Impacts per unit weight in catch by two types of fisheries on a chub mackerel population

By using data on the age-specific annual fecundity and catches-at-age by each fishery in a chub mackerel (Scomber japonicus) population in the Pacific Ocean off Japan during 1970 to 1992, we evaluated the long-term fluctuation in impacts of two types of fisheries on the chub mackerel population. The purse-seine fishery consistently had a larger impact on the population than did the dip-net fishery, mainly because the catch by the former was much larger than that by the latter. To evaluate impact per unit weight in catch, we calculated the average reproductive value per unit weight over individuals caught by each fishery as an indicator of efficient use of bioresource. Because the proportion of immature fish caught by the purse-seine fishery was usually larger than that by the dip-net fishery, the impact per unit weight in catch by the purse-seine fishery was not always less than that by the dip-net fishery.     

Types and extent of fishing gear losses and their causes in the artisanal fisheries of Istanbul,Turkey

Fishing gear losses remain a serious problem for marine life; these losses are also the source of an invisible fishing mortality. This study is an analysis of this problem within the artisanal fisheries of Istanbul. From September 2009 through May 2010, face‐to‐face interviews were conducted in 27 fishing ports for a total of 282 questionnaires. Estimates of lost fishing gear were 229.48 km of set nets, 2700 m of longlines, and 14 fish traps. Turbot nets had the highest loss ratio (54.73%), followed by bonito nets (16%), red mullet nets (7.36%), and encircling trammel nets (4.83%). The four major causes of net loss were: conflicts with other gear types (trawl and purse seine), conflicts with cargo vessels, bottom structure hindrances, and bad weather conditions. Bottom structures were the single factor in net losses for longlines and fish traps. The study observed that large quantities of nets had been lost, and that each net type showed a positive relationship between the number of nets used and the number of nets lost. Separate zones for artisanal and industrial fisheries are recommended as a realistic approach to reduce the losses of fishing gear and the impact of ‘ghost fishing’.     

人工集鱼装置对热带金枪鱼类行为模式的影响

金枪鱼类会聚集在漂浮物周围,人类依据该行为特性研制出人工集鱼装置(fish aggregation devices,FADs)诱集金枪鱼,从而使金枪鱼围网的产量和捕捞效率大幅提高.但目前科学界仍不确定FADs为何能够吸引金枪鱼以及其广泛使用是否会对金枪鱼资源和大洋中上层生态系统产生潜在影响.针对这些问题,国外学者展开了大量以FADs周围金枪鱼为研究对象的个体行为学试验.本文归纳并整理了过去30多年中较可靠和经典的相关试验,从金枪鱼的趋向性行为、集群行为、随附行为、摄食行为和垂直移动行为5个方面分别阐述了漂流FADs和锚泊FADs下金枪鱼的行为模式,并对国内今后开展相关研究的重点方向和注意事项进行了展望.     

The reproductive traits of Scomber japonicus (Houttuyn, 1782) in the Eastern Adriatic Sea

The aim of the present study was to investigate the fisheries biology of Scomber japonicus (Houttuyn, 1782) in the Adriatic Sea, to enable implementation of appropriate regulatory measures for fisheries. Reproductive biology and sexual patterns of S. japonicus (chub mackerel) were examined from monthly random samples of commercial catches from purse seine nets (10 mm stretched mesh size) in the eastern Adriatic Sea. The annual mean chub mackerel fork length (FL) was examined from 1998 to 2007. Average fork lengths were approximately 25 cm between 1998 and 2002, decreasing to 22 cm between 2003 and 2007. In addition, sex ratios fluctuated as a function of size and month: females were more abundant in the smaller length classes, as well as before and after spawning; males were more abundant in the larger length classes and during spawning. The overall sex ratio was 0.68; females were significantly predominant. 50% of the chub mackerel population was sexually mature at a FL of 18.3 cm, and both males and females reached sexual maturity at FLs of 20.4 cm and 16.8 cm, respectively. Based on gonad maturity stages, gonad weight and gonadosomatic index, chub mackerel spawned from May to August, with peak spawning in June for both sexes. The mean absolute fecundity was 181 277 ± 62 090 oocytes per ovary. A positive exponential correlation was found between fecundity and fork length, gonad weight, and total chub mackerel weight (r² = 0.640; r² = 0.686 and r² = 0.607, respectively).     

Studying small purse‐seine vessel fishing behavior with tuna catch data: Implications for eastern Pacific Ocean dolphin conservation

Despite achievements in dolphin conservation for the tuna purse‐seine fishery of the eastern Pacific Ocean, debate continues about the magnitude and importance of dolphin mortality caused by small (unobserved) vessels. In‐port sampling of tuna catch size composition is a potentially cost‐effective means of identifying unobserved vessels that may be catching tunas associated with dolphins because yellowfin tuna caught in association with dolphins are larger, on average, than those caught in other types of purse‐seine sets. A classification algorithm to predict purse‐seine set type (“dolphin” vs. “nondolphin”) was built from port‐sampling data on yellowfin tuna length‐frequencies and the date and location of fishing of large (observed) vessels. This classification algorithm was used to screen the port‐sampling data of small vessels collected during 2006‐2009, assuming the fishing practices of the two groups resulted in similar catch characteristics. From these results, hypothetical time series of dolphin mortality for small vessels were constructed and incorporated into a population dynamics model, along with mortalities of large vessels. Results suggest that any dolphin mortality of small vessels is unlikely to be substantially affecting trends in dolphin abundance. These results underscore the importance of in‐port sampling, in combination with at‐sea observation and fishery‐independent surveys, to effective management.     

Identification and measurement of tropical tuna species in purse seiner catches using computer vision and deep learning

Fishery monitoring programs are essential for effective management of marine resources, as they provide scientists and managers with the necessary data for both the preparation of scientific advice and fisheries control and surveillance. The monitoring is generally done by human observers, both in port and onboard, with a high cost involved. Consequently, some Regional Fisheries Management Organizations (RFMO) are opting for electronic monitoring (EM) as an alternative or complement to human observers in certain fisheries. This is the case of the tropical tuna purse seine fishery operating in the Indian and Atlantic oceans, which started an EM program on a voluntary basis in 2017. However, even when the monitoring is conducted though EM, the image analysis is a tedious task manually performed by experts. In this paper, we propose a cost-effective methodology for the automatic processing of the images already being collected by cameras onboard tropical tuna purse seiners. Firstly, the images are preprocessed to homogenize them across all vessels and facilitate subsequent steps. Secondly, the fish are individually segmented using a deep neural network (Mask R-CNN). Then, all segments are passed through other deep neural network (ResNet50V2) to classify them by species and estimate their size distribution. For the classification of fish, we achieved an accuracy for all species of over 70%, i.e., about 3 out of 4 individuals are correctly classified to their corresponding species. The size distribution estimates are aligned with official port measurements but calculated using a larger number of individuals. Finally, we also propose improvements to the current image capture systems which can facilitate the work of the proposed automation methodology.     

Changes in fish bycatch during the shrimp fishing season along the eastern coast of the mouth of the Gulf of California

One of the main concerns of shrimp fisheries is the associated impact on ecosystem biodiversity, particularly on fish assemblages that are poorly characterized yet likely very relevant to the health of the ecosystem. The continental shelf along the eastern coast of the mouth of the Gulf of California is a region of high biodiversity that harbors highly productive fisheries. This study aimed to analyze the changes in the soft bottom fish assemblages caught as bycatch in the shrimp fishery located in this region. Sampling was conducted with commercial trawls at 16 fixed stations during the 2006–2007 shrimp‐fishing season. A total of 103 fish species from 80 genera and 47 families were collected. The ecological and taxonomic diversity as well as the composition and abundance of the fish community caught as bycatch in the shrimp trawl fishery were found to be significantly different in the autumn and winter. Ordination and similarity analyses also revealed differing patterns. Species abundance was strongly associated with sea bottom temperature, depth and latitude. The effects of these abiotic variables on the observed diversity patterns and the possible influences of the fishery are discussed.     

Modelling the Spatial Behaviour of a Tropical Tuna Purse Seine Fleet

Industrial tuna fisheries operate in the Indian, Atlantic and Pacific Oceans, but concerns over sustainability and environmental impacts of these fisheries have resulted in increased scrutiny of how they are managed. An important but often overlooked factor in the success or failure of tuna fisheries management is the behaviour of fishers and fishing fleets. Uncertainty in how a fishing fleet will respond to management or other influences can be reduced by anticipating fleet behaviour, although to date there has been little research directed at understanding and anticipating the human dimension of tuna fisheries. The aim of this study was to address gaps in knowledge of the behaviour of tuna fleets, using the Indian Ocean tropical tuna purse seine fishery as a case study. We use statistical modelling to examine the factors that influence the spatial behaviour of the purse seine fleet at broad spatiotemporal scales. This analysis reveals very high consistency between years in the use of seasonal fishing grounds by the fleet, as well as a forcing influence of biophysical ocean conditions on the distribution of fishing effort. These findings suggest strong inertia in the spatial behaviour of the fleet, which has important implications for predicting the response of the fleet to natural events or management measures (e.g., spatial closures).     

Length–weight relationships of five fish species from an Atlantic coastal drainage in Brazil

Length–weight relationships (LWR) are presented for five fish species from the Restinga de Maricá, southeastern Brazil. Specimens were caught in pools and streams with different types of fishing gear: seine net, dip net, and sieve. The LWRs of three species are new for this region, and of Phalloptychus januarius are published for the first time.     

Elasmobranch captures in shrimps trammel net fishery off the Gulf of Gabès (Southern Tunisia,Mediterranean Sea)

Small‐scale fisheries are generally promoted as a sustainable alternative to large‐scale industrial fisheries. However, there is recent growing evidence that small‐scale fisheries may be the largest threat to marine species of conservation concern. The objective of this study was to evaluate the potential impact of the trammel net fishery on elasmobranchs in the Gulf of Gabès, Southern Tunisia. Data are based on 191 shrimp trammel net set (40 mm stretched mesh size) surveys conducted aboard commercial fishing vessels from May to July 2009. Five species of the small coastal elasmobranchs (Mustelus mustelus (Linnaeus, 1758), Mustelus punctulatus Risso 1827, Dasyatis pastinaca (Linnaeus, 1758), Dasyatis marmorata (Steindachner, 1892) and Torpedo torpedo (Linnaeus, 1758)) and two species from the large coastal shark (Carcharhinus plumbeus (Nardo, 1827) and Carcharhinus brevipinna (Müller & Henle, 1839)) were recognized as by‐catch in this fishery. Elasmobranch by‐catch was dominated by sharks (90.3%), smoothhound sharks Mustelus sp. being by far the most important (88.9%) and reflecting their abundance in the area; 58% of the sets caught at least one specimen, with 4.8 ± 1.3 caught per set. Captures were composed essentially of neonate and juvenile sharks, while the batoids were dominated by mature individuals. This study shows that shrimp trammel nets represent a considerable source of mortality for early life stages of elasmobranch species in the Gulf of Gabès. Additionally, there was a high density of neonates and small juvenile M. mustelus in the Sfax zone, suggesting that these nearshore waters are a nursery grounds for smoothhound sharks. Further research should focus on the incidents of by‐catch and evaluate the potential solutions to allow trammel net fisheries to coexist alongside the elasmobranch species.     

Trophic niche width and overlap of two sympatric gulls in the southwestern mediterranean

The diets of two potential competitor species, Audouin's Larus audouinii and yellow-legged gulls Larus cachinnans, were examined while they bred at the Chafarinas Islands during 1993, 1994, and 1995. Data were collected during two commercial fishing regimes: (1) trawling and purse seine fisheries, and (2) diurnal trawlers only. Since the food supply for the gulls in this area was heavily reliant on the activity of purse seine fisheries, these contrasting situations allowed us to analyze short-term effects, induced by daily changes in food supply, on niche width, dietary shift, and niche overlap between the two species. Overall, both species relied mainly on fish for food, especially Clupeiforms, in the case of Audouin's gull irrespective of the fishing situation, and in the case of the yellow-legged gull, only when purse seine fishing was in operation. When purse seine boats did not operate (food shortage), yellow-legged gulls broadened their niche, consuming equal amounts of all the feeding resources, and they showed a dietary shift toward a greater consumption of prey from refuse tips. In contrast, Audouin's gulls did not change their niche width, but showed a slight dietary shift away from the consumption of epipelagic fish, compensated by an increase in reliance on benthic-mesopelagic resources. Niche overlap was clearly higher on days when both fishing fleets operated, probably because a superabundant food resource facilitates high overlap without affecting coexistence between the two species. Since our study was developed on the basis of daily variations in food supply, and competition effects are to be expected on a longer-term basis, these changes can be seen as the outcome of the coexistence of two species in stable competitive equilibrium. Received: 4 October 1996 / Accepted: 20 May 1997     

Environmental assessment of sardine (Sardina pilchardus) purse seine fishery in Portugal with LCA methodology including biological impact categories

Purpose

The purse seine fishery for sardine is the most important fishery in Portugal. The aim of the present study is to assess the environmental impacts of sardine fished by the Portuguese fleet and to analyse a number of variables such as vessel size and time scale. An additional goal was to incorporate fishery-specific impact categories in the case study.

Methods

Life Cycle Assessment methodology was applied, and data were collected from nine vessels, which represented around 10 % of the landings. Vessels were divided into two length categories, above and below 12 m, and data were obtained for the years 2005 to 2010. The study was limited to the fishing phase only. The standard impact categories included were energy use, global warming potential, eutrophication potential, acidification potential and ozone depletion potential. The fishery-specific impact categories were overfishing, overfishedness, lost potential yield, mean trophic level and the primary production required, and were quantified as much as possible.

Results and discussion

The landings from the data set were constituted mainly by sardine (91 %), and the remainders were other small pelagic species (e.g. horse mackerel). The most important input was the fuel, and both vessel categories had the same fuel consumption per catch 0.11 l/kg. Average greenhouse gas emissions (carbon footprint) were 0.36 kg CO₂ eq. per kilo sardine landed. The fuel use varied between years, and variability between months can be even higher. Fishing mortality has increased, and the spawning stock biomass has decreased resulting in consequential overfishing for 2010. A correlation between fuel use and stock biomass was not found, and the stock condition does not seem to directly influence the global warming potential in this fishery. Discards were primarily non-target small pelagic species, and there was also mortality of target species resulting from slipping. The seafloor impact was considered to be insignificant due to the fishing method.

Conclusions

The assessment of the Portuguese purse seine fishery resulted in no difference regarding fuel use between large and small vessels, but differences were found between years. The stock has declined, and it has produced below maximum sustainable yield. By-catch and discard data were missing but may be substantial. Even being difficult to quantify, fishery impact categories complement the environmental results with biological information and precaution is need in relation to the stock management. The sardine carbon footprint from Portuguese purse seine was lower than that of other commercial species reported in.     

First record of Seriola vivoliana Cuvier, 1833 in the Mediterranean

One specimen of Almaco jack Seriola rivoliana is recorded for the first time in the Mediterranean Sea. It was caught in a purse seine off Lampedusa Island in June 2000 and is listed as a new alien fish from the Atlantic Ocean.     

基于地统计分析西印度洋黄鳍金枪鱼围网渔获量的空间异质性

西印度洋公海海域是世界上围网黄鳍金枪鱼渔业的主要作业海域之一,根据印度洋金枪鱼委员会1999—2004年的1°×1°的各月黄鳍金枪鱼围网渔获量统计数据,采用地统计方法探索该海域黄鳍金枪鱼渔获量的空间异质性特征及其相关生态动力过程。进行了如下分析:(1)利用GIS制图观察渔获量的时空分布特征,发现其空间格局的变异受到的季节变化和年际变化共同影响,且前者明显强于后者。(2)采用地统计方法计算各月渔获量的空间异质性参数,并按照年际和季节情况分别进行了统计分析,发现渔获量的地统计参数值和变异函数模型有明显的季节和年际差异;渔获量的空间相关距离(变程)平均在1000nm左右,冬季要小于夏季;渔获量的空间变异函数模型主要为相关距离较大且空间依赖性较弱的指数模型;渔获量的空间结构方差比例(平均为65.82%)远大于随机性方差比例(平均为34.18%);渔获量在1°×1°尺度下具有明显的空间自相关性。(3)对地统计参数值和渔获量的相关关系研究,并探讨季节变化下渔获量的空间异质性特征与相关生态动力过程关系,发现各月渔获量随着空间总变异(基台值)增加而增加,两者存在强相关性;各月渔获量和南北和西北-东南向分维数值有一定相关性,意味着海洋动力过程在南北和西北—东南向过程越强,渔获量越低。西印度洋黄鳍金枪鱼围网渔获量的空间变异原因在于季风气候和ENSO循环过程引起的海洋流场、营养盐和温跃层等变化外在因素,以及围网捕捞方式和鱼类的行为方式的内在因素共同导致的。     

Reproductive biology of the golden snapper Lutjanus inermis (Perciformes: Lutjanidae) in the central Mexican Pacific

Reproductive aspects and information on the effect of fishery activities over this species stock are scarce, despite the imperative need of effective protection and resource management programs. To support the possible establishment of closed seasons and catch levels for the area, our study aimed to evaluate the spawning season of the Golden snapper (Lutjanus inermis). For this, fish caught by artisanal fisheries in the Navidad, Tenacatita and Chamela bays (Jalisco, Mexico) were sampled monthly from 1999-2008, and analyzed sex ratios, spawning season and size at first maturity. A total of 311 (53.1%) females and 275 (46.9%) males were caught, and the observed sex ratio was 1:0.88. The total length range was 14.4-37.0cm and total weight range from 48-575g. The length at first maturity was 23.9cm TL for females and 23.6cm TL for males. The gonadosomatic index showed two principal reproductive periods in the year (February-April and September-November), when the largest number of mature gonads were observed. Ovaries were of asynchronic development type and seven oocyte development stages were identified. Testicles showed lobular development and spermatozoa were observed in the center of the cysts and in the collecting ducts. It is important to mention that our results support the current suitable exploitation of this species in the area.     

The artisanal fishery of Metangula,Lake Malawi/Niassa,East Africa

The artisanal fishery of Metangula, on the remote Mozambique coast of Lake Malawi/Niassa, was studied for four months during the rainy season from December 1998 to March 1999. Catch, catch composition and fishing effort were determined for the most important gear types. The different gears exploited different stocks of fish. Copadichromis spp. were caught mostly in deep-water seine (chirimila) nets and accounted for >50% of the total catch. Oreochromis spp. were the major catch in the beach seine fishery. Labeo mesops and Opsaridium microcephalus were the most important catches in gill nets. The catfishes Bathyclarias spp. and Bagrus meridionalis dominated the long line fishery. Since 1983 there has been a considerable increase in fishing effort. The number of beach seines, chirimila nets and long lines increased 2.8 times, 2.9 times and 2.5 times, respectively, and there was a fourfold increase in the number of gear owners and fishing assistants. Comparison with data for Chembe Village in Malawi indicates that the fish populations at Metangula are not yet as impacted as they are on the populous and accessible Malawi coast. Some constraints on the fishery include the lack of management and financial support, poor gear and infrastructure, and the lack of access to markets.     

Impacts of fish aggregation devices on size structures of skipjack tuna Katsuwonus pelamis

Tuna purse seine fisheries target fish aggregated in schools, including free schools that are formed naturally based on fish biology and aggregations associated with natural and/or artificial drifting objects. Using data collected from skipjack tuna (Katsuwonus pelamis) fisheries, we evaluated differences in size structures between drifting-floating-object-associated schools and unassociated schools. We developed a generalized linear model to remove impacts of environmental variables on skipjack size composition. This study indicates that the drifting-floating-object-associated schools tended to have significantly wider size ranges than the unassociated schools. This suggests that unassociated schools were likely formed based on similarity in sizes among individuals within a school while drifting-floating-object-associated schools were probably composed of individuals of large size ranges and their formation was not based on the “size selection” rule. We concluded that the unassociated schools and the drifting-floating-object-associated schools were formed through different mechanisms, and drifting floating objects could aggregate unassociated schools of different size structures. Thus, a large scale of deployment of man-made floating objects might disrupt the spatial aggregation pattern of fish that otherwise tended to school based on their sizes in the absence of floating objects.     

River flow, Atlantic salmon (Salmo salar L.) movement and rod catch in the Aberdeenshire Dee

The relationship between river flow and rod and net catches of salmon and grilse have been analysed for four of the major fisheries on the Aberdeenshire Dee. On the lower two fisheries there is a good correlation between the rod catch and the average flow on the day of the catch and the preceding 3 days but there is no such correlation at the highest fishery. There is also a good correlation between the annual flow during the rod season and the total annual rod catch at the lowest fishery, while there is an inverse correlation between the flow during the rod season and the net catch. When the nets are off there is no longer any correlation between river flow and rod catch at the lowest fishery.