Longline Fishing Research Articles

The Effect of Bait Types on the Catch of Bottom Long Line in Bantan Sari Village Bantan District Bengkalis Regency

The main factor for the success of bottom longline fishing depends on the type of bait, both natural bait and artificial bait. The bait serves as an attractant for the target fish so that it is attracted to prey on it. In this study, the bait used was a machete, puput, and layur fish. The purpose of this study was to determine the amount, weight, and type of catch based on the appropriate type of bait so that it can be a reference for fishermen for optimal use of bait in the operation of longline fishing gear. This research was conducted in February 2022, located in the waters of Bantan Sari Village, Bantan District, Bengkalis Regency. The method used is the experimental fishing method, by operating the fishing gear directly and analyzing using the analysis of variance and the Least Significant Difference test. Based on the research, the catches obtained were debuk fish, gelama , stingrays, and puffer, with the highest catches in terms of weight, namely stingrays as much as 61800 g.

Optimal time of year and fishing methods for controlling exotic fishes in Longluan Lake, Taiwan

Aim: This study aimed to identify the optimal time and fishing methods for removing exotic fishes, including striped snakehead (Channa striata), marble goby (Oxyeleotris marmorata), tilapia (Oreochromis spp.), three-spot gourami (Trichopodus trichopterus), and predatory carp (Chanodichthys erythropterus), from Longluan Lake, which is located in Kenting National Park in Taiwan. Methodology: The selected fishing methods included lure fishing, longline fishing, and fyke netting. A total of 2,284 individuals were collected over 12 removal events in Longluan Lake from 2017 to 2019. Among the collected fish, 1,640 fish represented exotic species, and 644 fish represented native species. Results: Among the collected fish, 1,640 fish represented exotic species, and 644 fish represented native species. Based on the results of this study, we suggest that the optimal time for managing exotic fishes is from April to June, when is the period representing lower water levels in Longluan Lake. For removing specific exotic fish in Longluan Lake, employing lure fishing in natural habitat is effective for C. striata and Oreochromis spp., utilizing fyke netting in natural habitat is workable for T. trichopterus and C. erythropterus, and operating fyke netting in artificial habitat is useful for O. marmorata. Interpretation: The habitat preferences and sampling efficiency of gears vary among exotic fishes, however, a combination of applying lure fishing and fyke netting in both habitat types will achieve the greatest advantage for controlling exotic fishes in the Longluan Lake.

Relationship between ocean area and incidence of anthropogenic debris ingested by longnose lancetfish (Alepisaurus ferox)

Marine debris is present between the sea surface and the sea floor, but few studies have investigated plastic in water column. Therefore, we chose longnose lancetfish (Alepisaurus ferox) as a sample, this study samples mesopelagic species that ingest marine debris in the water column. We conducted a survey of the stomach contents of longnose lancetfish caught by longline fishing in three areas (Sagami Bay, Northwestern Pacific Ocean about 190 km southeast of Kyushu, Indian Ocean about 1200 km southwest of Sumatra Island, Indonesia). A total of 164 longnose lancetfish were caught. Our results highlighted four marine debris patterns. First, longnose lancetfish caught near the coast had a higher frequency of ingested anthropogenic items (Sagami Bay: 69%) than longnose lancetfish caught in the open ocean area (Northwestern Pacific Ocean: 13%, Indian Ocean: 18%). Second, the size of the plastic present in the ocean in the sea area close to the coast ingested by longnose lancetfish tended to be smaller than in the open ocean area. Third, 93% of the anthropogenic items obtained from the stomach were plastic, of which ¿90% was either polypropylene (PP) or polyethylene (PE). And last, the sources of marine debris in the middle and deep regions of the open ocean are fishing activities carried out in that sea area and items that drift from the land without losing buoyancy. Our research makes new discoveries about characteristics of the marine debris in the ocean.

Allocation of the skipper's attention depending on the longline fishing process of the coastal composite fishing vessel

Allocation of the skipper's attention depending on the longline fishing process of the coastal composite fishing vessel

Thirty-five years of tiger shark Galeocerdo cuvier relative abundance near Bimini, The Bahamas, and the Southeastern United States with a comparison across jurisdictional bounds.

Abundances of large sharks are reported to have declined worldwide, and in response various levels of fisheries management and conservation efforts have been established. For example, marine-protected areas have been suggested as a means to protect large expanses of ocean from fishing and other industrial activities (e.g., habitat destruction), and in 2011 The Commonwealth of The Bahamas established The Bahamas Shark Sanctuary. Nonetheless, assessing the effectiveness of conservation efforts is challenging because consistent long-term data sets of shark abundances are often lacking, especially throughout the Caribbean and The Bahamas. In this study, the authors investigated the catch rates and demographics of tiger sharks Galeocerdo cuvier caught in a fishery-independent survey near Bimini, The Bahamas, from 1984 to 2019 to assess relative abundance trends following the banning of longline fishing in 1993 and the subsequent establishment of the shark sanctuary. To contextualize the relative abundance trends near Bimini, the authors compared this to the relative abundance of tiger sharks in a fishery-dependent survey from the Southeastern USA (SE USA), conducted from 1994 to 2019. The data of this study suggest that local abundance of tiger sharks has been stable near Bimini since the 1980s, including after the ban of longline fishing and the implementation of the shark sanctuary. In comparison, the abundance near the SE USA has slowly increased in the past decade, following potential declines in the decade preceding the USA Shark Management Plan. The results of this study provide some optimism that current conservation efforts in The Bahamas have been effective to maintain local tiger shark abundance within the protected area. In addition, current fisheries management in the SE USA is allowing this species to recover within those waters.

Bet-hedging strategies determine daily choices in effort allocation for Nile perch fishers of Lake Victoria

Small scale fishers experience high variability in daily catches within a resource space limited in extent by operational constraints, and biophysical factors affect daily choices in spatial effort allocation. We focus on the management consequences of the extent of the individual fisher’s resource space and his options to handle risk arising from daily catch variability through a portfolio of sizes and species from within that resource space. Gillnet and longline Nile perch fishers in south-eastern Lake Victoria, Tanzania were provided with a GPS and recorded their position together with their daily catch and operations. Three different gillnet and longline fishing strategies could be discerned. All had bet-hedging characteristics, differing in the size of their resource space of on average 120 – 141 km2, distance from the shore fished and emphasis on the mix of sizes of Nile perch and other species caught. Daily choice of fishing locations did not relate to previous days’ catch success. Still, fishers used the general inshore to offshore distributional patterns of small and large Nile perch in their daily choices of mesh and hook sizes. The mix of sizes and species reduced day-to-day catch variability due to a portfolio effect. Current mesh and landing size regulations based on classical arguments around growth-overfishing interfere with these strategies and force individual fishers to specialise in size, species, and area. They must accept higher uncertainties by either choosing their fishing locations further offshore or accepting a more variable lower catch, leading to higher personal and occupational risk or ongoing management conflicts when disregarding regulations. Portfolio management of fished resources by compromising on mesh size regulations would make sense by allowing fishers to utilise a certain proportion of smaller mesh or hook sizes that are now illegal as part of their fishing strategies.

Length‐weight relationships of three demersal reef fishes caught by longline inhabiting the marine waters of gulf of Mannar, India

The length-weight relationships were estimated for three reef fish species caught in the Gulf of Mannar, India using experimental longlines. The longline fishing took place from December, 2019 to September, 2021 in fortnightly intervals, using longlines (2400 m, 2700 m and 3360 m each), equipped with each 600 various “J” type fishing hooks (straight, reversed, kirbed). The hook sizes used were standard size numbers 6, 9, and 12. The longlines fabricated with polyamide monofilament line were operated from 20 to 50 m depth for 3–5 hours each time. Overall, 81,000 hooks were deployed in 45 fishing trials. The total length and total weight of the combined sex group was recorded nearest to 0.1 cm and 0.01 g, respectively. By using the logarithmic transformed data, linear regression analysis was performed to calculate a and b values for three fish species to establish length-weight relationships. The parameters for the length-weight equations for three species are provided along with respective coefficient of correlation and the 95% confidence intervals. A new maximum total length was recorded for two grouper species, viz., Epinephelus faveatus (36.5 cm) and Cephalopholis urodeta (46.0 cm).

Threats of Longline Fishing to Global Albatross Diversity.

Simple SummaryThis research examines the impact potential illegal longline fishing vessels have on albatrosses. Using environmental criminology as a guiding theoretical framework, this research: (a) examines the patterns of concentration of potentially illegal longline fishing efforts and their relationships with the spatial distributions of commercially sought-out and illegally-caught fish species; and (b) examines how their interactions affect the average risk of albatrosses. The results indicate that: (a) potentially illegal longline fishing activities are highly spatially concentrated in areas with the highest concentration of the presence of known illegally-caught fish species; and (b) the average risk score of albatrosses is significantly higher in areas where these illegal longline fishing vessels operate. These findings provide strong grounding that illegal longline fishing poses a particularly serious threat to the survival of seabirds. These findings also call for the bird conservation lobby to work closely with regional fisheries management organizations to devise and implement targeted interventions. Albatrosses are among the most threatened seabird species. Often entangled in gillnets or hooked while longline fishing gear is being set, albatrosses are affected by fishing. This is assumed to be especially true in cases where illegal longline fishing vessels are involved, as they are less likely to implement the bycatch mitigation measures implemented to reduce the risk of albatrosses being caught on their hooks. This is the assumption that was tested in the current study, which uses environmental criminology as its guiding theoretical framework. Using the spatial units of one-half-degree by one-half-degree longitude/latitude cells, this research examined the patterns of concentration of potentially illegal longlining efforts and their relationships to commercially sought-out and illegally caught (i.e., CRAAVED—concealable, removable, abundant, accessible, valuable, enjoyable, disposable) fish species concentrations, as well as their effects on the average risk of albatrosses. The results indicated that (a) potentially illegal longlining activity is spatially concentrated; (b) this concentration is exhibited in areas with the highest concentrations of the presence of CRAAVED fish; and (c) the average risk score of albatrosses, as measured by their International Union for Conservation of Nature (IUCN) Red List status, is significantly higher in the areas where illegal longlining vessels are found controlling for the activities of legal longlining vessels. These findings provide strong grounding that illegal longline fishing poses a particularly serious threat to the survival of albatrosses. These activities, however, are not randomly spread across the vast oceans, but rather are highly spatially concentrated. Therefore, the bird conservation lobby should work closely with regional fisheries management organizations to devise and implement targeted interventions aimed at reducing potential illegal longline fishing, which, in turn, will likely have positive effects on albatrosses.

Can biodegradable materials reduce plastic pollution without decreasing catch efficiency in longline fishery?

Longlining is a widely used fishing method. During longline fishing, some of the snoods connecting the hooks to the mainline are often lost at sea. Since snoods are made of nylon or polyester, lost snoods contribute to marine plastic pollution. Replacing nylon or polyester with a new material made of biodegradable plastics can potentially reduce macro- and microplastic pollution that is caused by lost snoods. In this study, we estimated the risk for snood loss in a longline fishery targeting haddock (Melanogrammus aeglefinus (Linnaeus, 1758)) and Atlantic cod (Gadus morhua (Linnaeus, 1758)) in Barents Sea. Further, we compared catch efficiency in this fishery for snoods made of biodegradable and nylon materials. No significant differences were found between the two materials. Therefore, catch efficiency does not represent a barrier for using biodegradable materials in snoods.

Drivers of at-vessel mortality of the blue shark (Prionace glauca) and oceanic whitetip shark (Carcharhinus longimanus) assessed from monitored pelagic longline experiments

Elasmobranchs make up a significant part of bycatch in pelagic longline fisheries, whose induced mortality can be a major threat to endangered species. It is therefore crucial to understand the drivers of at-vessel mortality (AVM) for this fishing gear to enhance postrelease survival. To this end, we analysed scientific data collected during monitored longline fishing experiments conducted in French Polynesia to ( i) estimate AVM for each species based on bootstrapped samples and ( ii) to assess AVM drivers using multivariate logistic regression models for the blue shark ( Prionace glauca) and oceanic whitetip shark ( Carcharhinus longimanus). We found that AVM varies widely between species. Oceanic whitetip sharks are more likely to die when caught in waters outside their comfort temperature range, and their odds of survival increase with body length. For the blue shark, the only driver related to AVM is hooking duration. These results indicate that to reduce the AVM of these two species, the vertical distribution of hooks and soak duration should be considered as mitigation measures related to pelagic longlining.

A Dendrophyllia ramea Population in the Ionian Sea (Central Mediterranean Sea) Threatened by Anthropogenic Impacts

This study reports the first attempt to quantitatively describe a Dendrophyllia ramea population on the Apollo bank (Ionian Sea), revealed in summer 2021 through a remotely operated vehicle (ROV) survey. The habitat description, bathymetric distribution, population density, and structure of the species were assessed by image analysis. A well-developed population of D. ramea, located on boulders on a sedimentary plateau at 70–80 m depth, was observed. The density ranged on average between 0.17 ± 0.04 and 0.8 ± 2.4 colonies m–2 with dense patches up to 8 colonies m–2. The population consisted primarily of many isolated single corallites and colonies of various sizes, some of which reached a maximum height of more than 40 cm. Deepwater fishing activities, primarily longline fishing, negatively affected this species. The newly collected data add knowledge about this vulnerable scleractinian coral. The documented negative effect of fishing activities on vulnerable marine ecosystem (VME) species further highlights the need for urgent conservation measures.

Economic Conditions for New Entrants in Coastal Fishing in Miyazaki Prefecture, Japan

A significant decrease in the number of fishery workers is be-coming a problem in Japan. For new entrants to become estab-lished in the region, they must be profitable as fishing busi-nesses. Using the case of Miyazaki prefecture in Japan, this paper identifies the economic conditions required to make longline fishing and bottom gillnet fishing profitable by ap-plying the net present value (NPV) method. When operating on 200 days, which is the guideline for new entrants in longline fishing, if the value of investment is less than 44.1% of the minimum required, the investment will not provide positive returns. However, the study also finds that new entrants using both longline and bottom gillnet fishing can easily generate the revenue required to cover investments and can, therefore, be profitable. For 226 operating days, which is the guideline for new entrants in longline and bottom gillnet fishing, investment will offer positive returns when it exceeds ¥ 5.698 million. Moreover, increasing the number of operating days by 13.3% to 256 raises the return on investment by 14.0%. Therefore, the value of investment is proportional to an increase in operating days. If the price of half-smooth golden pufferfish, the main catch in longline fishing, increases by 5% to ¥ 624.1 per kilo-gram, the number of operating days can be reduced by up to 8.9%. If local initiatives raise the value of half-smooth golden pufferfish, new entrants can significantly reduce their number of operating days, thereby promoting fisheries management and reducing their labor burden.

Analisis Teknis dan Finansial Usaha Perikanan Tangkap Longline

This study aims to analyze the technical aspects of longline fishing gear, as well as calculate the economic aspects of the longline fishing business, and analyze the level of feasibility of the longline business at PPS Cilacap from a financial perspective. The method used in this study is a descriptive survey method with the object of assessment of fishermen being longline fishing gear. The sampling method is purposive sampling. The data analysis method used is technical and financial analysis. The results of the study based on financial analysis concluded that the longline fishing business in Cilacap PPS is feasible to be developed with an NPV value of IDR 5,303,563,607, IRR = 40% (IRR> i), Payback Period = 0.63 with a payback period of 3 years and B/C Ratio = 1.28 (> 1).

Bycatch Estimates From a Pacific Tuna Longline Fishery Provide a Baseline for Understanding the Long-Term Benefits of a Large, Blue Water Marine Sanctuary

Bycatch on pelagic tuna longlines has contributed to population declines in several far-ranging, oceanic species and presents a conservation challenge that area-based management tools are increasingly promoted to address. In January 2020 the Republic of Palau, concerned about the impacts of longline fishing in its waters, closed 80% of its exclusive economic zone to all extractive activities, reserving the remaining 20% for a domestic fishing zone (DFZ). One of a growing number of very large marine protected areas, the Palau National Marine Sanctuary (PNMS) spans ∼500,000 km2 and was established inter alia to allow for the recovery of fish stocks adversely impacted by tuna longline fleets. Given that the main tuna stocks targeted in the western Pacific are not overexploited, the benefits of protection potentially afforded by the sanctuary are likely greater for vulnerable bycatch species. Evaluations of the sanctuary’s performance require, in part, a baseline of historical catch rates and effort distribution in the distant-water fleet (DWF) and locally based fleet (LBF) operating in Palau prior to sanctuary implementation. We describe the fishing effort, catch rates, catch estimates and fishing mortality in Palau’s longline fishery based on logbook, observer and electronic monitoring data. We defined bycatch as any species, retained or discarded, other than targeted tunas. Between 2010 and 2020, 104.8 million hooks were deployed, catching over 2 million individuals from 117 taxa at an overall target:bycatch ratio of 1:1, with a retention rate of ∼62%. Pronounced differences in fishing strategies and spatial distribution of effort between fleets were associated with large variations in catch rates and composition. The LBF had a larger effect on populations of at-risk species relative to the DWF, with higher catch rates and magnitudes for several vulnerable species and higher observable fishing mortality rates (64% vs 50% in the DWF). The sanctuary reshaped Palau’s longline fishery, contracting the fishery’s area and capacity. The relocation of the DFZ eliminated the LBF and constrained the DWF to an area where the fleet’s total catch rates and those of a number of vulnerable species were historically lower relative to former fishing grounds now closed by the sanctuary. Our results highlight the importance of consistent bycatch monitoring and emphasize the need for regional area-based approaches for managing longline fisheries.

Aspek Finansial Usaha Perikanan Pancing (Long Line) Di TPI Hamadi Kota Jayapura (Studi Kasus: Nelayan Kelurahan Hamadi)

Hamadi Fish Landing Base (Pengkalan Pendaratan Ikan; TPI Hamadi) is the largest in Papua Province. Most fishermen in TPI Hamadi are long line fishermen. Long line is a fishing gear used to catch pelagic and demersal fish. The purpose of this study is to determine the feasibility of analyzing the business from the financial aspect of the fishing business (long line) at the Hamadi Fish Auction Place (Tempat Pelelangan Ikan; TPI Hamadi) Jayapura City. Data collection methods in this study are the observation method, interview method, documentation method, data analysis related to the financial aspects of the business which include; NPV (Net Present Value), PP (Payback Period) and B/C Ratio (Benefit Cost Ratio). The technical aspects of catching include basic longline fishing gear, operating methods and catches. The results obtained are; The basic longline fishing gear consists of a main rope of 10,000 m long, 30 cm branch rope, swivel, 2,000 cork buoys, stone weights weighing 5-8 kg, and fishing hooks of 10,000 seeds. The operating method of basic longline fishing gear consists of setting, and hauling. The financials of the basic longline catching business at TPI Hamadi show that the fishing business is feasible. The feasibility of basic longline catching business can be seen with the NPV value of 7,154,663 (NPV> 0), IRR 24% (IRR > 19%), Payback Period is 2.28 (PP < 3 years) including the fast return category, and the B/C Ratio is 1,19 (B/C > 1), so it can be concluded that the basic longline fishery business is declared financially feasible. Key Words: Net Present Value; Internal Rate of Return; Payback Period; Benefit Cost Ratio; TPI Hamadi

Lightsticks cause adverse effects on behavior and mortality of marine mysids Promysis atlantica

Lightsticks baits are discharged into the ocean after their use in longline fishing. The traditional Brazilian community of Costa dos Coqueiros, Bahia, uses lightsticks as a medicine for rheumatism, vitiligo, and mycoses. It may affect marine life when its content leak into the ocean. This study assessed the toxicity identification and evaluation (TIE) of lightsticks constituents on marine mysids Promysis atlantica. The internal solution was dissolved in seawater with ethanol. The lethal concentration of the contaminant that causes mortality in 50% of the exposed population (LC50) after 3h was 0.001%, demonstrating that lightstick is exceptionally toxic because low concentrations cause mortality to mysids P. atlantica. Due to lightsticks' high toxicity, the TIE baseline was 0.005% SSE (stock solution ethanol), and the selected endpoints were behavior and lethality. The sample submitted to aeration presented a significant reduction (P < 0.05) in toxicity (0.005% SSE) because the volatile compounds caused the toxic effect. The sodium thiosulfate treatment induced an insignificant decrease in toxicity. Thus, a new assay was conducted considering aeration and sodium thiosulfate. This combination reduced lightstick toxicity compared to the baseline lightstick, suggesting that volatile compounds and oxidants were responsible for toxicity; even in low concentrations, lightstick can promote significant behavior changes and deleterious effects. It is recommended to create new mechanisms to inspect fishing vessels, thus avoiding the improper disposal of attractors at sea and common garbage.

New records of scleractinian cold-water coral (CWC) assemblages in the southern Tyrrhenian Sea (western Mediterranean Sea): Human impacts and conservation prospects

Scleractinian cold-water corals (CWCs) are among the main habitat engineers of the deep Mediterranean Sea, hosting a high diversity of species and playing a significant ecological role. In the last two decades, many new living scleractinian CWC sites throughout the Mediterranean Basin have been recorded and their distribution has been updated. In the summer of 2018, new scleractinian CWC assemblages were discovered by means of remotely operated vehicle (ROV) and multibeam echosounder (MBES) surveys on the Aceste–Tiberio seamount and Marettimo bank in the southern Tyrrhenian Sea, at depths ranging from 240 to 310 m. In the explored areas, megabenthic communities were dominated by habitat-forming species, some of which have never been reported before on these submarine structures. Healthy patches of Madrepora oculata and Desmophyllum pertusum, together with the solitary coral D. dianthus, were found on rocky pinnacles between inclined silted bottoms, as well as on a wreck. Deep-water fishing activities, mainly longline fishing, negatively affected these communities, particularly coral species. The discovery of these new sites adds new knowledge about the distribution of scleractinian CWCs in the Mediterranean Sea. Moreover, the documented negative effect of fishing activities on CWC species further stresses the need for urgent and specific conservation measures. In this regard, the co-occurrence of several long-lived, slow-growing, and vulnerable species on these seamounts and banks supports the establishment of specific marine protected areas [i.e., offshore Natura 2000 sites, in accordance with the Habitats Directive (92/43/EEC) - Habitat 1170 - Reefs].

Chemical Contents of Disposed Light Sticks Affect the Physiology of Rocky Crab Pachygrapsus transversus and Gray Shrimps Litopennaeus vanammei.

Light-sticks shine resulting from a chemiluminescent reaction between two components kept separate by a glass ampoule. Light-stick baits are discarded in the ocean after being used in longline fishing. The traditional Brazilian community of Costa dos Coqueiros, Brazil, uses the discarded light-sticks chemical contents found on beaches as medicine for rheumatism and mycoses. This study assessed the effects that light-sticks (chemical contents) have on Pachygrapsus transversus and Litopennaeus vanammei. Assays of metabolic changes involved rates of ammonia excretion and oxygen consumption. The EC50-60min to juveniles and adults P. transversus were 0.0004% and 0.0046%, respectively; and L. vanammei revealed a susceptible species: EC50-60min of 0.0006% for oxygen uptake and 0.0072% for ammonia excretion, and also was observed a hormesis effect in the ammonia excretion. Light-stick contents could promote significant metabolic changes in rocky crabs and gray shrimp. Educational actions are needed that make the population aware of and avoid the dangerous misuse of the light-sticks.

Mitigating the impact of longline fisheries on seabirds: Lessons learned from the South Georgia Patagonian toothfish fishery (CCAMLR Subarea 48.3)

Seabird mortality in fisheries is a global problem and a major driver of the continued decline of many seabird populations. Unless appropriate mitigation is in place, longline fishing can cause high levels of seabird mortality. Here we describe the development and implementation of seabird mitigation measures in the Patagonian toothfish Dissostichus eleginoides fishery around the sub-Antarctic islands of South Georgia (CCAMLR Subarea 48.3), since the fishery began in the late 1980s. The initial high bycatch mortality (>5000 birds / 0.59 birds per 1000 hooks in 1996) has been reduced to negligible levels (<0.01 per 1000 hooks) through implementation of a suite of mitigation measures and a high level of compliance. The principal species killed in the fishery were black-browed albatross and white-chinned petrels, with most of the mortality occurring in April and early May. Whilst the synchronous introduction of much of the mitigation makes it is difficult to confirm which measures have been most effective, there is compelling evidence that the restriction of the fishery to the austral winter was a major factor. Night-setting and line-weighting measures have also been important in reducing mortality and the 100% observer coverage in the fishery has encouraged high levels of compliance. We also consider how different measures may be effective for different species and how novel measures, such as the use of marked hooks, have helped encourage compliance. The mitigation measures developed in the South Georgia fishery have subsequently been adopted in other CCAMLR fisheries and have helped guide global best practice in addressing seabird bycatch.

Longline Hook Selectivity for Branchiostegus japonicus (Houttuyn, 1782) and Dentex tumifrons (Temminck &amp; Schlegel, 1843) in the East China Sea

Bottom longline fishing of red tilefish (Branchiostegus japonicus) is one of the most important commercial of fishing in the East China Sea. The present study aimed to investigate hook selectivity in B. japonicus and D. tumifrons, by means of experiments using three hook sizes (“J”: #15, #13 and #11) and was conducted in the East China Sea from June to August 2018. Altogether 602 B. japonicus fish and 858 D. tumifrons fish were caught. With respect to the size of the hook used, the total length-frequency varied significantly for both B. japonicus and D. tumifrons that were caught. The total length and four mouth parameters (upper and lower jaw length as well as height and width of mouth opening) of the two species showed a positive linear relationship. A logistic model created using the maximum likelihood method was used for elucidating hook selectivity; the best fit model with the minimum Akaike’s Information Criterion value was selected as the final model. The 50% selection lengths were 224.827 and 233.179 mm for B. japonicus; 201.461 and 202.603 mm for D. tumifrons using “J” #13 and “J” #11 hooks, respectively. To preserve the reproductive potential of younger fish in the stocks, the size of the “J” #13 hook was selected as the minimum hook size that should be used for the sustainable development of bottom longline fishing for B. japonicus and D. tumifrons.