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Dolphins don't mind hot sauce: testing the effect of gill net coating on depredation rates
... While a number of dolphin depredation deterrents have been tested in the Mediterranean Sea, the results have broadly been inconsistent, often showing either no effect or a short-term reduction of depredation rates (e.g. Snape et al. 2018, Buscaino et al. 2021, Bruno et al. 2021, Garagouni et al. 2022a). Perhaps a more to-the-point fishing modification might be to reinforce the lower part of gillnet panels or enhance their acoustic reflectivity (e.g. ...
Understanding the foraging strategies of marine megafauna that interact with fisheries is key to conflict mitigation. Bottlenose dolphins Tursiops truncatus in the northern Aegean Sea frequently depredate bottom-set nets, but whether they exhibit prey selection within depredation events remains unknown. We conducted 80 fishing trials over 2 seasons (2020 and 2021) using gillnets in the Thermaikos Gulf, and investigated patterns in the catch and gear damage to determine whether bottlenose dolphins target certain genera over others. A high preference index was calculated for demersal fish like Mullus and Trachurus , as well as less frequently occurring pelagic fishes like Sphyraena . We also found a strong indication that dolphins target certain sizes of fish in certain genera, namely the shorter specimens of larger fishes and the larger specimens of shorter fishes. In conjunction with the patterns in the vertical position of holes torn in the nets, our findings suggest that bottlenose dolphins take advantage of whichever fish are seasonally prevalent.
... Nets were inspected for damage upon hauling and mended prior to redeployment, in order to maintain the gear's efficiency. During the second season, the number of holes was recorded systematically, and the size of each was measured (length x width) and subsequently classed into four size categories: tiny (<10 cm 2 ), small (10-99 cm 2 ), medium (100-999 cm 2 ), and large (≥1000 cm 2 ) (see also Garagouni et al., 2022), as not all hole sizes affect catchability to the same extent. Prior to redeployment, the holes were repaired with twine of a different colour to that of the net panel, to ensure that they would not be counted again if they re-opened due to tension in other parts of the net. ...
Common bottlenose dolphins (Tursiops truncatus) are known to depredate fishing gear, resulting in damage to the catch and/or the gear itself. The extent of this damage and estimated financial loss varies between areas, métiers, and survey methods. We quantified losses due to bottlenose dolphin depredation in a coastal gillnet fishery in the Thermaikos Gulf, Greece, in terms of CPUE reduction, catch damage, and gear damage. Experimental fishing effort was carried out over two seasons (2020 and 2021), along with concurrent questionnaire surveys over the second season (2021). Depredation frequency (∼35%) and CPUE changes due to depredation (a significant decrease of 45–50%) were similar for both sampling schemes. The number of damaged fish in experimental hauls increased significantly with dolphin depredation, but did not fully account for the sizeable loss in marketable catch, indicating that large numbers of fish were removed from the nets entirely. Damage to experimental nets increased with dolphin presence and group size, with an average of 0.59% of net surface area damaged per depredation event. Both datasets point to annual economic losses of over €5000 per vessel in this fishery, while the similarity between direct observations and self-reported losses highlights the usefulness of frequent questionnaire surveys.
Existing literature on dolphin-fisheries interaction focused on Greece reveals both an undeveloped area for research, but also a lack of relevant data in this field. Although imperative, relevant research has been slow on innovation and cooperation among universities, official bureaus, and NGOs that are obliged to work together as European and national laws dictate. Most of the research in this new field focuses on the interaction between marine mammals and local fisheries, suggesting that this relationship may be problematic for both parties since the former are being treated (at least occasionally) with brutality, while the latter try to deal with economic loss. Dolphins and fishermen operate within the same ecological niches for their survival, the main area of conflict being nutritious fish. Anthropological research on ethnic identity has long dealt with antagonistic relationships over resources between adjacent groups of people. Marine biologists' research in Greece focuses on the human factor, and some of its shortcomings may well be seen as the result of limited, or an absence of, training in social sciences. This article attempts to draw from anthropological theory to shed light on a particular symbiosis between humans and dolphins. Multidisciplinary approaches gain ground in a wide range of research interests and seem to be fruitful in terms of theoretical and practical results.
We investigated the effect of trap-like gear deployment on the survival of European squid Loligo vulgaris and common cuttlefish Sepia officinalis eggs laid on various surfaces of these gears. In parallel, a detailed assessment of the two species’ egg deposition patterns on such gears was performed with respect to both the fishing season and their preferences for artificial spawning substrates. Hemp ropes with floats were the most preferred spawning substrate for squid, whereas cuttlefish mostly deposited their egg clusters on the plastic mesh of rectangular pots. Almost no egg laying was observed on traps where netting frame was coated with antifouling paints (copper oxide or zinc pyrithione). A high proportion of squid egg mops and cuttlefish egg clusters were shown to either be lost or to die after a period of continuous operation (i.e. hauling and retrieval at frequent intervals), which exceeded egg incubation periods. It is thus advised that coastal fishers either completely avoid operating static gears, which act as artificial spawning substrates on the spawning fields or use gears with materials that are repellent for these animals to approach and lay their eggs, such as nets coated with antifouling substances.
The need to minimize bycatch of toothed whales (odontocetes) in gillnets has long been recognized, because they are often top predators and thus essential to ecosystem resilience. It is likely that a key to achieving this goal is the improvement of gillnet acoustic visibility, because these species use underwater sonar for orientation. Previous work on increasing gillnet detectability for echolocating animals by making the nets more recognizable has been based on trial and error, without understanding the fundamental acoustic properties of the tested modifications. Consequently, these studies have produced mixed and sometimes contradictory results. We systematically identified small, passive reflective objects that can improve the visibility of gillnets at a broad range of frequencies, i.e., for many odontocetes. We simulated the acoustic reflectivity of a wide range of materials in different shapes, sizes, and environmental conditions, with a focus on polymer materials. We verified the simulation results experimentally and calculated detection distances of the selected modifications. For example, if 8 mm acrylic glass spheres are attached to the net at intervals smaller than 0.5 m, the spheres have the same target strength (TS) at 130 kHz as the most recognizable part of a gillnet, the floatline. Modifications of the netting material itself, e.g., using barium sulfate additives, do not substantially increase the acoustic reflectivity of the net.
Fisheries depredation by marine mammals is an economic concern worldwide. We combined questionnaires, acoustic monitoring, and participatory experiments to investigate the occurrence of bottlenose dolphins in the fisheries of Northern Cyprus, and the extent of their conflict with set-nets, an economically important metier of Mediterranean fisheries. Dolphins were present in fishing grounds throughout the year and were detected at 28% of sets. Net damage was on average six times greater where dolphins were present, was correlated with dolphin presence, and the associated costs were considerable. An acoustic deterrent pinger was tested, but had no significant effect although more powerful pingers could have greater impact. However, our findings indicate that effective management of fish stocks is urgently required to address the overexploitation that is likely driving depredation behaviour in dolphins, that in turn leads to net damage and the associated costs to the fisheries.
Electronic supplementary material
The online version of this article (10.1007/s10745-018-9989-7) contains supplementary material, which is available to authorized users.
In the Gulf of Corinth (GOC), a 2,400 km2 semi-enclosed embayment in Greece, three odontocete species occur within 11 km of the nearest coast. Striped dolphins Stenella coeruleoalba are abundant (1,420 animals, 95%CI 1,275-1,566) and live in mixed groups with 26 short-‐beaked common dolphins Delphinus delphis (95%CI 13-39) and 58 individuals of intermediate pigmentation, indicating hybrids (95%CI 38-79). Additionally, in 2011-2014 we estimated fewer than 40 common bottlenose dolphins Tursiops truncatus per year, of which some are transient. We investigated dolphin distribution and interactions with fisheries through (1) boat‐based visual surveys totalling 16,289 km; (2) dolphin follows encompassing 1,663 km (296 h); and (3) 98 interviews with small-scale fishers deploying bottom-set nets across 29 ports. Based on survey data, multiple geographic, bathymetric, oceanographic and anthropogenic variables were incorporated in generalized additive models (GAMs) and generalized estimation equations (GEEs) to describe dolphin presence, taking into consideration intensity of survey effort and sea state conditions. Modelling indicated that bottlenose dolphins strongly prefer the shallower waters of the northern GOC (as well as areas near finfish farms, that only exist in the north). Conversely, striped, common and apparent hybrid dolphins prefer deep waters in the central and southern GOC. Depredation by presumed dolphins was reported by 69 fishers (70.4%). Fishers in the northern sector of the Gulf reported significantly greater damage (X2=22.21, p<0.001). Perceived economic loss averaged €1,398/boat/yr in the north (SD=1,950, range 0-10,000), and €81/boat/yr in the south (SD=254, range 0-1,000): a significant difference (p<0.001, Mann-Whitney U=154). Our results suggest that despite a high abundance of striped dolphins near southern ports, these animals (or common dolphins) were unlikely to depredate nets. Depredation occurred primarily in the north, where bottlenose dolphins and fishing effort overlap. Interviews and sighting records indicate that loggerhead sea turtles Caretta caretta contributed to depredation in both areas.
A large part of the literature on sensory perception and behavior in dolphins is devoted to its well-developed vocal and echolocation abilities. In this review, we aim to augment current knowledge by examining the literature on dolphins’ entire “Merkwelt” (which refers to everything a subject perceives, creating a crucial part of the subject’s Umwelt). We will show that despite extensive knowledge on audition, aspects such as context relatedness, the social function of vocalizations or socio-sexual recognition, remain poorly understood. Therefore, we propose areas for further lines of investigation. Recent studies have shown that the sensory world of dolphins might well be much more diverse than initially thought. Indeed, although underwater and aerial visual systems differ in dolphins, they have both been shown to be important. Much debated electro- and magnetoreception appear to be functional senses according to recent studies. Finally, another neglected area is chemoreception. We will summarize neuroanatomical and physiological data on olfaction and taste, as well as corresponding behavioral evidence. Taken together, we will identify a number of technical and conceptual reasons for why chemosensory data appear contradictory, which is much debated in the literature. In summary, this article aims to provide both an overview of the current knowledge on dolphin perception, but also offer a basis for further discussion and potential new lines of research.
The unclear environmental performance of nonivamide limits its application as a marine antifoulant. In this study, the natural degradation of nonivamide was studied in seawater and tap water. The half-life was 5.8 d, 8.8 d, 12.2 d, and 14.7 d in seawater and tap water in photolysis and biolysis, respectively. Furthermore, the ecotoxicity of nonivamide was assessed using marine microalgae,
Chlorella vulgaris
and
Platymonas
sp.;
E
C
50
,
6
d
values on the growth of
Chlorella vulgaris
and
Platymonas
sp. were 16.9 mg L
−1
and 19.21 mg L
−1
, respectively. The toxicity and environmental risk of nonivamide on microalgae were significantly decreased due to the natural degradation in seawater.
In this study, an economic analysis of the effect of pingers as "anti-depredation" devices on artisanal fisheries and dolphin depredation was performed. By comparing the data of the gross Profit Per Unit Effort (PPUE) over 29 fishing days for two identical nets (900-m long, one was equipped with pingers, and the other did not have pingers), was assessed the following: the different production trends of the nets (Advantage of Production, AP) and the Return Of Investment (ROI) for the purchase of the pingers. Considering the difference in the PPUE values of the two nets, the frequency of the dolphin interaction, and the effort of fishing activities, was assessed the one-year economic losses (ED) due to dolphin depredation. Moreover, was assessed the economic damage caused by the destroyed area of the nets. The AP over 29 fishing days for the use of the pinger net with respect to the control net is 25.7 Euros for each 50 m of net. The ROI for the initial investment of the pingers (4 pinger = 800 Euro) is 50 fishing days, and the ED is 1400 Euros. The damages suffered by the control and the pinger nets were 33 m2 (90 Euros) and 22 m2 (91 Euros), respectively. The analysis of the results demonstrates that the critical factors that determine the success of the pinger technology could be represented by the return of investment (ROI) and the use of the economic incentives provided by the European Fisheries Fund (EFF).
Direct fisheries interactions pose a serious threat to the conservation of many populations and some species of marine mammals. The most acute problem is bycatch, unintended mortality in fishing gear, although this can transition into unregulated harvest under some circumstances. A growing issue in some fisheries is depredation, in which marine mammals remove captured fish from nets or lines. Depredation reduces the value of catch and may lead to a greater risk of entanglement and the potential for retaliatory measures taken by fishermen. The conservation threat caused by direct fisheries interactions is most dire for small populations of cetaceans and dugongs. Immediate action is needed to assess the magnitude of bycatch, particularly in many areas of Africa and Asia where little work has been conducted. New and innovative solutions to this problem are required that take account of the socioeconomic conditions experienced by fishermen and allow for efficient transfer of mitigation technology to fisheries of the developing world.
Mortality due to capture in longline fisheries has been implicated as a significant factor contributing to population declines for several species of threatened or endangered sea turtles. Identification of methods to reduce or prevent sea turtle bycatch is a high priority for fisheries managers and a necessary component of conservation efforts. One approach to reducing sea turtle interactions with longline fisheries is to take into account the behavior of sea turtles and the factors that lead them to interact with fishing gear. An understanding of the sensory cues that attract sea turtles to longline gear could help guide efforts to develop gear and bait that is less attractive, non-detectable, or even repellent to sea turtles. This paper presents a review of morphological, physiological, and behavioral studies conducted to assess the auditory, chemosensory, and visual capabilities of sea turtles, as well as the large pelagic fishes that are targeted by longline fisheries. We discuss the potential for exploiting differences in the sensory biology of these evolutionarily distinct groups to refine longline fishing techniques and reduce incidental bycatch of sea turtles without impacting the catch rates of targeted fish species. Based on the current evidence, differences in visual capabilities of sea turtles and pelagic fishes provide a promising avenue for development of a sensory-based deterrent.
Mooney, T. A., Au, W. W. L., Nachtigall, P. E., and Trippel, E. A. 2007. Acoustic and stiffness properties of gillnets as they relate to small cetacean bycatch. – ICES Journal of Marine Science, 64: 1324–1332.
Small cetaceans are incidental bycatch in gillnet fisheries. Dolphin and porpoise bycatch has been reduced by the use of barium sulphate-enhanced gillnets. This decreased entanglement is likely the result of either higher acoustic reflectivity or greater stiffness for barium nets. To address these variables, our study quantified the acoustic reflectivity and stiffness of six net types including barium sulphate, iron oxide-enhanced and control demersal gillnets of sizes which typically target cod (Gadus morhua) and monkfish (Lophius americanus). Acoustic reflectivity, or target strength (TS), was assessed using dolphin and porpoise-like sonar signals from 0° to 40°. TS values were used to calculate likely detection ranges. Barium sulphate- and iron oxide-enhanced nets showed increased reflectivity compared with control nets, with the barium sulphate nets generating the highest TS values. Dolphins should detect these nets in time to avoid contact, but porpoises, with typically lower source levels, may not detect nets at a range great enough to avoid entanglement. Barium sulphate line was significantly stiffer than comparable nylon line. All lines lost stiffness when soaked in seawater for 24 h. Barium sulphate nets proved stiffer and more acoustically reflective, and both factors are likely important in reducing harbour porpoise bycatch.
We investigated the inhibitory effect of capsaicin fertilizer on feeding in deer. We tested four captive adult female deer. In Experiment 1, in addition to the treatment (intact) containing only a solid feed (HC), we mixed the fertilizer not containing capsaicin (F) or the capsaicin fertilizer (CF) in the solid feed. In addition, the solid feed was put on a wire net that capsaicin fertilizer was placed 5 cm below (SCF). We investigated their feeding behavior response. In Experiment 2, we changed the amount of substance (fertilizer and capsaicin fertilizer) mixed in the HC. We mixed different amounts (0, 50, 100, and 200 g) of the treatments other than the intact with HC and presented them to the deer, and investigated their feeding behavior response. In Experiment 1, intake in the F and CF decreased (p < .05). In Experiment 2, HC intake was significantly lower in the 100 and 200 g CF (p < .05). However, HC intake relatively increased by the last day in the CF 200 g too. The capsaicin fertilizer decreased the feeding behavior of deer by directly touching the mucous membranes of the deer nose and lips. However, the effects were decreased over time.
1. Despite their geographic proximity, the Gulf of Ambracia and the Inner Ionian Sea Archipelago are
remarkably different in terms of environmental features, human activities, and dolphin species composition
and densities.
2. Interviews of small-scale professional fishermen (n = 100) showed that younger generations do not see any
future in fisheries and that the traditionally-oriented fishing community is rapidly changing.
3. Fish captures have reportedly decreased dramatically during the last 20 years. The main factors having an
adverse impact on the sustainability of small-scale fisheries differed significantly between areas.
4. Net damage as a consequence of dolphin predation was almost unanimously reported. Hence, fishermen
seemed genuinely interested in collaborating in future research initiatives to evaluate the damage caused by
dolphins and to explore potential mitigation strategies.
5. Dolphins were not the only animals held responsible for net damage, nor those reportedly causing the largest
economic loss to small-scale fisheries, which was attributed to either sea turtles or the critically endangered monk
seal, depending on the area.
6. The fishermen of the Gulf of Ambracia advocated the introduction of measures to curtail habitat degradation
as the top priority, while their colleagues of the Inner Ionian Sea Archipelago identified fisheries management
measures and effective law enforcement as the most urgently needed actions.
7. Given the high dependency of local communities on fisheries, ensuring their sustainability is crucial to
providing local fishers with sufficient income. The top management measures identified by local small-scale
fishermen perfectly match the priorities set out within the Natura 2000 network, achievable through an
ecosystem-based approach. Failure to take action in a timely manner may lead to irreversible environmental
damage coupled with the need for harsher regulatory measures.
The echolocation behavior of harbor porpoises Phocoena phocoena around gillnets was monitored to test their response to chemically (BaSO4) enhanced gill nets, designed to be more acoustically reflective than commercial nets. Field trials were conducted. between 22 July and 31 August 2000 in the Bay of Fundy, Canada. Echolocation clicks were continuously monitored with Porpoise Echolocation Detectors (PODs). Commercial and experimental (chemically enhanced) gill nets were set for groundfish in water depths from 100 to 130 m. Echolocation occurrence (the proportion of 10 s intervals during which clicks were detected) and echolocation rate (the number of clicks h(-1)) were measured. The PODs varied in their detection ability, so comparisons between commercial and enhanced nets were made with individual PODs. Neither echolocation rate nor occurrence differed with net type for any POD. Significantly more echolocation was detected during the day than at night. Echolocation rate and echolocation occurrence varied with depth and location, possibly reflecting concomitant variation in the relative abundance of porpoises and/or their prey: We conclude that porpoises do not respond to the acoustic reflectivity of the modified nets. Rather, the effectiveness of these nets is apparently due to other factors, such as their physical properties, particularly their stiffness.
Studying interactions between cetaceans and humans is fundamental to assess their ecological significance and the impact of human activities on marine wildlife. Delphinids have historically been associated with human maritime activities, and while evidence suggests that such interactions are becoming more frequent worldwide, these remain poorly studied. Areas of poten-tial interaction and differences in dolphin affinity to interact with humans were used to test hypotheses about the spatial dis-tribution and temporal variation in dolphin –fisheries interactions off the highly productive Alvarado lagoon, in the western Gulf of Mexico. Line-transect surveys yielded 928 dolphin, 980 vessel, and 320 fishing gear target records, the latter involving mostly the shrimp fishery. No temporal differences were found in daily relative abundance of dolphins (x ¯ ¼ 8.1 h 21 , SD ¼ 9.7), vessels (x ¯ ¼ 7.8 h 21 , SD ¼ 5.9) or fishing gear (x ¯ ¼ 2.4 h 21 , SD ¼ 2.6) between two consecutive years. Non-random spatial distributions indicated higher target concentrations at the lagoon entrance; however, dolphins and fishers were found to evade each other, possibly to prevent competition; dolphins only interacted with gillnets (28.6% of vessels and 22.6% of fishing gear). We observed small areas of potentially intentional and random encounters outside the entrance of the lagoon and low or null potential for interactions elsewhere. Only 18.9% of dolphin schools (44.8% of the 172 photo-identified animals) interacted with fisheries mostly by chance. Resident individuals (N ¼ 23) tended to avoid humans, likely in response to negative reinforcement caused by aggressions from fishers. Hence, the potential intentionality of a few individuals to interact with fisheries, show they bare higher risks while attempting to benefit from gillnetted prey. This research unveils the chronic and acute exposure of the dolphin community to artisanal fisheries within the area, having important reciprocal consequences on their distributions and activities.
Developing additional techniques for reducing animal feed contamination by rodents and controlling rodent populations is critical to efforts aimed at reducing the occurrence of Salmonella spp infection on poultry farms. Capsaicin, a compound found in chili peppers of the genus Capsicum, produces a burning sensation in the mouth of mammals and is used effectively as an animal deterrent for some pest species. Applied to poultry feed, capsaicin may be effective as an aversive agent to deter rodent feeding and enhance acceptability of rodenticide baits. We tested capsaicin-treated poultry diets (2000 and 3000 Scoville Heat Units, SHU) in no-choice feeding trials at four active New York farms in the winter of 1997-1998. At all farms, consumption of the 2000 SHU diet by rodents (Norway rats, Rattus norvegicus (Berk), and house mice, Mus musculus L) was significantly less than consumption of a control diet. Consumption of the 3000 SHU diet by rodents was significantly less than consumption of a control diet at three of the four farms. Overall, consumption of treated diets was 58-97% and 55-98% less than consumption of the control diet, for the 2000 and 3000 SHU diets, respectively. These reductions appeared to be related closely to the availability of alternative feed sources at these farms. Two-choice feeding trials involving a rodenticide bait (0.05 g kg(-1) brodifacoum) and the 3000 SHU diet demonstrated that Norway rats preferred the rodenticide to the capsaicin-treated poultry feed. Overall, rodenticide bait acceptance was high (95.6%) when offered simultaneously with capsaicin-treated poultry feed. Although poultry managers must utilize several techniques to manage rodent pests, the use of capsaicin-treated diets to reduce feed losses and increase rodenticide bait acceptance appears promising. Use of capsaicin-treated feed on poultry farms may substantially reduce feed contamination by rodents and ultimately the incidence of Salmonella infection in poultry.
Marine mammals:their distribution and interaction with fisheries in the Greek seas
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Overview of mitigation measures to reduce the incidental catch of vulnerable species in fisheries
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Sacchi, J. (2021). Overview of mitigation measures to reduce the incidental catch of vulnerable species in fisheries. Studies and
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Chemical shark repellent: Myth or fact? The effect of a shark necromone on shark feeding behavior
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Tests of repellent bait to reduce turtle bycatch in longline fisheries
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Tests of repellent bait to reduce turtle bycatch in longline fisheries
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