John F. Walter

Red Snapper Distribution on Natural Habitats and Artificial Structures in the Northern Gulf of Mexico

AbstractIn 2011, an intensive, multiple-gear, fishery-independent survey was carried out in the northern Gulf of Mexico (GOM) to collect comprehensive age and length information on Red Snapper Lutjanus campechanus. Based on this synoptic survey, we produced a spatial map of Red Snapper relative abundance that integrates both gear selectivity effects and ontogenetically varying habitat usage. Our methodology generated a spatial map of Red Snapper at a 10-km2 grid resolution that is consistent with existing knowledge of the species: Red Snapper occurred in relatively high abundances at depths of 50–90 m along the coasts of Texas and Louisiana and in smaller, patchy “hot spots” at a variety of depths along the Alabama coast and the west Florida shelf. Red Snapper biomass and fecundity estimates were higher for the northwestern GOM than for the northeastern GOM, as the latter area contained mostly smaller, younger individuals. The existence of similar surveys on petroleum platforms and artificial reefs also e...

Reducing Bias and Filling in Spatial Gaps in Fishery-Dependent Catch-per-Unit-Effort Data by Geostatistical Prediction, I. Methodology and Simulation

AbstractGeostatistical prediction can address two difficult issues in interpreting fishery-dependent catch per unit effort (CPUE): the lack of a sampling design and the need to fill spatial gaps. In this paper we demonstrate the spatial weighting properties of geostatistics for treating data collected without a sampling design or with a selection bias, two basic traits of fishery-dependent data. We then examine the bias and precision of geostatistical prediction of CPUE based on fishery-dependent data through simulation. We create data sets with known variograms, sample them with a preference for sites with high abundance, and then estimate variograms and CPUE as the geostatistical mean relative abundance. The variograms obtained from the simulated fishery samples correctly estimated the range but underestimated the sill, and the geostatistical mean substantially improved the estimation of CPUE over the arithmetic mean. Though the geostatistical mean still overestimated the true value, the error was prima...

Reducing Bias and Filling in Spatial Gaps in Fishery-Dependent Catch-per-Unit-Effort Data by Geostatistical Prediction, II. Application to a Scallop Fishery

AbstractFishery-dependent catch per unit effort (CPUE) comprises critical input for many stock assessments. Construction of CPUE indices usually employs some method of data standardization. However, conventional methods based on linear models do not effectively deal with the fact that samples are collected with a selection bias or with the problem of filling spatial gaps. Geostatistical interpolation methods can ameliorate some of the biases caused by both of these problems while remaining complementary to traditional linear model-based CPUE standardization. In this paper we present geostatistical estimates of sea scallop Placopecten magellanicus CPUE from tows recorded by onboard observers during an opening of Georges Bank Closed Area II in 1999. By selecting tows for which there was little prior effort (on the basis of accumulated effort measured by vessel monitoring systems), we obtained tows that reflected initial abundance as closely as possible. These tows were used to obtain a variogram which was u...

Factors related to the decline and rebuilding of billfish stocks in the Atlantic and Indian oceans

Original Article Factors related to the decline and rebuilding of billfish stocks in the Atlantic and Indian oceans Rishi Sharma*, Maite Pons, Sarah Martin, Laurie Kell, John Walter, Matthew Lauretta, and Michael Schirripa HMS, SEFSC, NOAA, 75 Virginia Beach Drive, Miami, FL 33149, USA School of Aquatic and Fishery Sciences, University of Washington, Box 355020, Seattle, WA 98195, USA IOTC (Indian Ocean Tuna Commission), Le Chantier Mall (2nd Floor), PO Box 1011, Victoria, Mahé, Seychelles ICCAT (International Commission for the Conservation of Atlantic Tunas) Secretariat, Coraz on de Mar ıa 8, Madrid 28002, Spain *Corresponding author: tel: þ1 305 361 4487; fax: 305 361 4499; e-mail: rishi.sharma@noaa.gov.

Correction: Atlantic Bluefin Tuna ( Thunnus thynnus ) Biometrics and Condition

[This corrects the article DOI: 10.1371/journal.pone.0141478.].