Artisanal fishing,dolphins, and interactive pinger: A study from a passive acoustic perspective

1. Dolphins interact with many types of fishing gear, causing damage to fishing activities and in some cases facing harm and becoming entangled as bycatch.
2. In this study, the behaviour of bottlenose dolphins during their interaction with set nets, equipped with and without interactive pingers, was investigated. Acoustic monitoring of the nets was conducted for a total of 56 hauls and 814.9 hr of recordings, from the 16 October to 13 November 2015, along the coast of Lampedusa island (Sicilian Channel, Italy, Mediterranean Sea).
3. The level of interaction between dolphins and the nets was evaluated considering the number of dolphin clicks grouped over time (single acoustic incursion on each net), the duration of every acoustic incursion, and the number of dolphin clicks per incursion. Moreover, the catch rate was measured as the number of fish per hour for each net.
4. Based on the recording time of dolphin clicks, the spatio-temporal development of the interaction with the nets located in different bays of the island was assessed.
5. The duration of the interaction between dolphins and nets significantly increased over the study period, with a concomitant reduction in catch rate. The interactive pinger showed efficacy in protecting the nets from dolphin depredation during the first period of 36 hauls and 11 fishing days (higher catch rates and lower incursion durations), whereas no differences were found in any interaction parameters between pinger and control nets in the second period (20 hauls and six fishing days).
6. Interactive pingers may be an effective, short-term (2–3 weeks) tool in deterring depredation by bottlenose dolphins in small-scale artisanal fisheries. Other mitigation approaches, such as gear modification, lessons learned through outreach, and passive acoustic monitoring of the nets, could improve the management of the interactions between fisheries and bottlenose dolphins.

     

Interactions between fisheries and cetaceans in the Thracian sea (Greece) and management proposals

Greek fisheries (purse seine, trawling and small‐scale coastal, by order of importance) mostly operate in the Thracian Sea, which despite its relatively small size relative to the Aegean Sea (≈4.4%) is the most productive region in Greek waters due to its elevated nutrient concentration. The Thracian Sea is also vital to several species of cetaceans, mainly bottlenose dolphin, Tursiops truncatus (Montagu), and common dolphin, Delphinus delphis L. The area has been proposed as a potential cetacean conservation hotspot. For this reason, the interactions between fishing activities and local cetacean populations have been investigated through reports of stranded dolphins, interviews with fishers, surveys and detailed dolphin stomach content analysis. Reports of stranded cetaceans and interviews with fishers revealed cases of cetacean entanglement in fishing nets, as well as frequent dolphin damage to fishing nets. Necropsy stomach analysis of stranded dolphins revealed a preference for fish and cephalopods of low commercial value, indicating a low trophic overlap between cetaceans and commercial fisheries. Recommendations for the management of fisheries–cetacean interactions in the Thracian Sea are provided.     

Effect of trawling with traditional and ‘T90’ trawl codends on fish size and on different quality parameters of cod <Emphasis Type="Italic">Gadus morhua</Emphasis> and haddock <Emphasis Type="Italic">Melanogrammus aeglefinus</Emphasis>

The effect of trawling on fish size and on different quality parameters of cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) was evaluated after conducting 16 valid hauls using two trawls in a double rig fitted with a traditional and a novel ‘T90’ codend, respectively. The total catch volume during the fishing period was 47.6 metric tons, with an average catch per codend of 1.5 (range 0.5–2.9) tons. The mean haul duration was 5 h. The catch was assessed according to fish size, mortality, external damage, initial white muscle pH and development of rigor mortis. Fillet quality (colour, blood spots, gaping) was assessed after 1 week of freeze-storage. Our results showed there was no difference between the two types of nets in terms of catch volume, but significantly slightly bigger fish were caught with T90 than with the traditional trawl net (p < 0.05). Haddock caught with the traditional trawl net had more external injuries related to the trawl gear than haddock caught with the T90 gear (p < 0.05). The gaping frequency for cod caught with the traditional trawl net tended to be higher than cod caught with the T90 gear, but the difference was not significant (p = 0.07). No other differences in fish quality between fish caught in the trawl nets were observed.     

Probarbus jullieni and Probarbus labeamajor: the management and conservation of two of the largest fish species in the Mekong River in southern Laos

• 1. Probarbus jullieni and Probarbus labeamajor are two of the largest carps in the Mekong River Basin, each reaching a maximum weight of about 70 kg. P. jullieni is listed in Appendix 1 of the Convention on the International Trade in Endangered Species, and both are listed on the IUCN Red List of Threatened Species, the first as ‘endangered’ and the second as ‘data deficient’.
• 2. Six years of quantitative monitoring of a large‐meshed gill net fishery for Probarbus just below the Khone Falls in Khong district, Champasak province, in southern Laos shows that 78% of the overall catch is comprised of Probarbus, with P. jullieni making up 65% of landings.
• 3. Over the 6‐year period catches of Probarbus declined significantly. However, catch‐per‐unit effort statistics do not indicate that the fishery is in decline, although fishers are convinced that real stock reductions are a large part of the reason for catch declines and decreases in fishing effort.
• 4. A number of ecological and social factors are affecting the number and quality of gill nets in use, the length of fishing seasons, and gill net efficiency, making it difficult to compare catch‐per‐unit effort between years.
• 5. There has been a shift from using large‐meshed gill nets for catching Probarbus to targeting smaller species using gill nets with smaller mesh‐sizes. This is an example of the ‘fishing down’ of a Mekong fish community, in which large long‐lived species are the first to be affected by heavy fishing pressure.

Copyright © 2006 John Wiley & Sons, Ltd.     

Modelling dolphin distribution within an Important Marine Mammal Area in Greece to support spatial management planning

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闽东渔场底层三重流刺网作业调查分析

底层三重流刺网作业是福建省闽东地区近几年发展起来具有一定代表性的作业。笔者通过调查霞浦县三沙镇189艘流刺网作业船,占全镇总数的89%,分析其经济效益及对渔业资源的利用情况。结果表明,目前闽东的底层三重流刺网已经完全替代了传统的流刺网。该网具的渔获物选择性较强,渔场适应性广,生产水平高,效益好,但由于网目规格偏小,对经济鱼类的幼鱼损害较大,要适度发展该作业则应限制网目使用最小规格,以减少渔业资源损害,保障渔业资源的可持续利用。     

Catch‐related fish injury and catch efficiency of stow‐net‐based fish recovery installations for fish‐monitoring at hydropower plants

Hydropower‐related damage to fish remains a great challenge, making objective monitoring of turbine‐related fish injury a necessity. The catch of fish at turbine outlets is currently realised by net fishing, but potential catch‐related injuries are largely unknown. Catch efficiency and fish‐friendliness in relation to fish handling, exposure time, floating debris and fish biomass of four fish recovery installations were assessed using seven species. Highly species‐specific lethal and sublethal effects were observed. Exposure time had the strongest effects on catch‐related damage, being up to 150‐fold increase after 12 hr compared to 1 hr. Up to 84% mortality occurred in the most sensitive species Thymallus thymallus L. Besides exposure time, higher current speed and biomass within the net resulted in greater fish damage. To minimise catch‐related effects, keeping emptying periods <1–2 hr and considering the effects of current speed, fish and debris biomass are crucial to increase data comparability among studies.     

基于渔捞日志的海阳市流刺网船渔获状况分析

为探明流刺网船的捕捞作业情况,根据海阳市2014—2016年流刺网船的渔捞日志,对流刺网船渔获状况进行了分析,并对近海渔业资源利用动态进行了初步探讨。研究表明:流刺网船分为4种作业类型,分别是A类:交替使用海蜇(Rhopilema esculentum)漂流三重刺网、鲅鱼漂流单片刺网和对虾漂流三重刺网;B类:交替使用海蜇漂流三重刺网、对虾漂流三重刺网和青鳞小沙丁鱼(Sardinella zunasi)漂流单片刺网;C类:交替使用海蜇漂流三重刺网、鲅鱼漂流单片刺网、对虾漂流三重刺网和单拖网;D类:交替使用海蜇漂流三重刺网、对虾漂流三重刺网、青鳞小沙丁鱼漂流单片刺网和单拖网。B类的全年单船日平均渔获量低于同一年的其它3类,C、D两类的全年单船日平均渔获量年间波动较大,C类和D类大部分月份单船日平均渔获量都高于A类和B类。结果显示,不同类型各年常见优势种为海蜇、口虾蛄(Oratosquilla oratoria)和三疣梭子蟹(Portunus trituberculatus),夏季4类作业类型渔获物群落结构相似度较高,A、C类在春季或秋季的部分月份渔获物群落结构相似度高,B、D类在春季和秋季的部分月份群落结构相似度较高。     

Biomass removal by dolphins and fisheries in a Mediterranean Sea coastal area: do dolphins have an ecological impact on fisheries?

• 1. Dolphins are often claimed to compete with fisheries, including through removal of substantial biomass. To calculate the biomass removed by fisheries and the degree of resource overlap with dolphins in a coastal area of Greece, estimates of dolphin abundance based on photographic capture–recapture were combined with an assessment of fishing effort and catch.
• 2. The estimated total biomass consumed annually by local dolphin populations – 15 short‐beaked common dolphins and 42 common bottlenose dolphins – was 15.5 and 89.8 tonnes, respectively. The total biomass removed by the local fishing fleet (307 fishing boats) was 3469.2 tonnes, i.e. about 33 times greater than that removed by dolphins.
• 3. Dolphins removed 2.9% of the total biomass, fisheries 97.1%. Nine purse seiners (representing only 3% of the active fishing fleet) were responsible for 31.9% of biomass removal. Similarity of biomass composition between dolphins and fisheries was expressed by a Pianka index of 0.46 for common dolphins and 0.66 for bottlenose dolphins.
• 4. Overlap differed according to fishing gear. Common dolphin overlap was higher with purse seiners (0.82), and lower with beach seiners (0.31), bottom trawlers (0.11) and trammel boats (0.06). There was virtually no overlap with longliners (0.02). Bottlenose dolphin overlap was higher with trammel boats (0.89) and bottom trawlers (0.75), and lower with longliners (0.38), purse seiners (0.24) and beach seiners (0.18). There was minimal overlap (0.12) between the two dolphin species.
• 5. This study suggests that ecological interactions between dolphins and fisheries in this coastal area have minor effects on fisheries. Conversely, prey depletion resulting from overfishing can negatively affect dolphins. Fisheries management measures consistent with national and EU legislation are proposed to ensure sustainability and to protect marine biodiversity. Copyright © 2010 John Wiley & Sons, Ltd.

     

Common bottlenose dolphin (Tursiops truncatus) interaction with fish farms in the Gulf of Ambracia,western Greece

1. Marine aquaculture, and its fast-growing development, has the potential for wider environmental, ecosystem, and biodiversity impacts. This study assesses the impact of fish farming on a bottlenose dolphin (Tursiops truncatus) population within the Gulf of Ambracia (western Greece) between 2007 and 2018. Two different study areas were defined in order to investigate differences on occurrence, abundance, behaviour, and seasonal fluctuations between them: a ‘control area’, in the north-western side of the Gulf; and a ‘fish farm area’, in the south west, where the highest density of fish farm cages is found.
2. A total of 169 daily surveys were dedicated to the control area and 74 days were dedicated to the fish farm area, yielding 104 and 37 sightings, respectively. Both the probability of detecting dolphins (U = 6,763.000, P = 0.002) and the group sizes (U = 578.000, P < 0.001) were smaller around fish farms.
3. Seasonality analyses were restricted to 2007–2008, as this was the period with year-round effort. Results revealed that dolphins were more frequently seen around fish farms in the winter (Kruskal–Wallis test, P = 0.036).
4. From the 40 identified individuals that were re-sighted at least 10 times during the study period, 21 used the fish farm area less than expected according to sampling effort, and 10 of them were never observed in that area (binomial test, P < 0.05).
5. The results revealed an impact of fish farms on the distribution of bottlenose dolphins in the Gulf of Ambracia. This information should be taken into consideration when defining ecosystem-based management measures within the management plan, which is currently in preparation for this Natura 2000 site.

     

Dolphins and coastal fisheries within a marine protected area: mismatch between dolphin occurrence and reported depredation

• 1. Dolphins are often blamed for reducing fisheries catches and may be killed in retaliation. Depredation of fishing gear in coastal Mediterranean waters is normally caused by bottlenose dolphins. Economic impact, however, may be modest even within areas of reportedly acute conflict.
• 2. Boat surveys and interviews were conducted to investigate dolphin occurrence and interactions with fisheries within the 167 km² Porto Cesareo Marine Protected Area (MPA) in southern Italy. Based on 69 interviews with fishermen using bottom‐set trammel and gill nets, there was reportedly a high occurrence of depredation by bottlenose dolphins. Depredation was reported by 92% of the fishermen operating in or near the MPA, and 67% of them claimed an economic cost in excess of €1000 per year, with a mean reported cost of €2561: a higher impact than in other Mediterranean studies.
• 3. According to local fishermen, dolphin occurrence and depredation peaked in spring and autumn, coincident with the study's surveys at sea. Dedicated visual surveys totalling 1255 km of effort, however, resulted in no encounters with cetaceans. Information from interviews and boat surveys was therefore contradictory, suggesting that reports of acute depredation do not imply a constant presence of dolphins within the MPA.
• 4. While depredation in the MPA might be caused by wide‐ranging dolphins or incursions occurring overnight, damage may well be overestimated or over‐reported. As local fishermen had previously benefited from subsidies, interviews made during this study could be perceived by some as an opportunity to influence future decision‐making regarding monetary compensation for the impact of depredation.
• 5. Evidence from interviews also indicated that species and factors other than dolphins were responsible for part of the damage. Copyright © 2011 John Wiley & Sons, Ltd.

     

Analysis of mesh breaking loads in cotton gill nets: Possible solution to ghost fishing

ABSTRACT:   A small number of fishers in Chiba Prefecture of eastern Japan use cotton gill nets to catch Japanese spiny lobster Panulirus japonicus. To examine the advantages of cotton gill nets, we analyzed changes in mesh breaking load of a new cotton gill net used in a fishing operation. A new cotton gill net was also soaked in a seawater tank to simulate ghost fishing conditions. The average mesh breaking load of new cotton mesh was 50.3 N. This value decreased to 19.0 N after 38 days (∼912 h), and after 82 days (∼1968 h) the mesh could be easily torn (breaking load 0.07 N). Under fishing conditions, the cumulative soak time was only 744.4 h over 19 months. The average breaking load at the end of this period was 43.1 N, a strength 86% that of the presoaked mesh. The mesh breaking load of a cotton gill net continuously soaked for 744.4 h was 26.1 N, as estimated from tank experiment data. Thus, a cotton gill net maintains reasonable strength under typical use conditions, but will degrade if lost at sea.     

A framework for adaptive gear and ecosystem‐based management in the artisanal coral reef fishery of Papua New Guinea

• 1. Artisanal fishing on coral reefs in Papua New Guinea is an important livelihood activity that is managed primarily at the level of local communities. Pockets of overexploitation exist and are expected to increase with plans for increased commercialization.
• 2. This paper provides a current assessment of the artisanal multi‐species coral reef fishery by examining selectivity of the dominant gear, namely line fishing, spearguns, and gill nets. Each gear has its own strengths and weaknesses in terms of use and conservation of resources, with no clear problem gear.
• 3. The three gears utilize different resources but there was moderate overlap in the species caught, particularly between gill nets and line fishing and marginally between lines and spearguns. Gill nets have the disadvantage of being destructive to coral and the advantage of catching commercial species. Line fishing catches an intermediate number of species but mostly large‐bodied and predatory species that could potentially reduce predation and the mean trophic level of the fishery. Spearguns catch the highest numbers of species, including many non‐commercial and herbivorous fish and could reduce the diversity of fish and encourage algal growth.
• 4. This information could be used in combination with scientific monitoring and traditional ecological knowledge to develop an adaptive management framework that uses local restrictions on the various gears to restore or balance the fishery and ecosystem. Restrictions could be selectively imposed: on gill nets when coral cover is low, line fishing when large‐bodied predators are depleted, and spearguns when biodiversity is reduced and algal abundance high.

Copyright © 2008 John Wiley & Sons, Ltd.     

Relationship between soak time and number of enmeshed animals in experimentally lost gill nets

In order to determine the effects of ghost fishing by lost gill nets, the relationship was examined between soak time and number of enmeshed animals in experimentally lost gill nets by using diving observations. Two experimental gill nets were set at 13 m depth in Tateyama Bay, Chiba Prefecture, Japan for approximately 200 days. One gill net was deployed in a small trough surrounded by artificial reefs, and the other was deployed on an adjacent open sandy bed. Twelve species of crustaceans, six species of gastropods, and five species of bony fish were enmeshed in the experimental gill nets. The number of enmeshed animals in the artificial reef gill net was substantially larger than that in the sandy bed gill net. The number of enmeshed animals in the experimental gill nets increased rapidly within one month after deployment, and then declined gradually showing fluctuations caused by the decrease in newly enmeshed animals, and the drop off from gill nets caused by the decomposition of dead animals. The decrease in the number of enmeshed animals was expressed by logarithmic equations, and based on these equations, the duration of capture function for the lost gill nets was calculated to be 284–561 days in the artificial reef gill net and 200 days in the sandy bed gill net. The duration of capture function for the lost gill nets for non-commercial by-catch species such as small crustaceans and gastropods was longer than for commercial species such as Japanese spiny lobster and bony fish.     

Changes in life history and ecological characteristics of coral reef fish catch composition with increasing fishery management

Abstract Length, life history and ecological characteristics of landed fish communities were studied over a 10‐year period to test theories of fishing disturbance during a time of increased gear and closure management in heavily utilised fisheries. It was predicted that with greater management restrictions: (1) the earliest and fastest responses in the fishery will be seen in those species with faster turnovers, or relatively lower vulnerabilities to fishing; (2) the fishery would transition to a landed catch with higher mean trophic levels, and greater mean body lengths. In addition, the removal of a non‐selective, small‐mesh seine nets should benefit the catch of gears that previously had the greatest species selectivity overlap with the seine net. Many predictions were supported, although maximum lengths and lengths at maturity responded more rapidly than anticipated. The response to eliminating the non‐selective seine net was a more rapid increase in sizes caught by gears with a larger overlap in size (hook and lines) than species selectivity (gill nets). The simultaneous comparison of management systems over time indicates that open‐access fishing grounds can benefit from restrictions imposed in adjacent fishing grounds. The study indicated that multi‐species coral reef fisheries management objectives of maximising yields, as well as maintaining the fish community’s life‐history diversity, require management trade‐offs that balance local socio‐economic and biodiversity needs.     

Distribution and habitat characteristics of three sympatric cetacean species in the coastal waters of Matang,Perak, Peninsular Malaysia

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Effects of algae particle size on the breathing and feeding of filter‐feeding silver carp (Hypophthalmichthys molitrix Val.)

A variety of parameters associated with breathing and feeding of silver carp were measured in response to declines in dissolved oxygen (DO) levels when the fish were fed microalgae Padorina morum (PM group) and Chlorella ellipsoidea (CE group), respectively, to explore the relationship between breathing and feeding while filtering microalgae particles at different DO levels. The results indicated that (i) respiratory frequency (f_R) of the fish in CE group were higher significantly than those in PM group at DO levels of 0.98–7.49 mg/L (P < 0.05); respiratory stroke volume (V_S.R), gill ventilation (V_G) and V_G/VO₂ the fish in two groups began to increase sharply while DO levels declined to below 4.04 mg/L (P < 0.05); oxygen extraction efficiency (EO₂) of the fish in two groups increased significantly with decline of DO levels from 7.49 mg/L to 0.98 mg/L (P < 0.05); (ii) the infiltration rate (FR) and filtering efficiency (E) of the fish in two groups began to decrease significantly while DO levels declined to below 4.04 mg/L (P < 0.05); clearance rate (CR) of fish in PM group was sixfold higher than that in CE group at DO levels of 0.98–7.49 mg/L (P < 0.05). In addition, antifiltering response appeared at DO levels of 2.21 mg/L and 0.98 mg/L in both groups. This study indicated that ‘filtration effect’ is dominant when the fish filter algae particles larger than its gill raker gaps, while the ‘food sinking effect’ is dominant when the fish filter algae particles smaller than its gill raker gaps.     

A comparison of methods for calculating Catch Per Unit Effort (CPUE) of gill net catches in lakes

Fish constitute an important component of lake ecosystems and many different methods have been used for fish assessment. Based on gill net catches in two stratified (max depth = 14–22 m) eutrophic Danish lakes, relative fish abundance measured as Catch Per Unit Effort (CPUE) was calculated. We used three different methods of which two followed the European standard based on benthic nets (CEN (European Committee for Standardization), 2005: EN 14757. Water quality – Sampling of fish with multi-mesh gill nets. Brussels, 27 pp.), one assuming equal volumes in all depth strata and the other using calculated volumes in the depth strata. The third method followed a modified CEN standard, adopted as a new Danish (DK) standardized method based on calculated benthic and pelagic water volumes and by including both benthic nets and, compared to the CEN standard, an increased fishing effort with pelagic nets. Fish were concentrated in the littoral/benthic part of the upper two depth strata (0–6 m depth) with an up to 8 fold higher abundance than in the pelagic. Calculated CPUE is highly sensitive to the morphometry of the lakes. In lakes with extreme morphometry (unequal volumes in depth strata) it is important to use calculated water volumes for the depth strata. By including information derived from the pelagic nets, total lake CPUEs were 42–56% lower than CPUE values based on benthic nets only. We further show that the relative contribution of CPUE between habitats changes markedly with the nutrient level in 12 deep lakes. It is concluded that for deep lakes it is of key importance to include pelagic nets when comparing fish assemblages and abundances among lakes and when evaluating effects of major changes in key environmental factors, such as nutrient loading and climate.