Net Fishery Research Articles

Drivers of spatiotemporal variability in bycatch of a top marine predator: First evidence for the role of water turbidity in protected species bycatch

Abstract Bycatch of protected species in static net fisheries is a global conservation concern and is currently considered the dominant anthropogenic threat facing many marine mammal species. Effective bycatch mitigation remains challenging, contingent on an understanding of the underlying mechanisms that cause individuals to become entangled. We combined data collected by scientific observers and fishers to identify predictors of seal bycatch in static net fisheries along the west, southwest and south coasts of Ireland. We first analysed the broad regional and seasonal trends in seal bycatch before identifying environmental variables that could explain these patterns. Based on negative binomial generalized linear mixed effects models, seal bycatch significantly varied with season and decreased with greater distance to major seal colonies and in clearer, less turbid water. Synthesis and applications. Our results suggest that distance to major seal colonies was a significant driver of spatial variation in seal bycatch, and water turbidity a major driver of seasonal trends. These findings will enable us to identify future bycatch risk and target mitigation measures effectively. This is the first study to identify the effect of water turbidity on bycatch of a protected marine species. Increasing net visibility in turbid waters may provide a novel approach to mitigating against protected species bycatch in static net fisheries.

An illuminating idea to reduce bycatch in the Peruvian small-scale gillnet fishery

Found in the coastal waters of all continents, gillnets are the largest component of small-scale fisheries for many countries. Numerous studies show that these fisheries often have high bycatch rates of threatened marine species such as sea turtles, small cetaceans and seabirds, resulting in possible population declines of these non-target groups. However, few solutions to reduce gillnet bycatch have been developed. Recent bycatch reduction technologies (BRTs) use sensory cues to alert non-target species to the presence of fishing gear. In this study we deployed light emitting diodes (LEDs) - a visual cue - on the floatlines of paired gillnets (control vs illuminated net) during 864 fishing sets on small-scale vessels departing from three Peruvian ports between 2015 and 2018. Bycatch probability per set for sea turtles, cetaceans and seabirds as well as catch per unit effort (CPUE) of target species were analysed for illuminated and control nets using a generalised linear mixed-effects model (GLMM). For illuminated nets, bycatch probability per set was reduced by up to 74.4 % for sea turtles and 70.8 % for small cetaceans in comparison to non-illuminated, control nets. For seabirds, nominal BPUEs decreased by 84.0 % in the presence of LEDs. Target species CPUE was not negatively affected by the presence of LEDs. This study highlights the efficacy of net illumination as a multi-taxa BRT for small-scale gillnet fisheries in Peru. These results are promising given the global ubiquity of small-scale net fisheries, the relatively low cost of LEDs and the current lack of alternate solutions to bycatch.

Assessment of bag net fishery of Narmada estuary, Gujarat: A case study

Bag net, locally known as ‘Golava,’ is an important means of fishing in the middle stretch of Narmada estuary for the livelihood security of many stakeholders. The present study was conducted during 2015-16 to find out species composition and economic evaluation of bag net fishery in the Narmada estuarine region. Bag net was operated for 7-8 months with peak duirng November to February. A total of 7-8 sets of bag nets were found to be operated from Bhadhut (21o 41' 108" N, 72o 51’ 198" E) to Mehgam (21o 40' 44" N, 72o 45’ 27" E) region. In a single set, a total of 12-22 numbers of bag nets were installed with an average individual net length of 25-27 m with 10 mm cod-end mesh size. The nets were installed in the current-driven area during low as well as high tides to harvest fishes during high tides and low tides, respectively. A total of 8-12 fishers were involved in the total installation. The operational time of the bag net is around 10-12 hours. The mean catch per unit effort (CPUE) was recorded 2.5-9.5 kg/day/ operation during the study periods. Mullets were the dominated group contributing 30% to the catch, followed by Otolithoides pama (15%), Lates calcarifer (14%), Macrobrachium rosenbergii (12%), catfishes (8%), Harpadon neherius (6%), Cynoglossus cynoglossus (4%), Eleutheronema tetradactylum (3%), juvenile Tenualosa ilisha (2%) and others (6%) during peak season (November-February). The mean profit per net per year was estimated to be 0.14 and 0.18 lakh for Bhadbhut and Mehgam centres, respectively. Due to less profit, high capital requirement, and operational cost, bag net fishery is gradually declining in the Narmada estuary. Bag net fishery was found to be destructive and needs to be replaced with alternative nets with higher mesh sizes for sustainable exploitation of the resources.Key words Bag net fishery; catch composition; profitability; sustainability; Narmada estuary

The perverse fisheries consequences of mosquito net malaria prophylaxis in East Africa

Malaria is a serious global health issue, with around 200 million cases per year. As such, great effort has been put into the mass distribution of bed nets as a means of prophylaxis within Africa. Distributed mosquito nets are intended to be used for malaria protection, yet increasing evidence suggests that fishing is a primary use for these nets, providing fresh concerns for already stressed coastal ecosystems. While research documents the scale of mosquito net fisheries globally, no quantitative analysis of their landings exists. The effects of these fisheries on the wider ecosystem assemblages have not previously been examined. In this study, we present the first detailed analysis of the sustainability of these fisheries by examining the diversity, age class, trophic structure and magnitude of biomass removal. Dragnet landings, one of two gear types in which mosquito nets can be utilised, were recorded across ten sites in northern Mozambique where the use of Mosquito nets for fishing is common. Our results indicate a substantial removal of juveniles from coastal seagrass meadows, many of which are commercially important in the region or play important ecological roles. We conclude that the use of mosquito nets for fishing may contribute to food insecurity, greater poverty and the loss of ecosystem functioning.

The present status of fixed lift net fishing in Banten Bay Indonesia

Banten Bay is the main fishing ground for small scale fishing activity in Banten Province. The fishers use several fishing gears, such as gillnet, trap, hook and line, danish seine, and lift net. However, a lift net fishery has a significant contribution to fish production in Archipelagic Fishing Port of Karangantu, Serang City. The purpose of this study is to analyze the status of fixed lift net fishing in Banten Bay. The research was conducted on Mei to July 2019 through survey and field observation. There are more than 150 units of fixed lift net operated in Banten Bay, that have landing place in Karangantu and Panjang Island. The rectangle lift nets (10Wx10L m2) are fixed at six to ten-meter depth. The fishers used four to six pressure kerosene lamps as a light source before 2010. However, since 2010 the fishers changed the lamp to the electrical light source due to high price, and limited availability of kerosene. In peak season, the lift nets have high productivity (500-1000 kg/trip). The productivity was decreased in the low season (< 100 kg/trip). The main target species in fixed lift net fishing are anchovies and squids with a potential margin more than IDR 60 million per year.

Age, growth and per-recruit stock assessment of southern mullet Chelon richardsonii in Saldanha Bay and Langebaan Lagoon, South Africa

The southern mullet Chelon richardsonii (Mugilidae) is the main target species of the inshore net fishery (gillnet and beach-seine) on the west coast of South Africa. The stock has displayed symptoms of overfishing, with a 28% reduction in the standardised catch per unit effort (CPUE) between 2008 and 2016, and a 36.5-mm reduction in mean total length (TL) of fish in the commercial catch between 1998 and 2017. The socioeconomic importance of the inshore net fishery and concern regarding stock status necessitated an assessment of the C. richardsonii stock. This work presents an update of the life-history parameters and the first stock assessment of C. richardsonii at the centre of its distribution—Saldanha Bay and Langebaan Lagoon—using CPUE standardisation and per-recruit analysis. The sexes exhibited distinctive growth, with females growing larger, and their length-at-first-maturity was estimated at 205 mm TL, corresponding to age 2 years. Estimated natural mortality was 0.718 y–1, total mortality was 1.599 y–1, and fishing mortality was 0.881 y–1. Current spawner- biomass-per-recruit was estimated at 24.5% of the pristine (unfished) levels, indicating a stock at risk of recruitment failure. An increase in the minimum stretched mesh size of the gillnets to 51 mm and a reduction in fishing mortality to 0.60 y–1 (approximately 30%) would facilitate the recovery of the spawner biomass to the target of 40% of pristine (SB40).

Effects of Yininemertes pratensis on Glass Eels from the Han River, Korea

Nemerteans (ribbon worms) mostly inhabit benthic habitats. The nemertean Yininemertes pratensis was recently reported to a negatively affect the glass eel net fishery in the Han River, Korea, but the causative mechanism has not yet been fully investigated. The present study was performed to investigate the mechanisms associated with the death of these eels by Y. pratensis. Our results showed that eel survival rates were not affected by exposure to a Y. pratensis polypeptide extract nor by coincubation with Y. pratensis in a sufficiently spacious environment. Yininemertes pratensis secretes tetrodotoxin and small molecular toxins under stressful conditions; therefore, co-incubated in a restricted spaced. Yininemertes pratensis decreased eel survival rate and accelerated eel death. In this study, we demonstrated that mucus secreted by Y. pratensis was associated with ell deaths.

Net Fisheries’ Métiers in the Eastern Mediterranean: Insights for Small-Scale Fishery Management on Kalymnos Island

Small-scale fisheries constitute an important component of coastal human societies. The present study describes the small-scale net fisheries on Kalymnos Island (south-east Aegean Sea) that harbors the largest small-scale fleet in the eastern Mediterranean Sea. In addition, this study aims to evaluate their characteristics and economics. Relevant métiers were identified through a multivariate analysis by inputting the main resources and fishing gear data that were recorded during landings. Four main practices were observed being used as fishing gears, gillnets and trammel nets, targeting the species Mullus barbatus, Boops boops, Mullus surmuletus, Scorpaena porcus, and Sepia officinalis. Further analysis, which incorporated data concerning the type of the gear used, revealed 11 distinct métiers. Most of these métiers are practiced by other Mediterranean small-scale fisheries as well, in terms of target species, gear and seasonality. However, the métier that had its target species as B.boops is not practiced in other Mediterranean small-scale fisheries. The seasonal rotation of métiers was determined by the availability of different species rather than their market price. The results revealed the difference in fishing practice used by the fishermen in the study area compared to other fishing practices in the Mediterranean Sea. In particular, the fishermen of this study area targeted more species (B.boops) with a very low market price. They also provided essential information for the development and implementation of management plans aiming at the sustainability of small-scale fisheries.

Comparison between the wage and profit-sharing systems to the portion of fishermen in fishing business in Kulon Progo Regency

Fishermen’s income is basically obtained from wages for their efforts. However, the portion is depends on the systems set out in the prevailing agreement based on consensus or mutual agreement. Comparison between the systems is intriguing to be studied. This study aims to determine the implementation of profit-sharing system and the wage system applied on gill net fisheries business in Trisik Beach of Kulon Progo, Yogyakarta, Indonesia, to determine the break even point (BEP) that is applied as a limitation in determining the implementation of the profit-sharing system and to compare the wage system obtained by fishermen labors and ship owners with the existing fisherman wage in Yogyakarta area. The methods used in this study included case study, sampling, data collection and analysis. The results of this study indicate that the income received by fisherman labors is Rp2,284,000 per month and Rp10,420 per hour, fisherman captain income is Rp6,602,000 per month and Rp300,420 per day or Rp37,552 per hour. However, for employees in the company, they earn Rp1,144,812 per month and Rp38,160 per day and Rp4,770 per hour. The profit-sharing system in gill net monofilament business in Trisik Beach is more advantageous, compared to the wage system in the area.

Fish species composition and size structure exploited by gill net fishery in The New Calabar River, Nigeria

The purpose of this study was to investigate the species composition and size selectivity of gillnets commonly used by the artisanal fishers in the New Calabar River, Rivers State, Nigeria. The data was collected during February-July 2018 from 3 sampling stations: SI Choba, S2 Ogbogoro, and S3 Iwofe all along the stretch of the river. Twenty-eight fish species were found belonging to 15 families. The prevalent families were Cichlidae, Mugilidae and Clupeidae representing 32.22%, 30.36% and 10.23% of the total catch, respectively. The most dominant species in terms of number were Liza falcipinnis (12.58%) and Mugil cephalous (12.26%) while in terms of biomass, the most abundance species were Xenomystus nigri (24.12%) and Lutjanus agennes (12.50 %). The girth and total lengths of the fishes ranged from 5.20±0.20 to 21.00±0.00 cm and 8.85±0.15 to 28.19±1.13 cm respectively. The length at first capture (L50%) for the most abundant species (Liza falcipinnis) was calculated to be 14.13 cm while that of L25% and L75% were 12.70cm and 15.25cm respectively. It was concluded that the gill nets used in the New Calabar River exploit fish species of small sizes and few medium sized specimens relative to species potential maximum size. It is therefore recommended that for an improved and sustainable exploitation fish stock of the New Calabar River, the use of gillnets of less than 25 mm-mesh sizes and “other gears” should be prohibited.Keywords: gill nets; species composition; mesh size; selectivity; New Calabar River

Fishermen's perceptions of coastal fisheries management regulations: Key factors to rebuilding coastal fishery resources in Taiwan

Although Taiwan has taken conservation measures for coastal and offshore fishery resources in recent years, the effectiveness of resources rebuilding is unclear. Many initiatives, such as marine protected areas (MPAs), are frequently opposed by fishermen. This research reviewed management measures and interviewed 313 fishermen by purposive stratification and snowball sampling. Data were analyzed by fishery, age, and vessel size to address the attitudes and perceptions of fishermen toward twelve fisheries management measures. Descriptive statistics, as well as chi-squared tests and independent t-tests, were used for basic analysis and differences comparison between groups. The results showed that illegal fishing vessels from China (71%), overfishing (69.5%), and ghost fishing (64%) are considered as major threats to Taiwan marine resources. The measures from voyage data recorders, larval anchovy, precious coral, and shark management result in higher satisfaction because of strict monitoring. The satisfaction measures for three net-type measures, i.e., trawler area closure, torch-light limitation, and gillnet limitation, were low. Line-type and small-scale vessel fishermen are more concerned with “small mesh size” and “ghost fishing”. Net-type, large-scale vessels and young fishermen were concerned about “climate change” and “inappropriate measures”. In conclusion, the priorities are to (1) establish a comprehensive scientific research framework; (2) strengthen enforcement to ensure resources rebuilding, especially for large-scale net fisheries; (3) promote public awareness and build communication between stakeholders to obtain support; and (4) communicate among policymakers and fishermen to increase mutual understanding.

Fisheries management in the face of uncertainty: Designing time-area closures that are effective under multiple spatial patterns of fishing effort displacement in an estuarine gill net fishery.

A commonly cited reason for the failure of time-area closures to achieve fisheries management goals is the displacement of fishing effort from inside the closure into the surrounding area still open to fishing. Designing time-area closures that are predicted to achieve management goals under multiple spatial patterns of effort redistribution will increase chances of success. Using data from an estuarine gill net fishery, we tested if there are time-area closures predicted to reduce bycatch of two protected species groups while maintaining target catch under four simulated effort redistribution patterns. We found that the pattern of effort redistribution had a substantial impact on the amount of predicted bycatch in each closure scenario. Multiple closures were predicted to reduce bycatch of these species under all four simulations of effort redistribution. However, some combinations of closure and effort redistribution pattern resulted in estimated bycatch being higher than without a closure. We did not find any time-area closures that resulted in a predicted reduction in bycatch while maintaining target catch at original levels. We demonstrate a simple way for fisheries managers to account for the uncertainty in fishers' behavior by designing time-area closures that are predicted to reduce bycatch under multiple potential patterns of spatial redistribution of fishing effort.

Catch dynamics of set net fisheries in Israel

Artisanal fisheries are globally common, providing almost 50% of total world landings. However, due to overfishing, they are worldwide on the verge of collapse. Fisheries in the eastern Mediterranean Levantine Basin must additionally cope with extreme thermal conditions, meaning that fish are typically smaller relative to other regions. In Israel, mesh size restriction has been suggested as a means to rebuild stocks, but data on artisanal fishing landings across mesh size are extremely sparse. The aim of this study was to quantify set net catches across different mesh sizes in order to identify fishing methods that can benefit both fish populations and fishers. We hope to identify which mesh size provide the highest ratio of commercial to non-commercial fished biomass, the lowest variance in fisher’s revenues and benefits the reproductive potential of the resource by targeting mature individuals. We found that across the range of mesh sizes examined, smaller mesh sizes (i.e. 25, 28, 30) did not catch a larger proportion of individuals below reproductive size but, rather, smaller species. The 43 mm mesh, caught larger individuals with lower total biomass but of larger species, with similar proportions of individuals below reproductive size to smaller mesh sizes. Net mesh size was not associated with fisher revenue. Trammel nets were found to be the least selective in relation to non-commercial by-catch, although the proportion of mature individuals in the catch was larger than for the other nets examined. These findings suggest that mesh size restrictions, across the range of mesh sizes examined, will not result in a decrease in catch of individuals below reproductive size but rather shift the species composition of the catch towards large-bodied, often high trophic level, species. Thus, mesh size restrictions are unlikely to rebuild fish stocks of high-value commercial species nor increase fisher revenue. We suggest that artisanal fisheries management in the Levantine Basin should evaluate new management measures and consider reducing overall fishing pressure along with implementing ecosystem-based fisheries management, such as the closure of fish reproduction and recruitment areas and establishment of marine protected areas.

Perbandingan Pendapatan Nelayan Pekerja dengan Standar Upah Minimum Regional (UMR) Kabupaten Kulon Progo

Penelitian ini bertujuan untuk mengetahui pelaksanaan system bagi hasil dan system upah yang diterapkan pada usaha perikanan Gill Net di Pantai Trisik kabupaten Kulon Progo, untuk mengetahui tingkat BEP yang diterapkan sebagai batasan dalam menentukan pelaksanaan system bagi hasil dan untuk membandingkan antara system upah dan system bagi hasil yang diperoleh nelayan dan pemilik kapal dengan UMR yang ada di daerah Yogyakarta. Penelitian ini dilaksanakan di Pantai Trisik Desa Banaran, Kecamatan Galur, Kabupaten Kulon Progo pada awal bulan Agustus sampai dengan awal bulan Nopember 2017. Metode yang digunakan dalam penelitian ini meliputi metode study kasus, pengambilan sample, pengumpulan data dan analisa data. Dari hasil penelitian ini menunjukan bahwa pendapatan yang diterima oleh ABK Rp. 2.284.000,- per bulan dan Rp.10.420,- per jam , Pendapatan Nahkoda Rp.6.602.000,- per Bulan dan Rp.300.420,- per hari atau Rp. 37.552,- per jam. Namun untuk karyawan di Perusahaan mendapat penghasilan Rp. Rp.1.144.812,- per Bulan dan Rp. 38.160,- per hari serta Rp.4.770,- per Jam. Dengan demikian lebih menguntuingkan system bagi hasil pada usaha perikanan Gill Net monofilament di Pantai trisik kabupaten Kulon Progo bila dibandingkan dengan UMR tahun 2017 yang ada di daerah itu, sebesar Rp. 1.373.600,--

Research on the fitness between the mesh size and the length of threadfin bream (&lt;i&gt;Nemipterus sp.&lt;/i&gt;) in stow net fishery

The study has used 4 different mesh sizes and mesh shapes in codends, catching 40 trial hauls in Nai lagoon to collect data. The fishing process has collected 2,041 individual threadfin bream (Nemipterus sp.) for analysis of fish weight and length, and using Wileman's method of assessing the selective ability to determine selective parameters for threadfin bream.&#x0D; The research results show that the fish length with the probability of 50% retained in the codends (L50) of the samples M1, M2, M3 and M4 is respectively 5.02cm, 6.40cm, 6.49cm and 7.80cm. The selection factor (SF) of the diamond mesh is 3.56 and the square mesh is 7.21. The appropriate the mesh size for fishing with L50 is 21mm for both diamond mesh and square mesh.&#x0D; Key words: Nemipterus sp., stow net fishery, mesh size, fishing gear selectivity.

Commercial catches and discards of a Mediterranean small-scale cuttlefish fishery: implications of the new EU discard policy

The cuttlefish (Sepia officinalis) trammel net fishery is one of the most important small-scale fisheries in the Mediterranean Sea. Here we describe the main catch, by-catch and discard patterns found in this fishery on Mallorca Island by onboard surveys of 1005 netting walls from 23 fishing trips. The number of items captured, their size and their subsequent use, i.e. kept for sale or discarded, were recorded. Furthermore, the immediate survival of the unwanted items (i.e. vitality state when the gear came on board) and the medium-term survival of a subsample were assessed. The cuttlefish was the dominant species in the commercial fraction of the catch, particularly during the fishing season peak (March). However, S. officinalis catches quickly decreased further into the season, with other high-value fish, such as Scorpaena scrofa, increasing in the commercial fraction of the catch. As species composition is continuously changing, it is often difficult to determine the main target species of this fishery. This strategy possibly complicates management but maximizes fishing revenue, which was an average of €175 per trip. With respect to discards, up to 104 different species were caught but not commercialized. The most abundant were Holothuria sp. and Torpedo marmorata. Their immediate survival was 100% and 20%, respectively. In both cases, the medium-term survival and the vitality status were high after seven days in monitored captivity. Therefore, in these cases, their immediate release to the sea should be promoted, given that they are exempt from the EU landing obligation. Interviews with fishers revealed that the perceived quantity of discards was lower than the amount recorded by the present study. Currently, just a small percentage (1.5%) of these discards will be affected by the landing obligation enforced by the new European discards ban.

Reducing unwanted catches of trammel nets: experimental results of the “guarding net” in the caramote prawn, &lt;em&gt;Penaeus kerathurus&lt;/em&gt;, small-scale fishery of the Ligurian Sea (western Mediterranean)

This study aimed to test the effectiveness of a “guarding net”, a device placed at the bottom of a trammel net, for reducing unwanted catches in the caramote prawn trammel net fishery of the Ligurian Sea. This specialized and profitable fishery is affected by unwanted catches that generate high discard rates and damage to the nets, with environmental impacts and costs for fishermen. The experimental study consisted in comparing the catches of a standard trammel net (STN) with those of two “experimental” trammel nets, e.g. STNs provided with a guarding net of 19 cm (TGN20) and 24 cm height (TGN25), respectively. The guarding net, a strip of gillnet placed at the bottom of the net, can be considered a by-catch reducer device (BRD). Some fishermen of the investigated fishery have been using this device for several years. The results of the 15 experimental fishing trials performed from June to July 2016 indicate that the guarding nets significantly reduce discards (e.g. crabs and other invertebrates); the biomass of the unwanted species caught was 75% lower than that produced by the STN. The catch rates of the target species obtained with TGN20 and TGN25 were also significantly lower than those of the STN, though of a lesser amount. Nonetheless, this economic loss can be compensated by the decrease in sorting time and material and labour costs that can be achieved using the guarding net.

Reducing discards in trammel net fisheries with simple modifications based on a guarding net and artificial light: contributing to marine biodiversity conservation

Experimental fishing trials with standard (control) and modified trammel nets were conducted to assess the possible reduction of discards. The standard trammel net was the commercial net used in the area (80 mm stretched mesh inner panel) targeting Sepia officinalis. This configuration produced 19% discards in weight. The modifications researched were of two kinds: a “guarding net” consisting of a 2.5-mesh-high (200 mm stretched mesh) net between the footrope and the trammel net and artificial lights of two colours (white or green) mounted on the floating ropes. Catches were identified, measured and categorized (commercial, discards and reason for discarding), and the different configurations were tested for statistical differences. Our results show that trammel net deployments with guarding net produce 32% higher catches of commercial species and as much as 95% higher catches of the target cuttlefish. Artificial lights produced a low but significant increase in total catches of commercial species of 13%, with no differences due to light colour. The amount of discards in deployments with guarding net was 6%, i.e. ca. 1/4 of the amount produced by the standard configuration. The effect of lights on discard reduction was not significant.

Fishery in the Tobol-Ishim interfluve in the neolithic and early metal age

Landscapes of the Tobol-Ishim interfluve were not stable in the Holocene and varied from forests and drowned floodplains at the beginning of the V and III millennia BC to steppificated territories with a lowered water level at the beginning of the Atlantic Period and in the middle of the Subboreal Period, which determined the main types of economic activities, one of them was fishing. Changes in hydrological regime of water bodies influenced the methods of fishing, including the use of different traps. Thus, in the Neolithic, when the water level decreased, the location of settlements in the system river-creek-lake (for example, Mergen 6), a large number of fish bones, bone harpoons, fishing spears, fishing tackles for catching pike and a total absence of plummets were indicative of individual fishing for large fish and, perhaps, of stop net fishery, which was facilitated by a decrease in the width of watercourses and tombolos. Stop net (stake net) fishery led to a settled lifestyle of the population, collective activities and the emergence of long-term settlements with deep foundation pits of dwellings. When the water level in rivers and lakes increased and floods became more frequent, the life support system changed, the population began to develop coasts more widely, its mobility increased, and they started to build framed above-ground dwellings. Following those changes, biconic, cigar-shaped, and corniculate plummets emerged in the Tobol River Basin and on the adjacent western and north-western territories in the III and early II millennium BC. When the water level was high, it was efficient to fish using traps, seines and, probably, nets, although the latter could also be used in drive hunting for shedding geese and ducks. Subrectangular plummets with one or two ties for fastening, and disk-shaped plummets with a tie in the center had been prevailing since the beginning of the II millennium BC; they existed until the first third of the I millennium BC. This period, the transition time from the Bronze Age to the Early Iron Age, is characterized by the absence of clay plummets, while there are large accumulations of fish scales and bones in the settlement layers. We can suppose that the population of that time (local Late Bronze Age population, mixed with northern migrants who made utensils with cross ornamentation) switched from net fishing to stop net fishing.

The introduction, spread and ecology of redclaw crayfish Cherax quadricarinatus in the Zambezi catchment

Two of the four crayfish species brought to Zambia for aquaculture since 1979 are now naturalised. Procamburus clarkii occurs in the Maramba River at Livingstone, close to a former fish farm, whereas Cherax quadricarinatus, deliberately introduced to a number of sites in the Zambezi and Kafue River catchments since 2001, is now widespread and highly invasive. High rates of dispersal, up to 111 km y−1 downstream, might be the result of passive transport on floating vegetation. Significantly more synodontid Synodontis sp. catfish were caught in Fladen traps in the Kafue River in crayfish-free areas compared with crayfish-infested areas, but the possibility that synodontids became trap averse in the presence of crayfish was not ruled out. No difference was found in the numbers of Single-spined River Crab Potamonautes unispinus caught in crayfish-free and infested areas. Alien temnocephalans, commonly found on crayfish, are now also present on crabs P. unispinus on the Kafue Flats. The artisanal gill net fishery has been harmed by the introduction of C. quadricarinatus and no significant commercial fishery has developed. However, without more information on the adverse impacts, and stronger fisheries regulation, there is a high risk C. quadricarinatus and P. clarkii will be introduced to uninfested catchments with irreversible consequences for artisanal fishermen and the environment.