129 resultados para VEGETATION HISTORY
Resumo:
Yellowfin sole, Pleuronectes asper, is the second most abundant flatfish in the North Pacific Ocean and is most highly concentrated in the eastern Bering Sea. It has been a target species in the eastern Bering Sea since the mid-1950's, initially by foreign distant-water fisheries but more recently by U.S. fisheries. Annual commercial catches since 1959 have ranged from 42,000 to 554,000 metric tons (t). Yellowfin sole is a relatively small flatfish averaging about 26 cm in length and 200 g in weight in commercial catches. It is distributed from nearshore waters to depths of about 100 m in the eastern Bering Sea in summer, but moves to deeper water in winter to escape sea ice. Yellowfin sole is a benthopelagic feeder. It is a longlived species (>20 years) with a correspondingly low natural mortality rate estimated at 0.12. After being overexploited during the early years of the fishery and suffering a substantial decline in stock abundance, the resource has recovered and is currently in excellent condition. The biomass during the 1980's may have been as high as, if not higher than, that at the beginning of the fishery. Based on results of demersal trawl surveys and two age structured models, the current exploitable biomass has been estimated to range between 1.9 and 2.6 million t. Appropriate harvest strategies were investigated under a range of possible recruitment levels. The recommended harvest level was calculated by multiplying the yield derived from the FOI harvest level (161 g at F = 0.14) hy an average recruitment value resulting in a commercial harvest of 276,900 t, or about 14% of the estimated exploitable biomass.
Resumo:
PREFACE: Four species of menhaden, Brevoortia spp., are found along the Atlantic and Gulf of Mexico coasts of the United States. The Atlantic menhaden, B. tyrannus, is found from Nova Scotia, Can., to West Palm Beach, Fla.; the yellowfin menhaden, B. smithi, is found from Cape Lookout, N. C., to the Mississippi River Delta, La.;the Gulf menhaden, B. patronus, is found from Cape Sable, Fla., to Veracruz, Mex.; and the finescale menhaden, B. gunteri, is found from the Mississippi River Delta, La., to Campeche, Mex. Menhaden are euryhaline species that inhabit coastal and inland tidal waters. Spawning occurs principally at sea (in northern areas some spawning occurs in bays and sounds). Eggs hatch at sea and the larvae are moved to estuaries by ocean currents where they metamorphose and develop as juveniles.
Resumo:
Four recognized species of menhaden, Brevoortia spp., occur in North American marine waters: Atlantic menhaden, B. tyrannus; Gulf menhaden, B. patronus; yellowfin menhaden. B. smithi; and finescale menhaden, B. gunteri. Three of the menhaden species are known to form two hybrid types. Members of the genus range from coastal waters of Veracruz, Mex., to Nova Scotia, Can. Atlantic and Gulf menhaden are extremely abundant within their respective ranges and support extensive purse-seine reduction (to fish meal and oil) fisheries. All menhaden species are estuarine dependent through late larval and juvenile stages. Depending on species and location within the range, spawning may occur within bays and sounds to a substantial distance offshore. Menhaden are considered to be filter-feeding, planktivorous omnivores as juveniles and adults. Menhaden eggs, immature developmental stages, and adults are potential prey for a large and diverse number of predators. North American menhadens, including two hybrids, are hosts for the parasitic isopod, Olencira praegustator, and the parasitic copepod, Lemaeenicus radiatus. Although the data are quite variable, a dome-shaped Ricker function is frequently used to describe the spawner-recruitment relationship for Atlantic and Gulf menhaden. Each of these species is treated as a single stock with respect to exploitation by the purse-seine reduction fishery. Estimates of instantaneous natural (other) mortality rates are O.45 for Atlantic menhaden and 1.1 for Gulf menhaden.
Resumo:
Raritan Bay is the body of water bounded by New York and New Jersey and lying immediately south of New York City (Fig. 1). It has close proximity to the most concentrated urban and industrial area in the United States. Its history has been one of extensive multiple use by the surrounding human population. Dating from the precolonial and colonial periods, people have employed many types of gear to catch and gather its once abundant fishes and shellfishes. Its beaches were once popular for sun bathing and swimming, but after the 1940's they were essentially abandoned because the water became too polluted. Another large use has been for pleasure boating and the transit and dockage of merchant, passenger, and military vessels. Channels and basins were dug in the bay, bulkheads and jetties were constructed along its shores, and it was a donor source of sand and gravel for construction projects. It has also been a receptor for large quantities of domestic and industrial wastes and, mainly for this reason, it is one ofthe most deteriorated estuaries in the United States.
Resumo:
The 1980's seems to have been the decade for conservation anniversaries. Celebrating centennials have been the U.S. Fishery Bulletin (1981), NMFS Woods Hole Laboratory (1985), Journal of the Marine Biological Association (1987) and the Association itself (1984), Pacific halibut fishery (1988), Marine Biological Laboratory at Woods Hole, Mass. (1988), and England's Ministry of Agriculture, Fisheries, and Food (1989). While the U. S. Department of Commerce turned 75 (1988), 50th anniversaries were nlarked by the NMFS Northwest and Alaska Fisheries Center (1981), The Wildlife Society and its Journal ofWildlife Management (1987), National Wildlife Federation (1986), International Game Fish Association (1989), and, of course, the Marine Fisheries Review (1988), which provided the raison d'etre for this special issue being devoted to "Marine Fisheries History."
Resumo:
The genesis and the early history of the Woods Hole Laboratory (WHL), to a lesser extent the Marine Biological Laboratory (MBL), and to some degree the Woods Hole Oceanographic Institution (WHOI), were elegantly covered by Paul S. Galtsoff (1962) in his BCF Circular "The Story of the Bureau of Commercial Fisheries Biological Laboratory, Woods Hole, Massachusetts." It covers the period from the beginning in 1871 to 1958. Galtsoffs more than 35-year career in the fishery service was spent almost entirely in Woods Hole. I will only briefly touch on that portion of the Laboratory's history covered by Galtsoff. Woods Hole, as a center of marine science, was conceived and implemented largely by one man, Spencer Fullerton Baird, at that time Assistant Secretary of the Smithsonian and who was also instrumental in the establishment of the National Museum and Permanent Secretary of the newly established American Association for the Advancement of Science. He was appointed by President Ulysses S. Grant in 1871 as the first U.S. Commissioner of Fisheries. Fisheries research began here as early as 1871, but a permanent station did not exist until 1885.
Resumo:
A benthic survey was carried out from November 1998 to December 1999 in the tidal flats of Bahía Samborombón (Río de la Plata estuary, Argentina), in order to study the population structure, reproductive aspects, growth and secondary production of Capitella capitata (Fabricius, 1780). Growth was analyzed using ELEFAN routine, and the secondary production was estimated by Hynes and Coleman's method (1968). C. capitata did not present periods of very important recruitments throughout the year; however, the abundance of smallest size classes was higher during summer and autumn. The summer cohort showed a growth rate (K) of 2.05 and a seasonal growth oscillation (C) of 0.6, pointing out that worms grew very slowly during winter months. The life span of this cohort was 13 months. The autumn cohort showed a lower growth rate (K= 1.5) and its growth was lowest during winter. The life span was 15 months for this cohort. C. capitata in Punta Rasa presented an extended reproductive period, with absence of activity during winter months. The type of eggs and larvae suggest that C. capitata has benthic larval development in the study area, destining its reproductive effort to the production of a low number of eggs, and assuring larvae survival through incubation in brooding tubes. The annual mean biomass in Punta Rasa was 0.117 g m-2 (AFDW), with a mean secondary production of 0.23 g m-2 y-1 and a P/B ratio of 1.96 y-1. The relatively low density, biomass production and P/B ratio of C. capitata in Punta Rasa can be considered as reference values for this species inhabiting undisturbed or moderately disturbed areas.
Resumo:
This is the history of contamination in sediments from the Mersey Estuary: Development of a chronology for the contamination of the Mersey Estuary by heavy metals and organochlorines Report produced by the Environment Agency in 1998. This report looks at the history of industrial contamination of the Mersey and Ribble Estuaries back to the early part of the last century, many decades before the start of monitoring programmes providing a remarkably detailed picture of very complex changes. There is a clear record in the sediment of the contamination by each heavy metal (including: Cu, Cr, Hg, Pb, Zn) and organochlorine chemical (including DDT isomers and PCB congeners) studied. The results of the study clearly show the increases in levels of contamination as industry expanded early last century followed by various improvements as this century progressed. Each pollutant has its own idiosyncratic pattern of change with some improvements predating modern environmental concerns whilst other changes seem to relate directly to recent improvements in legislative control. Overall, for the pollutants studied, the results clearly demonstrate the magnitude of improvement that has been achieved in what was a very polluted area. The only major reservation to this story is that despite the wide range of substances covered, many other potentially important pollutants remain to be studied in a similar manner.
Resumo:
This is the Mersey Estuary Saltmarsh vegetation survey 2002 report produced by the English Nature Cheshire in 2003. This report looks at the mapping of vegetation communities on the saltmarsh of the Mersey Estuary. The total area of saltmarsh and associated communities within the Mersey Estuary was found to be 724.1 ha. Most of the saltmarsh in the Mersey Estuary is presently ungrazed or only very lightly grazed, creating a very rank sward in excess of 20 cm in height which is not generally suitable for grazing or roosting birds. On the northern side of the Mersey Estuary, the saltmarsh around the Hale Decoy was lightly grazed by horses, but the remainder was ungrazed. On the south side, the saltmarsh was fairly heavily sheep-grazed along the Frodsham Score, very lightly grazed at Ince Banks by sheep straying from Frodsham and ungrazed at Stanlow Banks. Despite much of it presently being ungrazed, the saltmarsh of the Mersey Estuary is relatively poor in plant species. It appears that this is because the ungrazed areas have been so for less than 20 years and have thus not had time to develop the diversity of a long-established ungrazed marsh. However, withdrawal or depletion of grazing has produced a rank sward which is less valuable to grazing and roosting birds.