Do environmental factors influence the movement of estuarine fish? A case study using acoustic telemetry

Telemetry methods were used to investigate the influence of selected environmental variables on the position and movement of an estuarine-dependent haemulid, the spotted grunter Pomadasys commersonnii (Lacepède 1801), in the Great Fish Estuary, South Africa. Forty individuals (263–698 mm TL) were surgically implanted with acoustic coded transmitters and manually tracked during two periods (7 February to 24 March 2003; n = 20 and 29 September to 15 November 2003; n = 20). Real-time data revealed that spotted grunter are euryhaline (0–37) and are able to tolerate large variations in turbidity (4–356 FTU) and temperature (16–30 °C). However, the fish altered their position in response to large fluctuations in salinity, temperature and turbidity, which are characteristic of tidal estuarine environments. Furthermore, tidal phase had a strong influence on the position of spotted grunter in the estuary

Prøvefiske i Kråkenesvatn og Hanangervatn April 1982

Etter at Lista Aluminiumsverk begynte å ta kjølevann fra Kråkenesvatn og Hanangervatn, har aurebestanden i de to innsjøene gått tilbake, til tross for at det er foretatt kompensasjonsutsettinger av yngel i flere år. Det utførte prøvefiske hadde som mål å klargjøre årsaken til tilbakegangen og forklare hvorfor settefiskeutsettingen ikke har gitt det forventede resultat. Det skulle dessuten utarbeides handlingsprogram med sikte på å restaurere aurebestander i de to innsjøene. Hovedårsaken til tilbakegangen synes å være reduserte reproduksjonsmuligheter samt at utsettingsmaterialet har vært for lite og dårlig egnet i innsjøene. Det foreslås utsetting av større og flere fisk av egen stamm

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

Movement patterns of an endangered fishery species, Lithognathus lithognathus (Sparidae), and the role of no-take marine protected areas as a management tool

Understanding movement behaviour is essential for effective management of fishery species. Dart tags were used to study coastal movement patterns of white steenbras Lithognathus lithognathus, an overexploited seabream (Sparidae) in South Africa. In total, 6 962 fish (190–1 080 mm fork length) were tagged throughout the species’ distributional range, in four long-term fish-tagging programmes. The predominant behaviour recorded was residency, with relatively short-ranging movements. More than 60% of the 351 recaptured fish were recaptured within 1 km of their tagging site, some of which were at liberty in excess of three years. Most of the juveniles (93.9%), subadults (71.7%) and adults (64.0%) were recaptured within 10 km. Occasional long-distance movements of up to 800 km were recorded. Recapture distances were positively, but weakly, correlated with fish fork length (n = 257 fish measured at recapture; r2 = 0.166, p < 0.001). Low levels of connectivity among coastal areas suggest that large-scale annual spawning migrations, as previously hypothesised for this species, are unlikely, which raises the possibility of multiple spawning sites. Seventy-seven percent of L. lithognathus tagged within three marine protected areas (MPAs) were recaptured within the same MPA, suggesting that area closures provide protection for L. lithognathus through the post-estuarine juvenile, subadult and adult life stages. We confirm that the country’s current network of coastal MPAs plays a vital role in sustaining this species, and suggest that additional closures, or otherwise substantial reductions in catch rates, are necessary for the species’ recovery.Keywords: dart tagging, fish movements, IUCN red-listed fish, recapture distance, research angling, seabream, South Africa, white steenbra

First assessment of estuarine space use and home range of juvenile white steenbras, Lithognathus lithognathus

The spatial dynamics and home range sizes of early juvenile white steenbras (Lithognathus lithognathus Cuvier, 1829) in the permanently open Great Fish Estuary, South Africa, were assessed using acoustic telemetry. Seven individuals (154–184 mm fork length) tagged with acoustic transmitters spent the majority of their time in the mesohaline to oligohaline regions of the estuary, between five and seven kilometres from the mouth. Mean home range size was small (97 399 ± 22 557 m2, mean ± S.D.) relative to the size of the estuary (approx. 1 360 000m2). Mean length of the estuary used by an individual was 1707m(±S.D.=1663 m). The fish were highly resident within the estuary, and showed fidelity towards their site of capture.Key words: acoustic telemetry, estuarine fish, Great Fish Estuary, South Africa, Sparidae

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

When plenty is not enough: an assessment of the white stumpnose (Rhabdosargus globiceps) fishery of Saldanha Bay, South Africa

White stumpnose Rhabdosargus globiceps is the main target of the linefishery in Saldanha Bay. Increased fishing pressure over the last three decades, particularly by the recreational sector, has led to concerns regarding sustainability of the local white stumpnose stock. The fishery was exceptionally productive between 2006 and 2008, with an estimated annual catch of 141.2 tonnes (t). Only 3% of boat outings surveyed were commercial boats targeting white stumpnose, yet this sector accounted for 39.3 t (31%) of the average annual catch. The recreational boat sector accounted for most of the catch (70.0 t), and the recreational shore sector the least (31.9 t). Commercial boat catch per unit effort (CPUE; 3.7 fish angler–1 h–1) was more than 10 times that of recreational boats (0.3 fish angler–1 h–1). White stumpnose catch length-frequency differed significantly (p < 0.01) between the fishing sectors, with the commercial sector retaining larger fish (34.7 cm [SD 5.9]) than the recreational boat (33.9 cm [SD 5.9]) and shore (30.4 cm [SD 5.8]) sectors. A decline in commercial CPUE (2000–2015) of approximately 40% and a concomitant severe decline (>95%) in survey data for juvenile white stumpnose CPUE (2007–2016) indicate that the current rate of exploitation is not sustainable. Recovery of the white stumpnose stock will require a decrease in fishing mortality. Possible management regulations include sector-specific effort limitations, extending the ‘no take’ marine protected area, reducing the recreational-sector bag limit to 5 fish person–1 day–1, implementing a commercial-sector bag limit, and increasing the minimum size limit to 30 cm TL.Keywords: angling, annual yield, catch and effort, Langebaan Lagoon, linefish, recruitment survey, roving creel survey, temperate spari