A Covered Cod-End and Tow-Path Evaluation of Midwater Trawl Gear Efficiency for Catching Delta Smelt (Hypomesus transpacificus)

Mitchell, Lara; Newman, Ken; Baxter, Randall D.

doi:10.15447/sfews.2017v15iss4art3

Cited by 15 publications

(45 citation statements)

References 16 publications

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“…Another caveat is that the estimated length‐based contact selectivity functions, the

{\overset{p}{true}}_{g} false(L false)

(Mitchell et al. , ), may be biased and inadequate. Skepticism about the ascending and descending limbs of dome‐shaped selectivity curves led to sensitivity analysis using the truncated curves and the effects on the resulting abundance indices were sizable, e.g., up to a 10‐fold decrease from nontruncated to truncated estimates.…”

Section: Discussionmentioning

confidence: 99%

“…Support for the juvenile and later life stages’ being more surface oriented comes from observations that surface tows done during the summer, fall, and winter result in higher catch densities than oblique tows done during the same seasons (Souza ; Mitchell et al. ).…”

Section: Methodsmentioning

confidence: 99%

“…Length‐based, gear‐specific contact selectivity functions were obtained from Mitchell et al. (, ). In Mitchell et al.…”

Section: Methodsmentioning

confidence: 99%

“…In Mitchell et al. (), a cover was placed over the cod end of the FMWT (and SMWT) gear and the assumption was made that all fish that slipped through the cod end mesh were retained by the cover. In Mitchell et al.…”

Section: Methodsmentioning

confidence: 99%

“…Support for the early life stage volume specification is provided by Rockriver (2004), who found that younger fish appeared to be relatively evenly and deeply distributed throughout the water column. Support for the juvenile and later life stages' being more surface oriented comes from observations that surface tows done during the summer, fall, and winter result in higher catch densities than oblique tows done during the same seasons (Souza 2002;Mitchell et al 2017).…”

Section: Methodsmentioning

confidence: 99%

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Using Multistage Design‐Based Methods to Construct Abundance Indices and Uncertainty Measures for Delta Smelt

2019

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Population abundance indices and estimates of uncertainty are starting points for many scientific endeavors. However, if the indices are based on data collected by different monitoring programs with possibly different sampling procedures and efficiencies, applying consistent methodology for calculating them can be complicated. Ideally, the methodology will provide indices and associated measures of uncertainty that account for the sample design, the level of sampling effort (e.g., sample size), and the capture or detection probabilities. We develop and demonstrate consistent methodology for multiple monitoring programs that sample different life stages of Delta Smelt Hypomesus transpacificus, a critically endangered fish species endemic to the San Francisco Estuary, whose abundance indices have been at the center of much controversy given the regulatory consequences of their listed status. Current indices use different and incomparable methods, do not account for gear selectivity, and do not provide measures of uncertainty. Using recently available information on gear‐specific, length‐based conditional probabilities of capture given availability, we develop new abundance indices along with measures of uncertainty by means of a single methodological approach. These new indices are highly correlated with existing ones, but the approach taken here illuminates different sources of bias and quantifies between‐year variation using probabilistic statements where the previous indices cannot. Decomposition of uncertainty into its constituent sources reveals that early life stage uncertainty is dominated by gear inefficiency while later life stage uncertainty is dominated by sample size, thus providing guidance for improvements to existing surveys. An additional result of general methodological interest is a demonstration, via simulation intended to reflect realistic data properties, that a lognormal distribution is preferable to the normal distribution for making probabilistic statements about the indices. The work here facilitates the fitting of models attempting to identify factors associated with the dynamics and decline of the species.

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“…Another caveat is that the estimated length‐based contact selectivity functions, the

{\overset{p}{true}}_{g} false(L false)

Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

“…Length‐based, gear‐specific contact selectivity functions were obtained from Mitchell et al. (, ). In Mitchell et al.…”

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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Using Multistage Design‐Based Methods to Construct Abundance Indices and Uncertainty Measures for Delta Smelt

2019

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Space‐for‐time is not necessarily a substitution when monitoring the distribution of pelagic fishes in the San Francisco Bay‐Delta

Duarte

Peterson

2021

Ecology and Evolution

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Occupancy models are often used to analyze long-term monitoring data to better understand how and why species redistribute across dynamic landscapes while accounting for incomplete capture. However, this approach requires replicate detection/non-detection data at a sample unit and many long-term monitoring programs lack temporal replicate surveys. In such cases, it has been suggested that surveying subunits within a larger sample unit may be an efficient substitution (i.e.

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Hydrodynamics and habitat interact to structure fish communities within terminal channels of a tidal freshwater delta

et al. 2023

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Terminal channels were historically a common feature of tidal delta ecosystems but have become increasingly rare as landscapes have been modified. Tidal hydrodynamics are a defining feature in tidal terminal channel ecosystems from which native aquatic communities have evolved.However, few studies have explored the relationship between fish community structure and hydrodynamics in these tidal terminal channel ecosystems. We sampled fish communities throughout a network of terminal channels within the northeasternmost region of the San Francisco Estuary to determine the relationship between fish community structure and hydrodynamics within these environments. We collected two years (2017 and 2018) of fish community samples using gill nets and analyzed data using multivariate community analyses and count models. We found metrics of fish diversity and counts of native fishes to be greatest upstream (farthest from tidal influence) of the tidal excursion within terminal channels. Counts of non-native fishes were less affected by this hydrodynamic feature of terminal channels and more tightly correlated to local habitat conditions (e.g., water temperature, depth). Our results suggest that channel hydrodynamics plays a role in structuring fish communities within terminal channels, particularly native fishes. These results indicate that hydrodynamics in tidal delta ecosystems may be able to be altered in ways that benefit native fishes without the cost of water pumping.K E Y W O R D S backwater slough, Cache Slough complex, multivariate, San Francisco Estuary, spatial scale, tidal excursion, tidal marsh † Deceased

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A Covered Cod-End and Tow-Path Evaluation of Midwater Trawl Gear Efficiency for Catching Delta Smelt (Hypomesus transpacificus)

Cited by 15 publications

References 16 publications

Using Multistage Design‐Based Methods to Construct Abundance Indices and Uncertainty Measures for Delta Smelt

Using Multistage Design‐Based Methods to Construct Abundance Indices and Uncertainty Measures for Delta Smelt

Space‐for‐time is not necessarily a substitution when monitoring the distribution of pelagic fishes in the San Francisco Bay‐Delta

Hydrodynamics and habitat interact to structure fish communities within terminal channels of a tidal freshwater delta

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