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Interactions between the Indian River Lagoon blue crab fishery and the bottlenose dolphin, Tursiops truncatus
Abstract
A bstract
Anecdotal reports from blue crab fishermen in the Indian River Lagoon (IRL), Florida suggested that bottlenose dolphins ( Tursiops truncatus ) followed their boats, and stole bait fish from crab pots soon after they were deployed. To investigate these reports, we made biweekly observations from IRL commercial crab boats from January 1998 to January 1999 (670 h). Only 2.8% of the 18,891 crab pots surveyed revealed evidence of dolphin/crab pot interaction. Dolphin interactions included: (1) begging at boats, (2) feeding on discarded bait fish, (3) engaging in crab pot tipping behavior, and (4) dolphin mortality from crab pot float line entanglement. Overall, 16.6% of the 1,296 dolphins sighted interacted with fishing boats. Seasonal trends were evident, with fishery interactions peaking in the summer. Crab pot interactions ranged from 0% to 36% of the traps checked daily. Different methods of securing the bait‐well door and the role of trap locality were tested using a replicated experimental design. Results showed significant differences in successful bait removal by dolphins, among the degrees of door security ( P < 0.001) and between trap location ( P < 0.01). Thus, increased door security may help to reduce the negative impacts to the fishery and dolphins involved.
... A survey of blue crab fishers was conducted to gain fishers' perceptions of the degree of interaction between bottlenose dolphins and the blue crab fishery, as well as to determine if similar types of interaction seen in Florida's Indian River Lagoon (Noke and Odell, 2002) occur in South Carolina. Ten fishers, representing seven water bodies, were surveyed for this project. ...
... Generally, these animals were robust and healthy, and showed internal evidence of fishery interaction such as a stomach full of fish remains and foam in the lungs and bronchi, indicating asphyxiation. Stomachs full of fish remains may indicate fishery interaction as some theories suggest that marine mammals may actively forage in the presence of fishing gear or follow fisheries as they feed on discarded bait and manipulate gear to obtain food (Fertl and Leatherwood, 1997;Noke and Odell, 2002). In addition, the 'confirmed' cases often had approximately 1cm wide, haemorrhagic rope wounds located around the base of the flukes and occasionally on other parts of the body (Figs 4 and 5). ...
... Dolphins were seen on 11 of 12 fishing trips, and group size ranged from one to four. The behaviour of dolphins during fishing operations included mill, close approach and travel (Irvine et al., 1981;Noke and Odell, 2002). During fishing trips conducted for this study, the close approach behaviour was seen only once. ...
In the USA, commercial fisheries that interact with marine mammals are categorised according to the number of incidental takes of marine mammals relative to the defined Potential Biological Removal (PBR) for the population. Three categories exist for such commercial fisheries: Category I, II and III, each varying in the degree of regulation. Fishery categorisation is based on a five-year running average of the number of incidental entanglements in that fishery and is published annually in the Federal Register. The Atlantic blue crab (Callinectes sapidus) fishery is one of South Carolina’s largest commercial fisheries in terms of volume and value and was recently re-categorised as a Category II fishery, resulting in heightened regulation. The Atlantic blue crab fishery exists in known areas of bottlenose dolphin (Tursiops truncatus) habitat; therefore, interaction between the two is probable. This study uses historical marine mammal stranding data and on-board investigations of the blue crab fishery in South Carolina to investigate the degree of fishery and dolphin interaction. Analysis of historical strandings showed that approximately 24% of the 42 entanglement cases in South Carolina from 1992-2003 resulted from the blue crab fishery. In nine of the 12 years examined, bottlenose dolphin mortality rates were found to be greater than or equal to 10% of the South Carolina Management Unit’s PBR, which is significant according to the US Marine Mammal Protection Act’s (MMPA) definitions for the Atlantic Coastal Stock of bottlenose dolphins. In addition, results from this study showed that the average number of bottlenose dolphin entanglements per year in the South Carolina blue crab fishery has exceeded 1% of PBR across a five-year period (1999-2003), which defines a Category II fishery. Thus, entanglement data from South Carolina from 1992-2003 support the re-categorisation of the blue crab fishery and the introduction of heightened regulations under the MMPA.
... This provides an opportunity for bottlenose dolphins to associate food with anthropogenic sources (e.g., fishermen, vessels). In Indian River Lagoon, Florida, bottlenose dolphins became conditioned to approach commercial blue crab boats, possibly reinforced by the discards of old bait (Noke & Odell, 2002;Durden, 2005). A solitary bottlenose dolphin in Belize, known to interact with humans in the water, became conditioned to humans after fishermen threw fish and conch to it (Dudzinski et al., 1995). ...
... As bottlenose dolphins lose their wariness toward humans and are conditioned to approach boats, they become more likely to be struck by a boat or entangled in fishing gear (Donaldson et al., 2010). Several studies have noted injuries and deaths while observing bottlenose dolphins interacting with fisheries (Corkeron et al., 1990;Noke & Odell, 2002;Durden, 2005;Cunningham-Smith et al., 2006;Powell, 2009). Additionally, some fishermen blame bottlenose dolphins for damage to gear or competition for catch, resulting in the reported use of guns and seal bombs to deter the animals or retaliate for lost catch or gear (Zollett & Read, 2006). ...
... Bottlenose dolphins that were rewarded for begging at shrimp trawlers may have then transferred the behavior to other targets, like recreational boats. While this is only a hypothetical situation, it is supported by a similar chain of events involving bottlenose dolphins (Orams, 1995;Noke & Odell, 2002;Durden, 2005) as well as boto (de Sá Alves et al., 2009). Although trawler associations may be responsible for some of the begging observed near Savannah, Kovacs (2012) found that almost half of beggars near Savannah (45.5%) were never sighted with a shrimp trawler. ...
The common bottlenose dolphin (Tursiops truncatus) has been known to forage in association with shrimp trawlers by feeding on fish caught in or disturbed by nets and on discarded bycatch. In addition, common bottlenose dolphins in the estuarine waterways near Savannah, Georgia display a high rate of begging behavior, and it is hypothesized that interactions between bottlenose dolphins and the shrimp trawl fishery may be a contributing factor. The purpose of this study was to determine which activities of the shrimp trawl fishery resulted in associations between trawlers and bottlenose dolphins, and which activities resulted in bottlenose dolphins begging from the trawler. The presence of common bottlenose dolphins around a commercial shrimp trawler and the activity of the trawler were recorded for 129 h over 20 d from August to November 2010 and June to October 2011. Bottlenose dolphins associated with the shrimp trawler (i.e., within 150 m of the trawler) for 68 +/- 33% of the day; and they associated with the vessel for the majority of the time spent in the net positions of haulback (90 +/- 20%) and trawling (89 +/- 17%). However, bottlenose dolphins approached the vessel (i.e., within 10 m) most often while the fishermen were manipulating and cleaning the nets (60 +/- 23%) and least often during trawling (2 +/- 5%). Begging was observed on 90% of days and occurred most often when the fishermen were cleaning the nets and bringing the trawl doors onboard the vessel (79% of days). Whether or not a bottlenose dolphin interacted with a trawler was dependent on several factors, including trawler activity, net position, and fisherman behavior. Furthermore, bottlenose dolphins that forage behind active trawlers may later engage in begging behavior as a result of direct interactions with fishermen, perpetuating the begging problem near Savannah.
... Dolphins likely entangle in the trap pot line accidently, either through passive or active interaction with the trap-pot and line/ buoy rig (McFee et al., 2007). Dolphins have been observed feeding around pots (Noke and Odell, 2002), and are believed to be attracted to fish that aggregate around the pot and line/buoy. In some instances dolphins have been observed pot-tipping in an attempt to get at the bait inside the trap (Noke and Odell, 2002;Haymans, 2005). ...
... Dolphins have been observed feeding around pots (Noke and Odell, 2002), and are believed to be attracted to fish that aggregate around the pot and line/buoy. In some instances dolphins have been observed pot-tipping in an attempt to get at the bait inside the trap (Noke and Odell, 2002;Haymans, 2005). Noke and Odell (2002) suggest that entanglements in TPG may correspond to seasonal pot fisheries and the density of pots in a given area. ...
... In some instances dolphins have been observed pot-tipping in an attempt to get at the bait inside the trap (Noke and Odell, 2002;Haymans, 2005). Noke and Odell (2002) suggest that entanglements in TPG may correspond to seasonal pot fisheries and the density of pots in a given area. Noke and Odell (2002) also found that location of the traps played a significant role in the number of crab pot interactions that occurred. ...
Documenting the extent of fishery gear interactions is critical to wildlife conservation efforts, especially for reducing entanglements and ingestion. This study summarizes fishery gear interactions involving common bottlenose dolphins (Tursiops truncatus truncatus), Florida manatees (Trichechus manatus latirostris) and sea turtles: loggerhead (Caretta caretta), green turtle (Chelonia mydas), leatherback (Dermochelys coriacea), hawksbill (Eretmochelys imbricata), Kemp’s ridley (Lepidochelys kempii), and olive ridley (Lepidochelys olivacea) stranding in Florida waters during 1997–2009. Fishery gear interactions for all species combined were 75.3% hook and line, 18.2% trap pot gear, 4.8% fishing nets, and 1.7% in multiple gears. Total reported fishery gear cases increased over time for dolphins (p < 0.05), manatees (p < 0.01), loggerheads (p < 0.05) and green sea turtles (p < 0.05). The proportion of net interaction strandings relative to total strandings for loggerhead sea turtles increased (p < 0.05). Additionally, life stage and sex patterns were examined, fishery gear interaction hotspots were identified and generalized linear regression modeling was conducted.
... For example, both gears can catch unwanted species and sizes, which are then discarded, with associated mortality 240 (Simonson and Hochberg 1986; Farrell et al. 2001; Tallack 2007; Broadhurst et al. 2009; Smith and 10 Scharf 2011; Dawson et al. 2013). Other organisms, including the target species, may escape during 242 the fishing or hauling processes (Baker and Schindler 2009; Lundin et al. 2012), while some animals can easily remove and consume catches from gillnets (Gazo et al. 2008) or baits from traps (Noke and 244 Odell 2002). Further, both gears can damage habitats, causing additional, unwanted and unaccounted mortality to fauna and flora and, if lost, have the potential to ghost fish (Eno et al. 2001; Humborstad 246 et al. 2003; Shester and Micheli 2011; Coleman et al. 2013). ...
... Gillnets appear to 794 be more susceptible to a broader range of predators, simply because of their size, visibility and distribution throughout the water column (Trippel et al. 2008; Wang et al. 2010; López Barrera et al. 796 2012). In this regard, the vertical deployment of nets in relation to the location of predatory species is clearly important (Dawson 1991); also because seasonality in their distribution and/or prey choice may 798 dictate the level of interactions (Noke and Odell 2002; Rosas-Ribeiro et al. 2012). 30 Irrespective of the causes, the rates at which predators consume catches need to be added to any unaccounted mortality estimates for their prey species (Brown and Caputi 1986). ...
... discard mortality; Bjørge et al. 2002; Noke and Odell 2002). Depredation can potentially nullify efforts to reduce discard, escape or drop-out mortalities (e.g. ...
Gillnets and traps often are considered to have fewer holistic environmental impacts than active fishing gears. However, in addition to the targeted catches, gillnets and traps still cause unwanted mortalities due to (i) discarding, (ii) ghost fishing of derelict gear, (iii) depredation, (iv) escaping or dropping out of gear, (v) habitat damage, and potentially (vi) avoiding gear and predation and (vii) infection of injuries sustained from most of the above. Population-level concerns associated with such ‘unaccounted fishing mortalities’ from gillnets and traps have been sufficient to warrant numerous attempts at mitigation. In this article, we reviewed relevant research efforts, locating 130 studies in the primary literature that concomitantly quantified mortalities and their resolution through technical modifications, with the division of effort indicating ongoing concerns. Most studies (85) have focused on discard mortality, followed by ghost-fishing (24), depredation (10) and escape (8) mortalities. The remaining components have been poorly studied (3). All problematic mortality components are affected by key biological (e.g. species), technical (e.g. fishing mechanisms) and/or environmental (e.g. temperature) factors. We propose that these key factors should be considered as part of a strategy to reduce impacts of these gears by first assessing modifications within and then beyond conventional configurations, followed by changes to operational and handling practices. Justification for this three-tiered approach is based not only on the potential for cumulative reduction benefits, but also on the likely ease of adoption, legislation and compliance.
... This behavioural flexibility contributed to their success in diverse habitats, and the best example of the dolphin's flexibility is probably the great diversity recorded in foraging behaviours and techniques (Shane 1990b;Rossbach and Herzing, 1997;Acevedo, 1999;Nowacek, 2002;Sargeant et al., 2005). With the increase of human demography in coastal habitats, marine mammals are more and more exposed to a variety of human activities, and are therefore subject to potential injury or disturbance from anthropogenic activities (Nowacek et al., 2001;Noke and Odell, 2002). Several activities were identified as potentially impacting on marine mammal species at the individual or population level, such as noise pollution from military/industrial activities, coastal degradation, vessel collisions, interactions with fishing gear, and tourism (Wells and Scott, 1994;Wells and Scott, 1997;Nowacek et al., 2001;Jauniaux et al., 2002;Noke and Odell, 2002;Buckstaff, 2004;Laura, 2009). ...
... With the increase of human demography in coastal habitats, marine mammals are more and more exposed to a variety of human activities, and are therefore subject to potential injury or disturbance from anthropogenic activities (Nowacek et al., 2001;Noke and Odell, 2002). Several activities were identified as potentially impacting on marine mammal species at the individual or population level, such as noise pollution from military/industrial activities, coastal degradation, vessel collisions, interactions with fishing gear, and tourism (Wells and Scott, 1994;Wells and Scott, 1997;Nowacek et al., 2001;Jauniaux et al., 2002;Noke and Odell, 2002;Buckstaff, 2004;Laura, 2009). Whether, Article 3 direct effects of human activities on marine mammals, such as injuries from boat collisions, are easy to observe, indirect effects have been also documented on the behavioural patterns of animals. ...
... We also could observe that the distribution of one female and her calf, was tightly linked to the presence of boats, while other dolphins show a widespread distribution. Similar problems of fishing gear ingestion have been documented in the Indian River Lagoon (Texas), in Shark Bay (Western Australia), and in Sarasota Bay (Florida) (Mann, 1995;Noke and Odell, 2002). Along the central Florida west coast, two cases of fishing gear ingestion, leading directly or not to the death of two of 23 dead-stranded bottlenose dolphins were documented (Gorzelany, 1998). ...
Between 2004 and 2007, field surveys were conducted to study bottlenose dolphins (Tursiops truncatus) in the seaside resort of Panama City, Northwest Florida. Using boat-based photo-identification surveys, mark-recapture surveys were performed to estimate the abundance of bottlenose dolphins. According to months, the estimate population size varied between 57 to 178 individuals, with the lowest abundance occurring during the spring. A total of 263 different dolphins were photo-identified. Site fidelity of bottlenose dolphins revealed that only 7% (n=18) of individuals were considered as “common” (i.e. dolphins seen during more than 13 captures occasions) in the study area. While 58% are observed only in one year and are thus defined as transient dolphins, 12% of dolphins are considered as resident animals, since they were seen within the four years of the study. The spatio-temporal distribution of dolphins revealed that animals showed preferred habitat, mainly concentrated in and around the Channel Entrance. Mean group size composed of 5 dolphins, showed significant variations according to the observed zone, the time of the day, the presence of young individuals and the behaviours of dolphins. The behavioural study aimed to define the diurnal patterns of dolphins behaviours as well as the habitat use of dolphins throughout the study area. Evidence of feeding peaks in the morning and evening were recorded, while playing, sexual and begging were more frequently observed in the afternoon. Using a Geographic Information System (GIS), a foraging hotspot was detected within the study area. Human activities, especially tourism and recreational fishing revealed significant impacts on dolphins behaviours, with several individuals seen to beg regularly close to boats. This unnatural behaviour of begging, were more often observed during the tourism season (between April to August), and occurred mainly near shore the East jetties. Social structure is an important component of the bottlenose dolphin populations. Therefore, with the program SOCPROG 2.3, we described the association patterns of 46 individuals observed at least ten times during the study period. Coefficient of Associations (CoAs) of these individuals were calculate using the Half-Weight-Index (HWI). Dolphins were associated on average HWI of 0.11, but preferred long-term and stronger associations between individuals were nevertheless observed. The cluster analysis showed no clear division in the social organisation of bottlenose dolphins in Panama City, excepted strong pairs and trios of associates. Highly significant differences were found in associations between and within sex classes. Indeed, males associations were stronger than between inter-sexual associations or between females only. Sociogram of males revealed a complex network with strong associations between pairs or trios. The population structure seems to be temporally stable over the study with constant companionship observed in the dolphin population in Panama City. Movements of dolphins between Panama City and the adjacent bay of St Joseph Bay have been highlighted by comparison of the photo-ID catalogues available for both populations. First results showed that 69 dolphins were identify in both study areas. Finally, a preliminary study on the behavioural personality of ten adults bottlenose dolphins easily recognised were assessed. Variations in the behavioural patterns of individuals were observed: some dolphins are considered as «regular beggars»; some dolphins appeared more sexually active than others; while some individuals tend to travel more than others.
... Conversely, fish-based baits elicit similar or potentially al. 2022) and can cause interactions with dolphins (Tursiops truncates; Burdett and McFee 2023). Dolphins have been observed manipulating crab pots to obtain the food inside (Noke and Odell 2002) and actively forage on prey species near fishing gear (Fertl and Leatherwood 1997;Noke and Odell 2002), thus increasing their liklihood of entanglement and subsequent death. Artificial lures may present a solution; during our trap trial, the crab traps were effective at capturing octopus with a plain bright orange crab artificial lure, which presented only visual and no olfactory stimuli, as would be associated with natural baits. ...
... Conversely, fish-based baits elicit similar or potentially al. 2022) and can cause interactions with dolphins (Tursiops truncates; Burdett and McFee 2023). Dolphins have been observed manipulating crab pots to obtain the food inside (Noke and Odell 2002) and actively forage on prey species near fishing gear (Fertl and Leatherwood 1997;Noke and Odell 2002), thus increasing their liklihood of entanglement and subsequent death. Artificial lures may present a solution; during our trap trial, the crab traps were effective at capturing octopus with a plain bright orange crab artificial lure, which presented only visual and no olfactory stimuli, as would be associated with natural baits. ...
An understanding of octopus behaviour and their capture by fishing gears is required to inform efficient, sustainable, and ethical octopus fisheries. Here, the behaviour of Octopus tetricus was assessed in response to different bait and trap combinations in an outdoor mesocosm experiment. Eight wild octopuses were collected, maintained in individual tanks with flow-through seawater and aeration, and monitored with a 24-h video surveillance system. Six different traps and four different baits were presented to each octopus in various combinations during four sequential trials. Fine-mesh crab traps were the most successful in capturing octopus, accounting for 23 of the total 30 captures across all trials. Whereas solid trigger traps produced the greatest number of other interactions (e.g., octopus sitting on trap/in the entrance), averaging 43 interactions per trial, but were rarely triggered. Bait type did not influence octopus capture, trap interaction frequency, or octopus activity; however, only artificial bait types were trialled, and fresh natural baits may elicit a stronger response and should be investigated in future research. Generally, octopus were inactive, dedicating only 9.5% of their total time to active behaviours. Octopus activity varied with time of day, with peak activity during morning daylight (0800–1200) and the lowest activity during the dark hours of the very early morning (0000–0400). Additionally, capture numbers, trap interactions, and activity varied among individuals, with bolder personalities in some octopus. This natural variation among individual octopuses may lead to fishery-induced selection associated with the elevated capture frequency of bold or more active individuals.
... La implicación de estos encuentros, radica en el despliegue de diversas conductas con fines alimentarios que ejecutan los delfines en su entorno (interacción mayor biomasa capturada de especies particularmente consumidas por el tursión, aunque sus resultados no fueron estadísticamente significativos (Rechimont, 2015). En relación con las interacciones de los tursiones con otras artes de pesca, los registros han sido escasos; no obstante, existen reportes con jaulas utilizadas para la pesca del cangrejo azul en la India, donde delfines saquean los cebos y alteran los equipamientos; ante esta situación, los pescadores optaron por modificar sus equipos aumentando la seguridad de las artes evitando de esta manera daños por parte de los delfines (Noke y Odell, 2002). La disminución de daños en las artes fue evidente; sin embargo, conductas asociadas como el "limosneo" y el acompañamiento al lado de las embarcaciones para el aprovechamiento de la pesca de descarte durante la captura del cangrejo, se mantuvieron durante la actividad pesquera independientemente de la modificación de la técnica de pesca (Noke y Odell, 2002). ...
... En relación con las interacciones de los tursiones con otras artes de pesca, los registros han sido escasos; no obstante, existen reportes con jaulas utilizadas para la pesca del cangrejo azul en la India, donde delfines saquean los cebos y alteran los equipamientos; ante esta situación, los pescadores optaron por modificar sus equipos aumentando la seguridad de las artes evitando de esta manera daños por parte de los delfines (Noke y Odell, 2002). La disminución de daños en las artes fue evidente; sin embargo, conductas asociadas como el "limosneo" y el acompañamiento al lado de las embarcaciones para el aprovechamiento de la pesca de descarte durante la captura del cangrejo, se mantuvieron durante la actividad pesquera independientemente de la modificación de la técnica de pesca (Noke y Odell, 2002). ...
relationship of organisms with their environment influences their behavioral plasticity, modifying their behavior in response to stimuli or pressures, and consequently affecting the ecological relations of species. The expansion of human activities leads to conflicts between humans and wildlife, and these are mainly associated with interactions during competition for space and / or food availability. These conflicting interactions have been reported on the shores of the Gulf of Mexico, where the artisanal fishermen denounce the looting and damage of their equipment by tursiones (Tursiops truncatus), which are sometimes injured or killed. The objective of this work was to study the behavior of bottlenose dolphins in their interaction with artisanal fishery in the coastal waters of Alvarado, establishing: 1) the first etogram for the case, 2) the behavioral differences associated with fishing, and 3) the variations in relation to the age and group size of the dolphins interacting with this activity. Between 2015 and 2016, 64 groups have been observed by sampling scanning from boats and fixed points. We obtained 4,898 records that used body patterns and other characteristics associated with the behavioral deployment form. The events were organized in the states: food, locomotion, social, socio-sexual, play and rubbing with objects. There were significant differences in the frequency (X2 = 55.93, gl = 5, p <0.001) and the local rate of behavior in the presence and absence of fishing activity (X2 = 25.16, gl = 5; However, their intensity was lower than in the absence of fishing (5.3 min-1 vs 7.0 min-1) and in relation to the other behaviors, that in general had low frequencies. During the fishing activity, the dolphins that interacted most were adults, however, no significant group differences were found in the proportion of individuals by age in relation to the fishery ( X2 = 1429, gl = 2, p <0.4894). The average group size comprised two individuals in both conditions (without = 42% and con = 54% interaction), so no differences were observed (X2 = 1.56, gl = 15, p <0.001); however, the direct operational interaction to the net was performed by 51% individually, and mostly (84%) in the first 30 m. The behavioral differences partially support the hypotheses and evidence the influence of human activities on the behavioral display of the T. truncatus dolphins in Alvarado. The lack of evidence on differences in age and group size suggest the need for a larger sample size, as well as the habituation of some dolphins to the fishery interaction, possibly being these experienced dolphins that will pass; these dolphins would have to be photo-identified to determine their contribution in the effects on the behavior of the population, derived from their interaction with the artisanal fishery.
... These animals are impacted by several factors that warrant an improved understanding of their population biology. IRL dolphins may be directly (e.g., boat strikes and fishing gear entanglement) (Noke & Odell, 2002;Durden, 2005;Stolen et al., 2007;Bechdel et al., 2009;Stolen et al., 2013) and indirectly (e.g., introduction of marine contaminants) Fair et al., 2010) impacted by human activities. As a long-lived top-level predator, IRL dolphins are exposed to and accumulate persistent pollutants that may increase their susceptibility to disease (Fair & Becker, 2000). ...
... Given that a single community of dolphins occupies a large portion of these two basins (Titcomb et al., 2015), the impacts of both ecological disturbances and reoccurring mortality events on this community warrants further investigation. Furthermore, while the impacts of indirect anthropogenic activities are not well understood, IRL dolphins face significant direct threats from injury and mortality associated with recreational and commercial fishing gear (Noke & Odell, 2002;Stolen et al., 2013). Likewise, high concentrations of mercury, and papilloma and skin disease presence are causes for concern regarding the health of this population (Caldwell et al., 1975;Reif et al., 2006;Durden et al., 2007Durden et al., , 2009Bossart, 2007;Murdoch et al., 2008). ...
Systematic long-term monitoring of abundance and distribution is essential to management and conservation and necessary to assess mortality trends and anthropogenic impacts for cetacean stock assessment. Line-transect aerial surveys (n = 42) were conducted to assess bottlenose dol-phin (Tursiops truncatus) abundance, distribu-tion, and group composition in the Indian River Lagoon (IRL) estuary system, Florida, from 2005 to 2011. Multiple covariate distance sampling was used to estimate abundance, and experimental trials were utilized to estimate dolphin availabil-ity. Abundance estimates varied seasonally, rang-ing between 483 (95% CI = 345 to 672; summer 2008) and 1,947 dolphins (95% CI = 1,198 to 2,590; winter 2009-2010), with a mean abun-dance of 1,032 dolphins (95% CI = 809 to 1,255). The largest abundance estimates for IRL dolphins occurred during extremely cold winter events, suggesting seasonal changes may influence dol-phin movements. Mean visibility depth (125.14 ± 38.29 cm) suggested the availability bias did not largely influence estimates of dolphins in this shallow estuary when surveys are conducted under optimal sighting conditions. However, there was some evidence of seasonal changes in avail-ability that may influence abundance estimation, and this should be further investigated. Seasonal trends and corresponding genetic and movement data suggest Mosquito Lagoon may be a disjunct community from the IRL proper. This study pro-vides abundance data to assess the IRL bottle-nose dolphin stock prior to the largest Unusual Mortality Event on record for this population, which occurred in 2013.
... Depredation by a predator is the act of stealing or damaging a prey item already captured by some other process (Zollett and Read 2006). Depredation of commercial and recreational fishing gear by cetaceans is a growing problem around the world and has been documented in areas such as Australia, the Pacific Ocean, southern Brazil, the Mediterranean Sea, and the eastern United States (Broadhurst 1998, Secchi and Vaske 1998, Donoghue et al. 2002, Noke and Odell 2002, SPREP 2002, Cox et al. 2003, Lauriano et al. 2004, Brotons et al. 2008, and Sigler et al. 2008. Long-line fisheries depredation by larger odontocetes has recently been recognized as increasing in frequency, geographic extent, and severity (Read 2008). ...
... Depredation of commercial and recreational fishing gear by cetaceans is a growing problem around the world (Broadhurst 1998, Secchi and Vaske 1998, Noke and Odell 2002, Somoa 2002, Cox et al. 2003, Lauriano et al. 2004, Brotons et al. 2008, and Sigler et al. 2008. Long-line fisheries depredation by larger odontocetes has recently been recognized as increasing in frequency, geographic extent, and severity (Read 2008). ...
Typical depredation behavior by cetaceans involves stealing or damaging prey items already captured by recreational or commercial fishing gear. Depredation among cetaceans has been reported to be increasing in both severity and frequency globally. This behavior is of particular concern for small stocks of cetaceans since any interaction with fishing gear has the potential to injure or kill animals leading to unsustainable losses. In Florida, depredation became evident in 2006 when the number of bottlenose dolphin (Tursiops truncatus) strandings resulting from fishing gear ingestion or entanglement sharply increased. For the resident dolphin community in Sarasota Bay, modeling showed continued mortalities from recreational fishing gear interactions were not sustainable.
The major goals of this study were to 1.) characterize depredation and recreational angler interactions involving dolphins in Sarasota Bay, 2.) reduce dolphin-angler interactions through outreach, 3.) examine a case study to investigate the link between dolphin hearing loss and angler interaction behavior, 4.) test the effectiveness of passive acoustics in monitoring dolphin depredation at a fishing pier. Findings from this study provided a better understanding of depredation and angler interactions. Results indicated that dolphin-angler interactions in Sarasota Bay are increasing in frequency and are affecting an increasing number of dolphins, specifically adult males. Some dolphins in Sarasota Bay appear to utilize depredation as a foraging method (not just an opportunistic behavior) and were significantly more likely to be within 50 m of an active fishing line.
Depredation and angler interaction behavior appear to increase in times of prey depletion (such as during a red tide) and heightened angler fishing activity. Educational outreach using an informational card proved successful in a case study showing about a 30% reduction in dolphin provisioning rates. The case study of F201 offers preliminary evidence that hearing loss is linked to depredation behavior and death for wild dolphins. Also, by detecting echolocation clicks as a proxy for dolphin presence, passive acoustics showed potential as an inexpensive method for monitoring depredation in problematic areas. Conclusions from this study can be utilized by scientists and managers when assessing depredation rates for a cetacean community and implementing an action plan.
... The interaction between loggerhead sea turtles and the blue crab fishery is not the only example of negative impacts of protected species on commercial fisheries. Marine mammals, particularly bottlenose dolphins Tursiops truncatus, have been causing similar damage to crab pots in other regions (Noke and Odell 2002;NCDENR 2004). Researchers have tested methods of securing bait wells on the crab pots to deter tampering by bottlenose dolphins (Noke and Odell 2002), and managers have restricted the lengths of crab pot lines to avoid dolphin entanglements (NCDENR 2004). ...
... Marine mammals, particularly bottlenose dolphins Tursiops truncatus, have been causing similar damage to crab pots in other regions (Noke and Odell 2002;NCDENR 2004). Researchers have tested methods of securing bait wells on the crab pots to deter tampering by bottlenose dolphins (Noke and Odell 2002), and managers have restricted the lengths of crab pot lines to avoid dolphin entanglements (NCDENR 2004). ...
North Carolina's fishery for the blue crab Callinectes sapidus is experiencing problems with gear damage during the summer season. Individuals of a protected species, the loggerhead sea turtle Caretta caretta, are the likely culprits of crab pot damage, bait theft, and reduced crab catch, perhaps with important economic impacts. In summer 2005, we conducted a fishing study in cooperation with a pair of crabbers operating one commercial blue crab boat in Core Sound, North Carolina, to characterize location, timing, and extent of damage to crab pots. We examined spatial and temporal overlap of fishing activity with loggerhead sea turtle sightings and quantified blue crab catch. Eighty-seven percent of pots were damaged throughout the course of the study, and gear damage peaked in late June to early July. We measured a 40% reduction in blue crab catch in crab pots that were damaged. Loggerhead sea turtle sightings were consistent with areas of high gear damage. Our results should be considered by managers, who may be able to guide crabbers to concentrate fishing effort at times and areas of reduced overlap with loggerhead sea turtles so as to minimize damage.
... Dolphins inhabiting estuaries are particularly vulnerable to cumulative stressors as these habitats are highly dynamic in which drastic changes in water temperature and salinity can be physiologically challenging to dolphins [13,14]. Further, estuaries are prone to higher anthropogenic activity than offshore waters, which increases the likelihood of dolphins being exposed to stressors such as vessel strikes [15,16], fishery entanglements [17], point and non-point source contaminants [18], and disease [19]. Therefore, knowledge of the spatial distribution and habitat preferences of dolphins within estuarine environments is necessary for continued management and conservation efforts. ...
The Charleston Estuarine System Stock (CESS) of Tamanend’s bottlenose dolphins (Tursiops erebennus) exhibit long-term site fidelity to the Charleston Harbor, and the Ashley, Cooper, and Wando Rivers in Charleston, South Carolina, USA. In the Cooper River, dolphins have been irregularly sighted in upper regions where salinity levels are below what is considered preferred dolphin habitat. We conducted unoccupied aerial system (UAS) surveys in high-salinity (>15 parts per thousand) and low-salinity (<15 parts per thousand) regions (n = 8 sites) of the Cooper River and surrounding waters to assess dolphin distribution in terms presence/absence, detection rate, abundance, and density. We also assessed the influence of ecological factors (salinity, water temperature, season, and prey availability) on dolphin distribution. Dolphins were detected at five sites, with higher salinity and water temperature being significant predictors of presence and abundance. Dolphins were detected year-round across high-salinity sites, and were infrequently detected in low-salinity sites during months with warmer water temperatures. The results from this study contribute to the overall understanding of dolphin distribution across various habitats within the Charleston Estuary System and the potential drivers for their movement into low-salinity waters.
... There are reports of entanglement from fishing and aquaculture gear across a range of bird and mammal species in net structures and discarded gear (Lloyd, 2003). Many reports also relate to interactions with human intervention, such as dolphins becoming entangled whilst stealing bait in crab fisheries (Noke and Odell, 2002), or seals attempting to gain access to fin fish installations (Pemberton and others, 1991). However, there are a lack of data that scientifically reports negative entanglements (i.e. ...
Seaweed production in England and Wales is an emerging industry. The aim of this contract was to increase understanding of the methods used for mechanised harvesting and seaweed aquaculture, potential environmental effects or impacts, potential management measures, and to develop recommendations for best practices.
... Recent studies have documented diminished health in IRL dolphins including high concentrations of mercury [40], lingual and genital papillomas [41], and skin disease (lacaziosis) [42,43]. Moreover, interactions with both commercial and recreational fisheries account for up to 12% of the annual mortality [8,44]. ...
Common bottlenose dolphins (Tursiops truncatus truncatus) inhabiting the Indian River Lagoon (IRL) estuarine system along the east coast of Florida are impacted by anthropogenic activities and have had multiple unexplained mortality events. Given this, managers need precise estimates of demographic and abundance parameters. Mark-recapture photo-identification boat-based surveys following a Robust Design were used to estimate abundance, adult survival, and temporary emigration for the IRL estuarine system stock of bottlenose dolphins. Models allowed for temporary emigration and included a parameter (time since first capture) to assess evidence for transient individuals. Surveys (n = 135) were conducted along predetermined contour and transect lines throughout the entire IRL (2016–2017). The best fitting model allowed survival to differ for residents and transients and to vary by primary period, detection to vary by secondary session, and did not include temporary emigration. Dolphin abundance was estimated from 981 (95% CI: 882–1,090) in winter to 1,078 (95% CI: 968–1,201) in summer with a mean of 1,032 (95% CI: 969–1,098). Model averaged seasonal survival rate for marked residents was 0.85–1.00. Capture probability was 0.20 to 0.42 during secondary sessions and the transient rate was estimated as 0.06 to 0.07. This study is the first Robust Design mark-recapture survey to estimate abundance for IRL dolphins and provides population estimates to improve future survey design, as well as an example of data simulation to validate and optimize sampling design. Transients likely included individuals with home ranges extending north of the IRL requiring further assessment of stock delineation. Results were similar to prior abundance estimates from line-transect aerial surveys suggesting population stability over the last decade. These results will enable managers to evaluate the impact of fisheries-related takes and provide baseline demographic parameters for the IRL dolphin population which contends with anthropogenic impacts and repeated mortality events.
... High spatial density of fishing equipment and low selectivity of gear, as well as discarding practices, were described as acting as attractants for large predators (Gilman, 2007;Nishida & Tanio, 2001;Noke & Odell, 2002;Pardalou & Tsikliras, 2018;Reyes, Hucke-Gaete, & Torres-Florez, 2013;Rocklin et al., 2009). Predictability strongly influences the likelihood of predators feeding on human subsidies (Oro, Genovart, Tavecchia, Fowler, & Martínez-Abraín, 2013). ...
The sustainable mitigation of human–wildlife conflicts has become a major societal and environmental challenge globally. Among these conflicts, large marine predators feeding on fisheries catches, a behaviour termed “depredation,” has emerged concomitantly with the expansion of the world’s fisheries. Depredation poses threats to both the socio‐economic viability of fisheries and species conservation, stressing the need for mitigation. This review synthesizes the extent and socio‐ecological impacts of depredation by sharks and marine mammals across the world, and the various approaches used to minimize it. Depredation was reported in 214 fisheries between 1979 and 2019 (70% post‐2000) and affected fleets from 44 countries, in all sectors (commercial, artisanal and recreational), and in all major fishing techniques (nets, traps and hook‐and‐lines). A total of 68 predator species were involved in depredation (20 odontocetes, 21 pinnipeds and 27 sharks), and most (73%) were subject to either by‐catch and/or retaliatory killing from fishers when interacting with gear. Impacts on fishers were primarily associated with catch losses and gear damage but often lacked assessments. Deterrence was a major mitigation approach but also the least effective. Gear modifications or behavioural adaptation by fishers were more promising. This review highlights the need for improved monitoring, and interdisciplinary and integrated research to quantify the determinants and impacts of depredation in the socio‐ecological dimension. More importantly, as the conflict is likely to escalate, efforts directed towards changing perceptions and integrating knowledge through adaptive co‐management are raised as key directions towards coexistence between fisheries and large marine predators.
... However, increasing demand for fish in the market with growing human population caused depleting fish population for aquatic mammals as well as for humans. The increasing fishing pressure results in the by-catch mortality and injury of the aquatic mammals and becoming the most significant issue of conservation of these animals (Mitchell, 1975;Woodley and Lavigne, 1991;Perinet al., 1994;Broadhurst, 1998;Secchi and Vaske, 1998;Read et al., 1998;Donoghue et al., 2002;Noke and Odell, 2002;Cox et al., 2004;Laurianoet al., 2004;Read et al., 2006;Brotonset al., 2008;Read, 2005;Sigler et al., 2008;Read, 2008). Hall (1996) defined it in a more negative connotation for the fishers or environmentalists, who says 'it is that part of the capture that is discarded in the water, dead (or injured to the extent that death is the result).' ...
The growing need for fish extraction for livelihood is resulting in the by-catch mortality and injury of the aquatic mammals through fishing gear entanglement. It is one of the most significant issues of conservation of Ganges Dolphin. The inability of Ganges dolphins to identify the presence of monofilament gill nets results in entanglement and death due to suffocation. In this study, the interactions of Ganges dolphin with fishing gear (Gill net) by attaching Pingers have been investigated. It was assumed that the proximity zone around the fishing gear is the risk zone for the Ganges dolphin. Visual observation was made in an experimental set up of Control Net (Without reflectors or Pingers), Net with reflectors (used locally to attract fish), Pinger with frequency and source-level lower than what is used by Ganges dolphins (10KHz and 132 decibels) and Pingers with Ganges dolphin frequency (70KHz and 145 decibels). A significant difference in mean sighting distance of Ganges dolphins from different experimental setups has been estimated. The nearest proximity in the control net was <1m with a sighting rate of 1.41 sightings/hr whereas for Dolphin Pingers it was 5 to 10m with a sighting rate of 0.12 sightings/hr. Dolphins seem to avoid fishing gear with active Pingers and hence the experiment was to be carried forward to the next level of estimation for determining whether there was an attraction or change in catch per unit effort (CPUE) of fish or habituation of dolphin. Popularising the efficiency of Pingers among management stakeholders and introducing it to the fisher communities can be the next significant step to conserve the species.
... A majority of the cases represent offshore activities and debris (e.g. pelagic ghost nets, longline by-catch, plastics ingestion by ocean-faring seabirds), but entanglement in and ingestion of marine debris in the coastal and estuarine environment also threatens estuarine species, such as locally resident populations of bottlenose dolphins (Noke & O'Dell 2002, Wells et al. 2008, as well as estuarine and coastal habitats (Uhrin & Schellinger 2011). Manatees are primarily estuarine residents (but utilize freshwater and nearshore environments as well) and thus are subject to harm from active or lost fishing gear and other marine debris, and may serve as a 'sentinel' species for marine debris issues in the coastal and estuarine environment (sensu Bonde et al. 2004). ...
Entanglement in and ingestion of marine debris by marine life has become a re -
cognized threat worldwide, and the endangered Florida manatee is no exception. Manatees are
known to become entangled in various types of fishing gear and other marine debris, and foreign
objects are often found in the gastrointestinal tract of dead manatees. We examined a 20 yr dataset
(1993 to 2012) of manatee rescue and necropsy records for evidence of entanglement in or ingestion
of marine debris. In over 6500 manatee necropsy reports, over 11% either had ingested or
showed evidence of entanglement in marine debris (or both). Fifty manatees died as a direct result
of either entanglement in or, most commonly, ingestion of marine debris; fishery-related gear was
involved in over 70% of these cases. With respect to live manatee rescues (n = 1244), over 25%
were related to entanglement in or ingestion of fishery gear or marine debris, making entanglement
the top anthropogenic reason for rescue during this time. Fishing gear, primarily trap lines
and monofilament fishing lines, was a factor in over 85% of these rescues. Female manatees in
particular were disproportionally affected by marine debris. The Florida manatee represents an
example of estuarine fauna that is subject to harm from marine debris, and continued efforts to
reduce and remove marine debris from estuarine environments will benefit manatees and other
estuarine species.
... Dolphins have actually learned to exploit catches from fishing operations as a new food source (Reeves et al., 2001); they remove fish directly from nets, resulting in a loss of fish for fishers and damage to nets. However, consequences of dolphin interactions with fishing activities have often been neglected (Noke and Odell, 2002), although negative impacts on fisheries have already been reported from Morocco (Zahri et al., 2004), Sardinia (Lauriano et al., 2004;Díaz-López, 2006), and the Balearic Islands (Brotons et al., 2008). ...
... Provisioning dolphins conditions them to approaching humans and boats for food where they may then attempt to aggressively prey on hooked bait and catches, creating conflicts with fishermen (Zollett and Read, 2006;Read, 2008). Depredation of both commercial and recreational fisheries is a growing problem globally (Noke and Odell, 2002;Brotons et al., 2008;Powell and Wells, 2011). In addition, activities that bring dolphins into close proximity with fishing gear have the potential to seriously injure or kill the animals through ingestion, entanglement, or even vessel strikes (Zollett and Read, 2006;Read, 2008;Wells et al., 2008;Barco et al., 2010;Powell and Wells, 2011;Stolen et al., 2013). ...
The panhandle region of the Gulf of Mexico is known by scientists, regulatory agencies and conservation organizations as a “hotbed” area of dolphin harassment. Interactions between humans and wild dolphins routinely occur through close vessel approaches or through direct contact associated with commercial or recreational fisheries, swim-with, or feeding activities. Such interactions are of serious concern for wild dolphin welfare and conservation under the U.S. Marine Mammal Protection Act, as well as for human safety. In recent years, an alarming number of dolphins in this region have been fatally wounded by gunshot, hunting arrows, or sharp tools (i.e., screwdriver). The potential to mitigate the detrimental impacts resulting from these human-dolphin encounters requires a comprehensive outreach strategy to address increasing incidents of harassment and vandalism, as well as an evaluation of the serious trends and challenges hampering dolphin protection in this region. In addition to the identification and conviction of perpetrators through the application of existing law, voluntary outreach programs offer real potential to educate and reform public attitudes and behaviors through community-based stewardship initiatives, which can foster dolphin protection in areas of high human-dolphin conflict. The development of these types of programs underlines the potential for non-regulatory approaches to serve as an effective means to reach and activate the public on some of the most pressing local and regional marine conservation issues. In tandem with regulations and enforcement, voluntary stewardship programs can provide stakeholders an opportunity to engage in local dolphin conservation efforts through a positive approach aimed to inspire accountability.
... There are many examples of cetaceans interacting with fishers or tourists in novel ways to obtain food. For example, dolphins and whales in numerous locations depredate long-lines (Ashford, Rubilar, & Martin, 1996;Hamer, Childerhouse, & Gales, 2012;Nolan, Liddle, & Elliot, 2000;Purves, Agnew, & Balguerias, 2004;Visser, 2000;Yano & Dahlheim, 1995), steal prey from traps or fish farms (Kemper et al., 2003;Noke & Odell, 2002), and follow trawlers or trammel nets in hopes of consuming stray prey or discards (Chilvers & Corkeron, 2001;Gonzalvo, Valls, Cardona, & Aguilar, 2008;Jefferson, 2000;Leatherwood, 1975;Pennino, Mendoza, Pira, Floris, & Rotta, 2013). In many cases these behaviors start out at low frequency, but rapidly spread to the rest of the population, possibly indicating an initial innovation event and its subsequent social transmission among sympatric cultural units or clusters (e.g., Chilvers & Corkeron 2001;Donaldson, Finn, Bejder, Lusseau, & Calver, 2012;Fearnbach et al., 2013;Whitehead et al., 2004). ...
In this chapter, we explore examples of novel, unusual, and atypical behavior by both wild and captive whales and dolphins in an effort to inform our understanding of cetacean innovative and creative abilities. While innovative and perhaps creative behavior occurs in a variety of contexts for both suborders, far more examples have been observed in odontocetes than mysticetes, which may be due to differences in ecology, morphology, life history, and/or cognitive ability, or simply reflect biases in the available data. In comparison to other taxa, data from cetacean research is less complete, but does provide important comparative insights into who innovates and why.
... Results suggest that special attention be paid to bottom-set lines of traps in studies of small cetaceans that feed demersally. Similar gear have only rarely been noted as a risk for cetacean bycatch in the wider literature (Noke and Odell 2002, Burdett and McFee 2004, Johnson et al. 2005, McFee et al. 2006, Song et al. 2010. ...
Addressing the urgent conservation threat of marine mammal bycatch in small-scale fisheries requires information on bycatch magnitude, gear types, population impacts, and risk. However, data on these proximate attributes are widely lacking in developing countries. This study used a multi-methods approach integrating boat surveys and interviews with fishermen (n = 526) to assess proximate attributes of bycatch for the Critically Endangered subpopulation of Irrawaddy dolphins (Orcaella brevirostris) in Malampaya Sound, Philippines. Given an updated population estimate of 35 individuals (CV = 22.9%), the estimated rate of bycatch fatalities exceeds the potential biological removal rate. Spatial overlap scores were calculated to characterize overlap between dolphins and fisheries as a proxy of bycatch risk. These scores identified particularly high risk areas that could be prioritized for gear bans. However, completely reducing bycatch risk would require more widespread bans beyond these high risk areas. Implementing gear restrictions will be immensely challenging, given serious obstacles to fisheries management at this site. The multi-methods approach describes the urgency of the bycatch problem and the changes required for mitigation, setting the stage for identifying and evaluating potential solutions. It can be readily applied to developing country sites to guide more efficient and complete data collection and conservation efforts.
... The threat of entanglement could potentially be reduced through the use of alternative seaweed farming methods that do not employ ropes (see Titlyanov & Titlyanova, 2010). Mortalities of small cetaceans through entrapment in static underwater structures have been occasionally noted in the past (e.g., Noke & Odell, 2002;Díaz López & Bernal Shirai, 2007). ...
Dugongs (Dugong dugon) are threatened by inci-dental capture in small-scale fisheries, but other static underwater structures could present a simi-lar entanglement risk. In December 2013, an adult male dugong was entangled in the ropes of a sea-weed farm in Busuanga, Palawan, Philippines, and drowned. Anecdotal reports of similar incidents suggest that this was not an isolated occurrence. Given that dugong populations are slow to repro-duce and cannot sustain even low levels of mortal-ity, effective marine spatial planning is essential to minimize overlap between dugong habitat and mariculture operations.
... Dolphins have now learned to consider catches of fishing operations as a new food resource (Reeves et al., 2001); they remove fish directly from nets, resulting in a loss of fish for fishers and damage to nets. The consequences of dolphin interactions with fishing activities, however, have often been neglected ( Noke and Odell, 2002), although negative impacts on fisheries have already been reported from Morocco ( Zahri et al., 2004), Sardinia ( Díaz-Ló pez, 2006), and the Balearic Islands ( Brotons et al., 2008). ...
These last decades have been characterized by a great development of fishing techniques, contributing to the overexploitation of numerous marine fish stocks. In order to limit this collapse and to restore impacted communities, the implementation of management measures was necessary. Marine Protected Areas (MPAs), initially developed to protect remarkable habitats and associated biodiversity, are more and more used as a tool for spatial management of fishing activities, by adult export and/or larvae migrations from protected zones to surrounding fisheries. The aim of this PhD was to use indicators and predictive models for evaluating the impact of the Bonifacio Strait Natural Reserve (Corsica) implementation on fish communities and the benefits of such management measures for the local artisanal fishery. Artisanal fishery catch data from south Corsica has permitted to highlight the indirect impact of recreational fishing on exploited fish communities structure and biomass. Although a decrease in fishing effort may contribute to increasing catches per unit effort (CPUE), the analysis using response groups helped us to reveal a distinct increase in the artisanal fishery
catches for target species of spearfishing. We then developed a model and tested management scenarios for maintaining the spiny lobster resource, in decline in the reserve, into a sustainable exploitation way. Our results show that even if the BSNR legislation represents a benefit for many species, it is not sufficient to allow for the recovery of the red spiny lobster. Indicators issued from the ISIS-Fish model showed that higher restrictions on this resource access are necessary. After comparing various management measures, it appeared that the best compromise should be to authorize lobster nets use only during the summer season (July and August), for limiting the collapse of the population while offering a long term benefit for fishers, in the objective of sustainable fisheries.
... However, mortality due to entan-glement in fishing gears such as gillnets, trawls and crab pots is the main threat to the survival of many of these populations (e.g. Noke & Odell 2002, Díaz López 2006, Gonzalvo et al. 2008. In recent years there have been increased efforts to investigate the impact of fisheries on cetaceans and how to mitigate it (e.g. Brown et al. 2013, Stolen et al. 2013, Waples et al. 2013. ...
Many anthropogenic actions have an impact on coastal dolphins, with bycatch being one of the main threats. We describe the distribution patterns of common bottlenose dolphins Tursiops truncatus and periods of higher entanglement risk by the artisanal gillnet fishery in the Patos Lagoon estuary and along the adjacent coast of southern Brazil. A total of 136 dolphin groups and 187 gillnets were encountered in 69 surveys conducted between September 2006 and July 2009. Data were analyzed in relation to environmental, spatial and temporal variables using generalized additive models and a spatially adaptive local smoothing algorithm for model selection. In both areas, dolphin densities increased as distance to the estuary mouth decreased. For the estuary area, water salinity and temperature influenced dolphin distribution. Along the adjacent coast, dolphin densities were higher with distance to shore as well as in the north area during the warm period. Patterns of dolphin distribution were probably a response to the presence of preferred prey or avoidance of human-related disturbance. Kernel density showed that fishing effort was distributed along the entire surveyed area inside the estuary, while along the adjacent coast it was higher in the south compared to the north area in the warm period. The overlap between gillnets and dolphins increased considerably from the cold (33.8%) to the warm (48.6%) period. Seasonal variation in fishing effort and distribution affect the overlap and the risk of dolphin entanglement. Based on the findings of this study, a fishing exclusion area aimed at reducing bycatch was established by the Brazilian Environmental Agency.
... Elevated mercury concentrations in IRL dolphins are associated with disturbances of multiple hepatic, renal, endocrine, and hematological parameters suggesting deleterious health effects (Schaefer et al. 2011). Additionally, other anthropogenic factors in the IRL and CHS, such as increased recreational boating and fishery-related interactions (Noke & Odell 2002, Burdett & McFee 2004, may play a role in the nonspecific dermatitides observed. Furthermore, past studies indicate that the IRL dolphin population, in particular, is impacted by complex infectious or inflammatory diseases often associated with concurrent immunologic perturbations (Reif et al. 2006, 2013, Bossart et al. 2010, 2011, Goldstein et al. 2012. ...
Mucocutaneous lesions were biopsied from free-ranging Atlantic bottlenose dolphins Tursiops truncatus inhabiting the Indian River Lagoon (IRL), Florida, and estuarine waters of Charleston (CHS), South Carolina, USA, between 2003 and 2013. A total of 78 incisional biopsies from 58 dolphins (n = 43 IRL, n = 15 CHS) were examined. Thirteen dolphins had 2 lesions biopsied at the same examination, and 6 dolphins were re-examined and re-biopsied at time intervals varying from 1 to 8 yr. Biopsy sites included the skin (n = 47), tongue (n = 2), and genital mucosa (n = 29). Pathologic diagnoses were: orogenital sessile papilloma (39.7%), cutaneous lobomycosis (16.7%), tattoo skin disease (TSD; 15.4%), nonspecific chronic to chronic-active dermatitis (15.4%), and epidermal hyperplasia (12.8%). Pathologic diagnoses from dolphins with 2 lesions were predominately orogenital sessile papillomas (n = 9) with nonspecific chronic to chronic-active dermatitis (n = 4), TSD (n = 3), lobomycosis (n = 1), and epidermal hyperplasia (n = 1). Persistent pathologic diagnoses from the same dolphins re-examined and re-biopsied at different times included genital sessile papillomas (n = 3), lobomycosis (n = 2), and nonspecific dermatitis (n = 2). This is the first study documenting the various types, combined prevalence, and progression of mucocutaneous lesions in dolphins from the southeastern USA. The data support other published findings describing the health patterns in dolphins from these geographic regions. Potential health impacts related to the observed suite of lesions are important for the IRL and CHS dolphin populations, since previous studies have indicated that both populations are affected by complex infectious diseases often associated with immunologic disturbances and anthropogenic contaminants.
... In addition to protecting dolphins, predictive models could also help fisherman avoid interactions with nuisance dolphins. Dolphins have been responsible for reductions in catch per unit effort in many areas (Noke and Odell, 2002;Read, 2008). Access to predictive maps could reduce the potential for these interactions, which could ultimately enhance the economic vitality of fisheries. ...
Spatial distribution models (SDMs) have been useful for improving management of species of concern in many areas. This study was designed to model the spatial distribution of bottlenose dolphins among seasons of the year in the Mississippi Sound within the northern Gulf of Mexico.
Models were constructed by integrating presence locations of dolphins acquired from line‐transect sampling from 2011–2013 with maps of environmental conditions for the region to generate a likelihood of dolphin occurrence for winter (January–March), spring (April–June), summer (July–September), and autumn (October–December) using maximum entropy.
Models were successfully generated using the program MaxEnt and had high predictive capacity for all seasons (AUC (area under curve) > 0.8). Distinct seasonal shifts in spatial distribution were evident including increased predicted occurrence in deepwater habitats during the winter, limited predicted occurrence in the western Mississippi Sound in winter and spring, widespread predicted occurrence over the entire region during summer, and a distinct westward shift of predicted occurrence in autumn.
The most important environmental predictors used in SDMs were distance to shore, salinity, and nitrates, but variable importance differed considerably among seasons.
Geographic shifts in predicted occurrence probably reflect both direct effects of changing environmental conditions and subsequent changes in prey availability and foraging efficiency.
Overall, seasonal models helped to identify preferred habitats for dolphins among seasons of the year and can be used to inform management of this protected species in the northern Gulf of Mexico.
Copyright © 2015 John Wiley & Sons, Ltd.
... Cetaceans may also feed on fi sh that are ancillary to the catch, as in the case of bottlenose dolphins feeding on bycatch from trawl fi sheries for shrimp and prawn ( Fertl and Leatherwood, 1997 ). Whales and dolphins may interfere with traps or pots ( Fig. 3 ), such as bottlenose dolphins in the Indian River Lagoon in Florida interacting with the crab pot fi shery, apparently to steal bait fi sh ( Noke and Odell, 2002 ). ...
Marine mammal interactions with fisheries may be characterized as biological (ecological) or operational. Interference with fisheries might negatively affect fisheries by resulting in loss of bait, damage to fishing gear, decreased catches, reduced fish weight (in the case of fish farms), or increased time spent during fishing operations. Difficult to assess is hidden damage, i.e., the amount of fish wholly removed from nets without a trace and the catch losses due to the presence of marine mammals. Fishing operations concentrate food of interest, decreasing energy expenditure associated with foraging by marine mammals. Nursing females may especially benefit from this feeding technique. Fishing operations may permit marine mammals to select food of higher caloric value. Some food niches, not otherwise available to some marine mammals, may be opened up; making prey easier to access that might be normally more difficult.
... Depredation of fisheries by bottlenose dolphins has been studied at numerous other locations. The greatest impacts are typically those involving gill net fisheries (Cox et al. 2003, Read 2005, Read et al. 2003b), but there have been studies on depredation of long-line, crab pot, trammel net, trolling, and recreational pier fishing as well (Kobayashi and Kawamoto 1995, Bearzi et al. 2008, Donoghue et al. 2003, Noke and Odell 2002, Lauriano et al. 2004, Zollett and Read 2004, Powell and Wells 2011. The impact to dolphins as well as the affected fishery was usually negative. ...
Bottlenose dolphins (Tursiops truncatus) inhabit coastal and estuarine habitats across the globe. Well-studied dolphin communities thrive in some peninsular Florida bays, but less is known about dolphins in the Florida panhandle where coastal development, storms, algal blooms, fishery interactions, and catastrophic pollution have severely impacted their populations. Dolphins can react to disturbance and environmental stressors by modifying their movements and habitat use, which may put them in jeopardy of conflict with humans. Fishery interaction (FI) plays an increasing role in contributing to dolphin mortalities.
I investigated dolphin movements, habitat use, residency patterns, and frequency of FI with sport fishing. Dolphins were tracked using radio tags and archival data loggers to determine fine-scale swimming, daily travels, and foraging activity. Dolphin abundance, site fidelity, ranging, stranding mortality, and community structure was characterized at Choctawhatchee and Pensacola Bays in the Florida Panhandle via small boat surveying and photo-identification. Reported increases in dolphin interactions with sport anglers were assessed at deep sea reefs and coastal fishing piers near Destin, FL and Orange Beach, AL. Results from these studies yield insights into the ranging and foraging patterns of bottlenose dolphins, and increase our knowledge of them in the northern Gulf of Mexico.
Dolphins were tagged with short-term Trac Pac tags (N=23) and bolt on radio-tags (N=5) during 1995-2007. Swim speeds averaged 1.6 m/s (±0.43 SD), which agreed with the predicted mean cost of transport. On average, 48% of their day was spent transiting between habitats. Swimming and activity rates did not vary significantly with time of day/night. Foraging and social interactions constituted 39% of their day. Increased foraging was detected by stomach temperature changes that revealed dolphins fed during daylight, but also at night with a peak starting just after sunset. Tagged dolphins exhibited behaviors suggesting ‘sleep’ during slow speed swimming, which represented 15% of their day on average. Dolphins made daily movements beyond their expected core area, heading up river tributaries, and to the open sea.
Surveys in Choctawhatchee Bay began in 2006 and later expanded to include Pensacola Bay in 2010 following concern of dolphin mortalities in concert with the Deepwater Horizon spill and two extremely cold winters. Photo-identification revealed dolphins moved frequently between the bays. Of 655 individuals identified in 2010-11, 22% were seen during all seasons, with highest abundance in the fall. Resident dolphins showed site fidelity to specific areas (42%) or traveled between parts of the bays (58%). Three communities of dolphins were identified from stable isotope analysis and photo-id: 1) tidal inlet associated, 2) estuarine specific, and 3) river delta associated. Dolphins traveled over 70 km via the near-shore Gulf between the inlets, and through the inshore waterways. The findings suggest dolphin communities in these bays overlap and many dolphins had a high probability of oil exposure in 2010.
I observed sport fishing trips to assess frequency and nature of FI over 28 months. FI was seen at 18% of fishing reef spots. Scavenging of discarded fish was seen most often, while depredation of catch occurred in 40% of FI observations. Of 103 dolphins identified on offshore reefs, 13% were encountered repeatedly. At coastal fishing piers, dolphins came within 100 m on 42% of visits, while FI was seen on 17% of visits. Most dolphins at the fishing piers were known inlet and estuarine residents, while offshore reef dolphins were never seen near the beach. This indicates that discrete communities are involved. Harmful interactions with dolphins on reefs and at fishing piers negatively affect these resident communities. Mitigation of FI is suggested by use of avoidance strategies, gear modifications, and improved fish release practices.
... dolphins), which are more vulnerable to bycatch in nets than to entanglement due to their smaller size. Entanglement records involving a range of dolphin species do, however, exist, from different areas including the south-eastern U.S.A. (bottlenose dolphins [Tursiops truncatus]; Noke and Odell, 2002; McFee et al., 2006), Brazil (tucuxis [Sotalia guianensis]; Azevedo et al., 2008), and Taiwan (Indo-Pacific humpback dolphins [Sousa chinensis]; Ross et al., 2010). These cases are typically associated with ropes from fishing gears. ...
... The data suggest that these modifications could counteract increasing interactions between loggerhead sea turtles and the blue crab fishery, allowing crabbers to continue fishing through the summer months. These modifica- tions may also help crabbers in other areas who are experiencing similar gear damage by marine mammals (NOAA Fisheries 2001;Noke and Odell 2002). ...
Loggerhead sea turtles Caretta caretta have been found to damage crab pots and reduce catch of blue crabs Callinectes sapidus in North Carolina sounds. In response, crabbers have avoided fishing at locations and times of peak loggerhead sea turtle activity and have experimented with modifications to make their gear more robust. We field tested a new, lightweight, and inexpensive modification: self-righting floats tethered to the inside of the crab pots. Thirty pairs of regular and modified pots were fished between 16 June and 31 July 2006. Damage by loggerhead sea turtles was found in 38% of all replicates, and blue crab catch was 57% lower in crab pots that had been discovered by loggerhead sea turtles. The float modification effectively reduced damage, but stronger effects were found when using plastic bait-well covers that the crabbers had introduced. The modified pots were significantly less damaged (average damage index [ADI] = 1.38 with plastic covers and 2.01 with cardboard covers) than regular pots (ADI = 1.78 with plastic covers and 2.38 with cardboard covers). Average blue crab catch was significantly higher in pots with plastic bait-well covers (15 crabs/modified pot, 18 crabs/regular pot) than in pots with cardboard covers (13 crabs/modified pot, 11 crabs/regular pot). However, there was a significant interaction of pot type with bait-well cover type. When plastic covers were used, average blue crab catch was higher in regular pots (18 crabs/pot) than in modified pots (15 crabs/pot). The opposite case was observed when cardboard covers were used: catch was higher in modified pots (13 crabs/pot) than in regular pots (11 crabs/pot). A drawback to the float modification was a qualitative increase in pot drift and loss in high winds, resulting in the need for costly retrieval measures; crab pot loss may also jeopardize estuarine species that become trapped in derelict gear. Adopting these techniques, however, may help crabbers reduce gear damage, catch loss, and negative interactions with loggerhead sea turtles in this fishery.
... Bottlenose dolphins inhabiting the IRL estuarine system are impacted by several factors that warrant an improved understanding of the population. IRL dolphins may be directly (e.g., boat strikes and fishing gear entanglement) (Noke & Odell, 2002;Durden, 2005;Stolen et al., 2007;Bechdel et al., 2009) and indirectly (e.g., introduction of marine contaminants) ( Durden et al., 2007;Fair et al., 2010) impacted by human activities. As a long-lived toplevel predator, IRL dolphins are exposed to and accumulate persistent pollutants ( Durden et al., 2007) that may increase their susceptibility to disease (Fair & Becker, 2000). ...
Information on the abundance and distribution of cetaceans is essential to management and conservation and necessary to assess mortality trends and anthropogenic impacts for stock assessment. Line-transect aerial surveys (n = 45) were conducted to assess bottlenose dolphin (Tursiops truncatus) abundance, distribution, and group composition in the Indian River Lagoon (IRL) estuary system, Florida, from 2002 to 2004. Calves composed 9.41% of all known age class animals sighted. Multiple covariate distance sampling was used to estimate abundance. Abundance estimates varied seasonally, ranging between 362 (95% CI = 192 to 622; summer 2003) and 1,316 dolphins (95% CI = 795 to 2,061; winter 2002-2003), with a mean abundance of 662 dolphins (95% CI = 544 to 842). Abundance estimates for the Mosquito Lagoon sub-basin exhibited the greatest seasonal variability. Seasonal differences in abundance within strata suggest seasonal movement patterns. This study provides the first abundance estimate for IRL dolphins in over 30 y. Further studies that investigate evidence of influx/efflux are needed to better understand the population biology of IRL dolphins.
... Welded bars or netting placed in some pot traps to prevent pinnipeds or otters from entering them and preying on the target catch (such as eels). Bungee trap guards have also shown success at reducing bottlenose dolphin interactions with crab pots (Noke and Odell, 2002). ...
Unintended injuries and fatalities to non-target marine species—a major component of "bycatch"—is one of the principal threats to the survival of many endangered marine populations and species. This paper describes both proposed and existing fishing tech- niques for reducing non-target species bycatch, and reviews their focus across different fisheries and wildlife groups. The intent of this inventory was to gain a better understanding of the range of techniques available and to highlight priorities for research and develop- ment. In all, 55 techniques were identified, with the majority directed at reducing bycatch in longline fisheries, and intended to benefit primarily seabirds, sea turtles, and small mam- mals. Bycatch reduction is a dynamic field with many examples of effective techniques, though some underserved fisheries and wildlife groups should receive more attention.
... is the act of a predator stealing or damaging bait or prey item already captured by some other process (Zollett and Read 2006). Depredation of commercial and recreational fishing gear by cetaceans is a growing problem around the world (Broadhurst 1998, Secchi and Vaske 1998, Donoghue et al. 2002, Noke and Odell 2002, Cox et al. 2003, Lauriano et al. 2004, Brotons et al. 2008, Sigler et al. 2008). Longline fishery depredation by larger odontocetes has recently been recognized as increasing in frequency, geographic extent, and severity (Read 2008). ...
Abstract Odontocete depredation involves stealing or damaging bait or prey already captured by fishing gear. The increase in depredation is of concern for small stocks of cetaceans because interactions with fishing gear can lead to serious injury or mortality through entanglement or ingestion. Using long-term data sets available for the bottlenose dolphin (Tursiops truncatus) community in Sarasota Bay, Florida, we investigated recreational fishing gear interactions by (1) examining temporal patterns in depredation and associated behaviors from 2000 to 2007; (2) quantifying the behavior of dolphins that depredate or engage in associated behaviors; and (3) identifying factors associated with the rise in depredation locally. The number of incidents of dolphins (primarily adult males) interacting with recreational anglers and boaters increased following 2004. Depredation and associated behaviors increased during red tide lags and tourist seasons during times of prey depletion and heightened angler and boater activity. Dolphins with a history of fishing gear interactions shifted away from natural activity patterns and were more likely to be within 50 m of fishing lines. Recreational fishing gear interactions were attributed to a two percent population decline in Sarasota Bay in 2006 and need to be considered along with other cumulative human impacts in the development of conservation measures for dolphins.
The unintentional capture of non-target species, known as by-catch, and the subsequent release of unwanted catch back into the ocean, referred to as discards, pose significant challenges to marine biodiversity, ecosystem health, and the sustainability of fisheries worldwide. These issues are exacerbated by the wastage of valuable resources and the ecological impacts they cause. A range of solutions have been developed to address this problem, including advancements in fishing gear technology, regulatory measures, and ecosystem-based management methods. To effectively manage by-catch and discard, a multidisciplinary approach is essential, which includes scientific research, stakeholder engagement, and efficient governance mechanisms. This paper addresses the advancements in fishing gear technology, alongside strategic regulatory actions, and ecosystem-based management methods, which aim to reduce by-catch and discard issues, organisations working on this issue. These approaches aim not just to mitigate the ecological impacts but also to pave the way for a future where fisheries and marine ecosystems can thrive together.
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.
Traps (or pots) are one of the oldest and most widespread scientific survey gears for fish and decapod crustaceans around the world. Here, I review and synthesize the extensive scientific literature describing the various benefits and drawbacks of using traps as a survey gear in scientific studies. The widespread use of traps in fish and decapod surveys is due to several characteristics like their low cost, flexible design, ease of use, ability to fish unattended, and being amenable to pairing with other gears. However, there are a number of significant drawbacks of using traps, including highly variable catches due to environmental fluctuations or behavioral interactions or lost traps that continue catching and killing animals, that must be considered and accounted for when initiating trap surveys. This study highlights the types of habitats and species most and least suited for monitoring by traps, and emphasizes the importance of matching the goals and objectives of a trap survey with the correct trap design, mouth entrance, bait type, soak time, and pairing of gears. Pilot studies are also recommended before surveys are initiated to quantify the selectivity patterns of traps and identify the various factors that may influence trap catch.
Mortality patterns in cetaceans are critical to understanding population health. Common bottlenose dolphins (Tursiops truncatus truncatus) inhabiting the Indian River Lagoon (IRL), Florida have been subjected to four unusual mortality events (UMEs), highlighting the need to evaluate morbidity and mortality patterns. Complete gross examinations were conducted on 392 stranded dolphins and histopathological analyses were conducted for 178 animals (2002-2020). The probable causes of mortality were grouped by etiologic category: degenerative, metabolic, nutritional, inflammatory (infectious and noninfectious disease), and trauma. Probable cause of mortality was determined in 57% (223/392) of cases. Inflammatory disease (infectious/noninfectious) and trauma were the most common. Inflammatory disease accounted for 41% of cases (91/223), with the lungs (pneumonia) most commonly affected. Trauma accounted for 36% of strandings (80/223). The majority of trauma cases were due to anthropogenic activities (entanglement, fishing gear or other debris ingestion, and propeller strikes), accounting for 58% of trauma cases (46/80). Natural trauma (prey-associated esophageal obstruction or asphyxiation, shark bites, and stingray interactions) accounted for 12% of all cases (26/223), and trauma of undetermined origin was identified in 4% of cases (8/223). Starvation or inanition (nutritional) were the probable cause of mortality in 17% of cases and peaked during the 2013 UME (61% of cases). Degenerative and metabolic etiologies accounted for 5% of cases. This study represents the most comprehensive evaluation of morbidity and mortality patterns in IRL dolphins. Because IRL dolphins are routinely exposed to anthropogenic threats and have endured multiple UMEs, these baseline data are critical to the conservation and management of this population.
Interactions between bottlenose dolphin and recreational rod and reel fisheries are a complex issue for resource managers in the United States, which may impact anglers' catch and lead to dangerous situations for scavenging or depredating dolphins. To examine this issue, we analyzed data collected by observers on for‐hire fishing vessels off the eastern U.S. Gulf Coast from 2009 to 2020. A generalized additive model indicated number of anglers, number of discarded fish, proximity to shore, prior scavenging events, type of released fish, and area fished were all significant predictors of scavenging by dolphins. The Florida panhandle had the highest odds of scavenging, while scavenging in the Big Bend and Tampa Bay has increased through time. The Florida panhandle is a well‐known area for illegal feeding of dolphins, suggesting human behavior may be influencing fisheries interactions. Model outputs indicate that dolphins are primarily cuing on fishing activity rather than number of discards, but are more likely to scavenge discards from the family Lutjanidae (snappers), which comprised 40% of observed discards but 80% of scavenging events. This study highlights factors influencing the frequency of dolphin scavenging events, guiding managers and scientists on additional studies and mitigation measures needed to address this issue.
Accurate estimates of abundance are critical to species management and conservation. Common bottlenose dolphins (Tursiops truncatus truncatus) inhabiting the Indian River Lagoon (IRL) estuarine system along the east coast of Florida are impacted by anthropogenic activities and have had multiple unexplained mortality events, necessitating precise estimates of demographic and abundance parameters to implement management strategies. Mark-recapture methodology following a Robust Design survey was used to estimate abundance, adult survival, and temporary emigration for the IRL estuarine system stock of bottlenose dolphins. Models included a parameter (time since first capture) to assess evidence for transient individuals. Boat-based photo-identification surveys ( n = 135) were conducted along predetermined contour and transect lines throughout the entire IRL (2016-2017). The best fitting model included the “transient” parameter to survival, allowed survival to vary by primary period, detection to vary by secondary session, and did not allow temporary emigration. Dolphin abundance ranged from 981 (95% CI: 882-1,090) in winter to 1,078 (95% CI: 968-1,201) in summer with a mean of 1,032 (95% CI: 969 -1,098). Model averaged seasonal survival rate for marked residents ranged from 0.85-1.00. Capture probability ranged from 0.20 to 0.42 during secondary sessions and transient rate from 0.06 to 0.07. This study represents the first Robust design mark-recapture survey effort to estimate abundance for IRL dolphins and provides parameter estimates to optimize sampling design of future studies. Transients included individuals with home ranges extending north of the IRL requiring further assessment of stock delineation. Results were remarkably similar to prior abundance estimates resulting from line-transect aerial surveys and were consistent with a stable population. Data will enable managers to evaluate the impact of fisheries-related takes as well as enable future comparisons of demographic parameters for a dolphin population that continues to sustain large scale mortality events and anthropogenic impacts.
Some mammalian species that have not succumbed to pervasive human impacts and encroachments have managed to adapt to certain types of human activities. Several odontocetes have modified their behavior to persist, and in some cases even prosper, in human-altered riverine, coastal, and oceanic habitat. Examples include cooperation with fishers to catch fish, depredation on fishing gear, scavenging, and other kinds of opportunistic foraging (e.g., behind trawlers, around fish farms, or near built structures such as dams and offshore platforms). Some populations have adapted to life in human-made channels and waterways. We review information on the variety of odontocete adaptations to human encroachment, highlight some of the risks and benefits, and try to single out factors that may trigger or contribute to adaptation. Adaptation often brings wildlife into close contact with humans, which leads to conflict. We discuss the challenges of coexistence and contend that we humans, too, need to adjust our behavior and change how we perceive and value wildlife for coexistence to be possible. In addition to good management and conservation action, tolerance on our part will be key for allowing wildlife—odontocetes included—to persist. We advocate cultural and even spiritual shifts that can foster tolerance, nurture the social change that leads to appreciation for wildlife, and create more opportunities to preserve nature.
Common bottlenose dolphins (Tursiops truncatus) live in a large variety of habitats, where they confront a wide range of ecological challenges to which they have developed diverse behavioral solutions. They inhabit shallow marsh creeks, estuaries, bays, open coasts, islands, shelves, and deep open ocean. Abiotic factors such as physiography, salinity, temperature, depth, tidal excursions, and currents influence ecological factors that in turn help shape behaviors of bottlenose dolphins, within their morphological and physiological constraints. Among the ecological factors of greatest importance for influencing bottlenose dolphin behavior is its prey, and foraging serves as the focus of this review. Bottlenose dolphins consume a wide variety of prey, primarily fish and squid, that typically are taken in one bite. Prey vary in size, energy content, behavior, schooling tendency, speed, maneuverability, seasonal availability, sensory abilities, sound production, defenses, location in the water column, and use of habitat features or structures. The availability of potential prey to the dolphins is dictated largely by the dolphins’ biology and the development of appropriate skills for detecting, capturing, and handling prey. The interplay of characteristics of the fish, features of their environment, and capabilities of the dolphins themselves shape the dolphins’ foraging behaviors and influence dolphin sociality.
Fisheries bycatch is one of the biggest threats to marine mammal populations. A literature review was undertaken to provide a comprehensive assessment and synopsis of gear modifications and technical devices to reduce marine mammal bycatch in commercial trawl, purse seine, longline, gillnet and pot/trap fisheries. Successfully implemented mitigation measures include acoustic deterrent devices (pingers) which reduced the bycatch of some small cetacean species in gillnets, appropriately designed exclusion devices which reduced pinniped bycatch in some trawl fisheries, and various pot/trap guard designs that reduced marine mammal entrapment. However, substantial development and research of mitigation options is required to address the bycatch of a range of species in many fisheries. No reliably effective technical solutions to reduce small cetacean bycatch in trawl nets are available, although loud pingers have shown potential. There are currently no technical options that effectively reduce marine mammal interactions in longline fisheries, although development of catch and hook protection devices is promising. Solutions are also needed for species, particularly pinnipeds and small cetaceans, that are not deterred by pingers and continue to be caught in static gillnets. Large whale entanglements in static gear, particularly buoy lines for pots/traps, needs urgent attention although there is encouraging research on rope-less pot/trap systems and identification of rope colours that are more detectable to whale species. Future mitigation development and deployment requires rigorous scientific testing to determine if significant bycatch reduction has been achieved, as well as consideration of potentially conflicting mitigation outcomes if multiple species are impacted by a fishery.
Shark depredation, where a shark partially or completely consumes an animal caught by fishing gear before it can be retrieved to the fishing vessel, occurs in commercial and recreational fisheries worldwide, causing a range of negative biological and economic impacts. Despite this, it remains relatively understudied compared to other fisheries issues. This is the first review of the literature relating to shark depredation, which also includes an overview of the potential mechanisms underlying its occurrence and options for mitigation. Furthermore, this review highlights key research gaps that remain to be investigated, thereby providing impetus for future research. In total, 61 studies have been published between 1955 and 2018, which include information on shark depredation. These studies recorded quantitative rates of depredation between 0.9 and 26% in commercial and recreational fisheries and during research fishing, identified 27 shark species from seven families that were responsible for depredation and discussed potential factors influencing its occurrence. Information from research into bycatch mitigation and the testing of shark deterrent approaches and technologies is also presented, in the context of applying these approaches to the reduction of shark depredation. This review presents an holistic overview of shark depredation in fisheries globally and, in doing so, provides a central resource for fisheries researchers and managers focusing on this topic to stimulate further collaborative research on this important fisheries issue.
Socially maintained behavioural traditions in non-human species hold great interest for biologists, anthropologists and psychologists. This book treats traditions in non-human species as biological phenomena that are amenable to the comparative methods of inquiry used in contemporary biology. Chapters in the first section define behavioural traditions, and indicate how they can arise in non-human species, how widespread they may be, how they may be recognized and how we can study them. The second part summarizes cutting-edge research programmes seeking to identify traditions in diverse taxa in contributions from leading researchers in this area. The book ends with a comparison and evaluation of the alternative theoretical formulations and their applications presented in the book, and lays out recommendations for future research building on the most promising evidence and lines of thinking. The Biology of Traditions will be essential reading for students and researchers in the fields of anthropology, biology and psychology.
We documented depredation by bottlenose dolphins (Tursiops truncatus) in the Florida king mackerel (Scomberomorus cavalla) troll fishery. Between March and June 2003, we conducted 26 interviews of charter and commercial fishermen in Islamorada, Florida, and 23 along Florida's east coast from Fort Pierce south to Lake Worth Inlet. All fishermen indicated they had observed bottlenose dolphins depreciating bait or catch-king mackerel being the species most often taken by dolphins. During on-board observations of depredation between March and June 2003, we found that dolphins took 6% of king mackerel caught by charter fishermen and 20% of fish caught by commercial fishermen. We concluded that depredation by bottlenose dolphin occurs commonly in this fishery and has the potential to incur a significant economic cost to king mackerel fishermen. To address this concern, we conducted preliminary tests of a gear modification designed to reduce depredation in the king mackerel fishery between December 2003 and January 2004. These tests demonstrated that a modification to the outrigger planer will successfully deter bottlenose dolphins from engaging in depredation, without causing a reduction in catch.
El Mar Argentino cuenta con una importante diversidad de mamíferos marinos que totalizan aproximadamente 50 especies. Si bien en nuestro país no existe en la actualidad captura intencional de mamíferos marinos, se han identificado otras amenazas que pueden afectar su estado de conservación, entre las cuales se destacan la captura incidental por las artes de pesca.
El 3 de diciembre de 2015 el Consejo Federal Pesquero aprobó mediante Resolución CFP Nº 11/2015 el “Plan de Acción Nacional para Reducir la Interacción de Mamíferos Marinos con Pesquerías en la República Argentina (PAN Mamíferos Marinos)”, cuyo objetivo principal es contribuir al manejo ecosistémico de las pesquerías del Mar Argentino, evaluando las interacciones entre éstas y los mamíferos marinos a fin de disminuir los impactos negativos sobre ambos. Dicho PAN fue elaborado en forma conjunta por la Subsecretaría de Pesca y Acuicultura de la Nación y esta Secretaría, con la participación de organismos provinciales, instituciones científicas y académicas y ONGs.
La preparación final de este PAN fue realizada por María Laura Tombesi y Débora Winter (Secretaría de Ambiente y Desarrollo Sustentable). El capítulo “Pesquerías en Argentina” fue elaborado por Ramiro P. Sánchez, Gabriela Navarro, Mariano Monsalvo y Gustavo Martínez Puljak (Subsecretaría de Pesca y Acuicultura de la Nación) y contó con la colaboración de Laura Prosdocimi. El capítulo “Introducción a la captura incidental y los impactos de las interacciones operacionales y específicas” fue elaborado por Enrique Alberto Crespo, Silvana Laura Dans, Susana Noemí Pedraza, Néstor Aníbal García (Centro Nacional Patagónico y Universidad Nacional de la Patagonia) y Mariano Koen Alonso (Department of Fisheries and Oceans, Saint John’s, Newfoundland, Canada). El capítulo “Captura incidental de franciscana” fue elaborado por Luis Cappozzo (Museo de Ciencias Naturales Bernardino Rivadavia) y el capítulo “Mitigación de la captura incidental de mamíferos marinos” por Pablo Bordino (Fundación Aquamarina).
El estudio de las condiciones ambientales y su relación con la abundancia y distribución de los cetáceos incluye raramente las actividades humanas, las cuales pueden tener efectos negativos sobre los organismos. En este estudio se caracterizó la relación entre la distribución temporal y espacial de las operaciones marinas (pesquera, comercial y recreativa) y la de los tursiones (Tursiops truncatus) dentro del Parque Nacional Sistema Arrecifal Veracruzano. Se realizaron 25 navegaciones en transectos lineales entre julio de 2006 y junio de 2007, para registrar el número, tipo y ubicación geográfica de las actividades humanas y de las manadas de delfines. La abundancia relativa diaria (IAR= número de objetos∙h-1) se calculó para cada variable y se comparó entre temporadas (secas, lluvia y nortes). Las densidades (número de objetos∙km-2) se calcularon para cada variable mediante un sistema de información geográfica y se compararon con las divisiones de la zona de estudio en función de su distancia a la costa. En total
se navegaron 167 h, registrando 180 delfines (IAR= 1.23∙h-1), 1,489 embarcaciones (IAR= 9.59∙h-1) y 201 operaciones de pesca (IAR= 1.3∙h-1). El IAR de los delfines no mostró diferencias significativas entre temporadas (Kruskal-Wallis = KW, p> 0,05), a diferencia de las embarcaciones y las artes de pesca (KW, p<0.05). La distribución de los delfines y las actividades humanas presentaron mayores densidades alrededor de la desembocadura del Río Jamapa (KW, p<0.05), pero sólo las embarcaciones tuvieron mayor presencia a lo largo de la zona costera (KW, p<0.05). Las actividades humanas fueron muy diversas y se encontraron en áreas distintas, por lo que no coincidieron con los delfines de forma instantánea. Dado que la distribución espacial general del tráfico marítimo se superpone con el área ocupada por los delfines y las operaciones de pesca, esto sugiere una evasión recíproca.
Bycatch, the incidental capture of any marine animal in fishing gear, occurs globally in nearly every type of fishing gear. This paper consolidates the existing published and unpublished information about bycatch of protected species and other species of concern in commercial fishing gear on the east coast of the United States. A total of 49 commercial fisheries were reviewed, 39 of which had documented bycatch. The study identifies documented and potential bycatch of marine mammal, sea turtle, sea bird, fish, and invertebrate species in addition to existing bycatch mitigation and management in these fisheries. This information can be used as a resource for scientists, managers, and conservation practitioners in understanding the extent of bycatch and bycatch mitigation on the US east coast.
Each fi shery presents its own challenges for observers to document by-catch. The North Carolina (NC) stop net fi shery is especially challenging because it uses anchored gear (the stop net) that soaks up to 15 days to herd fi sh, which are then hauled to shore via another gear (a beach seine). Three Tursiops truncatus (Bottle-nose Dolphin) entanglements in stop nets and six Bottlenose Dolphin strandings, each suspected of having been entangled in stop net gear based on injuries noted (lesions) and spatio-temporal overlap with the fi shery, were documented by the NC Marine Mammal Network between 1992 and 2007. In 2001–2002, new observational techniques and surveys were used to observe this fi shery to estimate bycatch and to document dolphin behavior around the gear. Techniques included observations from the beach during net retrievals and in situ surveys using a vessel with a sonar-video camera system. No entangled dolphins were observed, and, in fact, observations indicated dolphins were not attracted to stop nets and generally changed direction to avoid the gear. Nonetheless, characteristics of the fi shery impose severe limitations on the effi cacy of bycatch observer methods, rendering those results unreliable. Giv-en low levels of known or suspected entanglements and the challenges of observing this fi shery, stranding network data may be the most practical and effective method to monitor dolphin bycatch.
The blue crab, Callinectes sapidus Rathbun (Portunidae), supports large commercial and recreational fisheries along Florida's coasts. Documentation of the development and magnitude of the commercial fishery exists, but little is known about the recreational fishery. Blue crabs are harvested in both the hard- and soft-shell states in Florida. Various types of gear have been employed to capture blue crabs, but in recent years the buoyed, wire-mesh trap has superseded all other gear types. This gear type is used to capture both hard- and soft-shell blue crabs. By far the largest component of the commercial fishery is the hard-shell fishery. The annual commercial harvest of hard-shell blue crabs consistently ranks among the top ten of the fisheries in the state in both quantity and ex-vessel value. The blue crab fishery in Florida began in the late 1800s and has continually expanded. The quantity of blue crabs harvested has historically varied among coastal counties of Florida. In recent years, various peninsular Florida counties on the Gulf of Mexico have contributed the majority of annual landings of hard-shell blue crabs. Most of these crabs are harvested during the warmer months of the year. Management of the blue crab fishery in Florida has historically focused on protecting ovigerous females and minimizing inadvertent mortality of unharvested blue crabs, particularly juveniles. Regulations focus principally on gear type, gear configuration, and restricting harvests made with gear other than wire-mesh traps. In recent years, hard-shell blue crab landings in Florida have stabilized or decreased slightly, but the number of fishers in the industry has increased. As a result, standardized harvest (pounds per fishing trip) has decreased; this trend is more pronounced in Atlantic coastal counties than in gulf coastal counties. The processing, marketing, and retailing components of the seafood industry in Florida are well developed and could absorb additional production of blue crab products in the state. However, competition with other crab and imitation-crab products, degradation of coastal habitats important in the blue crab life cycle, increases in fishing effort and efficiency, fluctuations in blue crab population sizes, and other concerns limit the potential for further expansion of the Florida blue crab fishery.
Cetaceans interact with trawls to an undetermined extent. A preliminary review of global data indicates that individuals of 25 cetacean species (two mysticete, 23 odontocete) have been documented to have died in working trawls or discarded trawling gear. Cetacean interactions with trawls are complex, in part because both fishermen and cetaceans are drawn to areas of high prey density. Furthermore, within such areas, cetaceans are probably often attracted to trawling activities because they make it easier for the animals to exploit a concentrated food source. Individuals of 15 (possibly 16) cetacean species (13 odontocete, and one or even two mysticete) have been reported to feed in association with trawls. Animals follow working nets (feeding on stirred-up organisms or fish gilled in mesh) and also feed on discarded by-catch. Damage to gear as a result of feeding interactions or entanglement has been reported. Such damage results in (1) harm to the animals, (2) creation of negative opinions of cetaceans by fishermen (regardless of whether a cetacean or a shark is, in fact, responsible for the damage in question), and (3) loss of time and money for repair and replacement of gear. The relationships of cetaceans with trawls need to be further studied to determine what effects the trawl fisheries have on the ecology and population status of the whales and dolphins involved.
A tagging-observation program was conducted to study the behavioral ecology of Atlantic bottlenose dolphins near Sarasota, Florida. Forty-seven bottlenose dolphins (24 males, 23 females) werecaptured. tagged, and released a total of 90 times from 29 January 1975 through 25 July 1976. Tagged animals were identified during regular boat surveys, and information was collected on all individuals and groups encountered. A total of997 tagged or marked bottlenose dolphins were sighted. A population of bottlenose dolphins was identified in an estuarine-nearshore area extending about 40 km to the south from Tampa Bay and up to 3 km into the Gulfof Mexico. Social organization was characterized by small dynamic groups that appeared to be subunits ofa larger socially interacting herd. Average group size of 688 groups was 4.8 bottlenose dolphins (standard error = 0.16), Bottlenose dolphins concentrated in different areas seasonally, possibly in response to distribution changes of important prey species. Feeding strategies of the bottlenose dolphins apparently varied according to available water depth and differed from strategies of pelagic small cetaceans. Calving apparently occurred from spring to early fall.
The description of the appearance, behaviour and movements of a wild bottlenose dolphin are given. The dolphin, which was a male, was measured as approximately 360 cm in length during May 1976. The dolphin was estimated to be a mature adult. Certain distinguishing permanent body scars on the head and dorsal fin areas, and a damaged tooth, were a convenient means of identification of the dolphin.The movements of the dolphin were traced to April 1972. Between then and March 1975 it was resident in the coastal areas around the Isle of Man. Between April 1975 and January 1976 the dolphin had moved to and remained resident in the region around Milford Haven in Pembrokeshire. From January 1976 until December 1976, the dolphin moved south again, and patrolled an area stretching from St. Ives on the north coast of Cornwall to Falmouth on the south coast of Cornwall, although during most of this time favoured localities were St. Ives and Mousehole, where it remained for long periods. All areas which were ‘adopted’ for any length of time showed similarities, in that boating traffic, fishing activity, mooring buoys, and usually diving and swimming activities were present. The bays were usually about 10 m deep or less, often with rocky shore and sandy bottom.Behaviour observed included playing with, chasing and manoeuvring boats, playing with divers, swimmers, and floating objects, interfering with boat propellors and outboard engines, indiscriminate sexual activity with boats, and a general sociable attitude to people. The dolphin was a solitary animal, and apart from one brief incident in the Isle of Man, was never seen with other dolphins.The general history and behaviour of the dolphin in comparison with records of other similar incidences of sociable yet wild Cetacea, and also captive dolphins lead one to believe that this animal is quite healthy and normal, apart from the unusual aspect of his sociability with man.
A cetacean swimming in its natural environment must frequently encounter a variety of sources for returning echos. An echolocation system which only allowed for the detection of objects would be insufficient for gathering information necessary to meet needs like prey location and predator avoidance. The ability of cetaceans to differentiate and recognize characteristics of objects via echolocation has an obvious biological benefit. The purpose of this paper is to review the behavioral experiments that have examined delphinid abilities to differentiate between objects differing in size, shape, or material.
Seven major types of sampling for observational studies of social behavior have been found in the literature. These methods differ considerably in their suitability for providing unbiased data of various kinds. Below is a summary of the major recommended uses of each technique: In this paper, I have tried to point out the major strengths and weaknesses of each sampling method. Some methods are intrinsically biased with respect to many variables, others to fewer. In choosing a sampling method the main question is whether the procedure results in a biased sample of the variables under study. A method can produce a biased sample directly, as a result of intrinsic bias with respect to a study variable, or secondarily due to some degree of dependence (correlation) between the study variable and a directly-biased variable. In order to choose a sampling technique, the observer needs to consider carefully the characteristics of behavior and social interactions that are relevant to the study population and the research questions at hand. In most studies one will not have adequate empirical knowledge of the dependencies between relevant variables. Under the circumstances, the observer should avoid intrinsic biases to whatever extent possible, in particular those that direcly affect the variables under study. Finally, it will often be possible to use more than one sampling method in a study. Such samples can be taken successively or, under favorable conditions, even concurrently. For example, we have found it possible to take Instantaneous Samples of the identities and distances of nearest neighbors of a focal individual at five or ten minute intervals during Focal-Animal (behavior) Samples on that individual. Often during Focal-Animal Sampling one can also record All Occurrences of Some Behaviors, for the whole social group, for categories of conspicuous behavior, such as predation, intergroup contact, drinking, and so on. The extent to which concurrent multiple sampling is feasible will depend very much on the behavior categories and rate of occurrence, the observational conditions, etc. Where feasible, such multiple sampling can greatly aid in the efficient use of research time.
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