1,269 research outputs found
Stock assessment and management recommendations for Pacific sardine (Sardinops sagax) in 1997
The primary goal of sardine management as directed by the California Fish and Game Code is rehabilitation of the resource with an added objective of maximizing sustained harvest. Accordingly, the Code states that the annual sardine quota can be set at an amount greater than
1,000 tons, providing that the level of take allows for continued increase in the spawning population.
We estimated the sardine population size to have been 464,000 short tons on July 1, 1997. Our estimate was based on output from a modified version of the integrated stock assessment model called CANSAR (Deriso et al. 1996). CANSAR is a forward-casting, age-structured analysis using fishery-dependent and fishery-independent data to obtain annual estimates of sardine abundance, year-class strength and age-specific fishing mortality for 1983 through the
first semester of 1997. Non-linear least-squares criteria are used to find the best fit between model estimates and input data.
Questions about stock structure and range extent remain major sources of uncertainty in assessing current sardine population biomass. Recent survey results and anecdotal evidence suggest increased sardine abundance in the Pacific Northwest and areas offshore from central and
southern California. It is difficult to determine if those fish were part of the stock available to the California fishery. In an attempt to address this problem, the original CANSAR model was reconfigured into a Two-Area Migration Model (CANSAR-TAM) which accounted for sardine
lost to the areas of the fishery and abundance surveys due to population expansion and net emigration. While the model includes guesses and major assumptions about net emigration and recruitment, it provides an estimate which is likely closer to biological reality than past
assessments. The original CANSAR model was also used and estimates are provided for comparison.
Based on the 1997 estimate of total biomass and the harvest formula used last year, we recommend a 1998 sardine harvest quota of 48,000 tons for the California fishery. The 1998 quota is a decrease of 11% from the final 1997 sardine harvest quota for California of 54,000
tons. (55pp.
Status of the Pacific sardine (Sardinops sagax) resource and fishery
California Fish and Game Code states that the annual sardine quota can be set at a level greater than 1,000 tons, providing that the level of take allows for continued increase in the spawning population. The primary goal of management as directed by the Code is rehabilitation of the
resource, with an added objective of maximizing the sustained harvest.
We estimate the sardine population size to have been 353,000 short tons on July 1, 1995. Our estimate was based on output from an integrated stock assessment model called CANSAR
(Deriso 1993). CANSAR is a forward-casting age-structured analysis using fishery-dependent and fishery-independent data to obtain annual estimates of sardine abundance, year-class strength and age specific fishing mortality for 1983 through the first semester of 1995. CANSAR couples a
simulation model with sardine population dynamics. Non-linear least-squares criteria are used to tune the model to match catch-at-age data and other indices of sardine abundance.
To calculate the 1996 fishery quota, we used the harvest formula selected as the preferred option in the draft Coastal Pelagic Species-Fishery Management Plan (CPS-FMP). That formula has undergone extensive scientific and user-group review as part of the Pacific Fishery Management Council's (PFMC) CPS-FMP adoption process and has the endorsement of the fishing industry and the scientific community. Use of this formula will result in a reduced fishing mortality rate compared to the formula used to calculate the quota in 1995. We conclude that it is
particularly important to reduce fishing mortality for 1996 because the rates may have been excessive in recent years, especially for older aged sardines.
Accordingly, we recommend a 1996 sardine harvest quota of 35,000 short tons. (21pp.
Sampling-Based Query Re-Optimization
Despite of decades of work, query optimizers still make mistakes on
"difficult" queries because of bad cardinality estimates, often due to the
interaction of multiple predicates and correlations in the data. In this paper,
we propose a low-cost post-processing step that can take a plan produced by the
optimizer, detect when it is likely to have made such a mistake, and take steps
to fix it. Specifically, our solution is a sampling-based iterative procedure
that requires almost no changes to the original query optimizer or query
evaluation mechanism of the system. We show that this indeed imposes low
overhead and catches cases where three widely used optimizers (PostgreSQL and
two commercial systems) make large errors.Comment: This is the extended version of a paper with the same title and
authors that appears in the Proceedings of the ACM SIGMOD International
Conference on Management of Data (SIGMOD 2016
QuickSel: Quick Selectivity Learning with Mixture Models
Estimating the selectivity of a query is a key step in almost any cost-based
query optimizer. Most of today's databases rely on histograms or samples that
are periodically refreshed by re-scanning the data as the underlying data
changes. Since frequent scans are costly, these statistics are often stale and
lead to poor selectivity estimates. As an alternative to scans, query-driven
histograms have been proposed, which refine the histograms based on the actual
selectivities of the observed queries. Unfortunately, these approaches are
either too costly to use in practice---i.e., require an exponential number of
buckets---or quickly lose their advantage as they observe more queries.
In this paper, we propose a selectivity learning framework, called QuickSel,
which falls into the query-driven paradigm but does not use histograms.
Instead, it builds an internal model of the underlying data, which can be
refined significantly faster (e.g., only 1.9 milliseconds for 300 queries).
This fast refinement allows QuickSel to continuously learn from each query and
yield increasingly more accurate selectivity estimates over time. Unlike
query-driven histograms, QuickSel relies on a mixture model and a new
optimization algorithm for training its model. Our extensive experiments on two
real-world datasets confirm that, given the same target accuracy, QuickSel is
34.0x-179.4x faster than state-of-the-art query-driven histograms, including
ISOMER and STHoles. Further, given the same space budget, QuickSel is
26.8%-91.8% more accurate than periodically-updated histograms and samples,
respectively
Stock assessment of Pacific sardine for 1998 with management recommendations for 1999
The primary goal of sardine management as directed by the California Fish and Game Code is rehabilitation of the resource with an added objective of maximizing sustained harvest. Accordingly, the Code states that the annual sardine quota can be set at an amount greater than
1,000 tons, providing that the level of take allows for continued increase in the spawning population.
We estimated the sardine population size within the range of the fishery and survey data (Ensenada, Baja California to San Francisco, California) to have been 1,182,881 short tons on July 1, 1998. Our estimate was based on output from a modified version of the integrated stock assessment model called CANSAR (Deriso et al. 1996). CANSAR is a forward-casting, age-structured analysis using fishery-dependent and fishery-independent data to obtain annual estimates of sardine abundance, year-class strength and age-specific fishing mortality for 1983 through the first semester of 1998. Non-linear least-squares criteria are used to find the best fit between model estimates and input data.
Questions about stock structure and range extent remain major sources of uncertainty in assessing current sardine population biomass. Recent survey results and anecdotal evidence suggest increased sardine abundance in the Pacific Northwest and areas offshore from central and southern California. It is difficult to determine if those fish were part of the stock available to the California fishery. Last year, in an attempt to address this problem, the original CANSAR model was reconfigured into a Two-Area Migration Model (CANSAR-TAM; Hill et al. 1998) which accounted for sardine lost to the areas of the fishery and abundance surveys due to population expansion and net emigration. While the model includes guesses and major assumptions about net emigration and recruitment, it provides an estimate which is likely closer to biological reality than original CANSAR assessments. Corroborative results from a new,
preliminary sardine stock assessment model, 'SAM', are also presented in this report.
Based on the 1998 estimate of age 1+ biomass within the range of the fishery and survey data, and a proposed harvest formula in the draft Coastal Pelagic Species Fishery Management Plan (Amendment 8), we recommend a 1999 sardine harvest quota of 132,800 tons for the California fishery. The 1999 quota is a significant increase from the final 1998 sardine harvest quota for California of 48,000 tons. (93pp.
A Comparison of Paralichthid Flounder Size-Structure in Northwest Florida Based on Trammel Net Catches Adjusted for Mesh Selectivity and Collection by SCUBA Divers
By applying a selectivity model for trammel net catches of Gulf flounder, we found that the resulting adjusted length distribution was similar to the offshore diver-sampled length distribution. We found two dominant size modes that seem to be consistent inshore and offshore, a lower mode composed of males and females and an upper mode composed exclusively of females. Southern flounder demonstrated a lower mode of males and small females but also showed larger females and possibly multiple-size modes after trammel net captures were adjusted for size selectivity. The two species showed very similar values for 91 (91 = 76.2-79.2), a coefficient affecting the mode of the gamma function used for selectivity. Our findings support the idea that the initial approximation of the mesh selectivities may be simple and could be based on parameters determined from related species. Gulf flounder were more abundant in the trammel net catch than were southern flounder, atid Gulf flounder comprised 80% of the net catches but was the only paralichthid flounder we collected offshore. Because southern flounder have been reported offshore from similar depths and habitats along the southeastern U.S. coast, partitioning of spawning habitat may be occurring in our area
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