The distribution of larval fishes of the Charleston Gyre Region off the southeastern United States in winter shaped by mesoscale, cyclonic eddies

Serial, cyclonic, mesoscale eddies arise just north of the Charleston Bump, a topographical rise on the continental slope and Blake Plateau, and characterize the U.S. outer shelf and upper slope in the region of the Charleston Gyre. This region was transected during the winters of 2000, 2001, and 2002, and hydrographic data and larval fishes were collected. The hydrodynamics of the cyclonic eddies of the Charleston Gyre shape the distribution of larval fishes by mixing larvae from the outer continental shelf and the Gulf Stream and entraining them into the eddy circulation at the peripheral margins, the wrap-around filaments. Over all years and transects (those that intercepted eddies and those that did not), chlorophyll a concentrations, zooplankton displacement volumes, and larval fish concentrations were positively correlated. Chlorophyll a concentrations were highest in filaments that wrapped around eddies, and zooplankton displacement volumes were highest in the continental shelf–Gulf Stream–frontal mix. Overall, the concentration of all larval fishes declined from inshore to offshore with highest concentrations occurring over the outer shelf. Collections produced larvae from 91 fish families representing continental shelf and oceanic species. The larvae of shelf-spawned fishes—Atlantic Menhaden Brevoortia tyrannus, Round Herring Etrumeus teres, Spot Leiostomus xanthurus, and Atlantic Croaker Micropogonias undulatus—were most concentrated over the outer shelf and in the continental shelf–Gulf Stream–frontal mix. The larvae of ocean-spawned fishes—lanternfishes, bristlemouths, and lightfishes—were more evenly dispersed in low concentrations across the outer shelf and upper slope, the highest typically in the Gulf Stream and Sargasso Sea, except for lightfishes that were highest in the continental shelf–Gulf Stream–frontal mix. Detrended correspondence analysis rendered groups of larval fishes that corresponded with a gradient between the continental shelf and Gulf Stream and Sargasso Sea. Eddies propagate northeastward with a residence time on the outer shelf and upper slope of ∼1 month, the same duration as the larval period of most fishes. The pelagic habitat afforded by eddies and fronts of the Charleston Gyre region can be exploited as nursery areas for feeding and growth of larval fishes within the southeastern Atlantic continental shelf ecosystem of the U.S. Eddies, and the nursery habitat they provide, translocate larvae northeastward.

Spatial and temporal variability in the relative contribution of king mackerel (Scomberomorus cavalla) stocks to winter mixed fisheries off South Florida

King mackerel (Scomberomorus cavalla) are ecologically and economically important scombrids that inhabit U.S. waters of the Gulf of Mexico (GOM) and Atlantic Ocean (Atlantic). Separate migratory groups, or stocks, migrate from eastern GOM and southeastern U.S. Atlantic to south Florida waters where the stocks mix during winter. Currently, all winter landings from a management-defined south Florida mixing zone are attributed to the GOM stock. In this study, the stock composition of winter landings across three south Florida sampling zones was estimated by using stock-specific otolith morphological variables and Fourier harmonics. The mean accuracies of the jackknifed classifications from stepwise linear discriminant function analysis of otolith shape variables ranged from 66−76% for sex-specific models. Estimates of the contribution of the Atlantic stock to winter landings, derived from maximum likelihood stock mixing models, indicated the contribution was highest off southeastern Florida (as high as 82.8% for females in winter 2001−02) and lowest off southwestern Florida (as low as 14.5% for females in winter 2002−03). Overall, results provided evidence that the Atlantic stock contributes a certain, and perhaps a significant (i.e., ≥50%), percentage of landings taken in the management-defined winter mixing zone off south Florida, and the practice of assigning all winter mixing zone landings to the GOM stock should

Global Climate Change Impacts in the United States: a state of knowledge report from the U.S. Global Change Research Program

Executive Summary: Observations show that warming of the climate is unequivocal. The global warming observed over the past 50 years is due primarily to human-induced emissions of heat-trapping gases. These emissions come mainly from the burning of fossil fuels (coal, oil, and gas), with important contributions from the clearing of forests, agricultural practices, and other activities. Warming over this century is projected to be considerably greater than over the last century. The global average temperature since 1900 has risen by about 1.5ºF. By 2100, it is projected to rise another 2 to 11.5ºF. The U.S. average temperature has risen by a comparable amount and is very likely to rise more than the global average over this century, with some variation from place to place. Several factors will determine future temperature increases. Increases at the lower end of this range are more likely if global heat-trapping gas emissions are cut substantially. If emissions continue to rise at or near current rates, temperature increases are more likely to be near the upper end of the range. Volcanic eruptions or other natural variations could temporarily counteract some of the human-induced warming, slowing the rise in global temperature, but these effects would only last a few years. Reducing emissions of carbon dioxide would lessen warming over this century and beyond. Sizable early cuts in emissions would significantly reduce the pace and the overall amount of climate change. Earlier cuts in emissions would have a greater effect in reducing climate change than comparable reductions made later. In addition, reducing emissions of some shorter-lived heat-trapping gases, such as methane, and some types of particles, such as soot, would begin to reduce warming within weeks to decades. Climate-related changes have already been observed globally and in the United States. These include increases in air and water temperatures, reduced frost days, increased frequency and intensity of heavy downpours, a rise in sea level, and reduced snow cover, glaciers, permafrost, and sea ice. A longer ice-free period on lakes and rivers, lengthening of the growing season, and increased water vapor in the atmosphere have also been observed. Over the past 30 years, temperatures have risen faster in winter than in any other season, with average winter temperatures in the Midwest and northern Great Plains increasing more than 7ºF. Some of the changes have been faster than previous assessments had suggested. These climate-related changes are expected to continue while new ones develop. Likely future changes for the United States and surrounding coastal waters include more intense hurricanes with related increases in wind, rain, and storm surges (but not necessarily an increase in the number of these storms that make landfall), as well as drier conditions in the Southwest and Caribbean. These changes will affect human health, water supply, agriculture, coastal areas, and many other aspects of society and the natural environment. This report synthesizes information from a wide variety of scientific assessments (see page 7) and recently published research to summarize what is known about the observed and projected consequences of climate change on the United States. It combines analysis of impacts on various sectors such as energy, water, and transportation at the national level with an assessment of key impacts on specific regions of the United States. For example, sea-level rise will increase risks of erosion, storm surge damage, and flooding for coastal communities, especially in the Southeast and parts of Alaska. Reduced snowpack and earlier snow melt will alter the timing and amount of water supplies, posing significant challenges for water resource management in the West. (PDF contains 196 pages)

Species composition, distribution, and relative abundance of fishes in the coastal habitat off the southeastern United States

Ichthyofauna of the coastal «10 m depth) habitat of the South Atlantic Bight were investigated between Cape Fear, North Carolina, and the St. John's River, Florida. Trawl collections from four nonconsecutive seasons in the period July 1980 to December 1982 indicated that the fish community is dominated by the family Sciaenidae, particularly juvenile forms. Spot (Leiostomus xanthurus) and Atlantic croaker (Micropogonias undulatus) were the two most abundant species and dominated catches during all seasons. Atlantic menhaden (Brevoortin tyrannus) was also very abundant, but only seasonally (winter and spring) dominant in the catches. Elasmobranch fIShes, especially rajiforms and carcharinids, contributed to much of the biomass of fishes collected. Total fish abundance was greatest in winter and lowest in summer and was influenced by the seasonality of Atlantic menhaden and Atlantic croaker in the catches. Biomass was highest in spring and lowest in summer, and was influenced by biomass of spot. Fish density ranged from 321 individuals and 12.2 kg per hectare to 746 individuals and 25.2 kg per hectare. Most species ranged widely throughout the bight, and showed some evidence of seasonal migration. Species assemblages were dominated by ubiquitous year-round residents of the coastal waters of the bight. Diversity (H') was highest in summer, and appeared influenced by the evenness of distribution of individuals among species. (PDF file contains 56 pages.)

Zusammenhang zwischen Schadstoffen aus der Elbe und missgebildeten Fischembryonen in der Deutschen Bucht.

The trends of malformation prevalence in embryos of dab, Limanda limanda, in the southern North Sea after the year 1990 mirrored the drop in major pollutants in the rivers draining into the German Bight. Despite this general decline we detected a pollution event in the southern North Sea in winter 1995/1996 employing the prevalence of malformations in dab embryos as an indicator. An abrupt rise in malformation prevalence in the embryos of dab, corresponded to a dramatic increase in DDT levels in parent fish from the same area, indicating a hitherto unnoticed introduction of considerable quantities of DDT into the system. This input could be traced back to discharges of unknown origen into the River Elbe.

Zur Verbreitung der einzelnen Altersklassen des Köhlers, Pollachius virens (L.), in der nördlichen Nordsee (ICES-Div. IV a)

The distribution was studied by analysing the catches during four research vessel cruises in summer and eight cruises in winter in the period 1985 - 1993. The emmigration of young saithe, spending the larval and first juvenil stages in the inshore waters of Norway and Scotland, starts during the summer in an age of two years.

Changes in physical and chemical variables

An article reviewing the work undertaken looking at the seasonal variation of chemical conditions in water at various depths in lakes. The laboratory tests undertaken for the research is outlined, as well as details of the sampling locations and the staff involved with the work. One figure shows the seasonal variation in the amounts of dissolved substances in the surface water of Windermere during 1936. Another figure shows seasonal varation inthe dry weight of phyto- and zooplankton in Windermere. Seasonal changes are discussed further and a table is included showing chemical conditions in winter and summer for Windermere.

Seasonal changes in growth of coho salmon (Oncorhynchus kisutch) off Oregon and Washington and concurrent changes in the spacing of scale circuli

In this study we present new information on seasonal variation in absolute growth rate in length of coho salmon (Oncorhynchus kisutch) in the ocean off Oregon and Washington, and relate these changes in growth rate to concurrent changes in the spacing of scale circuli. Average spacing of scale circuli and average rate of circulus formation were significantly and positively correlated with average growth rate among groups of juvenile and maturing coho salmon and thus could provide estimates of growth between age groups and seasons. Regression analyses indicated that the spacing of circuli was proportional to the scale growth rate raised to the 0.4−0.6 power. Seasonal changes in the spacing of scale circuli reflected seasonal changes in apparent growth rates of fish. Spacing of circuli at the scale margin was greatest during the spring and early summer, decreased during the summer, and was lowest in winter or early spring. Changes over time in length of fish caught during research cruises indicated that the average growth rate of juvenile coho salmon between June and September was about 1.3 mm/d and then decreased during the fall and winter to about 0.6 mm/d. Average growth rate of maturing fish was about 2 mm/d between May and June, then decreased to about 1 mm/d between June and September. Average apparent growth rates of groups of maturing coded-wire−tagged coho salmon caught in the ocean hook-and-line fisheries also decreased between June and September. Our results indicate that seasonal change in the spacing of scale circuli is a useful indicator of seasonal change in growth rate of coho salmon in the ocean.

Soft Flesh in Sablefish, Anoplopoma fimbria, of Southeastern Alaska: Relationships with Depth, Season, and Biochemistry

The condition of soft-textured flesh in commercially harvested sablefish, Anoplopoma fimbria, from southeastern Alaska was investigated by National Marine Fisheries Service (NMFS) scientists from the Alaska Fisheries Science Center’s Auke Bay Laboratories (ABL) in Alaska and the Northwest Fisheries Science Center in Seattle, Wash. Sablefish were sampled by longline, pot, and trawl at five sites around Chichagof Island at depths of 259–988 m in the summer of 1985 and at depths of 259–913 m in the winter of 1986. At the time of capture and data collection, sablefish were categorized as being “firm” or “soft” by visual and tactile examination, individually weighed, measured for length, and sexed. Subsamples of the fish were analyzed and linear regressions and analyses of variance were performed on both the summer (n = 242) and winter (n = 439) data for combinations of chemical and physical analyses, depth of capture, weight vs. length, flesh condition, gonad condition, and sex. We successfully identified and selected sablefish with firm- and soft-textured flesh by tactile and visual methods. Abundance of firm fish in catches varied by season: 67% in winter and 40% in summer. Winter catches may give a higher yield than summer catches. Abundance of firm fish catches also varied with depth. Firm fish were routinely found shallower than soft fish. The highest percentage of firm fish were found at depths less than 365 m in summer and at 365–730 m in winter, whereas soft fish were usually more abundant at depths greater than 731 m. Catches of firm fish declined with increasing depth. More than 80% of the fish caught during winter at depths between 365 and 730 m had firm flesh, but this declined to 48% at these depths in summer. Longlines and pots caught similar proportions of firm and soft fish with both gears catching more firm than soft fish. Trawls caught a higher proportion of soft fish compared to longlines and pots in winter. Chemical composition of “firm” and “soft” fish differed. On average “soft” fish had 14% less protein, 12% more lipid, and 3% less ash than firm fish. Cooked yields from sablefish with soft-textured flesh were 31% less than cooked yields from firm fish. Sablefish flesh quality (firmness) related significantly to the biochemistry of white muscle with respect to 11 variables. Summer fish of all flesh conditions averaged 6% heavier than winter fish. Regulating depth of fishing could increase the yield from catches, but the feasibility and benefits from this action will require further evaluation and study. Results of this study provide a basis for reducing the harvest of sablefish with soft flesh and may stimulate further research into the cause and effect relationship of the sablefish soft-flesh phenomenon.

Beluga, Delphinapterus leucas, Habitat Associations in Cook Inlet, Alaska

A review of available information describing habitat associations for belugas, Delphinapterus leucas, in Cook Inlet was undertaken to complement population assessment surveys from 1993-2000. Available data for physical, biological, and anthropogenic factors in Cook Inlet are summarized followed by a provisional description of seasonal habitat associations. To summarize habitat preferences, the beluga summer distribution pattern was used to partition Cook Inlet into three regions. In general, belugas congregate in shallow, relatively warm, low-salinity water near major river outflows in upper Cook Inlet during summer (defined as their primary habitat), where prey availability is comparatively high and predator occurrence relatively low. In winter, belugas are seen in the central inlet, but sightings are fewer in number, and whales more dispersed compared to summer. Belugas are associated with a range of ice conditions in winter, from ice-free to 60% ice-covered water. Natural catastrophic events, such as fires, earthquakes, and volcanic eruptions, have had no reported effect on beluga habitat, although such events likely affect water quality and, potentially, prey availability. Similarly, although sewage effluent and discharges from industrial and military activities along Cook Inlet negatively affect water quality, analyses of organochlorines and heavy metal burdens indicate that Cook Inlet belugas are not assimilating contaminant loads greater than any other Alaska beluga stocks. Offshore oil and gas activities and vessel traffic are high in the central inlet compared with other Alaska waters, although belugas in Cook Inlet seem habituated to these anthropogenic factors. Anthropogenic factors that have the highest potential negative impacts on belugas include subsistence hunts (not discussed in this report), noise from transportation and offshore oil and gas extraction (ship transits and aircraft overflights), and water quality degradation (from urban runoff and sewage treatment facilities). Although significant impacts from anthropogenic factors other than hunting are not yet apparent, assessment of potential impacts from human activities, especially those that may effect prey availability, are needed.

Biological Characteristics and Fishery Assessment of Alaska Plaice, Pleuronectes quadrituberculatus, in the Eastern Bering Sea

Alaska plaice, Pleuronectes quadrituberculatus, is one of the major flatfishes in the eastern Bering Sea ecosystem and is most highly concentrated in the shallow continental shelf of the eastern Bering Sea. Annual commercial catches have ranged from less than 1,000 metric tons (t) in 1963 to 62,000 t in 1988. Alaska plaice is a relatively large flatfish averaging about 32 cm in length and 390 g in weight in commercial catches. They are distributed from nearshore waters to a depth of about 100 m in the eastern Bering Sea during summer, but move to deeper continental shelf waters in winter to escape sea ice and cold water temperatures. Being a long-lived species (>30 years), they have a relatively low natural mortality rate estimated at 0.20. Maturing at about age 7, Alaska plaice spawn from April through June on hard sandy substrates of the shelf region, primarily around the 100 m isobath. Prey items primarily include polychaetes and other marine worms. In comparison with other flatfish, Alaska plaice and rock sole, Pleuronectes bilineatus, have similar diets but different habitat preferences with separate areas of peak population density which may minimize interspecific competition. Yellowfin sole, Pleuronectes asper, while sharing similar habitat, differs from these two species because of the variety of prey items in its diet. Competition for food resources among the three species appears to be low. The resource has experienced light exploitation since 1963 and is currently in good condition. Based on the results of demersal trawl surveys and age-structured analyses, the exploitable biomass increased from 1971 through the mid-1980’s before decreasing to the 1997 level of 500,000 t. The recommended 1998 harvest level, Allowable Biological Catch, was calculated from the Baranov catch equation based on the FMSY harvest level and the projected 1997 biomass, resulting in a commercial harvest of 69,000 t, or about 16% of the estimated exploitable biomass.

Changes in frost frequency and desert vegetation assemblages in Grand Canyon, Arizona

The effect of decreasing frost frequency on desert vegetation was documented in Grand Canyon by replication of historical photographs. Although views by numerous photographers of Grand Canyon have been examined, 400 Robert Brewster Stanton and Franklin A. Nims views taken in the winter of 1889-1890 provide the best information on recent plant distribution. In Grand Canyon, where grazing is limited by the rugged topography, vegetation dynamics are controlled by climate and by demographic processes such as seed productivity, recruitment, longevity and mortality. The replicated photographs show distribution and abundance of several species were limited by severe frost before 1889. Two of these, brittlebush (Encelia farinosa) and barrel cactus (Ferocactus cylindraceus), have clearly expanded their ranges up-canyon and have increased their densities at sites where they were present in 1890. In 1890, brittlebush was present in warm microhabitats that provided refugia from frost damage. Views showing desert vegetation in 1923 indicate that Encelia expanded rapidly to near its current distribution between 1890 and 1923, whereas the expansion of Ferocactus occurred more slowly. The higher frequency of frost was probably related to an anomalous increase in winter storms between 1878 (and possibly 1862) and 1891 in the southwestern United States.

Trends in counts of manatees Trichechus manatus latirostris from 1987 to 2006 in waters of Sarasota County, Florida, USA

To demonstrate the utility of distributional surveys for assessing relative abundance and trends in counts for a discrete area of coastline, aerial survey data from Sarasota County, Florida, USA, were analyzed for the years 1987 to 2006. The study area was divided into 3 regions: the Sarasota Bay Region (SBR; N = 353 surveys), Lemon Bay (N = 368), and the Myakka River (N = 209). Manatee counts varied significantly across seasons (p < 0.0001) for all 3 regions. Manatees within Sarasota County utilized open bays primarily in the warmer months. Such usage may have been influenced by resource availability. Conversely, usage of the Myakka River peaked in winter months when manatees seek warm-water refugia such as Warm Mineral Spring. Marginal means for yearly counts within Lemon Bay and the SBR increased significantly, beginning midway through the survey period (1996) until the early 2000s. In contrast, mean yearly counts within the Myakka River decreased over this time period. After record lows in 2003 for Lemon Bay and the Myakka River, and a considerable decline in 2004 for the SBR, mean yearly counts for all 3 regions showed an increasing trend over the remaining 2 yr of the study. Greater protection of manatee habitat and availability of forage coincided with the increase in numbers of manatees using Sarasota County waters during the 1990s, and the subsequent decline in numbers may be indicative of the increase in mortality in recent years due to watercraft collisions and severe red tide events.

Contrasting seasonal patterns in dimethylsulfide, dimethylsulfoniopropionate, and chlorophyll a in a shallow North Carolina estuary and the Sargasso Sea

Time series measurements of dimethylsulfide (DMS), particulate dimethylsulfoniopropionate (DMSPp), chlorophyll a (chl a), algal pigments, major nutrients, and the potential activity of DMSP lyase enzymes were made over a 2 yr period (6 March 2003 to 28 March 2005) near the mouth of the shallow, tidally mixed Newport River estuary, North Carolina, USA. DMSPp had a mean of 43 ± 20 nM (range = 10.5 to 141 nM, n = 85) and DMS a mean of 2.7 ± 1.2 nM (range = 0.9 to 7.0 nM). The mean DMS in Gallants Channel was not significantly different from that measured in the Sargasso Sea near Bermuda during a previous 3 yr time series study (2.4 ± 1.5 nM), despite there being a 43-fold higher mean chl a concentration (4.9 ± 2.4 µg l–1) at the coastal site. In winter, DMS was low and chl a was high in the surface waters of the Sargasso Sea, while the opposite was true at the coastal site. Consequently, DMS concentrations per unit algal chl a were on average 170 times higher in the Sargasso Sea than at the coastal site during the summer, but only 7 times higher during the winter. The much higher chl a-specific DMS concentrations at the oceanic site during the summer were linked to higher ratios of intracellular DMSP substrate and DMSP lyase enzyme per unit chl a. These differences in turn appear to be linked to large differences in nutrient concentrations and solar UV stress at the 2 sites and to associated differences in the composition of algal assemblages and physiological acclimation of algal cells.

The early life history of swordfish (Xiphias gladius) in the western North Atlantic

Lengths and ages of sword-fish (Xiphias gladius) estimated from increments on otoliths of larvae collected in the Caribbean Sea, Florida Straits, and off the southeastern United States, indicated two growth phases. Larvae complete yolk and oil globule absorption 5 to 6 days after hatching (DAH). Larvae <13 mm preserved standard length (PSL) grow slowly (~0.3 mm/d); larvae from 13 to 115 mm PSL grow rapidly (~6 mm/d). The acceleration in growth rate at 13 days follows an abrupt (within 3 days) change in diet, and in jaw and alimentary canal structure. The diet of swordfish larvae is limited. Larvae <8 mm PSL from the Caribbean, Gulf of Mexico, and off the southeastern United States eat exclusively copepods, primarily of one genus, Corycaeus. Larvae 9 to 11 mm eat copepods and chaetognaths; larvae >11 mm eat exclusively neustonic fish larvae. This diet indicates that young larvae <11 mm occupy the near-surface pelagia, whereas, older and longer larvae are neustonic. Spawning dates for larvae collected in various regions of the western North Atlantic, along with the abundance and spatial distribution of the youngest larvae, indicate that spawning peaks in three seasons and in five regions. Swordfish spawn in the Caribbean Sea, or possibly to the east, in winter, and in the western Gulf of Mexico in spring. Elsewhere swordfish spawn year-round, but spawning peaks in the spring in the north-central Gulf of Mexico, in the summer off southern Florida, and in the spring and early summer off the southeastern United States. The western Gulf Stream frontal zone is the focus of spawning off the southeastern coast of the United States, whereas spawning in the Gulf of Mexico seems to be focused in the vicinity of the Gulf Loop Current. Larvae may use the Gulf of Mexico and the outer continental shelf off the east coast of the United States as nursery areas. Some larvae may be transported northward, but trans-Atlantic transport of larvae is unlikely.