Bottom-set Gillnets Research Articles

Developing and testing a computer vision method to quantify 3D movements of bottom-set gillnets on the seabed

AbstractGillnets are one of the most widely used fishing gears, but there is limited knowledge about their habitat effects, partly due to the lack of methodology to quantify such effects. A stereo imaging method was identified and adapted to quantify the dynamic behaviour of gillnets in-situ. Two cameras took synchronized images of the gear from slightly different perspectives, allowing to estimate the distance from the observation unit to the gear such as in the human 3D vision. The sweeping motion on the seabed and the penetration into the sediment of the leadline of light and heavy commercial bottom gillnets deployed in sandy habitats in the Danish coastal plaice fishery were assessed. The direct physical disruption of the seabed was minimal as the leadline was not penetrating into the seabed. Direct damage to the benthos could however originate from the sweeping movements of the nets, which were found to be higher than usually estimated by experts, up to about 2 m. The sweeping movements were for the most part in the order of magnitude of 10 cm, and resulted in a total swept area per fishing operation lower than any of the hourly swept area estimated for active fishing gears. Whereas the general perception is that heavy gears are more destructive to the habitat, light nets were moving significantly more than heavy ones. The established methodology could be further applied to assess gear dynamic behaviour in situ of other static gears.

Reef fish diversity of bottom set gillnet landings at Pamban, Tamil Nadu, India

The coral reef areas of Gulf of Mannar support a rich fauna of fishes and bottom set gill net is one of the important gears employed in this area. Reef fishes landed at Pamban fish landing centre by bottom-set gillnets operated in Gulf of Mannar, for a period of three years from January, 2009 to December, 2011 were studied based on fortnightly sampling. A total of 69 species belonging to 29 families were recorded during the study and as per IUCN, two species, Himantura uarnak and Rhinoptera javanica are included under the Vulnerable category. The landings amounted to 1761 tonnes during the period with a maximum contribution of 44% during 2011 and it was the minimum during 2010 with a share of 27%. Species-wise landings indicated the dominance of Lethrinus nebulosus (11.5%) followed by Neotrygon kuhlii (10.6%). The richness and diversity indices showed a gradual increase from 2009 to 2011 and all the year wise points in the funnel plot for variation in taxonomic distinctness (λ+) are within the expected limit. The qualitative and quantitative abundance along with different diversity measures are presented and discussed in this paper. The results of the present investigation suggest that the bottom set gill net fishery is in a healthy condition with respect to Pamban fish landing centre.

The use of Local Ecological Knowledge as a complementary approach to understand the temporal and spatial patterns of fishery resources distribution

BackgroundAcquiring fast and accurate information on ecological patterns of fishery resources is a basic first step for their management. However, some countries may lack the technical and/or the financial means to undergo traditional scientific samplings to get such information; therefore affordable and reliable alternatives need to be sought.MethodsWe compared two different approaches to identify occurrence patterns and catch for three main fish species caught with bottom-set gillnets used by artisanal fishers from northeast Brazil: (1) scientific on-board record data of small-scale fleet (n = 72 trips), and (2) interviews with small-scale fishers on Local Ecological Knowledge (LEK) (n = 32 interviews). We correlated (Pearson correlations) the months cited by fishers (LEK) as belonging to the rainy or to the dry season with observed periods of higher and lower precipitation (SK). The presence of the three main fish species at different depths was compared between LEK and SK by Spearman correlations. Spearman correlations were also used to compare the depths of greatest abundance (with the highest Capture per Unit Effort - CPUE) of these species; the CPUEs were descendly ordered.ResultsBoth methods provided similar and complementary bathymetric patterns of species occurrence and catch. The largest catches occured in deeper areas, which also happened to be less intensively fished. The preference for fishing in shallower and less productive areas was mostly due to environmental factors, such as weaker currents and less drifting algae at such depths.ConclusionBoth on-board and interview methods were accurate and brought complementary information, even though fishers provided faster data when compared to scientific on-board observations. When time and funding are not limited, integrative approaches such as the one presented here are likely the best option to obtain information, otherwise fishers’ LEK could be a better choice for when a compromise between speed, reliability and cost needs to be reached.

First record of Acanthurus monroviae (Osteichthyes: Perciformes: Acanthuridae) in southern Portugal, with notes on its recent distributional spread in the northeastern Atlantic and Mediterranean

The present study reports the first record of the Monrovia doctorfish, Acanthurus monroviae (Steindachner, 1876) in the Algarve coast (southern Portugal). A female (257 mm TL) was caught 21 April 2016 off the beach of Olhos d’Agua by a small-scale fishing boat operating bottom-set gill nets at approximately 15 m depth. Morphometric and meristic parameters of the specimen are reported and compared with previous records of A. monroviae. This is the second occurrence of this tropical fish species in Portuguese waters and the second northernmost capture ever reported for the northeastern Atlantic. The present record is an additional example of tropicalisation of the ichthyofauna in temperate waters by a thermophilic tropical species. Indeed, although not established in the study area, A. monroviae found a suitable seawater temperature regime in southern Portugal and further expanded its distributional range along the Iberian coasts. For biogeographic purposes, all reported occurrences of this species in the northeastern Atlantic and Mediterranean (including very recent records and sightings) are compiled and mapped.

Seal depredation in bottom-set gillnet and entangling net fisheries in Irish waters

Reports from the fishing industry suggest that seal depredation in Irish bottom-set gillnets and entangling net fisheries has increased substantially in recent years. A dedicated observer program was conducted in a range of such fisheries off the southwest and west coasts of Ireland to provide the first quantitative estimates of seal depredation. Zero inflated negative binomial and Poisson regression models found positive correlations between depredation and factors such as latitude, depth, timing of a haul within a trip and quantities of gear hauled. Soak time was significant in the inshore gillnet fishery for pollack species (Pollachius spp.) but not significant in the deeper more offshore gillnet fishery for hake (Merluccius merluccius). Results suggest that soak times should be kept short in shallow areas while faster hauling speeds, and systems which actively deter seals from the vicinity of Vessels operating in deep water should be explored.

First Report on Recruits of Bigeye Thresher Shark Alopias Superciliosus (Laminiformes: Alopidae) with Largest Birth Size from Indian Waters

Four embryonic bigeye thresher sharks Alopias superciliosus (126–158 cm total length) were collected from two females caught by bottom set gillnet and hook and line (operating in 120–800 m depth) caught from off Kanyakumari area and landed in Cochin Fisheries Harbour on 11-06-2012 . Detailed morphometric measurements are provided. The ratio of size at birth (Lb) and maximum observed length (L max ) in this study was 0.36, the largest when compared to earlier reports available till date. The bigeye thresher shark (Alopias superciliosus) is listed as Vulnerable globally because of declining population (IUCN 2007, Amorim et al. 2009). The production of a large neonate at parturition has the advantage of

Fish species composition, distribution and abundance trends in the open-coastal waters of northeastern Lake Ontario, 1992–2012

Bottom set gill nets were used to describe and track the fish community in northeastern Lake Ontario from 1992–2012. Six fixed, depth-stratified transects, spread more or less evenly from the mouth of the St. Lawrence River in the Kingston Basin to Brighton in central Lake Ontario, were sampled annually during summer. The balanced sampling design provided a broad picture of the warm, cool and coldwater fish community inhabiting open-coastal waters out to about 30 m water depth. Catch results were summarized by geographic area and depth strata to describe species distribution patterns, and presented graphically to illustrate annual abundance trends of the most important fish species (Alewife, Lake Trout, Yellow Perch, Walleye, Round Goby, Lake Whitefish, Brown Trout, Rock Bass, Smallmouth Bass, Chinook Salmon, Burbot, Cisco and Round Whitefish). Many of these dominant species showed peak abundance levels in the early 1990 s followed by decline. Of particular note, members of the coldwater benthic-oriented species assemblage, having all declined dramatically in the 1990s, remain at very low abundance levels, and their future prognosis appears bleak.

Developing ultraviolet illumination of gillnets as a method to reduce sea turtle bycatch

Fisheries bycatch of marine animals has been linked to population declines of multiple species, including many sea turtles. Altering the visual cues associated with fishing gear may reduce sea turtle bycatch. We examined the effectiveness of illuminating gillnets with ultraviolet (UV) light-emitting diodes for reducing green sea turtle (Chelonia mydas) interactions. We found that the mean sea turtle capture rate was reduced by 39.7% in UV-illuminated nets compared with nets without illumination. In collaboration with commercial fishermen, we tested UV net illumination in a bottom-set gillnet fishery in Baja California, Mexico. We did not find any difference in overall target fish catch rate or market value between net types. These findings suggest that UV net illumination may have applications in coastal and pelagic gillnet fisheries to reduce sea turtle bycatch.

Finless porpoise bycatch in Ariake Sound and Tachibana Bay, Japan

Bycatch of narrow-ridged finless porpoises Neophocaena asiaeorientalis in gillnets was estimated for the Ariake Sound/Tachibana Bay population in Japan using interview-based surveys. In 2007 and 2008, the minimum number (actual number reported by all interviewees) of bycatch was 31 to 35 individuals (ind.) yr �1 . The number of interviewees was 131 to 136 in each year. The bycatch estimate was 238 (95% CI 123 to 353) to 270 (95% CI 148 to 391) ind. yr �1 . The estimate exceeded the potential biological removal level of this population, 27 ind., which was cal- culated on the basis of a published abundance estimate. The bycatch estimate accounted for 8% of the abundance. The bycatch rate was 0.237 ind. gillnetter �1 yr �1 in 2007 and 0.257 ind. gillnet- ter �1 yr �1 in 2008. Additional analysis of information on bycatch in the bottom-set gillnet fisheries collected from 1987 to 1992 suggested an increase in bycatch during fall and winter seasons, the possible existence of a calving ground, and age-sex related habitat use patterns. Neonates were found in a restricted area, whereas nursing calves and possible calves were seen in a wide range of waters, implying outward movement of mothercalf pairs from a calving ground. Neither neonates nor nursing calves were captured in waters deeper than 30 m.

Hawksbill turtles Eretmochelys imbricata in El Salvador: nesting distribution and mortality at the largest remaining nesting aggregation in the eastern Pacific Ocean

El Salvador has a series of nesting beaches that together host the highest remaining nesting abundance of hawksbill turtles Eretmochelys imbricata in the eastern Pacific Ocean. How- ever, the distribution of hawksbill turtle nesting and causes of hawksbill mortality along the Salvado- ran coast are yet to be described. Here, we report on life history information of this population, in - cluding body size of nesting hawksbill turtles and clutch size, and mortality along nesting habitat at the following 3 areas in El Salvador: Los Cobanos Reef Marine Protected Area (Los Cobanos), Bahia de Jiquilisco-Xiriualtique Biosphere Reserve (Bahia), and Punta Amapala. In 2008, we recorded 310 nesting events by hawksbill turtles over 51.6 km of nesting habitat, giving an overall nesting density of 6.0 nests km -1 ; nearly 62% of total nesting activity and the highest reproductive output occurred in the Bahia. Morphometric data were collected from 26 nesting turtles that ranged from 74 to 88 cm curved carapace length (mean ± SD; 81.6 ± 3.6 cm) and 63 to 76 cm curved carapace width (70.1 ± 3.4 cm). Between 2004 and 2008, a total of 24 hawksbill turtles died in the mangrove and estuarine habitats of the Bahia (18 attributed to blast fishing) and in 2008, 8 hawksbill turtles died due to bycatch in bottom-set gillnets in Los Cobanos. Given the severely depleted status of hawksbill turtles in the eastern Pacific, conservation action is urgently needed to mitigate their incidental capture in artisanal fisheries gear at primary nesting and foraging areas in El Salvador.

The artisanal elasmobranch fishery of the Pacific coast of Baja California, Mexico

Artisanal fisheries account for up to 80% of elasmobranch fishing activity in Mexican waters, yet details associated with fishing effort and species composition are generally unavailable. This paper describes a survey of the artisanal elasmobranch fishery of the Pacific coast of Baja California, Mexico from 2006 to 2008. The objectives were to determine the geographic extent, size, and targets of the artisanal fishery, and to describe the catch characteristics at Laguna Manuela, an artisanal camp where elasmobranchs are the primary target. For the latter, we used a combination of beach surveys and a novel survey method involving the identification of discarded carcasses. Forty-four artisanal fishing camps were identified, of which 29 (66%) targeted elasmobranchs at least seasonally, using primarily bottom-set gillnets and longlines. At Laguna Manuela 25 species of elasmobranchs were documented. Gillnetting accounted for 60% of fishing effort, and the most commonly captured species were Rhinobatos productus, Zapteryx exasperata, and Myliobatis californica. Longline fishing accounted for 31% of fishing effort, and the most commonly captured species were Prionace glauca and Isurus oxyrhinchus. Catch was composed of mainly juveniles for many species, indicating that the immediately surrounding area (Bahia Sebastian Vizcaino) may be an important elasmobranch nursery habitat. The results of this study will serve as a baseline for determining future changes in the artisanal fishery, as well as changes in species demography and abundance.

Protection of Cetaceans in European Waters—A Case Study on Bottom-Set Gillnet Fisheries within Marine Protected Areas

AbstractThis article explores the legal regime of the protection of marine species and habitats within European waters by taking the protection of harbour porpoises in the German territorial sea and exclusive economic zone as an example. The analysis is based on a scientific assessment of the occurrence of and the anthropogenic impacts on harbour porpoises in the North Sea. The relationship between the protection of marine species within the European Union (EU) on the one hand and the Common Fisheries Policy of the EU on the other constitutes a classic example of a user-environment conflict. The article explores how such conflicts ought to be solved under the pertinent legal rules.

Insights on leatherback turtle movements and high use areas in the Southwest Atlantic Ocean

Leatherback sea turtles, Dermochelys coriacea, undertake broad oceanic movements while traveling between breeding and foraging areas. While satellite telemetry has been used to investigate long-term movements and diving patterns of leatherback turtles around the world, behavioral information for this species in the South Atlantic Ocean is limited. Here we present the first data on movements, habitat use and diving behavior of leatherback turtles in the Southwest Atlantic Ocean (SWA). Four leatherback turtles (two females, one male and one subadult) were fitted with satellite relayed data loggers (SRDL) in 2005 and 2006 after being incidentally captured by industrial (high seas pelagic longlines) and artisanal (coastal bottom-set gillnets) Uruguayan fisheries. Turtles tended to remain in the western side of the South Atlantic Ocean where specific areas were frequented, in one instance showing a round-trip migration between temperate and tropical waters. Previously unidentified high use areas were recognized along continental shelf and break waters in the SWA, both in temperate and tropical regions. Leatherback turtles exhibited seasonal migration patterns and displayed marked changes in diving behavior between high use areas. Furthermore, our results highlight the importance of the Rio de la Plata estuary as a key foraging area for D. coriacea in the SWA which should be considered a central focus of attention for future research and conservation efforts.

The artisanal elasmobranch fishery on the east coast of Baja California, Mexico: Characteristics and management considerations

The Mexican elasmobranch fishery ranks among the most important in the world, but details associated with fishing effort and species composition are generally unavailable, particularly for the extensive artisanal fishery. Seasonal surveys were conducted during 1998–1999 in the state of Baja California to determine the extent and activities of the artisanal elasmobranch fishery along its Gulf of California coast. Artisanal fishermen were highly opportunistic, and temporally switched targets depending on the local abundance of teleost, invertebrate, and elasmobranch fisheries resources. At least 17 species of shark, 13 species of ray, and 2 species of skate were identified among the 4495 specimens observed. Small, coastal sharks and rays were typically landed with bottom set gillnets during all surveyed seasons (spring–autumn) and large sharks were targeted with surface set (drift) gillnets during summer and autumn. Sharks and rays contributed similarly to elasmobranch landings, comprising 50.9% and 48.3%, respectively, of the total recorded catch. Overall landings were dominated by mustelid sharks (Mustelus henlei, Mustelus spp.) and the shovelnose guitarfish (Rhinobatos productus), with Alopias pelagicus, Gymnura spp., Heterodontus mexicanus, Mobula munkiana, Myliobatis californica, and Squatina californica also representing important components of the landings. Alopias vulpinus had previously been unreported for the Gulf of California and a new maximum size record was documented for Myliobatis longirostris. Catch rates (mean elasmobranchs/vessel/trip ± standard error) were lowest during autumn (17.4 ± 3.9) and highest in spring (35.3 ± 14.1). Adult, commonly gravid, A. pelagicus, Carcharhinus falciformis, and R. productus females comprised a disproportionately greater component of the landings than did their male counterparts. Given the decades of largely unrestricted exploitation of elasmobranchs in Mexican waters, population declines and shifts in size structure are likely to have occurred among those species with the lowest fecundity and latest ages at maturity.

Temporal variation in the artisanal elasmobranch fishery of Sonora, Mexico

Baseline, species-specific information is largely unavailable for artisanal elasmobranch fisheries, but is essential for the monitoring of exploited populations and the development of effective management plans. Seasonal surveys were conducted during 1998–1999 in Sonora, Mexico to determine the extent and activities of artisanal elasmobranch fisheries operating in the eastern Gulf of California. Nineteen fishing sites were documented, the majority of which (84.2%) targeted elasmobranchs during some part of the year. Most small demersal sharks and rays were landed in bottom set gillnet fisheries that also targeted demersal teleosts, whereas large sharks were usually taken in directed surface longline or, to a lesser extent, drift gillnet fisheries. Rays numerically dominated sampled landings in Sonora (63.4%, n = 100,136), and catch rates exceeded those of sharks during spring and summer months. The shovelnose guitarfish, Rhinobatos productus, was the primary fishery target during these seasons. During autumn, small sharks, especially mustelids ( Mustelus spp.) were numerically dominant, but rays (e.g., Dasyatis dipterura) were also caught in large numbers. Winter landings in Sonora were principally composed of mustelid sharks, which represented the greatest seasonal catch rates of all elasmobranch taxa during this study. Large sharks were of comparably minor importance, with a limited summer fishery operating in the southern part of the state. Variation in catch composition was evident in association with differential interannual environmental conditions (El Niño and La Niña) and seasonal temperature fluctuations. Size composition of landings varied greatly by species, but relatively small size classes of sharks and rays were abundant and large, often gravid females of several ray species (e.g., R. productus and Narcine entemedor) supported spring and summer fisheries in nearshore waters. Populations of many large shark species (e.g., Carcharhinus leucas, Carcharhinus limbatus, Carcharhinus obscurus and Galeocerdo cuvier) have likely been overfished, prompting a shift in effort towards coastal populations of smaller elasmobranchs.

The Occurrence and Distribution of Dolphins in Zanzibar, Tanzania, with Comments on the Differences Between Two Species of <i>Tursiops</i>

Incidental catches (bycatch) in gillnet fisheries off Zanzibar (Unguja Island), as a source of mortality among several species of dolphins, were reported in a questionnaire survey conducted in 1999. As a follow-up to that survey, from January 2000 to August 2003, we monitored the incidental catches of dolphins collected from 12 fish landing sites. Six species of dolphins were recorded from 143 specimens retrieved from bycatches in drift- and bottom set gillnets. Of these, 68 (48%) were Indo-Pacific bottlenose dolphins (Tursiops aduncus), 44 (31%) spinner dolphins (Stenella longirostris), 12 (8%) Risso's dolphins (Grampus griseus), 11 (8%) Indo-Pacific humpback dolphins (Sousa chinensis), 6 (4%) Pan-tropical spotted dolphins (Stenella attenuata) and 2 (1%) common bottlenose dolphins (Tursiops truncatus). Most of the bycatches (71%) were in nets set off the north coast of Unguja Island. In this paper, bycatch records are examined to describe the occurrence and distribution of dolphin species in Unguja Island coastal waters. The relatively large numbers of bycatch dolphins recorded indicate that bycatch may be a potential threat to local populations that need to be addressed in future conservation and management efforts in the region. Keywords: incidental catch, occurrence, distribution, dolphins, Unguja Island, Zanzibar West Indian Ocean Journal of Marine Science Vol. 4 (1) 2005: pp. 85-94

Reduction of harbour porpoise ( Phocoena phocoena) bycatch by iron-oxide gillnets

Reduction of harbour porpoise bycatch by use of high-density iron-oxide (IO) gillnets was tested in sea trials in the Danish North Sea bottom set gillnet fishery in September–October 2000. The trials were conducted as a controlled experiment with conventional gillnets as the control group. Eight porpoises were caught in the control nets and none in the IO nets, a highly significant reduction ( P < 0.01). Of the four fish species analysed only catch rates of cod ( Gadus morhua) were significantly ( P < 0.01) different between the two net types, with CPUE in the IO nets being ca. 70% of the CPUE in the control nets. Subsequent investigations in seawater tanks revealed that the difference in acoustic target strength of the two net types was not significant and that the nets behaved similarly under various water flow conditions. Based on laboratory tests of twine samples and analyses of catch composition we conclude that it is the mechanical properties of the IO nets, primarily the measured increase in stiffness, that are the main reasons for the differences in catch rates for cod and for porpoises between IO and conventional nets.

. Predation on Australian sea lions Neophoca cinerea by white sharks Carcharodon carcharias in South Australia

From January 1988 to December 2002, 182 Australian sea lions Neophoca cinerea with injuries attributable to white sharks Carcharodon carcharias were recorded in the N. cinerea colony at Seal Bay, Kangaroo Island. The mean number per month was 1.0 (s.d. 1.3), and the number per calendar year varied from 5 to 25 (mean 12.1, s.d. 6.1). The incidence was highest in summer (December to February) and autumn (March to May). The month with the greatest incidence of injured sea lions was January, when it was 17% of the total. This coincides with the higher proportion of white shark records around Kangaroo Island in summer and autumn than in other seasons (Bruce 1992). Adult female and juvenile sea lions were attacked most frequently, with 38% and 26%, respectively. Adult females pass through the waters near the colony more frequently than other sea lions, which makes them more susceptible than other age-sex groups to attacks by white sharks. Most (42%) injuries were to the head and central parts of the sea lions' bodies and 39% were to the rear of their bodies ('rear trunk' and 'hind flippers' areas). The stomach contents of a white shark caught in a bottom-set monofilament gill-net at Cape Gantheaume, Kangaroo Island in April 1992 included two N. cinerea pups aged 10-12 months. They formed about 75% of the shark?s stomach contents.

Ecological differences between two closely related morphologically similar benthic whitefish(Prosopium spilonotusandProsopium abyssicola) in an endemic whitefish complex

Identifying the differences in ecology between closely related species occupying the same environment contributes to our understanding of community diversity, ecosystem structure, and species conservation. Endemic Bear Lake whitefish (Prosopium abyssicola) and Bonneville whitefish (Prosopium spilonotus) are benthic, morphologically similar, and closely related, yet the extent of differential resource use remains poorly understood. To determine the ecological differences between these two species, we studied their seasonal distribution and diet in Bear Lake, Utah–Idaho. We used bottom-set gill nets to examine how catch of each species of whitefish varied in relation to depth and season (spring and summer). In both spring and summer, Bonneville whitefish dominated the shallower depths (5–30 m), whereas Bear Lake whitefish dominated the deeper depths (45–55 m). Bonneville whitefish ate a variety of benthic invertebrates, but mostly Chironomidae, whereas Bear Lake whitefish fed mostly on Ostracoda. These data describe a closely related morphologically similar, yet ecologically distinct group of whitefish in an ecoregion completely different from those studied before. These results indicated that each species has a very different role in the Bear Lake ecosystem. To conserve this unique fish assemblage, both shallow and deepwater habitats need to be protected.

Movement heterogeneity of dugongs, Dugong dugon (Müller), over large spatial scales

Seventy dugongs were fitted with satellite PTTs and/or GPS transmitters in sub-tropical and tropical waters of Queensland and the Northern Territory, Australia. Twenty-eight of the 70 dugongs were also fitted with time-depth recorders. The dugongs were tracked for periods ranging from 15 to 551 days and exhibited a large range of individualistic movement behaviours; 26 individuals were relatively sedentary (moving < 15 km) while 44 made large-scale movements (> 15 km) of up to 560 km from their capture sites. Male and female animals, including cows with calves, exhibited large-scale movements (LSM; > 15 km). Body length of travelling dugongs ranged from 1.9 to 3 m. At least some of the movements were return movements to the capture location, suggesting that such movements were ranging rather than dispersal movements. LSMs included macro-scale regional movements (> 100 km) and meso-scale inter-patch local movements (15 to < 100 km) and were qualitatively different from tidally-driven micro-scale commuting movements between and within seagrass beds (< 15 km). The mean ± S.E. macro-scale movement distance per individual was 243.8 ± 35.4 km ( N = 14 individuals that travelled > 100 km), with a mean ± S.E. travel time of 179.8 ± 29.0 h. The mean ± S.E. meso-scale movement distance per individual was 49.7 ± 3.3 km ( N = 28 individuals that made movements of 15–100 km), with a mean ± S.E. travel time of 52.3 ± 7.1 h. LSMs were rapid and apparently directed (mean ± S.E. travel speeds for GPS tagged animals; meso-scale movements = 1.3 ± 0.11 km/h, min = 0.3, max = 3.0; macro-scale movements = 1.6 ± 0.16 km/h, min = 0.8, max = 1.3). Tracked dugongs rarely travelled far from the coast (mean ± S.E. max distance = 12.8 ± 1.3 km). Dive profiles from the time-depth recorders suggest that dugongs make repeated deep dives while travelling rather than remaining at the surface, increasing their likelihood of capture in bottom set gill nets. Some animals caught in the high latitude limits of the dugongs' range on the Australian east coast in winter apparently undertook long distance movements in response to low water temperatures, similar to migrational movements by Florida manatees. Our findings that dugongs frequently undertake macro-scale movements have implications for management at a range of scales, and strengthen the aerial survey and genetic evidence for management and monitoring at ecological scales that cross jurisdictions.