Pair Trawl Fishery Research Articles

At sea mortality estimates of loggerhead turtle (Caretta caretta) in Southwestern Atlantic Ocean

Sea turtles are vulnerable to various threats, with incidental capture in fisheries being a main concern. Limited knowledge exists regarding sea turtle mortality at sea, and stranding events serve as an indicator of such mortality. However, stranding data only represent a fraction of the turtles killed in the ocean. The southern coast of Brazil is an important foraging area for loggerhead turtles. This study aimed to estimate loggerhead turtle mortality at sea in southern Brazil using stranding data. Between 2012 and 2016, a total of 70 incidentally caught and dead turtles in pair trawl fisheries were tagged and released back into the sea, with the recording of date and geographic position. Biweekly beach surveys were conducted in an effort to retrieve these carcasses. Bayesian logistic regression models were employed to assess the influence of meteoceanographic and geographic variables on the stranding probabilities of tagged turtles. Considering the total number of stranded loggerhead turtles in the study area and the predicted stranding probabilities, the annual mortality of the species at sea was estimated. Season, distance from the shore, and currents were identified as variables influencing the stranding probability. The stranding probability was 19.72 % for the warm period and 12.96 % for the cold period. A total of 1897 loggerhead turtles stranded between 2012 and 2016. The estimated mortality during this period was 14,377 loggerhead turtles killed. This high mortality can have a substantial impact on the population, thus conservation measures that effectively protect sea turtles are in urgent need.

A 14-year time series of marine megafauna bycatch in the Italian midwater pair trawl fishery

Fisheries bycatch is recognised as a global threat to vulnerable marine megafauna and historical data can contribute to quantify the magnitude of the impact. Here, we present a collection of three datasets generated between 2006 and 2019 by a monitoring programme on marine megafauna bycatch in one of the main Italian fisheries, the northern central Adriatic midwater pair trawl fishery. The three datasets consist of: (i) monitored fishing effort; (ii) bycatch and biological data of dolphins, sea turtles and elasmobranchs; (iii) and dolphin sightings. Some information included in these datasets has already proved to provide a unique opportunity to estimate total incidental capture of species of conservation concern and trends of their relative abundance over time in the northern - central Adriatic Sea. These datasets are expected to be considered by different end users to improve the conservation of species and fishery management approaches to assess the impact of a fishery on species of conservation concern.

Flume tank testing, computer simulation and full-scale sea trials of a modified bottom trawl made of ultra-high-molecular-weight polyethylene twine for pair trawl fishery off Shimane Prefecture

島根県沖合底びき網漁業を対象として，現用網の袖網および身網の一部に超高分子量ポリエチレン繊維製網地を導入して網糸直径を細くした改良網1，さらに天井部の目合を拡大した改良網2について，模型実験と数値解析によって抵抗削減効果を推定した。現用網から改良網2に変更することで網抵抗は29.6％，網抵抗と海底との摩擦抵抗の合計は9.9％減少し，網形状はほとんど変化しないと考えられた。実物網を用いた海上実験では，通常の曳網速力3ノットで改良網2では現用網と比べてハンドロープ張力が19.3％減少した。

Bycatch of Loggerhead Turtle (Caretta caretta) in the Italian Adriatic Midwater Pair Trawl Fishery

Despite the fact that Mediterranean loggerhead turtles are listed as ‘Least Concern’ by the IUCN, they are among the most threatened long-lived marine species worldwide, because of fishery-related incidental captures. The northern central Adriatic Sea is one of the most overfished basins of the Mediterranean Sea and it supports a very valuable marine biodiversity, including sea turtles. This study assesses the spatial and seasonal impact of the northern central Adriatic pelagic/mid-water pair trawl fishery on loggerhead turtle (Caretta caretta) by examining incidental catches recorded between 2006 and 2018 and environmental variables. The model predicted seasonal variation of loggerhead distribution. According to previous studies, data analysis indicates that most bycatch events of loggerhead turtle occurred in the northern Adriatic Sea. The present data confirm that the northern Adriatic may be an important foraging area for loggerhead turtle. They also highlight the urgent need for a better understanding of the interactions between sea turtles and fisheries to develop and apply suitable, ad hoc management measures in critical habitats.

Checklist of marine demersal fishes captured by the pair trawl fisheries in Southern (RJ-SC) Brazil

Abstract: Demersal fishery resources are abundant on continental shelves, on the tropical and subtropical coasts, making up a significant part of the marine environment. Marine demersal fishery resources are captured by various fishing methods, often unsustainably, which has led to the depletion of their stocks. In order to inventory the marine demersal ichthyofauna on the Southern Brazilian coast, as well as their conservation status and distribution, this study analyzed the composition and frequency of occurrence of fish captured by pair trawling in 117 fishery fleet landings based in the State of São Paulo between 2005 and 2012. The ichthyofauna consisted of 245 species (81 families, 32 orders and 2 classes). Among the species, 50 species were classified as constant, 38 accessory and 157 accidental. Still, 13.47% of the species were listed as endangered; 35.29% of the Chondrichthyes and 11.85% of the Actinopterygii (15.1% of the total species) belong to the endemic fauna of the Biogeographic Province of Argentina. The richness was directly related to the oceanographic features of the study area, which determined the southern boundary of occurrence of several tropical species and the northern boundary of occurrence for temperate species. This is the region with the highest abundance of fishery resources in Brazil.

Influence of environmental and operational variables in commercial fishery landings: The case of pair trawlers in southeastern Brazil

Faced with the overexploitation reality of many of the world fish stocks and climate change, understanding the relationships between catches, fishing strategies and environmental conditions becomes crucial. In this context, this study aimed to describe the correlations between operational and environmental variables in landings of the main fish categories by pair trawl fisheries off the coast of southeastern Brazil. Catch composition varied greatly between 2003 and 2011. This change was mainly related to the shift of the fishing area to greater latitudes and variations in sea surface temperature and chlorophyll concentrations. The physical characteristics of the vessels and fishing gear did not change during the study period. Environmental variables most likely influence stock catchability, primarily by changing their distribution pattern, indicating a shift in ocean characteristics that will influence this dynamic. This draws attention to the need to maintain monitoring programs to apply adequate management measures for the protection of fish populations, consequently ensuring fishing activities in the area.

Application of a bioeconomic model to Spanish mackerel in the seas of Korea

By focusing on a single species and multiple fisheries, this study provides a stock assessment of the Spanish mackerel caught mostly by Korean large trawl (LT), large purse seine (LPS), and large pair trawl (LPT) fisheries. We standardize the fishing efforts for the three fisheries by using a general linear model. We also employ a surplus production model, the Clarke–Yoshimoto–Pooley (CYP) model, based on the Gompertz growth function. The CYP model estimates the maximum sustainable yield, allowable biological catch (ABC), and associated fishing efforts, while a bioeconomic model is used to estimate the maximum economic yield and associated fishing efforts. Furthermore, the study analyzes the economic interactions among the LT, LPS, and LPT fisheries in the Republic of Korea. The economic analysis compares the net profits of the three different axes accruing to the three fisheries from the estimated ABC. The results show that fishing efforts to catch Spanish mackerel have recently risen in the seas of Korea; however, the stock has reduced because of overfishing. Thus, the study’s findings suggest that total allowable catch management is necessary for single species and multiple fisheries in order to preserve the Spanish mackerel stock in Korea.

An ecosystem-based assessment of hairtail (Trichiurus lepturus) harvested by multi-gears and management implications in Korean waters

Hairtail (Trichiurus lepturus) has been traditionally harvested by multi-gear types in the Yellow Sea and the East China Sea, except for the East Sea (Sea of Japan) in Korean waters. Six different fishery types such as offshore stownet fishery, offshore longline fishery, large pair-trawl fishery, large purse seine fishery, large otter trawl fishery and offshore angling fishery target to harvest the hairtail stock accounting for about 90% of the total annual catch. We attempted to develop an ecosystem-based fisheries assessment approach, which determines the optimal allocation of catch quotas and fishing efforts for major fisheries. We conducted standardization of fishing effort for six types of hairtail fisheries using a general linear model (GLM), and then estimated maximum sustainable yield (MSY) and maximum economic yield (MEY). Estimated MSY and MEY for the hairtail stock were estimated as 100,151 mt and 97,485 mt, respectively. In addition, we carried out an ecosystem-based risk analysis to obtain species risk index (SRI), which was applied to adjusting the optimal proportion of fishing effort for six hairtail fisheries as a penalty or an incentive. As a result, fishing effort ratios were adjusted by SRI for the six fisheries types. Also, the total allowable catch (TAC) was estimated as 97,485 mt and the maximum net profit at TAC by the hairtail fisheries was estimated as 778 billion won (USD 765 million).

전과정평가방법에 의한 쌍끌이 대형기선저인망의 온실가스 배출량 정량적 분석

The negative factors of fishery in environmental aspect of view are Greenhouse gas emission problems by high usage of fossil fuel, destruction of underwater ecosystem by bottom trawls, reduction of resources by fishing and damage of ecosystem diversity. Especially, the Greenhouse gas emission from fisheries is an important issue due to Cancn meeting, Mexico in 1992 and Kyoto protocol in 2005. However, the investigation on the GHG emissions from Korean fisheries did not much carry out. Therefore, the quantitative analysis of GHG emissions from Korean fishery industry is needed as a first step to find a relevant way to reduce GHG emissions from fisheries. The purpose of this research is to investigate which degree of GHG emitted from fishery. Here, we calculated the GHG emission from Korean bottom pair trawl fishery using the LCA (Life Cycle Assessment) method. The system boundary and input parameters for each process level are defined for LCA analysis. The fuel use coefficient of the fishery is also calculated. The GHG emissions from the representative fishes caught by bottom pair trawl will be dealt with. Furthermore, the GHG emissions for the edible weight of fishes are calculated with consideration to the different consuming areas and slaughtering process also. The results will be helpful to understand the circumstances of GHG emissions from Korean fisheries.

以西底びき網漁業における超高分子量ポリエチレン繊維（ダイニーマ）製漁網が燃油消費量，水揚量および操作性に与える影響

以西底びき網漁業における超高分子量ポリエチレン繊維（ダイニーマ）製漁網が燃油消費量，水揚量および操作性に与える影響

생태계 기반 어업평가의 위험도 추정에 관한 개선연구

This study identified problems of the existing ecosystem-based fisheries assessment approach, and suggested new methods for scoring risk and for the estimation of fishery risk index. First, risk scores of zero to two for target and limit reference points for each indicator were replaced by those of zero to three, and the risk scores were calculated from new formulae which were developed in this study. Second, a new method for estimating fishery risk index (FRI) was developed in this study, considering the level of indicators. New method was applied to the Korean large purse seine fishery, large pair trawl fishery and drag net fishery. More precise and detailed risk scores were obtained from the new method, which can explain the risks by the wider range of both risk levels for 'better than target' and 'beyond limit'. The new method for estimating FRI could avoid the basic problem related with duplicated computations of fishery-level indicators, which improved the estimated FRI to be more accurate. Also, a method for estimating variance of FRI using the bootstrap was proposed in this study.

Seabird and marine-mammal attendance and by-catch in semi-industrial trawl fisheries in near-shore waters of northern Argentina

Seabird and marine-mammal attendance and by-catch in mid-water and bottom otter semi-industrial coastal pair-trawl fisheries were assessed for the first time in northern Argentina. Observers were placed onboard trawlers between autumn 2007 and autumn 2008. Fifteen marine top-predator species were associated with the vessels. The most abundant and frequent seabirds (trawl fisheries combined) were the kelp gull, Larus dominicanus (~70% of total birds and >96% occurrence), and the Olrog’s gull, L. atlanticus (~12% and >50%, respectively). Other seabird taxa such as Procellariiforms and Sphenisciforms, among others, were represented in very low numbers. The only mammal species recorded was the South American sea lion, Otaria flavescens (1% and 2%, respectively). Analysis of environmental and operational variability affecting the abundance of gulls indicated a significant increase in abundance with fishing depth, time of day, seasonality, wind intensity and wind direction. Incidental mortality of top predators was low and comprised only Magellanic penguins, Spheniscus magellanicus, in the mid-water gear. The results of the present study showed that the semi-industrial trawl fisheries operating in coastal waters in northern Argentina may a have a relatively minor impact on marine top-predator populations, at least in terms of incidental capture.

Interactions between short-beaked common dolphin (Delphinus delphis) and the winter pelagic pair-trawl fishery off Southwest England (UK)

During offshore and onshore studies (2004 to 2009), the interactions between pair-trawls and short-beaked common dolphins (Delphinus delphis) were studied to better understand the impact of bycatch. A ‘hotspot’ area where pair-trawls overlapped with high dolphin abundance was identified. We made comparisons between boat-based data collected in absence and presence of pair-trawlers. The relative abundance and group-size of dolphins was significantly higher in the presence of pair-trawlers. Dolphins were observed associating with towing and hauling procedures. Significantly, more carcasses occurred in areas with hauling-activity than those without. Body-temperatures obtained from carcasses found near operating pair-trawlers indicated that bycatch mostly occurred at night. During necropsy studies, difficulties were encountered in identifying the fishing-gears responsible. Strandings data highlighted that the number of dead stranded dolphins was probably much higher than previously reported and there was a significant difference in the age and gender-composition of carcasses. Mature/sub-adult males appeared at greater risk from entanglement in pair-trawls offshore, whilst females with young appeared more vulnerable to inshore gillnets. Our findings show that the overlap between pelagic fisheries and the common dolphin hotspot is causing direct mortality through bycatch and, together with recent range-shifts, may have contributed to a localised decline of this species in this winter hotspot since 2007. Key words: Bycatch, common dolphin, Delphinus delphis, pair-trawl fishery, gillnets, strandings, English Channel, conservation, abundance, trawling, mortality.

동중국해 참조기자원에 대한 단위노력당어획량(CPUE)의 표준화

Yellow croaker (Larimichthys polyactis) is a major target species of large pair trawl fishery in the East China Sea. To standardize catch per unit effort (CPUE) of yellow croaker for the large pair trawl fishery, generalized linear model (GLM) was applied to evaluate and eliminate the influence of the explanatory factors (year, month, horse power and gross tonnage of vessel) on daily catches per boat collected and compiled by National Fisheries Research and Development Institute (NFRDI) from 1990 to 2007 at the fishery auction places of Busan, Masan and Incheon in Korea. Results of GLM showed that all of the factors significantly influenced on CPUE, explaining 36% of the total deviance. The standardized CPUE indicated that the abundance of yellow croaker in 2000's was 1.7 times higher than the CPUE in 1990's.

Migrations, fishery interactions, and management units of sea bass (Dicentrarchus labrax) in Northwest Europe

Abstract Pawson, M. G., Pickett, G. D., Leballeur, J. Brown, M., and Fritsch, M. 2007. Migrations, fishery interactions, and management units of sea bass (Dicentrarchus labrax) in Northwest Europe. – ICES Journal of Marine Science, 64: 332–345. A total of 4959 sea bass was tagged between 2000 and 2005 around the coasts of England, Wales, southern Ireland, and the Channel Isles to investigate whether movement patterns documented in 1987 have changed and to estimate the level of competition for sea bass between inshore and offshore fisheries. Most (54%) of the recaptures of adult bass (fish >40 cm) tagged inshore and made between May and October were within 16 km of the release positions. From November on, an increasing proportion was recaptured at least 80 km south or southwest of tagging sites. Bass tagged on offshore spawning grounds in March and April showed reciprocal movement, 75% of recaptures between May and October being at least 80 km from the release site. These observations reaffirm the hypothesis that adult sea bass may move considerable distances to offshore winter spawning areas, but there was little evidence of the spawning migrations between the North Sea and the western Channel that were observed in the early 1980s. Just 3% of the recaptures of bass >36 cm tagged in UK inshore fisheries were reported from the offshore pairtrawl fishery, whereas half the recaptures of bass tagged in that fishery were made inshore along the UK coast. When weighted by the respective catches, this suggests that the effects of management measures implemented in the UK inshore fishery are largely restricted to that fishery. A proposal for stock units for assessment and management of NW European sea bass fisheries is presented.

Sensitivity of the BEAM4 fisheries bioeconomic model to the main biological input parameters

Several runs of the BEAM4 model were carried out, combining several sets of input parameters from von Bertalanffy's growth curve ( Lt= L ∞[1− e - k( t- to) ]) and the natural mortality ( M), with sets of parameters from the length–weight relationship ( W= aL b ). Further simulations were made with variations of ±20% in the input parameters: recruitment ( R), catchability coefficient ( q), and the lengths at which 50 and 75% of the fishes are retained by the net ( L 50% and L 75%,). The data used were those of the pair trawl fisheries for “corvina” Micropogonias furnieri, off southeastern Brazil. Results showed variations in the output (landed weight) ranging from −62 to 147% associated with the diverse sets of VBGF and LWR parameters, and lower variations associated with the other input parameters tested.

A bio-economic appraisal of pair trawl fisheries off southeastern Brazil

A study of the pair trawl fisheries was made in an attempt to introduce bio-economic models into fishery management in southern and southeastern Brazil. The biological parameters of demersal fishes found in the literature were used to mount the bio-economic model. Since there are no historical data on the economics of the fishery industry, the present market values of fish and of the diverse items that compose the costs of the catch have been used. The results show that the fleet was oversized in the period 1976-1981. The number of boats was reduced from 28 pairs to only 11 in 1996, but was still considered too big. The size of the fleet is reflected in the economic results of the analysis which shows negative returns. However, the fact that some of the fixed costs are not actually spent by the owners of the boats, as many of them have no insurance and most of the boats are already completely paid off and do not accrue costs on the capital invested must all be taken into account. On the other hand, the income figures used in this analysis did not take into account the value of the by-catch landed.

日本海西南海域およびその周辺海域における近年のムシガレイの漁獲と資源の動向

During the period of 1969 to 1985, annual catch of roundnose flounder increased gradually with some fluctuations till 1978 and then began to decrease in a medium pair trawl fishery of the south-western Japan Sea and its adjacent wasers. This paper examined a recent trend of this stock, using lenght compositions and catch by market size categories in the fishery from 1980 to 1985. The estimated age compositions gave 1.2-1.3 year-1 as estimates of total mortality coefficient in the period of 1980 to 1985. The age compositions also revealed that a recruitment index exponentially decreased at an annual rate of 18% with year at least in the period of 1979 to 1984. Moreover, the exploitation rate for the 1-year-old flounder of 1982 and 1983 year classes decreased to be about one-half of that of 1978-1981 year classes, which were relatively large. Consequently, a decrease of the stock is considered to be caused mainly by a high fishing pressure exerted on the stock, especially on young age classes, in the late 1970's when other important target species continued to decline.

Exploited fish and shellfish species in the Moray Firth

SynopsisThe Moray Firth has been intensively fished for many years and has been of great historic importance to the development of Scottish fisheries. The stocks of exploited species in the firth and their relations to other stocks in Scottish waters are described.Exploited demersal species include haddock, cod, whiting, plaice and lemon sole. The firth is an important nursery area for plaice, and is the most important plaice spawning ground in the North Sea.The Moray Firth is also an important nursery area for herring. Evidence suggests that these fish recruit to adult stocks in the Minch. In the early 1960s a pair trawl fishery for sprats started and the firth became the most important sprat fishing area in Scotland. However, recruitment of recent year classes has been too poor to sustain the fishery, which has now been closed in order to protect the juvenile heiring which were landed as by-catch.The distributions of shellfish species are closely related to the bottom sediments. Landings have become increasingly important as the demersal and pelagic fisheries have declined or moved further offshore. The fishery on the Norway lobster is now of particular importance and the catch per unit effort data do not suggest any decline in stock size. Other exploited species include squid, scallops, crabs and lobster.