Fish populations, gill net selectivity, and artisanal fisheries in the Okavango River, Namibia. Recommendations for a sustainable fishery.

Hay, C.J., Næsje, T.F., Breistein, J., Hårsaker, K., Kolding, J., Sandlund, O.T. & van Zyl, B. 2000. Fish populations, gill net selectivity, and artisanal fisheries in the Okavango River, Namibia. Recommendations for a sustainable fishery. — NINA-NIKU Project Report 010: 1-105. Objective: The objective of this report is to produce guidelines for a sustainable management of the fisheries in the Okavango River, Namibia, based on fish survey data for the years 1992-1999. Data were also coHected regarding the subsistence fishery in the river. The rationale for the report is the 1995 White Paper "Responsible Management of the Inland Fisheries of Namibia" and the draft bill on inland fisheries. These have the objectives of ensuring a sustainable and optimal utilisation of the freshwater resources, and to favour utilisation of fish resources by subsistence households over commercialisation. The stated policy takes into consideration the large differences among water systems in Namibia and proposes adoption of sepa rate management regimes for the various river systems. Material and study area: Fish were collected in seven main areas (Matava, Musese, Bunya, Rundu, Cuito, Mbambi, and Kwetze) with survey gill nets (22-150 mm stretched mesh) and 16 other sampling methods, such as seine nets, mosquito nets, cast nets, angling, electrofishing apparatus, rotenone and different traditional gears. These are later collectively called "other gears". The stations were selected to include all main habitats present in the Okavango River. The gill nets were mainly used in relatively deep water, whereas the other gears were mainly used in shallow and vegetated habitats. All seven localities were sampled at least once a year between 1992 and 1999. A total of 47438 fishes were sampled, 13559 in gill nets, and 33879 in other gears. The Okavango River originates in the central highlands of Angola at approx. 1700 m a.s.l. and enters Namibia at Katwitwi. The river forms the border between Namibia and Angola before turning south towards Botswana. Along the Namibian section of the river, there are large floodplains with sandy substrates and rocky outcrops, and abundant aquatic vegetation. After a distance of 460 km within Namibia, the river enters Botswana where it evaporates in the swamps of the Okavango Delta. The annual flood in the Namibian portion of the Okavango starts during December reaches its peak in March-April and recedes during May. The annual discharge of the Ol avango at Rundu is between 5,000 and 6,000 million m3. Below the confluence with the Cuito River, the annual discharge nearly doubles to over 10,000 million m3. More than 136,000 people live in the Okavango region. An estimated 90 % of the population live within 10 km of the river, and many of the economic and social activities in the region are connected to the river. More than 50 % of the human population along the river do fish, both with traditional gears such as baskets, funnel traps and fences constructed of plant material, and with some modern gears such as gill nets, seines, hook and line, and mosquito-nets. For more than 90 % of the households fish is a source of subsistence, and sales of fish provide some income for approximately 45 % of the households. The highest population density is at Rundu, whereas no people live at Kwetze, which is within the Mahongo Game Park. It is assumed that the fishing pressure is correlated to the riparian population density

Hybrids between common and Antarctic minke whales are fertile and can back-cross

Background: Minke whales are separated into two genetically distinct species: the Antarctic minke whale found in the southern hemisphere, and the common minke whale which is cosmopolitan. The common minke whale is further divided into three allopatric sub-species found in the North Pacific, southern hemisphere, and the North Atlantic. Here, we aimed to identify the genetic ancestry of a pregnant female minke whale captured in the North Atlantic in 2010, and her fetus, using data from the mtDNA control region, 11 microsatellite loci and a sex determining marker. Results: All statistical parameters demonstrated that the mother was a hybrid displaying maternal and paternal contribution from North Atlantic common and Antarctic minke whales respectively. Her female fetus displayed greater genetic similarity to North Atlantic common minke whales than herself, strongly suggesting that the hybrid mother had paired with a North Atlantic common minke whale. Conclusion: This study clearly demonstrates, for the first time, that hybrids between minke whale species may be fertile, and that they can back-cross. Whether contact between these species represents a contemporary event linked with documented recent changes in the Antarctic ecosystem, or has occurred at a low frequency over many years, remains open

Fish populations, gill net selectivity, and artisanal fisheries in the Okavango River, Namibia. Recommendations for a sustainable fishery.

Hay, C.J., Næsje, T.F., Breistein, J., Hårsaker, K., Kolding, J., Sandlund, O.T. & van Zyl, B. 2000. Fish populations, gill net selectivity, and artisanal fisheries in the Okavango River, Namibia. Recommendations for a sustainable fishery. — NINA-NIKU Project Report 010: 1-105. Objective: The objective of this report is to produce guidelines for a sustainable management of the fisheries in the Okavango River, Namibia, based on fish survey data for the years 1992-1999. Data were also coHected regarding the subsistence fishery in the river. The rationale for the report is the 1995 White Paper "Responsible Management of the Inland Fisheries of Namibia" and the draft bill on inland fisheries. These have the objectives of ensuring a sustainable and optimal utilisation of the freshwater resources, and to favour utilisation of fish resources by subsistence households over commercialisation. The stated policy takes into consideration the large differences among water systems in Namibia and proposes adoption of sepa rate management regimes for the various river systems. Material and study area: Fish were collected in seven main areas (Matava, Musese, Bunya, Rundu, Cuito, Mbambi, and Kwetze) with survey gill nets (22-150 mm stretched mesh) and 16 other sampling methods, such as seine nets, mosquito nets, cast nets, angling, electrofishing apparatus, rotenone and different traditional gears. These are later collectively called "other gears". The stations were selected to include all main habitats present in the Okavango River. The gill nets were mainly used in relatively deep water, whereas the other gears were mainly used in shallow and vegetated habitats. All seven localities were sampled at least once a year between 1992 and 1999. A total of 47438 fishes were sampled, 13559 in gill nets, and 33879 in other gears. The Okavango River originates in the central highlands of Angola at approx. 1700 m a.s.l. and enters Namibia at Katwitwi. The river forms the border between Namibia and Angola before turning south towards Botswana. Along the Namibian section of the river, there are large floodplains with sandy substrates and rocky outcrops, and abundant aquatic vegetation. After a distance of 460 km within Namibia, the river enters Botswana where it evaporates in the swamps of the Okavango Delta. The annual flood in the Namibian portion of the Okavango starts during December reaches its peak in March-April and recedes during May. The annual discharge of the Ol avango at Rundu is between 5,000 and 6,000 million m3. Below the confluence with the Cuito River, the annual discharge nearly doubles to over 10,000 million m3. More than 136,000 people live in the Okavango region. An estimated 90 % of the population live within 10 km of the river, and many of the economic and social activities in the region are connected to the river. More than 50 % of the human population along the river do fish, both with traditional gears such as baskets, funnel traps and fences constructed of plant material, and with some modern gears such as gill nets, seines, hook and line, and mosquito-nets. For more than 90 % of the households fish is a source of subsistence, and sales of fish provide some income for approximately 45 % of the households. The highest population density is at Rundu, whereas no people live at Kwetze, which is within the Mahongo Game Park. It is assumed that the fishing pressure is correlated to the riparian population density

The orthodontic condition of children in the United Kingdom, 2003

Background The 2003 Children's Dental Health Survey is the fourth in a series of decennial national children's dental health surveys in the United Kingdom. Aims This paper reports on the orthodontic condition of children aged 12 and 15 years. Methodology A representative sample of children across the UK were invited to participate in a clinical dental examination in school. Two thousand, five hundred and ninety-five 12-year-olds and 2,142 15-year-olds were examined. Current and past orthodontic treatment and type of appliance worn were recorded. Orthodontic treatment need was assessed by the Modified IOTN in those not undergoing treatment. A postal questionnaire sought parents' views on the orthodontic condition of their children and perceived need for treatment. Results At age 12, 35% were judged to have an orthodontic treatment need, 57% had no need and 8% were wearing an appliance. The corresponding figures at age 15 were, 21% (need), 65% (no need) and 14% (wearing appliance). A higher proportion of girls (p < 0.05) were wearing an appliance than boys. A greater proportion of 15-year-olds were undergoing treatment than in the 1993 and 1983 surveys and the use of fixed appliances had increased. Conclusions In this representative sample of UK children, one in five were still judged as having an orthodontic treatment need at age 15 years, as determined by the modified index of orthodontic treatment need. However, considerable variation was observed between professional and lay perceptions of need