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The number of migrating alewives in the Parker River, Massachusetts, can be counted visually by standing at the upper end of each of the 6 fish ladders in the system. Estimating the entire run of up to a month’s duration by this procedure is not economically feasible, but we suggest a subsampling procedure that can provide sufficient accuracy and be economical. The reliability of periodic sample counts when used to estimate population numbers of anadromous alewives (Alosa pseudoharengus) was indicated by the low variance of paired counts, small random errors of individual counts, and by the low variability between counts on days of large runs in the Parker River. Analyses of computer-simulated runs using actual data suggested that short counts taken frequently are superior to longer counts taken less often. Both field and computer-simulated data suggested that ten-minute counts taken hourly will estimate the true population of alewife runs within 10% error at the .05 level of probability. 相似文献
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Graham D. Sherwood Rick M. Rideout Susan B. Fudge George A. Rose 《Deep Sea Research Part II: Topical Studies in Oceanography》2007,54(23-26):2794
Cod populations in Newfoundland and Labrador waters have shown differing growth, condition and recruitment since near-universal declines in these properties during the cold period of the late 1980s and early 1990s. To assess the influence of variable prey communities on these parameters, we compared cod energetics and diet in populations off Labrador and the northeast and south coasts of Newfoundland. Many properties were highest in the southern group(s) and lowest in the northern group(s), including growth, somatic condition, liver index and age-at-maturity. Most differences could be explained by variations in diet, as measured by stomach contents and stable carbon isotopes (δ13C). The diet of Labrador cod consisted almost entirely of northern shrimp (Pandalus borealis), and these cod displayed the most benthic δ13C signatures. Northeast cod had a more varied diet that included capelin and other fish, but still had mostly benthic δ13C signatures, suggesting the importance of benthic prey like shrimp in this population. South coast cod exhibited the most varied diet, including capelin (Mallotus villosus), zooplankton, crabs and other fish, and had the most pelagic δ13C signatures. Among and within populations, the benefits of a more pelagic diet in medium-sized (30–69 cm) cod included higher somatic condition, higher liver index (lipid stores) and greater spawning potential (decreased incidence of atresia). It is hypothesized that major rebuilding of Newfoundland and Labrador cod stocks will require a return to a system that supports mostly pelagic feeding (i.e. capelin) in cod. 相似文献
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In geographically extensive fish populations the potential exists for reproductive traits to vary over the population’s range but, the impact that such intrapopulation variability has on overall population reproductive potential has not been formally assessed. Here intrapopulation spatial variability in size at maturity and fecundity are demonstrated for Grand Bank American plaice (Hippoglossoides platessoides) and yellowtail flounder (Limanda ferruginea). Recognition of intrapopulation variability in these reproductive traits coupled with spatial variability in abundance resulted in an increase in estimated population total egg production (TEP) by as much as 1014 eggs for American plaice and 1015 eggs for yellowtail flounder as compared to assessment of TEP for the population as a whole. Results highlight the need to explore variability in life history traits not only between but, also within populations and emphasizes the need for sufficient spatial coverage during sampling in order to assess the reproductive potential of fish populations. 相似文献
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Automated GPS processing for global total electron content data 总被引：4，自引：2，他引：4
A software package known as MIT Automated Processing of GPS (MAPGPS) has been developed to automate the processing of GPS data into global total electron density (TEC) maps. The goal of the MAPGPS software is to produce reliable TEC data automatically, although not yet in real time. Observations are used from all available GPS receivers during all geomagnetic conditions where data has been successfully collected. In this paper, the architecture of the MAPGPS software is described. Particular attention is given to the algorithms used to estimate the individual receiver biases. One of the largest sources of error in estimating TEC from GPS data is the determination of these unknown receiver biases. The MAPGPS approach to solving the receiver bias problem uses three different methods: minimum scalloping, least squares, and zero-TEC. These methods are described in detail, along with their relative performance characteristics. A brief comparison of the JPL and MAPGPS receiver biases is presented, and a possible remaining error source in the receiver bias estimation is discussed. Finally, the Madrigal database, which allows Web access to the MAPGPS TEC data and maps, is described. 相似文献
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