An Economic Analysis of Texas Shrimp Season Closures

Management of the Texas penaeid shrimp fishery is aimed at increasing revenue from brown shrimp, Penaeus aztecus, landings and decreasing the level of discards. Since 1960 Texas has closed its territorial sea for 45-60 days during peak migration of brown shrimp to the Gulf of Mexico. In 1981 the closure was extended to 200 miles to include the U.S. Exclusive Economic Zone. Simulation modeling is used in this paper to estimate the changes in landings, revenue, costs, and economic rent attributable to the Texas closure. Four additional analyses were conducted to estimate the effects of closing the Gulf 1- to 4-fathom zone for 45 and 60 days, with and without effort redirected to inshore waters. Distributional impacts are analyzed in terms of costs, revenues, and rents, by vessel class, shrimp species, vessel owner, and crew.

Review of size- and age-dependence in batch spawning: implications for stock assessment of fish species exhibiting indeterminate fecundity

Most assessments of fish stocks use some measure of the reproductive potential of a population, such as spawning biomass. However, the correlation between spawning biomass and reproductive potential is not always strong, and it likely is weakest in the tropics and subtropics, where species tend to exhibit indeterminate fecundity and release eggs in batches over a protracted spawning season. In such cases, computing annual reproductive output requires estimates of batch fecundity and the annual number of batches—the latter subject to spawning frequency and duration of spawning season. Batch fecundity is commonly measured by age (or size), but these other variables are not. Without the relevant data, the annual number of batches is assumed to be invariant across age. We reviewed the literature and found that this default assumption lacks empirical support because both spawning duration and spawning frequency generally increase with age or size. We demonstrate effects of this assumption on measures of reproductive value and spawning potential ratio, a metric commonly used to gauge stock status. Model applications showed substantial sensitivity to age dependence in the annual number of batches. If the annual number of batches increases with age but is incorrectly assumed to be constant, stock assessment models would tend to overestimate the biological reference points used for setting harvest rates. This study underscores the need to better understand the age- or size-dependent contrast in the annual number of batches, and we conclude that, for species without evidence to support invariance, the default assumption should be replaced with one that accounts for age- or size-dependence.

Effects of reducing nutrient loads to surface waters within the Mississippi River Basin and the Gulf of Mexico: Topic 4 Report for the Integrated Assessment on Hypoxia in the Gulf of Mexico

The overall goal of this assessment was to evaluate the effects of nutrient-source reductions that may be implemented in the Mississippi River Basin (MRB) to reduce the problem of low oxygen conditions (hypoxia) in the nearshore Gulf of Mexico. Such source reductions would affect the quality of surface waters—streams, rivers, and reservoirs—in the drainage basin itself, as well as nearshore Gulf waters. The task group’s work was divided into addressing the effects of nutrient-source reductions on: (1) surface waters in the MRB and (2) hypoxia in the Gulf of Mexico.

Flux and sources of nutrients in the Mississippi-Atchafalaya River Basin: Topic 3 Report for the Integrated Assessment on Hypoxia in the Gulf of Mexico.

Ths report addresses the following two questions: 1) What are the loads (flux) of nutrients transported from the Mississippi-Atchafalaya River Basin to the Gulf of Mexico, and where do they come from within the basin? 2) What is the relative importance of specific human activities, such as agriculture, point-source discharges, and atmospheric deposition in contributing to these loads? These questions were addressed by first estimating the flux of nutrients from the Mississippi-Atchafalaya River Basin and about 50 interior basins in the Mississippi River system using measured historical streamflow and water quality data. Annual nutrient inputs and outputs to each basin were estimated using data from the National Agricultural Statistics Service, National Atmospheric Deposition Program, and point-source data provided by the USEPA. Next, a nitrogen mass balance was developed using agricultural statistics, estimates of nutrient cycling in agricultural systems, and a geographic information system. Finally, multiple regression models were developed to estimate the relative contributions of the major input sources to the flux of nitrogen and phosphorus to the Gulf of Mexico.

Heat-stress and light-stress induce different cellular pathologies in the symbiotic dinoflagellate during coral bleaching

Coral bleaching is a significant contributor to the worldwide degradation of coral reefs and is indicative of the termination of symbiosis between the coral host and its symbiotic algae (dinoflagellate; Symbiodinium sp. complex), usually by expulsion or xenophagy (symbiophagy) of its dinoflagellates. Herein, we provide evidence that during the earliest stages of environmentally induced bleaching, heat stress and light stress generate distinctly different pathomorphological changes in the chloroplasts, while a combined heat- and light-stress exposure induces both pathomorphologies; suggesting that these stressors act on the dinoflagellate by different mechanisms. Within the first 48 hours of a heat stress (32°C) under low-light conditions, heat stress induced decomposition of thylakoid structures before observation of extensive oxidative damage; thus it is the disorganization of the thylakoids that creates the conditions allowing photo-oxidative-stress. Conversely, during the first 48 hours of a light stress (2007 µmoles m−2 s−1 PAR) at 25°C, condensation or fusion of multiple thylakoid lamellae occurred coincidently with levels of oxidative damage products, implying that photo-oxidative stress causes the structural membrane damage within the chloroplasts. Exposure to combined heat- and light-stresses induced both pathomorphologies, confirming that these stressors acted on the dinoflagellate via different mechanisms. Within 72 hours of exposure to heat and/or light stresses, homeostatic processes (e.g., heat-shock protein and anti-oxidant enzyme response) were evident in the remaining intact dinoflagellates, regardless of the initiating stressor. Understanding the sequence of events during bleaching when triggered by different environmental stressors is important for predicting both severity and consequences of coral bleaching

2007 biennial report to Congress on the progress and findings of studies of striped bass populations

The 1997 reauthorization of the Atlantic Striped Bass Conservation Act (Striped Bass Act) mandated biennial reports to Congress and to the Atlantic States Marine Fisheries Commission (Commission) from the secretaries of the Department of Commerce and the Department of the Interior concerning the progress and findings of studies of Atlantic striped bass (Morone saxatilis). The Striped Bass Act specifically requests updates on studies that include, but are not limited to: annual stock assessments, investigations on the causes of fluctuations in Atlantic striped bass populations, the effects of environmental factors on the recruitment, spawning potential, mortality, and abundance of Atlantic striped bass populations, and investigations of interactions between Atlantic striped bass and other fish. This document is the fifth such report to Congress and includes data available through 2007 with emphasis on the 2005 and 2006 calendar years.

Accelerating loss of seagrasses across the globe threatens coastal ecosystems

Coastal ecosystems and the services they provide are adversely affected by a wide variety of human activities. In particular, seagrass meadows are negatively affected by impacts accruing from the billion or more people who live within 50 km of them. Seagrass meadows provide important ecosystem services, including an estimated $1.9 trillion per year in the form of nutrient cycling; an order of magnitude enhancement of coral reef fish productivity; a habitat for thousands of fish, bird, and invertebrate species; and a major food source for endangered dugong, manatee, and green turtle. Although individual impacts from coastal development, degraded water quality, and climate change have been documented, there has been no quantitative global assessment of seagrass loss until now. Our comprehensive global assessment of 215 studies found that seagrasses have been disappearing at a rate of 110 square kilometers per year since 1980 and that 29% of the known areal extent has disappeared since seagrass areas were initially recorded in 1879. Furthermore, rates of decline have accelerated from a median of 0.9% per year before 1940 to 7% per year since 1990. Seagrass loss rates are comparable to those reported for mangroves, coral reefs, and tropical rainforests and place seagrass meadows among the most threatened ecosystems on earth.

Age, growth, mortality, and distribution of pinfish (Lagodon rhomboides) in Tampa Bay and adjacent Gulf of Mexico waters

Life-history dynamics of pinfish (Lagodon rhomboides) were examined from data derived from random station surveys conducted in Tampa Bay and adjacent Gulf of Mexico waters during 1993–97. In addition, patterns in spatial distribution and abundance in Gulf of Mexico waters were investigated. Ages determined from whole otoliths ranged from 0 to 7 years, and von Bertalanffy growth models for males and females were not significantly different. Von Bertalanffy growth model parameters were L∞=219.9 mm SL, k =0.33/yr, and t0 =–1.10 years for all fish combined. High gonadosomatic indices during October–December indicated that some spawning may occur in Tampa Bay. Estimated lengths at 50% maturity were 132 mm SL for males and 131 mm SL for females. Total instantaneous mortality rates derived from the Chapman-Robson estimator ranged from 0.88 to 1.08/yr, and natural mortality was estimated to be 0.78/yr. In Gulf of Mexico waters, pinfish catch rates declined with increasing depth, and most pinfish were caught in <17 m of water. Length distributions showed that pinfish segregate by size with increasing depth.

Simulation and diagnosis of large-scale atmospheric moisture and surface hydrology over North America

We describe a preliminary investigation into large-scale atmospheric and surface moisture variations over North America. We compare large-scale hydrologic budgets in the Los Alamos general circulation model (GCM) to observed precipitation and vertically integrated atmospheric moisture fluxes derived from the National Meteorological Center's operational analyses. THe GCM faithfully simulates the integrated flux divergence and P-E differences. However, the integrated moisture content is too low, and precipitation and evaporation are too high. The model produces summertime soil moisture dryness, which supports previous studies showing increased droughts under warmer conditions.

The Los Alamos General Circulation Model hydrologic cycle

As the global population has increased, so have human influences on the global environment. ... How can we better understand and predict these natural and potential anthropogenic variations? One way is to develop a model that can accurately describe all the components of the hydrologic cycle, rather than just the end result variables such as precipitation and soil moisture. If we can predict and simulate variations in evaporation and moisture convergence, as well as precipitation, then we will have greater confidence in our ability to at least model precipitation variations. Therefore, we describe here just how well we can model relevant aspects of the global hydrologic cycle. In particular, we determine how well we can model the annual and seasonal mean global precipitation, evaporation, and atmospheric water vapor transport.

Chronological records of climate-related events and societal consequences [abstract]

EXTRACT (SEE PDF FOR FULL ABSTRACT): A chronology of documented regional and global warm and cold event records is collated along with documented ecosystem response records and health threat/sequellae records for the historical period. Patterns of societal response to cold periods punctuated by warm periods have been associated with considerable human health impacts, stimulated by blooms in disease vectors such as rodents and insects.