endurance than fasted fish from the same population. Thus, high rates of growth and the consumption of large meals clearly diminish swimming performance, which likely increases vulnerability to predation and decreases survival and relative fitness. The submaximal growth rate of southern M. menidia appears to be adaptive, resulting from balancing selection on rates of somatic growth.

Recruitment dynamics are complicated in species in which multiple cohorts of young-of-the-year (YOY) are produced each year. Each summer, two cohorts of YOY bluefish (Pomatomus saltatrix), representing fish spawned in spring and summer, recruit to Mid-Atlantic Bight estuaries, but little is known about their interannual variability, environmental forcing, and relative contributions to later life stages. We addressed these questions by examining the distribution and abundance of YOY on the continental shelf of the US east coast in autumn from 1973 through 1995. Abundance on the continental shelf increased in autumn owing to emigration from estuaries. We found clear evidence of two cohorts in autumn length-frequency distributions in most years and used this information to construct cohort-specific indices of abundance, which were then compared with relevant environmental variables. Spring-spawned fish dominated the catch in 20 of the years examined. The summer cohort dominated only in 1992. The abundance of the two cohorts was positively correlated, rejecting the hypothesis that dominance of the spring cohort is the result of cannibalism on the summer cohort. Spring cohort abundance was not correlated with either shelf warming-rate or warm-core ring streamer activity. A strong relationship was found between winds in April and May and the abundance of spring-spawned bluefish, possibly indicating that wind-driven surface flow aids the transport of larvae and/or juveniles across the shelf-slope region. (C) 2000 International Council for the Exploration of the Sea.

A call for marine reserves has emerged at the forefront of natural resource policy and management for three reasons. First, reserves can protect critical habitat for fishery resources that have been depleted through overharvesting or habitat destruction. Second, they can help conserve marine diversity. Third, in some circumstances, they might be able to enhance the harvest of stocks outside the reserve. The enthusiasm for marine reserves reflects their fit with five themes that recur in current management theory: the desirability of risk-averse resource management, the practical management of human activity, the necessity for new scientific information, the wisdom of protecting habitat damaged by fishing effort, and the perception that new, immediate measures are needed to help restore our fisheries. This symposium was designed to address several questions surrounding these themes. These include questions about when reserves would work best, the optimal siting of reserves, the role of reserves within broader management schemes, the social issues surrounding the implementation of reserves, and whether reserves can actually perform the roles that fisheries scientists hope they will. There is consensus on some of the answers, but not on all; most critically, how well existing reserves can enhance the stock outside of the reserves remains a subject of intense debate.

We measured bluefish (Pomatomus saltatrix) weights, densities, and prey sizes during the summers of 1992 and 1993 and diets over a 4-year period (1990-1993) in the Hudson River estuary. This information was used to estimate the loss of young-of-the-year (YOY) striped bass (Morone saxatilis) resulting from YOY bluefish predation. We then compared this predation mortality with the total loss of striped bass in the system. Data from sampling surveys conducted since the mid-1970's were used to examine relationships between bluefish abundance and striped bass recruitment levels. YOY striped bass, bay anchovy (Anchoa mitchilli), Atlantic silverside (Menidia menidia), and Alosa spp. dominated YOY bluefish diets. There were ontogenetic and interannual differences in YOY bluefish diets. Bluefish avoided striped bass at low densities but selected for them at high densities, suggesting a density-dependent feeding response. In the early summer of 1993, bluefish predation accounted for 50-100% of the total estimated loss of YOY striped bass. A significant negative correlation exists between the relative magnitude of striped bass recruitment and bluefish abundance. We conclude that YOY bluefish are important predators of estuarine fish and can have a substantial impact on their recruitment.

The bluefish, Pomatomus saltatrix, has long been considered a key predator on U.S. east coast fish species. Many of its prey species are also landed by humans, but no comparison of prey biomass harvested by bluefish versus fishermen has been attempted previously. We used data an growth, mortality, gross growth efficiency, and abundance to model the total prey consumption rate by bluefish at the population level. This estimate and previously published information on diet were used to calculate the biomass of individual resource species "harvested" by bluefish. The prey biomass consumed by bluefish annually along the U.S. Atlantic coast is equal to eight times the biomass of the bluefish population. Bluefish consume a much higher biomass of squid and butterfish than is currently harvested by commercial fisheries for these species. Bluefish consumption of Atlantic menhaden, however, was below the current fisheries landings for this species. For resource species that are shared with bluefish, our findings highlight the need for multi-species assessment and management.

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 growth efficiencies prevented full recovery of their growth losses. Low growth efficiencies may have resulted from an induced developmental handicap or an energetic penalty for prolonged feeding on an Anemia diet. The timing of age-0 bluefish recruitment into estuarine environments can have a lasting influence on size attained during the first growing season.