湛江近海虾拖网虾蟹类渔获组成

在2012 年8 月进行的南海北部虾拖网海上调查的基础上,对虾蟹类渔获的种类组成、生物学特征和幼 体比例等进行了分析。结果显示,渔获种类一共71 种,其中虾蟹类15 种,但其产量却占总产量的82.34%;虾类优势 种为日本囊对虾（Marsupenaeus japonicus）、刀额新对虾（Metapenaeus ensis）、近缘新对虾（M. affinis）和周氏新对虾（M. joyneri）;蟹类优势种为红星梭子蟹（Portunus sanguinolentus）、三疣梭子蟹（P. trituberculatus）和远海梭子蟹（P. pelagicus）;刀额新对虾的幼虾比例为73.36%,三疣梭子蟹的幼蟹比例为78.79%。最后,探讨了促进南海虾蟹类资源 合理利用的措施。     

闽南、台湾浅滩渔场灯光围网渔业状况分析

根据福建省1987～2003年闽南、台湾浅滩渔场(116°00′～119°30′E,22°00′～24°30′N)灯光围网作业生产统计数据和资源监测资料,分析研究了福建省在该渔场灯光围网作业状况、发展演变和资源利用现状。结果表明:由于单拖作业和流刺网作业的发展,灯光围网作业持续萎缩,在海洋渔业中的地位不断下降;渔船大型化,渔场向深水推进,灯源配置及集鱼并灯技术取得重大突破;主要渔获物中蓝圆鲹占绝对优势,鲐鱼所占比例有上升的趋势,金色小沙丁鱼年间波动明显,颌圆鲹则快速减少,竹鱼近年来产量快速增长。文章还提出改进和提高灯光围网作业捕捞技术和自身竞争力,合理引导部分疏目快拖作业参与中上层鱼类资源的开发利用等优化海区捕捞作业结构、合理开发利用海区渔业资源的管理建议。     

我国海洋休闲渔业发展模式初探 --以舟山蚂蚁岛省级休闲渔业示范基地为例的实证分析

休闲渔业已经成为我国海洋旅游的新亮点和海岛经济发展的新兴产业。本文通过分析舟山蚂蚁岛成功打造省级休闲渔业示范基地的模式，提出海洋休闲渔业的发展应注重挖掘海洋文化和地方特色，与旅游等三产发展相结合，与落实“五个统筹”、建设社会主义现代化新型渔农村以及构建和谐社会相结合，并探讨了我国海洋休闲渔业的发展模式。提出了规划要科学化、统筹化，经营要产业化、集约化，管理要规范化、法制化，发展要可持续化等对策建议。     

南四湖的水生生物和渔业生态初析

南四湖是指位于山东省南部的微山、昭阳、独山和南阳四个湖,现有水面11.9万公顷。目前的平均鱼产量是94.05公斤/公顷。1983—1984 年我省对该湖进行了全面的渔业资源调查。南四湖的溶氧含量平均为 8.71毫克/升,pH为 7.1—9.7。湖水中的磷酸盐是0.0108毫克/升,三态氮是0.465 毫克/升。水生维管束植物的生物量是 2584.2毫克/米~2,浮游植物和浮游动物的平均生物量分别为1.709和0.601毫克/升,底栖动物的平均生物量是92.65克/米~2。鱼类的优势种类是鲫鱼、黄颡鱼、乌鳢、红鳍鲌、长春编、鲶鱼、鲤鱼。并为开发它们提出了初步建议。     

Effects of fishing practice changes on pelagic shark longline captures in the Gulf of Gabes,Tunisia

1. In order to increase their catches, longliners targeting sharks in the Gulf of Gabes, Tunisia, have increased the number of hooks per basket and have included new bait types instead of mackerel (Scomber scombrus). This paper reports the effects of these changes on catch composition, catch rates, size distribution, life‐stage captures, and mortality at haulback.
2. Data from 48 and 96 longline sets, carried out during the shark fishing seasons of 2007 and 2008, with two hooks per basket, and 2016 and 2017, with five hooks per basket, respectively, were examined to assess the effect of gear change. Moreover, the effects of bait types were inspected based on 33 fishing sets using whole mackerel, 19 using salema (Sarpa salpa) halves, and 27 using pieces of stingray (Dasyatis spp.), sampled during 2016 and 2017.
3. The species composition indicated that longliners expand the vertical distribution of their hooks to operate from the surface to the bottom. The catches with both longline designs were dominated by sandbar shark (Carcharhinus plumbeus). Despite gear changes, the catch rate of C. plumbeus decreased by 42.21%, suggesting population decline. The size composition indicated a shift towards larger specimens, mainly adult females, which could jeopardize the shark population. Moreover, the mortality of the main species at haulback seems to be affected by the design of the longline.
4. The bait used, mainly pieces of stingray, significantly increased the catch rate of sandbar shark, which suggests a greater attractiveness of the new bait; however, fish size and mortality rates at haulback were unchanged in response to bait variation.
5. The fishery operates in shark nursery grounds, which exposes these fish (principally C. plumbeus) to considerable exploitation pressure. The new fishing practices intensified the pressure and thus the risk of a rapid depletion of populations. To preserve the shark species in the area, the use of new gear and attractive bait should be banned.

     

Are circle hooks effective management measures in the pelagic longline fishery for sharks in the Gulf of Gabès?

1. This study evaluated the circle hook use as a tool for shark management in the pelagic longline fishery in the Gulf of Gabès.
2. The usual J‐hook No. 2 with 10° offset, which has been traditionally used by the fishery, was compared to the 18/0 non‐offset circle hook in an alternating fashion along the main line. In total, 22 experimental longline sets were deployed through the shark fishing seasons of 2016 and 2017 to examine the effects of hook types on the catch composition, the catch rates, the hooking location, and the status at haulback.
3. The catch composition differed significantly among hook types. Moreover, an overall increase in catch rates for the main species, the sandbar shark Carcharhinus plumbeus, and the shortfin mako shark Isurus oxyrinchus, was observed when using circle hooks.
4. There was no size‐selective effect of circle hooks for the common species. The circle hooks were not effective at reducing at‐haulback mortality of sandbar shark. Conversely, shortfin mako and smooth‐hound shark Mustelus mustelus showed significantly lower relative mortality at haulback with circle hooks than with J‐hooks. Furthermore, circle hooks were more frequently hooked externally than the J‐hooks for the three shark species.
5. Results demonstrated that the use of 18/0 non‐offset circle hooks in the pelagic shark longline fishery can reduce mortality at haulback for some species without any benefit for the dominant species, the sandbar shark.
6. Overall, it is difficult to promote the adoption of the use of circle hooks as a management measure in this specialized fishery. Management measures focusing on fishing effort controls, fishing closures in critical habitats, and size limits could have significant benefits for the conservation of shark species and may help to improve the sustainability of the shark fishery in the Gulf of Gabès.

     

Ecological consequences of invasive lake trout on river otters in Yellowstone National Park

The introduction of lake trout (Salvelinus namaycush) to Yellowstone Lake in Yellowstone National Park has contributed to a significant decline in the endangered Yellowstone cutthroat trout (Oncorhynchus clarki bouvieri), leading to concern over the persistence of this subspecies but also to piscivorous predators in this community. We assessed the impact of lake trout on a key piscivore, the river otter (Lontra canadensis) in two lakes in Yellowstone National Park. Yellowstone Lake continues to support a native cutthroat trout population, although the recent introduction of lake trout has dramatically impacted the cutthroat trout population. Nearby Lewis Lake has an entirely introduced fish fauna of lake trout, brown trout (Salmo trutta), and Utah chub (Gilia atraria) but lacks cutthroat trout. Analysis of otter scat from Yellowstone Lake implicated trout (lake or cutthroat trout) as a major prey item (57% of scat), whereas stable isotopes identified longnose suckers (Catostomus catostomus) as the primary prey there (58% of diet). By contrast, scat from Lewis Lake implicated minnows, presumably Utah chub, as the primary prey for otters occupying that lake (86%), while stable isotopes implicated brown trout (64%) over both lake trout and Utah chub (36% combined). Our data establish the importance of alternative prey to otters and suggest that lake trout-induced reductions in cutthroat trout may not be catastrophic for otter populations here. These data do not necessarily exonerate lake trout, as their impact on other species, most notably grizzly bears (Ursus arctos) and piscivorous birds, has been documented to be substantial, and further data on the nutritional value of alternate prey are required to confirm or refute a working hypothesis that otter populations will continue to thrive in the face of the lake trout invasion.     

Long-term trends in the competitive shore fishery along the KwaZulu-Natal coast,South Africa

Twenty-four years (1977–2000) of competitive shore angling catch and effort data from the KwaZulu-Natal Coastal Anglers Union for the province of KwaZulu-Natal were analysed. Of a minimum of 117 species recorded, the most commonly caught species were dusky shark (Carcharhinus obscurus) (26%), milk shark (Rhizoprionodon acutus) (18%) and shad (Pomatomus saltatrix) (10%). By weight, the top species were dusky shark (34%) and diamond ray (Gymnura natalensis) (19%). All the above species showed considerable inter-annual variation in their respective contributions to annual catch. Probably as a result of changes in fishing patterns, dusky shark and milk shark showed a general decline in percentage contribution to catch over the period, while contributions of lesser guitarfish (Rhinobatos annulatus), giant guitarfish (Rhynchobatus djiddensis), diamond ray (Gymnura natalensis) and brown ray (Himantura gerrardi) increased. Mean overall annual cpue by number and weight showed a non-significant increase over the period, while each of the investigated species showed a constant trend in mean annual weight. There were high proportions of juveniles in the catches of dusky shark (100%), dusky kob (92%) and giant guitarfish (78%). Improvements made to the structure of shore angling competitions and the overall contribution of competition angling to resource management in South Africa is discussed.     

Notes on the Bathypelagic Fauna of the Seas Around South Africa

The preliminary results of a study of the endemic giant tortoise population of Aldabra Atoll in the Indian Ocean (Geochehne gigantea Schweigger) are briefly described. Their number would appear to have increased dramatically since the turn of the century to their present level of some 141 000 individuals. Crude estimates of mortality and reproductive rates are also given.