Management strategies to prevent overfishing while achieving optimum yield vary according to the available data and life history of the fished stock. I evaluated two sets of management strategies for Pacific coast rockfish: strategies to set harvest limits for data-poor stocks, and strategies intended to protect the age structure of fished stocks. Setting Harvest Limits for Data-poor Stocks - The collapse of canary rockfish, Sebastes pinniger, in the northeast Pacific began more than two decades before the stock was officially declared overfished. The 2006 reauthorization of the Magnuson-Stevens Fishery Conservation and Management Act requires a scientifically-based harvest limit for all fished stocks, including those with data limited to catch. Two such "data-poor" methods are currently in use for the management of west coast stocks, depletion-corrected average catch (DCAC) and depletion-based stock reduction analysis (DB-SRA). To evaluate the performance of each method when challenged with catch and biological uncertainty, I retrospectively applied the methods to the catch and biological data available at the time of the first and second canary rockfish stock assessments in 1984 and 1990. In 1980 canary rockfish would be classified as "data-poor", and in 1990 as "data-rich". To evaluate the sensitivity of DCAC and DB-SRA to error in the catch data, harvest limits were estimated using both the historic catch data from each assessment, and the reconstructed catch data from the most recent stock assessment. In addition, harvest limits were estimated using simulated catch data sets for the years 1916 to 1983 with increasing variability around the true catch. DCAC and DB-SRA estimated harvest limits were significantly lower than the catch recommended in both the data-poor and data-rich stock assessments, but higher than the "true" overfishing limit. Use of current catch data improved the estimated harvest limit when the stock was data-poor, but not when the stock was data-rich. The simple methods responded to increasing error in the catch time series with decreasing mean estimates of the harvest limit, indicating that these methods are highly precautionary for this species, when the catch time series is the only source of error. Age Structure Management Strategies - In a variable oceanographic environment, a population with many reproductive age classes benefits not only from the increased fecundity of older fish; but also, in some species, an increase in larval fitness. Older females may also spawn at different times or over longer periods than younger females, increasing the probability of larvae encountering favorable environmental conditions. Despite the accumulating evidence for the importance of age structure to long-term population viability in harvested fish populations, long-lived west coast rockfish (Genus Sebastes) are managed with a biomass-based harvest control rule. I compared three strategies for age structure management, and evaluated the strategies relative to the status quo, biomass-based harvest control rules, across three rockfish life histories. I examined the tradeoff between yield and traditional management reference points, as well as performance measures that could serve as management reference points for age structure. Yield was reduced by strategies that maintain "old growth" age structure, but annual variation in the catch and the probability of becoming overfished were also reduced. The longest-lived rockfish benefited the most from strategies that maintained older fish in the population through dome-shaped selectivity. The shorter-lived rockfish benefited from adjustments in the catch limit based on the age composition of the catch one year previous. Achieving "pretty good yield" with management strategies that also decrease the potential for overexploitation is an important goal for stocks that are well-studied and those that are poorly understood; these investigations contribute to a growing literature on alternative approaches to sustainable fisheries management. / Graduation date: 2012

Abstract Methane (CH4) and nitrous oxide (N2O) are not only important but also long-lived greenhouse gases. Unfortunately, in Taiwan, although there are some data on CH4 emission from rivers and lakes there is no data about N2O emission from rivers, lakes and coasts. So this study investigated CH4 and N2O distribution in natural waters around Taiwan. In Taiwan, the average CH4 concentration in rivers is about 3082¡Ó12399nM (n=152). The average CH4 concentration in mountain lakes is about 2899¡Ó7291nM (n=51). The average CH4 concentration in lower elevation lakes and reservoirs is about 1825¡Ó2755nM ppmv (n=95). The average CH4 concentration in near-shore waters is about 36.7¡Ó285nM (n=476). The CH4 distribution is rivers> mountain lakes>low-elevation lakes and reservoirs >seawater. In southeastern China, the average CH4 concentration in rivers is about 1029¡Ó2487nM ppmv (n=36). The average CH4 concentration of samples taken from rivers in southeastern China is lower than Taiwan rivers. But the highest CH4 concentration of all samples is in Chih-Kan river of southeastern China (14914nM), due to uneven population distribution as well as different levels of development among cities and suburbs. In Taiwan, the average N2O concentration in rivers is about 32.8¡Ó69.1nM (n=58). In southeastern China, the average N2O concentration in rivers is about 29.7¡Ó9.05nM (n=36). The average N2O concentration in Taiwanese rivers is higher than found in southeastern China. This is likely because farmers in Taiwan use more synthetic fertilizers so the soil becomes full of N element, and then rivers and rains rinse the soil. This process has increased the concentration of N and N2O in rivers. In summer, the average CH4 and N2O concentrations in northern Taiwan Strait are about 3.27¡Ó2.42nM and 7.22¡Ó0.62nM (n=7), respectively; and the average CH4 and N2O fluxes are about 0.17¡Ó0.43£gmol/m2/h and 0.14¡Ó0.26 £gmol/m2/h, respectively. The average CH4 and N2O concentrations in southern Taiwan Strait are about 3.35¡Ó1.97nM and10.31¡Ó2.51nM (n=30), respectively; and the average CH4 and N2O fluxes are about 0.04¡Ó0.09£gmol/m2/h and 0.19¡Ó0.22 £gmol/m2/h, respectively. In winter, the average CH4 and N2O concentrations in northern Taiwan Strait are about 4.74¡Ó1.43nM and 8.41¡Ó0.46nM (n=9), respectively; and the average CH4 and N2O fluxes are about 0.10¡Ó0.14£gmol/m2/h and 0.008¡Ó0.033 £gmol/m2/h, respectively. The average CH4 and N2O concentrations in southern Taiwan Strait are about 4.70¡Ó2.42nM and 8.36¡Ó0.97nM (n=17), respectively; and the average CH4 and N2O fluxes are about 0.17¡Ó0.46£gmol/m2/h and 0.11¡Ó0.12 £gmol/m2/h, respectively. Taiwan Strait is a source of CH4 and N2O regardless of whether it is summer or winter. In summer, the average CH4 and N2O concentrations in the South China Sea are about 4.34¡Ó2.33nM and 8.23¡Ó1.5nM (n=55), respectively; and the average CH4 and N2O fluxes are about 0.33¡Ó0.35£gmol/m2/h and 0.20¡Ó0.24 £gmol/m2/h, respectively. It is a source of CH4 and N2O to the atmosphere. In summer, the average CH4 and N2O concentrations in the West Philippines Sea are about 3.18¡Ó1.57nM and 4.64¡Ó0.39nM (n=60), respectively; and the average CH4 and N2O fluxes are about 0.23¡Ó0.33£gmol/m2/h and -0.28¡Ó0.30 £gmol/m2/h, respectively. It is a source of CH4 but a sink of N2O to the atmosphere.

A total of 10 vertical 226Ra profiles from the North Pacific was published as part of the GEOSECS program. These profiles are located on an east-west section along ~300N. The purpose of this thesis is to use one-dimensional and two-dimensional diffusion-advection models to estimate some important geochemical parameters. There are some discrepancies between the modeling results and the observed tracer distributions due to restrictions on end-members in the models. Fitting the observed data to the model, one obtains values of the Z* between 0.8 and 1.0 km from potential temperature and that of JBa/w between 0.0020 and 0.0064 nM/kg/m from Ba. Where Ba profiles are available, the corresponding 226Ra profiles are similar from the surface to the deep water, showing a linear correlation with a slope at 0.22 dpm/100nM or 4.4¡Ñ10-9 for the Ra/Ba molal ratio. The slope has an intercept of 0.48 nM/kg on the Ba axis. That 226Ra is linearly correlated with Ba from surface water to deep water is probably because algebraic sum of the production term and the radioactive decay is nearly constant. Thus the revised model has a form equivalent to that for Ba. Where Ba profiles are available, one can fit the observed data to the model to obtain the needed parameters with (JRa-£fCRa)/JBa as a constant. The upwelling velocity, w, obtained from model calculations on the Ba profiles is: 3.8 m/yr at 204; 4.8 m/yr at 212; 3.5 m/yr at 226, 1.2 m/yr at 224. These values are consistent with those (1 to 12m/yr) reported for the Pacific deep water based on other methods. Fitting 226Ra profile data to the vertical one-dimensional diffusion-advection model for the in-situ production rate, J, and the associated upwelling velocity, w, one finds that J and w are coupled with a negative correlation. This is consistent with that reported in the literature. Profiles from the northeast Pacific show a deep Ra maximum, with an ¡§excess¡¨ which extends westward while decreasing and finally vanishing in the northwest Pacific near Japan. A horizontal diffusivity of 5 ¡Ñ105 cm2/s was obtained based on this ¡§excess¡¨ 226Ra with a horizontal 1-D model by Chung and Craig (1980). A numerical finite-difference method is applied to the 2-D model fitting on the potential temperature data for the horizontal diffusivity, Kx. A Kx of 4.58 ¡Ñ105 cm2/s is obtained within the depth range of 1000m to 3000m. The value is 4.82 ¡Ñ105 cm2/s for the depth range from 1000m to 4000m. These two approaches yield nearly identical results.

Thesis (M.S. in Meteorology)--Naval Postgraduate School, March 2004. / Thesis advisor(s): Patrick A. Harr, Russell L. Elsberry. Includes bibliographical references (p. 117-118). Also available online.

At the 1996 World Fisheries Congress, Donald A. McCaughran declared seventyfive years of regulatory success for the International Pacific Halibut Commission. The Commission's mandate was to reverse the precipitous decline in halibut stocks that had become apparent in the 1910's, and save this fishery from economic extinction. The biologists and fishermen who sat on the Commission assumed that the appropriate biological target was the one that yielded the maximum sustainable harvest. Using a bioeconomic model of the fishery and regression analysis, I argue the Commission's use of global quotas to achieve its biological goal of maximum sustained yield was most certainly an economic failure. I also argue its policies were very likely a biological failure, as well. While arguably accomplishing its biological goal of the maximum sustainable yield in 1960, dynamic bioeconomic theory indicates their policies probably destabilized the biological fishery. The paper will first sketch the historical background of the industry. Then the regulatory history will be discussed. Then the economic literature will be reviewed as it applies to the Pacific halibut industry. Finally, the historical data will be examined and the proposition that the regulatory management of the halibut fishery was a success will be tested. The period 1928 to 1960 is covered as it provides both reliable data and a continuous period of regulation, at the end of which the biological goal of maximum sustainable yields was apparently achieved. In conclusion, I find that statistically the fishermen were insensitive to the direct effects of the quota and the total quantity of fish available, and instead responded to the quota's indirect effects on the fishermen's costs, which induced the inflow of greater fishing capital than otherwise would have occurred.

No description available.

The first part of this thesis is an assessment of the ability of global climate models to reproduce observed features of the leading Empirical Orthogonal Function (EOF) mode of North Pacific sea surface temperature (SST) anomalies known as the Pacific Decadal Oscillation (PDO). The simulations from 13 global climate models I am analyzing were performed under phase 3 of the coupled model intercomparison project (CMIP3). In particular, I am investigating whether these climate models capture tropical influences on the PDO, and the influences of the PDO on North American surface temperature and precipitation. My results are that 1) the models as group produce a realistic pattern of the PDO. The simulated variance of the PDO index is overestimated by roughly 30%. 2) The tropical influence on North Pacific SSTs is biased systematically in these models. The simulated response to El Niño-Southern Oscillation (ENSO) forcing is delayed compared to the observed response. This tendency is consistent with model biases toward deeper oceanic mixed layers in winter and spring and weaker air-sea feedbacks in the winter half-year. Model biases in mixed layer depths and air-sea feedbacks are also associated with a model mean ENSO-related signal in the North Pacific whose amplitude is overestimated by roughly 30%. Finally, model power spectra of the PDO signal and its ENSO-forced component are “redder” than observed due to errors originating in the tropics and extratropics. 3) The models are quite successful at capturing the influence of both the tropical Pacific related and the extratropical part of the PDO on North American surface temperature. 4) The models capture some of the influence of the PDO on North American precipitation mainly due to its tropical Pacific related part. In the second part of this thesis, I investigate the ability of one such coupled ocean- atmosphere climate model, carefully initialized with observations, to dynamically predict the future evolution of the PDO on seasonal to decadal time scales. I am using forecasts produced by the Canadian climate data assimilation and prediction system employing the Canadian climate model CanCM3 for seasonal (CHFP2) and CanCM4 for decadal (DHFP1) predictions. The skill of this system in predicting the future evolution of the PDO index is then inferred from a set of historical “forecasts” called hindcasts. In this manner, hindcasts are issued over the past 30 years (seasonal), or over the past 50 years (decadal) when they can be verified against the observed historical evolution of the PDO index. I find that 1) CHFP2 is successful at predicting the PDO at the seasonal time scale measured by mean-square skill score and correlation skill. Weather “noise” unpredictable at the seasonal time scale generated by substantial North Pacific storm track activity that coincides with a shallow oceanic mixed layer in May and June appear to pose a prediction barrier for the PDO. PDO skill therefore depends on the start season of the forecast. PDO skill also varies as a function of the target month. Variations in North Pacific storminess appear to impact PDO skill by means of a lagged response of the ocean mixed layer to weather “noise”. In CHFP2, times of increasing North Pacific storm track activity are followed by times of reduced PDO skill, while the North Pacific midwinter suppression of storm track activity with decreasing storminess is followed by a substantial recovery in PDO skill. 2) This system is capable of forecasting the leading 14 EOF modes of North Pacific SST departures, that explain roughly three quarters of the total SST variance. CHFP2 is less successful at predicting North Pacific SSTs, i.e., the combination of all the EOF modes, at the seasonal time scale. 3) Besides the skill in Pacific SST, CHFP2 skillfully predicts indices that measure the atmospheric circulation regime over the North Pacific and North America such as the Pacific/North American pattern (PNA) (skillful for three out of four start seasons) and the North Pacific index (NPI) (skillful for all four start seasons). 4) CHFP2 is successful at forecasting part of the influence of Pacific SST on North American climate at the seasonal time scale. Measured by 12-month average anomaly correlation skill, in this system the PDO is a better predictor for North American precipitation (skillful for all four start seasons) than temperature (skillful for one out of four start seasons). In CHFP2, ENSO is a better predictor for North American temperature (skillful for all four start seasons) than the PDO. Both ENSO and the PDO are, however, good predictors for North American precipitation (skillful for all four start seasons). Finally, DHFP1 is less successful at forecasting the PDO at the decadal time scale. Ten-year forecasts of the PDO index exhibit significantly positive correlation skill exclusively in the first year of the forecast. When the correlation skill of the predicted index averaged over lead years is considered, the PDO skill in this system stays significantly positive during the first three years of the decadal forecast. In other words, this climate data assimilation and prediction system is expected to skillfully predict the future three year averaged evolution of the PDO index, but not the evolution of the index in each year individually. / Graduate

The time-averaged velocity field in the North Pacific was estimated in two sets of inverse calculations. The planetary geostrophic equations were the basis for dynamical models of the flow in each case. The inverse estimates of the circulation were obtained by minimizing a positive-definite cost function, which measured the inconsistency of the model's predictions against a set of observations comprised of a large, high-quality hydrographic data set, and surface fluxes of heat, fresh water, and momentum. In the first part of this work, four solution methods for the generalized inverse of a linear planetary geostrophic model of the North Pacific are compared. A conjugate gradient solver applied to the equation for the generalized inverse, expressed in terms of a representer expansion, was the most computationally efficient solution method. The other methods, in order of decreasing efficiency, were, a conjugate gradient descent solver (preconditioned with the inverse of the model operators), a direct solver for the representer coefficients, and a second conjugate gradient descent solver (preconditioned so that the diagonal elements of the cost Redacted for Privacy function Hessian were unity). All but the last method were successful at minimizing the penalty function. Inverse estimates of the circulation based on the linear planetary geostrophic model were stable to perturbations in the data, and insensitive to assumptions regarding the model forcing and boundary condition uncertainties. A large calculation, which involved approximately 18,000 observations and 60,000 state variables, indicated that the linear model is remarkably consistent with the observations. The second part of this work describes an attempt to use a nonlinear planetary geostrophic model (which included realistic bottom topography, lateral momentum mixing, out-cropping layers, and air-sea fluxes of heat, freshwater, and momentum) to assimilate the same hydrographic data set as above. Because of the nonlinearity in the model, descent methods (rather than a representer-based method) were used to solve the inverse problem. The nonlinearity of the model and the poor conditioning of the cost function Hessian confounded the minimization process. A solver for the tangent-linearization of the planetary geostrophic system should be used as a preconditioner if calculations of this type are attempted in the future. / Graduation date: 1996

Graduation date: 1987

Graduation date: 1999 / Best scan available for figures. Original has a moray pattern.