Swimming patterns of wild harbour porpoises Phocoena phocoena show detection and avoidance of gillnets at very long ranges

Nielsen, Torben P.; Wahlberg, Magnus; Heikkilä, Sanja; Jensen, Maria; Sabinsky, Puk Faxe; Dabelsteen, Torben

doi:10.3354/meps09630

Cited by 26 publications

(17 citation statements)

References 17 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…It has been suggested that porpoises may be capable of detecting fishing nets at distances of up to 80 m (Nielsen et al 2012; but see Dawson & Lusseau 2013, Nielsen et al 2013. If porpoises are able to detect gillnets up to 80 m away, it may only be relevant to alert them to a net within this range if they are preoccupied e.g.…”

Section: Habitat Displacementmentioning

confidence: 99%

Pingers cause temporary habitat displacement in the harbour porpoise Phocoena phocoena

Kyhn¹,

Jørgensen²,

Carstensen³

et al. 2015

Mar. Ecol. Prog. Ser.

Self Cite

View full text Add to dashboard Cite

Several studies have shown that pingers mitigate porpoise bycatch and thus pinger use is now mandatory in some fisheries -although the long-term effects of pinger exposure on porpoises have not been well studied. The effects of 2 types of pingers (Airmar: 10 kHz tone; SaveWave Black Saver: 30−160 kHz sweep) on the presence of wild harbour porpoises, Phocoena phocoena, were investigated in 2 areas. Pinger spacing within the areas was similar to that used in commercial fisheries. Two scenarios were tested: (1) pingers were periodically activated and deactivated during 6 periods resembling the deployment and recovery of nets in a gillnet fishery, and (2) pingers were active continuously for 28 d. Acoustic dataloggers (T-PODs) were deployed, 4 within the pinger areas and 3 in control areas, and detected porpoise echolocation activity throughout the entire study. During the periodic-exposure scenario, the porpoise detection rate was reduced by 56% when pingers were active. The reduction was larger for the SaveWave pingers (65%) than for the Airmar pingers (40%). There was a tendency for the encounter rate to increase after the first 2−4 periodic exposures, which could indicate gradual habituation. During the continuous-exposure scenario, the detection rate was reduced by 65% throughout the 28 d with no sign of habituation. In the control areas (2.5, 3 and 5 km distant), neither a decrease nor an increase in detection rate was observed, suggesting that porpoises were displaced either < 2.5 km or > 5 km away. If pingers are used as deterrent devices, the impact of habitat exclusion must therefore be considered concurrently with mitigation of bycatch, especially when regulating fisheries in Marine Protected Areas.

show abstract

Section: Habitat Displacementmentioning

confidence: 99%

Pingers cause temporary habitat displacement in the harbour porpoise Phocoena phocoena

Kyhn¹,

Jørgensen²,

Carstensen³

et al. 2015

Mar. Ecol. Prog. Ser.

Self Cite

View full text Add to dashboard Cite

show abstract

“…Wild porpoises have since been recorded producing SLs up to 30 dB greater than those of captive animals; therefore, the estimated potential detection range of gillnets by this species was increased to around 13 to 26 m (Villadsgaard et al 2007). More recently, a study has shown that free-ranging harbour porpoises detect and avoid gillnets at distances up to 80 m (Nielsen et al 2012); distances at which the small increase in TS provided by acoustically reflective nets is unlikely to have much influence. Additionally, Cox & Read (2004) found no difference in echolocation rate or echolocation intensity of harbour porpoises around BaSO 4 gillnets compared to around standard gillnets, indicating that porpoises did not change their echolocation behaviour in response to the reflective net.…”

mentioning

confidence: 99%

Franciscana bycatch is not reduced by acoustically reflective or physically stiffened gillnets

Bordino¹,

Mackay²,

Werner³

et al. 2013

Endang. Species. Res.

View full text Add to dashboard Cite

The incidental capture of franciscana Pontoporia blainvillei in gillnet fisheries of Argentina, Uruguay and Brazil represents a major conservation threat to this species. We report on an experimental trial that compared franciscana bycatch rates in standard gillnets to gillnets with 1 of 2 modifications: increased acoustic reflectivity by infusion of barium sulphate (BaSO 4 ) or increased flexural stiffness of the nylon twine. Field trials were conducted in association with artisanal fishermen at San Clemente del Tuyu in Bahia Samborombon, Argentina, between October 2009 and March 2010. Depth sensors were used to record the underwater fishing behaviour of the 3 net types. Seventy-seven dolphins were observed incidentally captured in 807 monitored gillnet hauls, with similar fishing effort observed for each net type. There was no significant difference in franciscana bycatch rates (p > 0.05) or target fish catches (p > 0.05) among the 3 net types. The stiff net twine had a slightly but significantly higher flexural stiffness (FS) than the reflective or control net twine. The FS of the dry stiff twine was similar to that previously reported for BaSO 4 twine with a similar diameter; in contrast, the FS of the reflective nylon was, unexpectedly, much lower. However, the difference in the FS between wet, submerged stiff twine and control twine used in the field was estimated at 19.4%. The BaSO 4 net fished with a significantly lower mean float line height than either the control or stiffened net. These results show that the use of reflective or stiff nets does not lead to a reduction in franciscana bycatch rates; therefore, other management strategies need to be developed to reduce the impact of incidental captures of this species. KEY WORDS: Bycatch · Gillnet · Franciscana · Artisanal fishery Resale or republication not permitted without written consent of the publisher FREE REE ACCESS CCESS Contribution to the Theme Section 'Techniques for reducing bycatch of marine mammals in gillnets'Endang Species Res 21: [1][2][3][4][5][6][7][8][9][10][11][12] 2013 species is listed as Vulnerable by the IUCN (Reeves et al. 2008) and is considered to be the most threatened cetacean in the Southwest Atlantic (Secchi 2010). In coastal waters of Buenos Aires Province, Argentina, an estimated 650 dolphins are bycaught annually (Bordino & Albareda 2004). The most recent population estimate for this species in Argentinean waters is 14 000 individuals (Crespo et al. 2010), so it is unlikely that current bycatch levels are sustainable, and management measures are, therefore, urgently required to reduce the incidental bycatch of the species.The use of acoustic alarms has been shown to significantly reduce the bycatch rates of franciscana (Bordino et al. 2002) and other cetaceans in gillnets (Kraus et al. 1997, Carretta et al. 2008), but the financial cost of implementation and enforcement of pinger use limits their applicability in many smallscale fisheries (Read 2008). Concerns that the widespread use of acoustic alarms cou...

show abstract

“…Pingers have been reported to deter harbour porpoises from nets (Cox et al, 2001;Culik et al, 2001) and to efficiently reduce bycatch (Kraus et al, 1997;Larsen et al, 2013). Although previous studies indicate that harbour porpoises can detect gill nets at sufficient distance to avoid them (Kastelein et al, 2000;Koschinski et al, 2006;Villadsgaard et al, 2007;Nielsen et al, 2012), for unknown reasons they are still being caught in nets both with and without pingers (Dawson et al, 1998). In addition, there may be several potential problems with a large-scale use of pingers such as habituation and noise pollution.…”

mentioning

confidence: 99%

“…Given the source level and propagation loss of harbour porpoise echolocation clicks (e.g., Villadsgaard et al, 2007) and the detection threshold of the data loggers (around 140 dB re 1 µPa p), the loggers can pick up these signals at a range of several hundreds of meters. Harbour porpoises are able to detect fishing gear at somewhat shorter, but still comparable, ranges (presumably using acoustic cues; see Nielsen et al, 2012).…”

mentioning

confidence: 99%

“…It was assumed that harbour porpoise click trains detected within a predefined duration of sampling, 5 min, have been caused by the same harbour porpoise (or harbour porpoise group). The duration of 5 min was used from what is known of harbour porpoise swimming behaviour from other studies performed by the authors and from the literature (e.g., Koschinski et al, 2006;Nielsen et al, 2012). Thus, a harbour porpoise encounter was determined as one or several click trains contained within a 5-min window, with an additional encounter occurring only if there was a pause longer than 5 min to the next train detection.…”

mentioning

confidence: 99%

See 1 more Smart Citation

Short Note: Acoustic Activity of Harbour Porpoises (Phocoena phocoena) Around Gill Nets

Boström

Crog²,

Kindt-Larsen

et al. 2013

Aquat Mamm

View full text Add to dashboard Cite

Swimming patterns of wild harbour porpoises Phocoena phocoena show detection and avoidance of gillnets at very long ranges

Cited by 26 publications

References 17 publications

Pingers cause temporary habitat displacement in the harbour porpoise Phocoena phocoena

Pingers cause temporary habitat displacement in the harbour porpoise Phocoena phocoena

Franciscana bycatch is not reduced by acoustically reflective or physically stiffened gillnets

Short Note: Acoustic Activity of Harbour Porpoises (Phocoena phocoena) Around Gill Nets

Contact Info

Product

Resources

About