Cetacean Interactions Research Articles

Evaluating dolphin interactions with bottom-set net fisheries off Southern Iberian Atlantic waters

The present study, covering 2018–2022, evaluated the cetacean interactions with a bottom-set net fishery along the mainland Portuguese Southern coast (Algarve), estimating bycatch, depredation, gear damage and net length influence on Landing per Unit Effort (LPUE). The fishery employed various métiers (gillnets - mesh sizes: < 60, 60–75, 80 and 220 mm; trammel nets - 120 inner and 640 mm outer panels). Observations from 655 hauls revealed depredation by bottlenose dolphins in 17.7 % of hauls, while bycatch (isolated events of 4 bottlenose dolphins and one common dolphin) occurred in < 1 %. Depredation typically results in heavy damage to the net and occurs throughout the year, with elevated rates observed during the spring and winter months. Depredation rates varied among métiers, being higher in gears targeting red mullet and hake. The impact of depredation on LPUE varied based on net length and the targeted fish species. However, when comparing LPUE in hauls without depredation, there was no significant influence on the total and hake LPUE for nets shorter or longer than 6 km (p > 0.05). Interestingly, in hauls targeting red mullets without depredation, nets shorter than 6 km had a significantly higher LPUE (p < 0.01) compared to nets 6 km or longer, suggesting that longer nets increase fishing effort due to prolonged soaking times and a higher likelihood of depredation.

Interactions between Cetaceans (suborder Odontoceti) and Artisanal Fishing in Brazil: an ethnoecological approach

Studies based on the relationship between humans and the natural environment have been proven to be important tools for understanding the influence, knowledge, and perceptions associated with the web of interactions between humans, species and ecosystems. Here, we highlight the interactions between cetaceans and artisanal fishing. Thus, this study aimed to: a) compile studies that consider artisanal fishing and its interactions with small cetaceans in Brazil; b) understand research trends over the years; c) analyse the distribution of studies by country region; d) perform authorship and citation analyses; e) classify the interactions between cetaceans and artisanal fishing recorded by authors and f) identify dolphin species registered in the study. To achieve this, we reviewed the current status of national publications related to the interactions of cetaceans (suborder Odontoceti) with artisanal fishing in Brazil, focusing on ethnoecological studies. Seven databases were used to survey the studies. To classify the interactions, we adopted the categorization proposed by Freitas-Netto and adapted by Di Beneditto. Based on the data analysis, we registered 12 types of interactions, seven of which were grouped according to the descriptions proposed by Di Beneditto and five new categories were described based on the results of this study. The studies reported the interaction of 43.2% (n=16) of the 37 odontocete species reported to occur in Brazil, with emphasis on the species Sotalia guianensis, Tursiops truncatus, Pontoporia blainvillei, Inia geoffrensis and Sotalia fluviatilis. From our research it was possible to observe that ethnoecological studies allow us to answer important questions about the occurrence of species and aspects of fishing. Furthermore, we reinforce the importance of developing studies which focus on the knowledge of the existing relationships between cetaceans and traditional fishing methods, since studies on this topic can generate data that contribute to the establishment of mitigation strategies and the management of species and ecosystems.

Cetaceans playing with single-use plastics (SUPs): A widespread interaction with likely severe impacts

Play is a common behaviour in wild cetaceans that includes the manipulation of natural, as well as artificial objects such as marine debris. Yet, very little is known about these interactions despite the potential impacts on cetacean health. We combined a detailed review of the scientific literature and social media with 12 years of observations to examine cetacean interactions with plastic litter. A total of 11 odontocete species (Tursiops truncatus, Stenella longirostris, Delphinus delphis, Grampus griseus, Steno bredanensis, Stenella frontalis, Sotalia guianensis, Pseudorca crassidens, Orcinus orca, Globicephala melas and Physeter macrocephalus) were documented in 59 events carrying or throwing plastic litter with their head and/or flippers suggesting a form of play. Interactions occurred in the Atlantic, Pacific, Indian Ocean, Mediterranean, and Red Sea, with single-use plastics composing the main typology registered. While these interactions appeared harmless to the observers, they can pose a significant risk through subsequent entanglement or ingestion.

A review of cetacean interactions with longline gear

Fishery-cetacean interactions, including those with longline gear, give rise to economic, ecological and social concerns. This paper reviews problems resulting from cetacean-longline interactions, considers potential strategies to reduce interactions and identifies research priorities and approaches. Depredation by cetaceans (removal and damage of hooked fish and bait from fishing gear) and damage and loss of fishing gear create economic problems; however, the magnitude of this problem is poorly understood. There is also insufficient information to determine whether there are population-level effects resulting from injury and mortality of cetaceans (from incidental entanglement and hooking and from deliberate actions to discourage depredation). Fishery-cetacean interactions may also: change cetacean foraging behaviour and distribution; increase fishing effort to make up for fish taken from gear by cetaceans; and create errors in fish stock assessments that do not account for cetacean depredation. Negative public perceptions of longline fishing can result from news of incidental and deliberate injury and mortality of cetaceans associated with longlining. Information on how to reduce cetacean interactions with longline gear is also limited, as is the understanding of the mechanisms responsible for them. Strategies already employed in some fleets include refraining from setting or cutting sets short when problematic species of cetaceans are observed and fleet coordination of daily fishing times and positions. Many fishermen perceive depredation as an inevitable part of fishing. This paper discusses a number of other possible cetacean avoidance strategies that warrant consideration, including: (1) fleet communication to enable vessels to avoid temporally and spatially unpredictable and sporadic hotspots of aggregations of cetaceans; (2) underwater acoustic masking devices to conceal the sound of the vessel, gear, and setting and hauling activities; (3) quieter vessels to reduce cetaceans’ ability to target longline vessels; (4) encasement of caught fish to reduce cetacean access to or interest in the catch; (5) use of bait or gear with an unpleasant smell or taste to reduce the attractiveness of gear, bait and catch to cetaceans; (6) use of pre-recorded fishing vessel sounds played from stations throughout a fleet’s fishing grounds to distract cetaceans from actual fishing vessels; (7) use of acoustic devices to mask returning cetacean echolocation signals; and (8) use of tethered sonobuoys to track cetaceans and enable fleet avoidance. Vessels with relatively low cetacean interaction rates should be examined for design and operational differences from vessels with high interaction rates, possibly allowing identification of effective avoidance methods. There is a need for experimentation in individual longline fisheries over several seasons to assess fisheryspecific efficacy and commercial viability of cetacean avoidance strategies. This is necessary as different cetacean species likely respond differently to an avoidance method and cetaceans may habituate to an avoidance strategy, especially in fisheries interacting with resident cetaceans.

A note on the species occurrence, distributional ecology and fisheries interactions of cetaceans in the Mergui (Myeik) Archipelago, Myanmar

A vessel-based line-transect survey for cetaceans conducted during 23 February-6 March 2005 of the nearshore waters (to a depth of 40- 60m) of the Mergui (Myeik) Archipelago of southern Myanmar searched along 955km of trackline resulting in 30 cetacean sightings. These included Indo-Pacific bottlenose dolphins Tursiops aduncus (n=15), Indo-Pacific humpback dolphins Sousa chinensis (n=3), spinner dolphins Stenella longirostris (n=4; the largest of these was mixed with pantropical spotted dolphins Stenella attenuata), Irrawaddy dolphins Orcaella brevirostris (n=1), finless porpoises Neophocaena phocaenoides (n=1), Bryde’s whales Balaenoptera edeni/brydei (identification tentative; n=1), one unidentified baleen whale (probably also a Bryde’s whale) and four unidentified delphinid groups. Irrawaddy dolphins and finless porpoises were found in shallow, brackish waters, Indo-Pacific humpback dolphins also in shallow waters but those less affected by freshwater inputs and Bryde’s whales and Indo-Pacific bottlenose, spinner and spotted dolphins in deeper and clearer waters. In total 2,565 gill netters/long liners (95% CI=1,228-3,903), 1,301 squid jiggers (95% CI=611-1,992) and 532 stern trawlers (95% CI=154-910) were estimated to be operating in the study area. Concentrations of gill netters/long liners were particularly high in shallow nearshore waters and at least 150 were operating in the bay where the only sightings of Irrawaddy dolphins and finless porpoises were made. There is a need to better assess nearshore cetacean populations, investigate whether or not incidental and intentional catches are sustainable and incorporate a cetacean element into an initiative to establish a marine protected area network in the Mergui Archipelago.

Fishermen’s perception of interactions between fisheries and cetaceans in the Bulgarian Black Sea area

The eastern part of Bulgaria entirely borders the Black Sea, which defines it as a maritime country. The Bulgarian coast is an important fishing region for local people and has a high potential for interactions between fisheries and cetaceans. Depredation caused by cetaceans and damage to fishing gears can potentially lead to substantial economic loss for fishermen, while cetacean bycatch raises conservation concerns. Over the period 2016 - 2019, we conducted face-to-face interviews with fishermen in local fishing areas to better understand the fisheries – cetacean interactions in the Bulgarian part of the Black Sea. The research objectives were to identify the current fishermen’s attitudes toward cetaceans, understand the damage caused by local marine mammals to the different types of fishing gear, and gather fishermen’s proposals to resolve the problems. To record all of this, a specially designed structured survey was conducted. The results showed that fishermen’s attitude towards cetaceans was mostly positive and was not influenced by the type of fishing gear used. We found that fisheries - cetacean interactions are frequent, especially with dalyans gear and set gillnets. Cetacean bycatch mortality was reported to be highest for set gillnets, and the most vulnerable species was the Phocoena phocoena. Although interview data may be biased due to differences in perceptions and experience of the interviewees, and therefore should be interpreted with caution, this method allowed us to cover multiple types of interactions between cetaceans and Bulgarian fisheries.

Friend or foe: Risso's dolphins eavesdrop on conspecific sounds to induce or avoid intra-specific interaction.

The detection and use of emitters' signals by unintended receivers, i.e., eavesdropping, represents an important and often low-cost way for animals to gather information from their environment. Acoustic eavesdropping can be a key driver in mediating intra- and interspecific interactions (e.g., cooperation, predator-prey systems), specifically in species such as cetaceans that use sound as a primary sensory modality. While most cetacean species produce context-specific sounds, little is known about the use of those sounds by potential conspecific eavesdroppers. We experimentally tested the hypothesis that a social cetacean, Risso's dolphin (Grampus griseus), is able to gather biologically relevant information by eavesdropping on conspecific sounds. We conducted playback experiments on free-ranging dolphins using three context-specific sounds stimuli and monitored their horizontal movement using visual or airborne focal follow observations. We broadcasted natural sequences of conspecific foraging sounds potentially providing an attractive dinner bell signal (n = 7), male social sounds simulating a risk of forthcoming agonistic interaction (n = 7) and female-calf social sounds representing no particularly threatening context (n = 7). We developed a quantitative movement response score and tested whether animals changed their direction of horizontal movement towards or away from the playback source. Dolphins approached the foraging and the social female-calf sounds whereas they avoided the social male sounds. Hence, by acoustically eavesdropping on conspecifics, dolphins can discriminate between social and behavioural contexts and anticipate potential threatening or beneficial situations. Eavesdropping and the ensuing classification of 'friend or foe' can thus shape intra-specific social interactions in cetaceans.

Retrospective Study of Fishery Interactions in Stranded Cetaceans, Canary Islands.

Estimating cetacean interactions with fishery activities is challenging. Bycatch and chronic entanglements are responsible for thousands of cetacean deaths per year globally. This study represents the first systematic approach to the postmortem investigation of fishery interactions in stranded cetaceans in the Canary Islands. We retrospectively studied 586 cases necropsied between January 2000 and December 2018. Of the cases with a known cause of death, 7.4% (32/453) were due to fishery interactions, and the Atlantic spotted dolphin (Stenella frontalis) was the most affected species [46.9% (15/32)]. Three types of fishery interactions were recognized by gross findings: bycatch [65.6% (21/32)], chronic entanglements [18.8% (6/32)], and fishermen aggression [15.6% (5/32)]. Among the bycaught cases, we differentiated the dolphins that died because of ingestion of longline hooks [23.8% (5/21)] from those that died because of fishing net entrapments [76.2% (16/21)], including dolphins that presumably died at depth due to peracute underwater entrapment (PUE) [37.5% (6/16)], dolphins that were hauled out alive and suffered additional trauma during handling [43.8% (7/16)], and those that were released alive but became stranded and died because of fishery interactions [18.7% (3/16)]. Gross and histologic findings of animals in each group were presented and compared. The histological approach confirmed gross lesions and excluded other possible causes of death. Cetaceans in good-fair body condition and shallow diving species were significantly more affected by fishery interactions, in agreement with the literature. Low rates of fishery interactions have been described, compared with other regions. However, within the last few years, sightings of entangled live whales, especially the minke whale (Balaenoptera acutorostrata) and Bryde's whale (B. edeni), have increased. This study contributes to further improvement of the evaluation of different types of fishery interactions and may facilitate the enforcement of future conservation policies to preserve cetacean populations in the Canary Islands.

Long-term trends and a risk analysis of cetacean entanglements and bycatch in fisheries gear in Australian waters

Assessments of fisheries interactions with non-target species are crucial for quantifying anthropogenic threatening processes and informing management action. We perform the first multi-jurisdictional analysis of spatial and temporal trends, data gaps and risk assessment of cetacean interactions with fisheries gear for the entire Australian Exclusive Economic Zone. Bycatch and entanglement records dating from 1887 to 2016 were collected from across Australia (n = 1987). Since 2000 there has been a substantial increase in reported bycatch and entanglements and this is likely the result of improved monitoring or recording by some jurisdictions and fisheries as well as changing fishing effort, combined with continuing recovery of baleen whale populations after cessation of commercial whaling. A minimum of 27 cetacean species were recorded entangled, with over 30% of records involving interactions with threatened, vulnerable or endangered species. Three times the number of dolphins and toothed whales were recorded entangled compared to baleen whales. Inshore dolphins were assessed as most vulnerable to population decline as a result of entanglements, though humpback whales, common bottlenose dolphins, and short-beaked common dolphins were the most frequently caught. Only one-quarter of animals were reported to have survived entanglement, either through intervention or self-release from fishing gear. Spatial mapping of the records highlighted entanglement hotspots along the east and west coast of the continent, regions where high human population density, high fishing effort, and high density of migrating humpback whales all occur, augmented by high captures of dolphins in shark control gear along the east coast. Areas of few entanglements were more remote, highlighting substantial bias in entanglement reporting. Our gap analysis identified discrepancies in data quality and recording consistency both within and between jurisdictions. Disparities in the types of fisheries data provided for the analysis by different state agencies limited our ability to compile bycatch data in a representative and systematic way. This research highlights the need for improved standardised data recording and reporting by all agencies, and compulsory sharing of detailed fisheries interaction and effort data, as this would increase the value of entanglement and bycatch data as a conservation and management tool.

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

AbstractGreek 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.

Extrapolating cetacean densities to quantitatively assess human impacts on populations in the high seas.

As human activities expand beyond national jurisdictions to the high seas, there is an increasing need to consider anthropogenic impacts to species inhabiting these waters. The current scarcity of scientific observations of cetaceans in the high seas impedes the assessment of population‐level impacts of these activities. We developed plausible density estimates to facilitate a quantitative assessment of anthropogenic impacts on cetacean populations in these waters. Our study region extended from a well‐surveyed region within the U.S. Exclusive Economic Zone into a large region of the western North Atlantic sparsely surveyed for cetaceans. We modeled densities of 15 cetacean taxa with available line transect survey data and habitat covariates and extrapolated predictions to sparsely surveyed regions. We formulated models to reduce the extent of extrapolation beyond covariate ranges, and constrained them to model simple and generalizable relationships. To evaluate confidence in the predictions, we mapped where predictions were made outside sampled covariate ranges, examined alternate models, and compared predicted densities with maps of sightings from sources that could not be integrated into our models. Confidence levels in model results depended on the taxon and geographic area and highlighted the need for additional surveying in environmentally distinct areas. With application of necessary caution, our density estimates can inform management needs in the high seas, such as the quantification of potential cetacean interactions with military training exercises, shipping, fisheries, and deep‐sea mining and be used to delineate areas of special biological significance in international waters. Our approach is generally applicable to other marine taxa and geographic regions for which management will be implemented but data are sparse.

Performance of bycatch reduction devices varies for chondrichthyan, reptile, and cetacean mitigation in demersal fish trawls: assimilating subsurface interactions and unaccounted mortality

To improve bycatch mitigation of chondrichthyans, reptiles and cetaceans for a tropical demersal fish-trawl fishery, species-specific responses to bycatch reduction devices (BRDs) were investigated using both in situ subsurface and onboard observations. There are few, if any, studies that have determined mitigation performances of BRDs from subsurface interactions for these species, as most are rarely encountered and thus require substantial levels of observer coverage for robust assessments. This study combined in-net and onboard (774 day trawls and 1320 day trawl hours of subsurface observer coverage) electronic monitoring on all fish-trawl vessels (n = 3) to compare bycatch mitigation performances among nine megafauna groups, based on escape rates and interaction durations for three BRDs over 6 months (June to December 2012). Overall, 26.9% of day trawls had no megafauna interactions and 38.3% of the 1826 interactions escaped, with most in rapid time (91.4% in ≤ 5 min). The upward inclined exclusion grid significantly improved the escape proportions for most chondrichthyans by 20–30%. All BRDs were highly effective in reducing reptile (turtles and seasnakes) bycatch, but irrelevant for the few sawfish (n = 13) that readily entangled in the anterior of the net. Cetacean (bottlenose dolphins only) interactions with BRDs were very rare (n = 7) despite high levels of attendance and depredation during trawling. Loss of targeted teleosts through the BRD hatch was rare (1.3% of day trawls). This relatively cost-effective method of electronic monitoring achieved very high levels of subsurface observer coverage (60% of day trawls or 56% of day trawl hours), and provided evidence that the subsurface expulsion of megafauna in poor condition is negligible. Furthermore, this study provides species-specific improvements toward bycatch mitigation strategies for demersal fish trawling.

Annotated checklist and fisheries interactions of cetaceans in Togo, with evidence of Antarctic minke whale in the Gulf of Guinea

Based on strandings and captures, 9 cetacean species, including 6 odontocetes and 3 mysticetes, are documented (photos and specimens) in Togo's coastal waters (newly-recorded species marked with an asterisk): Antarctic minke whale (Balaenoptera bonaerensis*), Bryde's whale (Balaenoptera brydei or B. edeni), humpback whale (Megaptera novaeangliae), sperm whale (Physeter macrocephalus), pygmy sperm whale (Kogia breviceps*), short-finned pilot whale (Globicephala macrorhynchus*), pantropical spotted dolphin (Stenella attenuata*), common bottlenose dolphin (Tursiops truncatus) and common dolphin Delphinus sp. An anecdotal sighting record for killer whale (Orcinus orca) is considered reliable. The lack of Sousa teuszii records in Togo is consistent with its apparent contemporaneous absence in Ghana. The B. bonaerensis specimen, entangled in a purse seine set on small pelagics, is a first record for the Gulf of Guinea. The occurrence of this Southern Ocean species north of the equator underscores the severe gaps in our understanding of cetacean distribution off western Africa. The majority of artisanal fishermen operating in Togolese coastal waters are of Ghanaian origin and are thought to promote trade and consumption of cetacean bushmeat. Because captures are illegal, enforced with some success in the main fishing centers, covert landings of cetaceans are exceedingly difficult to monitor, quantify or sample. Concern is expressed about pollution of Togo's coastal waters with heavy metals due to phosphorite mining and export from the coastal basin near Hahotoé and Kpogamé.

Acoustic time synchronization among tags on porpoises to observe their social relationships

Observing and monitoring underwater social interactions of cetaceans is challenging. Because cetaceans spend most of their time underwater, it is important to monitor their underwater behavior individually. The finless porpoise is small and has no available natural identification marks that causes little knowledge of its sociality. Here we used acoustic datalogger to synchronize individual depth profile among individuals within a second. Acoustic and behavior tags were deployed on six free-ranging finless porpoises simultaneously and released in open water. Echolocation sounds were used as the trigger signal to synchronize the clock of all logging systems. Synchronous dives characterized by similar time-depth profile were used as an index of association. Two pairs tended to participate in long periods of synchronized diving more frequently than 13 other possible pairs, indicating that these four porpoises chose their social partners. Initiator and follower could be identified by precisely time synchronized data. The adult males tended to follow the immature female and juvenile male, respectively. However, the role of an initiator often changed within the pair during synchronized diving, and their body movements appeared to be non-agonistic.The time-synchronized bio-logging method was useful for observation of the social relationships of free-ranging aquatic animals.

Criteria and case definitions for serious injury and death of pinnipeds and cetaceans caused by anthropogenic trauma

Post-mortem examination of dead and live stranded beach-cast pinnipeds and cetaceans for determination of a cause of death provides valuable information for the management, mitigation and prosecution of unintentional and sometimes malicious human impacts, such as vessel collision, fishing gear entanglement and gunshot. Delayed discovery, inaccessibility, logistics, human safety concerns, and weather make these events challenging. Over the past 3 decades, in response to public concern and federal and state or provincial regulations mandating such investigations to inform mitigation efforts, there has been an increasing effort to objectively and systematically investigate these strandings from a diagnostic and forensic perspective. This Theme Section provides basic investigative methods, and case definitions for each of the more commonly recognized case presentations of human interactions in pinnipeds and cetaceans. Wild animals are often adversely affected by factors such as parasitism, anthropogenic contaminants, biotoxins, subclinical microbial infections and competing habitat uses, such as prey depletion and elevated background and episodic noise. Understanding the potential contribution of these subclinical factors in predisposing or contributing to a particular case of trauma of human origin is hampered, especially where putrefaction is significant and resources as well as expertise are limited. These case criteria descriptions attempt to acknowledge those confounding factors to enable an appreciation of the significance of the observed human-derived trauma in that broader context where possible.

Pilot whales attracted to killer whale sounds: acoustically-mediated interspecific interactions in cetaceans.

In cetaceans’ communities, interactions between individuals of different species are often observed in the wild. Yet, due to methodological and technical challenges very little is known about the mediation of these interactions and their effect on cetaceans’ behavior. Killer whales (Orcinus orca) are a highly vocal species and can be both food competitors and potential predators of many other cetaceans. Thus, the interception of their vocalizations by unintended cetacean receivers may be particularly important in mediating interspecific interactions. To address this hypothesis, we conducted playbacks of killer whale vocalizations recorded during herring-feeding activity to free-ranging long-finned pilot whales (Globicephala melas). Using a multi-sensor tag, we were able to track the whales and to monitor changes of their movements and social behavior in response to the playbacks. We demonstrated that the playback of killer whale sounds to pilot whales induced a clear increase in group size and a strong attraction of the animals towards the sound source. These findings provide the first experimental evidence that the interception of heterospecific vocalizations can mediate interactions between different cetacean species in previously unrecognized ways.

Do porpoises choose their associates? A new method for analyzing social relationships among cetaceans.

BackgroundObserving and monitoring the underwater social interactions of cetaceans is challenging. Therefore, previous cetacean studies have monitored these interactions by surface observations. However, because cetaceans spend most of their time underwater, it is important that their underwater behavior is also continuously monitored to better understand their social relationships and social structure. The finless porpoise is small and has no dorsal fin. It is difficult to observe this species in the wild, and little is known of its sociality.Methodology/Principal FindingsThe swim depths of 6 free-ranging finless porpoises were simultaneously recorded using a time-synchronized bio-logging system. Synchronous diving was used as an index of association. Two pairs, #27 (an immature female estimated to be 3.5 years old) and #32 (an adult male), #28 (a juvenile male estimated to be 2 years old) and #29 (an adult male), tended to participate in long periods of synchronized diving more frequently than 13 other possible pairs, indicating that the 4 porpoises chose their social partners. The adult males (#32, #29) tended to follow the immature female (#27) and juvenile male (#28), respectively. However, during synchronized diving, the role of an initiator often changed within the pair, and their body movements appeared to be non-agonistic, e.g., rubbing of bodies against one another instead of that on one-side, as observed with chasing and escaping behaviors.Conclusions/SignificanceThe present study employed a time-synchronized bio-logging method to observe the social relationships of free-ranging aquatic animals based on swimming depth. The results suggest that certain individuals form associations even if they are not a mother and calf pair. Long synchronized dives occurred when particular members were reunited, and this suggests that the synchronized dives were not a by-product of opportunistic aggregation.

Small cetacean captures in Peruvian artisanal fisheries: High despite protective legislation

We detail the first direct, at sea monitoring of small cetacean interactions with Peruvian artisanal drift gillnet and longline fisheries. A total of 253 small cetaceans were captured during 66 monitored fishing trips (Gillnet: 46 trips; Longline: 20 trips) from the port of Salaverry, northern Peru (8 o14′S, 78 o59′W) from March 2005 to July 2007. The most commonly captured species were common dolphins ( Delphinus spp.) (47%) , dusky dolphins ( Lagenorhynchus obscurus) (29%), common bottlenose dolphins ( Tursiops truncatus) (13%) and Burmeister’s porpoises ( Phocoena spinipinnis) (6%). An estimated 95% of common dolphin bycatch was of long-beaked common dolphins ( Delphinus capensis). Overall bycatch per unit effort for gillnet vessels (mean ± sd) was estimated to be 0.65 ± 0.41 animals.set −1 (range 0.05–1.50) and overall catch (bycatch and harpoon) was 4.96 ± 3.33 animals.trip −1 (range 0.33–13.33). Based upon total fishing effort for Salaverry we estimated the total annual average small cetacean bycatch by gillnet vessels as 2412 animals.year −1 (95% CI 1092–4303) for 2002–2007. This work indicates that, in at least one Peruvian port, bycatch and harpooning of small cetaceans persist at high levels and on a regular basis, particularly in driftnet vessels, despite the existence since the mid-1990s of national legislation banning the capture of marine mammals and commerce in their products. It is concluded that the coast of Peru is likely still one of the world’s principal areas for concern regarding high small cetacean bycatch and there is clearly an urgent need to increase the geographic scope of observer effort to elucidate the full magnitude of this issue.

Interspecific cetacean interactions during the breeding season of humpback whale (Megaptera novaeangliae) on the north coast of Bahia State, Brazil

The large majority of cetacean interspecific studies report only on dolphin interactions, while studies on interactions between odontocete and mysticete are less common. The present work aims to report on sightings of cetacean interactions, during the breeding season of humpback whales(Megaptera novaeangliae), along 370 km of the Bahia State, north-eastern Brazil, addressing aspects of cetacean distribution and behaviour. During 7 seasons (2000–2006), a total of 230 research cruises were performed, in which 38 events of interactions among humpback whales and other cetaceans(Tursiops truncatus, Steno bredanensis, Peponocephala electraandBalaenoptera acutorostrata)were observed, plus another 5 encounters without the whale's presence, includingT. truncatus, S. bredanensis, P. electra, Stenella clymeneandStenella attenuata. Our results confirm the occurrence of multiple cetacean species in the Bahia State, being the first study in the world to report on a large range of interactions involving another 4 cetacean species, grouped with up to 3 mixed species per sighting, with humpback whales in their annual breeding ground.

Bottlenose dolphin (Tursiops truncatus) depredation resulting in larynx strangulation with gill-net parts

Cetacean interactions with fishing gear are reported regularly and most frequently involve incidental capture. However, limited records exist related to depredation resulting in fishing gear ingestion. Here, we present cases of depredation resulting from ingestion of gill-net parts and larynx strangulation documented for the first time in a cetacean species. The bottlenose dolphin (Tursiops truncatus) is the only resident species in the Adriatic Sea, where small-scale commercial and private fisheries use gill nets throughout the year. A total of 120 dead-stranded bottlenose dolphins found along the Croatian coast of the Adriatic Sea were examined from 1990 to March 2008; 12 of them (10%) were affected by larynx strangulation with gill-net parts. The larynx of all affected animals showed at least one of the following pathological changes: edema, mucosal injury, and hypergranulation. In the majority of cases, it was a chronic condition. Larynx strangulations were found only in adult animals and appeared more often in animals with reduced ability to catch free-swimming prey.