Prey selection patterns of bottlenose dolphins depredating bottom-set gillnets in the northern Aegean Sea

Garagouni, M; Ganias, K

doi:10.3354/meps14302

Cited by 4 publications

(2 citation statements)

References 54 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In the studied fishing ground, the main reason for discarding fishes appears to be morphologically damaged individuals that could not be sold; most frequently the target species Mullus surmuletus, Sphyraena sphyraena and Pagellus erythrinus. Body damage is due primarily to depredation by active predators (dolphins, cormorants, sea turtles, and larger fishes; Garagouni & Ganias, 2023) and secondarily to injuries during the disentanglement process for example, dermal wounds, damaged opercula, etc. Among fishes, only the damselfish C. chromis was categorized as non-commercial.…”

Section: Discussionmentioning

confidence: 99%

High bycatch rate of the coral Cladocora caespitosa offsets the low discards ratio in Thermaikos Gulf gillnet fishery

GANIAS,

ZAFEIRIADOU,

GARAGOUNI

et al. 2023

Medit. Mar. Sci.

View full text Add to dashboard Cite

While hanging nets may have fewer overall environmental impacts than towed gears, they still catch unwanted species and sizes, which are then discarded. Gillnets are one of the most common types of nets used in Mediterranean small-scale fisheries, with commercial catches and discards containing a diverse range of fish and invertebrate species. In this study, the catch profile of gillnets in the Thermaikos Gulf (NE Mediterranean) was analyzed with a focus on the discarding of species with unfavorable conservation status, such as the Mediterranean-endemic scleractinian coral Cladocora caespitosa, which is listed as endangered due to declining population sizes. Our survey was conducted over two seasons (May to October in 2020 and 2021) and included 69 fishing trials under realistic fishing conditions. In general, gillnets exhibited a relatively low discards ratio (17.2%; 7.1% when only fish were considered) and a low prevalence and capture intensity of endangered or threatened species; during the entire survey, only one chondrichthyan was captured (1 specimen of Raja radula), while only two out of 54 fish species were of vulnerable IUCN status. These advantages were offset in part by the high catchability of C. caespitosa colonies, which occurred in 61% of hauls and accounted for 53% of total invertebrate biomass and 30% of total discarded biomass. The likelihood of hauling living colonies of C. caespitosa was higher when fishing over known coral beds (81% vs. 43%), and the overall probability of hauling C. caespitosa in any state was 18% higher over coral beds, suggesting that gillnets frequently detach colonies from the seafloor, which are then dispersed over a larger area as fragments with probably low survival potential. Our findings highlight the importance of identifying C. caespitosa beds so that fishermen avoid setting their nets in these areas, provided that they are well-informed and educated about the ecological significance of this endemic, threatened, and ecologically important species.

show abstract

Section: Discussionmentioning

confidence: 99%

High bycatch rate of the coral Cladocora caespitosa offsets the low discards ratio in Thermaikos Gulf gillnet fishery

GANIAS,

ZAFEIRIADOU,

GARAGOUNI

et al. 2023

Medit. Mar. Sci.

View full text Add to dashboard Cite

show abstract

“…Data loggers or echolocation click detectors, such as the Cetacean POrpoise Detector (C‐POD) (Chelonia Ltd., 2022) are a user‐friendly, relatively inexpensive device that can be deployed for continuous monitoring periods of 3–6 months. C‐PODs detect individual echolocation clicks between 20 and 160 kHz and have been a popular tool used to study odontocete ecology and behavior worldwide (e.g., Carstensen et al, 2006; Garagouni, 2019; Jaramillo‐Legorreta et al, 2017; Nykänen, 2016; Simon et al, 2010). Although no waveform data are stored by the devices, summary data on each click are preserved allowing post‐deployment classification of detected sounds into sequences called click trains.…”

Section: Introductionmentioning

confidence: 99%

What the F‐POD? Comparing the F‐POD and C‐POD for monitoring of harbor porpoise (Phocoena phocoena)

Todd

Kavanagh

Rogan

et al. 2023

Ecology and Evolution

View full text Add to dashboard Cite

Passive acoustic monitoring (PAM) is a cost‐effective method for monitoring cetacean populations compared with techniques such as aerial and ship‐based surveys. The Cetacean POrpoise Detector (C‐POD) has become an integral tool in monitoring programs globally for over a decade, providing standardized metrics of occurrence that can be compared across time and space. However, the phasing out of C‐PODs following the development of the new Full waveform capture POD (F‐POD) with increased sensitivity, improved train detection, and reduced false‐positive rates represents an important methodological change in data collection, particularly when being introduced into existing monitoring programs. Here, we compare the performance of the C‐POD with that of its successor, the F‐POD, co‐deployed in a field setting for 15 months, to monitor harbor porpoise (Phocoena phocoena). While similar temporal trends in detections were found for both devices, the C‐POD detected only 58% of the detection‐positive minutes (DPM), recorded by the F‐POD. Differences in detection rates were not consistent through time making it difficult to apply a correction factor or directly compare results obtained from the two PODs. Generalized additive models (GAMs) were used to test whether these differences in detection rates would have an effect on analyses of temporal patterns and environmental drivers of occurrence. No differences were found in seasonal patterns or the environmental correlates of porpoise occurrence (month, diel period, temperature, environmental noise, and tide). However, the C‐POD failed to detect sufficient foraging rates to identify temporal patterns in foraging behavior, which were shown by the F‐POD. Our results suggest that the switch to F‐PODs will have little effect on determining broad‐scale seasonal patterns of occurrence but may improve our understanding of fine‐scale behaviors such as foraging. We highlight how care must be taken interpreting F‐POD results as indicative of increased occurrence when used in time‐series analysis.

show abstract

Shark and odontocete depredation on the catch of the tuna longline fishery in New Caledonia (South Pacific Ocean)

Mollier,

Mazé,

Prioul

et al. 2024

ICES Journal of Marine Science

View full text Add to dashboard Cite

Large marine predators feeding on fish caught on fishing gear, referred to as ‘depredation’, occur in a wide range of fisheries worldwide. Depredation can result in negative ecological and socio-economic impacts, leading to conflict between fishers and depredating species. However, depredation remains understudied in many fisheries, and this hampers the development of effective mitigation solutions. In this study, 21 years of fishing data (2002–2022) were used to assess shark and odontocete depredation in the pelagic tuna longline fishery of New Caledonia. Using generalized linear models, the year, season, effort, soaking time, and vessel were identified as variables significantly influencing the probability of depredation to occur. Results showed that while shark depredation occurred more frequently than odontocete depredation (58.5% vs. 9.2% of the longline sets), they damaged a lower proportion of fish (3.9% vs. 12.3%) over the study period. Unlike sharks, odontocetes selectively depredate tuna, with their highest occurrence during periods of high tuna catch rates, suggesting a co-occurrence with fishing activities. Together, these results indicate that depredation in the New Caledonian fishery is high compared to other regions and provide essential information on the dynamics and impacts of the issue as a basis for considering management and mitigation options.

show abstract

Prey selection patterns of bottlenose dolphins depredating bottom-set gillnets in the northern Aegean Sea

Cited by 4 publications

References 54 publications

High bycatch rate of the coral Cladocora caespitosa offsets the low discards ratio in Thermaikos Gulf gillnet fishery

High bycatch rate of the coral Cladocora caespitosa offsets the low discards ratio in Thermaikos Gulf gillnet fishery

What the F‐POD? Comparing the F‐POD and C‐POD for monitoring of harbor porpoise (Phocoena phocoena)

Shark and odontocete depredation on the catch of the tuna longline fishery in New Caledonia (South Pacific Ocean)

Contact Info

Product

Resources

About