L. Neil Frazer

Epizootics of wild fish induced by farm fish

The continuing decline of ocean fisheries and rise of global fish consumption has driven aquaculture growth by 10% annually over the last decade. The association of fish farms with disease emergence in sympatric wild fish stocks remains one of the most controversial and unresolved threats aquaculture poses to coastal ecosystems and fisheries. We report a comprehensive analysis of the spread and impact of farm-origin parasites on the survival of wild fish populations. We mathematically coupled extensive data sets of native parasitic sea lice (Lepeophtheirus salmonis) transmission and pathogenicity on migratory wild juvenile pink (Oncorhynchus gorbuscha) and chum (Oncorhynchus keta) salmon. Farm-origin lice induced 9–95% mortality in several sympatric wild juvenile pink and chum salmon populations. The epizootics arise through a mechanism that is new to our understanding of emerging infectious diseases: fish farms undermine a functional role of host migration in protecting juvenile hosts from parasites associated with adult hosts. Although the migratory life cycles of Pacific salmon naturally separate adults from juveniles, fish farms provide L. salmonis novel access to juvenile hosts, in this case raising infection rates for at least the first ≈2.5 months of the salmons marine life (≈80 km of the migration route). Spatial segregation between juveniles and adults is common among temperate marine fishes, and as aquaculture continues its rapid growth, this disease mechanism may challenge the sustainability of coastal ecosystems and economies.

Practical aspects of reflectivity modeling

This paper is intended to help those not familiar with the “lore” of layered earth modeling to avoid some common problems. In the computation of the reflectivity function, an easily incorporated phase‐integral approximation is used away from turning points when the velocity gradient is smaller than the frequency. Hanning windows, or segments thereof, work well for both the slowness integral and the frequency integral. For the quadrature of the slowness integral the Filon method of Frazer is easily coded and vectorizes well; Levin’s Filon method and the Clenshaw‐Curtis‐Filon method of Xu and Mal are more difficult to vectorize, but more powerful because they require fewer evaluations of the reflectivity function. A modification of Strick’s power law is a convenient way to calculate complex frequency‐dependent seismic velocities. The complex frequency technique for avoiding time aliasing is explained by use of the Poisson sum formula. In writing code for vector computers, such as the CRAY, if frequency‐inde...

The Predictive Accuracy of Shoreline Change Rate Methods and Alongshore Beach Variation on Maui, Hawaii

Abstract Beach erosion has direct consequences for Hawaiis tourist-based economy, which depends on the attraction of beautiful sandy beaches. Within the last century, however, beaches on Oahu and Maui have been narrowed or completely lost, threatening tourism and construction development. In order for the counties and state of Hawaii to implement coastal regulations to prevent infrastructure damage, it is necessary to find a statistically valid methodology that accurately delineates annual erosion hazard rates specific to Hawaii. We compare the following erosion rate methods: end point rate (EPR), average of rates (AOR), minimum description length (MDL), jackknifing (JK), ordinary least squares (OLS), reweighted least squares (RLS), weighted least squares (WLS), reweighted weighted least squares (RWLS), least absolute deviation (LAD), and weighted least absolute deviation (WLAD). To evaluate these statistical methods, this study determines the predictive accuracy of various calculated erosion rates, including the effects of a priori knowledge of storms, using (1) temporally truncated data to forecast and hindcast known shorelines and (2) synthetic beach time series that contain noise. This study also introduces binning of adjacent transects to identify segments of a beach that have erosion rates that are indistinguishable. If major uncertainties of the shoreline methodology and storm shorelines are known, WLS, RWLS, and WLAD better reflect the data; if storm shorelines are not known, RWLS and WLAD are preferred. If both uncertainties and storm shorelines are not known, RLS and LAD are preferred; if storm shorelines are known, OLS, RLS, JK, and LAD are recommended. MDL and AOR produce the most variable results. Hindcasting results show that early twentieth century topographic surveys are valuable in change rate analyses. Binning adjacent transects improves the signal-to-noise ratio by increasing the number of data points.

Rapid computation of multioffset vertical seismic profile synthetic seismograms for layered media

Abstract : PNSEB is a set of FORTRAN programs for calculating the response of a layered elastic medium using the reflectivity method as described in Mallick and Frazer (Practical Aspects of Reflectivity Modeling, Geophysics 52, 1355-1364, 1987; Rapid Computation of Multi-offset VSP Synthetic Seismograms for Layered Media, Geophysics 53, 479-491, 1988). PNSEB consists of two basic modules, each of which consists of more than one major option. The first module, PNSN, calculates the earths response (Greens function) in frequency-wavenumber (omega-p) space. Using the proper option, the program can calculate the response at very small or very large offsets. No lateral variability or anisotropy are allowed, but the full response including interface waves is calculated. The second module, PNSYN, in its main form converts the output from PNSN to time- distance (t-x) space, which can then be plotted by the VSPLT module or by other plotting packages. The program has been written and optimized for vector computers, such as a Cray or Convex, but also runs well on scalar computers such as Sun workstations.

Localization of marine mammals near Hawaii using an acoustic propagation model

Humpback whale songs were recorded on six widely spaced receivers of the Pacific Missile Range Facility (PMRF) hydrophone network near Hawaii during March of 2001. These recordings were used to test a new approach to localizing the whales that exploits the time-difference of arrival (time lag) of their calls as measured between receiver pairs in the PMRF network. The usual technique for estimating source position uses the intersection of hyperbolic curves of constant time lag, but a drawback of this approach is its assumption of a constant wave speed and straight-line propagation to associate acoustic travel time with range. In contrast to hyperbolic fixing, the algorithm described here uses an acoustic propagation model to account for waveguide and multipath effects when estimating travel time from hypothesized source positions. A comparison between predicted and measured time lags forms an ambiguity surface, or visual representation of the most probable whale position in a horizontal plane around the array. This is an important benefit because it allows for automated peak extraction to provide a location estimate. Examples of whale localizations using real and simulated data in algorithms of increasing complexity are provided.

Single‐hydrophone localization

It is shown that Clay’s single‐hydrophone time‐domain localization algorithm is a member of a large class of algorithms {χmn} that require exact knowledge of the source time function w(t). The single‐hydrophone Clay algorithm is χ∞2; however, χ∞1 often localizes better than χ∞2. Next, five new families of single‐hydrophone localization algorithms are introduced. The first of these, {μmn}, also requires a knowledge of w(t), and is introduced mainly to emphasize that Clay localization is the ratio of norms. The four new localizer families, {φmn}, {θmn}, {βmn}, and {νmn}, require almost no knowledge of w(t). These new algorithms actually yield an estimate of the source spectrum W(ω), as well as the location of the source. The localizers φ, θ and ν work best when ‖W(ω)‖, the amplitude spectrum of the source, is smooth, although w(t) need not be a pulse. The β localizers work best when w(t) is a pulse. If it happens that an estimate of W(ω) is available, then φ, θ, β, and ν can use this information and their p...

P- and S-wave attenuation logs from monopole sonic data

In this paper, a modification of an existing method for estimating relative P-wave attenuation is proposed. By generating synthetic waveforms without attenuation, the variation of geometrical spreading related to changes in formation properties with depth can be accounted for. With the modified method, reliable P- and S-wave attenuation logs can be extracted from monopole array acoustic waveform log data. Synthetic tests show that the P- and S-wave attenuation values estimated from synthetic waveforms agree well with their respective model values. In‐situ P- and S-wave attenuation profiles provide valuable information about reservoir rock properties. Field data processing results show that this method gives robust estimates of intrinsic attenuation. The attenuation profiles calculated independently from each waveform of an eight‐receiver array are consistent with one another. In fast formations where S-wave velocity exceeds the borehole fluid velocity, both P-wave attenuation (QP-1) and S-wave attenuation...

Sea-cage aquaculture, sea lice, and declines of wild fish.

A sea cage, sometimes referred to as a net pen, is an enclosure designed to prevent farm fish from escaping and to protect them from large predators, while allowing a free flow of water through the cage to carry away waste. Farm fish thus share water with wild fish, which enables transmission of parasites, such as sea lice, from wild to farm and farm to wild fishes. Sea lice epidemics, together with recently documented population-level declines of wild salmon in areas of sea-cage farming, are a reminder that sea-cage aquaculture is fundamentally different from terrestrial animal culture. The difference is that sea cages protect farm fish from the usual pathogen-control mechanisms of nature, such as predators, but not from the pathogens themselves. A sea cage thus becomes an unintended pathogen factory. Basic physical theory explains why sea-cage aquaculture causes sea lice on sympatric wild fish to increase and why increased lice burdens cause wild fish to decline, with extirpation as a real possibility. Theory is important to this issue because slow declines of wild fish can be difficult to detect amid large fluctuations from other causes. The important theoretical concepts are equilibrium, host-density effect, reservoir-host effect, and critical stocking level of farmed fish (stocking level at which lice proliferate on farm fish even if wild fish are not present to infect them). I explored these concepts and their implications without mathematics through examples from salmon farming. I also considered whether the lice-control techniques used by sea-cage farmers (medication and shortened grow-out times) are capable of protecting wild fish. Elementary probability showed that W ≈ W* - εF (where W is the abundance of wild fish, W* is the prefarm abundance, F is the abundance of farm fish, and ε is the ratio of lice per farm fish to lice per wild fish). Declines of wild fish can be reduced by short growing cycles for farm fish, medicating farm fish, and keeping farm stocking levels low. Declines can be avoided only by ensuring that wild fish do not share water with farmed fish, either by locating sea cages very far from wild fish or through the use of closed-containment aquaculture systems. These principles are likely to govern any aquaculture system where cage-protected farm hosts and sympatric wild hosts have a common parasite with a direct life cycle.

Accommodating lateral velocity changes in Kirchhoff migration by means of Fermat’s principle

When velocity varies laterally as well as with depth, an exact Kirchhoff depth migration requires that rays be traced from each depth point in the section to each source/receiver location. Because such a procedure is prohibitively expensive, Kirchhoff migration is usually carried out by using a velocity function that depends only on depth. This paper introduces a new method, based on Fermat’s principle, which is a compromise between these two extremes. The slowness (reciprocal velocity) function is written as the sum of two functions, the first of which is large and depends only on depth, while the other is small and varies both with depth and position along the line. Raypaths are traced for the first slowness function and are used to calculate migration curves. For each depth point these same raypaths are used to calculate traveltime perturbations due to the laterally varying part of the slowness. The traveltime perturbations are added to the migration curve to obtain an approximation to the exact migrat...

Historical Shoreline Change, Southeast Oahu, Hawaii; Applying Polynomial Models to Calculate Shoreline Change Rates

Abstract Here we present shoreline change rates for the beaches of southeast Oahu, Hawaii, calculated using recently developed polynomial methods to assist coastal managers in planning for erosion hazards and to provide an example for interpreting results from these new rate calculation methods. The polynomial methods use data from all transects (shoreline measurement locations) on a beach to calculate a rate at any one location along the beach. These methods utilize a polynomial to model alongshore variation in the rates. Models that are linear in time best characterize the trend of the entire time series of historical shorelines. Models that include acceleration (both increasing and decreasing) in their rates provide additional information about shoreline trends and indicate how rates vary with time. The ability to detect accelerating shoreline change is an important advance because beaches may not erode or accrete in a constant (linear) manner. Because they use all the data from a beach, polynomial models calculate rates with reduced uncertainty compared with the previously used single-transect method. An information criterion, a type of model optimization equation, identifies the best shoreline change model for a beach. Polynomial models that use eigenvectors as their basis functions are most often identified as the best shoreline change models.