Status of the Pacific Mackerel resource during 1997 and management recommendations for the fishery

Based on a California Department of Fish and Game (CDFG) projected biomass estimate of 91,200 metric tons for July 1, 1997, the recommended commercial fishery quota for the 1997/98 fishing season is 22,000 metric tons. Age-specific abundance for 1996 was estimated using output from a stock assessment model called ADEPT and certain assumptions about growth and fishing mortality during the first half of 1997. In this year's assessment, abundance estimates made by ADEPT were expanded back in time to cover the 68-year period of 1929 through 1996. The commercial fishery quota recommendation is based upon the prescribed harvest formula for Pacific mackerel that is specified in the California Fish and Game Code. Several sources of information are available for the Pacific mackerel stock, all of which suggest a smaller biomass than was present in the 1980's. Landings from both California and Ensenada, Mexico have sharply decreased and catch rates from the southern California Commercial Passenger Fishing Vessel (CPFV) fleet have declined. Fishery-independent indices of abundance from aerial spotter observations and California Cooperative Oceanic Fisheries Investigations (CalCOFI) ichthyoplankton surveys show similar trends. The 1997 biomass estimate is higher than last year's estimate of 47,160 metric tons because data added to the model this year increased abundance for fish of 1994 and older year classes (age 2+). This year's results indicate there were more fish in the older year classes than estimated in previous assessments. (27pp.

Stock assessment and management recommendations for Pacific sardine (Sardinops sagax) in 1997

The primary goal of sardine management as directed by the California Fish and Game Code is rehabilitation of the resource with an added objective of maximizing sustained harvest. Accordingly, the Code states that the annual sardine quota can be set at an amount greater than 1,000 tons, providing that the level of take allows for continued increase in the spawning population. We estimated the sardine population size to have been 464,000 short tons on July 1, 1997. Our estimate was based on output from a modified version of the integrated stock assessment model called CANSAR (Deriso et al. 1996). CANSAR is a forward-casting, age-structured analysis using fishery-dependent and fishery-independent data to obtain annual estimates of sardine abundance, year-class strength and age-specific fishing mortality for 1983 through the first semester of 1997. Non-linear least-squares criteria are used to find the best fit between model estimates and input data. Questions about stock structure and range extent remain major sources of uncertainty in assessing current sardine population biomass. Recent survey results and anecdotal evidence suggest increased sardine abundance in the Pacific Northwest and areas offshore from central and southern California. It is difficult to determine if those fish were part of the stock available to the California fishery. In an attempt to address this problem, the original CANSAR model was reconfigured into a Two-Area Migration Model (CANSAR-TAM) which accounted for sardine lost to the areas of the fishery and abundance surveys due to population expansion and net emigration. While the model includes guesses and major assumptions about net emigration and recruitment, it provides an estimate which is likely closer to biological reality than past assessments. The original CANSAR model was also used and estimates are provided for comparison. Based on the 1997 estimate of total biomass and the harvest formula used last year, we recommend a 1998 sardine harvest quota of 48,000 tons for the California fishery. The 1998 quota is a decrease of 11% from the final 1997 sardine harvest quota for California of 54,000 tons. (55pp.

AN ECONOMIC EVALUATION OF LOW INVESTMENT SWINE PRODUCTION SYSTEMS

This publication summarizes an evaluation of smaller and lower investment swine production systems. The systems analyzed range from pasture operations with production during the warmer months to rather intense year-round use of remodeled buildings. In each case the system emphasizes use of facilities that can be constructed and remodeled by the farm operator. The report includes one section for each type of hog production: feeder pig production, farrow-to-finish operations and hog finishing.Livestock Production/Industries,

Status of the Pacific mackerel resource and fishery in 1998

Based on the projected Pacific mackerel biomass estimate of 132,500 tons for July 1, 1998, the commercial fishery quota for the 1998/99 fishing season was recommended and set at 33,700 short tons. The 1998 biomass was estimated using output from a stock assessment computer model called ADEPT and certain assumptions about fishing mortality during the first half of 1998. Several important changes were made to improve our assessment during 1998. The assessment model was changed from a quarterly to an annual one and now covers sixty-nine years of fishery data. New indices of relative abundance were added to the analysis to account for changes in mackerel biomass off central and northern California. The July 1, 1998, biomass estimate is slightly higher than last year's CDFG estimate of 101,000 tons for 1997. This year's results indicate there were more fish in the older year classes than previously estimated. (62pp.

Modeling Newborn Piglet Thermal Interactions with a Surface Energy Balance Model

A mathematical model was developed to describe the radiative and convective thermal interactions between a newborn piglet and it’s surroundings. The model incorporates surface energy balances for each surface in the enclosure. The model was verified with results from a simulated creep area and from published calorimetric studies on newborn pigs. Mathematical results were all within 5.5% of the measured results from a simulated creep-area. Compared with published studies, the mathematical model over-predicts heat loss in high-demand environments and under predicts heat loss in low-demand environments

Defining the Newborn Piglet’s Thermal Environment with an Effective Environmental Temperature

An effective environmental temperature (EET) developed for newborn piglets describes the thermal environment by incorporating the mean radiant temperature, dry-bulb temperature, and air velocity near the newborn. The adequacy of the defined EET was analyzed by comparing with three published studies on newborn sensible heat loss. Results from the published studies indicate that the EET predicted between 87% and 98% of the variability in the data

Three-Dimensional Buoyant Turbulent Flows in a Scaled Model, Slot-Ventilated, Livestock Confinement Facility

A three-dimensional turbulence model was used to determine the effects of animal-generated buoyant forces on the airflow patterns and temperature and airspeed distributions in a ceiling-slot, ventilated, swine grower facility. The model incorporated the Lam-Bremhorst turbulence model for low-Reynolds Number airflow typical of slot-ventilated, livestock facilities. The predicted results from the model were compared with experimental results from a scaled-enclosure. The predicted and measured results indicated a rather strong cross-stream recirculation zone in the chamber that resulted in substantial three-dimensional temperature distributions for moderate to highly buoyancy-affected flows. Airflow patterns were adequately predicted for Arc \u3e 40 and J values \u3c 0.00053. For Arc \u3c 40 and J values \u3e 0.00053, the visualized patterns indicated that the jet separated from the ceiling before the opposing end-wall. This discrepancy was attributed to variations in the experimental and numerical inlet flow development assumptions

Biology and population dynamics of cowcod (Sebastes levis) in the southern California Bight

Cowcod (Sebastes levis) is a large (100-cm-FL), long-lived (maximum observed age 55 yr) demersal rockfish taken in multispecies commercial and recreational fisheries off southern and central California. It lives at 20–500 m depth: adults (>44 cm TL) inhabit rocky areas at 90–300 m and juveniles inhabit fine sand and clay at 40–100 m. Both sexes have similar growth and maturity. Both sexes recruit to the fishery before reaching full maturity. Based on age and growth data, the natural mortality rate is about M =0.055/yr, but the estimate is uncertain. Biomass, recruitment, and mortality during 1951–98 were estimated in a delay-difference model with catch data and abundance indices. The same model gave less precise estimates for 1916–50 based on catch data and assumptions about virgin biomass and recruitment such as used in stock reduction analysis. Abundance indices, based on rare event data, included a habitat-area–weighted index of recreational catch per unit of fishing effort (CPUE index values were 0.003–0.07 fish per angler hour), a standardized index of proportion of positive tows in CalCOFI ichthyoplankton survey data (binomial errors, 0–13% positive tows/yr), and proportion of positive tows for juveniles in bottom trawl surveys (binomial errors, 0–30% positive tows/yr). Cowcod are overfished in the southern California Bight; biomass during the 1998 season was about 7% of the virgin level and recent catches have been near 20 metric tons (t)/yr. Projections based on recent recruitment levels indicate that biomass will decline at catch levels > 5 t/yr. Trend data indicate that recruitment will be poor in the near future. Recreational fishing effort in deep water has increased and has become more effective for catching cowcod. Areas with relatively high catch rates for cowcod are fewer and are farther offshore. Cowcod die after capture and cannot be released alive. Two areas recently closed to bottom fishing will help rebuild the cowcod stock

Assessment of Ventilation Management Training Workshops

To achieve optimum swine performance, producer understanding of environmental control systems in mechanically or naturally ventilated facilities is extremely important. A ventilation workshop: “Managing Your Unseen Employee: The Ventilation System” was established. The primary objective of the training was to give swine producers and managers enough quality information so they could go back to their operations and properly assess their own ventilation systems and make appropriate adjustments as needed. The training workshops were established to be a multi-state and multi-disciplinary effort between South Dakota, Nebraska, Iowa and Minnesota universities. Ag engineers and animal scientists from each state participated in developing the workshop materials and delivery of the program. Four basic needs emerged that would enhance program delivery. These needs included basic environmental factors and their effects on pigs, ventilation system design principles, trouble-shooting ventilation problems, and hands-on demonstrations of instrumentation and ventilation equipment. A 1.8 m by 2.4 m by 2.4 m mobile ventilation room was used for the hands-on training. The mobile ventilation room was equipped with two variable-speed, 30-centimeter fans and one 30-cm, single-speed fan; a four-stage controller; and three types of air inlets. From 2002 to 2007, over 1000 people producing over 20 million pigs participated in more than 60 workshops. The backgrounds of participants included managers, feed consultants, extension educators, and veterinarians. Key points gained by producers included proper ventilation settings, trouble-shooting techniques, temperature control, and the effects of static pressure on airflow

The Real World of Ventilation Troubleshooting: A Swine Case Study

Swine finishing facility ventilation has become relatively complex and is often mismanaged as a system. One of the few ways to truly understand these systems is to spend time systematically going through the many components of the building. To learn to help producers better, a team of university Extension specialists that included agricultural engineers and animal scientists spent an extended period carefully documenting conditions in a deep-pit swine finishing building with two 1,000-head rooms. Exhaust fans in the pit and walls operated at various stages throughout the year as a negative-pressure ventilation system. A computerized controller activated exhaust fans, a ventilation curtain actuator, and heaters. Gravity baffled ceiling inlets were evenly spaced in the building to provide good air distribution during cold and mild weather conditions. Following the review of current conditions and operating parameters, performance deficiencies were identified and recommendations were given regarding controller settings, inlet settings, and curtain management. The overall operating characteristics of the ventilation system and air quality in the animal space were documented ventilation and related management changes were discussed with the owner/operator