James M. Nance

An Evaluation of an Electronic Logbook as a More Accurate Method of Estimating Spatial Patterns of Trawling Effort and Bycatch in the Gulf of Mexico Shrimp Fishery

Abstract Penaeid shrimp trawling effort in the Gulf of Mexico is not measured directly but is estimated from landings and interview data gathered by port agents of the National Marine Fisheries Service (NMFS). The total pounds landed from each trip are assigned to one or more of the 219 statistical area-depth zone cells for which a catch rate (pounds per nominal day fished or catch per unit effort (CPUE)) is also obtained. Each month, the total landings in pounds for each cell are divided by the CPUE of the cell to determine effort or days fished. These values are summed across all cells and months to provide an estimate of total effort. The accuracy of total effort estimates is directly proportional to the accuracy of the landings allocations and estimated CPUE values. It has been assumed that allocation errors are random and that directional bias is negligible. In a previous paper, we described an electronic logbook (ELB) that enables accurate measurement of the spatial patterns of fishing effort. Herei...

Feasibility of improving the economic return from the Gulf of Mexico brown shrimp fishery

Abstract A bioeconomic model was developed to investigate the feasibility of improving the economic return from the fishery for brown shrimp Penaeus aztecus through cooperative federal and state management closures in the U.S. Gulf of Mexico. Four different closure periods were simulated with the model. The closure options were evaluated for Texas only (current condition) and for the entire U.S. Gulf of Mexico (proposed condition). The model provided an accurate biological simulation of the brown shrimp fishery in the Gulf of Mexico. Each of the evaluated closures gave positive net profits to the fishery as a whole, However, these benefits were mainly for larger vessels (>50 ft in length). None of the proposed closures increased the profits for boats (undocumented vessels of unknown lengths), and only some closures increased the profits for smaller vessels (≤50 ft in length).

Description of a Simple Electronic Logbook Designed to Measure Effort in the Gulf of Mexico Shrimp Fishery

Abstract The magnitude and spatial distribution of fishing effort in the Gulf of Mexico penaeid shrimp fishery has been the subject of great contention. Here, we describe a simple and inexpensive electronic logbook (ELB) and algorithms tested to describe the temporal and spatial patterns of fishing effort, based on nothing more than the position of the vessel at 10-min intervals; these algorithms were tested with 788 tows (4,558 h of trawling). On average, the difference between ELB estimates and recorded levels of effort were less than 1%; spatial agreement was also good. On a spatial basis, ELB estimates accounted for more than 84–97% of the variance observed in recorded effort, depending on the grid size used in the analysis. Further, analysis of data from more than 18,000 tows yielded a strong within-trip relationship between catch and effort. This relationship enables accurate allocation of the total landings from a trip to the subareas fished, based on nothing more than trawling times within each su...

Effects of oil/gas field produced water on the macrobenthic community in a small gradient estuary

Little is known about how climatic events (i.e., drought) inhibit or enhance movement of petroleum hydrocarbon laden sediments in estuarine systems and how this in turn effects the macrobenthic populations exposed to these sediments. Seventeen collection stations were established and monitored at New Bayou, Texas, a small gradient estuary which receives petroleum products via oil/gas field produced water discharge. Hydrographic, geologic and biotic samples were taken monthly from each station during a period of reduced rainfall.Both temperature and dissolved oxygen data taken during the study followed patterns typical for the area. Salinity values increased into the polyhaline range at near-bay stations during the reduced rain period, while upper bayou stations remained within the oligohaline range.Sediment grain sizes along the bayou were generally in the silty-clay range. Sediment hydrocarbon concentrations were highest (11.4 mg g−1 dry sediment) around the produced water discharge site and lowest at near-bay stations (0.2 mg g−1 dry sediment). Ninety-six macrobenthic species were collected during the study. General effects from produced water discharge on macrobenthic populations followed the classical pattern outlined by other research in shallow bay systems. A sediment hydrocarbon concentration of 2.5 mg g−1 dry sediment was found to reflect the average value needed to depress population abundances. Both abundance and diversity values were lowest at central stations near the discharge site. This zone of depressed macrobenthic populations extended from the discharge site at least 107 m downstream and 46 m upstream. The zone of stimulated macrobenthic populations occurred 1486 m downstream and 381 m upstream from the discharge site.

Shrimp Loss Associated with Turtle Excluder Devices: Are the Historical Estimates Statistically Biased

Abstract Estimates of penaeid shrimp losses associated with the use of turtle excluder devices (TEDs) in offshore waters of the southeastern USA are derived from a single study conducted from 1988 to 1990. The estimates were based on paired tows in which the inboard and outboard nets on one side of the vessel were equipped with TEDs while the nets on the other side were not. Comparison of the mean catch rates from the TED and control nets provided an estimate of shrimp loss. However, the net positions were not rotated by trip, the try net (i.e., a small shrimp trawl fished off one side of the vessel in front of the trailing inboard net) was fished in front of the inner standard net 70% of the time, and the data show that catches in the standard net trailing the try net were significantly reduced by operation of the try net. These findings warranted a new analysis excluding data from inner net pairs, as is done in the modern gear testing protocol. The reanalysis suggests that the shrimp loss rates for Geor...

Spatial Allocation of Shrimp Catch Based on Fishing Effort: Adjusting for the Effects of the Texas Opening

Abstract Estimates of fishing effort for the Gulf of Mexico penaeid shrimp fishery depend on the ability of National Marine Fisheries Service port agents to accurately assign fractional catches within a fishing trip to 5-fathom-depth bins within 21 Gulf of Mexico statistical areas. In previous studies, we showed that the method used for assigning landings was inaccurate and developed an algorithm for assigning landings based up observer and captains logbook data on fishing effort and catch. The resulting algorithm explained over 92% of the variance in actual catch. Results of regression analyses of new observer data collected for over 7,700 tows confirm that the algorithm provides reliable estimates of fractional catches associated with the different subareas fished within a trip (adjusted r 2 = 0.96 when 11 outliers are removed from 1,845 observations). Nine of the 11 outliers occurred within a month of the Texas opening, a period when catches are initially high but then decay rapidly. Here, we have inc...

Three decades of U.S. Gulf of Mexico white shrimp, Litopenaeus setiferus, commercial catch statistics

Gulf of Mexico, white shrimp, Litopenaeus setiferus, catch statistics have been collected by NOAA’s National Marine Fisheries Service for over 50 years. Recent occurrences such as natural and manmade disasters have raised awareness for the need to publish these types of data. Here we report shrimp data collected from 1984 to 2011. These 28 years of catch history are the time series used in the most recent Gulf of Mexico white shrimp stock assessment. Fishing effort for this stock has fluctuated over the period reported, ranging from 54,675 to 162,952 days fished. Catch averaged 55.7 million pounds per year, increasing significantly over the times series. In addition, catch rates have been increasing in recent years, with CPUE levels ranging from 315 lb/day fished in 2002, to 1,175 lb/ day fished in 2008. The high CPUE’s we have measured is one indication that the stock was not in decline during this time period. Consequently, we believe the decline in effort levels is due purely to economic factors. Current stock assessments are now using these baseline data to provide managers with further insights into the Gulf L. setiferus stocks.