Higher Catch Rates Research Articles

Improving species and size selectivity in the Baltic cod trawl fishery with two simple codend designs

The eastern Baltic cod (Gadus morhua) stock is at a critically low level and recruitment of the western Baltic cod stock is at the lowest observed level in over 30 years. The EU (European Union) landing obligation was introduced in 2015 for cod and in 2017 for plaice (Pleuronectes platessa). Size selective codend designs have been used in the Baltic cod trawl fishery for 25 years; however, there are still relatively high discard rates for cod, plaice and European flounder (Platichthys flesus; henceforth flounder) in the trawl fishery and landings of individuals below the minimum conservation reference size (MCRS). These problems call for additional improvements of species and size selectivity in the cod trawl fishery. In this study, two trawl codend designs were developed and tested to improve species and size selectivity in the Baltic cod trawl fishery. The codends were tested onboard a commercial trawler and the test codends were compared to the conventional Bacoma codend, which was fished simultaneously in a twin trawl rig. New codend designs were based on the Bacoma design, where the first test codend had a bottom net panel made of larger diamond meshes (nominal 130 mm mesh size) to improve selectivity in a cod fishery with high catch rates of flatfish. This codend showed a reduction of plaice and flounder, and cod below 45 cm, in the catches. The other test codend was a full square mesh codend (nominal 120 mm mesh size) developed for a cod directed fishery with low flatfish catches, and showed a marked reduction in the catch of cod below 50 cm, with no differences for flounder and plaice catches. With cod stocks at critically low levels and relatively high discard rates of cod, plaice and flounder, the simple codend designs tested in this study could benefit the sustainability of the Baltic cod trawl fishery, but with some loss of commercially targeted sizes.

Modelling fishing location choice and spatial behaviour of fishers near a marine protected area

PurposeThis study investigates whether higher catch rates near a marine protected area (MPA), and/or in other fishing areas within a choice set, attract more fishers. A survey conducted in the fishing grounds near an MPA located in south east of Mauritius in the Indian Ocean shows concentration of fishers in regions with lower catch rates. This contrasts with the predictions of the “fishing the line” hypothesis and the ideal free distribution (IFD) that fishers are likely to be attracted near the MPA with higher resource abundance.Design/methodology/approachUsing the random utility model as the framework and the random parameter logit (RPL) model, the study attempts to explain spatial behaviour of fishers. Expected catch and catch variability are modelled using the Just and Pope (JP) production function. The study also estimates effort elasticities with respect to expected catch and catch variability and simulates the relocation of effort from area closure.FindingsThe paper concludes that higher catch does attract fishers but is a partial and very restrictive explanation of fishers' behaviour. The “fishing the line” hypothesis does hold to some extent, but it should not be taken for granted that rising catch rates in adjacent waters will increase fishing pressure. The paper concludes that factors such as catch variability, distance from homeport to fishing ground, potential physical risk and attitudes towards risk of fishers affect spatial behaviour of fishers and should be considered for the placement and size of MPAs. The study also finds that the responsiveness of effort to catch rates is lowest in areas which are already heavily fished and easily accessible.Practical implicationsThe identification of fishing areas as complements (when fishing in one area increases fishing effort in another) and substitutes is valuable information for determining the placement and size of an MPA. A larger reserve is likely to have more displacement effect in this case than a smaller one. Therefore, a small or a network of a small reserve may be appropriate. The premise to select the site and size of the reserve is to avoid overconcentration of fishers in alternative fishing areas, which can be vulnerable to excessive fishing and unintended effects from fishers.Originality/valueThe paper contributes to an understanding of fishing behaviour and its impact on the configuration of marine reserves. It discusses the importance of effort elasticities to determine the placement and size of an MPA. Studies on this topic are very scanty in the Indian Ocean region. It also shows the application of location choice model, the RPL model and the JP production function in the fisheries sector for a small island.

Evaluation of Habitat Use by a Catch‐and‐Release Regulated Flathead Catfish Population in Branched Oak Reservoir, Nebraska, USA

AbstractA series of rock jetty and A‐Jack structures was built in 1998 at Branched Oak Reservoir, Nebraska, in an attempt to reduce shoreline erosion and cove degradation. In conjunction with the habitat enhancement project, Flathead Catfish Pylodictis olivaris were stocked to help control the abundant White Perch Morone americana population. Previous research found that Flathead Catfish utilized the habitats created by the enhancement project; however, the research was conducted while the Flathead Catfish population was still developing and the reservoir water elevation was held for an extended period below conservation pool. We sampled three habitat types (rock jetty structures, concrete A‐Jack structures, and new‐growth trees) during the summer months from 2015 to 2019 using daytime low‐frequency electrofishing to determine differences in size distribution and relative abundance among habitat types. Flathead Catfish utilization of the rock jetty structures was characterized by high catch rates (137 fish/h) and smaller fish (<400 mm). Lower catch rates were found in the A‐Jack structures (86 fish/h) and new‐growth trees (36 fish/h); however, these habitats were primarily utilized by larger fish (>600 mm). Habitat use changed with the developing population and the availability of a new habitat type, inundated new‐growth trees. The catch‐and‐release regulation changed both density and size structure of the Flathead Catfish population in Branched Oak Reservoir. The results of this study can assist fisheries managers in locating or enhancing favorable reservoir habitats for Flathead Catfish.

The Effect of Bait on The Catch Composition of Square Folding Trap in Rawa Pening Semarang Regency

This study aims to determine the effect of the type of bait on the composition of the catch fish, catch rate, and trap rate using square folding traps. The study was conducted at three fishing locations in October 2019-January 2020 using the experimental fishing method. The operation of square folding traps was done by a total of 60 units. The types of bait used are golden snails, shrimp paste, and trash fish. Fish catches were recorded in number, type, length, and weight, and analyzed using one-way anova test and kruskal wallis test. The composition of the square folding traps catches consists of six species. Marble goby (Oxyeleotris marmorata) is the most dominant catch (60%). The highest catch rate was obtained from box folding traps which were given golden snail bait at 173.50 g/trip, then trash fish bait at 76.88 g/trip and shrimp paste feed at 59.22 g/trip. The highest trap rate is golden snail bait of 12.33%. The bait treatment gives a real difference to the amount and weight of the catch, the golden snail bait gives the highest total number and weight of the catch compared to other baits.

SPATIO-TEMPORAL VARIATIONS OF YELLOWFIN TUNA CAUGHT BY HANDLINE IN THE INDIAN OCEAN, SOUTH OF NUSA TENGGARA

One of the main targets from small-scale handline tuna fishery is yellowfin tuna (Thunnusalbacares), where most, if not all of its operation depended heavily on the installment of the fish aggregating device (FAD). The objective of the study was to investigate the spatial and temporal distribution of catch and size of yellowfin tuna from FAD-associated handline fishery. The study was conducted from January to December 2018 with main observation location was in Labuhan Lombok fishing port, West Nusa Tenggara. The results showed that the highest catch rate was obtained during April-June, followed by the frequent emergence of large yellowfin tuna (>100 cm FL). On the other hand, January-March was considered as a low season, where most of the catch was dominated by juvenile yellowfin tuna (<50 cmFL). The spatial distribution of yellowfin tuna abundance is closely related to the presence of FADs, where all fishing operations are carried out around FADs. Also, aggregation of fish was more likely influence by temporal variation rather than the quantity of FAD. More abundant yellowfin tuna were found during the east monsoon (April-June) compared to another season where less fish occurred.

Efficiency changes in bottom trawling for flatfish species as a result of the replacement of mechanical stimulation by electric stimulation

AbstractAlthough fishing with electricity is illegal in the European Union, a number of temporary licences allowed converting beam trawlers to pulse trawling. To analyse how the adaption of pulse trawling changed this fishery, we studied fishing speeds and landings per unit effort as proxies for catch efficiencies for the main target species. Compared to conventional tickler chain beam trawls, pulse trawls were towed at lower speeds (small vessels −10%, large vessels −23%). Large vessels that switched from conventional beam trawls to pulse trawls at the end of 2009 gradually increased catch efficiency for sole over the period of almost 1 year. While pulse trawling was found to have higher catch rates (kg/h) for sole (small vessels +74%, large vessels +17%), lower catch rates were observed for plaice (small vessels −31%, large vessels −32%). Vessels that switched later achieved immediate gains in catch efficiency for sole. The change in catch efficiency is likely due to the difference in cramp response between the species.

Effects of the trap entrance designs on the catch efficiency of swimming crab Charybdis feriata fishery

The swimming crab Charybdis feriata fishery is important to the coastal fishing communities of Vietnam, particularly in the province of Quang Nam. Trapping is considered a low impact and fuel-efficient fisheries capture technique that is drawing increasing attention as concerns regarding the impact of fisheries on ecosystems and the environment grow. However, traps typically have low capture efficiency for most crab species and there is considerable interest to improve catchability. In this study we investigated the impact of modifying the number of trap entrances on a traditional trap design, and also the colour of entrance-netting, on the catch rate of swimming crab in the Vietnam trap fishery. In the first experiment we compared catch rates between a traditional three-entrance trap and a modified one-entrance trap design, and found that the modified one-entrance trap had a 24 % higher catch rate. In second experiment, we compared catch rates of one-entrance traps having green or yellow entrance-netting and found that yellow netting increased catch rates by 31 %. This study shows that fishing enterprises could improve their swimming crab trap fishery by using modified one-entrance traps with yellow entrance netting.

Fishing for euros: how mapping applications can assist in maintaining revenues under the Landing Obligation

Abstract With the introduction of the Landing Obligation (LO) in EU fisheries, there is an increasing need for fishers to avoid unwanted catches while maximizing revenues. Improving understanding of the spatio-temporal dynamics of unwanted catches could assist the fishing industry optimize catches by altering where they fish. How following such advice relates to revenues and fishery dynamics requires more consideration. We take an existing hotspot mapping methodology and examine how it could be used to identify fishing opportunities under the LO in Irish (Celtic Sea) and Danish (North Sea and Skagerrak) demersal fisheries. We consider if fishing effort can be relocated to avoid unwanted catches while maintaining revenues. The value per unit effort of fishing activity in both areas was often linked to high catch rates of key demersal species (cod, haddock, hake, and whiting). Our analyses indicated, however, that there are options to fish in areas that could provide higher revenues while avoiding below minimum conservation reference size catches and choke species. This was evident across both case study areas demonstrating that hotspot mapping tools could have wide applicability. There does, however, remain a need to explore how the displacement of vessels may further alter species distributions and fleet economics.

Effect of pelagic longline bait type on species selectivity: a global synthesis of evidence

Fisheries can profoundly affect bycatch species with ‘slow’ life history traits. Managing bait type offers one tool to control species selectivity. Different species and sizes of marine predators have different prey, and hence bait, preferences. This preference is a function of a bait’s chemical, visual, acoustic and textural characteristics and size, and for seabirds the effect on hook sink rate is also important. We conducted a global meta-analysis of existing estimates of the relative risk of capture on different pelagic longline baits. We applied a Bayesian random effects meta-analytic regression modelling approach to estimate overall expected bait-specific catch rates. For blue shark and marine turtles, there were 34% (95% HDI: 4–59%) and 60% (95% HDI: 44–76%) significantly lower relative risks of capture on forage fish bait than squid bait, respectively. Overall estimates of bait-specific relative risk were not significantly different for seven other assessed taxa. The lack of a significant overall estimate of relative capture risk for pelagic shark species combined but significant effect for blue sharks suggests there is species-specific variability in bait-specific catch risk within this group. A qualitative literature review suggests that tunas and istiophorid billfishes may have higher catch rates on squid than fish bait, which conflicts with reducing marine turtle and blue shark catch rates. The findings from this synthesis of quantitative and qualitative evidence support identifying economically viable bycatch management measures with acceptable tradeoffs when multispecies conflicts are unavoidable, and highlight research priorities for global pelagic longline fisheries.

Association of Environmental Factors in the Taiwan Strait with Distributions and Habitat Characteristics of Three Swimming Crabs

Information regarding the oceanic environment is crucial for determining species distributions and their habitat preferences. However, in studies on crustaceans, especially swimming crabs, such information remains poorly utilized, and its effects on crab communities in the Taiwan Strait (TS) has not been well documented. The purpose of this study was to understand the relationship between the catch rates of three swimming crab species and environmental factors in the TS. We fitted generalized additive models (GAMs) to logbooks and voyage data recorder data from Taiwanese crab vessels (2011–2015), developed a species distribution model, and predicted catch rates for these three swimming crab species based on the GAM output. The chlorophyll-a (Chl-a) concentration was related to the high catch rates of Chrybdis feriatus and Portunus sanguinolentus, whereas bottom temperature (BT) was related to high catch rates of Portunus pelagicus. The variance percentages for each crab species indicated that high catch rates of C. feriatus and P. sanguinolentus occurred in a Chl-a concentration &gt; 0.5 mg/m3, whereas P. pelagicus catch rates exhibited negative correlations with BTs &gt; 25 °C. The model predicted high catch rates of C. feriatus in the north of the TS during autumn and winter, whereas P. pelagicus was observed to the south during summer and autumn. P. sanguinolentus was predicted to be widely distributed around the TS and distributed further to the northern area during autumn and winter. These findings revealed that each species responds to spatiotemporal environmental variations. Understanding the distributions and habitats of these three crabs is vital in fisheries resource management and conservation planning.

Status of Fisheries in Agusan Marsh: Lapaz and Talacogon, Agusan del Sur, Mindanao

In support to policy formulation of fisheries in Agusan Marsh, a stock assessment was conducted for the period of May 2014 to December 2016 using the data collected from Lapaz and Talacogon, Agusan del Sur within the Agusan Marsh. Results showed that Lapaz contributed 54% of the catch over Talacogon. A total of eighteen species, belonging to 13 genera and 11 families with 7 native and 11 introduced species were found in the marsh. Majority of the total catch consisted of Channa striata, Oreochromis niloticus, and Cyprinus carpio (35%, 27%, and 26%, respectively). Osphronemus laticlavius, Glossogobius celebius and Mugil cephalus were listed as seasonal species. An invasive janitor fish (Pterygoplichthys disjunctivus) was observed as by-catch. A strong pattern of high catch rates occurred during the rainy months of January, February, June, and December. Ten types of commonly used fishing gears were found, majority of which include fish pots, set gillnets, electrofishing and set long lines. Multivariate analysis showed similarity in species composition both in Lapaz and Talacogon. Exploitation of dominant species showed unsustainable level for O. niloticus, C. batrachus, C. caprio, andC. gariepinus, mainly due to excessive capture of immaturesized fishes by major fishing gears. The estimated exploitation rate is beyond the optimum level for O. niloticus and C. carpio in both years and followed by C. striata and C. gariepinus in 2016. Only C. bartachus is estimated to be exploited below the optimum level. Generally, the key species in Agusan Marsh are at risk of overfishing, hence, immediate policy measures must be given high attention.

Environmental influences on Aedes aegypti catches in Biogents Sentinel traps during a Californian "rear and release" program: Implications for designing surveillance programs.

As Aedes aegypti continues to expand its global distribution, the diseases it vectors (dengue, Zika, chikungunya and yellow fever) are of increasing concern. Modern efforts to control this species include “rear and release” strategies where lab-reared mosquitoes are distributed throughout the landscape to replace or suppress invasive populations. These programs require intensive surveillance efforts to monitor their success, and the Biogents Sentinel (BGS) trap is one of the most effective tools for sampling adult Ae. aegypti. BGS trap catches can be highly variable throughout landscapes, so we investigated the potential impacts of environmental factors on adult Ae. aegypti capture rates during a “rear and release” program in California to better understand the relative contributions of true variability in population density across a landscape and trap context. We recorded male and female Ae. aegypti catches from BGS traps, with and without CO2, throughout control sites where no mosquitoes were released and in treatment sites where males infected with Wolbachia were released. BGS trap catches were positively influenced by higher proportions of shade or bushes in the front yard of the premises as well as the presence of potential larval habitats such as subterranean vaults. In contrast, an increase in residential habitat within a 100 m radius of trap locations negatively influenced BGS trap catches. For male Ae. aegypti, increased visual complexity of the trap location positively influenced capture rates, and the presence of yard drains negatively affected catch rates in control sites. Lastly, for BGS traps using CO2, higher catch rates were noted from traps placed greater than one meter from walls or fences for both male and female mosquitoes. These results have important implications for surveillance programs of Ae. aegypti throughout the Californian urban environment including adult monitoring during “rear and release” programs.

Insights into the users of a citizen science platform for collecting recreational fisheries data

Citizen science platforms, including smartphone applications, that allow anglers to report information about fishing trips and catches may be a low-cost source of data that can feed into the science and management of recreational fisheries. However, information about potential biases in these data, such as the representativeness of user characteristics and retention patterns is largely lacking. Here, we examine the characteristics and retention patterns of the users of a Danish citizen science smartphone application and website that allow anglers to report data from fishing trips. Using data from a roving creel survey of sea trout (Salmo trutta) anglers as an independent source for calibration, we found that users of the citizen science platform were younger, more specialized, and had higher catch rates than non-users. On the citizen science platform, 21% of the users were active (i.e., contributed data at least once, three months after creating an account), with an additional 22% using the platform as a source of information (e.g., catch statistics or regulations) for at least three months. These sustained users were older and ascribed a higher importance to angling as a hobby compared to those who stopped using the platform within three months. Data from similar platforms are unlikely to be representative of all anglers and, as a result, research is required to determine what issues this will bring for population extrapolations.

Modeling the spatiotemporal distribution of the deep-sea shrimp Aristeus antennatus (Crustacea: Decapoda) on the northwestern Mediterranean continental margin crossed by submarine canyons

Abstract Submarine canyons aggregate numerous marine species and can affect the structure of benthic communities. However, analyses dedicated to assess the spatial distribution variability among several canyons are rare. In the northwestern Mediterranean Sea, three major submarine canyons consecutively indent the narrow margin. There, the abundance of deep-sea blue and red shrimp Aristeus antennatus (Crustacea: Decapoda), one of the most important fishery-targeted species in the western and central Mediterranean Sea, sustains relatively high incomes for the nearest fishing harbors. To date, the spatial distribution of this shrimp species has only been assessed on known fishing grounds, but it has neither been modeled simultaneously covering several submarine canyons nor according to the environmental conditions. In this study, we aimed to look over the spatiotemporal shrimp distribution in a region of the northwestern Mediterranean Sea with a particular interest in variations in the three submarine canyons. From summer landing data between 2005 and 2014, we implemented a species distribution model with georeferenced catches linked to environmental data of the shrimp habitats. The model showed that the bottom topography was one of the most essential variables to explain the spatial distribution of the catches and that the highest catch rates were between 475 m and 575 m depth. Overall, two canyons (Blanes and Palamos) sheltered high estimates of catches on the shallow and narrow part of their margins (at 510 and 565 m depth). Among them, 60% of estimated summer catches came from the Palamos Canyon, but this estimate shifted to the Blanes Canyon in summer 2008, probably due to variations in fishing fleet behavior. Modeled hypothetical temperature changes scenarios (to 1 °C warmer than the average) suggested the shrimp catches would decrease less in the Blanes Canyon (3% fewer catches than the average) than in the Palamos Canyon (20% fewer catches than the average). The information produced by the species distribution model allowed setting spawning locations and depths, which is useful to better understand the canyon influence on benthic communities and to parameterize larval transport models.

Predation mortality from ambush and cruising predators on newly-settled 0-group gadoids

We investigated predation from an ambush predator (shorthorn sculpin) and two cruising predators (Atlantic cod and saithe) on bottom-settled 0-group cod and saithe juveniles in a fjord in northern Norway. Stomach contents of potential fish predators caught by gill net in shallow waters (depth of 3–10 m) during September in 2013–2015 were analysed. The frequency of occurrence (FO) of 0-group gadoid prey was highest for shorthorn sculpin (FO = 10%) and cod (FO = 9%), while it was lower for saithe (FO = 0.8%). Each predatory fish species had different alternative prey to 0-group gadoids: shrimps for cod; sandeels for saithe; and Brachura/Anomura for shorthorn sculpin. Amongst the fish predators, shorthorn sculpin had the highest catch rates in gill nets. The mean number of 0-group cod and saithe in shorthorn sculpin stomachs increased with increasing abundance of prey as measured by beach seine hauls.Predation mortality from shorthorn sculpin was estimated based on abundance of shorthorn sculpins, number of 0-group cod and saithe juveniles in predator stomachs, prey recognition times and abundance of 0-group cod and saithe. The average predation mortality rate from shorthorn sculpin on 0-group gadoid juveniles varied from 0.40 to 1.14 month−1 between years and the pooled estimate from 2013 to 2015 was 0.70 month−1 (95%CI: 0.30, 1.73). This is comparable to mortality rates from other studies on newly-settled 0-group Atlantic cod, other gadoid species and plaice. Based on gill-net catches and stomach data from this study and literature values for gill-net catching area, calculated predation mortalities from the cruising cod and saithe were less than 47% of the sculpin predation mortality rates. This show that predation mortality from the ambush sculpin predator was much higher than from the cruising Atlantic cod and saithe.

Following the edge of the flood: use of shallow-water habitat by larval silver carp Hypophthalmichthys molitrix in the upper Mississippi river system

We examined the use of “edge of flood” habitats by larval silver carp during the extensive flooding that occurred in Pool 26 of the Upper Mississippi River near Alton, IL, USA and St. Louis, MO, USA during the summer of 2015. We captured over 12,700 individual fishes including eight taxa, over 12,000 of which (> 95%) were larval silver carp between 5 and 21 mm standard length. Peak catch rates occurred near the confluence of the Illinois and Mississippi rivers. These findings suggest that larval silver carp have an affinity for edge of the flood habitat and further study is needed to better understand how this affects the dynamics of this invasive species in the Mississippi River. The high catch rates observed at the confluence of the Illinois and Mississippi rivers suggests that the Illinois River is an important source of larval silver carp to the Upper Mississippi River.

Highly resolved spatiotemporal simulations for exploring mixed fishery dynamics

To understand how data resolution impacts inference on mixed fisheries interactions we developed a highly resolved spatiotemporal discrete-event simulation model MixFishSim incorporating: i) delay-difference population dynamics, ii) population movement using Gaussian Random Fields to simulate patchy, heterogeneously distributed and moving fish populations, and iii) fishery dynamics for multiple fleet characteristics based on population targeting under an explore-exploit strategy. We applied MixFishSim to infer community structure when using data generated from: commercial catch, a fixed-site sampling survey design and the true (simulated) underlying populations. In doing so we thereby establish the potential limitations of fishery-dependent data in providing a robust characterisation of spatiotemporal distributions. Different spatial patterns were evident and the effectiveness of a simulated spatial closure was reduced when data were aggregated across larger spatial areas. The simulated area closure showed that aggregation across time periods has less of a negative impact on the closure success than aggregation over space. While not as effective as when based on the true population, closures based on high catch rates observed in commercial data were still able to reduce fishing on a protected species. Our framework allows users to explore the assumptions in modelling observational data and evaluate the underlying dynamics of such approaches at fine spatial and temporal resolutions. From our application we conclude that commercial data, while containing bias, provides a useful tool for managing catches in mixed fisheries if applied at the correct spatiotemporal scale.

Potential distribution and population trends of the smalltail shark Carcharhinus porosus inferred from species distribution models and historical catch data

Abstract Updated distribution ranges are crucial for conservation status assessments. Comprehensive analyses combining published literature and available data on historical catches and species distribution models (SDMs) are effective tools that could improve the prediction of more realistic scenarios for some species, especially those with limited information available and facing multiple threats. The present study aimed at generating an updated distribution for the smalltail shark Carcharhinus porosus, one of the most threatened and understudied shark species of the western Atlantic Ocean. Estimates of the key areas for this species conservation based on the SDMs, and trends in catch probabilities throughout its distribution range are provided. Four algorithms (BIOCLIM, Domain, Mahalanobis, and Maximum Entropy) were used to model the distribution of C. porosus and calculate its habitat suitability based on marine environmental variables. To assess historical catch probability trends, we built a generalized linear model from published and grey literature data. This analysis was used to estimate catch probability as an indication of population trends. SDMs suggest that the northern coast of South America (NCSA) harbours the most suitable habitats for C. porosus in the world, which was expected given its historically high catch rate in this region. In addition, there was a continuously declining catch probability trend starting in the 1970s. However, the decline was smaller for the NCSA as compared with the Gulf of Mexico and the eastern South America coast. Results indicate that the NCSA should be considered the currently most important area in the world for this species conservation. Furthermore, the lack of data throughout Central and South American marine regions hampers the evaluation of extinction risk throughout its updated distribution. Thus, research in these areas is urgently required for a more comprehensive conservation status assessment.

Composition and catch rate of fishing pot as eco-friendly fishing gear at the estuary of Bogowonto River in Kulon Progo Regency

The estuary of Bogowonto river in Kulon Progo Regency was habited by various species such as fish, shells, crabs, and snails. This research aimed to know the composition and catch rate of the fishing pot using various kinds of fodder. The method used in this research was catch identification and assessment of type, length and weight of the catch, and also the fishing pot’s effectiveness as eco-friendly fishing gear. Data analysis was conducted by measuring fish length, catch composition, and catch rate of the fishing pot. The result showed the catch composition consisted of 8 types of species which are mangrove crab (5%), freshwater crab (0.81%), pufferfish (3.38%), orange-spotted grouper fish (0.14%), green tiger prawn (0.14%), giant tiger prawn (0.41%), banana prawn (0.14%) and freshwater snail (90%). The pot with fresh fish fodder had the highest number of catch (66.08%) compare to salted fish (23.51%) and roasted coconut (10.41%) fodder. The highest catch rate of fishing pot was observed on fresh fish fodder (35.42 g/fishing pot) compare to salted fish fodder (11.19 g/fishing pot) and roasted coconut fodder (4.61 g/fishing pot). Based on the result, fresh fish is considered a more effective fodder compared to salted fish and roasted coconut.

The Pelagic Habitat of Swordfish (Xiphias gladius) in the Changing Environment of the North Indian Ocean

Swordfish (Xiphias gladius) are a highly migratory keystone species, found in tropical and temperate seas that are influenced by environmental parameters. In the Bay of Bengal, the Arabian Sea, and the ocean region around Sri Lanka, the environment is gradually changing as a result of climate change. In this study, we identified the preferable environmental conditions for swordfish using satellite-derived environmental data and in-situ fish catch data. We modeled the relationships between fish distribution and the environment changes using Boosted Regression Trees (BRT) and Generalized Additive Model (GAM) methods. The monthly mean fishing effort is comparatively high from October to March and the fish catch rates are high from September to November. Chlorophyll-a concentration has a positive relationship with catch rates while sea surface temperature (SST), sea salt surface mass concentration (SSS), and effort show negative relationships. Approximately 0.3–0.4 mgm−3 of chlorophyll-a, 28–28.5 °C SST, and (3–5)10−8 kgm−3 of SSS were significantly correlated with high swordfish catch rates. According to the optimum environmental conditions identified using the above models, the suitable environmental spatial and temporal distribution was mapped. The results show that the optimum conditions for swordfish are in the eastern region of Sri Lanka, around Thailand and Myanmar, from June to August, and around Bangladesh, Myanmar, Pakistan, the west coast of Sri Lanka, and the east coast of India during September to November.