Estimation of bycatch in shrimp trawl fisheries: a comparison of estimation methods using field data and simulated data

Bycatch, or the incidental catch of nontarget organisms during fi shing operations, is a major issue in U.S. shrimp trawl fisheries. Because bycatch is typically discarded at sea, total bycatch is usually estimated by extrapolating from an observed bycatch sample to the entire fleet with either mean-per-unit or ratio estimators. Using both field observations of commercial shrimp trawlers and computer simulations, I compared five methods for generating bycatch estimates that were used in past studies, a mean-per-unit estimator and four forms of the ratio estimator, respectively: 1) the mean fish catch per unit of effort, where unit effort was a proxy for sample size, 2) the mean of the individual fish to shrimp ratios, 3) the ratio of mean fish catch to mean shrimp catch, 4) the mean of the ratios of fish catch per time fished (a variable measure of effort), and 5) the ratio of mean fish catch per mean time fished. For field data, different methods used to estimate bycatch of Atlantic croaker, spot, and weakfish yielded extremely different results, with no discernible pattern in the estimates by method, geographic region, or species. Simulated fishing fleets were used to compare bycatch estimated by the fi ve methods with “actual” (simulated) bycatch. Simulations were conducted by using both normal and delta lognormal distributions of fish and shrimp and employed a range of values for several parameters, including mean catches of fish and shrimp, variability in the catches of fish and shrimp, variability in fishing effort, number of observations, and correlations between fish and shrimp catches. Results indicated that only the mean per unit estimators provided statistically unbiased estimates, while all other methods overestimated bycatch. The mean of the individual fish to shrimp ratios, the method used in the South Atlantic Bight before the 1990s, gave the most biased estimates. Because of the statistically significant two- and 3-way interactions among parameters, it is unlikely that estimates generated by one method can be converted or corrected to estimates made by another method: therefore bycatch estimates obtained with different methods should not be compared directly.

An evaluation of back-calculation methodology using simulated otolith data

I simulated somatic growth and accompanying otolith growth using an individual-based bioenergetics model in order to examine the performance of several back-calculation methods. Four shapes of otolith radius-total length relations (OR-TL) were simulated. Ten different back-calculation equations, two different regression models of radius length, and two schemes of annulus selection were examined for a total of 20 different methods to estimate size at age from simulated data sets of length and annulus measurements. The accuracy of each of the twenty methods was evaluated by comparing the back-calculated length-at-age and the true length-at-age. The best back-calculation technique was directly related to how well the OR-TL model fitted. When the OR-TL was sigmoid shaped and all annuli were used, employing a least squares linear regression coupled with a log-transformed Lee back-calculation equation (y-intercept corrected) resulted in the least error; when only the last annulus was used, employing a direct proportionality back-calculation equation resulted in the least error. When the OR-TL was linear, employing a functional regression coupled with the Lee back-calculation equation resulted in the least error when all annuli were used, and also when only the last annulus was used. If the OR-TL was exponentially shaped, direct substitution into the fitted quadratic equation resulted in the least error when all annuli were used, and when only the last annulus was used. Finally, an asymptotically shaped OR-TL was best modeled by the individually corrected Weibull cumulative distribution function when all annuli were used, and when only the last annulus was used.

An experiment conducted with a floating trawl net off Cochin

The paper deals with an experiment with a floating trawl net off Cochin, using a pair of curved otter boards and a transducer mounted on the head rope of the net. 32 hauls were made with different towing speeds and warp length keeping one factor constant for varying parameters of the other factor. The working data for 32 hauls are presented and the effect in the fishing depth of the net due to the variation in one factor is mentioned. The 'fishing depth' is indicated in this paper as the distance between the head rope and the bottom. The usefulness of similar experiments with added information on the angle of leading warp at the stern for the exploitation of column fishes in Indian waters is indicated.

THEORETICAL ROAD DAMAGE DUE TO DYNAMIC TYRE FORCES OF HEAVY VEHICLES. PART 2: SIMULATED DAMAGE CAUSED BY A TANDEM-AXLE VEHICLE.

The literature relating to road surface failure and design is briefly reviewed and the conventional methods for assessing the road damaging effects of dynamic tire forces are examined. A new time domain technique for analyzing dynamic tire forces and four associated road damage criteria are presented. The force criteria are used to examine the road damaging characteristics of a simple tandem-axle vehicle model for a range of speed and road roughness conditions. It is concluded that for the proposed criteria, the theoretical service life of road surfaces that are prone to fatigue failure may be reduced significantly by the dynamic component of wheel forces. The damage done to approximately five per cent of the road surface area during the passage of a theoretical model vehicle at typical highway speeds may be increased by as much as four times.

All-optical 3R regeneration and wavelength conversion in an integrated SOA/DFB laser: Experiment and simulation

The simultaneous all optical 3R regeneration and format conversion in a simple, single integrated device was examined. The integrated device consisted of a semiconductor optical fiber (SOA) monolithically integrated with a distributed feedback (DFB) laser. Gain saturation was employed for the transmission of a data signal regenerated all-optically in the laser/amplifier device. The regeneration of the electrically filtered eye diagrams was observed by noise removal and extinction ratio-improvement by the device.

Simulated superior performance of superjuction bipolar transistors

This paper presents for the first time an investigation and comparison of the superjunction IGBT (SJBT) as proposed in [1,2] and the current state of art Field Stop IGBT [3,4]. Simulation results indicate the superior performance of the superjunction IGBT under switching conditions. For the same conditions, at a collector current density of 100A/cm2 and on-state voltage 1.6 V the switching off losses for a SJBT and Field-Stop IGBT are 1 and 4.5 mJ/cm 2 respectively. © 2006 IEEE.

Mandrel peeling of a flexible laminate with a pressure-sensitive adhesive: Comparison of experiment with numerical analysis

Mandrel peel tests with mandrels or rollers of varying diameters have been carried out using Mylar backing of several thicknesses and a commercial synthetic acrylic adhesive. The results are critically compared with the numerical predictions of the peeling software package ICPeel. In addition, a finite element model of the mandrel peeling process has been completed which gives good agreement with experiment provided appropriate mechanical properties of adherend and adhesive are used which must include the effects of adherent constraint. The influence of the thickness of the backing is also considered and both experiment and analysis confirm that there is a backing thickness at which the peel force for a laminate of this sort will show a maximum. © 2010 Blackwell Publishing Ltd.

Viability of Penaeus monodon eggs after simulated transport conditions

P. monodon spawners, transported from maturation pens suffer from stress which in turn may lead to lowered spawning rate or fertility. Spawning the females in the maturation site and transporting the eggs to the hatchery site is being considered as an alternative. Egg transport costs may be reduced to a minimum by using eggs from ablated spawners, transported at high density with no aeration. Experiments on higher egg densities as well as on transport of nauplii should, however, be undertaken.

Experiment on larval rearing of Penaeus monodon fed with cultured diatom Chaetoceros calcitran and fermented vegetable trash

A brief account is given of experiments undertaken rearing Penaeus monodon larvae fed on diatom (Chaetoceros calcitran) and fermented vegetable trash, which included fruits and their peels, vegetables and rice. The possible use of high protein content trash materials as a feed substitute is examined briefly.

A statistical index of growth condition in an aquaculture experiment

A simple statistical index, for evaluating the condition of growth in an aquaculture experiment and indicating the extent of effect of any plausible rival hypothesis, is presented.