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VALUTAZIONE DELLE CATTURE ACCIDENTALI DI SPECIE PROTETTE NEL TRAINO PELAGICO -Estensione 2011 RELAZIONE FINALE DEL PROGETTO
Abstract
Bycatch is one of the main sources of anthropogenic mortality of species of conservation concern worldwide. Between January 2011 and May 2012, ISPRA coordinated a monitoring programme of cetacean bycatch in Italian pelagic trawlers (BYCATCH III extension 2011), funded in compliance with the Regulation (EC) No.812/2004. Other 3 partners participated in the monitoring, data collection and analyses: CoNISMa, CNR ISMAR of Ancona and the University of Florence. Thirteen independent observers monitored a total of 2,735 hauls. The average observation coverage was 2.4% during the duration of the entire project, ranging between 3.4-4.4 % of the regional fishing effort in 2011. Almost all bycatch events were recorded in the northern Adriatic Sea. Bycatch rates of bottlenose dolphins (Tursiops truncatus) and loggerhead turtles (Caretta caretta) were 0,001 (3 events) and 0,010 (18 events) specimen/haul, respectively. The 2011 estimated annual number of bycaught bottlenose dolphins in this fishery for the GSA 17 was 72 specimens (CV=0.55; 95% CIs=39-104). Despite the high degree of uncertainty, this
estimate rise some concern about the sustainability of this accidental captures at the Adriatic level. It is urgent to determine whether or not the scale of this mortality, in addition to that caused by all other fishing gears, is sufficient to pose a threat at the population level. The 2011 estimated annual number of bycaught sea turtles in this fishery for the GSA 17 was 358 specimens (CV=0.29; 95% CIs=296-402), 99% of which released alive. The extent of lethal interactions for common thresher shark (Alopias vulpinus), eagle ray (Myliobatis aquila) and bull rays (Pteromylaesus bovinus) should also be evaluated. Bycatch of elasmobranchs commercial species (e.g. Squalus acanthias and Mustelus spp) should also be carefully considered.
... Midwater trawlers (also called pelagic trawlers or 'volanti,' the latter meaning 'flying' in Italian) operate in pairs; the net's mouth can be 30-45-m wide and 7-12-m high (Sala, 2013). While midwater pair trawlers normally target pelagic and epipelagic species, in the shallow waters of the north-western Adriatic, their gear ends up fishing relatively close to the seafloor (Fortuna et al., 2010;Sala et al., 2018). ...
... in association with Adriatic trawl gear to repel bottlenose dolphins (e.g. De Carlo et al., 2012;Sala et al., 2018) must consider any negative impacts on the animals. Noise from acoustic devices may impair dolphin communication and cause hearing harm (Dawson et al., 2013;Waples et al., 2013), while also having unintended negative impacts on marine organisms and fish behaviour, with potential effects on fishing yields (Kastelein et al., 2007). ...
... Noise from acoustic devices may impair dolphin communication and cause hearing harm (Dawson et al., 2013;Waples et al., 2013), while also having unintended negative impacts on marine organisms and fish behaviour, with potential effects on fishing yields (Kastelein et al., 2007). These negative impacts may end up exceeding any real or supposed conservation benefit in terms of lower dolphin bycatch, also considering that: 1) incidental mortality rates in Adriatic midwater trawls appear to be low (Fortuna et al., 2010;De Carlo et al., 2012;Sala et al., 2018); 2) mortality rates in Adriatic otter trawls remain unknown; 3) compelling evidence on the long-term effectiveness of acoustic devices as a way of reducing bottlenose dolphin bycatch in trawl gear is lacking; 4) acoustic devices might function as 'dinner bells' once bottlenose dolphin have become accustomed to their noise (Cox et al., 2003;Carretta & Barlow, 2011); and 5) several studies strongly suggest that acoustic devices may not bring the intended benefits in terms of reducing conflict between bottlenose dolphins and trawlers (Stephenson & Wells, 2008;Allen et al., 2014;Goetz et al., 2014;Santana-Garcon et al., 2018). ...
• Many species and populations of odontocetes have modified their behaviour to take advantage of feeding opportunities provided by fishing activities, with depredation of fishing gear being the most common type of adaptation.
• The northern Adriatic Sea has been identified as an important marine mammal area because of a regular occurrence of common bottlenose dolphins. Boat surveys were conducted within a 3,000 km² sector of the Adriatic Sea off the coast of Veneto, Italy, between April and October 2018–2019. Based on 76 days at sea, 10,711 km of navigation, and 81 h 26 min of dolphin tracking, this study contributes novel quantitative information on dolphin spatial distribution, and on their occurrence in the wake of beam trawlers, otter trawlers, and midwater pair trawlers.
• A combined generalized additive model and generalized estimation equation framework indicated that trawling—along with other physiographic, biological and anthropogenic variables—influenced dolphin distribution. In days of trawling, the chance of encountering dolphins increased by ~4.5 times (95% confidence interval 1.8–11.0) near active beam trawlers, by ~16.0 times (7.1–36.0) near otter trawlers, and by ~28.9 times (12.0–69.6) near midwater pair trawlers.
• Spatial modelling was used to create maps of predicted distribution, suggesting differences in habitat use between trawling and no‐trawling days. Spatial modelling for all days identified a dolphin distribution hotspot of 832 km², situated off the Po river delta.
• Evidence contributed by this study can be used to inform management action within one of the world's areas most heavily impacted by fishing and other human encroachment. Such management action would help enforce the European Union's Habitats Directive and Marine Strategy Framework Directive, while also informing EU's Maritime Spatial Planning.
... Since 2006, an extensive monitoring programme of accidental catches of long-lived species like cetaceans, sea turtles, and elasmobranchs by Italian pelagic trawlers has been conducted in the northern central Adriatic Sea [21][22][23]. The information collected in its framework provides a unique opportunity to assess the operational details of capture events and the abundance trends of species over time. ...
... aquila). In the Adriatic Sea, their interactions with fishing gears have usually been ascribed to bottom trawlers [48,49], trammel nets [50] and, recently, pelagic/midwater trawlers [21][22][23]51]. The present data show that demersal elasmobranchs were also caught by pelagic/midwater trawlers in the northern Adriatic Sea, which is characterized by relatively shallow waters (< 50 m). ...
... Nevertheless, the present findings are consistent with previous evidence of the presence of pelagic stingray in the northern Adriatic Sea [65][66][67][68]. Its scarce commercial value entails that over the past few decades it has usually been discarded at sea [21][22][23]66]. The IUCN has assessed pelagic stingray as a Least Concern species in the Mediterranean [69]. ...
Elasmobranchs are among the most threatened long-lived marine species worldwide, and incidental capture is a major source of mortality. The northern central Adriatic Sea, though one of the most overfished basins of the Mediterranean Sea, supports a very valuable marine biodiversity, including elasmobranchs. This study assesses the impact of the northern central Adriatic pelagic trawl fishery on common smooth-hound (Mustelus mustelus), spiny dogfish (Squalus acanthias), common eagle ray (Myliobatis aquila), and pelagic stingray (Pteroplatytrygon violacea) by examining incidental catches recorded between 2006 and 2015. The distribution of bycatch events was evaluated using geo-referenced data. Generalized Linear Models were computed to standardize the catch of the four species and to predict the relative abundance of bycatch events. Data analysis shows that most bycatch events involving all four species occurred in the northern Adriatic Sea. The models predicted significant, distinct temporal patterns of standardized catches in line with previous investigations. Water depth, season, and fishing region were the best predictors to explain bycatch events. The present data suggest that the northern Adriatic may be an important nursery area for several elasmobranchs. They also highlight the urgent need for a better understanding of the interactions between elasmobranchs and fisheries to develop and apply suitable, ad hoc management measures.
... Subsequently, another survey was carried out over the period from February 2015 to February 2016. Overall, 464 fishing trips were monitored for a total of 1 797 hauls; out of 587 bottlenose dolphin individuals interacting with fishing operations, only one incidental catch was recorded, for an estimated catch rate of 0.002, corresponding to two expected catches per year (Sala et al., 2018). The last available report of this project is referred to in the 2016-2017 survey. ...
... The objective was to test the effects of different types of acoustic deterrent devices on the behaviour of cetaceans and assess their real efficacy as a mitigation measure for this fishing activity. The first results seemed encouraging, but statistical analysis of the entire project revealed that the pinger influence on dolphin behaviour was not significant, highlighting a gradual reduction of the effects over time Sala et al., 2018). Other studies provide good evidence for the effectiveness of pingers in reducing the incidental catch of some cetacean species (Gazo, Gonzalvo and Aguilar, 2008;Brotons et al., 2008;Dawson et al., 2013), but a definitive answer for achieving effective mitigation overall is still lacking (Zahri et al., 2007;Buscaino et al., 2009). ...
... Subsequently, another survey was carried out over the period from February 2015 to February 2016. Overall, 464 fishing trips were monitored for a total of 1 797 hauls; out of 587 bottlenose dolphin individuals interacting with fishing operations, only one incidental catch was recorded, for an estimated catch rate of 0.002, corresponding to two expected catches per year (Sala et al., 2018). The last available report of this project is referred to in the 2016-2017 survey. ...
... The objective was to test the effects of different types of acoustic deterrent devices on the behaviour of cetaceans and assess their real efficacy as a mitigation measure for this fishing activity. The first results seemed encouraging, but statistical analysis of the entire project revealed that the pinger influence on dolphin behaviour was not significant, highlighting a gradual reduction of the effects over time Sala et al., 2018). Other studies provide good evidence for the effectiveness of pingers in reducing the incidental catch of some cetacean species (Gazo, Gonzalvo and Aguilar, 2008;Brotons et al., 2008;Dawson et al., 2013), but a definitive answer for achieving effective mitigation overall is still lacking (Zahri et al., 2007;Buscaino et al., 2009). ...
This publication offers an overview of historical and current trends in the bycatch of five
important groups of vulnerable species in the Mediterranean and the Black Sea: seabirds, sea turtles, elasmobranchs, marine mammals and macrobenthic invertebrates. Interactions between these groups and fisheries are known to occur in the context of nearly all commonly used types of fishing gear and can result in injury or death to the animals. Each chapter in this review focuses on one of the five groups of vulnerable species, describing and presenting data from surveys and studies conducted over recent decades. The chapters are further subdivided according to fishing gear and GFCM subregion (western, central and eastern Mediterranean, the Adriatic Sea and
the Black Sea). The incidental catch records included in this review are derived from a variety of approaches. Surveys completed by onboard observers, while demanding more time and resources, represent the most comprehensive and accurate of these methods. Less reliable data come from non-systematic, opportunistic data collection, such as questionnaire surveys answered by fishers. Though many geographic areas and vessel groups remain underrepresented in the available data, coverage has generally increased in recent years and insight continues to emerge on the key dynamics governing
the bycatch of vulnerable species in the Mediterranean and Black Sea. Seabird bycatch has mainly been recorded from the western Mediterranean and in longline fisheries. Bottom trawlers, on the other hand, have the greatest impact on sea turtles, especially
in the northern Adriatic Sea, Tunisia, Egypt and Turkey. The vessel groups most implicated
in elasmobranch bycatch vary by subregion, with longliners accounting for nearly 80 percent of incidental captures in the central Mediterranean, for example, while pelagic trawlers are responsible for an even greater majority of incidental captures in the neighbouring Adriatic Sea. Historically, marine mammals were often caught in large-mesh driftnets, but the incidental capture of these species has declined since bans on driftnets were put in place in the late 1990s. Unsurprisingly, macrobenthic invertebrates, including soft and hard corals, sponges, echinoderms and molluscs, are most affected by bottom trawls, as they are dragged across the seafloor these species inhabit.
Vulnerable species are not the only ones to come out the worse for wear from their interactions with fishing activities. Fishers also risk economic losses resulting from damage done to their nets by entrapped individuals or from the depredatory behaviour of species that feed on bait meant to lure target species. Raising awareness amongst fishers and relevant stakeholders of the threats currently facing vulnerable populations across the Mediterranean and the Black Sea, as well as their importance to local ecosystems, will help to improve relations between fisheries and these species and to ease transitions toward safer practices. New technologies that can mitigate
the bycatch of vulnerable species must continue to be tested and implemented in fisheries and standardized procedures for data collection should be established to better understand the many factors influencing bycatch in the region.
... km/h; the net's mouth can be 30-45-m wide and 7-12-m high (Sala, 2013). While midwater trawlers normally target pelagic and epipelagic species, in the shallow waters of the north-western Adriatic their gear ends up fishing relatively close to the seafloor (Fortuna et al., 2010;Sala et al., 2018). ...
The Adriatic Sea is one of the areas most exposed to trawling, worldwide. We used four years (2018–2021) and 19,887 km of survey data to investigate factors influencing daylight dolphin distribution in its north-western sector, where common bottlenose dolphins *Tursiops truncatus* routinely follow fishing trawlers. We validated Automatic Identification System information on the position, type and activity of three types of trawlers based on observations from boats, and incorporated this information in a GAM-GEE modelling framework, together with physiographic, biological and anthropogenic variables. Along with bottom depth, trawlers (particularly otter and midwater trawlers) appeared to be important drivers of dolphin distribution, with dolphins foraging and scavenging behind trawlers during 39.3% of total observation time in trawling days. The spatial dimension of dolphin adaptations to intensive trawling, including distribution shifts between days with and without trawling, sheds light on the magnitude of ecological change driven by the trawl fishery.
... Since 2006, an extensive monitoring program of bycatch of long-lived species like cetaceans, sea turtles, and elasmobranchs by Italian midwater pair trawlers has been conducted in the northern central Adriatic Sea (Fortuna et al., 2010;Sala et al., 2016Sala et al., , 2018. The information collected in its framework provides a unique opportunity to assess the operational details of capture events and the abundance trends of species over time . ...
Despite the fact that Mediterranean loggerhead turtles are listed as “Least Concern” by the International Union for the Conservation of Nature (IUCN), they are among the most threatened marine megafauna worldwide, because of fishery-related incidental captures. The northern central Adriatic Sea is one of the most overfished basins of the Mediterranean Sea and it supports a very valuable marine biodiversity, including sea turtles. This study assesses the spatial and seasonal impact of the northern central Adriatic midwater pair trawl fishery on loggerhead turtle (Caretta caretta) by examining incidental catches recorded between 2006 and 2018 and environmental variables. The model predicted seasonal variation of loggerhead distribution. According to previous studies, data analysis indicates that most bycatch events of loggerhead turtle occurred in the northern Adriatic Sea. The present data confirm that the northern Adriatic may be an important foraging area for loggerhead turtle. They also highlight the urgent need for a better understanding of the interactions between sea turtles and fisheries to develop and apply suitable, ad hoc management measures in critical habitats.
Several populations of odontocete cetaceans, including at least 19 species, have modified
their behavior and adapted to foraging in association with trawlers. We review information on odontocete interactions with different types of trawlers across 13 Food and Agriculture Organization fishing areas around the world. We also review knowledge gaps, the effects on odontocete ecology, distribution, behavior and social organization, the main mitigation options, and some management avenues that could help reduce incidental mortality. Trawlers involved in the interactions varied greatly in gear and target species, implying odontocetes have developed behavioral specializations to forage under a variety of conditions. Specialized behavior included venturing into a moving trawl net to feed on the organisms trapped in the net, feeding on fish stirred up by the net, extracting fish from the outer mesh, feeding on catch lost during hauling, and scavenging on discarded catch. Foraging behind trawlers facilitates access to prey, and in some instances may compensate for scarcity of natural prey within areas exposed to intensive fishing or environmental degradation. This opportunistic foraging strategy, however, exposes the animals to potential
harm and mortality in trawl gear. The combined effect of facilitated foraging and bycatch on the status and trends of odontocete populations is unknown. The economic damage caused by odontocetes, e.g. in terms of loss of marketable catch and gear damage, remains largely conjectural. Attempts to reduce depredation and/or bycatch in trawl gear have included
acoustic deterrents and exclusion devices installed in nets, although neither technique has proven to be consistently effective.
--- https://doi.org/10.1007/s11160-022-09712-z
Osservatorio economico sulle strutture produttive della pesca marittima in Italia
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