The U.S. Gulf of Mexico Pink Shrimp, Farfantepenaeus duorarum, Fishery: 50 Years of Commercial Catch Statistics

U.S. Gulf of Mexico, pink shrimp, Farfantepenaeus duorarum, catch statistics have been collected by NOAA’s National Marine Fisheries Service, or its predecessor agency, for over 50 years. Recent events, including hurricanes and oil spills within the ecosystem of the fishery, have shown that documentation of these catch data is of primary importance. Fishing effort for this stock has fluctuated over the 50-year period analyzed, ranging from 3,376 to 31,900 days fished, with the most recent years on record, 2008 and 2009, exhibiting declines up to 90% relative to the high levels recorded in the mid 1990’s. Our quantification of F. duorarum landings and catch rates (CPUE) indicates catch have been below the long-term average of about 12 million lb for all of the last 10 years on record. In contrast to catch and effort, catch rates have increased in recent years, with record CPUE levels measured in 2008 and 2009, of 1,340 and 1,144 lb per day fished, respectively. Our regression results revealed catch was dependent upon fishing effort (F=98.48df=1, 48, p<0.001, r2=0.67), (Catch=1,623,378 + (520) × (effort)). High CPUE’s measured indicate stocks were not in decline prior to 2009, despite the decline in catch. The decrease in catch is attributed in large part to low effort levels caused by economical and not biological or habitat related conditions. Future stock assessments using these baseline data will provide further insights and management advice concerning the Gulf of Mexi

Simulation of Tail Weight Distributions in Biological Year 1986–2006 Landings of Brown Shrimp, Farfantepenaeus aztecus, from the Northern Gulf of Mexico Fishery

Size distribution within re- ported landings is an important aspect of northern Gulf of Mexico penaeid shrimp stock assessments. It reflects shrimp population characteristics such as numerical abundance of various sizes, age structure, and vital rates (e.g. recruitment, growth, and mortality), as well as effects of fishing, fishing power, fishing practices, sampling, size-grading, etc. The usual measure of shrimp size in archived landings data is count (C) the number of shrimp tails (abdomen or edible portion) per pound (0.4536 kg). Shrimp are marketed and landings reported in pounds within tail count categories. Statistically, these count categories are count class intervals or bins with upper and lower limits expressed in C. Count categories vary in width, overlap, and frequency of occurrence within the landings. The upper and lower limits of most count class intervals can be transformed to lower and upper limits (respectively) of class intervals expressed in pounds per shrimp tail, w, the reciprocal of C (i.e. w = 1/C). Age based stock assessments have relied on various algorithms to estimate numbers of shrimp from pounds landed within count categories. These algorithms required un- derlying explicit or implicit assumptions about the distribution of C or w. However, no attempts were made to assess the actual distribution of C or w. Therefore, validity of the algorithms and assumptions could not be determined. When different algorithms were applied to landings within the same size categories, they produced different estimates of numbers of shrimp. This paper demonstrates a method of simulating the distribution of w in reported biological year landings of shrimp. We used, as examples, landings of brown shrimp, Farfantepenaeus aztecus, from the northern Gulf of Mexico fishery in biological years 1986–2006. Brown shrimp biological year, Ti, is defined as beginning on 1 May of the same calendar year as Ti and ending on 30 April of the next calendar year, where subscript i is the place marker for biological year. Biological year landings encompass most if not all of the brown shrimp life cycle and life span. Simulated distributions of w reflect all factors influencing sizes of brown shrimp in the landings within a given biological year. Our method does not require a priori assumptions about the parent distributions of w or C, and it takes into account the variability in width, overlap, and frequency of occurrence of count categories within the landings. Simulated biological year distributions of w can be transformed to equivalent distributions of C. Our method may be useful in future testing of previously applied algorithms and development of new estimators based on statistical estimation theory and the underlying distribution of w or C. We also examine some applications of biological year distributions of w, and additional variables derived from them

Intensity-Resolved Above Threshold Ionization of Xenon with Short Laser Pulses

We present intensity-resolved above threshold ionization (ATI) spectra of xenon using an intensity scanning and deconvolution technique. Experimental data were obtained with laser pulses of 58 fs and central wavelength of 800 nm from a chirped-pulse amplifier. Applying a deconvolution algorithm, we obtained spectra that have higher contrast and are in excellent agreement with characteristic 2 $U_p$ and 10 $U_p$ cutoff energies contrary to that found for raw data. The retrieved electron ionization probability is consistent with the presence of a second electron from double ionization. This recovered ionization probability is confirmed with a calculation based on the PPT tunneling ionization model [Perelomov, Popov, and Terent'ev, Sov. Phys. JETP 23, 924 (1966)]. Thus, the measurements of photoelectron yields and the proposed deconvolution technique allowed retrieval of more accurate spectroscopic information from the ATI spectra and ionization probability features that are usually concealed by volume averaging.Comment: 21 pages, 7 figure

Bone-to-bone and implant-to-bone impingement : a novel graphical representation for hip replacement planning

Bone-to-bone impingement (BTBI) and implant-to-bone impingement (ITBI) risk assessment is generally performed intra-operatively by surgeons, which is entirely subjective and qualitative, and therefore, lead to sub-optimal results and recurrent dislocation in some cases. Therefore, a method was developed for identifying subject-specific BTBI and ITBI, and subsequently, visualising the impingement area on native bone anatomy to highlight where prominent bone should be resected. Activity definitions and subject-specific bone geometries, with planned implants were used as inputs for the method. The ITBI and BTBI boundary and area were automatically identified using ray intersection and region growing algorithm respectively to retain the same ‘conical clearance angle’ obtained to avoid prosthetic impingement (PI). The ITBI and BTBI area was then presented with different colours to highlight the risk of impingement, and importance of resection. A clinical study with five patients after 2 years of THA was performed to validate the method. The results supported the study hypothesis, in that the predicted highest risk area (red coloured zone) was completely/majorly resected during the surgery. Therefore, this method could potentially be used to examine the effect of different pre-operative plans and hip motions on BTBI, ITBI, and PI, and to guide bony resection during THA surgery

Scattering a pulse from a chaotic cavity: Transitioning from algebraic to exponential decay

The ensemble averaged power scattered in and out of lossless chaotic cavities decays as a power law in time for large times. In the case of a pulse with a finite duration, the power scattered from a single realization of a cavity closely tracks the power law ensemble decay initially, but eventually transitions to an exponential decay. In this paper, we explore the nature of this transition in the case of coupling to a single port. We find that for a given pulse shape, the properties of the transition are universal if time is properly normalized. We define the crossover time to be the time at which the deviations from the mean of the reflected power in individual realizations become comparable to the mean reflected power. We demonstrate numerically that, for randomly chosen cavity realizations and given pulse shapes, the probability distribution function of reflected power depends only on time, normalized to this crossover time.Comment: 23 pages, 5 figure

Gels under stress: the origins of delayed collapse

Attractive colloidal particles can form a disordered elastic solid or gel when quenched into a two-phase region, if the volume fraction is sufficiently large. When the interactions are comparable to thermal energies the stress-bearing network within the gel restructures over time as individual particle bonds break and reform. Typically, under gravity such weak gels show a prolonged period of either no or very slow settling, followed by a sudden and rapid collapse - a phenomenon known as delayed collapse. The link between local bond breaking events and the macroscopic process of delayed collapse is not well understood. Here we summarize the main features of delayed collapse and discuss the microscopic processes which cause it. We present a plausible model which connects the kinetics of bond breaking to gel collapse and test the model by exploring the effect of an applied external force on the stability of a gel.Comment: Accepted version: 10 pages, 7 figure

Development of Wave Energy Converters at Ocean Power Technologies (Extended Abstract)

This abstract contains information relevant to the use of wave information for naval operations, education, and alternative energy technologies, and was used, along with the Session Presentation, to facilitate discussion during Session 1 (the use of wave measurements to support operations)