Analysis of bycatch in the South African midwater trawl fishery for horse mackerel Trachurus capensis based on observer data

The South African midwater trawl fishery targets adult horse mackerel Trachurus capensis. The bulk of the catch is taken by a single freezer-trawler, the biggest fishing vessel operating in South African waters. As fishing takes place off the south coast in ecologically sensitive areas, there are concerns about the potential impacts of this fishing operation on non-target species. Fishing behaviour and bycatch of this fishery from 2004 to 2014 were investigated by analysing observer records with regard to catch composition, volume and temporal and spatial patterns. The midwater trawl fishery was estimated to have caught 25 415 tonnes annually, with a bycatch of 6.9% of the total catch, by weight. There are species overlaps with various fisheries, namely the demersal trawl, small-pelagic, line, shark longline and squid fisheries, yet the total bycatch estimates from this fishery are generally small relative to catches taken in the target fisheries. Bycatch species with the highest average annual catches were chub mackerel Scomber japonicus, redeye roundherring Etrumeus whiteheadi, ribbonfish Lepidopus caudatus and hake Merluccius spp. Large-fauna bycatch species included sunfish Mola mola as well as a number of CITES II- and IUCN-listed species, such as Cape fur seal Arctocephalus pusillus, dusky shark Carcharhinus obscurus, smooth hammerhead shark Sphyrna zygaena and thresher sharks Alopias spp. The 97.9% observer coverage is high and the 6.9% bycatch rate low compared to other South African fisheries; however, due to the large size of the individual hauls (average of 46.3 t), the average sampling rate of 1.56% is low. Our analyses suggest that bycatch in the South African midwater trawl fishery has been lower than in other South African fisheries and similar fisheries elsewhere, but due to the combination of high catch volumes and low sampling rates, estimation errors for rare species are high and there is a substantial risk of incidental unmonitored bycatch of rare large fauna and aggregations of small fauna. This could be mitigated by spatio-temporal management of this fishery, to avoid fishing in high-risk areas, and the introduction of an electronic monitoring programme.     

Macrobenthic invertebrate responses to prolonged drought in South Africa's largest estuarine lake complex

St Lucia, the largest estuarine lake complex of its type in Africa, is characterised by natural physico-chemical spatial and temporal fluctuations. This estuary functions as an important nursery area making use of a number of different habitat types and associated environmental conditions. The system has been subject to a number of natural episodic events such as cyclonic flooding and cyclical droughts, the most current has persisted since 2001, resulting in almost permanent mouth closure. Furthermore, high levels of evaporation have reduced lake levels and resulted in compartmentalisation of the system for up to several years at a time. St Lucia is sensitive to evaporation and therefore to vast salinity fluctuations and hypersaline conditions. The upper reaches in North Lake are particularly sensitive to drying out and extended hypersaline events. The macrobenthos has been well studied, but no studies have concentrated on the entire system for such an extent of time. Macrobenthic samples were initially collected in 2004, again in 2005 and biannually from 2006 to 2008. This study was part of a larger multidisciplinary programme aimed at determining the effects of long term drought conditions on the ecology of the St Lucia system, and increasing current understanding of the system response to future catastrophic climatic events. Three areas were sampled (North and South Lake and Estuary) at five sites per area, over five years. Data were analysed by representing communities through time series depictions and discriminating sites and sampling periods to test multidimensional relationships. Linkages between biological distribution and selected environmental forcing variables were investigated. The system was found to be highly variable and supporting a large number of different habitats and co-occurring environmental conditions. This variability makes it difficult to discern spatial or temporal patterns in environmental conditions and macrobenthic ecology. However, some level of resilience to wide ranging environmental changes associated with drought is maintained. This study was able to determine that there exists a core of taxa able to persist even under shallow depth conditions and prolonged hypersalinity. These taxa clearly have a self recruiting strategy and are therefore not reliant on mouth opening to re-establish local populations. This finding alone has important bearing for future studies and management of the system under similar adverse conditions.     

Law and fisheries reform: Legislative and policy developments in South African fisheries over the decade 1994–2004

Following the enactment of the Constitution in 1996, the South African government undertook a process of legal reform in the fishing sector. This led to the publication of a new fisheries policy endorsing equity and sustainability, as reflected in the Marine Living Resources Act. This paper examines efforts to implement the policy, particularly the objective of “transformation”, against the background of law reform in fisheries over the last decade. The discussion is located within the context of related domestic legal developments and current trends in international fisheries law. Methods for enhancing effective implementation of the new fisheries policy are highlighted.     

Corruption and regulatory compliance: Experimental findings from South African small-scale fisheries

Although corruption is often mentioned as an obstacle to fisheries management, its negative effects have seldom been investigated empirically in a systematic manner. This article examines the impact of corruption on regulatory compliance among South African small-scale fishermen. Results from scenario experiments with 181 participants confirm that perceived corruptibility of the enforcing authority corrodes the willingness to comply with regulations. Both grand and petty types of corruption have significant effects. Attitudes related to moral support of the regulations, perceived inclusion in the decision making leading to regulations and an individual record of law breaking all affect the willingness to comply. However, these effects are trumped by the relative size of the negative impact of corruption. These findings underline the importance of curbing corruption involving public officials in the small-scale fisheries sector.     

Benchmarking the first decade of post-apartheid fisheries reform in South Africa

The paper uses the three legislative criteria of resource sustainability, economic stability and social equity to measure the past decade of fisheries reform in South Africa. All three components of the reform process have been successful, although this judgement is subject to a number of important qualifications. First, the data available to measure success are limited. Second, both sustainability and stability are vulnerable to volatile factors external to the reform process (particularly variability in recruitment, climate change and exchange rate fluctuations) capable of derailing the process. Substantial alteration of the fishing industry by internal transformation of existing companies and the reallocation of access rights to new black entrants has led to a composition that closely reflects that of society as a whole and therefore meets the goal of equity. In the process, however, bona fide traditional fishers with a historical dependence on fishing have largely been denied legitimate access to the fisheries, and meeting their aspirations remains a challenge.     

The integration of South African fisheries into the global economy: Past,present and future

The integration of the South African fisheries into the global economy has operated as a powerful constraint on post-apartheid fisheries reform. The shedding of South Africa's international pariah status and currency depreciation enhanced access to and competitiveness on global markets, sparking a demersal-led export boom, which has favoured incumbent producers. Increased exports have also allowed the post-apartheid state and nascent black capital to maximise their returns from the fisheries through cost recovery and share purchases. The protection and promotion of the fisheries’ “international competitiveness”, inter alia sought through “sustainable fishery” certification of the hake industry with the Maritime Stewardship Council (MSC), has in turn provided a cover-all for the refusal of populist redistribution demands and special treatment for black small capital.     

Bridges to best management: Effects of a voluntary bycatch avoidance program in a mid-water trawl fishery

The catch of non-target species or discarding of target species (bycatch) in commercial fisheries can result in negative species level and ecosystem wide impacts as well as adverse social and economic effects. Bycatch has become one of the foremost, global issues of fishery managers and conservationists, especially when the non-target species is from a protected or threatened population. However, the impact and spatial distribution of bycatch is frequently unknown making it difficult to develop effective, justifiable mitigation regulations. This challenge is exemplified by the bycatch of river herring (alewife, Alosa pseudoharengus, and blueback herring, A. aestivalis) and American shad (A. sapidissima) in the northwest Atlantic mid-water trawl fishery targeting Atlantic herring (Clupea harengus) and Atlantic mackerel (Scomber scombrus). As an alternative to immediate management action, a voluntary bycatch avoidance program was established through an industry, state government, and university partnership. Here the program is described and its impact is evaluated by comparing fleet behavior and bycatch prior to and during the program. The combined results suggest that consistent communication, facilitated by the avoidance program, positively influenced fishing habits and played a role in the approximately 60% decrease in total bycatch and 20% decrease in the bycatch ratio observed during the program. However, the success of small scale move-along strategies to reduce bycatch ratios varied greatly in different areas of the fishery and years. This suggests the program is best viewed as an intermediate or complimentary solution. Overall, this project exemplifies of how collaborative programs can help alleviate difficult management scenarios.     

Estimation of the non-seasonal production of Spartina maritima (Curtis) Fernald in a South African Estuary

Net aerial production of Spartina maritima (Curtis) Fernald, in a warm temperature estuary in Algoa Bay, South Africa, occurring possibly as an exotic, was estimated as 523–680 g dry weight m^?2 year^?1. The method of production measurement designed here used community structure data and accounted for the species' extremely slow shoot production (3.1–6.7 dry g m^?2 year^?1) and continuous leaf turnover (516–676 dry g m^?2 year^?1). Standard methods of production measurement for other Spartina species failed by not accounting for the non-seasonal growth of S. maritima. N, C, organic and energy content of live and dead shoots remained constant through the seasons. The P : B ratio is 1.1, which is lower than for other Spartina species, but agrees with the low vigour shown by negligible regrowth a year after clipping. Decomposition rates were 90 mg g^?1 month^?1 in winter and 305 mg g^?1 month^?1 in summer. Monthly decomposition values showed significant correlation with air temperature (r = 0.86; P < 0.01), and water temperature (r = 0.80; P < 0.01), suggesting that monthly litterbag losses are a valid means of determining decomposition rate.     

A prominent colour front in False Bay, South Africa: Cross-frontal structure, composition and origin

Colour fronts are a frequent occurrence in False Bay, South Africa, and their occurrence has been the subject of previous study and anecdotal conjecture. The opportunity arose to make a cross-frontal study of this feature in November 2005. Photographs were taken and, subsequently, satellite imagery was obtained. Measurements were made of temperature, salinity, turbidity, dissolved oxygen, suspended solids, plant nutrients and chlorophyll a. Cross-frontal comparisons were also made on particulate material using a scanning electron microscope (SEM) and elemental dispersive x-ray (EDX) analysis. Frontal waters were milky white-green in colour, in stark contrast to the adjacent clearer, green-blue waters. The milky white-green water (MW-GW) was found to be warmer, (apparently) less saline, more turbid, richer in nitrate and silicate and had a higher chlorophyll a concentration. The dissolved oxygen signal was less pronounced, both water types being supersaturated. Paradoxically, in spite of the higher turbidity in the MW-GW, both water types had similar weights of suspended solids, although the MW-GW material was found to be more abundant and fragmentary when compared with its green-blue water (G-BW) counterpart. The MW-GW was rich in calcium whereas the G-BW was silicon enriched. The central findings of this study are that the strong southerly, onshore wind conditions prior to MW-GW formation introduced calcium-rich, fine particulates into the waters of the surf-zone. The sources of these particulates are thought to be the sea bed sediments and the sea/land interface. The particulates are close to neutral buoyancy enabling the MW-GW to persist over the time-scale of days. A mechanism reinforced by the warming of this water in the nearshore zone. The water was then advected by wind-forcing and subsequently, its own inertia around the north-west corner of False Bay, at which stage it was easily observed and sampled. It is suggested that the eventual collapse of the front was due to the slowing down of inertial movement in combination with the passive sinking of fine particulates and evaporative cooling resulting in downward convection.     

Quantitative evaluation of the performance of a permit auction system in reducing bycatch of sea turtles in the Hawaii Swordfish longline fishery

Many authors have suggested the use of a cap and trade auction system to help reduce bycatch—the incidental take of species by fishing gear targeting other species—of sea turtles in the Hawaii-based swordfish longline fishery. However, we know of no quantitative evaluations of the method. We present a simple mathematical model to serve as a framework to evaluate bycatch auction systems quantitatively. We conclude that cap and trade auction systems have the potential to reduce sea turtle bycatch by creating a financial incentive, while keeping permit costs down to 2–3% of total revenues. While stringent regulations aimed at conserving endangered sea turtles would still be essential, implementation of an auction for issuing transferable bycatch permits would likely enhance the economic efficiency of the fleet. Sea turtle mortality could be reduced further if a shrinking cap on total turtle mortality was introduced, taking advantage of the incentives for reducing turtle mortality that are introduced by the cap and trade auction system.     

The ichthyofauna in the Port of Ngqura,South Africa

This study provides one of the first quantitative assessments of a fish community within a pre-operational deep-water port system. Between September 2006 and September 2007 a total of 4 559 fish, representing 47 species and 27 different families, were caught within the Port of Ngqura, Africa's deepest port, in 1 713 h of shore-angling (2.3 fish angler^?1 h^?1) and 239 h of boat-based angling (2.8 fish angler^?1 h^?1). Catches included species representative of both estuarine and shore fisheries. The majority (83.0%) of species caught were marine and most were less than size-at-50% maturity (71.4%). The most abundantly caught species were dusky kob Argyrosomus japonicus (25.5%), elf Pomatomus saltatrix (24.9%), garrick Lichia amia (17.7%) and dusky sharks Carcharhinus obscurus (10.7%). Fish assemblages differed significantly (p < 0.05) between three habitats within the port: Dolosse, Quay Wall and Sandy Shore. The Dolosse habitat supported the greatest abundance (3.1 fish angler^?1 h^?1) and diversity (43) of fish species. The Port of Ngqura is thus functioning as an important habitat for both juvenile and adult fish. The diversity and abundance of fish suggests the potential use of ports and other artificial structures for enhancing local fisheries in South Africa.     

The zooplankton community of the Mpenjati Estuary, a South African temporarily open/closed system

The aim of this study was to examine spatial and temporal variability in zooplankton abundance and biomass, both during the closed (dry season) and open (wet season) phases of the Mpenjati Estuary, South Africa. On average, nighttime abundance values were 1–3 orders of magnitude higher than daytime values. A total of 51 and 36 zooplankton taxa were identified during the open and closed phases, respectively. The estuarine species Pseudodiaptomus hessei, Acartia natalensis and Gastrosaccus brevifissura dominated the assemblage during both phases. During the open phase marine zooplankton species entered the estuary and increased the zooplankton species diversity. At the same time, the biomass of the estuarine zooplankton species decreased substantially due to scouring of the sediment, increase in salinity and turbulence, and possibly also in grazing pressure. Conversely, during the closed phase the zooplankton diversity decreased, since no marine organisms entered the estuary, but the biomass of typical estuarine species increased due to the stability of the estuary. The fluctuations in the zooplankton community structure between the closed and the open phases suggest that the opening and the closing of the estuary are very important processes in determining the food web of the estuary.     

Microalgal productivity in an estuarine lake during a drought cycle: The St. Lucia Estuary,South Africa

The St. Lucia estuarine lake on the north coast of KwaZulu-Natal, South Africa, is one of the largest estuarine systems in Africa and of unique importance for the adjacent marine and terrestrial ecosystems. The area regularly experiences periods of drought, resulting in hypersaline conditions in its shallow lakes and the closure of the estuarine mouth. This study aimed to assess the primary production rates of phytoplankton and microphytobenthos throughout an annual cycle of this drought phase. Primary production rates were assessed at representative sites, namely the Mouth, Narrows, South and North Lakes from June 2006 to May 2007. Because of the drought, the salinity gradient from the mouth to the head of the estuary was reversed by comparison to estuarine systems with a steady freshwater inflow and regular marine exchange. In March 2007, during the study, the mouth opened as a result of rough seas, and the marine influence broke the existing reversed gradient, producing a marine salinity throughout the system. Microphytobenthic primary productivity varied between 0 and 34 mg C m⁻² h⁻¹ and showed strong correlations with salinity, DIN:DIP ratios and irradiance. Benthic productivity was high across the system after breaching of the mouth. Pelagic primary productivity (between 0 and 180 mg C m⁻² h⁻¹), showed a correlation with temperature and irradiance and was highest across the system in February 2007 when the mouth was still closed. There was no significant correlation between production rates and biomass (chl-a) in either the benthic or pelagic habitats. The negative correlation between DIN:DIP ratio and benthic primary productivity indicated that phosphorus was the limiting nutrient. This study shows that salinity, along with seasonally dependent parameters such as temperature and irradiance, correlates with the rate of microalgal production. Hence, in these shallow lakes, the largest primary productivity can occur in either the pelagic or benthic subsystems, depending on prevailing conditions at the time.     

The 2004 re-assessment of the South African sardine and anchovy populations to take account of revisions to earlier data and recent record abundances

Hydroacoustic surveys off the coast of South Africa over the early years of the 21st century indicated that both the sardine Sardinops sagax and anchovy Engraulis encrasicolus populations had simultaneously reached record abundances. The South African pelagic fishery is regulated using an Operational Management Procedure (OMP). The OMP in use at that time had been developed using data from the two populations prior to this rapid and substantial increase in abundances. This paper documents the revised assessments that were urgently required to provide a basis to update the OMP. These assessments resulted in a changed perception of the status and productivity of these populations. In particular, estimates of the stock-recruitment relationships and the extent of variation about them, which play a key role in evaluating risk when developing OMPs, altered substantially from estimates derived from earlier assessments.     

Exploring the spatial distribution patterns of South African Cape hakes using generalised additive models

We developed delta generalised additive models (GAMs) to predict the spatial distribution of different size classes of South African hakes, Merluccius capensis and M. paradoxus, using demersal trawl survey data and geographical (latitude and longitude) and environmental features (depth, temperature, bottom dissolved oxygen and sediment type). Our approach consists of fitting, for each hake size class, two independent models, a binomial GAM and a quasi-Poisson GAM, whose predictions are then combined using the delta method. Delta GAMs were validated using an iterative cross-validation procedure, and their predictions were then employed to produce distribution maps for the southern Benguela. Delta GAM predictions confirmed existing knowledge about the spatial distribution patterns of South African hakes, and brought new insights into the factors influencing the presence/absence and abundance of these species. Our GAM approach can be used to produce distribution maps for spatially explicit ecosystem models of the southern Benguela in a rigorous and objective way. Ecosystem models are critical features of the ecosystem approach to fisheries, and distribution maps constructed using our GAM approach will enable a reliable allocation of species biomasses in spatially explicit ecosystem models, which will increase trust in the spatial overlaps and, therefore, the trophic interactions predicted by these models.     

Biodiversity and environmental characteristics of the bycatch assemblages from the tropical tuna purse seine fisheries in the eastern Atlantic Ocean

The impact of human activities such as fishing has been identified as a main factor in diversity loss in the open ocean. This paper studies the diversity patterns and environmental characteristics of the bycatch assemblages in Fish Aggregating Devices (FADs) and Free School sets (sets made on schools of tuna) from the tropical tuna purse seine fishery in the eastern Atlantic Ocean (35°W–15°E and 20°N–15°S). Data were collected from scientific observer programmes carried out between 2003 and 2011 on board Spanish and French fleets. The results showed different structure and diversity patterns of the bycatch assemblages depending on the fishing mode, with higher number of species and diversity found in FAD sets than in Free School sets. Bycatch assemblages showed preferences for specific oceanographic characteristics of the Atlantic Ocean, such as the equatorial and seasonal coastal upwelling systems, the Cape Lopez front system and the Guinea dome. The type of set and sea surface temperature play an important role to describe the diversity patterns of these species. These results confirm the importance of integrating different methods to study the marine ecosystem towards the correct implementation of the Ecosystem Approach to Fishery Management (EAFM).