Disentangling reproductive biology of the Patagonian toothfish <Emphasis Type="Italic">Dissostichus eleginoides</Emphasis>: skipped vs obligatory annual spawning,foraging migration vs residential life style

Patagonian toothfish Dissostichus eleginoides Smitt 1898, is an important commercially targeted Notothenioid species in South-Atlantic waters. In this study we aimed to clarify several aspects of reproductive biology of Patagonian toothfish in the Falkland Islands waters. Histological examination of female gonads indicates that with the beginning of maturation females maintain at least two populations of oocytes, suggesting that toothfish requires up to two years for oocytes development. Females become mature at an average size of 79.1 cm indicating a decrease of first maturity size if toothfish females in the Falkland Island waters. The majority of females spawn at the size from 101 to 130 cm total length. Distribution of reproductive phases shows an increase of females at developing stage in December and March prior to the spawning peaks in May and August respectively. However, the majority of the toothfish population consist of non-spawning individuals remaining in regressing phase (55.8 to 85.6%) including the spawning period. The skip-spawning for toothfish has been defined as reabsorbing non-reproductive and resting types. The abbreviation of oocytes development in the gonads was observed from 1 to 22.1% of females which omitted the spawning season. Most likely females which remain in the spawning area have the opportunity to spawn more often, whereas females which undergo foraging migration toward Northern parts of the Falklands waters return to the spawning ground less often. Females remain Northern area longer to accumulate necessary amount of energy. This hypnotise is supported by the presence of females in immature, developing and regressing phase throughout surrounding Falkland Islands waters. Presence of post-spawning females in regressing stage throughout the Falklands waters suggest that toothfish may undertake irregular spawning/foraging migration when favourable for spawning condition occur.     

Exploratory deep-sea fishing in the Falkland Islands, south-western Atlantic

Records of demersal deep-sea fish assemblages in waters around the Falkland Islands (Patagonian shelf area) are rare. Twenty deep-water stations to the east and south of the Falkland Islands were sampled by commercial bottom trawl deployed in upper, middle and lower benthopelagic zones (depth range of approximately 500-1000 m). Forty-one species (22 families) of teleost fish were recorded, 10 species (two families) of elasmobranch and one species of agnathan. Different assemblages of fish were found to characterize each depth zone (e.g. Moridae in deeper waters, Bothidae and Rajidae in shallower waters), with diversity being greatest in the mid-zone and biomass greatest in the upper and lower zones. Some species occurred in all zones but showed depth-related abundance. Four species, namely the grenadiers Macrourus carinutus and Coelorhynchus fasciatus , the southern blue whiting Micromesistius australis , and the Patagonian toothfish Dissostichus eleginoides , accounted for 85% by weight of all fish caught. Quantitative sampling of selected species revealed depth-related variations in their population structure. Length-frequency analyses are presented for M. carinatus and D. eleginoides and show a tendency for larger individuals to inhabit deeper water. Discard rates from the commercial catch were sometimes high, particularly for the smaller species, raising concerns about the impact of a fishery on by-catch species. The potential for deep-sea fisheries in Falkland waters is discussed and further studies are suggested in the light of developing oil, gas and fishing industries. The presence of some invertebrate taxa is recorded.     

Distribution and reproduction of the Patagonian toothfish Dissostichus eleginoides Smitt around the Falkland Islands

Population characteristics of the Patagonian toothfish Dissostichus eleginoides were investigated based on material collected from both trawl and longline fisheries in Falkland Islands' waters. The fish occurred between 56 and 2122 m and attained 225 cm total length ( L _T). Males matured earlier, L _T at 50% maturity was 86 cm for males v . 90 cm for females. Subadult fish foraged at depths of <600 m, whereas adult Patagonian toothfish lived at >600 m. Spawning occurred on slopes of the Burdwood Bank at c . 1000 m depth with a minor peak in May, and a major peak in July to August. Males arrived at the spawning grounds first. Between spawning peaks both sexes remained around the Burdwood Bank with males occurring at greater depths than females. The Patagonian toothfish in south‐east Patagonia and the Falkland Islands had a long juvenile and sub‐adult period in the relatively shallow and warm waters of the outer shelf and upper slope unlike that of juveniles in other Patagonian toothfish populations. The migratory life style of the south‐west Atlantic population is probably very different from that of other populations, which tend to be resident as they are inclined to inhabit the waters around oceanic islands and sea mounts with narrow shelf areas.     

Foraging interactions between Wandering Albatrosses Diomedea exulans breeding on Marion Island and long-line fisheries in the southern Indian Ocean

Wandering Albatrosses Diomedea exulans are frequently killed when they attempt to scavenge baited hooks deployed by long-line fishing vessels. We studied the foraging ecology of Wandering Albatrosses breeding on Marion Island in order to assess the scale of interactions with known long-line fishing fleets. During incubation and late chick-rearing, birds foraged further away from the island, in warmer waters, and showed high spatial overlap with areas of intense tuna Thunnus spp. long-line fishing. During early chick-rearing, birds made shorter foraging trips and showed higher spatial overlap with the local Patagonian Toothfish Dissostichus eleginoides long-line fishery. Tracks of birds returning with offal from the Toothfish fishery showed a strong association with positions at which Toothfish long-lines were set and most diet samples taken during this stage contained fishery-related items. Independent of these seasonal differences, females foraged further from the islands and in warmer waters than males. Consequently, female distribution overlapped more with tuna long-line fisheries, whereas males interacted more with the Toothfish long-line fishery. These factors could lead to differences in the survival probabilities of males and females. Non-breeding birds foraged in warmer waters and showed the highest spatial overlap with tuna long-line fishing areas. The foraging distribution of Marion Island birds showed most spatial overlap with birds from the neighbouring Crozet Islands during the late chick-rearing and non-breeding periods. These areas of foraging overlap also coincided with areas of intense tuna long-line fishing south of Africa. As the population trends of Wandering Albatrosses at these two localities are very similar, it is possible that incidental mortality during the periods when these two populations show the highest spatial overlap could be driving these trends.     

Population trends, breeding success and diet composition of gentoo Pygoscelis papua, magellanic Spheniscus magellanicus and rockhopper Eudyptes chrysocome penguins in the Falkland Islands. A review

Data on population size, breeding success and diet composition of gentoo (Pygoscelis papua), magellanic (Spheniscus magellanicus) and rockhopper (Eudyptes chrysocome) penguins, collected as part of the Falkland Island Seabird Monitoring Programme from 1986/1987 to 1998/1999, were analysed with regard to spatial and temporal variation, as well as potential interaction with local commercial fisheries. No significant population trends were detectable, mainly because of the short time-series and large spatial and inter-annual variation in the number of breeding pairs in the colonies monitored. However, the breeding success of all three penguin species has improved slightly over the last few years, indicating a potential for increasing populations in the near future. During the breeding season, all three penguin species preyed opportunistically on a mixture of fish, squid and crustaceans. Diet composition too showed a high degree of spatial and temporal variation. However, in all three penguin species studied, squid gradually disappeared from the diet over successive years, to be replaced by fish. Coincidentally, the commercial catches of the squid species Loligo gahi in Falkland Islands waters decreased and the by-catch of nototheniid fish increased. All three penguin species compete directly with the commercial fishing fleet for L. gahi; however, there may also be competition for Patagonian toothfish (Dissostichus eleginoides), hake (Merluccius sp.) and southern blue whiting (Micromesistius australis), because juveniles of these species were found regularly in penguin diets.     

Demographic parameters of black-browed albatrosses Thalassarche melanophris from the Falkland Islands

Black-browed albatrosses Thalassarche melanophris are currently classified as globally endangered. The most important populations of this species are believed to be declining due to, amongst other factors, unsustainable levels of incidental mortality in fishing gear. However, detailed demographic data are lacking for several critical populations, including the largest of all, nesting in the Falkland Islands. Here, we present data from the first Falkland Islands detailed demographic study (at New Island) and show that, from 2003 to 2009, the mean adult survival probability was 0.942 (95% CI: 0.930–0.952). Nesting frequency of adults is amongst the highest recorded for Thalassarche albatrosses and breeding success (0.564 chicks per egg) is within normal values. The nesting population in the intensively studied plots experienced an increase of 4% per year from 2004 to 2009. These results indicate that the Falklands population may not be as threatened as previously supposed, although studies from more sites and a longer time series are needed to confirm or refute this. The high survival rates may partly reflect recent efforts to mitigate bycatch made by the Falkland Islands and other fisheries in the region. The reinforcement of such initiatives may be critical to buffer the black-browed albatross population against ecosystem shifts and natural disasters (such as harmful algal blooms) that will likely become more frequent with ongoing global changes.     

Polymorphic microsatellite DNA markers for the Patagonian squid,Loligo gahi (Cephalopoda)

Squid populations are being put under rapidly increasing commercial fishing pressure worldwide. The same species are known to be susceptible to extreme population fluctuations, so detailed knowledge of population substructuring and genetic diversity is essential for rational management. We present a set of microsatellite DNA loci suitable for population genetic analysis of Loligo gahi, the squid species subject to the most detailed monitoring and fishery control (around the Falkland Islands), with the future aim of generating management‐related information to aid conservation of this valuable natural resource.     

International Influence of an Australian Nongovernment Organization in the Protection of Patagonian Toothfish

Soviet Union fishing fleets found Patagonian toothfish in 1985 off the Kerguelen Islands in the Southern Ocean. In a few short years, toothfish became heavily fished and the viability of the fishery was put in question. This pressure largely arose from illegal, unreported, and unregulated (IUU) fishing that undermined fisheries management by coastal states and the Convention for the Conservation of Antarctic Marine Living Resources (CCAMLR) Commission. The International Southern Oceans Longline Fisheries Information Clearing House (ISOFISH), based in Hobart, Tasmania, Australia, raised awareness about IUU fishing among governments, fishers, and the community. This article presents a case study of ISOFISH and the influence this nongovernment organization coalition exerted on the international community, including the deep-sea fishing industry, governments, and CCAMLR members, in an effort to protect toothfish stocks and reduce the incidental mortality of endangered seabirds and other nontarget marine species from longlining activities.­     

Optimum fishing strategies for Isostichopusfuscus (Echinodermata: Holothuroidea) in the Gulf Of California, Mexico

The Isostichopus fuscus fishery in Mexico was heavily exploited until 1994, when it was closed due to overfishing. However, no information existed on the status of the populations. The fishery was evaluated through an age structured simulation model, and according to our analysis of the stock, the fishery can be feasible and sustainable as long as fishing mortality and age of first catch are optimized. In order to evaluate exploitation strategies, several scenarios were simulated considering different combinations of fishing intensities and ages of first catch. Input data for the model included population parameters, commercial catch and costs and benefits of the fishing operations. Yield production was strongly influenced by the fishing pressure and by the age of first capture. When the first one increased, significant decreases in yield and profits occurred. The best exploitation strategy was these parameters: fishing mortality level F = 0.15, age at first capture t(c) = 4 years, and yielding of approximately 430 tons. However, since the species reproduces for the first time at 5 years, extracting younger specimens would collapse the population. The critical value of fishing mortality was detected at Fc = 0.25. If exceeded, the population tends to exhaustion and the fishery is no longer profitable. In conclusion, I. fuscus fishery is highly vulnerable to overfishing and age of catch. It must be taken into account that the management policies should be considered as pilot and used on a regional basis. Continuous monitoring of the stock, control of the number of fishing licenses and extracting only specimens 5 yeasr-old and older (around 20 cm and >400 g), will allow the populations to recover from fishing activities. Rev. Biol. Trop.     

A bioeconomic model of the pacific whiting

The Pacific whiting (Merluccius productus) is a highly migratory fish occupying the continental shelf and slope off the west coast of North America. The species spawns in January off southern California and northern Mexico. During spring and summer the older and larger fish will migrate as far north as central Vancouver Island. Recruitment is highlys variable, with strong year classes often supporting the commercial fishery during several years of low recruitment. The level of recruitment appears to be independent of the size of the spawning population. A simple bioeconomic model of the Pacific whiting is constructed with independent recruitment. Fishery production functions are estimated from data on U.S. catch, average annual biomass and the number of vessels in the U.S. fleet. A stochastic optimization problem, seeking to maximize the expected value of industry profit, is formulated. Its solution would require a joint distribution on future recruiment and other bioeconomic parameters. Such a distribution is problematic. As an alternative, the certainty-equivalent problem is solved yielding solution values for the stochastic equilibrium and an approximately-optimal rule that sets allowable catch based on an estimate of current-year biomass. Adaptive management can result in large changes in fleet size and allowable catch from year to year. The whiting fishery might be characterized as an opportunistic fishery, requiring a generalist fleet to expand or contract as bioeconomic conditions warrant. It is possible that longrun conditions would not support a profitable fishery, but that short-run fishing is profitable based on previous years of strong recruitment. The situation is not dissimilar to that facing the owner of a marginal gold mine that opens or closes depending on the price of gold. In the case of the whiting fishery, the optimal level of short-run fishing will depend not only on price, but on current biomass, the annual cost of fishing, the discount rate and vessel productivity. A simple interactive program is provided for would-be managers. This paper was written in July 1990 while the author was a Summer Faculty Fellow at the Southwest Fisheries Center, La Jolla, California. The author gratefully acknowledges the support of the U.S. National Marine Fisheries Service.     

Winter migration of rockhopper penguins (Eudyptes c. chrysocome) breeding in the Southwest Atlantic: is utilisation of different foraging areas reflected in opposing population trends?

Rockhopper penguins (Eudyptes chrysocome) breeding on Staten Island, Argentina, were satellite tracked in 2002 and 2003 during the onset of their winter migration. After their moult, the dispersal of 24 birds was monitored for a mean period of 50.0±40.3 days. Birds travelled at a mean velocity of 3.1±1.1 km/h. The mean minimum distance travelled was 1,640±1,425 km; the maximum distance to the colony was generally less than 1,000 km, although one bird travelled more than 2,000 km from the colony. The penguins dispersed over an area totalling about 1.3 million km2, ranging from 50 to 62°S and from 49°W in the Atlantic to 92°W in the Pacific, and covering polar, sub-polar and temperate waters in oceanic regions as well as shelf waters. Despite the very wide dispersal, both temporally and spatially, two important wintering grounds for rockhopper penguins from Staten Island could be identified, both located over shelf regions: one extended from Staten Island to the north along the coast of Tierra del Fuego up to the Magellan Strait; the other was located over the Burdwood Bank, an isolated extension of the Patagonian Shelf to the south of the Falkland Islands. The Drake Passage also appeared to be an important area for wintering penguins, although dispersal was far more widely spread. Comparison with data obtained during winter from rockhopper penguins originating from the Falkland Islands showed that the area off the coast of Tierra del Fuego was used more or less exclusively by birds from Staten Island, whereas the Burdwood Bank was shared with penguins coming from southern colonies in the Falkland Islands. The implications of these findings are discussed with regard to (a) opposing population trends of rockhopper penguins in the Southwest Atlantic, and (b) the urgent need to establish adequate conservation measures for species and habitat protection.     

2016年南极斯科舍海南极大磷虾种群结构的时空变化

斯科舍海是南极大磷虾资源分布最为密集的海域,也是磷虾的传统渔场,但该海域磷虾种群结构存在较为显著的年际、季节性与区域性差异.为了解该海域磷虾种群动态,本研究利用2016年1—9月由渔业调查随机收集的样本,对该海域磷虾种群结构的时空变动进行了分析.结果表明: 各月磷虾性比存在显著的差异,1—5月雌性明显占优,而6—9月则呈现相反的趋势.1—9月期间,仅1月出现幼体,且雌性成体的比例与2月相当,占比超过了40%;3—5月,雌性未成体的比例均超过了50%,而雌性成体的比例开始逐月下降;6—8月,雄性未成体的比例达到峰值;9月,雌性未成体的比例显著增加,而雄性成体的比例呈下降趋势.在布兰斯菲尔德海峡内,2—5月,雌性未成体的比例超过一半;1月,乔治王岛东北水域已排卵个体的比例(25.6%)显著高于其他个体,雌性临产个体的比例也较高;6—9月,南乔治亚岛东北水域雄性成体的比例约占一半,雌性成体的比例极低.性成熟度组成显示,1—2月为磷虾产卵盛期,而产卵场出现在乔治王岛东北水域以及布兰斯菲尔德海峡.     

Population dynamics of the wandering albatross (Diomedea exulans) on Macquarie Island and the effects of mortality from longline fishing

The estimated breeding population of wandering albatrosses on Macquarie Island increased from 17 in 1956 to a maximum of 97 in 1966, and then declined at an average rate of 8.1% per year. Mark-recapture analysis shows that the population is not closed (i.e., subject to immigration and emigration). The decline is correlated with the onset of large-scale fishing for tuna in the southern hemisphere using longlines. The effect of longline mortality on the population dynamics of the wandering albatross is estimated. An annual number of longline hooks in the southern hemisphere tuna fishery of 41.6 million is calculated as the ceiling below which the population would begin to recover.     

VMS-based fishing effort and population demographics for the European squid (Loligo vulgaris) off the Portuguese coast

This study presents a 1-year synopsis of the trawl fishery for the European squid Loligo vulgaris in Portuguese waters, integrating length-structured landings with corresponding geo-referenced fishing activities. From vessel monitoring system (VMS) data, landings and biological sampling, a “status-report” was obtained for 2003. Fishing pressure was found to be most intense in inshore areas of the northwest and the south coasts. Population size structure, classified into three categories, was not uniform throughout the fishing areas. Larger squid are found offshore in the northwest (International Council for the Exploration of the Sea—ICES rectangle 10E0) and in the south (rectangles 2E1 and 3E1), whereas all inshore western coast rectangles showed larger proportions of small squid relative to the southern rectangles. The analysis carried out in this study provides an insight into the possible impact of the fishing intensity pattern on the population structure in various zones. The results demonstrate the benefits of combining geo-referenced fisheries information with landings and size data, to produce explicit spatio-temporal information that can contribute to integrated planning and management for the sustainable exploitation of this resource.     

Assessing the impact of toothed whale depredation on socio-ecosystems and fishery management in wide-ranging subantarctic fisheries

Marine predators feeding on fisheries catches directly on the fishing gear, a behaviour termed “depredation”, has emerged as a major human-wildlife conflict globally, often resulting in substantial socio-economic and ecological impacts. This study investigated the extent of this conflict in commercial Patagonian toothfish (Dissostichus eleginoides) fisheries across subantarctic waters where both killer whales (Orcinus orca) and sperm whales (Physeter macrocephalus) feed on toothfish caught on longline hooks. Using long-term datasets from six major fishing areas, from southern Chile to the Indian Ocean sector of the Southern Ocean, statistical models were developed to quantify the catch removals due to whale depredation interactions. The results indicated that these removals were large, totalling more than 6600 t of toothfish between 2009 and 2016 with an annual mean of 837 t [95% CI 480–1195 t], comprised of 317 t [232–403 t] and 518 t [247–790 t] removed by killer whales and sperm whales, respectively. Catch removals greatly varied between areas, with the largest estimates found at Crozet, where on average 279 t [179–379 t] of toothfish per year, equivalent to 30% [21–37%] of the total catches. Together, these findings provide metrics to assess the impacts of depredation interactions on the fishing industry, whale populations, fish stocks and associated ecosystems. With an estimated $15 M USD worth of fish depredated every year, this study highlights the large geographic scale and economic significance of the depredation issue and its potential to compromise the viability of some toothfish fisheries which are the primary socio-economic activity in subantarctic regions.

     

南极半岛北部南极磷虾渔业空间点格局特征

南极磷虾作为南极生态系统中的关键物种,在空间分布上常表现出集群特征.这也反映到磷虾渔业生产的空间格局特征上.为了探讨捕捞能力有明显差异的船队在高/低单位捕捞努力量渔获量(CPUE)的情况下空间点分布格局特征及其生态学效应,基于南极半岛北部海域的两艘中国南极磷虾渔船(船A为专业南极磷虾渔船,船B为在智利竹筴鱼渔场与南极磷虾渔场转换的兼作渔船)的磷虾渔业数据,从空间点格局的角度出发,分别从两船的高、低CPUE的空间点格局在不同尺度上聚集特征,高、低CPUE在不同尺度上的二元点格局相关关系,以及CPUE点标记格局下的相关性关系等3个方面进行了分析.Ripley的L函数和标记相关函数分析结果表明: 研究对象在空间窗口所有尺度上的空间格局均表现为聚集性,高、低CPUE下均有聚集发生;在15 km尺度上,聚集强度近最大,在15~50 km尺度下,聚集程度稳定;总体上点格局分布的聚集强度依次为:船A高CPUE>船B低CPUE>船B高CPUE>船A低CPUE.船A高、低CPUE在0~75 km尺度上为正相关关系,在大于75 km尺度上为随机关系;船B在所有尺度上的高、低CPUE均为正相关,说明了低CPUE点事件伴随高CPUE的点事件同步发生,两者在大部分尺度下均显著相关.这是磷虾集群模式的动态性和复杂性造成.船A各点的CPUE值在0~44 km尺度上呈正相关,在44~80 km尺度上呈负相关;船B各点的CPUE值在50~70 km尺度上呈负相关,在其他尺度上无显著相关性;正相关反映了磷虾密集集群的种群分布特性,而负相关表明了磷虾群间由于食物和空间原因存在一定的竞争关系.捕捞能力强的船A和捕捞能力较弱的船B在点格局分布上存在较大差异.专业南极磷虾渔船更适于开展磷虾作业空间点格局分析及相关科学调查工作.     

The enigma of guanacos in the Falkland Islands: the legacy of John Hamilton

Aim To address the biogeographical enigma of why guanacos (Lama guanicoe) are in the Falkland Islands we investigated the following questions: (1) What was the origin of the introduced guanacos? (2) What were the initial population sizes? (3) Why are they found only on one island? and (4) Who was John Hamilton and what role did he play? Location The Falkland Islands are located in the South Atlantic Ocean 600 km east of Patagonia at the southern end of South America. While dominated by East and West Falkland Islands, the archipelago is composed of some 750 islands. Sedge and Staats Islands, two small outlying islands of West Falkland, are the focus of this paper. Methods Historical information was collected from known relevant documents housed at the Falkland Islands Government Archives in Stanley, and personal interviews conducted with past and present residents of West Falklands. Research expeditions were made to Staats Island in 1999, 2002 and 2003 to assess the guanaco population size, distribution and social structure. Results Guanacos were unsuccessfully introduced in 1862 to East Falkland south of Mt Pleasant where Prince Alfred hunted them in 1871. John Hamilton, Scottish immigrant to the Falklands and Patagonia of southern Argentina and Chile, was the driving force in the introduction of guanacos from the region of Rio Gallegos, Argentina during the 1930s. The guanaco was one of several wildlife species he introduced, however, only the guanaco, Patagonia grey fox (Dusicyon griseus) and perhaps the sea otter (Lutra felina) survive. Hamilton's acting agent, Jimmy Miller, imported four shipments totalling 26 guanacos from 1934 to 1939. In 1934 the Falkland Government authorized Miller to introduce guanacos to Sedge Island, all 11 of which disappeared. Whether intentional or accidental, 15 guanacos were taken to Staats Island, an islet of 500 ha on the western edge of the archipelago. Historically, guanacos are unexpected on Staats Island because documentation authorizing their introduction is unknown. Guanaco numbers have fluctuated widely on Staats Island for 65 years primarily due to culling. In 1959 the population was dangerously close to extirpation, but today 400 thrive there. A severely reduced gene pool and genetic bottlenecking were suggested by recent field studies, revealing preliminary evidence of deleterious consequences of inbreeding. Main conclusions John Hamilton, spirited and visionary Scottish immigrant to the Falklands in the early 1880s, was responsible for the introduction of guanacos into the Falkland Islands. While there are some gaps in the historical events, the enigma of how and why guanacos were introduced to a single island in the South Atlantic Ocean is understood. Today, Staats Island, as a closed system, is a rare natural experiment in progress. It offers unique opportunities for addressing advanced questions in ungulate population, behavioural and genetic ecology. The population potentially also represents breeding stock for farming the guanaco's highly valuable wool on other islands. Thus, among his many efforts to practice land stewardship and promote economic diversity through the introduction of Patagonian wildlife, a remaining legacy of John Hamilton to the Falkland Islands is unmistakably the guanacos of Staats Island.     

An impact of seasonal squid migrations and fishing on the feeding spectra of subantarctic notothenioids Patagonotothen ramsayi and Cottoperca gobio around the Falkland Islands

Seasonal changes in the diet of two abundant notothenioid fishes, rock cod Patagonotothen ramsayi (Nototheniidae) and frogmouth Cottoperca gobio (Bovichthidae) were studied on the Falkland Island shelf. The rock cod is a near-bottom browser, feeding mostly on gelatinous and crustacean plankton. The diet of juveniles [10–16 cm total length (TL)] includes mostly copepods in summer and comb jellies Mnemiopsis leydyi in winter. Adult rock cod (17–34 cm TL) in summer consumed mainly plankton, with comb jellies and salps being of primary importance. In winter they mainly took benthos, primarily ophiuroids and lobster krill ( Munida spp.), and the comb jelly. During the fishing season, rock cod also scavenge on fishing discards. The frogmouth is a benthic ambush predator; both small (11–30 cm) and large (31–80 cm) representatives feed on the rock cod throughout the year. During the seasonal offshore migration of the squid Loligo gahi (June–August), this prey predominated in the large frogmouth diet, with crab, Peltarion spinosulum , of secondary importance. The region is seasonally exploited by the squid trawl fishery. As the fishing season commences (August–September), discarded rock cod also becomes an important food item for the frogmouth. Seasonal offshore migrations of L. gahi into the common depth range of both notothenioids have a significant direct (change in the C. gobio diet) and indirect (scavenging on fishing discards and targeting bottom scavengers by P. ramsayi and C. gobio during the squid fishing) impact on their diets over the Falkland shelf. The niche breadth of rock cod varied from 2.63 to 3.21 and that of frogmouth varied from 2 to 6.29, depending on fish size and season.     

A plan for fisheries management in the lakes drained by the Oulujoki river

Freshwater fishery management is treated as a dynamic system comprising environment protection and improvement, fishing, fishery resources allocation, fish stocking programs and marketing policy. The aims of the plan are to increase the economic value of the catch and to protect the professional fishery. Fisheries statistics, catch per unit effort data and other material were collected during 1972–1976. The total allowable catch (TAC) for the most important fish species was estimated with MSY and population analysis models. The results of fish stockings were studied by tagging and population analysis calculations. Fishing of vendace and non-valuable species (perch, roach, smelt) can be increased, but the fishing pressure on other species should not be raised above the present level. Restrictions on whitefish fishing are needed in some areas. A balanced multispecies fishery is desirable, and suggestions are given for the composition of the fishing gear. Fish stocking can make possible a larger and more valuable catch, but at present its profitability is rather low. The stocking results are strongly affected by the fishery and the gear composition.     

Effects of commercial fishing on the population structure of spawning southern calamary (Sepioteuthis australis)

This study explored population dynamics of Sepioteuthis australis on a fine temporal scale before, during, and after a 3-month commercial fishing closure on the summer inshore spawning grounds of Great Oyster Bay, Tasmania, Australia. An abrupt change in male size (mantle length) and population sex ratio after the re-opening of the commercial fishery suggests that fishing alters the population structure on the spawning beds from a ‘natural’ structure which is highly biased towards males, to a more even ratio of males to females. Although jigs are taking a representative sample of the squid population using the spawning beds at any one time, the fishery is apparently still effectively selective for males, potentially as a function of differential spawning movements of the two sexes. Increased fishing pressure over the past 5 years had been correlated with a change towards a highly male-biased sex ratio on the spawning beds; however the current study suggests that increased fishing pressure in recent years may not have reduced the proportion of females. Instead, the inter-annual change in sex ratio may reflect changes in the degree of protection from fishing, with progressively longer closures allowing time for more males to accumulate on the beds and therefore, for the proportion of males to increase (as opposed to a decrease of females). As fishing is selective for males, fishing throughout the spawning season could potentially modify the process of sexual selection and the mating behaviors of the individuals within the spawning population, highlighting the need for closures over this crucial period. Additionally, examinations and comparisons of squid population structure need to be interpreted in light of fishing pressure and broader movement patterns.