Optimal harvesting of farmed Atlantic salmon at two cohort management strategies and different harvest operation restrictions

Abstract

The main harvest planning problem in commercial fish farms is to determine the best time‐sequence of harvesting different fish cohorts in order to maximize the overall farm profit. Due to both annual and fish‐size variations in market prices, future forecasts of fish growth and size distribution are required to optimize harvest plans. Two management strategies for harvesting size‐structured fish cohorts are considered. The first strategy allows the fish farmer, at any time, to size‐grade, harvest and sell the most profitable fish sizes from the standing stock. The second strategy allows the fish farmer to harvest and sell a fish batch with similar size distribution as that of the standing stock. In this paper, two size‐structured fish growth models have been built to fit the two management strategies. The growth models are integrated in a multiperiod linear programming model that optimizes the harvest outputs for each of the two management strategies. Model outputs demonstrate clearly that it is more profitable to size‐grade fish prior to harvest compared to harvesting a batch of fish with similar size distribution to that of the standing stock. Five different harvest operations constraints have been identified for commercial salmon farming. The decrease in profitability of fish farming is shown for a variety of harvest operation constraints.     

Risk factor analysis for sea lice, Caligus rogercresseyi, levels in farmed salmonids in southern Chile

Sea lice, Caligus rogercresseyi, are ectoparasitic copepods, which severely affect the salmon farming industry in southern Chile, reducing the health status of fish and producing both direct and indirect economic losses. Local farmers have reported increasing infestation levels since 2004, reaching a peak in 2007. In response to this situation, the Chilean Fisheries Service (Sernapesca) developed a surveillance programme; the first step of which consisted of a general survey of salmon farms. This survey included documenting counts of parasite burdens on fish and measurements of several husbandry and environmental factors providing an evaluation of risk factors for the observed infestation levels. The information collected was analysed using a linear mixed model technique, which takes into account the clustered structure of data, decomposing the unexplained variation and assigning it to different aggregation levels of the productive system. Geographical zones, fish species, treatment against sea lice performed 1 month before sampling, stocking density, fish weight and water salinity were the variables significantly associated with sea lice burdens. In contrast, treatments performed 2-3 months before sampling, use of photoperiod in sea cages and water temperature, were not significant. There was significant unexplained variation at all aggregation levels, i.e. sub-zone, fish farm and cage level, with the fish farm level showing the greatest variation.     

Influences of mean advection and simple behavior on the distribution of cod and haddock early life stages on Georges Bank

Results of a modeling study designed to explore the influences of physical advection and certain biological mechanisms on the distribution of cod (Gadus morhua) and haddock (Melarwgrammus aeglefinus) early life stages on Georges Bank are described. Using a late-winter/early-spring 3-D circulation field driven by the M₂ tidal current, mean wind stress and Scotian Shelf inflow, we examine the distribution of cod and haddock larvae spawned on the Northeast Peak of the Bank. The sensitivity to a March-April baroclinic field is also explored. Results indicate that larvae remaining in the surface Ekman layer are generally advected off-bank. However, downwelling associated with Ekman layer convergence near the shelf break provides a mechanism for larvae to exit from the off-bank surface drift. Larvae below the surface layer are transported south-westward along the southern flank of Georges Bank and are retained on the Bank if their position immediately upstream of the Great South Channel is shoalward of (roughly) the 70 m isobath. Within the Great South Channel region and between the 50 and 70 m isobaths, retention can depend on the phase of the tide. Spawning shoalward of the 50 m isobath on the Northeast Peak greatly increases the chances of retention. These results apply to passive larvae and to those with specified vertical distributions and migration based on observations. Directional on-bank swimming at rates of 0.5 to 1 body length per second would substantially enhance shoalward displacement, resulting in larval distributions during the first 2 months that are consistent with field observations.     

邵东县水田种植制度优化模型的研究

本文应用线性规划原理,建立了湖南中部丘陵地区邵东县水田种植制度优化模型。优化过程中,以净产值(不包括利息和税金)为目标函数,对总面积、主要作物播种面积、适宜用地、冬闲田等进行了约束。优化结果净产值可增加17801900元,增长了14.4%。     

Habitat associations of the Threatened pugnose minnow (Opsopoeodus emiliae) at the northern edge of the species range

Pugnose minnow (Opsopoeodus emiliae) is a small, reclusive species that is widespread in North America, but is one of the rarest fishes in Canada, found in less than 12 known localities in southwestern Ontario. In contrast to most pugnose minnow populations across the global range, Canadian populations are primarily found in turbid systems, potentially indicating persistence in suboptimal conditions. We used data from a multi-gear species and habitat survey in the Canard River, Ontario, a system dominated by agricultural inputs and the best-known capture site of the species in Canada, to parameterise multi-gear occupancy models for understanding the relationship between pugnose minnow occupancy and microhabitat features, including the role of turbidity. Almost 300 pugnose minnow were captured, representing the largest single collection of the species in Canadian history. The best occupancy model indicated that the probability of pugnose minnow occupancy was highest in the deepest sites with the lowest water clarity (i.e. high turbidity); however, competing models suggested that occupancy was highest at sites with wild celery (Vallisneria americana) and higher water clarity, signifying that habitats with low turbidity may be utilised if sufficient physical cover exists. Together, our results suggest that Canadian pugnose minnow populations occupy and potentially favour turbid conditions, possibly to avoid visual predators in clearer habitats. It remains uncertain whether this abiotic association represents a long-term, viable, local adaptation or whether persistence of pugnose minnow in the Canard River is at risk unless significant water quality improvements can be made.     

空间约束混合高斯运动目标检测

目的 针对传统混合高斯模型前景检测运算量过大问题,提出一种基于空间约束的混合高斯前景检测算法。方法 通过快速初始化缩短模型的初始建立过程;采用双重背景模型机制,以自适应背景减法的前景检测结果作为混合高斯前景检测的空间约束条件,降低模型在背景区域的冗余运算;运用多策略自适应模型更新,提高前景检测的准确性。结果 在各种测试场景下,与传统混合高斯法、CodeBook、GMG、偏差均值混合高斯模型(MODGMM)等算法相比,该算法具有更好的准确率以及4倍以上的处理速度。结论 在固定相机场景下的运动目标检测中,算法能有效提高传统混合高斯法的准确性且具有极高的实时性。     

Preliminary recovery of coastal sharks in the south‐east United States

Relative abundance of many shark species in the Atlantic is assessed by compiling data from several independently conducted, but somewhat spatially limited surveys. Although these localized surveys annually sample the same populations, resulting trends in yearly indices often conflict with one another, thereby hindering interpretation of abundance patterns at broad spatial scales. We used delta‐lognormal generalized linear models (GLMs) to generate indices of abundance for seven Atlantic coastal shark species from six fishery‐independent surveys along the US east coast and Gulf of Mexico from 1975 to 2014. These indices were further analysed using dynamic factor analysis (DFA) to produce simplified, broad‐scale common trends in relative abundance over the entire sampled distribution. Effects of drivers including the North Atlantic Oscillation index, the Atlantic Multidecadal Oscillation index, annually averaged sea surface temperature and species landings were evaluated within the DFA model. The two decadal oscillations and species landings were shown to affect shark distribution along south‐east US coast. Estimated common trends of relative abundance for all large coastal shark species showed similar decreasing patterns into the early 1990s, periods of sustained low index values thereafter and recent indications of recovery. Small coastal shark species exhibited more regional variability in their estimated common trends, such that two common trends were required to adequately describe patterns in relative abundance throughout the Gulf of Mexico and Atlantic. Overall, all species’ (except the Gulf of Mexico blacknose shark) time series concluded with an increasing trend, suggestive of initial recovery from past exploitation.     

基于有效积温的中国水稻生长模型的构建

有效积温是指作物生长至某一生育阶段所需要积累的有效温度,是反映气象条件对作物生长影响的主要指标,研究有效积温对作物生长过程的影响对提高农业生产效率具有重要意义。该文以有效积温作为气象因子,收集中国气象数据网中的气象数据和已发表的学术论文中的水稻生长数据,建立了描述水稻生长过程的叶面积指数和干物质积累量的普适Logistic模型,并研究了水稻最大叶面积指数与最大干物质积累量、收获指数(作物经济产量与生物产量的比值)及降水量之间的关系。结果表明:有效积温为1000℃左右时,水稻叶面积指数最大,且此时干物质增长速率最大;水稻最大叶面积指数与最大干物质积累量之间表现为线性关系;最大叶面积指数和收获指数、降水量之间为二次抛物线关系,当降水量为670.5 mm时,最大叶面积指数为7.93,对应的水稻收获指数达到最大值0.50。该研究对于构建其他作物的生长模型具有一定的参考意义。     

Giants' shoulders 15 years later: lessons,challenges and guidelines in fisheries meta‐analysis

Meta‐analysis has been an integral tool for fisheries researchers since the late 1990s. However, there remain few guidelines for the design, implementation or interpretation of meta‐analyses in the field of fisheries. Here, we provide the necessary background for readers, authors and reviewers, including a brief history of the use of meta‐analysis in fisheries, an overview of common model types and distinctions, and examples of different goals that can be achieved using meta‐analysis. We outline the primary challenges in implementing meta‐analyses, including difficulties in discriminating between alternative hypotheses that can explain the data with equal plausibility, the importance of validating results using multiple lines of evidence, the trade‐off between complexity and sample size and problems associated with the use of model output. For each of these challenges, we also provide suggestions, such as the use of propensity scores for dealing with selection bias and the use of covariates to control for confounding effects. These challenges are then illustrated with examples from diverse subfields of fisheries, including (i) the analysis of the stock–recruit relationship, (ii) fisheries management, rebuilding and population viability, (iii) habitat‐specific vital rates, (iv) life‐history theory and (v) the evaluation of marine reserves. We conclude with our reasons for believing that meta‐analysis will continue to grow in importance for these and many other research goals in fisheries science and argue that standards of practice are therefore essential.