从连续到偶发: 中华鲟在葛洲坝下发生小规模自然繁殖

归纳了白鲟、长江鲟、中华鲟近40年自然资源量变化情况,统计了长江鲟和中华鲟人工增殖放流数据,评估了增殖放流成效。因物种特性和分布的差异,放流无效的原因迥异。过度捕捞使人工放流长江鲟在放流后6个月之内难逃被“误捕”,而中华鲟放流数量不足及长江和近海过度捕捞导致中华鲟人工增殖放流的贡献甚微,其结果是长江鲟和中华鲟增殖放流均无法达到自然繁殖群体的补充水平。本文探究了近40年来白鲟、中华鲟和长江鲟在保护、管理和决策上存在的误区和不足,提出在生态大保护的背景下,① 应编制和实施《长江鲟拯救行动计划》优先项目;② 应以《中华鲟拯救行动计划》为指引,在就地保护、迁地保护和遗传多样性保护方面提出更具有可操作性的优先计划;③ 应设立中华鲟和长江鲟物种拯救行动计划专项,对现有涉栖息地或保护区生态补偿项目进行优化整合。唯有以恢复长江鲟和中华鲟自然繁殖为核心,才有望延续和恢复其自然种群,实现人与自然的和谐共处,推动长江流域社会经济绿色可持续发展。     

葛洲坝枢纽下游中华鲟自然繁殖的调查

中华鲟是一种大型的洄游性鱼类，最大个体达1，100余斤。成熟个体原来由海进入江河，性腺逐渐发育，至翌年秋季在长江上游产卵繁殖。1981年1月，葛洲坝枢纽大江截流，中华鲟的洄游路线受阻，而滞留于坝下江段。在这种情况下，中华鲟的性腺能否继续发育和有无可能在大坝下游自然繁殖的问题，通过两年来的调查研究，已经得到了肯定的回答。     

葛洲坝下中华鲟自然繁殖流速场的初步观测

2004和2005年10~11月间,在中华鲟产卵区葛洲坝至庙咀江段利用声学多普勒流速剖面仪(ADCP)对中华鲟(Acipenser sinensis)自然繁殖期间的流速进行了测量。在该江段沿水流方向设置监测断面共20个,其中2004年设12个(编号1~12),2005新增8个(编号A~H)。监测结果表明,产卵区内所有断面平均流速变化范围为72.99~175.23 cm/s,平均值为(128.89±26.28)cm/s;产卵区内12、和4号断面的垂向平均流速值较其他断面约高2.10 cm/s;从A至12号断面,各断面的平均流向大约从225.91°下降至164.39°,并且产卵区内1、2和4号断面的流向变幅较大,变异系数比其他断面约高18.4%;下产卵区内脉动流速测量结果表明平均流速变化较大,而平均流向变化相对较小,变异系数分别为7.1%和2.9%;葛洲坝下所进行的河势调整工程使中华鲟产卵场内的流速发生了较大程度的改变,主要表现为在导流堤两侧形成了一个流速较缓的区域。导流堤的建设可能会导致上产卵区的位置改变甚至消失,下产卵区改变其具体位置。     

水生所再次发现中华鲟自然繁殖

中国科学院水生生物研究所第一研究室鱼类生态组的科技人员，1984年在葛洲坝枢纽下游进行中华鲟自然繁殖调查时，取得了证明中华鲟在宜昌江段大规模自然繁殖的资料，这是自1982年以来连续3年观察到的中华鲟在宜昌江段自然繁殖规模最大的一次。     

葛洲坝下中华鲟自然产卵胚胎正常发育的证据

报道 2 0 0 2年度在葛洲坝下中华鲟产卵场采捞到的中华鲟卵的发育情况。在中华鲟产卵场 ,中华鲟能完成正常的自然产卵和胚胎发育 ,并孵出仔鱼。将采得的中华鲟卵在人工条件下孵育 ,也能完成胚胎发育和出膜。     

葛洲坝下中华鲟产卵情况初步调查及探讨

<正> 中华鲟(Acipenser sinensis Gray)是我国珍贵的鱼类,长江葛洲坝兴建后,对如何拯救中华鲟(以下简称鲟鱼)等问题,曾引起了广泛的讨论,其中对长江截流后,鲟鱼能否在坝下自然繁殖的问题,更引起人们的重视。1981年经调查,坝下发现有成熟的鲟鱼,同时了解到坝下江段有卵石、礁板石存在,繁殖季节坝下水温在17～20℃左右,这就是说,坝下也有鲟鱼产卵繁殖的外界条件。那么被阻于坝下的成熟鲟鱼,能否找到适宜的场所进行自然产卵繁殖呢?这个问题引起了我们的重视。1982年我们在承担图家科委下达的鲟鱼资源调查的若干内容的同时,在宜昌、石首等江段,进行了鲟鱼产卵的调查。     

葛洲坝下中华鲟产卵场的第二次调查

<正> 1982年我们经调查证实了葛洲坝下有中华鲟产卵繁殖。但自然产卵对坝下中华鲟(下简称鲟鱼)资源有多大影响,尚未得到肯定性结论。为了正确评论坝下产卵场的效果,需弄清坝下鲟鱼成熟比例、产卵亲鲟群体大小、产卵量、产卵场范围、敌害鱼类危害程度等情况,并与大坝截流前天然产卵场的情况进行比较分析,以认识坝下产卵场的     

葛洲坝产卵场中华鲟繁殖群体数量与繁殖规模估算及其变动趋势分析

采用声学探测的方法,进行中华鲟(Acipenser sinensis)繁殖群体数量的估算.2005～2007年,第1次产卵前的资源量分别为235尾、217尾和203尾;第1次产卵后的资源量分别为157尾、157尾和102尾.采用食卵鱼解剖统计和股分析的方法对中华鲟的自然繁殖规模进行估算.其结果为,2005～2007年间中华鲟的产卵量分别为356万粒、119.6万粒和238.6万粒.结合历史相关研究数据,对近10年的中华鲟繁殖群体数量和繁殖规模的变动趋势进行分析,结果显示,在20世纪90年代中期,第1次产卵前的中华鲟繁殖群体数量下降趋势明显,但2002年以来其数量趋于基本稳定,年际间的差异没有统计学意义(P>0.05).自2002年以来,第1次产卵后停留产卵场的中华鲟数量有增加的趋势,而中华鲟的繁殖规模近10年来呈现极其显著性的下降趋势(P<0.01).     

葛洲坝下中华鲟产卵场食卵鱼资源量的调查和分析

为了解葛洲坝下游中华鲟(Acipenser sinensis)产卵场食卵鱼的资源量,于2011年8—12月在葛洲坝下游江段,利用三层流刺网张网采集渔获物样品并进行鉴定分类。结果显示:采集渔获物共有24亚种,分属于3目5科,其中鲤形目鲤科鱼类最多,共有14种,未发现外来物种。食卵鱼铜鱼(Coreius heterodon)和瓦氏黄颡鱼(Pelteobagrus vachelli)在所捕获渔获物中所占比例较大,其中瓦氏黄颡鱼(Pelteobagrus fulvidraco)的捕捞量占总捕捞量的79.31%;在11月份的捕获物中,食卵鱼的捕捞数量足过10月和12月的2~8倍;在中华鲟产卵期间,食卵鱼的日捕获量达到最高峰。     

葛洲坝下中华鲟产卵场的调查研究

本文对葛洲坝下中华鲟产卵场的地点、范围、成熟比例、产卵量、敌害鱼类危害情况等进行了研究并作出了初步评价,同时为拯救中华鲟资源提出具体意见。     

Variations in spawning ground area and egg density of the Japanese sardine in Pacific coastal and oceanic waters

The spawning ground of the Japanese sardine, Sardinops melanostictus (Schlegel), was distributed over the oceanic waters as well as the coastal waters along the Pacific coasts of western and eastern Japan during 1978–1992. The area of the spawning ground in the coastal waters on the continental shelf has ranged from 95 000 km² in 1992 to 143 000 km² in 1988, constituting 44–77% of the total area of the spawning ground. The area of the coastal spawning ground was relatively constant in spite of the large fluctuations in egg abundance, i.e. size of the spawning population, from 88 trillion (1987) to 668 trillion (1989) in the waters. Spawning adults seemed to extend over the coastal waters irrespective of the size of the spawning population. In contrast to the coastal waters, the spawning area in the oceanic waters offshore of the continental shelf increased from 31 000 km² in 1978 to 183 000 km² in 1988 and then shrank to 83 000 km² in 1992, as a function of the spawning population size. The egg distribution density in the coastal waters stayed less than 6000 m⁻² mo⁻¹, but it reached as high as 27 400 m⁻² mo⁻¹ in the expanded spawning ground in the oceanic waters. The oceanic waters seemed to function as a reserve spawning ground for the sardine in years of extremely high spawning population.     

Solar and lunar influences on the spawning activity of Pacific bluefin tuna (Thunnus orientalis) in the south‐western North Pacific spawning ground

Pacific bluefin tuna (Thunnus orientalis) migrate to the south‐western North Pacific spawning grounds (area off Taiwan and the Ryukyu Islands) from mid‐April to early July. Reproductive traits of the species in this area have been studied for some time; however, temporal changes in spawning activity during this season are not well understood. In this study, the spawning fraction (proportion of females with post‐ovulatory follicles to total mature females) in relation to solar calendar date and lunar day was investigated using a generalized linear model. Sampling was conducted almost every day throughout the fishing season at Ishigaki Fishing Port (24°21′N, 124°09′E), southern Japan between 2012 and 2014, and a total of 212 ovaries were histologically observed. Spawning fraction continued to increase from the beginning to the end of the season. This indicates that the peak season of occurrence in the area and the peak of spawning activity did not co‐occur. Spawning fraction also changed with the lunar day and significantly increased around the new moon. Eggs and early larvae hatched around the new moon may have reduced the predation risk during night‐time. These findings improve the current knowledge of reproductive biology and resource evaluation of Pacific bluefin tuna and indicate that spawning activity is not constant, and has two or three peaks in each season.     

Spatio‐temporal trends of sailfish,Istiophorus platypterus catch rates in relation to spawning ground and environmental factors in the equatorial and southwestern Atlantic Ocean

Spatial and temporal trends of sailfish catch rates in the southwestern and equatorial Atlantic Ocean in relation to environmental variables were investigated using generalized additive models and fishery‐dependent data. Two generalized additive models were fit: (i) ‘spatio‐temporal’, including only latitude, longitude, month, and year; and (ii) ‘oceanographic’, including sea surface temperature (SST), chlorophyll‐a concentration, wind velocity, bottom depth, and depth of mixed layer and year. The spatio‐temporal model explained more (average ~40%) of the variability in catch rates than the oceanographic model (average ~30%). Modeled catch rate predictions showed that sailfish tend to aggregate off the southeast coast of Brazil during the peak of the spawning season (November to February). Sailfish also seem to aggregate for feeding in two different areas, one located in the mid‐west Atlantic to the south of ~15°S and another area off the north coast of Brazil. The oceanographic model revealed that wind velocity and chlorophyll‐a concentration were the most important variables describing catch rate variability. The results presented herein may help to understand sailfish movements in the Atlantic Ocean and the relationship of these movements with environmental effects.     

Characteristics and rehabilitation of the spawning habitats of the sea trout, Salmo trutta, in Gotland (Sweden)

Characteristics of the natural spawning habitat of sea trout, Salmo trutta L., were studied in Själsöån, a small stream of Gotland, Sweden, from 1992 to 1999. Each year, trout spawned on 17 ± 7 different areas (156 places ha^?1). Most of the spawning grounds were used every year. Overcutting was evident for at least 60% of the spawning grounds. Fish spawned on a gravel of 19 ± 7 mm in diameter. From 1978 to 1992, 242 artificial spawning grounds were constructed by the Gotland Sport Fishermen Association in four Gotland streams. A sediment trap was dug upstream to the spawning grounds. The artificial spawning ground comprised of a downstream V‐shape stream deflector of large stones with a log weir at the narrowest point of the deflector. Upstream of the dam, 15–60 mm diameter gravel was deposited to constitute the spawning ground substratum. To keep the installation efficient, maintenance is needed every year before the spawning season.     

Effect of partial or total replacement of forage fish by a dry diet on the quality of reproduction in pikeperch, Sander lucioperca

The aim of this preliminary study was to evaluate the influence of different feeding regimes on the quality of reproduction in pikeperch. Three diets were tested: forage fish (FF), a commercial dry feed (DD) and a mix of both (FD).  The diets were given to fish throughout a complete reproductive cycle. During the spawning season, couples were injected with human chorionic gonadotropin (hCG) and let to spawn on nests. Proportion of running males, spawning and hatching success and larval quality (weight, length, body protein, total lipid, fatty acid and lipid class compositions and resistances to osmotic shock and starvation stress tests at hatching) were evaluated. The proportion of running male was lower in the DD group than in the FF and FD groups (54% for DD against 76–89% for FF and FD). In addition, 25%, 62.5% and 75% of injected couples gave spawning that hatched in DD, FF and FD groups respectively. Larval quality parameters were not significantly different between treatments. The results indicate that overall quality of reproduction was higher in FF and FD treatments than in DD. It suggests that the dry feed used was not totally adequate for pikeperch reproduction. Relations between breeder reproductive performances and the feed compositions are discussed.     

Occurrence of Pacific bluefin tuna Thunnus orientalis larvae off the Pacific coast of Tohoku area,northeastern Japan: Possibility of the discovery of the third spawning ground

Recently, based on the histological studies it is suggested that Pacific bluefin tuna (PBF) spawns in the Kuroshio–Oyashio transition, off the Pacific coast of northeastern Japan, in addition to the previously identified two spawning areas of the northwestern Pacific around the Nansei Islands and the Sea of Japan. Distributional surveys for PBF larvae have not been conducted in the Kuroshio–Oyashio transition, and thus, we conducted PBF larval surveys at twenty stations in this area in early August 2018 to obtain evidence for the spawning of PBF. Twelve PBF larvae (3.9–7.2 mm in body length) were collected at six stations where sea surface temperature ranged from 27.2 to 28.2°C. Otolith microstructure analysis indicated that age of these larvae ranged from 4 to 11 days after hatching and the larvae hatched in late July. Growth of the collected larvae was comparable to those in the other two spawning grounds. Therefore, PBF spawns, hatches, and at least survives to the postflexion stage, 11 days after hatching in the Kuroshio–Oyashio transition. This fact potentially has a large impact on recruitment processes of PBF if they survive to recruitment in this third spawning ground.     

Role of urine in the spawning of female rose bitterling,Rhodeus ocellatus ocellatus

This study clarified the spawning mechanism of female rose bitterling, Rhodeus ocellatus ocellatus, with special emphasis on the physical role of urine. Ovulated females ingested a significantly greater quantity of water by drinking than non-ovulated fish. The body weight of ovulated females increased about 1.3% while it decreased 1.0% in non-ovulated females. Urine volume in the urinary bladder increased rapidly before spawning, synchronized with the spawning cycle. On the other hand, little urine remained in specimens which had completed spawning. Histological observation demonstrated that the oviduct and the ureter joined at the proximal part of the ovipositor. On the basis of these anatomical and physiological results, it is proposed that urine plays the physical role of pushing the ovulated eggs through the elongated ovipositor during spawning.