Trends In Catch Rates Research Articles

Trends in catch rates of sawfish on the Australian North West Shelf

Northwestern Australia is thought to have some of the world’s last remaining viable sawfish populations, although little quantitative data exists on their status or trends. This study examined 17 years of logbook bycatch records (n = 815) for green sawfish Pristis zijsron and narrow sawfish Anoxypristis cuspidata from a trawl fishery operating on the Australian North West Shelf. Incidental sawfish captures by the fishery are rare, occurring approximately once every 75 trawls (~199 trawl hours). To standardize catch rates and account for excess zeros in the data, we employed generalized additive models for location, scale, and shape (GAMLSSs) using a zero-inflated Poisson distribution. For green sawfish, catch rates approximately doubled over the study period, while an oscillating trend was observed for narrow sawfish catch rates. Reported captures occurred throughout the management boundaries of the fishery, which operates in mid-shelf waters from 48 to 121 m. A weak seasonal signal in catch rates was detected for both species, with the highest capture numbers occurring during autumn-winter, consistent with an expected inshore migration for parturition during spring-summer. Logbook trends were partly corroborated by independently verified data collected in a subset of years, which also showed an increasing proportion of green sawfish in the catch. Our findings emphasize the importance of sawfish populations in northwestern Australia within the context of global conservation efforts for this taxon.

Biology and ecology of the African blackspot shark Carcharhinus humani on the east coast of South Africa

The African blackspot shark Carcharhinus humani (until now commonly known as Human’s whaler shark) is a small-sized requiem shark (family Carcharhinidae) found in tropical coastal waters of the western Indian Ocean as far south as Port St Johns on the east coast of South Africa. It was only recently recognised as being distinct from the blackspot shark C. sealei, which occurs elsewhere in the Indo-Pacific. This study utilised four datasets to investigate the movements, temporal and geographic distributions, life history and population status of this species in South African waters. The recapture of eight individuals of 294 that were tagged by shore anglers revealed an average distance moved of 33 km (range 1–192 km). Competitive shore anglers caught an average of 39 C. humani per annum along the entire KwaZulu-Natal (KZN) coast, with no marked trend in catch rate over time. Catches in the KZN bather protection programme were extremely low but included 30 pregnant females which displayed a highly seasonal pattern of embryo development. Sightings of C. humani on stereo baited remote underwater video systems (stereo-BRUVS) in the iSimangaliso Marine Protected Area were dominated by females (7.7:1) and were mostly in deeper water of 26–35 m. In all datasets most of the individuals were mature and were present year-round, but with a clear peak in summer and autumn, especially in the catches taken by shore anglers. Competitive shore-angling catch data were used to conduct a risk assessment for the South African population, and, based on values of probability of encounter, the sampled population satisfies the IUCN Red List criteria for Least Concern.

Annual and seasonal environmental drivers of species- and gear-specific catch rates in the Visayan Sea, Philippines

Fisheries management requires a holistic understanding of the factors that influence the stocks and their variability. While previous investigations in the Visayan Sea – a major fishing ground in the Philippines – have acknowledged the potential influence of several environmental factors, the relationships remain largely unexplored. By applying multiple analytical approaches, we explored the observed trends and effects of a set of seasonally variable environmental parameters (sea surface temperature, chlorophyll-a, net primary productivity, rainfall, wind magnitude, Southern Oscillation Index and Pacific Decadal Oscillation) on the species-specific and gear-specific catch per unit of effort (CPUE) in the Visayan Sea. Increasing sea surface temperatures had generally significant negative effects on the CPUEs of all species except one. The positive modeled effects of wind and optimal rainfall levels are attributed to these factors’ favorable influence on net primary productivity and food availability, with implications on the successful early development of the different species and the condition of the parent stock. In addition to the biological responses, behavioral responses by the blue swimmer crabs were also found to influence the CPUEs. These results highlight the importance of identifying the variable influence of seasonal environmental factors to better interpret the observed temporal trends in catch rates, and serve as important first contributions to inform a more ecosystem-based and adaptive management response to the fisheries in the Visayan Sea.

Quantifying the historical development of recreational fisheries in Southeast Queensland, Australia

Recreational fisheries are of global socio-ecological importance and contribute significantly to local economies and fisheries harvests. In some regions of Australia, organized recreational fishing activities have existed for over 150 yr. However, historical understanding of the spatio-temporal development and resource usage of recreational fisheries has been hampered by the lack of continuous time-series catch and effort data. This study used historical newspaper articles of reported landings by fishing clubs to reconstruct catch rate trends and evaluate changes in catch composition of marine recreational fishing activities in Moreton Bay, Queensland, Australia, from 1920-1984. Using generalized additive mixed models, 2 catch rate metrics (no. of fish fisher-1 trip-1 and kg fish fisher-1 trip-1) were constructed as functions of time and distance travelled. Significant nonlinear relationships were found for no. of fish fisher-1 trip-1. Fluctuations in no. of fish fisher-1 trip-1 were strongly influenced by time, while increases in distance travelled predicted a larger no. of fish fisher-1 trip-1. Measures of kg fish fisher-1 trip-1 were tightly linked to increases in distance travelled but did not vary with time. Spatial analysis revealed shifts in areas fished, from inshore reefs during the 1920s and 1930s (pre-WWII) towards isolated offshore island systems in later decades (>1950s; post-WWII). Reported catches pre-WWII were strongly associated with reef species, while reported catches post-WWII were predominantly characterized by demersal coastal fish. Spatially resolved time-series fisheries data can be reconstructed from archival sources, providing valuable information about the development of recreational fishing activities and explaining the historical social-ecological dynamics that led to current ecosystem states.

Factors Driving Long Term Declines in Inland Fishery Yields in the Mekong Delta

The Mekong basin’s fisheries are important sources of food, income, and livelihoods for millions of people in six countries. However, fish yields appear to have declined in recent years according to reports from local fishers throughout the basin. It is important to understand the factors driving the decline in fisheries so that they can be adequately managed. We analysed interview data from 1020 fishers in the Mekong Delta in Vietnam in 2014 to identify trends in catch rates and the possible factors driving the trends. Most of the fishers (68–90%) reported that their catch rates had declined over the previous five years, although some fishers stated that their fish catches had remained stable or even increased. They identified eleven factors that they believed contribute to declines in fish catches, among which the use of illegal gears and overfishing were considered most important, with other factors relatively unimportant. Separately, long-term datasets (1995–2016) showed a general decline in commercial fish catches, which was positively correlated with peak water levels (which indicate flood levels), and negatively correlated with the intensification of rice farming, especially where flooding has been prevented to allow a third annual rice crop. Some data suggests that fishing effort has declined significantly in recent years, so an apparent downward trend in catches is not likely to be a result of overfishing as believed by fishers, which suggests that fishers are not aware of or under-rate the significance of hydrological and land-use/landscape changes. Due to the exceptional importance of the Mekong fishery and the interactions with other more dominant sectors, improved data collection is required to quantify changes in fisheries that result from land use and hydrological changes, and to guide planning which would better resolve competing demands for water and land use.

Short commentary on the population structure of Deepsea Shrimp, Aristeus alcocki from India.

According to FAO, shrimp production in India increased by 10% in 2018, due to the suitable climatic conditions and development of the fishery. Arabian red shrimp (Aristeus alcocki) is one of the important crustacean resources found in Indian seas. It has inhabited in the deep-sea regions and is widely distributed along the south-east and south-west coast of India with the depth of 200-3100 m. This shrimp is a highly perishable product in the export market, which has a shorter lifespan (6-7 years), compared to fishes, as a result, presence of high volume of free amino acids and other soluble nonnitrogenous substances. During earlier days, the landings of this shrimp was observed in more than ten major fishing harbours along the Indian coast, however in the later years, it is noticed only in Kerala and Tamil Nadu coasts. Conversely even now, more than 80% landings of this deep sea shrimp were observed from Sakthikulangara harbour of Kerala and there is no landing was noticed in Mumbai, Mangalore and Visakhapatnam coasts. The landing of recent years (2008 - 2017) were indicate that, the A. alcocki is the major species in order of biomass among the deep-sea penaeoid catch from the whole Indian coast. However trend in catch rates of the A. alcocki was showed declining phase during year of 2015-2016. The present study on “Investigation of genetic diversity and stock structure of Aristeus alcocki populations in the Indian coast” is providing baseline information, which is useful for the policy development and sustainable management of the resources in the future.

Trends and transitions observed in an iconic recreational fishery across 140 years

Abstract Recreational fishing has taken place for centuries and is a globally popular activity, yet a lack of monitoring data means historical trends in recreational fisheries are often little understood compared to their commercial counterparts. We examined archival sources and conducted fisher interviews to examine changes in the Queensland recreational snapper (Chrysophrys auratus) fishery throughout its documented history. We extracted data spanning the past 140 years on technological innovations, catch rate trends, and social and regulatory change. Technological innovations were evident throughout the history of the recreational fishery. During the 1960s, 1990s and 2000s, several periods of rapid technological transition occurred, where a technology was adopted by >50% of recreational fishers within 10 years of its introduction. Since the 1960s, the timing and rate of adoption of fish-finding technology by recreational fishers has kept pace with the commercial sector. These technological advances have profoundly increased recreational targeting ability, but despite these advances, recalled recreational catch rate trends demonstrated significant declines over the course of the 20th century. While minimum size limits have been imposed on the snapper fishery for over a century, in contrast, the introduction of recreational in-possession limits only commenced in the 1990s. At this time, the beginnings of a societal transition was also observed, where longstanding ‘take-all’ attitudes towards fishing began to be replaced by a more conservation-minded ethic. This shift was driven in part by the changing regulatory landscape, as well as wider attitudinal change influenced by the media and shifting societal norms, although whether this led to a reduction in total recreational catch remains unclear due to a lack of fishery-wide monitoring data and the open access nature of the recreational fishery. This study demonstrates that in the absence of systematic data collection, archival sources and fisher interviews can contribute an interdisciplinary knowledge base for understanding and interpreting historical fishery trends.

A Commentary – Lake Tanganyika fisheries: Current constraints and the way forward

A Commentary – Lake Tanganyika fisheries: Current constraints and the way forward

Habitat Use and Fishery Dynamics of a Heavily Exploited Coastal Migrant, Spanish Mackerel

AbstractSpanish Mackerel Scomberomorus maculatus support important commercial and recreational fisheries in the Gulf of Mexico (GOM). Although federally managed because of interstate migrations, harvest, essential fish habitat consideration, and management are largely state issues. Contrary to the accepted paradigm of a well‐mixed stock from the GOM to the Atlantic, Spanish Mackerel have been suggested to exhibit reduced movement, and hence mixing, which could lead to areas of localized depletion within the larger stock. We addressed how local abundance patterns responded to changes in harvest pressure, evaluated migration patterns via examining temporal trends in abundance, and determined whether the spatial abundance patterns resembled habitat specialization or generalization. Abundance trends of Spanish Mackerel in Alabama have remained relatively constant from 2001 to 2011 despite a significant increase in commercial harvesting. Seasonal patterns of catch rates coincided with the proposed annual migration. We also observed adult Spanish Mackerel in low salinities (0–10‰) at the mouth of Mobile River during the fall when river discharge is relatively low. This extends the known range of estuarine habitat use by adult Spanish Mackerel. Because Mobile Bay includes various habitat types differing from surf zone and coastal ocean habitats typically inhabited by Spanish Mackerel, capturing Spanish Mackerel near the mouth of Mobile River provides evidence for a habitat generalist strategy. Based on a relatively constant abundance index and year‐class strength, the stock seems to be relatively stable even after a drastic increase in commercial harvests in Alabama and heavy exploitation of age‐1–3 Spanish Mackerel. The resilience of catch rate trends to changes in local harvest pressure as well as evidence of synchrony among areas in terms of migration suggest the Alabama fishery is influenced by population dynamics of a larger population.Received July 3, 2014; accepted January 12, 2015

Artisanal Green Turtle, Chelonia mydas, fishery of Caribbean Nicaragua: I. Catch rates and trends, 1991-2011.

This is the first assessment of catch rates for the legal, artisanal green turtle, Chelonia mydas, fishery in Caribbean Nicaragua. Data were collected by community members, monitoring up to 14 landing sites from 1991 to 2011. We examined take levels, and temporal and spatial variability in catch rates for the overall fishery, by region, and community using General Additive Mixed Models (GAMMs). More than 171,556 green turtles were killed during the period, with a mean estimated minimum 8,169±2,182 annually. There was a statistically significant decline in catch rates overall. Catch rates peaked in 1997 and 2002, followed by a downward trend, particularly from mid-2008 to the end of the study period. Similar downward trends were evident in both study regions. Community specific catch rate trends also indicated declines with decreases ranging from 21% to 90%. Decrease in catch rates in Nicaragua is cause for concern even though the principal source rookery at Tortuguero, Costa Rica, shows an increase in nesting activity. Explanations for the apparent discrepancy between the increasing trend at Tortuguero and decreasing catch rate trends in Nicaragua include: i) an increase in reproductive output, ii) insufficient time has passed to observe the impact of the fishery on the rookery due to a time lag, iii) changes in other segments of the population have not been detected since only nesting activity is monitored, iv) the expansive northern Nicaragua foraging ground may provide a refuge for a sufficient portion of the Tortuguero rookery, and/or v) a larger than expected contribution of non-Tortuguero rookeries occurring in Nicaragua turtle fishing areas. Our results highlight the need for close monitoring of rookeries and in-water aggregations in the Caribbean. Where consumptive use still occurs, nations sharing this resource should implement scientifically based limits on exploitation to ensure sustainability and mitigate impacts to regional population diversity.

Longer is not always better: The influence of beach seine net haul distance on fish catchability

The aim of this study was to compare the influence of different haul distances of a codend beach seine on the catchability of fish in a surf zone. Two different surf zone sites (A and B) at the Cassino Beach (Rio Grande do Sul, Brazil) were sampled at three different distances, parallel to the beach (30, 60, and 90 m). Starting 40 m from the beach line, diagonal distances of approximately 50, 70, and 100 m were swept. The total CPUE and CPUA haul distances are compatible with a declining trend in catch rates with increased haul distance at both sites. However, statistically significant differences were observed only for the short distance CPUA (50 m) in relation to the other haul distances at one of the sites sampled. Two fish size groups were observed (TL 40 mm), but only small individuals (< 40 mm) captured in the shorter haul distance at site B showed significant differences in CPUA. This result indicates that size structure for hauls at different distances was equal and that smaller individuals determined the pattern of fish abundance. The net performance indicates that a short haul (< 50 m) is the best strategy to reduce net avoidance and fish escape when using this type of sampling gear.

Fishing the line: catch and effort distribution around the seasonal haddock (Melanogrammus aeglefinus) spawning closure on the Scotian Shelf

Permanent and seasonal area closures are a common regulatory strategy in multispecies fisheries; however, few studies have closely examined seasonal closures. We examined the impact of the Browns Bank spawning closure on the spatial distribution of fishing effort and how the fleet utilized a “fishing the line” strategy. Generalized estimating equations were used to examine changes in effort distribution when the closure was and was not in effect. Effort displaced from the bank concentrated primarily within two areas up to 30 km from the closure boundary, one along the east boundary line and one along the west. Trends in catch rate (as value) with distance from the line were further examined using generalized additive models during the closed period, with results differing between regions. In the east, areas of greater catch rate could be identified and typically corresponded to areas of greater effort, while in the west region, no trends in catch rates were often observed, potentially indicating vessel distributions that correspond to the ideal free distribution. Implementation of a seasonal area closure on Browns Bank resulted in concentrations of vessels near the closure boundary, suggestive of a fishing the line strategy, with specific catch rate trends depending on vessel spatial distributions and target species.

An analysis of the impacts of climatic variability and hydrology on the coastal fisheries, Engraulis encrasicolus and Sepia officinalis, of Portugal

Abstract The notion that climate change may impact coastal fish production suggests a need to understand how climatic variables may influence fish catches at different time scales. Evidence suggests that the effect of climatic variability and fishing effort on landed catches (as proxy of fish abundance) may vary at the regional scale. This study aims to assess the sensibility of two commercial species with a short life cycle ( Engraulis encrasicolus and Sepia officinalis ) to climatic and fisheries effects across different regions of the coast of Portugal: northwestern, southwestern and southern Portugal. The effect of environmental explanatory variables, i.e. NAO index, sea surface temperature (SST), upwelling (UPW) index, river discharge, wind magnitude (WmaG), wind direction (Wdir), and fishing variables (fishing effort) on catch rates time series were studied between 1989 and 2009. The sensibility of the species studied to climatic variability differed among regions and were explained by different climatic variables. River discharge had a significant effect on catch rates of the two species, region independently. However, wind driven phenomenon and UPW were the variables that better explained the observed fishing trends across the three regions. Changes in catch rate trends among the studied regions, at a given time, were mostly associated with the reproduction periods of the species. Therefore, regional analyses will significantly contribute to a better understanding of the relationship between climate change and coastal fisheries, aiming to improve integrated coastal zone management.

Population Growth Rates of Reef Sharks with and without Fishing on the Great Barrier Reef: Robust Estimation with Multiple Models

Overfishing of sharks is a global concern, with increasing numbers of species threatened by overfishing. For many sharks, both catch rates and underwater visual surveys have been criticized as indices of abundance. In this context, estimation of population trends using individual demographic rates provides an important alternative means of assessing population status. However, such estimates involve uncertainties that must be appropriately characterized to credibly and effectively inform conservation efforts and management. Incorporating uncertainties into population assessment is especially important when key demographic rates are obtained via indirect methods, as is often the case for mortality rates of marine organisms subject to fishing. Here, focusing on two reef shark species on the Great Barrier Reef, Australia, we estimated natural and total mortality rates using several indirect methods, and determined the population growth rates resulting from each. We used bootstrapping to quantify the uncertainty associated with each estimate, and to evaluate the extent of agreement between estimates. Multiple models produced highly concordant natural and total mortality rates, and associated population growth rates, once the uncertainties associated with the individual estimates were taken into account. Consensus estimates of natural and total population growth across multiple models support the hypothesis that these species are declining rapidly due to fishing, in contrast to conclusions previously drawn from catch rate trends. Moreover, quantitative projections of abundance differences on fished versus unfished reefs, based on the population growth rate estimates, are comparable to those found in previous studies using underwater visual surveys. These findings appear to justify management actions to substantially reduce the fishing mortality of reef sharks. They also highlight the potential utility of rigorously characterizing uncertainty, and applying multiple assessment methods, to obtain robust estimates of population trends in species threatened by overfishing.

Species at risk in Canada: Lessons learned from the listing of three species of wolffish

Abstract The Canadian Species at Risk Act (SARA) was implemented in 2003. Since 2003, no fully marine Atlantic Canadian fish species has been listed and some observers are seriously questioning the extent to which SARA is effectively protecting marine fish species. Three species of wolffish found in North Atlantic waters were placed onto the SARA list in 2003 when it was implemented. The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) originally listed these species in 2000 and 2001. The COSEWIC listings were based on catch-rate trends over large spatial scales from a relatively short time series of offshore research vessel survey data and status reports derived from research for an honours thesis. This case study of the wolffish listings draws on results from semi-structured interviews with key informants familiar with the listing and post-listing events, an analysis of existing documents and research on the SARA process, and on data from wolffish-focused Local Ecological Knowledge (LEK) interviews with commercial fish harvesters in the Northern Gulf of St. Lawrence. The results shed light on the wolffish listing process including perceptions of how the implementation of SARA has affected the process and prospects for listing fully marine species. The post-SARA listing developments in relation to wolffish, including harvesters' views about the listing are also explored. The results indicate mixed views about the benefits and problems associated with the requirement for public consultations and incorporation of stakeholder knowledge into the listing process under SARA. There is some evidence that the wolffish listing process has increased harvester stewardship and engagement and benefitted from their input into the safe release of wolffish. Finally, little attention has been paid by any of the stakeholder groups consulted to the potential future delisting of wolffish, arguably the most important goal of species conservation initiatives. Without delisting requirements or timelines set out in a species recovery plan it is impossible to establish concrete guidelines for recovery.

Using catch rate data for simple cost-effective quota setting in the Australian spanner crab (Ranina ranina) fishery

Abstract O'Neill, M. F., Campbell, A. B., Brown, I. W., and Johnstone, R. 2010. Using catch rate data for simple cost-effective quota setting in the Australian spanner crab (Ranina ranina) fishery. – ICES Journal of Marine Science, 67: 1538–1552. For many fisheries, there is a need to develop appropriate indicators, methodologies, and rules for sustainably harvesting marine resources. Complexities of scientific and financial factors often prevent addressing these, but new methodologies offer significant improvements on current and historical approaches. The Australian spanner crab fishery is used to demonstrate this. Between 1999 and 2006, an empirical management procedure using linear regression of fishery catch rates was used to set the annual total allowable catch (quota). A 6-year increasing trend in catch rates revealed shortcomings in the methodology, with a 68% increase in quota calculated for the 2007 fishing year. This large quota increase was prevented by management decision rules. A revised empirical management procedure was developed subsequently, and it achieved a better balance between responsiveness and stability. Simulations identified precautionary harvest and catch rate baselines to set quotas that ensured sustainable crab biomass and favourable performance for management and industry. The management procedure was simple to follow, cost-effective, robust to strong trends and changes in catch rates, and adaptable for use in many fisheries. Application of such “tried-and-tested” empirical systems will allow improved management of both data-limited and data-rich fisheries.

Alternative migration and host parasitism strategies and their long‐term stability in river lampreys from the River Endrick, Scotland

The stability of a discrete body size dimorphism of sexually mature river lamprey Lampetra fluviatilis from the River Endrick, Scotland, was examined over a 21 year period. Stable isotope analysis was used to test the hypothesis that the two size forms comprise individuals with differing migration and parasitic foraging strategies. Maturing river lamprey and the brook lamprey Lampetra planeri were trapped over 3 months each year in the periods 1983–1984 and 2004–2005. Brook lamprey catches and catches of both species combined showed no significant trend in catch rate with time. The catch rate of small body size river lamprey declined between 1983–1984 and 2004–2005 (although the difference did not reach statistical significance; P = 0·055). In contrast, there was a significant increase in the catch rate of the large body size river lamprey and as a consequence, a significant change in the relative proportion of each of the two river lamprey morphs over the study period. Analysis of the stable isotopes of C and N in muscle tissue showed that brook lamprey tissue derived its carbon from a freshwater source and had a δ13C more consistent with that of the River Endrick than with Loch Lomond. δ15N values for this species showed it to be feeding at the base of the food chain, consistent with filter feeding as an ammocoete. The large body size and the small body size river lamprey adults differed substantially in their δ13C values, with the small body size δ13C signature indicative of a freshwater carbon source and the large body size morph of a marine source. The small body size morph had a δ13C signature that was consistent with that of Loch Lomond powan Coregonus lavaretus suggesting that they share a common carbon source. The large body size morph was clearly feeding at a higher trophic level than the small body size morph. A single small body size river lamprey individual with typical morphology for that group, however, had C and N signatures that clustered with those of the large body size morphs. This individual had either migrated to sea to forage, as is typical for the species, or had been feeding on an anadromous fish with a strong marine C signature in fresh water. It is concluded that the body size dimorphism is indicative of a differential migration and foraging strategy in the parasitic phase of the life cycle of river lamprey at this site.

Trends in catch rates of sea turtles in North Carolina, USA

Sea turtles captured in pound nets during the autumn and early winter in the Pamlico- Albermarle Estuarine Complex, North Carolina, USA, were sampled 1995-1997 and 2001-2003 to monitor trends in catch rates during their autumn emigration from the temperate sounds. Juvenile loggerhead turtles Caretta caretta were the most frequent species encountered, followed by green turtles Chelonia mydas and Kemp's ridley turtles Lepidochelys kempii. Several different subpopula- tions with origins throughout the western North Atlantic were represented on these foraging grounds. The catch rates of loggerhead turtles increased significantly at a rate of 13% yr -1 . Despite annual increases in the major contributing nesting beach populations in excess of 10% yr -1 , we did not detect a trend in catch rates for either green or Kemp's ridley turtles, perhaps due to low statisti- cal power. There was a significant increase in size of loggerhead turtles over time. We also detected a significant difference in annual size distributions of green and Kemp's ridley sea turtles, but there was no discernable pattern. We conclude that long-term studies on the sea turtles' foraging grounds, at multiple sites, are needed to monitor the status of sea turtle populations.

Spatial distribution of effort by artisanal fishers: Exploring economic factors affecting the lobster fisheries of the Corn Islands, Nicaragua

Spatial distribution of fishing effort is increasingly recognised as an important consideration for fisheries management, as it can affect trends in catch rates, and be incorporated into planning of spatial management tools like marine protected areas (MPAs). One hundred and ninety-eight household questionnaires provided a coarse indication of effort distribution of artisanal lobster fishers around the Corn Islands, and 32 semi-structured interviews with skippers were used to map individual fishing sites and describe the operating costs and revenues of typical dive and trap-fishing operations. Artisanal fisheries had ranges of up to 50 km, and had moved significantly offshore within the previous 10 years. At the scale of a 5 × 5 min latitude/longitude grid, trap fishing effort was highly aggregated (dispersion coefficient = 3.5), while diving had a regular dispersion (d.c. = 0.1). Descriptions of catch composition at each site showed a clear spatial pattern in the distribution of two locally recognised types of lobster, potentially indicating local stock structures. Economic information was summarised into balance sheets for typical fishers and suggested that fuel accounted for about 52 and 37% of the operating costs of dive and trap fishing captains, respectively. Qualitative questions highlighted trap theft, adoption of geographical positioning system (GPS) technology and fuel costs as major factors affecting spatial behaviour. The costs and benefits of using more distant grounds were examined by testing for relationships between stated typical catch rates and distance of 90 trap-fishing grounds and between fuel expenditure and catches in 291 daily records of the activities of 3 divers. Maximum catch rates stated by trap fishers were significantly higher at more distant sites and daily catches by divers had a positive relationship with fuel expenditure, which suggested that increasing fuel expenditure to target more distant sites would lead to higher gross revenue as well as higher net revenues, after considering variable operating costs. Thus, there appears to be an economic incentive to extend the range of the fishery. However, fishers may not perceive these positive trends in catch rate with distance due to catch variability, and costs other than fuel, which complicate the trade-off between catch and distance.

Population status of 14 shark species caught in the protective gillnets off KwaZulu - Natal beaches, South Africa, 1978 - 2003

Shark nets have been set off the beaches of KwaZulu–Natal, South Africa, since 1952 to reduce the risk of shark attack. The nets fish in fixed localities 400 m from shore and both directly affect local shark populations and act as fisheries-independent monitoring devices. Reliable catch information at the species level was available for the period 1978–2003. Trends in catch rate and size were used to assess the population status of 14 commonly caught shark species. In addition, a demographic modelling approach was used in conjunction with the catch information to assess the potential effect of the nets on populations. Catch rates of four species (Carcharhinus leucas, C. limbatus, Sphyrna lewini and S. mokarran) showed a significant decline, as did the mean or median length of three species (Carcharhinus amboinensis, C. limbatus and female Carcharodon carcharias). For three species that showed declining catch rates or length the potential effect of the shark nets was assessed to be low, suggesting that other sources of catch were responsible for the declining status. The potential effect of the shark nets was assessed to be high for two species (Carcharhinus obscurus and Carcharias taurus, neither of which showed declines in catch rate or length), because of very low intrinsic rates of population increase.