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11.
R. BRUCE MACFARLANE STEPHEN RALSTON CHANTELL ROYER ELIZABETH C. NORTON 《Fisheries Oceanography》2005,14(5):321-332
We assessed growth in subyearling chinook salmon (Oncorhynchus tshawytscha) during the 1998 El Niño and 1999 La Niña in the Gulf of the Farallones, a region of the continental shelf off central California seaward of the Golden Gate and the southernmost ocean entry point for the species in North America. Juvenile salmon demonstrated greater growth during this strong El Niño, when water temperature anomalies of more than +3°C were recorded at local buoys, than during the similarly strong 1999 La Niña. Slopes of regressions of weight on length, length on age, and weight on age were all significantly greater for juvenile salmon during the 1998 El Niño compared with those in the 1999 La Niña. Daily otolith increment widths, an estimator of somatic growth, corroborated population data. Between June 1 and August 9, mean increment widths for juvenile chinook salmon in 1998 were 3.54 ± 0.03 μm, significantly larger than the 3.13 ± 0.03 μm found in juveniles during the same time interval in 1999. Condition factor for juvenile chinook salmon entering the ocean at the Golden Gate was the same in both years, but became significantly greater in ocean fish during the 1998 El Niño than in ocean fish during the 1999 La Niña. Energy storage was significantly greater in ocean juvenile salmon during the 1998 El Niño as well. Mean triacylglycerol/cholesterol ratios increased following ocean entry in 1998, whereas they declined in ocean juveniles during 1999. Thus, not only was growth better in the El Niño period compared with La Niña, but lipid accumulation was also better. Oceanographic data for 1998 indicated elevated temperatures, lower salinity, greater freshwater outflow from San Francisco Bay, northerly flowing coastal currents, and positive upwelling index anomalies. This combination of environmental factors resulted in greater zooplankton productivity that, in conjunction with higher temperatures, allowed metabolic processes to enhance growth. Although El Niño events have certainly produced large-scale, and often adverse, effects on ecosystems, the results of this study emphasize the importance of local oceanographic conditions to growth and other physiological and ecological processes. 相似文献
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The reproductive environment of the South-west Atlantic anchovy, Engraulis anchoita , in the southern Brazilian coast was investigated using maritime weather reports from the US National Climatic Center. These reports were summarized to yield seasonal distributions of sea surface temperature, wind stress and Ekman transport for 2-month segments of the seasonal cycle. The vertical oceanographic structure and dynamics were studied using temperature and salinity data collected from oceanographic cruises. The seasonal distribution and biomass of South-west Atlantic anchovy spawners were estimated by acoustic surveys. Anchoita spawns intensively off southern Brazil during winter and early spring when the Ekman transport is directed onshore, and the combined effects of freshwater run-off and the flow of cold water near the bottom result in a strong vertical stability over the continental shelf. During this season, primary production peaks due to nutrient input from Sub-Antarctic waters and freshwater run-off. These conditions would avoid dispersal of eggs and larvae offshore and favour the production and maintenance of fine-scale food particle aggregations required for successful first feeding of newly hatched larvae. In summer, the conditions are almost reversed and anchoita spawners are virtually absent from the area. Thus, the spawning strategy of anchoita in southern Brazil seems to be tuned in a way to optimize larval retention, minimize exposure to turbulent mixing and take advantage of enhanced plankton productivity. 相似文献
13.
Knowledge of the spatial and temporal distribution of specific mortality sources is crucial for management of species that are vulnerable to human interactions. Beachcast carcasses represent an unknown fraction of at-sea mortalities. While a variety of physical (e.g., water temperature) and biological (e.g., decomposition) factors as well as the distribution of animals and their mortality sources likely affect the probability of carcass stranding, physical oceanography plays a major role in where and when carcasses strand. Here, we evaluate the influence of nearshore physical oceanographic and wind regimes on sea turtle strandings to decipher seasonal trends and make qualitative predictions about stranding patterns along oceanfront beaches. We use results from oceanic drift-bottle experiments to check our predictions and provide an upper limit on stranding proportions. We compare predicted current regimes from a 3D physical oceanographic model to spatial and temporal locations of both sea turtle carcass strandings and drift bottle landfalls. Drift bottle return rates suggest an upper limit for the proportion of sea turtle carcasses that strand (about 20%). In the South Atlantic Bight, seasonal development of along-shelf flow coincides with increased numbers of strandings of both turtles and drift bottles in late spring and early summer. The model also predicts net offshore flow of surface waters during winter - the season with the fewest relative strandings. The drift bottle data provide a reasonable upper bound on how likely carcasses are to reach land from points offshore and bound the general timeframe for stranding post-mortem (< two weeks). Our findings suggest that marine turtle strandings follow a seasonal regime predictable from physical oceanography and mimicked by drift bottle experiments. Managers can use these findings to reevaluate incidental strandings limits and fishery takes for both nearshore and offshore mortality sources. 相似文献
14.
The South Atlantic Bight Recruitment Experiment (SABRE) brought together a interdisciplinary team of scientists to conduct research to enhance our understanding of the relationship between variation in environmental factors and the variable recruitment of 'estuarine dependent' fishes within the SAB. The project sought to develop a new fusion of government and academic scientists, each possessing unique skills, to address the difficult problem of recruitment variability in fishes. This fusion required the development of appropriate and at that time novel management and administrative strategies. SABRE initially focused on recruitment dynamics of Atlantic menhaden, Brevoortia tyrannus , in the South Atlantic Bight, but expanded over time to include several estuarine-dependent species and much of the Middle Atlantic Bight as well. The project was conducted from 1991 to 1997 and resulted in a substantial improvement in our understanding of the life history and ecology of Atlantic menhaden and the potential constraints upon its recruitment. SABRE also contributed to our understanding of the physical oceanography of the western North Atlantic shelf and adjacent coastal inlets and the implications of physical dynamics upon the potential pathways for larval transport. 相似文献
15.
The deep scattering layers (DSL) in the central equatorial Pacific form an important prey resource in a relatively oligotrophic habitat. In March of 2006, we used a calibrated 38‐kHz SIMRAD EK60 scientific sonar to assess the spatial distribution of the deep scattering layer relative to broad‐scale oceanographic features and fine‐scale physical and biological measurements. We conducted a single continuous transect from approximately 10°S to 20°N at 170°W while measuring acoustic backscatter, current velocity and direction, temperature, salinity, oxygen, and fluorescence with depth, coincident with marine mammal occurrence. These data were combined with remotely sensed sea surface height, chlorophyll, and sea surface temperature data to examine patterns in DSL distribution. To analyze DSL density with depth, acoustic backscatter was binned into surface (<200 m), mid (200–550 m) and deep (550–1000 m) layers. Backscatter was highly correlated with chlorophyll‐a and low sea surface height anomalies and was greatest near the equator. We found high diel variability in DSL depth and scattering intensity between the mid and surface layers as well as a shallowing of the deep layer moving northward across the equator. Marine mammal sightings consisted primarily of odontocetes with their distribution coincident with higher acoustic densities of their forage base. Shifts in DSL distribution and scattering intensity are an important component towards understanding the behavior and distribution of highly migratory predator species. 相似文献
16.
Seasonal variations in meteorological and oceanographic processes in the South Brazil Bight were studied to assess their influence on the Brazilian sardine Sardinella brasiliensis fishery. According to its environmental characteristics, the South Brazil Bight was divided into three sectors. The northern and southern sectors were similar during the spring and summer, showing areas of coastal upwelling and low rainfall rates. The middle sector was characterized by the presence of low-salinity coastal waters in the inner shelf and by high rainfall. During autumn and winter, the middle and southern sectors were similar, both being under the influence of sub-Antarctic waters. Multiple regression analyses showed significant correlation between environmental data and catches, although at a lower level in the northern sector ( r 2 = 0.57). In the middle and southern sectors, environmental data were highly correlated with the catches ( r 2 = 0.90 and 0.84). The sardine landings in the middle sector are principally affected by meteorological parameters, and in the south by oceanographic ones. In the middle sector, an inverse correlation between landings and rainfall is shown, while in the south, landings are positively correlated with salinity and sea temperature. The conclusion is that the seasonal landings of the Brazilian sardine within the South Brazil Bight are influenced by the distribution of less saline waters, the coastal waters and sub-Antarctic waters. 相似文献
17.
Northern rock sole recruitment in the eastern Bering Sea has been hypothesized to (a) depend on wind‐driven surface currents linking spawning and nursery areas, (b) be density‐dependent, and (c) be negatively impacted by cold bottom temperatures over a large nursery area during the first summer of life. A suite of models was developed to test these hypotheses. Data included 32 years of recruitment and spawning biomass estimates derived from a stock assessment model and wind and temperature indices customized to the environmental exposure of age‐0 northern rock sole in the eastern Bering Sea. The predictive ability of the models was evaluated, and the models were used to forecast recruitment to age‐4 for recent year classes which are poorly retained by the standard multi‐species bottom trawl survey gear. Models which included wind and temperature indices performed better than a naïve forecast based on the running mean. The best‐performing model was a categorical model with wind and temperature thresholds, which explained 49% of the variation in recruitment. Ricker models performed more poorly than models without a spawning biomass term, providing no evidence that recruitment is related to stock size. The models forecast higher recruitment for the most recent year classes (2015–2018) than for prior year classes with observed poor recruitment (2006–2013). These environment‐based recruitment forecasts may improve recruitment estimates for the most recent year classes and facilitate study of the effects of future climate change on northern rock sole population dynamics. 相似文献
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19.
P. N. Trathan A. S. Brierley M. A. Brandon D. G. Bone C. Goss S. A. Grant E. J. Murphy J. L. Watkins 《Fisheries Oceanography》2003,12(6):569-583
Oceanographic data collected to the north of South Georgia were examined for three consecutive summers (1996/97, 1997/98, 1998/99). The results show the existence of a shelf break front during each period. The most reliable means of defining the front was the potential density anomaly at the near‐surface potential temperature minimum. In each year, off‐shelf waters were separated from on‐shelf waters by water with a potential density anomaly between 27.22 and 27.29 kg m?3. During 1997/98, the near‐surface potential temperature minimum was much colder and much shallower than in other years and was consistent with waters originating from much further south than South Georgia; these differences were further evident at a single deep off‐shelf station. The oceanographic changes during 1997/98 were consistent with a mesoscale or large‐scale movement of the southern Antarctic Circumpolar Current front. Acoustically determined densities of Antarctic krill, Euphausia superba, at South Georgia showed consistent patterns between years. Densities were substantially higher over the shelf compared with off‐shelf, with the highest densities at the shelf edge; densities were also higher to the east of the island. During 1997/98, acoustic densities of krill were substantially higher than in other years. The coincidence of the elevated acoustic density and the cooler oceanographic conditions was explored. When data from all years were combined and analysed by Generalized Additive Model, an inverse relationship between acoustic density and temperature was apparent. Historical data were also examined and it was noted that the only other occurrence of such a high estimate of krill density at South Georgia, was when oceanographic conditions were also colder. 相似文献
20.
Remotely sensed mesoscale oceanography and the distribution of Illex argentinus in the South Atlantic 总被引：1，自引：0，他引：1
In this study, we consider the influence of mesoscale oceanographic processes around the Falkland Islands (Islas Malvinas) in the South-west Atlantic, during the period in which the commercial squid fishery for Illex argentinus operates. Spatially referenced fishery data and satellite-derived advanced very high resolution radiometry (AVHRR) sea surface temperature (SST) data were examined using geographic information system (GIS) techniques. The distribution and relative abundance of I. argentinus in the Falkland Islands fishery was examined for the period 1989–96. Three consistent areas of high abundance were observed to the north-east (shelf-break region) and north-west (shelf region) of the islands, and close to the northern coast of East Falkland. Areas of high sea surface temperature gradients (thermal gradients) extracted from remotely sensed satellite images were used as an indicator of mesoscale oceanographic activity and compared with the location of the fishery. I. argentinus were found to be associated with areas of thermal gradients, commonly seen at the interface of Falkland Current and Patagonian shelf waters. The techniques used in this analysis allow the overlay and analysis of physical oceanographic and fishery data with potential applications in fisheries management and operational fisheries oceanography. 相似文献