Vulnerability of individual fish to capture by trawling is influenced by capacity for anaerobic metabolism

The harvest of animals by humans may constitute one of the strongest evolutionary forces affecting wild populations. Vulnerability to harvest varies among individuals within species according to behavioural phenotypes, but we lack fundamental information regarding the physiological mechanisms underlying harvest-induced selection. It is unknown, for example, what physiological traits make some individual fish more susceptible to capture by commercial fisheries. Active fishing methods such as trawling pursue fish during harvest attempts, causing fish to use both aerobic steady-state swimming and anaerobic burst-type swimming to evade capture. Using simulated trawling procedures with schools of wild minnows Phoxinus phoxinus, we investigate two key questions to the study of fisheries-induced evolution that have been impossible to address using large-scale trawls: (i) are some individuals within a fish shoal consistently more susceptible to capture by trawling than others?; and (ii) if so, is this related to individual differences in swimming performance and metabolism? Results provide the first evidence of repeatable variation in susceptibility to trawling that is strongly related to anaerobic capacity and swimming ability. Maximum aerobic swim speed was also negatively correlated with vulnerability to trawling. Standard metabolic rate was highest among fish that were least vulnerable to trawling, but this relationship probably arose through correlations with anaerobic capacity. These results indicate that vulnerability to trawling is linked to anaerobic swimming performance and metabolic demand, drawing parallels with factors influencing susceptibility to natural predators. Selection on these traits by fisheries could induce shifts in the fundamental physiological makeup and function of descendent populations.     

Aerobic endurance, anatomical factors and time properties of laser Doppler recorded skin postocclusive hyperaemia

Aerobic endurance capacity is partly dependent on blood supply to and metabolic capacity of the active muscles. Recordings of lower limb skin postocclusive hyperaemia with laser Doppler flowmetry can differentiate between patients with lower limb atherosclerosis and healthy controls. In this study, we investigated the relationship between aerobic endurance, calf volume, common femoral artery diameter and time properties of the postocclusive laser Doppler curve. A group of 16 healthy male subjects with values for aerobic endurance which varied from those of untrained men to elite endurance trained athletes were examined. Duration of laser Doppler recorded skin postocclusive hyperaemia was significantly correlated to both aerobic power and anaerobic threshold (P less than 0.01). Hyperaemia in subjects with large common femoral artery diameter was of shorter duration (P less than 0.05). The peak and mean body mass related blood flow during hyperaemia was correlated to anaerobic threshold (P less than 0.05). These results were in agreement with previous studies indicating an effect of endurance training on the blood supply to the muscles concerned.     

秦岭细鳞鲑与拉氏鱥代谢特征及游泳能力的比较

为探究秦岭细鳞鲑(Brachymystax tsinlingensis)与其主要猎物鱼拉氏鱥(Phoxinus lagowskii)游泳能力的种间差异及其生理机制, 采用鱼类游泳代谢仪, 分别测定了两种实验鱼野生种群有氧运动能力[步法转换速度Gait transition speed (U_gait)和临界游泳速度Critical swimming speed (U_crit)]、无氧运动能力[匀加速游泳速度Constant acceleration test speed (U_cat)]、静止代谢率(Resting metabolic rate, RMR)、最大代谢率(Maximum metabolic rate, MMR)、有氧代谢空间(Aerobic metabolic scope, MS)、运动耗氧率及单位距离运动能耗(Energetic cost of transport, COT)等。结果表明: (1)秦岭细鳞鲑U_crit和U_cat高于拉氏鱥(P<0.05), 但二者rU_gait、rU_crit和rU_cat差异不显著(P>0.05); (2)秦岭细鳞鲑RMR、MMR、MS等代谢特征均显著高于拉氏鱥(P<0.05), 并且特定流速下秦岭细鳞鲑运动耗氧率及COT高于拉氏鱥; (3)秦岭细鳞鲑U_crit与MS、MMR呈现出显著正相关或正相关的趋势, 拉氏鱥U_crit与其MS和MMR均无显著相关性(P>0.05)。研究结果提示, 整体上秦岭细鳞鲑与拉氏鱥的相对游泳能力相近, 但秦岭细鳞鲑的游泳效率更低; 秦岭细鳞鲑的代谢潜能更大, 代谢潜能是维持其运动表现的重要动力。     

不同温度条件下运动和摄食对细鳞鲑幼鱼代谢模式的影响

为了揭示不同温度条件下运动和摄食对细鳞鲑幼鱼代谢模式的影响,在饱和溶氧(>8.0 mg·L^-1)条件下,分别测定了空腹组和摄食组在5个处理温度(4、8、12、16和20 ℃)下的运动前代谢率(MO_2p)、活跃代谢率(MO_2a)、代谢范围(MS)、临界游泳速度(U_C)以及10个流速水平下的实时游泳代谢率(MR).结果表明: 在各个温度条件下,摄食组的MO_2p和MO_2a均显著高于空腹组(P<0.05),且分别提高了15%和12%(4 ℃)、47%和23%(8 ℃)、30%和21%(12 ℃)、43%和36%(16 ℃)及8%和7%(20 ℃);摄食组与空腹组的U_C和MS均无显著性差异(P>0.05),但随着温度升高,两组的MS均呈现下降趋势;随流速的增加,各组的游泳代谢率呈先升高后降低的变化规律,且摄食组显著大于空腹组(P<0.05),各组的最大代谢率峰值均出现在低于U_C的流速条件下;在细鳞鲑幼鱼的游泳速度接近70%U_C的运动过程中,其代谢率不断增大至峰值,随后在游泳速度达到U_C的过程中,代谢率呈下降趋势.表明在一定温度范围条件下,细鳞鲑幼鱼的最大代谢率是由运动与摄食共同诱导产生的,在达到最大代谢率峰值的过程中代谢表现为添加模式;之后随游泳代谢率的下降,摄食诱导的代谢率被削减,该过程表现为运动优先代谢模式.     

Modelling the future hydroclimatology of the lower Fraser River and its impacts on the spawning migration survival of sockeye salmon

Short episodic high temperature events can be lethal for migrating adult Pacific salmon (Oncorhynchus spp.). We downscaled temperatures for the Fraser River, British Columbia to evaluate the impact of climate warming on the frequency of exceeding thermal thresholds associated with salmon migratory success. Alarmingly, a modest 1.0 °C increase in average summer water temperature over 100 years (1981–2000 to 2081–2100) tripled the number of days per year exceeding critical salmonid thermal thresholds (i.e. 19.0 °C). Refined thresholds for two populations (Gates Creek and Weaver Creek) of sockeye salmon (Oncorhynchus nerka) were defined using physiological constraint models based on aerobic scope. While extreme temperatures leading to complete aerobic collapse remained unlikely under our warming scenario, both populations were increasingly forced to migrate upriver at reduced levels of aerobic performance (e.g. in 80% of future simulations, ≥90% of salmon encountered temperatures exceeding population‐specific thermal optima for maximum aerobic scope; T_opt=16.3 °C for Gates Creek and T_opt=14.5 °C for Weaver Creek). Assuming recent changes to river entry timing persist, we also predicted dramatic increases in the probability of freshwater mortality for Weaver Creek salmon due to reductions in aerobic, and general physiological, performance (e.g. in 42% of future simulations≥50% of Weaver Creek fish exceeded temperature thresholds associated with 0–60% of maximum aerobic scope). Potential for adaptation via directional selection on run‐timing was more evident for the Weaver Creek population. Early entry Weaver Creek fish experienced 25% (range: 15–31%) more suboptimal temperatures than late entrants, compared with an 8% difference (range: 0–17%) between early and late Gates Creek fish. Our results emphasize the need to consider daily temperature variability in association with population‐specific differences in behaviour and physiological constraints when forecasting impacts of climate change on migratory survival of aquatic species.     

Adapt,move or die – how will tropical coral reef fishes cope with ocean warming?

Previous studies hailed thermal tolerance and the capacity for organisms to acclimate and adapt as the primary pathways for species survival under climate change. Here we challenge this theory. Over the past decade, more than 365 tropical stenothermal fish species have been documented moving poleward, away from ocean warming hotspots where temperatures 2–3 °C above long‐term annual means can compromise critical physiological processes. We examined the capacity of a model species – a thermally sensitive coral reef fish, Chromis viridis (Pomacentridae) – to use preference behaviour to regulate its body temperature. Movement could potentially circumvent the physiological stress response associated with elevated temperatures and may be a strategy relied upon before genetic adaptation can be effectuated. Individuals were maintained at one of six temperatures (23, 25, 27, 29, 31 and 33 °C) for at least 6 weeks. We compared the relative importance of acclimation temperature to changes in upper critical thermal limits, aerobic metabolic scope and thermal preference. While acclimation temperature positively affected the upper critical thermal limit, neither aerobic metabolic scope nor thermal preference exhibited such plasticity. Importantly, when given the choice to stay in a habitat reflecting their acclimation temperatures or relocate, fish acclimated to end‐of‐century predicted temperatures (i.e. 31 or 33 °C) preferentially sought out cooler temperatures, those equivalent to long‐term summer averages in their natural habitats (~29 °C). This was also the temperature providing the greatest aerobic metabolic scope and body condition across all treatments. Consequently, acclimation can confer plasticity in some performance traits, but may be an unreliable indicator of the ultimate survival and distribution of mobile stenothermal species under global warming. Conversely, thermal preference can arise long before, and remain long after, the harmful effects of elevated ocean temperatures take hold and may be the primary driver of the escalating poleward migration of species.     

Metabolic Costs of Feeding Predictively Alter the Spatial Distribution of Individuals in Fish Schools

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世居及移居高原青少年最大有氧能力的特征

本文报道海拔３４１７ｍ和４２８０ｍ地区世居藏族和移居汉族青少年运动状态下心肺功能的对比研究。结果显示：３４１７ｍ和４２８０ｍ世居藏族的最大氧耗量、无氧阈值及最大心输出量都明显大于汉族,血氧饱和度（Ｓａｏ２）随运动负荷的增加而降低。海拔３４１７ｍ藏、汉族的△Ｓａｏ２分别为７．４６％和１０．０３％,４２８０ｍ处为８．５７％和１３．７５％,最大心率随海拔升高而下降。研究提示,藏族青少年有较高的最大有氧能力,反映了他们对低氧环境的适应优势。     

The behavioural thermal preference of the common triplefin (Forsterygion lapillum) tracks aerobic scope optima at the upper thermal limit of its distribution

Ocean temperatures are rising and fish are redistributing themselves poleward and into deeper waters to retain a favourable thermal environment (11 and 30). To investigate whether biogeographical shifts might occur through behavioural redistribution into optimal environments, we examined whether a common triplefin species (Forsterygion lapillum) would behaviourally select (i.e. track) a temperature that matches its physiological optimum under laboratory conditions. F. lapillum were acclimated to 15, 18 or 21 °C for at least 4 weeks, after which various rates of oxygen consumption (MO₂) were measured using automated respirometry and their behavioural thermal preferenda assessed using an electronic shuttle choice tank. Aerobic metabolic scope (resolved as the difference between maximal and maintenance MO₂) did not differ across all thermal treatments (i.e. specimens acclimated to 15, 18 or 21 °C) revealing that F. lapillum is a eurythermal species with a range of optimal physiological performance that closely matches the environmental conditions they are exposed to. A comparably wide range of behavioural preference would perhaps be expected but all three acclimation groups showed a surprisingly narrow behavioural preference range of 20–21 °C. The results therefore suggest that, irrespective of acclimation, eurythermal species may have a tendency to select optimal temperatures at the upper limit of their thermal distribution range. The results are discussed in the context of the ecology and the expected response of F. lapillum to future thermal change.