Wavelet analysis of correlation among Canary Islands octopus captures per unit effort,sea-surface temperatures and the North Atlantic Oscillation

Short-term fluctuations in the octopus catches off the Canary Islands have been attributed to changes in the sea surface temperature (SST) and the North Atlantic Oscillation (NAO) pattern. These results have been found using stationarity assumptions. However, the behavior of environmental systems is not always linear, and environmental time series do not always satisfy the statistical property of stationarity. Wavelet spectral analysis is a methodology which can deal with non-linear, non-stationary and noisy time series. Cross wavelet analysis (wavelet coherence) is applied to investigate the environmental effects (SST, NAO) on octopus abundance fluctuations measured as capture per unit of effort (CPUE) from 1989 to 2007 in the waters of the Canary Islands. A slightly positive correlation exists between NAO and CPUE at lags and leads of a few months. Additionally, a good relationship between SST and CPUE exists on the same seasonal scale, but there is a relatively weak relationship between SST anomalies and the NAO. When the analysis is extended to the interannual scale, the wavelet coherence identifies a statistically significant relationship between CPUE and NAO, but this does not happen when the wavelet coherence between CPUE and SST is computed. These results suggest that fluctuations in octopus catches could be the result of SST fluctuations but in synergy with other unknown environmental variables which are also affected by the NAO pattern.     

Long-term catch trends and risk assessment of the Critically Endangered white-spotted wedgefish (Rhynchobatus djiddensis) from South Africa

1. The white-spotted wedgefish (Rhynchobatus djiddensis) is a Critically Endangered shark-like ray in the family Rhinidae. Throughout its Western Indian Ocean distribution, it is targeted for its valuable meat and fins and is reported to have undergone major population declines. However, there remains a need for species specific time-series data to accurately assess localized population declines.
2. This study used two independent long-term (37 and 40 years) time-series catch data from competitive shore angling and shark nets to investigate the size composition and catch per unit effort (CPUE) and conduct a risk assessment for the population on the east coast of South Africa.
3. From 1977 to 2017 the competitive shore fishery captured 7,703 individual R. djiddensis, whilst shark nets in the same region captured 2,856 individuals from 1981 to 2017. Individuals captured in the nets had a sex ratio of 1.8:1 females to males, and were larger than those caught by the anglers. Although the mean annual sizes of net-caught individuals were above the size of reported sexual maturity, there was little evidence to suggest that any individuals captured were reproductively active.
4. Both the competitive shore fishery and shark net catches exhibited strong seasonal trends with the majority of R. djiddensis catches occurring from October to May peaking in austral summer. Standardized CPUE from the competitive shore fishery declined substantially between 1977 and 2017 and shark net catches exhibited a significant (p < 0.05) fourfold decline in annual nominal CPUE from 1981 to 2017.
5. Ultimately, a risk assessment showed a 65.1% decline in abundance over a period of three generation lengths, which indicates that the sampled population of R. djiddensis in South Africa should be classified as Endangered according to the IUCN Red List using criterion A2b. The conservation implications of this are discussed.

     

南海北部金线鱼流刺网渔业情况分析

根据“粤阳东18023”渔船2006年1月至2007年12月的渔获销售记录,结合春、秋2季的渔获抽样测量数据,对使用单片刺网在南海北部作业的大型金线鱼流网船的生产情况进行了分析。结果显示,渔获以底层和近底层种类为主,带鱼Trichiurus haumela、长尾大眼鲷Priacanthus tayenus和金线鱼Nemipterus virgatus为渔获优势种,占产量的29．7％、13．3％和10．5％,占产值的27．4％、24．4％和15．7％;渔船全年作业,汛期在11月至翌年3月,其中1月为旺汛期,休渔期的产量和产值在全年中所占比重很小;优势种渔获以成鱼为主,其CPUE的高值期与汛期基本一致。     

An assessment of catches of shore sport fishing competitions along the coast of the Maltese Islands: Implications for conservation and management

Competitive shore‐based sport fishing is a popular recreational activity in the Maltese Islands. However, prior to this study, no scientific research surveys had been carried out during sport fishing competitions to investigate catches. Collaboration with Maltese sports fishermen was developed to target sustainable management. Recreational fishing catches were recorded between July 2012 and December 2015 by means of 1,633 roving‐access creel surveys, conducted during 79 sport fishing competitions, totalling a fishing effort of 7,548 hr. A total of 29,916 fish belonging to 80 species from 26 different families were caught at a mean catch‐per‐unit‐effort (CPUE) of 4.16 fish angler/hr (SD ± 3.79) and 0.18 kg angler/hr (SD ± 0.17) but with seasonal variation. Catch‐and‐release practices were implemented by all Maltese sport fishing clubs, however, the mean mortality rate stood at 35.5% (SD ± 42.1), indicating that more effort is required to improve survival of fish. The study outcomes provide conservation recommendations.     

Environmental influences on the availability of smooth pink shrimp, Pandalus jordani, to commercial fishing gear off Vancouver Island, Canada

Short time scale (less than seasonal) variability in commercial catch rates of smooth pink shrimp, Pandalus jordani, off the west coast of Vancouver Island, Canada, was examined in relation to changes in environmental conditions. Catch per unit of effort (CPUE) data were used as a proxy for catchability to identify environmental conditions affecting the availability of shrimp to the two main gear types in this fishery: otter trawls and beam trawls. Correlogram analyses of the 1996 CPUE (log-transformed) data from each gear type, and autocorrelation analyses of wind stress, tidal current speed, sea surface temperature and salinity, and hours of bright sunshine (the latter three as residuals from their seasonal trends) for 1996 indicated a mean decorrelation time scale of 7.7 days. This was used to construct smoothed time series of these CPUE and environmental data for 1996. Multiple regression analyses with CPUE as the dependent variable and the environmental data as independent variables were significant, explaining 44% of the variability in otter-trawl data and 35% of the beam-trawl variability. Three hypotheses are proposed to explain these results, involving interactions between the shrimp's behaviour and environmental conditions. A significant proportion of the within-season variability in CPUE (and therefore in the availability of shrimp to fishing gear) for P. jordani off Vancouver Island can result from variations in environmental conditions which, if included in stock analyses, should reduce the variability of population abundance estimates.     

Dynamics of floodplain fisheries in Bangladesh, results of 8 years fisheries monitoring in the Compartmentalization Pilot Project

Floodplain fisheries were monitored from 1992 until 2000 in the Compartmentalization Pilot Project in Tangail, Bangladesh. In permanent floodplains about 165 ± 28 kg ha^?1 of fish was caught annually. For seasonal floodplains, this figure was 83 ± 23 kg ha^?1 yr^?1. The fish catch exhibited a strong seasonal variation, with the highest catch in October, when the floodwater recedes towards the river, and the lowest catch during the dry season in April/May. The annual catch varied with the extent of flooding, with high catches in wet years and low catches in dry years. The extent of flooding was quantified through a Flood Index. Plotting the annual yields against this Flood Index provided a significant relation (P < 0.05), confirming the existence of a flood pulse. The fishing effort (f) and the catch‐per‐unit‐effort (CPUE) were significantly related (P < 0.05), whereby the fishing effort increased with increasing CPUE. The results are discussed within the frame of fisheries management in Bangladesh and highlight the need for long‐term data for proper evaluation of fisheries projects and the development of management schemes, and the difficulty of applying standard surplus production models in floodplain fisheries.     

基于结构方程模型研究环境因子对毛里塔尼亚双拖鲣CPUE的影响

探索渔业资源丰度与环境因子的关系, 并掌握种群分布对环境变化的响应机制, 是养护资源、实现渔业可持续发展的基础。然而, 渔业资源的变化受多个环境因素的综合影响, 这些因素之间存在复杂且相关的关系。目前的研究主要集中于环境因子对种群分布和资源丰度等直接影响, 而忽视了环境因素之间的相互作用。为了探索不同环境因子及其相互关系对毛里塔尼亚双拖鲣种群资源量的影响机制与路径, 本研究基于 2017—2019 年毛里塔尼亚海域双拖渔业鲣(Katsuwonus pelamis)单位捕捞努力量渔获量(CPUE), 采用结构方程模型(SEM)构建海表面温度 (SST)、海表面盐度(SSS)、海面高度异常(SLA)、溶解氧(DO)和叶绿素 a 浓度(Chl-a) 5 个环境因子对鲣 CPUE 直接和间接影响。结果表明: SEM 模型具有良好的拟合效果; SST、SSS、SLA、DO 和 Chl-a 对鲣 CPUE 均有直接影响, 其中 DO 和 SLA 对 CPUE 有着显著正相关影响, 而 SST、SSS 和 Chl-a 对 CPUE 有显著负相关影响; SST 等环境因子还会通过多种路径对鲣 CPUE 产生间接影响。研究揭示了毛塔海域 SST 通过直接影响或通过影响其他环境因子而间接影响鲣种群资源变动的潜在机制。     

The relative importance of lunar phase and environmental conditions on striped marlin (Tetrapturus audax) catches in sport fishing

We used generalized additive mixed models to analyze data on striped marlin (Tetrapturus audax) catches in Baja California sport fisheries (1987–1989) to investigate the relative importance of lunar phase, sea surface temperature (SST), El Niño/Southern Oscillation (ENSO) index, and vessel effects on catch per unit effort (CPUE). The results indicate that the moon phase has no or little (<1% of variance explained) influence on CPUE. In contrast, both SST (10%) and ENSO (6%) influenced CPUE positively. While most of the variation in CPUE remains unexplained (53%), the vessel identity explained small (ca. 1.5%) but significant amount of variance in CPUE. Hence, sport fishermen wishing to maximise their striped marlin catches would best plan their trips on the basis of weather conditions and boat/crew identities, rather than on the basis of lunar phase.     

Assessment of efficiency and impacts of gillnets on fish conservation in a tropical freshwater fishery

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Effects of Water Quality,Weather and Lunar Phase on Crawfish Catch1

The relationship between water quality, weather, lunar phase and daily changes in crawfish (Proearnbums clurkii) catch per unit effort (CPUE) was determined in five experimental crawfish ponds from March through May, 1984 and 1985. Air and water temperatures, solar radiation, dissolved oxygen, wind velocity, barometric pressure, precipitation and lunar phase were recorded daily during the harvesting phase of the study. Crawfish CPUE (g/trap/24 h) was significantly correlated with water temperature, dissolved oxygen, lunar phase, barometric pressure, wind velocity and the relative density of harvestable size crawfish. Most statistically significant environmental or climatological variables explained less than 20% total daily variation in crawfish CPUE. The nine environmental variables were reduced to four factors—temperature-harvestable crawfish, cold fronts, rain showers, and lunar phase—with principal-components analysis. Eighty-five percent of the variation in daily crawfish catch was attributed to water temperature and relative density of harvestable crawfish, and 7.1% was explained by lunar phase. Rain showers and cold fronts accounted for 4.8 and 2.5% of the daily variation in crawfish CPUE, respectively. Crawfish catch increased with an increase in water temperature and relative abundance of harvestable crawfish, and with short duration rain showers. Conversely, crawfish CPUE declined with the approach of full moon and with passage of cold fronts.     

The use of at‐sea‐sampling data to dissociate environmental variability in Norway lobster (Nephrops norvegicus) catches to improve resource exploitation efficiency within the Skagerrak/Kattegat trawl fishery

Research into the influence of environmental variables on the behaviour of Norway lobster (Nephrops norvegicus), and hence catch rates, dates back to the 1960s (e.g., Höglund and Dybern, Diurnal and seasonal variations in the catch‐composition of Nephrops norvegicus (L.) at the Swedish west coast. ICES CM 1965/I46; Simpson, Variations in the catches of Nephrops norvegicus at different times of day and night. Rapport et Proés‐verbaux des Réunions Conseil permanent international pour 1'Exploration de la Mer 156:186). However, the use of fishery‐dependent data in identifying influential factors is relatively limited and only includes a number of papers on a limited dataset (e.g., Redant and De Clark, Diurnal variations in CPUE and length composition of the catches in a Nephrops directed fishery in the Central North Sea. ICES CM 1984/K:3; Maynou and Sardà, Influence of environmental factors on commercial trawl catches of Nephrops norvegicus (L.). ICES J. Mar. Sci. 58:1318). Here, we aimed to dissociate environmental variability in Norway lobster catches to improve resource exploitation efficiency within the Skagerrak and Kattegat trawl fisheries by utilising data collected as part of an extensive at‐sea‐sampling programme spanning 16 years. Catch rates were modelled using Generalized Additive Mixed Models (GAMMs) and considered a range of response variables, including depth, temperature, current speed, season, moon phase and time of day. The results obtained herein showed that time of day, season, depth, temperature, year, trawl type and location all significantly affect catch rates of Nephrops.     

Effects of 17/0 circle hooks and bait on fish catches in a Southern Atlantic swordfish longline fishery

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Temperature conditions in the Argentine chub mackerel (Scomber japonicus) fishing ground: implications for fishery management

We describe the seasonal migrations of Argentine chub mackerel ( Scomber japonicus ) into the fishing ground in relation to sea surface temperature conditions and analyse the temperature evolution during the fishing season on the basis of 1955–97 time-series. The upper temperature limit for the presence of schools was around 19°C. At higher values, most schools leave coastal waters (< 50 m) for the shelf. An inverse relationship was observed between catches per unit of effort (CPUE) of the inshore fishery and sea surface temperature. The highest standardized CPUE values corresponded to temperatures lower than 19°C. Above this temperature, the probability of obtaining a standardized CPUE higher than 1 was extremely low, and the standard deviations were minimal. The economic benefit from catches was also analysed through the different months of the fishing season. It was found that the mean benefit corresponding to temperatures lower than 19°C exceeded approximately 15 times that obtained at higher temperatures. A simple fishing strategy was proposed to the commercial fleet in order to improve the economic benefit of the catches. The migratory pattern followed by mackerel during the spawning period was also analysed in relationship to other environmental factors like food availability. Zooplankton composition, size structure and abundance in coastal and shelf waters are described, and their implications for feeding ecology of larvae and adults of the species are discussed.     

基于不同模型研究环境因子对中西太平洋鲣资源丰度的影响

根据1998—2013年中西太平洋鲣(Katsuwonus pelamis)生产数据,选取时空因子(年、月、经纬度)和环境因子[海表面温度(SST)、海表面高度(SSH)、尼诺指数(ONI)和叶绿素a浓度]Chl-a)],通过两种不同的模型(广义加性模型GAM和提升回归树模型BRT)研究各因子对鲣资源丰度(以CPUE表示)的影响。研究结果认为,GAM模型中,经度对CPUE的影响最大,累计解释偏差超过50%,其次为纬度、年和月;在环境因子中,SSH最为重要,其次为ONI,而SST和Chl-a的影响相对较低。BRT模型分析结果与GAM分析结果类似,时空因子相对占据了重要的地位,其中经度的影响最大,其次为年、纬度和月;而在环境因子中,ONI的重要性相对更高,其次为SSH,SST和Chl-a同样影响较低。研究认为,两种模型均能较好地反映出因子对CPUE的影响。由于厄尔尼诺/拉尼娜现象引起的海洋环境变化会使鲣资源分布产生差异,因此在后续的渔情预报研究中,应该更多地考虑将ONI因子纳入渔情预报模型中,以提高预测精度。     

Fishing agreements in the lower Amazon: for gain and restraint

Abstract  Co-management agreements, whereby community rules for the management of local floodplain lake fisheries are legalised and enforced by the government, have become common in the lower Amazon. Agreements are intended to limit exploitation, in particular by commercial boats, to raise stock abundance and fisheries productivity for the benefit of local subsistence-oriented fishers and for conservation. A spatially replicated observational study was carried out to evaluate the performance of fishing agreements in terms of perceived rule compliance and actual impacts on fishing activities, catch and catch per unit of effort (CPUE, a measure of fisheries productivity and proxy for stock abundance). Perceived rule compliance was high, and this was corroborated by observed changes in fishing practices. Catch per unit of effort was significantly higher (by 48% on average) in areas subject to fishing agreements than in control areas without. Most likely this effect was attributable to the effective exclusion of mobile commercial fishing boats. Household fishing effort and catch in local communities were not significantly affected by the agreements, although a tendency towards slightly higher catches at lower effort was noticeable. In conclusion, the co-management agreements have led to greater local control over resources and brought significant productivity and conservation benefits.     

Effect of environmental variables on the number of births at California sea lion (Zalophus californianus) rookeries throughout the Gulf of California,Mexico

1. The 13 California sea lion breeding colonies in the Gulf of California (GoC), Mexico are each characterized by different population growth trends, including a variable number of births. Despite being located in a highly productive marine area, both the species’ population and the number of births have declined significantly over the past few decades.
2. The goal of this study was to assess the effects of certain environmental variables on the number of births at colonies in three regions (northern, central and southern) of the GoC (1995–2018). Data on diet, small pelagic fish catches by fisheries, the density of small pelagic fish schools, remotely sampled values of sea surface temperature and chlorophyll-a concentration and El Niño Southern Oscillation events were collected in order to evaluate whether these variables had an effect on the number of births using correlations and generalized linear models.
3. No significant relationships were found between the environmental variables and the number of births. However, the number of births decreased when the sea surface temperature anomalies exceeded 1°C in the northern and central regions of the GoC. Although no significant relationships were found between the small pelagic fish catches and the number of births, positive trends were observed between sardine catches and the number of births during certain periods in the central region. A positive correlation between the density of small pelagic fish schools and the number of births suggests a possible relationship between prey availability and reproductive success in the central region.
4. A Programme of Action for the Conservation of the Species should be promoted by the Federal Government and carried out in order to implement specific management actions. Specifically, surveillance efforts should increase, fishing gear conversion plans should be established and sea lion exclusion devices should be introduced, among other measures.

     

Interannual variability in stock abundance of the neon flying squid, Ommastrephes bartramii, in the North Pacific Ocean during 1979–1998: impact of driftnet fishing and oceanographic conditions

Variability in catch-per-unit-effort (CPUE) was examined for the autumn cohort of Ommastrephes bartramii collected with research driftnets during 1979–1998 along five longitudinal transects passing through the Subarctic, Transitional and Subtropical Domains in the North Pacific. CPUE was generally low during the period of intensive commercial driftnet fishing (1980–1992) and increased following the 1992 moratorium on the use of large-scale driftnets. However, CPUE levels were low for the cohorts hatched in 1992 and 1996 (captured in subsequent years owing to a one-year life of O. bartramii ) that experienced low sea surface temperatures from hatching to recruitment. Among similar-aged squid collected from 180° and 179°30'W in June, mantle lengths were significantly greater in 1997 than during 1995–96. These findings suggest that the driftnet fishery and sea surface temperatures from hatching to recruitment strongly affected stock abundance and possibly growth.     

A study on the variability of albacore (Thunnus alalunga) longline catch rates in the southwest Pacific Ocean

Relationships between albacore tuna (Thunnus alalunga) longline catch per unit effort (CPUE) and environmental variables from model outputs in New Caledonia’s Exclusive Economic Zone (EEZ) were examined through generalized linear models at a 1° spatial resolution and 10‐day temporal resolution. At a regional (EEZ) scale, the study demonstrated that a large part of albacore CPUE variability can be explained by seasonal, interannual and spatial variation of the habitat. Results of the generalized linear models indicated that catch rates are higher than average in the northwestern part of the EEZ at the beginning of the year (January) and during the second half of the year (July–December). In the northwestern region of the EEZ, high CPUEs are associated with waters <20.5° in the intermediate layer and with moderate values of primary production. Longline CPUE also appeared to be dependent on prey densities, as predicted from a micronekton model. Albacore CPUE was highest at moderate densities of prey in the epipelagic layer during the night and for relatively low prey densities in the mesopelagic layer during the day. We also demonstrated that the highest CPUEs were recorded from 1986 to 1998, which corresponds to a period with frequent El Niño events.     

Effect of baiting gillnets in the Canadian Greenland halibut fishery

Catch rates were compared between gillnets with and without bait in the Greenland halibut Reinhardtius hippoglossoides (Walbaum) fishery off Baffin Island, Canada. Two different types of baiting techniques were compared: bait bags where squid were placed into 2‐mm mesh bags, and tied bait where squid were tied into meshes. Both types of baited gillnets significantly increased the capture of the target species, Greenland halibut, with increases of 253.8% and 149.7% for the bait bag and tied bait, respectively. Common bycatch species showed mixed effects, with roughhead grenadier Macrourus berglax Lacépède showing no increase in catch per unit effort (CPUE) for either bait type (p > 0.05), and porcupine crab Neolithodes grimaldii (Milne‐Edwards and Bouvier) only had a higher CPUE with baited gillnets when bait bags were placed on the footrope. Less common bycatch species—but with threatened populations—showed an increase in CPUE, including Greenland shark Somniosus microcephalus (Bloch and Schneider) and Northern wolffish Anarhichas denticulatus Krøyer. Baiting gillnets affected the CPUE of gillnets in the Greenland halibut fishery, and management should consider how the increased CPUE of both target and bycatch species are affected by this new fishery trend.     

东海带鱼渔获量变动原因分析

利用1951~1984年东海带鱼年渔获量和捕捞努力量资料,以及降雨、风速和海表温度等的时间系列,分析了带鱼渔获量年际变化与捕捞努力量及环境因素的关系,并建立了渔获量对捕捞努力量和环境变量的回归模型。带鱼渔获量随捕捞努力量的变化可用Fox模型拟合(R=0·89,P<0·01),1951~1974年期间,渔获量随着捕捞努力量的增长而不断提高,但自1974年后,随着捕捞努力量的持续增长,渔获量开始下降。排除捕捞效应后的带鱼渔获量波动还与环境因素显著相关,分析结果表明,长江流域和东海沿岸地区年降水量、渤海海域年均风速、长江口年均风速、黄海和东海海表温度(2月)、东海中部年平均海表温度及南部冬季月平均海表温度等环境因子都与之显著相关。包含捕捞努力量和环境变量的渔获量模型的回归系数为0·97,其置信水平达到99%以上。运用1951~1984年的回归模型对1985和1986年的渔获量作出了预测,其预测值与实际渔获量的相对误差均小于5%,验证了其可靠性。研究的结果表明,带鱼渔获量变动不仅与捕捞作用有关,同时还受环境因素的影响,是两者综合作用的结果。