Plankton populations at the bifurcation of the North Pacific Current

As the eastward‐flowing North Pacific Current approaches the North American continent it bifurcates into the southward‐flowing California Current and the northward‐flowing Alaska Current. This bifurcation occurs in the south‐eastern Gulf of Alaska and can vary in position. Dynamic height data from Project Argo floats have recently enabled the creation of surface circulation maps which show the likely position of the bifurcation; during 2002 it was relatively far north at ∼53°N then, during early 2003, it moved southwards to a more normal position at ∼45°N. Two ship‐of‐opportunity transects collecting plankton samples with a Continuous Plankton Recorder across the Gulf of Alaska were sampled seasonally during 2002 and 2003. Their position was dependent on the commercial ship’s operations; however, most transects sampled across the bifurcation. We show that the oceanic plankton differed in community composition according to the current system they occurred in during spring and fall of 2002 and 2003, although winter populations were more mixed. Displacement of the plankton communities could have impacts on the plankton’s reproduction and development if they use cues such as day length, and also on foraging of higher trophic‐level organisms that use particular regions of the ocean if the nutritional value of the communities is different. Although we identify some indicator taxa for the Alaska and California currents, functional differences in the plankton communities on either side of the bifurcation need to be better established to determine the impacts of bifurcation movement on the ecosystems of the north‐east Pacific.     

Transnational Ecosystem Services: The Potential of Habitat Conservation for Waterfowl Through Recreational Hunting Activities

This article explores transnational ecosystem services in North America, provided by winter habitat for waterfowl in western Mexico coastal lagoons, and the hunting industry supported by these birds in the United States. This article shows that the number of waterfowl harvested in the United States is related to the abundance of waterfowl wintering in Mexico. On average, this flow of ecosystem services annually yields US$ 4.68 million in hunting stamp sales in the western United States. A demand curve, fitted to duck hunting licenses as a function of stamp price and previous-year waterfowl harvest, estimated US$3–6 million in consumer surplus produced in addition to governmental stamp sales revenue. This strongly suggests that waterfowl wintering habitat in western Mexico is economically valuable to U.S. hunters. Because hunters may benefit substantially from these habitats they may be willing to pay for conservation efforts in western Mexico that can result in transnational benefits received in the United States.     

极端低温对红圆蚧Aonidiella aurantii(Mask.)死亡率的影响

本研究探讨用Abdelrahman(1974)回归方程式预测田间自然条件下由极端低温造成的红圆蚧死亡率的可能性。结果表明极端低温引起的诸幼龄红圆蚧死亡率的实际观察值与用方程式计算所得的期望值相似;但对诸老龄红圆蚧来说,观察值明显地小于期望值。     

极端温度持续时间对红圆蚧(同翅目;盾蚧科)死亡率的影响

测定了极端温度(-2,+5及+45℃)持续时间(0至8小时)对红圆蚧 Aonidiella aura-ntii(Mask.)死亡率的影响,同时观察了红圆蚧在+10℃和+25℃恒温下的死亡率.在低温实验中,除了3龄雌虫及第二脱皮阶段雄虫外,红圆蚧大多数龄期、虫期在极端温度-2或+5℃的死亡率明显高于+10℃恒温时的死亡率。在高温实验中,红圆蚧在极端温度+45℃与在+25℃恒温下的死亡率相似;+45℃高温仅对第一脱皮阶段红圆蚧(不分雌雄)及第二脱皮阶段雄虫死亡率有明显影响。经历过+45℃高温处理的3龄雌虫,如能存活下来,成虫生殖能力与在+25℃恒温下生活的虫子相比没有差异。     

Identifying vulnerabilities, exploring opportunities: reconfiguring production, conservation, and consumption in California rice

This paper describes a role for rural sociology in linking agrifood system vulnerabilities to opportunities for encouraging sustainability and social justice. I argue that the California rice industry is particularly vulnerable for two reasons. First, a quarter of rice growers’ revenues derive from production-based subsidies that have been recently deemed illegal by the World Trade Organization. Second, about half of California’s rice sales depend on volatile export markets, which are susceptible to periodic market access disruptions. Such vulnerabilities present political opportunities to reconfigure the connection between production and consumption. By exploring how production subsidies could be transformed into multifunctionality payments, and investigating new regional markets, rural sociology can contribute to discussions about how to encourage a more sustainable and socially just California rice industry. My discussion aims to prompt rural sociologists to explore similar questions in comparable agrifood systems.

Evaluating alternative rodenticides for island conservation: roof rat eradication from the San Jorge Islands, Mexico

Introduced commensal rats (Rattus spp.) are a major contributor to the extinction and endangerment of island plants and animals. The use of the toxin brodifacoum to completely eradicate rats from islands is a powerful conservation tool. However, brodifacoum is toxic to animals other than rats and on some islands its use may not be feasible without prohibitively expensive mitigation. As part of a regional conservation program, we experimentally tested brodifacoum and two less toxic rodenticides, diphacinone and cholecalciferol, in eradicating Rattus rattus from three small islands in the northern Gulf of California, Mexico. All three rodenticides were successful in eradicating rats, suggesting that the less toxic diphacinone and cholecalciferol may be useful alternatives to brodifacoum for some island eradication programs. However, the choice of rodenticide must be balanced between efficacy and the risks to non-target species. Applied field research is needed on less toxic rodenticides, as well as improving palatability of baits. This may prove invaluable in preventing extinctions and in restoring larger and more diverse island ecosystems.     

Genetic differentiation in hatchery strains and wild white shrimp Penaeus (Litopenaeus) vannamei (Boone, 1931) from northwest Mexico

Ten enzymatic systems were analyzed to determine allozyme genetic differentiation among three hatchery strains (A, B and C) of white shrimp, Penaeus (Litopenaeus) vannamei, commonly used in shrimp farming in northwest Mexico. A wild population from northern Sinaloa was used as a reference. Fifteen loci were detected, nine of which were polymorphic (ACP-1*, ACP-2*, AKP-2*, EST-2*, EST-3*, EST-4*, EST-5*, LAP*, and LDH*). Polymorphism of A, B and C were 53, 53, and 40%. The mean observed heterozygosity per locus was 0.071, 0.093, and 0.050 without any significant difference among them or with respect to the wild population (0.056). In all samples observed heteroxygosity was smaller than expected. The mean number of alleles per locus was 1.8 in A and 1.87 in both B and C. Strain A was the only sample without rare alleles. Only EST-3* and LAP* of strain A were in Hardy-Weinberg equilibrium; the other loci were in disequilibrium in all samples. High inbreeding values and heterozygote deficiencies were detected in all samples. Distribution of allelic frequencies was heterogeneous among the samples (G-test), involving all polymorphic loci and suggesting a genetic differentiation. According to Fst, a moderate genetic differentiation (7.4%) was detected among the samples. Greater differences were between strains A and C. Based on genetic distance, the samples were grouped into two pairs, B-C and A-wild. Strain A is a young strain related to the wild sample, whereas strains B and C have a different geographic origin than the wild sample.     

Changes in marine faunal distributions and ENSO events in the California Current

Interannual variability in the California Current System is analyzed through its effects on the temporal distribution of fauna, particularly southern-origin organisms moving north during warming events and south during cooling ones. In temperate waters north of 24°N latitude, northward movements of southern fauna occur at intervals of about 5 yr. This is different from El Niño events, whose frequency of occurrence is mostly centered in the 3-yr period but with considerable dispersion. Possible causes for northward displacement of fauna include relaxation of the California Current, intensification of the countercurrent, and the formation and persistence of mesoscale eddies among others. Strong events appear to be a consequence of the decadal variation peaks.