The biology,life history and management needs of a large sciaenid fish,Argyrosomus coronus,in Angola

The West Coast dusky kob Argyrosomus coronus is an understudied yet important fishery species in Angola. During a five-year study (2005–2009), the species was recorded in all fishery sectors, but was most important in the inshore recreational fishery in southern Angola (Cunene Estuary to Namibe). Early juveniles (<300 mm total length, TL) were captured in the offshore artisanal fishery at Praia Pinda, whereas juveniles (300–600 mm TL), subadults (600–870 mm TL) and adults (>870 mm TL) were captured in all fisheries as far north as Namibe, and shoals of large adult fish (>1 000 mm TL) were occasionally captured in the offshore purse-seine commercial fishery between the Cunene Estuary and Lucira. Because some Argyrosomus species are morphologically cryptic, a DNA barcoding method was used to confirm the taxonomic status of the biological samples used in this study. The male:female sex ratio of examined samples was 1:1.4 (n = 225). The length-at-50% maturity was 823 mm and 904 mm TL for males and females respectively. Age-at-50% maturity was 4.4 and 4.3 years for males and females respectively. The periodicity of otolith ring formation was confirmed to be one year using a marginal zone and a chemical marking analysis. Growth (in mm TL) was best described by: L_t = 1 826(1—e^{?0.12(t + 1.60)}). Argyrosomus coronus fed predominantly on fish, mainly Sardinella aurita (62% frequency of occurrence). Early juveniles appeared to frequent the offshore zone (50–100 m depth), moving into the inshore region at approximately 300 mm TL. Juveniles and subadults were resident (57% recaptured at the same site) and were particularly abundant around the mouth of the Cunene Estuary as well as in central and northern Namibia. Adults undertake migrations that correspond with the movement of the Angola–Benguela frontal zone, moving north as far as Gabon in winter and returning to southern Angola in spring, when spawning appeared to take place offshore. There are currently no catch restrictions on A. coronus in Angolan waters. However, declining catches and increasing fishing effort suggest that some management intervention is required, commencing with a proposed closure of the Cunene Estuary mouth region to fishing.     

Evidence of deep genetic divergence between populations of an important recreational fishery species,Lichia amia L. 1758, around southern Africa

Lichia amia is an important coastal recreational fishery species with a cosmopolitan distribution in the eastern Atlantic. In southern Africa, it is distributed from southern Angola to northern KwaZulu-Natal in South Africa. A recent biological survey revealed differences between Angolan and South African individuals suggesting that they may represent separate stocks. As fishery management decisions should be based on accurate knowledge of population structure, an initial survey of the genetic substructuring of L. amia was conducted on samples collected in southern Angola and South Africa. Assessment of genetic diversity and population structure was conducted using a fragment of the mitochondrial Control Region. Obtained genetic diversity levels were within the expected range for marine teleosts (h = 0.867, π = 0.007), and two deeply divergent (southern Angolan and South African) populations were identified (average φ _ST = 0.78) across the Benguela Current system. These results suggest that Angolan and South African L. amia should be managed as two independent stocks. This work represents the first assessment of population genetic substructuring across the Benguela Current of a valuable coastal fishery resource, and has application for future fisheries management.     

Age and growth of narrow-barred Spanish mackerel Scomberomorus commerson in the coastal waters of southern Mozambique and KwaZulu-Natal,South Africa

The narrow-barred Spanish mackerel Scomberomorus commerson is one of the most important linefish species caught in KwaZulu-Natal and southern Mozambique waters, forming the basis of important commercial, artisanal and recreational fisheries. A total of 439 S. commerson were sampled along the east coast of southern Africa (KwaZulu-Natal, South Africa, and southern Mozambique) between April 2011 and March 2012. Retrospective length-at-age data observed from whole otoliths were used to compare and describe sex-specific growth. Growth rates obtained from otolith-derived data were compared with those estimated from 29 tag-recaptured fish. Overall, ages ranged from 0.48 to 14.6 years for females and 0.4 to 13.57 years for males. Otolith readings yielded an average percent error of 11.21%, lower than recorded in a previous study from the region. Marginal zone analysis provided strong evidence that one translucent and one opaque growth zone were laid down annually. Schnute growth-function parameters indicated significant differences in growth between sexes. Females approached their mean asymptotic length at a faster rate, and grew to a greater mean length-at-age, relative to males. Growth in both sexes was rapid, achieving 67.46 cm FL (females) and 65.4 cm FL (males) in their first year of life. Growth rates obtained from tag-recaptured S. commerson indicated slower growth for smaller/younger fish up until 70 cm FL after which growth was very similar to that observed from otolith-derived data. The results of this study provide accurate, validated life-history parameters for king mackerel that are important for the assessment of stock status in the region.     

Catch and effort of the shore and skiboat linefisheries along the South African Eastern Cape Coast

An assessment of catch and effort in the Eastern Cape shore and skiboat linefisheries was undertaken between 1994 and 1996 by means of roving creel and access point surveys. Catch-and-effort data were obtained from direct observation of 3 273 shore-fishers, 172 recreational and 223 commercial skiboat outings. Total effort in the region was high at 903 186 fisher-days year^?1 in the shore fishery and 64 266 and 24 357 fisher-days year^?1 in the commercial and recreational skiboat sectors respectively. The fisheries are multispecies in nature. The shore fishery consisted of 66 species, the recreational skiboat fishery 44 species and the commercial skiboat fishery 48 species. Just 10 species accounted for 75, 83 and 90% of the catch of the shore, recreational and commercial skiboat fishery respectively. The average catch per unit effort (cpue) was low in all sectors, 1.15 kg fisher^?1 day^?1 in the shorefishery, 9.4 kg fisher^?1 day^?1 in the recreational skiboat fishery and 21.5 kg fisher^?1 day^?1 in the commercial skiboat fishery. Catch data showed that professional and club anglers are more successful fishers. Comparisons with historic records for Port Elizabeth revealed that the cpue in the shore fishery had declined markedly, whereas the total effort increase was negligible (0.1%). In addition, the species composition of the fishery has changed.     

Fishery trends, resource-use and management system in the Ungwana Bay fishery Kenya

The present study assessed trends in resource-use, partitioning and management in the Ungwana Bay fishery, Kenya, using surplus production models. The fishery is one of East Africa’s important marine fisheries sustaining a bottom trawl commercial fishery and a resident-migrant artisanal fishery. Two models: Schaefer (1954) and Gulland and Fox (1975) were applied to catch-effort data over a 21-year period to model maximum sustainable yield (MSY) and optimal effort (f_MSY) to examine the status of resource exploitation and provide reference points for sustainable management. In the artisanal fishery, model MSYs range from 392-446 t to 1283-1473 t for shrimps and fish respectively compared to mean annual landings of 60 t for shrimp and 758 t for fish. These landings represent <50% of the model MSYs suggesting under exploitation in the sub-sector. Moreover, current fishing effort applied stands at <0.5 f_MSY. On the other hand, mean annual landings in bottom trawl commercial fishery, at about 330 t for shrimps and 583 t and fish represent about 90% of the model MSYs of 352-391 t and 499-602 t for shrimps and fish respectively. Therefore, the bottom trawl commercial fishery is likely under full exploitation. Similarly, the current effort is estimated at >0.7 f_MSY. Resource management in the bay is faced with numerous problems including resource-use conflicts, poor economic conditions in artisanal fishery, poor legislation, and inadequate research augmented by poor reporting systems for catch-effort statistics. Thus, the fishery lacks clearly defined exploitation regimes. Fisheries research and assessment of the marine resources are important for sustainability of the fishery. Moreover, income diversification in the poverty ridden artisanal fishery would go a long way in addressing resource-use conflicts and use of deleterious fishing methods in the sub-sector. Borrowing from the successes of the Japanese community-based fisheries resource management (CBFRM) which has easily resolved numerous fisheries management issues in coastal small-scale commercial fisheries, and the beach management unit (BMU) system which has been applied to the artisanal fisheries of south coast Kenya with enormous benefits, it is envisaged that a hybrid CBFRM-BMU system presents the best approach to sustainable resource-use in the Ungwana Bay fishery.     

Social,economic and trade characteristics of the elasmobranch fishery on Unguja Island,Zanzibar, East Africa

Understanding the socio-economic drivers underpinning fishers' decisions to target elasmobranchs is considered vital in determining sustainable management objectives for these species, yet limited empirical data is collected. This study presents an overview of elasmobranch catch, trade and socio-economic characteristics of Zanzibar's small-scale, artisanal fishery. The value of applying this information to future elasmobranch fisheries policy is demonstrated. In August 2015, interviews were conducted with fishers (n = 39) and merchants (n = 16) at two landing sites, Kizimkazi-Dimbani and Mkokotoni, along with the main market site in Stone Town. Additionally, elasmobranch catches were recorded across the same locations between June and August 2015. Elasmobranchs were listed as target species by 49% of fishers interviewed. Whilst most fishers (n = 30) stated that 76–100% of their household income came from fishing, there was variation in how elasmobranch catch and trade contributed. One-third of fishers (n = 36) that caught and sold elasmobranchs reported that 41–60% of their income came from elasmobranch catch. However, for some fishers (n = 8) elasmobranch catch represented 0–20% of their income, whilst for others (n = 4) it represented 81–100%. Differences in fisheries income and elasmobranch price could be attributed to several interacting factors including season, weather, fishing effort, fishing gear, target catch and consumer demand. Further, elasmobranch price was influenced by size and species. The study revealed information on catch, trade, markets and socio-economy that is important for future research, conservation and management of elasmobranchs and fisheries in Zanzibar. The methods utilised have potential for broader application to understudied, artisanal elasmobranch fisheries in the western Indian Ocean.     

Biological data from sharks landed within the United Arab Emirates artisanal fishery

Landing site and market surveys of sharks landed along the Arabian Gulf coast of the United Arab Emirates were undertaken between October 2010 and September 2012 to obtain biological data from this artisanal fishery. Data were collected on the size and sex of 12 482 individuals representing 30 species. Maximum sizes of Carcharhinus sorrah, C. amblyrhynchoides and Hemipristis elongata were extended by at least 300?mm total length (TL) compared with published global maxima. The size at 50% maturity was determined for males of five species and this indicated that the males of smaller shark species (<1 000 mm maximum TL) in the fishery were largely mature. For many species, including Loxodon macrorhinus and Mustelus mosis, overall sex ratios were male-biased, indicating that sexual segregation is likely in those species. Furthermore, sex ratios for several species, such as Rhizoprionodon acutus, showed differences across seasons. Overall, the landings contained a high proportion of juveniles, causing concerns about the sustainability of this fishery. Biological parameters of a number of species differed from those recorded earlier for the region, demonstrating a need for additional local data collection to support the development of management measures.     

The artisanal fishery for East Coast rock lobsters Panulirus homarus along the Wild Coast,South Africa

East coast rock lobsters Panulirus homarus are collected by the indigenous people of the Wild Coast, in the Eastern Cape, South Africa, and are sold to coastal hotels and holidaymakers. The South African government has proposed a small-scale commercial fishery based on P. homarus to improve socio-economic conditions in that region. Catch data and information on fishery operations were collected for the artisanal fishery from Coffee Bay, Presley Bay, Port St Johns and Mbotyi, as well as from a commercial buying station near the Mdumbi Estuary, between March 2003 and October 2005. The catch per unit effort of rock lobster poling varied from 13.5 ± 7.7 fisher^–1 outing^–1 at Port St Johns to 5.9 ± 3.1 fisher^–1 outing^–1 at Coffee Bay, but the number of fishers or fishing frequency could not be verified. About two-thirds of the lobsters caught (69%) were smaller than the minimum legal size. Hotels and the buying station complied with size limits, but cottages and campers often bought undersized lobsters. Smaller lobsters (females) are caught by poling than by diving. Geographical variations in poling effort and lobster mean sizes could be indicators of heavy fishing pressure on shallow, inshore reefs. The implications of commercialising the fishery and its associated management are discussed.     

Biological parameters reflecting the current state of the exploited pink dentex Dentex gibbosus (Pisces: Sparidae) population off the Canary Islands

A total of 639 pink dentex Dentex gibbosus was collected in Canary Islands waters between April 1991 and September 1993. Total lengths ranged from 14,2 to 95,2 cm. Females dominated smaller size-classes and males the larger ones. The species was characterized by protogynous hermaphroditism. The overall ratio of males to females was 1 : 1,45. The reproductive period extended from April to September, spawning peaking in June/July. The total lengths at 50% maturity were 34,7 cm for females and 38,6 cm for males. The length-mass relationship for the whole sample can be described by the parameters a = 0,01014 and b = 3,0812. Fish aged 0–16 years were present in the samples. The parameters of the Von Bertalanffy growth equation were: L _∞ = 101,2 cm, k = 0,149·year^?1, and t ₀ = ?0,111 years. The rates of total mortality Z and natural mortality M were 0,57 and 0,28·year^?1 respectively. Rates of fishing mortality F and exploitation E were 0,29 and 0,51·year^?1 respectively. The estimated length at first capture (LC ₅₀) was 17,8 cm total length.     

Status of Kuwait's fishery resources: Assessment and perspective

For the first time, the production of fisheries in Kuwait was assessed both quantitatively and qualitatively by comparing the production of the late 1980s and the mid-2000s using official data. The results indicate that total fisheries production has declined over time, with local production (artisanal and industrial) having decreased by approximately 25%, while imports increased by 25%, representing 62% of the total fisheries production over time. Current consumer preferences have led to increased demand of fish species formerly having inferior commercial importance. The verified per capita fish consumption in 2010 was 22.32 kg yr⁻¹ suggesting the existence of an unrecorded supplementary supply of fish. Predictions show a dramatic decrease in fishery production by 2025, with a low supply of only 0.5 kg per individual per annum. The results have practical implications for legislators’ management strategies for the sustainability of local fishery stocks.     

Reproductive biology of the leatherjacket,Meuschenia scaber (Monacanthidae) (Forster 1801) in the Hauraki Gulf,New Zealand

The leatherjacket Meuschenia scaber is widely distributed in Australasian waters, and is a valued bycatch of inshore bottom trawl fisheries although little is known of its life history. Here, we describe the reproductive biology of the species based on 651 leatherjackets sampled in the Hauraki Gulf, New Zealand, between July 2014 and March 2016. The maximum total length (L_T) recorded for females and males were 320 and 315?mm, respectively, with both sexes present in all size classes. Monthly analysis of gonad condition revealed a clear spawning season from late austral winter to early summer (August–December), and histological analysis of the ovaries revealed that M. scaber is an indeterminate serial spawning gonochorist. The estimated sizes at sexual maturity (L₅₀) for females (189.9?mm L_T) and males (188.4?mm L_T) did not differ significantly. Relatively small testes, sexual dimorphism and underwater observation of nesting suggest that M. scaber is a paired spawner.     

Relationship between somatic growth and otolith growth: a case study of the ornate jobfish Pristipomoides argyrogrammicus from the coast of Réunion (SW Indian Ocean)

The ornate jobfish Pristipomoides argyrogrammicus Valenciennes 1832 occurs in the Indo-West Pacific Ocean, where it is harvested by small-scale coastal fisheries. Management of this species is hindered by lack of adequate biological data. We sampled a total of 113 individuals from the landings of local artisanal fishers on the island of Réunion (southwestern Indian Ocean), from March 2014 to March 2015. The relationships between two types of body length (total and standard length, cm) and total weight (g) were shown to be significant (p < 0.05). The length–weight relationship was described by a power function, with the scaling factor estimated to be 0.008 and the exponent 3.146. Age was determined using whole otoliths. The von Bertalanffy growth equation was estimated to be TL_t = 30.68(1 – e^?0.52(t)). Otolith morphometry variables (length, width and area) were significantly correlated with age estimates (p < 0.05). No significant difference in age estimates was observed between left and right otoliths used as predictors. Readings from observed age and the estimates from modelled age indicated relatively good agreement, suggesting the potential to use whole otoliths for age estimation.     

The elasmobranch fisheries of the Azores

In the Northeast Atlantic, elasmobranchs are a common bycatch in many fisheries, including demersal trawls, longlines, or gillnets and many countries do not have regulations or any control over the amount taken. In the Mid Atlantic, the Azores EEZ (Exclusive Economic Zone), small-scale fishing operations, artisanal and hook-and-line fishing methods are responsible for part of local total landed elasmobranch biomass, although some species are specifically focused and severely harvested by international large-scale fleets. This work provides a review and analysis of the commercial elasmobranch fisheries in the Azores EEZ, and its evolution over the last two decades, highlighting management priorities, taking into account the Northeast Atlantic elasmobranch fisheries status. In the Mid-Atlantic, elasmobranch fisheries mainly target 4 species, that are usually landed as bycatch: the tope shark (Galeorhinus galeus) and the thornback ray (Raja clavata), captured mainly by local demersal artisanal fisheries, the blue shark (Prionace glauca) and the shortfin mako shark (Isurus oxyrinchus) captured by a more industrialised fleet, including those from foreign nations. Considering elasmobranchs life history traits and fishery history, caution is advised in the development of a management strategy focusing on these species, considering the Northeast Atlantic context and regional, local and national interests.     

The structure and evolution of the coastal migrant fishery of Kenya

The current study was carried out over a period of one year to characterise the coastal migrant fishery of Kenya. The study looked at gears and vessels used, and ownership, demographic factors including ages of the fishers and family sizes, migrant activity and resource conservation at two main fishing villages in Kenya; Vanga and Mayungu in the south and north coasts, straddling at 4.663°S and 39.215°E and 3.214°S and 40.135°E respectively. Further, the fishers were categorised with regard to fishing, gear and vessel operation and trade, and evolution upon entry into the fishery was also assessed in order to define fisher-stake in the fishery for resource management and conservation planning. Structured questionnaires were used to interview the fishers, and data and information recorded from 1018 fishers during the survey. Migrants accounted for over 63% of the fishers in the two study sites, with majority of the fishers lying in the 15–45 year age bracket. Dependence level averages at 4–6 person families per fisher. Entry to the fishery was mainly at seamen level, progressing to fishermen and finally to fish dealers (tajiris), with the latter holding >62% capital in the fishery. Resource management in the fishery was low and only 10% of the fishers were active participants in marine conservation and community beach management issues. Fisher migrations were mainly monsoon season-linked (>58%) although social factors such as family location determined to a great extent the expanse of the migrations. The revival of fisheries cooperatives and active participation in community resource management and conservation groups is envisaged as the key to the sustainability of both the marine resources and the economies associated with this high mobility, cross-border fishery.     

Comparison of the population structure and life-history parameters of Diplodus capensis (Sparidae) in exploited and unexploited areas of southern Angola

Blacktail seabream Diplodus capensis were sampled from proximate (10 km apart) exploited and unexploited areas in southern Angola to compare their population structures and life-history parameters. Females dominated the larger size and older age classes in the unexploited area. In the exploited area the length and age frequency distributions were more equitable, but there was a lack of large and old individuals in this area due to the selective nature of fishing gear. Growth zone deposition rate was validated as being annual using mark-recapture of chemically injected (oxytetracycline) fish. In the unexploited area, females attained larger sizes and greater ages than males; however, growth and longevity were more equitable between the sexes in the exploited area. Length- and age-at-50% maturity were similar between the sexes in both areas. The sex ratio was heavily female-skewed (1:4.7) in the unexploited area but less so in the exploited area (1:2.2). Although the growth curves were significantly different for fish between areas, this was likely due to a reduction in longevity rather than a physiological change in growth. The length- and age-at-50% maturity was also similar between areas, indicating that this species either does not have the ability to respond to exploitation through physiological change in these life-history characteristics, or that the current level of exploitation is not high enough to elicit such a response. However, the female dominance in the smallest size class in the exploited area (compared to the unexploited area) indicated that a threshold may have been reached, and that this species responds to exploitation by increasing the relative number of fish that mature as females.     

Reproductive biology of horse mackerel Trachurus capensis and Trachurus trecae in Namibia and Angola

Harvest control measures for Namibia and Angola are defined using reference points for spawning biomass, which requires knowledge of spawning potential and dynamics of fishery stocks. The reproductive biology of two species of horse mackerel, Trachurus capensis and Trachurus trecae, in these waters was investigated for spawning distribution in time and space. Samples were collected during two scientific cruises conducted in February and July/August 2007 off the coast of Namibia and Angola. A total of 396 fish ovaries was examined to determine the spawning dynamics of the two species. The ovaries were histologically analysed and their oocyte distributions mapped. The length (TL)–weight relationships of the two species differed significantly. The observed development of oocyte recruitment and absence of a hiatus in the oocyte distribution indicated that these species are indeterminate spawners. Analyses of the data from the NatMIRC database (2001–2004) indicated annual changes in gonadosomatic index (GSI) for T. capensis at different latitudes, but these changes were small. GSI also fluctuated between years and areas, but there were no clear spatial or temporal trends, with averages ≤4.0% at all stations. The GSI of both species was not indicative of the histologically determined development of gonad maturity. Oocyte maturation for T. capensis indicated that smaller and younger fish spawn first. Batch fecundity (F) for T. trecae was best described by F = 4 986 TL (cm) – 99 645 (r ² = 0.83). This study provided the first analyses of oocyte development in time and space for the two species in the region.     

Profitability and economic drivers of small pelagic fisheries in West Africa: A twenty year perspective

Small pelagics are the main fish resource in North West Africa. In Senegal, these are mainly sardinellas (Sardinella aurita and S. maderensis) and bonga shad (Ethmalosa fimbriata). The fisheries, mainly encircling gillnets and purse seines, are predominantly performed by artisanal fishers and are of great importance for the Senegalese economy and for food security in the region. However, in recent years, the main conditions for these fisheries have changed and recent observations have shown strong declines in profit. An analysis over the last twenty years (1993–2013) show that the fisheries lost profit between 65% and 100% while operating costs increased by 25% and 90%, for encircling gillnet and purse seine, respectively. While the fuel price dominates as determining factor during the survey period, important other drivers during the last five years were a decrease in fish biomass and an increase in fishing effort.     

Property relations and the co-management of small-scale fisheries in Costa Rica: Lessons from Marine Areas for Responsible Fishing in the Gulf of Nicoya

Marine fisheries in Costa Rica have become characterized by overexploitation, ineffective centralized management and increased conflict among fishing sectors. Despite high economic and socio-cultural importance of small-scale fisheries, no formal mechanisms existed until recently to facilitate the participation of fishers in management. Marine Areas for Responsible Fishing (Áreas Marinas para la Pesca Responsable, AMPR) were legally recognized in 2009 as a co-management approach, enabling the designation of spatial management areas to be implemented collaboratively by artisanal fishers and government agencies. In this paper, we examine property and access relations shaping this emerging participatory management model using case studies primarily from the Gulf of Nicoya region. The policy demonstrably improves upon some aspects of management, for instance, by allowing artisanal fishers to determine gear restrictions within designated areas. However, the model lacks other attributes of more successful co-management scenarios, particularly exclusive access. The fugitive nature of resources further complicates property relations over these fisheries. The cases explored also illustrate broader institutional and systemic issues that preclude effective participatory management. Lessons from the region are used to propose significant shifts to the management of small-scale fisheries in Costa Rica.     

The reproductive style of Diplodus capensis (Sparidae) in southern Angola: rudimentary hermaphroditism or partial protandry?

The reproductive style of Diplodus capensis was examined in an unexploited coastal area in southern Angola. The mean length of females was significantly greater than that of males and, although not significant, females dominated the older age classes. The overall sex ratio was 1 male:4.7 females and female dominance increased with size. Histological analysis of gonads revealed that this species is a rudimentary hermaphrodite, with individuals possessing a non-functional bipotential ovotes-tis in the juvenile phase. Histological examination of the gonads of four macroscopically staged ‘intersex’ individuals suggested that they were functional males with a persistent ovarian portion in their gonads from the juvenile ovotestis. The heavily female-biased sex ratio and female dominance in the larger length classes are thought to be an alternative to sex change that is more resilient to exploitation when compared with the protandrous strategy displayed by the South African population of D. capensis.     

Resolving environmental issues in the southern Brazilian artisanal penaeid-trawl fishery through adaptive co-management

Many conventional management strategies have been demonstrated to be ineffective in achieving sustainable fisheries, and new approaches are required to overcome existing environmental, social and economic problems. Adaptive co-management represents the combination of a learning-by-doing approach (adaptive management) involving all related and legitimate stakeholders in the decision-making process (collaborative management). In this study, the relevant experiences from a fishery in southern Brazil are reported. The first section of the paper summarizes the broad history of national fisheries and their management. Then the southern Brazilian artisanal penaeid-trawl fishery is briefly described and the three main problems associated with the common gears used are discussed, including their (1) poor size and species selectivities, (2) poor efficiencies, and (3) their mechanical impacts on benthic habitats. Finally, a framework is proposed to address the environmental and socio-economic issues in the fishery and its implementation discussed via an adaptive co-management approach.