The importance of environment and life stage on interpretation of silky shark relative abundance indices for the equatorial Pacific Ocean

Recent large fluctuations in an index of relative abundance for the silky shark in the eastern Pacific Ocean have called into question its reliability as a population indicator for management. To investigate whether these fluctuations were driven by environmental forcing rather than true changes in abundance, a Pacific‐wide approach was taken. Data collected by observers aboard purse‐seine vessels fishing in the equatorial Pacific were used to compute standardized trends in relative abundance by region, and where possible, by shark size category as a proxy for life stage. These indices were compared to the Pacific Decadal Oscillation (PDO), an index of Pacific Ocean climate variability. Correlation between silky indices and the PDO was found to differ by region and size category. The highest correlations by shark size category were for small (<90 cm total length [TL]) and medium (90–150 cm TL) sharks from the western region of the equatorial eastern Pacific (EP) and from the equatorial western Pacific. This correlation disappeared in the inshore EP. Throughout, correlations with the PDO were generally lower for large silky sharks (>150 cm TL). These results are suggestive of changes in the small and medium silky indices being driven by movement of juvenile silky sharks across the Pacific as the eastern edge of the Indo‐Pacific Warm Pool shifts location with ENSO events. Lower correlation of the PDO with large shark indices may indicate that those indices were less influenced by environmental forcing and therefore potentially less biased with respect to monitoring population trends.     

Dynamic use of coastal areas by bull sharks and the conciliation of conservation and management of negative human–wildlife interactions

1. Knowledge about spatial and temporal variability in the distribution and abundance of predators is necessary to adapt measures to mitigate human–wildlife interactions.
2. Acoustic telemetry and network analyses were used to investigate the spatial ecology of bull sharks, the species responsible for most shark bites in Reunion Island, one of the world's shark bite hotspots.
3. The west coast of the island was not used uniformly by every individual, with size predicting the movements of sharks along the coast.
4. Node-based metrics – closeness, node strength, and cumulated continuous residency times – derived from up to 181 monthly movement networks from 20 individuals, revealed that smaller sharks (<250 cm total length) primarily used the south-west coast while larger individuals spent most of their time in the northern region with regular visits to multiple areas along the coast.
5. This study provides essential knowledge on bull shark behaviour and central areas used at different periods of the year, which correlates well with the dynamics of observed shark bites. Our approach provides a non-invasive alternative to help predicting and anticipating human–shark conflicts and avoid shark culling programmes detrimental to the conservation of large predators such as sharks.

     

Demographic analysis of the night shark (Carcharhinus signatus, Poey, 1868) in the equatorial Southwestern Atlantic Ocean

A demographic analysis of the night shark (Carcharhinus signatus) was carried out to establish the conservation status of this species caught by longlines on oceanic banks off northeastern Brazil. The biological input parameters (age at first maturity, longevity, fecundity and natural mortality) used for the construction of life tables were taken randomly from their respective probability distributions, taking into account the uncertainty of the parameter estimates by employing Monte Carlo simulations. Nine scenarios were generated from natural (M), total (Z), initial (Z₀—corresponding to the first year of life of the cohort) and population equilibrium (Z′) mortality rates. Each scenario was executed 1000 times, varying the vital input rates for the estimation of the demographic parameters (net reproductive rate, R₀; mean generation length, G; and intrinsic rate of population increase, r). Age at first maturity for C. signatus is 10 years; 89.2% of the stock is made up of juveniles, with fishery recruitment beginning at 5 years of age. The scenarios reveal that catches prior to first sexual maturity result in a significant reduction in population (−8.1%/year) and that the population would only support current efforts if the individuals caught are over 10 years of age or if mortality due to fishing efforts corresponded to the equilibrium rate beginning with recruitment at 5 years of age. A low survival rate is estimated for the first year of life. In order for the population to remain in equilibrium with current mortality rates and recruitment age, survival should be around 0.9. The combination of a low initial survival rate, low fecundity, fishery efforts and the large number of juveniles caught indicates that the C. signatus population off northeastern Brazil is being overexploited.     

长鳍真鲨源哈氏弧菌的主要生物学性状研究

从两尾病死的观赏用长鳍真鲨Oceanic whitetip shark,Carcharhinus longimanus L．中分离到的细菌,进行了形态特征、理化特性和对抗菌类药物的敏感性等生物学性状检验。同时,测定了16S rRNA基因序列,分析了相关细菌相应序列的同源性,构建了系统发育树。结果表明,8株供试纯培养菌（编号：HQ050226—1至HQ050226—4、HQ050227-1至HQ050227—4）为弧菌属（Vibrio Pacini 1854）的哈氏弧菌（Vibrio harveyi Johnson and Shunk 1936）。所扩增的16S rRNA基因序列长度（不包括引物结合区）,HQ050226—1株为1463bp（GenBank登录号：EF635305）、HQ050227—1株为1464bp（GenBank登录号：EF635306）,与GenBank数据库中哈氏弧菌的同源性在98％及99％。药敏试验结果显示,对供试37种抗菌药物中的青霉素G等4种耐药,对头孢唑啉等33种敏感。     

Extinction of a shark population in the Archipelago of Saint Paul’s Rocks (equatorial Atlantic) inferred from the historical record

Detecting and determining the validity of local extinctions is an important conservation measure in order to uncover management failures. There are quantitative and qualitative methods that estimate extinction probability based on past sighting records. However, because current baselines about species’ abundances and distributions in the sea were mostly established after humans had started affecting marine populations, researchers must often rely on historical data to elucidate past environmental conditions. We review early historical records from the Archipelago of Saint Paul’s Rocks, together with data from recent expeditions, with the aim of testing the hypothesis that reef sharks (Carcharhinus spp.) have become extinct there. Our analyses are based on non-parametric probabilistic tests for extinction and on a qualitative framework to examine and judge as objectively as possible the likelihood of local extinction. Until the mid-20th century, visitors to St. Paul’s Rocks invariably commented on the remarkable number of sharks around the Archipelago. These observations contrast with those of expeditions carried out during the last decade, which report no carcharhinid reef sharks while scuba diving in the archipelago, despite many more hours of underwater fieldwork than previous expeditions. All quantitative and qualitative methods conclude that the reef shark Carcharhinus galapagensis is locally extinct at St. Paul’s Rocks after a sharp decrease in abundance that took place following the commencement of fishing. However, the persistence of occasional individuals of the once locally common Carcharhinus falciformis in the vicinity of the Archipelago, as a result of constant immigration of this oceanic species from outside the area, suggest that the population might recover if the present fishing pressure was removed.     

Blood pressure and heart rate during tonic immobility in the black tipped reef shark,Carcharhinus melanoptera

Tonic immobility was induced in black tipped reef sharks (Carcharhinus melanoptera) and heart rate and ventral aortic blood pressure recorded. Without branchial irrigation, tonic immobility was correlated with a significant depression in blood pressure and heart rate irrespective of the sharks being in air or in water. Tonic immobility with branchial irrigation resulted in a significant increase in blood pressure in sharks in air, but not in water. Heart rate was unchanged when the gills were irrigated. Intra-arterial injections of atropine abolished the bradycardia and blood pressure rise associated with tonic immobility. We conclude that, during tonic immobility, sharks are able to receive afferent information from the ventilatory system and make appropriate responses via the vagus nerve.     

海洋环境因子和渔具对吉尔伯特群岛海域镰状真鲨误捕率的影响

为了减少延绳钓渔业中镰状真鲨的误捕率,本研究利用2009年10月-12月和2010年11月-2011年1月在吉尔伯特群岛海域作业的延绳钓渔业调查数据:钓钩深度数据,温度、盐度、溶解氧浓度和叶绿素浓度垂直剖面数据,作业参数,渔获统计数据等,采用逐步回归的方法建立钓钩预测深度计算模型,利用Wilcoxon检验对2种钓具和2种钓钩钩型之间镰状真鲨误捕率进行显著性检验,利用统计和聚类分析的方法分析镰状真鲨的捕获环境.结果显示,(1)实验钓具和18/0圆型钓钩可显著降低镰状真鲨的误捕率;(2)镰状真鲨误捕率最高的深度、温度、盐度、叶绿素、溶解氧范围分别为40.0 ～79.9 m,24.0 ～ 24.9℃、29.0 ～ 29.9℃,35.40～35.99,0.120 ～0.199μg/L和4.50 ～ 4.99 mg/L.研究建议,(1)在生产中增加18/0圆型钓钩和80 m以深的钓钩投放量;(2)减少镰状真鲨误捕率最高的深度、温度、盐度、叶绿素和溶解氧范围内的钓钩数量.     

蓝点马鲛网箱养殖试验报告

在国内首次进行了蓝点马鲛网箱养殖试验。对网箱结构,苗种兼捕,苗种放养,饵料投喂,鱼病防治等整套技术进行了研究。７２ｍ＾２网箱共养养成商品鱼１５５１尾,成活率５５％,平均尾重５８０ｇ,饵料系数７．２,单位面积产量１２．５ｋｇ／ｍ＾２。专家鉴定认为,本研究填补了国内空白,达国内领先水平。     

Gelatin Films Containing Hydrolysates from Whitecheek Shark (Carcharhinus dussumieri) Meat

The effect of adding different concentrations of freeze-dried (FD-WCPH) and spray-dried (SD-WCPH) whitecheek shark (Carcharhinus dussumieri) protein hydrolysate to the physical properties (solubility in water, contact angle, water vapor permeability, and opacity), mechanical properties (tensile strength, elongation at break, and elastic modulus) and color of gelatin films has been studied. The results showed that FD-WCPH and SD-WCPH led to an increase in water solubility and water vapor permeability and a decrease in contact angle and opacity of gelatin films (P < 0.05). Fish protein hydrolysate concentration showed a linear relation with elongation at break and an inverse relation with the tensile strength and elastic modulus of the films (P < 0.05).