Restoration of a brown trout (Salmo trutta L.) population to Loch Enoch, an acified Loch in Galloway, South-West Scotland

The authors present the findings of a restoration project in Loch Enoch in Scotland. There are historical references that brown trout was present in Loch Enoch up to the 1920s but it is believed the acidity of loch triggered the disappearance of Salmo trutta. The recent observed reduction in the acidity of L. Enoch to a level close to that found in nearby lochs with trout populations, suggested that trout might now survive in L. Enoch. For a population to survive, all stages in the life-cycle of a species must be able to develop. Accordingly, tests were undertaken, first with eggs and fry. The availability of food was also studied. In October 1994, 3,000 yearling trout of L. Grannoch origin which had been reared in a local hatchery were distributed throughout the loch. The fish population was studied from 1995-98. The authors conclude that survival of the trout population is possible if the acidity of the loch water remains low.

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.

Using productivity and susceptibility indices to assess the vulnerability of United States fish stocks to overfishing

Assessing the vulnerability of stocks to fishing practices in U.S. federal waters was recently highlighted by the National Marine Fisheries Service (NMFS), National Oceanic and Atmospheric Administration, as an important factor to consider when 1) identifying stocks that should be managed and protected under a fishery management plan; 2) grouping data-poor stocks into relevant management complexes; and 3) developing precautionary harvest control rules. To assist the regional fishery management councils in determining vulnerability, NMFS elected to use a modified version of a productivity and susceptibility analysis (PSA) because it can be based on qualitative data, has a history of use in other fisheries, and is recommended by several organizations as a reasonable approach for evaluating risk. A number of productivity and susceptibility attributes for a stock are used in a PSA and from these attributes, index scores and measures of uncertainty are computed and graphically displayed. To demonstrate the utility of the resulting vulnerability evaluation, we evaluated six U.S. fisheries targeting 162 stocks that exhibited varying degrees of productivity and susceptibility, and for which data quality varied. Overall, the PSA was capable of differentiating the vulnerability of stocks along the gradient of susceptibility and productivity indices, although fixed thresholds separating low-, moderate-, and highly vulnerable species were not observed. The PSA can be used as a flexible tool that can incorporate regional-specific information on fishery and management activity.

Standard and routine metabolic rates of juvenile sandbar sharks (Carcharhinus plumbeus), including the effects of body mass and acute temperature change*

Standard and routine metabolic rates (SMRs and RMRs, respectively) of juvenile sandbar sharks (Carcharhinus plumbeus) were measured over a range of body sizes (n=34) and temperatures normally associated with western Atlantic coastal nursery areas. The mean SMR Q10 (increase in metabolic rate with temperature) was 2.9 ±0.2. Heart rate decreased with increasing body mass but increased with temperature at a Q10 of 1.8−2.2. Self-paired measures of SMR and RMR were obtained for 15 individuals. Routine metabolic rate averaged 1.8 ±0.1 times the SMR and was not correlated with body mass. Assuming the maximum metabolic rate of sandbar sharks is 1.8−2.75 times the SMR (as is observed in other elasmobranch species), sandbar sharks are using between 34% and 100% of their metabolic scope just to sustain their routine continuous activity. This limitation may help to explain their slow individual and population growth rates, as well as the slow recoveries from overfishing of many shark stocks worl

Estimating consumption rates of juvenile sandbar sharks (Carcharhinus plumbeus) in Chesapeake Bay, Virginia, using a bioenergetics model*

Using a bioenergetics model, we estimated daily ration and seasonal prey consumption rates for six age classes of juvenile sandbar sharks (Carcharhinus plumbeus) in the lower Chesapeake Bay summer nursery area. The model, incorporating habitat and species-specific data on growth rates, metabolic rate, diet composition, water temperature (range 16.8−27.9°C), and population structure, predicted mean daily rations between 2.17 ±0.03 (age-0) and 1.30 ±0.02 (age-5) % body mass/day. These daily rations are higher than earlier predictions for sandbar sharks but are comparable to those for ecologically similar shark species. The total nursery population of sandbar sharks was predicted to consume ~124,000 kg of prey during their 4.5 month stay in the Chesapeake Bay nursery. The predicted consumption rates support the conclusion that juvenile sandbar sharks exert a lesser top-down effect on the Chesapeake Bay ecosystem than do teleost piscivores and hu

A Review of Indian Ocean Fisheries for Skipjack Tuna, Katsuwonus pelamis, and Yellowfin Tuna, Thunnus albacares

Skipjack tuna, Katsuwonus pelamis, and yellowfin tuna, Thunnus albacares, together comprise the most important component of Indian Ocean tuna catches. Catches of these species by Indian Ocean fisheries have been increasing over the last decade and totaled 262,300 metric tons (t) in 1986 (Fig. 1; Table 1). Skipjack tuna was the most important species at 32 percent of the total tuna catch in 1986; yellowfin tuna was the second most important at 25 percent. Skipjack tuna are found throughout the Indian Ocean from the Gulf of Arabia in the north to lat. 40°S (Fig. 2). Yellowfin tuna are also distributed throughout the ocean to about lat. 50�

U. S. Trade in Tuna for Canning, 1987

U.S. tuna fleet activity, canned tuna processing, ex-vessel, wholesale and retail prices and imports in 1987 are described and compared to their counterparts in previous years. Industry statistics gathered from government agencies and industry contacts are presented in 14 figures and 8 tables. In 1987, U.S. tuna fisheries delivered 253,136 short tons (tons) of tuna to U.S. canneries. Domestic deliveries of albacore (white-meat) tuna were 2,836 tons, down 20 percent from 1986 levels. Domestic deliveries of tropical (light-meat) tuna (bigeye, blackfin, bluefin, skipjack, and yellowfin) were 251,000 tons, up 12 percent. Contract prices for tuna delivered by U. S. vessels to U. S. canneries increased dramatically in 1987. Depending on the size of fish in the delivery, ex-vessel prices of white-meat tuna increased as much as 27 percent, and prices of light-meat tuna increased as much as 47 percent. U. S. cannery receipts of imported and domestically caught raw frozen tuna for canning totaled 532,704 tons in 1987, up 2 percent from 1986 levels. U.S. cannery receipts of white-meat tuna were 104,197 tons, down 10 percent from 1986. Imports made up 97 percent of the total cannery supply. Total 1987 U. S. cannery receipts of raw, frozen light meat tuna were 428,507 tons, up 5 percent from 1986 levels. Imports made up 41 percent of the total cannery supply. The 1987 U.S. pack of canned tuna was 33.6 million standard cases, up 3 percent from 1986. The pack of white-meat tuna was 7.2 million standard cases, down 11 percent from 1986; the pack of light-meat tuna was 26.4 million standard cases, up 7 percent. U. S. imports of canned tuna in 1987 were 10.8 million standard cases, down 11 percent from 1986 levels, the first time in recent years that imports have declined. Per capita consumption of canned tuna in the United States was 3.5 pounds in 1987, down slightly from 1986. The retail composite price was $2.26 per pound, unchanged from 1986.