Reproduction in Gammarus (Crustacea, Amphipoda): female strategies

This paper attempts to review the literature on Gammarus and examine how it allocates its internal resources when producing eggs. There is an extensive literature on the fecundity of freshwater species but almost nothing is known about the sizes and energy contents of the eggs. More is known for saltwater species, in which the mean number of eggs per brood is inversely proportional to mean egg size and directly proportional to the female's body size. Theoretical aspects of egg size, numbers and reproductive effort are examined, along with the relation between sizes of eggs, broods and female body size. The reproductive effort and breeding cycles of both saltwater and freshwater species are reviewed, and reproductive strategies assessed.

Effects and impacts of physical stress on entrained organisms.

Environmental studies of power plants have recently shifted their emphasis from examination of the effects of heated discharges to studies of the impacts of entire cooling systems. One of the major impacts arises when planktonic organisms are carried into and through a plant with the cooling water. Because of their relatively immobile, free-floating character, planktonic organisms are highly vulnerable to being "entrained" or passively drawn into the cooling water condenser systems of power plants. More than 70% of estuarine animals have planktonic eggs and larvae. The environmental impact of entrainment is related to the composition and abundance of affected organisms, the numbers of organisms in the adjacent waters, survival rates during entrainment as related to natural survival, the ecological roles of entrained organisms, and their reproductive strategies.

Reproduction in Gammarus (Crustacea, Amphipoda): basic processes

Research on the basic reproduction processes of Gammarus is summarized and reviewed, reproductive strategies in males and females being left to two later papers. The author describes the reproductive systems, the development of eggs (oocytes) in the ovaries, courtship and precopulatory amplexus, mating and the production of sperms, egg laying, mortality and diapause.

Evaluation of the economic costs and benefits of methods for reducing nutrient loads to the Gulf of Mexico: Topic 6 Report for the Integrated Assessment on Hypoxia in the Gulf of Mexico.

In this report we analyze the Topic 5 report’s recommendations for reducing nitrogen losses to the Gulf of Mexico (Mitsch et al. 1999). We indicate the relative costs and cost-effectiveness of different control measures, and potential benefits within the Mississippi River Basin. For major nonpoint sources, such as agriculture, we examine both national and basin costs and benefits. Based on the Topic 2 economic analysis (Diaz and Solow 1999), the direct measurable dollar benefits to Gulf fisheries of reducing nitrogen loads from the Mississippi River Basin are very limited at best. Although restoring the ecological communities in the Gulf may be significant over the long term, we do not currently have information available to estimate the benefits of such measures to restore the Gulf’s long-term health. For these reasons, we assume that measures to reduce nitrogen losses to the Gulf will ultimately prove beneficial, and we concentrate on analyzing the cost-effectiveness of alternative reduction strategies. We recognize that important public decisions are seldom made on the basis of strict benefit–cost analysis, especially when complete benefits cannot be estimated. We look at different approaches and different levels of these approaches to identify those that are cost-effective and those that have limited undesirable secondary effects, such as reduced exports, which may result in lost market share. We concentrate on the measures highlighted in the Topic 5 report, and also are guided by the source identification information in the Topic 3 report (Goolsby et al. 1999). Nonpoint sources that are responsible for the bulk of the nitrogen receive most of our attention. We consider restrictions on nitrogen fertilizer levels, and restoration of wetlands and riparian buffers for denitrification. We also examine giving more emphasis to nitrogen control in regions contributing a greater share of the nitrogen load.

Coupling ecology and economy: modeling optimal release scenarios for summer flounder (Paralichthys dentatus) stock enhancement

Increasing interest in the use of stock enhancement as a management tool necessitates a better understanding of the relative costs and benefits of alternative release strategies. We present a relatively simple model coupling ecology and economic costs to make inferences about optimal release scenarios for summer flounder (Paralichthys dentatus), a subject of stock enhancement interest in North Carolina. The model, parameterized from mark-recapture experiments, predicts optimal release scenarios from both survival and economic standpoints for varyious dates-of-release, sizes-at-release, and numbers of fish released. Although most stock enhancement efforts involve the release of relatively small fish, the model suggests that optimal results (maximum survival and minimum costs) will be obtained when relatively large fish (75–80 mm total length) are released early in the nursery season (April). We investigated the sensitivity of model predictions to violations of the assumption of density-independent mortality by including density-mortality relationships based on weak and strong type-2 and type-3 predator functional responses (resulting in depensatory mortality at elevated densities). Depending on postrelease density, density-mortality relationships included in the model considerably affect predicted postrelease survival and economic costs associated with enhancement efforts, but do not alter the release scenario (i.e. combination of release variables) that produces optimal results. Predicted (from model output) declines in flounder over time most closely match declines observed in replicate field sites when mortality in the model is density-independent or governed by a weak type-3 functional response. The model provides an example of a relatively easy-to-develop predictive tool with which to make inferences about the ecological and economic potential of stock enhancement of summer flounder and provides a template for model creation for additional species that are subjects of stock enhancement interest, but for which limited empirical data exist.

Developing alternative shoreline armoring strategies: the living shoreline approach in North Carolina

This paper reviews the scientific data on the ecosystem services provided by shoreline habitats, the evidence for adverse impacts from bulkheading on those habitats and services, and describes alternative approaches to shoreline stabilization, which minimize adverse impacts to the shoreline ecosystem. Alternative shoreline stabilization structures that incorporate natural habitats, also known as living shorelines, have been popularized by environmental groups and state regulatory agencies in the mid-Atlantic. Recent data on living shoreline projects in North Carolina that include a stone sill demonstrate that the sills increase sedimentation rates, that after 3 years marshes behind the sills have slightly reduced biomass, and that the living shoreline projects exhibit similar rates of fishery utilization as nearby natural fringing marshes. Although the current emphasis on shoreline armoring in Puget Sound is on steeper, higher-energy shorelines, armoring of lower-energy shorelines may become an issue in the future with expansion of residential development and projected rates of sea level rise. The implementation of regulatory policy on estuarine shoreline stabilization in North Carolina and elsewhere is presented. The regulatory and public education issues experienced in North Carolina, which have made changes in estuarine shoreline stabilization policy difficult, may inform efforts to adopt a sustainable shoreline armoring strategy in Puget Sound. A necessary foundation for regulatory change in shoreline armoring policy, and public support for that change, is rigorous scientific assessment of the variety of services that natural shoreline habitats provide both to the ecosystem and to coastal communities, and evidence demonstrating that shoreline armoring can adversely impact the provision of those services.

Biology, ecology, control and management of the invasive Indo-Pacific lionfish: An updated integrated assessment

Venomous Indo-Pacific lionfish (Pterois miles and P. volitans) are now established along the Southeast U.S.A. and parts of the Caribbean and pose a serious threat to reef fish communities of these regions. Lionfish are likely to invade the Gulf of Mexico and potentially South America in the near future. Introductions of lionfish were noted since the 1980s along south Florida and by 2000 lionfish were established off the coast of North Carolina. Lionfish are now one of the more numerous predatory reef fishes at some locations off the Southeast U.S.A. and Caribbean. Lionfish are largely piscivores that feed occasionally on economically important reef fishes. The trophic impacts of lionfish could alter the structure of native reef fish communities and potentially hamper stock rebuilding efforts of the Snapper –Grouper Complex. Additional effects of the lionfish invasion are far-reaching and could increase coral reef ecosystem stress, threaten human health, and ultimately impact the marine aquarium industry. Control strategies for lionfish are needed to mitigate impacts, especially in protected areas. This integrated assessment provides a general overview of the biology and ecology of lionfish including genetics, taxonomy, reproductive biology, early life history and dispersal, venom defense and predation, and feeding ecology. In addition, alternative management actions for mitigating the negative impacts of lionfish, approaches for reducing the risk of future invasions, and directions for future research are provided.

Final Evaluation Memorandum: Strategies for Resolving Low Dissolved Oxygen and Methylmercury Events in Northern Suisun Marsh

The purpose of the project is to improve our understanding about best management practices that can be utilized on diked managed wetlands in Suisun Marsh for reducing the occurrence of low dissolved oxygen (DO) and high methylmercury (MeHg) events associated primarily with fall flood-up practices. Low DO events are of concern because they can lead to undue stress and even mortality of sensitive aquatic organisms. Elevated MeHg levels are of concern because MeHg is a neurotoxin that bio-magnifies up the food chain and can cause deleterious effects to higher trophic level consumers such as piscivorous fish, birds, and mammals (including humans). This study involved two years (2007-2008) of intensive field data collection at two managed wetland sites in northwest Suisun Marsh and their surrounding tidal sloughs, an area with prior documented low DO events. In addition, the study collected limited soils and water quality field data and mapped vegetation for three managed wetland sites in the central interior of Suisun Marsh, for the purpose of examining whether wetlands at other locations exhibit characteristics that could indicate potential for similar concerns. In Year 1 of the study, the objective was to identify the baseline conditions in the managed wetlands and determine which physical management conditions could be modified for Year 2 to reduce low DO and MeHg production issues most effectively. The objective of Year 2 was to evaluate the effectiveness of these modified management actions at reducing production of low DO and elevated MeHg conditions within the managed wetlands and to continue improving understanding of the underlying biogeochemical processes at play. This Final Evaluation Memorandum examined a total of 19 BMPs, 14 involving modified water management operations and the remaining five involving modified soil and vegetation management practices. Some of these BMPs were previously employed and others have not yet been tested. For each BMP this report assesses its efficacy in improving water quality conditions and potential conflicts with wetland management. It makes recommendations for further study (either feasibility assessments or field testing) and whether to consider for future use. Certain previously used BMPs were found to be important contributors to poor water quality conditions and their continued use is not recommended. Some BMPs that could improve water quality conditions appear difficult to implement in regards to compatibility with wetland management; these BMPs require further elaboration and feasibility assessment to determine whether they should be field tested. In practice for any given wetland, there is likely a combination of BMPs that would together have the greatest potential to address the low DO and high MeHg water quality concerns. Consequently, this report makes no sweeping recommendations applicable to large groups of wetlands but instead promotes a careful consideration of factors at each wetland or small groups of wetlands and from that assessment to apply the most effective suite of BMPs. This report also identifies a number of recommended future actions and studies. These recommendations are geared toward improving the process understanding of factors that promote low DO and high MeHg conditions, the extent of these problems in Suisun Marsh, the regulatory basis for the DO standards for a large estuarine marsh, the economics of BMPs, and alternative approaches to BMPs on diked managed wetlands that may address the water quality issues. The most important of these recommendations is that future BMP implementation should be carried out within the context of rigorous scientific evaluation so as to gain the maximum improvement in how to manage these water quality issues in the diked managed wetlands of Suisun Marsh.

Age and size composition, growth rate, reproductive biology, and habitats of the West Australian dhufish (Glaucosoma hebraicum) and their relevance to the management of this species

Samples of the commercially and recreationally important West Australian dhufish (Glaucosoma hebraicum) were obtained from the lower west coast of Australia by a variety of methods. Fish <300 mm TL were caught over flat, hard substrata and low-lying limestone reefs, whereas larger fish were caught over larger limestone and coral reef formations. Maximum total lengths, weights, and ages were 981 mm, 15.3 kg, and 39 years, respectively, for females and 1120 mm, 23.2 kg, and 41 years, respectively, for males. The von Bertalanffy growth curves for females and males were significantly different. The values for L∞, k, and t0 in the von Bertalanffy growth equations were 929 mm, 0.111/year, and –0.141 years, respectively, for females, and 1025 mm, 0.111/year, and –0.052 years, respectively, for males. Preliminary estimates of total mortality indicated that G. hebraicum is now subjected to a level of fishing pressure that must be of concern to fishery managers. Glaucosoma hebraicum, which spawns between November and April and predominantly between December and March, breeds at a wide range of depths and is a multiple spawner. The L50’s for females and males at first maturity, i.e. 301 and 320 mm, respectively, were attained by about the end of the third year of life and are well below the minimum legal length (MLL) of 500 mm. Because females and males did not reach the MLL until the end of their seventh and sixth years of life, respectively, they would have had, on average, the opportunity of spawning during four and three spawning seasons, respectively, before they reached the MLL. However, because G. hebraicum caught in water depths >40 m typically die upon release, a MLL is of limited use for conserving this species. Alternative approaches, such as restricting fishing activity in highly fished areas, reducing daily bag limits for recreational fishermen, introducing quotas or revising specific details of certain commercial hand-line licences (or doing both) are more likely to provide effective conservation measures.