scholarly journals Quantification of interactions between the Portuguese sardine purse-seine fishery and cetaceans

2015 ◽  
Vol 72 (8) ◽  
pp. 2438-2449 ◽  
Author(s):  
Ana Marçalo ◽  
Isidora Katara ◽  
Diana Feijó ◽  
Helder Araújo ◽  
Isabel Oliveira ◽  
...  
Keyword(s):  
Total Mortality ◽  
Purse Seine ◽  
Annual Number ◽  
Common Dolphin ◽  
The South ◽  
Delphinus Delphis ◽  
The North ◽  
Common Dolphins ◽  
Purse Seine Fishery ◽  
Purse Seining

Abstract Interactions between cetaceans and the purse-seine fishery operating along the whole Portuguese continental coast were studied based on on-board observations from 2010 to 2011. Cetacean presence and mortality were estimated and characteristics under which interactions were most likely to occur were identified. Observations were made on 163 fishing trips (0.7% of the average annual number of fishing trips) and 302 fishing operations/hauls. Cetaceans were present during 16.9% of fishing events; common dolphins (Delphinus delphis) accounted for 96% of occurrences, mostly overnight in summer and early autumn. Regression models showed that cetacean presence during a fishing set was significantly (p < 0.05) associated with sardine catches, effort, and latitude/longitude. Encirclement and mortality occurred in 2.3 and 1.0% of fishing events, respectively. Encircled species were the common dolphin, bottlenose dolphin (Tursiops truncatus), and harbour porpoise (Phocoena phocoena), but only common dolphin showed mortality (three individuals); raised to fleet level, estimated total mortality rates of common dolphins were 69 (95% CI 37–110) in the north and 91 (95% CI 55–165) in the south for 2010 and 78 (95% CI 47–140) in the south only for 2011. The estimated annual mortality rate due to purse seining is 113 (95% CI 3–264) common dolphins, which is ∼0.63% of the current most optimistic estimate of population size for the Portuguese fishing area (SCANS II). The wide confidence limits, as well as variation between years, reflect low observer coverage, emphasizing the need for increased monitoring to cover gaps in the spatial and seasonal distribution of observer effort and provide reliable estimates of bycatch.

Injuries, healing and management of common dolphins (Delphinus delphis) in human-impacted waters in the south Iberian Peninsula

2020 ◽  
Vol 100 (2) ◽  
pp. 315-325
Author(s):  
Liliana Olaya-Ponzone ◽  
Rocío Espada ◽  
Estefanía Martín Moreno ◽  
Isabel Cárdenas Marcial ◽  
José C. García-Gómez
Keyword(s):  
Iberian Peninsula ◽  
Healing Process ◽  
Local Population ◽  
Survival Rates ◽  
Whale Watching ◽  
The South ◽  
Delphinus Delphis ◽  
Photo Identification ◽  
Type Of Injury ◽  
Common Dolphins

AbstractThis study focuses on the dolphins populating the water between Gibraltar and Algeciras in the south Iberian Peninsula, an area subjected to pressure due to high human activity. The area is considered an important feeding and breeding ground for common dolphins (Delphinus delphis). Due to the degree of residence of some specimens, and the large gap in knowledge about the evolution of wounds in D. delphis specimens with lacerations, this work sought to perform the following analyses: identify lacerated individuals; characterize sequences of ‘before – during – after’ with respect to the occurrence of lacerations; and associate the type of injury with its severity. This work will inform future studies by expanding a database on injured individuals and contribute to periodical monitoring of specimens that frequent these geographic areas. Between 2013 and 2017, we were able to track the healing process of five injured individuals of common dolphins from a whale-watching platform thanks to photo identification. The animals exhibited fresh external wounds from different sources. In the majority of individuals, the wound-healing processes lasted 3–21 weeks. The frequency with which sightings are made and knowledge about the local population will help track injured animals, follow their wound evolution, and document their survival rates. The documented injuries inflicted by human interactions described in this paper may include fishing interactions and propeller strikes, probably as a consequence of the high intensity of recreational fishing and whale-watching activities in the area.

scholarly journals Cetaceans using the marine protected area of "Parque Estadual Marinho da Laje de Santos", Southeastern Brazil

2017 ◽  
Vol 65 (4) ◽  
pp. 605-613 ◽  
Author(s):  
Marcos Cesar de Oliveira Santos ◽  
Giovanna Corrêa e Figueiredo ◽  
Marie-Francoise Van Bressem
Keyword(s):  
Protected Area ◽  
Marine Protected Area ◽  
Unknown Origin ◽  
Mantel Test ◽  
Southeastern Brazil ◽  
Common Dolphin ◽  
Balaenoptera Acutorostrata ◽  
Stenella Frontalis ◽  
Delphinus Delphis ◽  
Common Dolphins

Abstract The aim of this study was to evaluate the presence of cetaceans in the waters surrounding the Marine Protected Area (MPA) known as “Parque Estadual Marinho da Laje de Santos (PEMLS)”, placed in coastal waters at the southeastern coast of Brazil. Boat-based surveys were conducted once a month from June 2013 to June 2015. A specific transect was followed to cover the area of the quoted MPA, as well as its borders. A total of 24 boat-surveys rendered 18 sightings of cetacean groups of the following species: Atlantic spotted dolphin (Stenella frontalis) (12), rough-toothed dolphin (Steno bredanensis) (2), common dolphin (Delphinus delphis) (1), Bryde’s whale (Balaenoptera edeni) (2) and common minke whale (Balaenoptera acutorostrata) (1). Sightings of S. frontalis, the commonest sighted species, was positively correlated with water depth (Mantel test; r = 0.8072; p < 0.05). Photoidentified individuals moved back and forth to inner and outer areas of the MPA, remaining in the area throughout the 2-year survey. “Paisley” cutaneous marks of unknown origin were reported in two common dolphins for the first time in local waters. As the PEMLS has been used as an important spot for SCUBA divers, it is recommended that cetacean sightings could still be gathered in a future partnership, as well as using the acoustics tool to detect their presence when researchers are not in the field.

scholarly journals Short-term effects of tourism on the behaviour of common dolphins (Delphinus delphis) in the Azores

2017 ◽  
Vol 98 (5) ◽  
pp. 1187-1196 ◽  
Author(s):  
Arianna Cecchetti ◽  
Karen A. Stockin ◽  
Jonathan Gordon ◽  
José M.N. Azevedo
Keyword(s):  
Transition Probabilities ◽  
High Energy ◽  
Tourism Industry ◽  
Common Dolphin ◽  
Short Term ◽  
Delphinus Delphis ◽  
Critical Activity ◽  
Time Required ◽  
Common Dolphins

Short-term measures of behavioural responses of cetaceans to tourism operations have been used in many studies to interpret and understand potential long-term impacts of biological importance. The short-beaked common dolphin (Delphinus delphis) is the species most frequently observed in the Azores and constitutes an important component of the marine mammal tourism industry in this region. This study investigated the potential effects of tour boats on the behaviour of common dolphins off São Miguel, Azores, with particular focus on the changes in activity budget and the time required to resume activities after a tour boat interaction. Behavioural data were collected from land using a group focal-follow methodology. Markov chains were applied to analyse control and interaction sequences and to assess behavioural transition probabilities in both scenarios. In the presence of tour boats, dolphins significantly reduced the time spent foraging and increased the time engaged in other high energy activities. Dolphins also took significantly longer to resume feeding after an interaction occurred. The average bout length varied significantly between control and interaction scenarios, with foraging bouts being shorter during tour boats interactions. The results presented have management implications since feeding is a biologically critical activity. Disruption of foraging behaviour could lead to a decrease in energy intake for this population. With cetacean tourism likely to increase in the future, a precautionary approach to issuing new licences is advisable and any expansion would warrant an appropriate monitoring programme.

Acoustic Assessment of Populations of Common Dolphin Delphinus Delphis In Conjunction With Seismic Surveying

1996 ◽  
Vol 76 (3) ◽  
pp. 811-820 ◽  
Author(s):  
John C. Goold
Keyword(s):  
Seismic Survey ◽  
Avoidance Reaction ◽  
Common Dolphin ◽  
Survey Area ◽  
Delphinus Delphis ◽  
Air Gun ◽  
Before And After ◽  
Seismic Surveying ◽  
Acoustic Contact ◽  
Common Dolphins

Common dolphin, Delphinus delphis (bairdi), were monitored acoustically across a survey area of 2747 km2 during a three month period before, during and after an oil industry two dimensional (2D) seismic reflection survey. Over 900 h of audio survey data were collected and analysed, along with GPS positional data, to reveal trends in presence and distribution of animals. The presence of dolphins was determined from vocalization events on the survey recordings. Dolphin presence was assessed by a system of percentage acoustic contact. This was highest before and after the seismic survey, with common dolphins showing a clear south-westerly skew within the survey area and a probable south-westerly migration of animals between September and December. Acoustic contact with dolphins during the seismic survey also showed a south-westerly skew within the survey area, although percentages were lower. Monitoring during the period of seismic activity was restricted to the immediate vicinity (1–2 km) of the seismic vessel, so percentage contact most likely reflects the response of dolphins to such immediate activity. The overall result suggests an avoidance reaction by common dolphins to air gun emissions, although certain observations suggest tolerance to these sounds outside a 1 km radius of the guns.

scholarly journals Citizen science in the marine environment: A case-study estimating common dolphin densities in the north-east Atlantic

2019 ◽  
Author(s):  
James R Robbins ◽  
Lucy Babey ◽  
Clare B Embling
Keyword(s):  
Citizen Science ◽  
Common Dolphin ◽  
Bay Of Biscay ◽  
English Channel ◽  
East Atlantic ◽  
Science Data ◽  
North East ◽  
The North ◽  
Celtic Sea ◽  
Common Dolphins

Background. Citizen science is increasingly popular and has the potential to collect extensive datasets at lower costs than traditional surveys. Ferries have been used to collect data on cetacean populations for decades, providing long-term time series allowing for monitoring of cetacean populations. One cetacean species of concern is the common dolphin, which have been found stranded around the north-east Atlantic in recent years, with high numbers on French coasts being attributed to fisheries bycatch. We estimate common dolphin densities in north-east Atlantic and investigate the power of citizen science data to identify changes in marine mammal densities and areas of importance. Materials & Methods. Data were collected by citizen scientists on ferries between April and October in 2006 - 2017. Common dolphin sightings data from two ferry routes in the Bay of Biscay (n= 569), Celtic Sea (n= 260), and English Channel (n= 75) were used to estimate detection probabilities with detection functions. Density Surface Models estimated density across ferry routes, accounting for the influence of environmental (chlorophyll a, sea surface temperature, depth, and slope), spatial (latitude and longitude) and temporal terms (year and Julian day). Results. Overall detection probability was highest in the English Channel (0.384) and Bay of Biscay (0.348), and lowest in the Celtic Sea (0.158). Common dolphins were estimated to occur in higher densities in the Celtic Sea (0.400 per km) and the Bay of Biscay (0.319 per km), with low densities in the English Channel (0.025 per km). Densities in the Celtic Sea have been relatively stable on the ferry route since 2006 with a slight decrease in 2017. Densities peaked in the Bay of Biscay in 2013 with lower numbers since. The general trend in the English Channel is for increasing densities of common dolphins over time since 2009. Discussion. This study highlights the effectiveness of citizen science data to investigate the distribution and density of cetaceans. The densities and temporal changes shown by this study are representative of those from wider-ranging robust estimates. We highlight the ability of citizen science to collect data over extensive periods of time which complements traditional surveys. Such long-term data are important to identify changes within a population; however, citizen science data may, in some situations, present challenges. We provide recommendations to ensure high-quality data which can be used to inform management and conservation of cetacean populations.

scholarly journals Trends in strandings and by-catch of marine mammals in north-west Spain during the 1990s

2002 ◽  
Vol 82 (3) ◽  
pp. 513-521 ◽  
Author(s):  
A. López ◽  
M.B. Santos ◽  
G.J. Pierce ◽  
A.F. González ◽  
X. Valeiras ◽  
...  
Keyword(s):  
Marine Mammals ◽  
Atlantic Coast ◽  
Western Coast ◽  
Common Dolphin ◽  
North West ◽  
The North ◽  
By Catch ◽  
Average Size ◽  
Autumn And Winter ◽  
Common Dolphins

Strandings of marine mammals on the north-western Spanish coast (Galicia) have been systematically recorded since 1990. A total of 1433 marine mammals belonging to 15 species was recorded from 1990 to 1999. The most frequently recorded species stranded were common dolphin (47%), bottlenose dolphin (11%) and harbour porpoise (7%). The number of strandings recorded increased annually over the study period, probably reflecting an increased observer effort. During 1996–1999, an average of 1·65 animals were stranded annually for each 10 km of coastline, the highest density of strandings recorded on the Atlantic coast of the Iberian Peninsula. More than 80% of the strandings were located on the western coast of Galicia, mainly in autumn and winter. During the study period, 42 proven incidental catches were recorded, although signs of by-catch were seen in a further 198 animals. The average size of stranded common dolphins and the proportion of males both increased towards the end of the calendar year.

Behaviour of free-ranging short-beaked common dolphins (Delphinus delphis) in Gulf St Vincent, South Australia

2013 ◽  
Vol 61 (4) ◽  
pp. 291 ◽  
Author(s):  
Nicole E. Filby ◽  
Mike Bossley ◽  
Karen A. Stockin
Keyword(s):  
Group Size ◽  
Water Depth ◽  
Large Scale ◽  
South Australia ◽  
Population Level ◽  
Common Dolphin ◽  
Time Data ◽  
Fishing Activity ◽  
Delphinus Delphis ◽  
Common Dolphins

Common dolphins are subject to large-scale fishing activity and tourism operations in South Australia; however, there is a paucity of data on this species. Understanding the behaviour of a population can contribute greatly to our knowledge of a species and how to manage potential population-level threats. This paper describes the behaviour of short-beaked common dolphins (Delphinus delphis) in Australian waters for the first time. Data were collected from 109 independent dolphin groups during boat-based surveys conducted in Gulf St Vincent, South Australia, between September 2005 and May 2008. Activity budgets were used to assess behaviour of common dolphins in relation to diel patterns, season, water depth, sea surface temperature (SST), group size and composition. Foraging (33.9%) and resting (2.8%) were the most and least frequently observed behaviours, respectively. Travelling (33.0%), socialising (20.2%) and milling (10.1%) accounted for the remainder of the activity budget. Diurnal differences were detected, with foraging (59.5%) and socialising (31.8%) groups most frequently observed from 10.00 to 11.59 hours. Behaviour did not vary seasonally or with water depth, SST, group size or composition. Behaviour varied significantly between single- and multispecies aggregations. Foraging was more frequent in multispecies aggregations, as 78.4% of all foraging behaviour observed for common dolphins occurred in the presence of other species. Multispecies aggregations were most frequently observed with flesh-footed shearwaters (Puffinus carneipes), which were present during 29.4% of common dolphin encounters. Behaviour varied significantly during aggregations with shearwaters, as 62.2% of foraging groups occurred in the presence of shearwaters. Resting, milling or socialising was rarely observed in the presence of any other species, indicating that the primary mechanism for aggregations is likely prey-related.

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