Fishing Intensity Research Articles

New perspective on the genetic structure and habitat adaptation of Pampus minor off the coast of China based on RAD-seq

Understanding the genetic diversity and habitat adaptation patterns of different geographic populations of marine organisms is essential for the rational maintenance, development, and utilization of their resources. Pampus minor Liu and Li 1998 is an economically valuable marine fish species. To determine the population genetic structure and elucidate the genetic mechanism underlying the habitat adaptation of this species, restriction site-associated DNA sequencing (RAD-seq) was used to scan the whole genomes of three P. minor putative populations along the coast of China for single-nucleotide polymorphism (SNPs) and outlier SNPs. Our population genetic structure analysis based on 2388 SNPs and 731 outlier SNPs throughout the genome revealed no significant genetic differentiation among the three populations. Results suggested that the life-cycle characteristics of P. minor, its relatively large population sizes, and ocean current transport might have shaped its current genetic pattern. The annotation information of both assembled sequences (which included outlier SNPs) and candidate loci associated with adaptations indicated that genes involved in many processes, including ion exchange, osmotic pressure regulation, metabolism, and the immune response, have been very important in the adaptations of P. minor to its heterogeneous habitats. Against the background of increased human activities, increased fishing intensity, and destruction of marine habitats, the results of this study provide basic genetic information for the accurate division of protection units of P. minor.

Understanding fishery interactions and stock trajectory of yellowfin tuna exploited by Iranian fisheries in the Sea of Oman

Abstract The predominant policy for remedying the world fishing crisis aims at maximum sustainable yield (MSY) by adjusting gear selectivity and fishing effort to maintain sustainable stock levels. The yellowfin tuna (Thunnus albacares) fishery in the Sea of Oman has experienced intense increases in removals since 1980, with particularly high levels since the 1990s. Here, we apply a statistical catch-at-age model to time-series of catches and fishery-dependent length composition data to obtain a preliminary and general understanding of the population dynamics of this stock since the start of the fishery in 1950–2019. Despite limited data, population models consistently indicate a sharp decline in population status since the beginning of the time-series across a variety of assumptions on stock productivity and life history. The gillnet fishery takes almost exclusively immature individuals, with high fishing intensity and removal rates. Both reference models indicate the population is essentially at the same relative stock status in 2019 (10% of unfished), but with very different future projections and higher absolute stock size when recruitment is estimated. The yellowfin tuna population in 2019 is below estimated MSY reference points (based either on unfished size or spawning output at MSY) for current relative stock size, and over the fishing intensity at MSY, indicating current overfishing. Adjusting the interactions of that fishery with the population, while continuing to collected biological composition data representative of each fleet in the fishery, will help mitigate current stock decline and provide the ability to refine future population status determination and forecasts through more informed stock assessments.

Long-Term Variability of Piscivorous Fish in China Seas Under Climate Change With Implication for Fisheries Management

Due to persistent fishing expansion in the China Seas over the past six decades, fisheries resources have been over-exploited; as a result, exploited fish have become smaller in size and younger in age. Marine piscivorous fish constituted a large portion of Chinese fisheries catch, long-term variability of which has rarely been investigated despite intense fishing pressure and climate change. In this study, we attempt to identify their responses to climate change and fishing activities and to provide scientific basis for sustainable exploitation of these resources. Seven taxa from pelagic to demersal species inhabiting either cold-water or warm-water were selected to represent the piscivorous fish assemblage in the China Seas. Total catch of these piscivorous fish in the China Seas increased during the early 1990s, stabilizing around 1.2 million tons after 1997. Principal component analysis (PCA) showed evident interannual-decadal variabilities in the catch of these fish with step changes around 1985/86 and 1997/98. Individual taxa, however, showed different trends in catches with sharks, rays, and lizardfishes manifesting downward trends while Pacific cod, eels, and hairtail increasing. Common dolphinfish and Japanese-Spanish mackerel increased largely in the 1990s but declined slightly during the 2000s. Although there were temporal overlaps between climate change and fishing variabilities, results of gradient forest analyses indicated that fishing effort imposed the most important influence on piscivorous fish. And among all climate variables explored in this study, sea surface temperature (SST) especially that of the East China Sea, had greatest impacts on variations in piscivorous fish catch, which may have been gradually exacerbated by the continued high fishing intensity. In addition, significant changes were identified in the life history traits in the species we evaluated, such as reduced average body sizes and truncated age compositions, strongly indicating the effect of fishing. We therefore advocate precautionary fishery practices under climate change.

Identification of Fishing Vessel Types and Analysis of Seasonal Activities in the Northern South China Sea Based on AIS Data: A Case Study of 2018

In recent years, concern has increased about the depletion of marine resources caused by the overexploitation of fisheries and the degradation of ecosystems. The Automatic Identification System (AIS) is a powerful tool increasingly used for monitoring marine fishing activity. In this paper, identification of the type of fishing vessel (trawlers, gillnetters and seiners) was carried out using 150 million AIS tracking points in April, June and September 2018 in the northern South China Sea (SCS). The vessels’ spatial and temporal distribution, duration of fishing time and other activity patterns were analyzed in different seasons. An identification model for fishing vessel types was developed using a Light Gradient Boosting Machine (LightGBM) approach with three categories with a total of 60 features: speed and heading, location changes, and speed and displacement in multiple states. The accuracy of this model reached 95.68%, which was higher than other advanced algorithms such as XGBoost. It was found that the activity hotspots of Chinese fishing vessels, especially trawlers, showed a tendency to move northward through the year in the northern SCS. Furthermore, Chinese fishing vessels showed low fishing intensity during the fishing moratorium months and traditional Chinese holidays. This research work indicates the value of AIS data in providing decision-making assistance for the development of fishery resources and marine safety management in the northern SCS.

Artemia as a sustainably cultured live feed for ornamental fish in zoological institutions with immunostimulant properties when bioencapsulated with spirulina (Arthrospria platensis).

Sustainable in-house cultures of bio-enriched live feeds for ornamental fish can enhance development, nutrition and welfare of the animal by improving immunity while further reducing economical costs to zoological institutions. Artemia is an easily harvestable feed with its nutritional profile highly dependent on its diet which is easily manipulated through bioencapsulation. This study evaluates the effects of two types of commonly used feeds for Artemia: spirulina and yeast, and how this affects the growth, feed conversion ratio (FCR), survival rate, immunity and colour intensity of ornamental fish, compared to a commercial pellet (control) diet. A total of 198 mature, mixed sex serpae tetra Hyphessobrycon eques were subjected to the three different diet treatments conducted in duplicate. There was no significant difference in growth weight, FCR, lysozyme, myeloperoxidase and alkaline phosphatase between treatments. Protease index of activity was significantly lower in fish fed with Artemia bio-enriched with spirulina (71.48%) and highest in the control diet (95.48%). The colour intensity and redness of the fish also significantly increased when fed Artemia bio-enriched with spirulina versus Artemia bio-enriched with yeast or a control diet.

AIS and VBD Data Fusion for Marine Fishing Intensity Mapping and Analysis in the Northern Part of the South China Sea

For the sustainable development of marine fishery resources, it is essential to comprehensively, accurately, and objectively obtain the spatial characteristics and evolution law of fishing intensity. However, previous studies have focused more on the use of single data sources, such as AIS (Automatic Information System) and VBD (VIIRS boat detection), to obtain fishing intensity information and, as such, have encountered some problems, such as insufficient comprehensive data coverage for ships, non-uniform spatial distribution of data signal acquisition, and insufficient accuracy in obtaining fishing intensity information. The development of big data and remote sensing Earth observation technology has provided abundant data sources and technical support for the acquisition of fishing intensity data for marine fisheries. Based on this situation, this paper proposes a framework that integrates the data of fishing vessels from two sources (AIS, with high space-time granularity, and VBD, with short revisit cycle and high sensitivity), in order to obtain such information based on closely matching and fusing the vector point data of ship positions. With the help of this framework and the strategy of indirectly representing fishing intensity by data point density after fusion, the spatial characteristics and rules of fishing intensity in typical seasons (February, April, September, and November) in the northern South China Sea in 2018 were systematically analyzed and investigated. The results revealed the following: (1) Matching and fusing AIS and VBD data can provide a better perspective to produce robust and accurate marine fishery intensity data. The two types of data have a low proximity match rate (approximately 1.89% and 6.73% of their respective inputs) and the matching success for fishing vessels in the data was 49.42%. (2) Single AIS data can be used for nearshore (50 to 70 km) marine fishery analysis research, while VBD data reflect the objective marine fishing in space, showing obvious complementarity with AIS. (3) The fishing intensity grid data obtained from the integrated data show that high-intensity fishing in the study area was concentrated in the coastal area of Maoming City, Guangdong (0–50 km); the coastal area of Guangxi Beihai (10–70 km); around Hainan Island in Zhangzhou (10–30 km); and the Sanya nearshore area (0–50 km). However, it did not decay with increasing offshore distance, such as at the Trans-Vietnamese boundary in the Beibu Gulf, near the China–Vietnam Common Fisheries Area (50 km) and high-intensity fishing areas. (4) The obtained fishing intensity data (AIS, VBD, and AIS + VBD) were quantitatively analyzed, showing that the CV (Coefficient of Variation) of the average for each month (after fusing the two types of data) was 0.995, indicating that the distribution of the combined data was better than that before fusion (before fusion: AIS = 0.879, VBD = 1.642). Therefore, the integration of AIS and VBD can meet the need for a more effective, comprehensive, and accurate fishing intensity analysis in marine fishery resources.

Environmental influence on the distribution of polychaete families and feeding guilds in benthic communities of the Grand Banks and Flemish Cap (NW Atlantic)

Many biodiversity patterns across the globe can be partially explained by energetics and habitat structure, including in the deep sea. Because of difficulties in logistics, studies focusing on deep-sea benthic systems often have limited sample sets that may be far apart in space. Here, we present analyses based on a well-sampled region, the northwest Atlantic, allowing us to relate patterns of polychaete community structure (using taxonomic families and feeding guilds) against well-resolved environmental gradients. We show that community structure is heterogenous in this area. We observe three major groups within polychaete communities which also show differences in feeding guilds. Several environmental gradients, including long-term variables, explained the differences between the groups. Both energetics and habitat structure variables were important, while past fishing intensity had a weak effect, although there was support for a difference in community composition for communities above and below the historical fishing limit of 1200 m. The effect of long-term environmental factors may indicate that the deep sea is not immune to climate change, and these effects must continue to be considered in future management of exploitation of this ecosystem.

Fishing pressure and lifespan affect the estimation of growth parameters using ELEFAN

Length-based methods of stock assessment to support scientific fisheries management are desirable in data-limited fisheries where formal stock assessments are commonly constrained. Based on length-frequency (LFQ) data, Electronic length frequency analysis (ELEFAN) is widely used to fit growth curves, but the performance of this method is sensitive to various factors especially the quality of data. Fishing pressure is one of the main drivers that modify the length composition of fish stocks, but the consequent effects on ELEFAN are not well understood. This study aims to clarify the role of fishing pressure on the performance of ELEFAN given fish species with different life history traits. We designed a simulation-estimation framework to simulate the population dynamics of short-, medium-, and long-lived fish species, and to evaluate the performance of ELEFAN under varying fishing scenarios. The simulation results demonstrate that ELEFAN is robust to changes in size-structure due to fishing, while its accuracy and precision of outputs depends on the intensity of fishing pressure and the life-history characteristics. The estimates of the parameters of the von-Bertalanffy growth function (VBGF) are reliable in short- and medium-lived species, while for long-lived species, fishing may substantially bias the estimates depending on the intensity of fishing pressure. ELEFAN may yield >70% bias in the estimates of K along with large confidence intervals for long-lived species subject to heavy fishing intensity. ELEFAN will perform such better with prior knowledge about quantities such as lifespan. This study may contribute to the understanding of the reliability of ELEFAN for exploited fisheries and to increasing confidence for adopting ELEFAN in data-limited fisheries.

Reprint of : Fishers who rely on mangroves: Modelling and mapping the global intensity of mangrove-associated fisheries

Mangroves are critical nursery habitats for fish and invertebrates, providing livelihoods for many coastal communities. Despite their importance, there is currently no estimate of the number of fishers engaged in mangrove associated fisheries, nor of the fishing intensity associated with mangroves at a global scale. We address these gaps by developing a global model of mangrove associated fisher numbers and mangrove fishing intensity. To develop the model, we undertook a three-round Delphi process with mangrove fisheries experts to identify the key drivers of mangrove fishing intensity. We then developed a conceptual model of intensity of mangrove fishing using those factors identified both as being important and for which appropriate global data could be found or developed. These factors were non-urban population, distance to market, distance to mangroves and other fishing grounds, and storm events. By projecting this conceptual model using geospatial datasets, we were able to estimate the number and distribution of mangrove associated fishers and the intensity of fishing in mangroves. We estimate there are 4.1 million mangrove associated fishers globally, with the highest number of mangrove fishers found in Indonesia, India, Bangladesh, Myanmar, and Brazil. Mangrove fishing intensity was greatest throughout Asia, and to a lesser extent West and Central Africa, and Central and South America.

Sustainable Exploitation of Dominant Fishes in the Largest Estuary in Southeastern China

Globally, marine fisheries have declined under multiple stresses including overfishing, climate change, and habitat degradation. The Min River Estuary, as the largest estuary in southeastern China, has confronted this situation over recent decades. In this study, the dominant species of fish stocks in the Min River Estuary, including Coilia mystus, Cynoglossus abbreviates, Collichthys lucidus, Amblychaeturichthys hexanema, Polydactylus sextarius, Harpodon nehereus, and Secutor ruconius, were evaluated by the length-based Bayesian biomass estimator method (LBB). Outcomes could be grouped into three categories as healthy, showing the lowest exploitation rate (E: 0.31–0.43) and highest relative biomass (B/Bmsy: 1.30–1.90), including S. ruconius, C. mystus, and H. nehereus; overfished, with a medium E (0.50–0.58) and B/Bmsy (0.68–0.79), including A. hexanema and C. abbreviates; and collapsed, with the highest E (0.89–0.92) and lowest B/Bmsy (0.03–0.21), including C. lucidus and P.sextarius. Corresponding imperative countermeasures such as using larger-sized mesh gears and reducing fishing intensity should be deployed according to the current status of each species for sustainable fishery exploitation and fish conservation.

Modeling recreational fishing intensity in a complex urbanised estuary

Urbanised estuaries, ports and harbours are often utilised for recreational purposes, notably recreational angling. Yet there has been little quantitative assessment of the footprint and intensity of these activities at scales suitable for spatial management. Urban and industrialised estuaries have previously been considered as having low conservation value, perhaps due to issues with contamination and disturbance. Studies in recent decades have demonstrated that many of these systems are still highly biodiverse and of high value to local residents. As a response, urbanised estuaries are now being considered by coastal spatial management initiatives, where assessments of recreational use in these areas can help avoid ‘user-environmental’ and ‘user-user’ conflict. The models of these activities need to be developed at a scale relevant to governments and regulatory authorities, but the few human-use models that do exist integrate fishing intensity to a regional or even continental scale; too large to capture the fine scale variation inherent in complex urban fisheries. Species Distribution Modeling (SDM) is a tool commonly used to assess drivers of species range, but can be applied to models of recreational fishing in complex environments, at a scale relevant to regulatory bodies. Using point-data from 573 visual surveys with recently developed Poisson point process models, we examine the recreational fishery in Australia's busiest estuarine port, Sydney Harbour. We demonstrate the utility of these models for understanding the distribution of boat and shore-based fishers, and the effects of a range of temporally static (geographical) and dynamic (weather) predictors on these distributions.

Small steps high leaps: Bio-economical effects of changing codend mesh size in the North Sea Brown shrimp fishery

Small mesh codends applied in the brown shrimp (Crangon crangon L.) fishery in the North Sea cause large bycatch of fish, invertebrates and undersized shrimp. We investigated the most obvious and enforceable mitigation measure: the increase of mesh size beyond 20 mm, which was the medium mesh size of the fleet before 2016. The predicted selectivity from different codend designs was applied in a yield-per-recruit model able to reproduce the seasonal pattern of landings and biomass by sex, size, and age. The model enables assessment and quantifying population responses to possible management actions, also considering other influential variables such as natural mortality, which vastly decreased during the 1990s to the contemporary low level due to the decrease of cod in the Southern North Sea. Model results show that the selectivity of 20 mm codends leads to the poorest fishery and population indexes. Any increase in mesh size within the range considered and in the present low-predator situation would lead to a larger shrimp stock and higher catches. Increasing mesh size reduces catches of undersized and small commercial-sized shrimps entering the fishery mainly in summer time, thus leading to surplus catches in autumn and spring. Model results reveal that an increase of mesh size diminishes growth overfishing and allows the formation of a larger stock that may better cope a fluctuating natural mortality and the steadily upwards creeping fishing intensity.

Diversity of Trichodina spp. on The Larvae of Freshwater Fish in Banyumas and Surrounding Areas of Central Java

Trichodina sp. has a fast-splitting reproduction ability, and it is widespread, infect more than one species of fish. Freshwater fish cultivation increases every year, but high mortality caused by this parasite occurs. Research to determine Trichodina sp. on freshwater fish larvae was conducted in the district of Exs. Banyumas Residency, Central Java. We used a survey method to collect the fish larvae samples consisting of tawes, mujaher, nilem, and bawal of hatchery centers in Purbalingga, Banyumas, and Banjarnegara. Isolation and identification of parasites were conducted at the Parasitology-Entomology Laboratory, Faculty of Biology. The results showed that the prevalence of Trichodiniasis in freshwater fish from Banyumas, Banjarnegara, and Purbalingga was lower than Trichodiniasis in gourami larvae. Trichodiniasis intensity in freshwater fish was moderate.

ENDO AND ECTO PARASITE PREVALENCE AND ABUNDANCE IN SOME FISH SPECIES FROM AKOMOJE, OGUN RIVER SOUTH-WEST NIGERIA

Parasites are the second most abundant microorganisms that infect and cause disease in wild and cultured fish after bacteria. The study investigated the parasite prevalence, abundance, mean intensity and dominance in some fresh water fish from Akomoje, Ogun River, Nigeria from February to May, 2016. Eight fish species were collected and identified to the species level. Experimental fish were measured and weighed. Endo- and ecto-parasites were examined for from Skin/scale, dorsal and caudal fins, gills, intestine and stomach of fish. Water sample was collected from shore, mid and extreme of the landing site and also analysed for parasite abundance. Prevalence percentage of parasite in all fish species varied slightly with size. Myxozoan group revealed the highest dominance of ecto- and endo-parasites in virtually all fish species while mean intensity and abundance of Myxozoan spp was highest in Oreochromis niloticus and Hemichromis fasciatus. Highest case of a single species of ecto- and endo-parasite in a fish sample was that of Nematode larva in Chrysicthys nigrodigitatus (41.43 %) and Trichocerca sp (Rotifera) in Mormyrus rume (52.9 %).Water analysis revealed three parasite groups that were present in the sampled fish. Conclusively, Akomoje landing site of Ogun River has a rich burden of parasites.

Sediment Transport Model Quantifies Plume Length and Light Conditions From Mussel Dredging

Mussel dredging causes resuspension of sediment particles that reduce water clarity and potentially leads to reduced eelgrass growth. In order to study the impact of resuspension from mussel dredging on light conditions in the water column, field experiments were conducted at two sites in the Limfjorden. Light loggers were placed in two circular arrays around the dredge area. Vertical profiles of current velocity were measured by an ADCP and the sediment particle size composition was obtained from sediment core samples. The field data was used to force, calibrate and validate a sediment transport model developed in the FlexSem model system. Changes in sediment concentrations during and after mussel dredging were modelled for the two sites and for seven scenarios. We found that the distance and direction of the plume in the model was in good agreement with light logger data. The plume duration was less than 1 hour, and the impact range was between 260-540 m. The scenarios showed that fishing intensity and current speeds were most important for shaping the sediment plumes. Changes in suspended sediment concentrations were 0.62 to 1.79 mg/l on median average and 1.22 to 11.61 mg/l for the upper quantile of the plume, which were on the same order of magnitude as background values in the Limfjorden. The amount of fishing days during the eelgrass growth season was 6-8% in Lovns Bredning and 16-35% in Logstor Bredning and less than 1-2% of the total area was dredged per season. Even though there are substantial changes in the light conditions from the sediment plumes, the overall spatio-temporal impact in the study area is considered low. We recommend that management plans in other areas could sustain a shellfish fishery by limiting fishing intensity and frequency near eelgrass beds. The presented approach combines observational data, sediment transport modelling and reported fishing activity. It is a step forward within sediment transport modelling and could be incorporated into environmental impact assessments. The results have recently been used as scientific background for recommendations to improve the management plans according to the Danish Mussel Policy and relevant EU Directives.

Spatial distribution, source identification, and risk assessment of organochlorines in wild tilapia from Guangxi, South China

Seventy-five wild tilapia samples from six rivers (ten sites) in Guangxi province were collected and analyzed for 53 organochlorine compounds. DDTs, endosulfan, and PCBs were the most dominant compounds found in this study. Tiandong County (TD) and Guigang City (GG) sites were found to be heavily contaminated with high levels of endosulfan (385–925 ng/g lw) and/or DDTs (20.1–422 ng/g lw). The diagnostic ratios indicated that the residues of DDTs and endosulfan in wild tilapia are associated with historical applications as well as the recent introduction of technical DDTs and endosulfan at some sampling sites. The correlation between total length, body mass, and organochlorines (OCs) was higher than the correlation between age and lipid content. There was no significant correlation between organochlorine pesticides (OCPs) and lipid content. Therefore, for organisms, the feeding intensity (related to length and mass) of fish could better reflect degree of pollution than exposure time (age) of fish. The hazardous ratios for the 50th and 95th percentile data of OCPs and PCBs in fish were both below 1, suggesting that daily exposure to OCPs and PCBs yields a lifetime cancer risk lower than 1 in 10,000.

A multivariate perspective on lithic technological organization at Housepit 54, Bridge River Site (EeRl4), British Columbia

The management of lithic raw materials is a significant concern to anthropological archaeologists interested in hunter-gatherer socio-economies. A wide range of studies have implicated quarry distance, work needs, occupational longevity, and consumer population to variation in tactics for reduction, use, and maintenance of chipped stone tools. Fewer studies have examined socio-political factors in the organization of stone tool technology. This study examines the interactive effects of population, occupational longevity, favored prey, and socio-political complexity on the tactics by which lithic raw materials were managed in a long-lived winter pithouse in North America’s interior Pacific Northwest. Results of bivariate and multivariate analyses implicate variability in toolstone economies as related to different classes of lithic items. Lithic cores and flake tools were more extensively reduced in contexts of productive subsistence economies, high populations, long winter occupations, and material wealth-based inequality. Bifaces were produced and maintained in relation to needs associated with intensity of deer hunting. The creation and maintenance of slate tools was affected at least in part by the intensity of salmon fishing. Combined, these data suggest that the organization of lithic tool technology responded to multiple factors across the lifespan of the house.

Fishers who rely on mangroves: Modelling and mapping the global intensity of mangrove-associated fisheries

Mangroves are critical nursery habitats for fish and invertebrates, providing livelihoods for many coastal communities. Despite their importance, there is currently no estimate of the number of fishers engaged in mangrove associated fisheries, nor of the fishing intensity associated with mangroves at a global scale. We address these gaps by developing a global model of mangrove associated fisher numbers and mangrove fishing intensity. To develop the model, we undertook a three-round Delphi process with mangrove fisheries experts to identify the key drivers of mangrove fishing intensity. We then developed a conceptual model of intensity of mangrove fishing using those factors identified both as being important and for which appropriate global data could be found or developed. These factors were non-urban population, distance to market, distance to mangroves and other fishing grounds, and storm events. By projecting this conceptual model using geospatial datasets, we were able to estimate the number and distribution of mangrove associated fishers and the intensity of fishing in mangroves. We estimate there are 4.1 million mangrove associated fishers globally, with the highest number of mangrove fishers found in Indonesia, India, Bangladesh, Myanmar, and Brazil. Mangrove fishing intensity was greatest throughout Asia, and to a lesser extent West and Central Africa, and Central and South America.

Contracaecum multipapillatum (Nematoda: Anisakidae) en peces de aguas continentales de Guanacaste, Costa Rica e Izabal, Guatemala

Contracaecum multipapillatum infecta peces como hospedadores intermediarios y al ser humano como hospedador accidental por consumo de carne de pescado cruda o semi cocinada. Este riesgo para la salud humana hace importante determinar su prevalencia, intensidad de infección y ubicación anatómica en peces destinados al consumo mediante pesca artesanal; y la influencia de parámetros físicoquímicos del agua sobre la infección en peces. Se recolectaron 214 peces en 6 ríos de Cañas, Guanacaste, Costa Rica y 203 peces en el Lago de Izabal y Río Dulce, Izabal, Guatemala. En los sitios de pesca se tomaron parámetros físicoquímicos del agua (temperatura, pH y oxígeno disuelto). La prevalencia de infección fue 16.8% y 25.1% en Guanacaste e Izabal, respectivamente, encontrándose 105 larvas de tercer estadio (L3) en 36 peces de Guanacaste y 135 L3 en 51 peces de Izabal. Se observó afinidad de L3 por órganos viscerales (22.4% en Guanacaste – 25.1% en Izabal) y menor por tejido muscular (2.0% en Guanacaste – 1.0% en Izabal). La intensidad de infección directamente proporcional con la talla y peso de los peces (una larva en 13 peces con peso y talla media de 66.7 g y 17.5 cm en Guanacaste, y siete peces de 214.9 g y 28.4 cm en Izabal; y 14 larvas en un pez de 148.8 g y 24 cm en Guanacaste y 12 larvas en un pez de 260 g y 40 cm en Izabal). No se observó asociación entre parámetros fisicoquímicos del agua y susceptibilidad de peces a infección.

Reef microhabitats mediate fish feeding intensity and agonistic interactions at Príncipe Island Biosphere Reserve, Tropical Eastern Atlantic

AbstractThe benthic assemblage of reefs provides an important resource of food and habitat for reef fishes. However, how benthic composition mediates reef fishes' biotic interactions at isolated environments such as oceanic islands remains largely unknown. Here, we aimed to investigate the role of four different reef microhabitats over biological interactions of fishes in an understudied oceanic island, Príncipe Island. For that, we recorded a total of 46 Underwater Remote Videos (RUVs) to document benthic composition and fishes' trophic and agonistic interactions. We used benthic cover estimates to group the samples into four microhabitats (dominated by epilithic algal matrix [EAM], sand/rock, corals and sponges), then quantified fishes' trophic and agonistic interactions in each microhabitat. All microhabitats presented a different structure of trophic and agonistic interactions of the fish assemblage. Feeding pressure (FP) and agonistic interactions were higher on the EAM microhabitat and lower in coral microhabitat. Herbivores were the main responsible group for the FP in all microhabitats. Territorial damselfishes used microhabitats differently for both trophic and agonistic interactions. We demonstrated that reef fish diversity and intensity of biotic interactions varied according the spatial distribution of benthic resources, which suggests that benthic composition plays an important role on structuring biological interactions at isolated reef systems.