Evaluation of the advantage of marine protected areas over the reduction of the fishing mortality coefficient

ABSTRACT:   In the present study, we compared the advantage of marine protected areas (MPA) to the reduction of the fishing mortality coefficient ( F ). We accomplished this by comparing the yield per recruitment (YPR) and spawner biomass per recruitment (SPR) under two controls. This was accomplished using a mathematical model. We used the following five measures as comparisons: (i) the condition of the fishery where the increase in YPR is possible; (ii) the increase in YPR or SPR obtained by allocating half the fishing ground as an MPA and by reducing F by half; (iii) the maximum YPR obtainable when the fishing mortality coefficient or the proportion of MPA in the fishing ground is completely controlled; (iv) the proportion of the MPA and the reduction ratio of F required for attaining 30% SPR; and (v) the YPR obtainable while maintaining 30% SPR. Our results show that the MPA has a minor disadvantage in terms of the first measure. The MPA is advantageous in increasing SPR in the second measure, with a low migration rate of fish. The MPA is also advantageous in increasing YPR in the second measure, with some intermediate migration. The MPA is disadvantageous in the third measure. The MPA is advantageous in the fourth measure, with a low migration rate. The MPA is disadvantageous in the fifth measure.     

山东近海口虾蛄单位补充量渔获量评估

为完善口虾蛄的基础生物学资料,并为口虾蛄资源的管理提供科学指导和理论依据,本研究根据2016至2017年山东近海渔业资源底拖网调查获得的口虾蛄体长、体质量数据,估算了口虾蛄的生长、死亡参数,构建了基于体长结构的单位补充量渔获量(YPR)模型,研究口虾蛄的资源动态和管理策略。采集调查口虾蛄样品共5 028尾,体长—体质量关系的表达式为W=0.014 5L2.88,为负异速生长;使用ELEFAN方法估算出口虾蛄的渐进体长L∞为19.87 cm,生长速率K为0.62 a-1。口虾蛄的生长表现出明显的季节性变化规律,生长参数的季节振幅C为0.76,10月份生长最快,4月份生长最慢。通过体长转换的渔获曲线估算出口虾蛄的总死亡系数Z为3.24 a-1,根据不同方法估算自然死亡系数M的范围为0.75～1.27 a-1,捕捞死亡系数F的估算范围为1.96～2.49 a-1,开发率的均值为0.67。YPR模型结果显示,随着F增大,YPR值呈现先上升后下降的趋势,生物学参考点F0.1和Fmax的值分别为0.92a-1和1.88a-1。口虾蛄资源处于过度开发的状态,应降低捕捞压力,同时调整开捕体长,以维持口...     

Weight-based virtual population analysis of Pacific cod Gadus macrocephalus off the Pacific coast of southern Hokkaido, Japan

ABSTRACT:   Age-based population assessment is widely used, but there are cases where information on age or even body length of landed fish is difficult to collect. In the present study, the biomass and fishing mortality of the southern Hokkaido stock of Pacific cod Gadus macrocephalus was estimated directly from body weight composition, using weight-based virtual population analysis, from 1994 to 2000. The estimated biomass over 1 kg body weight was 5607 t in 1994 and increased to 7908 t in 2000. The increase was explained by an increase in recruitment.     

基于地标点几何形态测量法识别北部湾4种白姑鱼矢耳石形态

为了评估银姑鱼资源开发状态,实验根据2016年在浙江南部海域底拖网的调查数据,研究了银姑鱼的生活史参数,并基于单位补充量模型对其资源状态进行评价,进而探讨不同自然死亡系数和捕捞选择性对资源评价结果的影响。结果显示,银姑鱼渐近体长估计值为25.36 cm,生长速率为0.32/年,当前开捕体长(13.52 cm)远小于其初次性成熟体长(17.79 cm);自然死亡系数估计值为0.74,总死亡系数为2.62,当前捕捞死亡系数为1.88。基于以上参数,构建了单位补充量渔获量YPR模型和单位补充量亲体生物量SSBR模型,随着F的增加,YPR先增大后减小,而SSBR则减少。银姑鱼生物学参考点F_0.1为0.78,F_max为3.43,F_20%为0.66,F_40%为0.33,可知当前捕捞强度远大于防止补充型过度捕捞警戒线F_20%。敏感性分析结果显示,自然死亡系数的不确定性将明显影响单位补充量模型的研究结果和相关生物学参考点的估算值,而不同选择性系数,尤其是开捕体长,也直接影响单位补充量模型的结果。研究表明,当前浙江南部近海银姑鱼种群已处于补充型过度捕捞状态,为维持渔业资源的可持续发展,建议适当减小开发力度,增大开捕体长;为提高资源状态评价的准确性,建议减小自然死亡系数的不确定性。本研究可为银姑鱼资源的养护和管理提供科学建议。

     

基于单位补充量模型的西江赤眼鳟种群资源利用现状评价

赤眼鳟(Squaliobarbus curriculus)是珠江中下游最重要的经济鱼类之一,本研究利用2009—2014年西江肇庆江段渔业捕捞调查监测数据,分析了其生长和死亡参数历史变化,利用单位补充量渔获量(yieldperrecruitment,YPR)模型、单位补充量产卵群体生物量(spawning biomass per recruitment, SBR)和生物学参考点评估了赤眼鳟资源利用状况。结果表明,赤眼鳟体长(L)和体重(W)关系为W=2×10^-5L^2.9527(R^2=0.9595,n=2346),生长方程为L_t=725.802[1-e^{-0.110(t+0.613})]。目前西江的捕捞强度(F=0.96/a)和开发状况(E=0.86)远超种群可持续开发水平,赤眼鳟种群处于生长型捕捞过度状态。根据实际情况,建议将西江赤眼鳟开捕年龄提高至3龄(或开捕体长增大至238 mm),则预计单位补充量渔获量可增加175%,在珠江禁渔期制度的协同保护下,种群实际保护效果可能更好。     

浙江南部海域银姑鱼的生活史参数估算及资源评价

为了评估银姑鱼资源开发状态,实验根据2016年在浙江南部海域底拖网的调查数据,研究了银姑鱼的生活史参数,并基于单位补充量模型对其资源状态进行评价,进而探讨不同自然死亡系数和捕捞选择性对资源评价结果的影响。结果显示,银姑鱼渐近体长估计值为25.36 cm,生长速率为0.32/年,当前开捕体长(13.52 cm)远小于其初次性成熟体长(17.79 cm);自然死亡系数估计值为0.74,总死亡系数为2.62,当前捕捞死亡系数为1.88。基于以上参数,构建了单位补充量渔获量YPR模型和单位补充量亲体生物量SSBR模型,随着F的增加,YPR先增大后减小,而SSBR则减少。银姑鱼生物学参考点F_0.1为0.78,F_max为3.43,F_20%为0.66,F_40%为0.33,可知当前捕捞强度远大于防止补充型过度捕捞警戒线F_20%。敏感性分析结果显示,自然死亡系数的不确定性将明显影响单位补充量模型的研究结果和相关生物学参考点的估算值,而不同选择性系数,尤其是开捕体长,也直接影响单位补充量模型的结果。研究表明,当前浙江南部近海银姑鱼种群已处于补充型过度捕捞状态,为维持渔业资源的可持续发展,建议适当减小开发力度,增大开捕体长;为提高资源状态评价的准确性,建议减小自然死亡系数的不确定性。本研究可为银姑鱼资源的养护和管理提供科学建议。     

Incorporating an environmental stock–recruitment relationship in the assessment of Pacific cod (Gadus macrocephalus)

The robustness of a previously described environmentally mediated stock–recruitment relationship for Pacific cod in Hecate Strait, BC, Canada was tested with 10 yr of additional data. The original analysis tested several alternative hypotheses and concluded that water transport through Hecate Strait, as indicated by sea level height, coupled with cod spawning biomass formed the best model. The present analysis indicates the relationship held through the 1990s. The implications of variation in sea level on stock production were investigated with a delay‐difference stock production model that included an environmentally mediated stock–recruitment relationship. The model predicted that the maximum fishery yield would vary between 1750 and 3670 t yr^?1 over the observed range of sea level height, and the estimated unsustainable fishing mortality during periods of low productivity would be only 0.5 times that in periods of high productivity.     

Value-per-recruit analysis of bighand thornyhead <Emphasis Type="Italic">Sebastolobus macrochir</Emphasis> caught off the Pacific coast of northern Honshu,Japan

The yield-per-recruit (YPR) analysis has been used to assess growth overfishing of exploited fish stocks. Since the ex-vessel price per weight widely depends on the size of the fish, the result of the YPR does not imply the revenue. The value-per-recruit (VPR) analysis, which is an economic expansion of the YPR analysis, was conducted for bighand thornyhead Sebastolobus macrochir caught off the Pacific coast of northern Honshu, Japan. The results showed that, for the current age at first capture (t _c = 3), the current fishing mortality (F = 0.12) was close to the optimum level. However, for the current F, optimum t _c in the VPR model was 8 years and would lead to a 47% increase compared to the current revenue. The maximum YPR was obtained at t _c = 6 years, but the revenue at t _c = 6 only gave a 20% increase in the maximum revenue. The difference was caused by the size dependency of the ex-vessel price per weight. The VPR model would generate fisheries management plans with both economical and biological consideration and would help in making general consensus of fisheries management strategies.     

西江鱼类群落多样性及其演变

该研究于2014年在西江封开段进行了8个月的渔获物调查,采集了526尾赤眼鳟 (Squaliobarbus curriculus) 的体长、体质量等生物学信息,利用体长频率分布估算赤眼鳟生长、死亡参数,并分析渔业资源利用状况。结果显示,赤眼鳟体长-体质量的幂函数关系参数a=0.028 8,b=2.858 2。von Bertalanffy生长参数渐近体长L_inf=74 cm,生长系数K=0.1,自然死亡系数M=0.19,总死亡系数Z=1.51,捕捞死亡系数F=1.32,开发率E=0.88。渔业资源量分析显示,2014年西江封开段赤眼鳟资源量为2 234 652尾、428.558 t。单位补充量渔获量 (Yield per recruit, YPR) 模型分析显示,当前赤眼鳟首次开捕体长为12.3 cm,F为1.32,YPR为1.89 g;当首次开捕体长调整为27.8 cm、F调整为0.45时,可获得YPR 7.76 g。当前赤眼鳟资源处于过度开发状态,建议将开捕体长设为27.8 cm,将捕捞强度降至0.45。

     

澳洲鲭太平洋群系的资源评估与管理策略

澳洲鲭是西北太平洋重要的经济种类,了解和掌握澳洲鲭太平洋群系资源开发状况对确保其可持续利用具有重要的意义。根据日本中央水产研究所提供的1995—2015年澳洲鲭太平洋群系的生产统计和资源调查资料,利用基于年龄结构的实际种群模型和单位补充量产量模型等进行资源量评估,分析澳洲鲭太平洋群系资源利用情况及其管理策略。结果显示,历年澳洲鲭太平洋群系资源量虽有波动但仍保持在较高水平,2015年资源量最高约为65万t;年平均捕捞死亡系数呈波动下降趋势,2015年捕捞死亡系数只有0.15,近五年平均捕捞死亡系数Fcur=0.33,单位补充量亲体量是未开发时的32.7%,不存在生长型捕捞过度,也不存在补充型捕捞过度,处于可持续开发状态。研究还探讨了水温变化引起自然死亡波动以及不同开捕年龄对澳洲鲭太平洋群系资源状况的影响。研究表明,该渔业目前开发和利用程度合理,建议使用F0.1做为管理参考点进行渔业资源的管理。     

Recruitment abundance index of Pacific bluefin tuna using fisheries data on juveniles

ABSTRACT:   The recruitment abundance index of Pacific bluefin tuna Thunnus orientalis was estimated from 1980 to 2003 fishing year by using the troll fishery data in Nagasaki Prefecture, western Japan. It has been shown that the troll fishery in Nagasaki Prefecture operates with good time–area coverage of the species habitat, and that the fishing power slightly changed during the period analyzed, based on fisheries statistics, published information, and interviews with the fishers. Average catch per unit effort (CPUEs) were standardized by a generalized linear model (GLM) considering the effects of fishing year, season and landing area. Standardized CPUE of age-0 bluefin tuna showed larger fluctuations year by year than the nominal CPUE combined for all ages. High CPUEs in fishing years of 1981, 1994, 1996 and 1999 were observed. Data from these years agreed with the higher recruitments estimated by virtual population analysis (VPA) or higher catch of age-0 fish reported for the Pacific side. The age-specific standardized CPUE of age-0 bluefin tuna in this study was judged to be a useful indicator of recruitment.     

An assessment of recreational fishery harvest policies for Murray cod in southeast Australia

Murray cod Maccullochella peelii peelii is one of the world’s largest freshwater fish and supports popular fisheries in southeast Australia, but no previous modelling efforts have evaluated the effects of fisheries regulations or attempted to develop sustainable harvest policies. We compiled existing population metrics and constructed an age-structured model to evaluate the effects of minimum length limits (MLLs) and fishing mortality rates on Murray cod fisheries. The model incorporated a Beverton and Holt stock recruit curve, age-specific survivorship and vulnerability schedules, and discard (catch and release) mortality for fish caught and released. Output metrics included yield (kg), spawning potential ratio (SPR), total angler catch, total harvest, and the proportion of angler trips that would be influenced by each regulation based on recent creel survey data. The model suggested that annual exploitation (U) should be held to less than 0.15 under the current MLL of 500 mm total length to achieve an SPR > 0.3, a target usually considered to prevent recruitment overfishing. Exploitation rates at or exceeding 0.3 would cause SPR values to drop below typical management targets unless the MLL was set at or above 700 mm. Regulations that protected Murray cod from overfishing created higher angler catches and higher catch of trophy fish, but at a cost of reducing the proportion of angler trips resulting in a harvested fish. Expressing model output on a per-angler trip basis may help fishery managers explain regulation trade offs to anglers.     

用补充曲线参数估算最大持续产量的方法

对于不同的补充-捕捞类型,用补充曲线参数估算最大持续渔获数(G)和最大持续渔获量(MSY或Ys)的方法是不同的。提出并讨论了2种补充-捕捞类型的评估方法：①一生只繁殖1次的连续捕捞类型,②一生繁殖多次、渔期短的季节性捕捞类型。把渔获量方程与Ricker繁殖模型和Beverton—Holt繁殖模型相结合,建立新的以渔获数表示的平衡渔获量方程。分别把Beverton-Holt渔获量方程(用于第1类型)和季节性渔业产量模型(用于第2类型)与Ricker繁殖模型和Beverton—Holt繁殖模型相结合,建立新的以重量表示的平衡渔获量方程。用这些方程式可以估算以数量表示的最大持续渔获数Cs、以重量表示的最大持续渔获量Ys,Cs所需的捕捞死亡系数(F‘s)和Ys所需的捕捞死亡系数(Fs)。计算了二种类型在同一自然死亡系数下的Cs、Ys、F‘s和Fs。结果表明：Fs不等于F‘s,同一种群的Fs可以小于F‘s,但Fs不可能大于F‘s。     

珠江禁渔对广东鲂资源补充群体的影响分析

继我国各大水系实施禁渔期制度之后,珠江水系于2011年4月1日至6月1日实现首次禁渔。广东鲂是珠江中下游地区主要的经济鱼类之一,为分析珠江实施禁渔期制度对广东鲂资源补充群体的影响,于珠江实施禁渔制度前(2006—2010年)和禁渔制度后(2011—2012年)在珠江下游肇庆江段设立固定采样点,利用定量弶网对流经该江段的广东鲂鱼苗补充群体进行调查。结果显示,禁渔前,珠江广东鲂鱼苗集中出现在4月中下旬至10月中旬,持续时间为(189±11)d,高峰期为6—8月。禁渔期制度实施之后,全年广东鲂鱼苗出现的起始时间变化不大,但是结束时间提前,持续时间略有缩短,4—5月份广东鲂鱼苗密度明显增大。广东鲂鱼苗总量及其在鱼苗补充群体中的比例均有所提高。根据禁渔前广东鲂鱼苗发生量与径流量之间存在的回归关系:LgY=0.988Lnx-4.932(R2=0.365,P0.01),结合禁渔后实际调查结果,对禁渔的实际作用进行了估算,2011年和2012年由于禁渔分别增加了9.43×108和651.81×108尾广东鲂鱼苗。研究表明,在径流量有保障的前提下,目前的禁渔制度可以有效增加广东鲂鱼苗补充群体资源量。     

Abiotic and biotic factors affecting recruitment variability of walleye pollock (Theragra chalcogramma) off the Pacific coast of Hokkaido,Japan

Abiotic and biotic factors affecting the recruitment variability of the Japanese Pacific stock (JPS) of walleye pollock (Theragra chalcogramma) were examined using a bivariate regression and multivariate combined model. Of the abiotic variables around Funka Bay (spawning ground), February sea surface temperature (SST) and wind direction index showed significant bivariate relationships with recruitment. February SST was positively related to recruitment, suggesting that warmer water temperature in February favors JPS recruitment. On the other hand, the relationship between February wind direction index and recruitment predicts high JPS recruitment under predominant northwest winds in February. For the biotic variables in the Doto area (nursery ground), significant and negative bivariate relationships with recruitment were observed for catch per unit effort of Kamchatka flounder (Atheresthes evermanni), Pacific cod (Gadus macrocephalus), and walleye pollock, implying an important impact of predation by these groundfishes on JPS recruitment. The overall model incorporating these abiotic and biotic factors successfully reproduced the variability in JPS recruitment. Temperature and wind conditions around the spawning ground along with predator condition in the nursery ground appear to play a dominant role in the recruitment dynamics of JPS. Based on these results and prior knowledge, we propose a new hypothesis to explain the processes controlling JPS recruitment.     

Greenland cod (Gadus morhua): modeling recruitment variation during the second half of the 20th century

Two approaches were used to qualify observed variability in Greenland cod (Gadus morhua) recruitment. In the first analysis, we used the linear trend of the Greenland cod recruitment time series and climatic variables, such as air temperatures from the Denmark Strait and wind conditions off East Greenland and Southwest Greenland, to explain the interannual variation in cod recruitment off Greenland. The model resulting from this ‘trend/environmental approach’, explained 79% of the interannual variation in cod recruitment off Greenland. In the second, analytical approach, the ‘regime approach’, multiple linear regression models were used, with the input data being the time series of cod recruitment and spawning stock biomass (SSB) from Iceland and Greenland, sea surface and air temperatures around Greenland, and zonal wind components between Iceland and Greenland. Model results indicated that, during the decades between 1950 and 1990, there were three different cause–effect regimes which significantly influenced the variability of cod recruitment. The three regimes included: (a) the 1950s and 1960s, a regime with favorable sea surface temperatures and a self‐sustaining cod stock off Greenland with high SSB that produced a series of above‐average, strong year classes; (b) the 1970s and 1980s, a regime of declining SSB and recruitment, with recruitment dependent on advection from Iceland; and (c) the 1990s, when the advective potential for recruitment from the Icelandic cod stock was the only available source for replenishment of the Greenland cod stocks, because cod recruitment in Greenland waters was negligible. The three models explained 76–77% of the observed interannual variation in cod recruitment off Greenland. Both approaches suggested that advective factors were the dominant influences for cod recruitment in the ‘Iceland–Greenland System’.     

Long-term stock assessment and growth changes of the Japanese sardine (Sardinops melanostictus) in the Sea of Japan and East China Sea from 1953 to 2006

We estimated the stock size of Japanese sardine ( Sardinops melanostictus ) in the Sea of Japan and East China Sea since 1953 using cohort analysis based on the changes of growth patterns. Growth of Japanese sardine, estimated by using annual rings on archived scales since 1961, showed that body lengths were extremely stunted in the 1980–1987 year-classes. The body length at age 3 from February to April in the 1980–1987 year-classes, a period when the stock size exceeded 4 million tons, was 180.0 ± 2.6 mm (mean ± SD), and in the other year-classes was 195.1 ± 7.6 mm. The body length at age 3 and wet weight of zooplankton in August in the offshore area of the Sea of Japan had a significantly positive correlation. We assumed three scenarios for maturation ratios, and estimated Ricker's spawner–recruitment relationships. We analyzed the correlations between logarithmic recruitment residuals (LNRR) and environmental factors in winter, represented by the North Pacific index (NPI), Aleutian low pressure index (ALPI), Pacific decadal oscillation (PDO), monsoon index (MOI), Arctic oscillation (AO) and Southern oscillation index (SOI). Significant correlations were observed between MOI and LNRR and between AO and LNRR. A combination of strong MOI and weak AO would increase the biomass of phytoplankton and zooplankton and subsequently increase the recruitment of Japanese sardine.     

Population ecological parameters and biomass of anchovy kilka <Emphasis Type="Italic">Clupeonella engrauliformis</Emphasis> in the Caspian Sea

ABSTRACT:   Through most of the last century, three endemic kilka species supported major commercial species in the Caspian Sea. It is clear that catches and abundance of all species have changed, but catch and sampling data are limited and stock assessments are inadequate. Recent changes in the Caspian Sea ecosystem have occurred as a consequence of climatic environmental change (sea level change) and ecologic change caused by the invasive ctenophore Mnemiopsis leidyi . This paper examines the effects of these changes on the population biology and biomass of anchovy kilka Clupeonella engrauliformis in Iranian waters of the Caspian Sea from 1995 to 2004. For most years during this 10-year period, we estimated the age structure of catch, length–weight relationship, von Bertalanffy growth parameters, condition factors, sex ratios, maturity stages determined from ovarian analysis, natural and fishing mortality, age at first capture, and spawning biomass. The instantaneous coefficient of natural mortality was estimated as 0.473/year and the instantaneous coefficient of fishing mortality varied during the 10-year period between 0.541 and 2.690/year. Biomass of anchovy kilka declined from about 186 000 t in 1996 to less than 12 000 t in 2004. Recent high fishing rates were not sustainable after the introduction of Mnemiopsis , so overfishing is part of the explanation for the collapse of anchovy kilka in the Caspian Sea.     

The dynamics of an exploited population of a siluroid catfish (Schilbe intermidius Reupell 1832) in the Cross River, Nigeria

We studied the breeding biology, growth, mortality, recruitment pattern and yield per recruit of a freshwater siluroid catfish (Schilbe intermedius) in the Cross River, Nigeria. Monthly variation in mean gonadosomatic and mean condition indices shows that the species breeds twice in a year (March and September). We used 12 consecutive months length–frequency data together with FiSAT software to study the population dynamics of this catfish which is exploited by artisanal fishermen. Fitting the seasonalized von Bertalanffy growth function to our length–frequency data gives the following growth parameters: L_∞=27.5 cm total length, K=0.29 yr⁻¹, C=0.5, WP=0.46. Using the seasonalized length converted catch curve, we estimated the instantaneous total mortality coefficient Z as 1.85 yr⁻¹. The instantaneous natural mortality coefficient M was 0.81 yr⁻¹ while the instantaneous fishing mortality coefficient F was 1.04 yr⁻¹, giving the current exploitation rate E=0.56. From the analysis of probability of capture of each length class we estimated the length at first capture L_c to be 10.9 cm. The relative yield per recruit analysis predicted the maximum exploitation rate E_max=0.54. The current exploitation rate E is more than this predicted maximum E_max. Thus, the species is on the verge of being overexploited.     

Long-term trends in fish recruitment in the north-east Atlantic related to climate change

This study investigates the temporal correspondence between the main patterns of recruitment variations among north‐east Atlantic exploited fish populations and large‐scale climate and temperature indices. It is of primary importance to know what changes in fish stock productivity can be expected in response to climate change, to design appropriate management strategies. The dominant patterns of recruitment variation were extracted using a standardized principal component analysis (PCA). The first principal component (PC) was a long‐term decline, with a stepwise change occurring in 1987. A majority of Baltic Sea, North Sea, west of Scotland and Irish Sea populations, especially the gadoids, have followed this decreasing trend. On the contrary, some herring populations and the populations of boreal ecosystems have followed an opposite increasing trend. The dominant signal in north‐east Atlantic sea surface temperature, also extracted by a PCA, was highly correlated with the increase in the Northern Hemisphere Temperature anomaly, which is considered to be an index of global warming. The first component of recruitment was inversely correlated with these changes in regional and global temperature. The second PC of recruitment was a decadal scale oscillation, which was not correlated with climate indicators. The analysis of correlations between population recruitment and local temperature also indicated that the dominant pattern of recruitment variation may be related to an effect of global warming. The influence of fishing on recruitment, via its effect on the spawning stock biomass (SSB), was also investigated by the analysis of correlations between fishing mortality, SSB and recruitment. Results indicate that fishing can be another factor explaining recruitment trends, probably acting in combination with the effect of climate, but cannot explain alone the patterns of recruitment variation found here.