Are circle hooks effective in reducing incidental captures of loggerhead sea turtles in a Mediterranean longline fishery?

Piovano, Susanna; Swimmer, Yonat; Giacoma, Cristina

doi:10.1002/aqc.1021

Cited by 40 publications

(54 citation statements)

References 19 publications

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“…Previous assessments of sea turtle bycatch in longline fisheries indicate significantly higher catch rates in fisheries setting gear at shallow depths (<60 m), typically targeting swordfish (Xiphias gladius), compared to most deep-set fishing targeting tuna (Lewison et al, 2004;Kaplan, 2005). Numerous investigations indicate a high percentage of turtles are released alive from shallow-set fishing gear (e.g., Swimmer et al, 2006Swimmer et al, , 2013Piovano et al, 2009;Sales et al, 2010;Swimmer and Gilman, 2012), however a proportion of these turtles are assumed to subsequently die as a result of injuries, with likelihood of mortality a function of anatomical hooking location and degree of gear removal (see Ryder et al, 2006;Carruthers et al, 2009). Mitigating the effects of fisheries bycatch is a conservation priority worldwide, yet both research and managements actions are hindered by statistical challenges when analyzing rare and episodic events, as in common many examples of fisheries bycatch.…”

Section: Introductionmentioning

confidence: 99%

Sea Turtle Bycatch Mitigation in U.S. Longline Fisheries

et al. 2017

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Capture of sea turtles in longline fisheries has been implicated in population declines of loggerhead (Caretta caretta) and leatherback (Dermochelys coriacea) turtles. Since 2004, United States (U.S.) longline vessels targeting swordfish and tunas in the Pacific and regions in the Atlantic Ocean have operated under extensive fisheries regulations to reduce the capture and mortality of endangered and threatened sea turtles. We analyzed 20 + years of longline observer data from both ocean basins during periods before and after the regulations to assess the effectiveness of the regulations. Using generalized additive mixed models (GAMMs), we investigated relationships between the probability of expected turtle interactions and operational components such as fishing location, hook type, bait type, sea surface temperature, and use of light sticks. GAMMs identified a two to three-fold lower probability of expected capture of loggerhead and leatherback turtle bycatch in the Atlantic and Pacific when circle hooks are used (vs. J hook). Use of fish bait (vs. squid) was also found to significantly reduce the capture probability of loggerheads in both ocean basins, and for leatherbacks in the Atlantic only. Capture probabilities are lowest when using a combination of circle hook and fish bait. Influences of light sticks, hook depth, geographic location, and sea surface temperature are discussed specific to species and regions. Results confirmed that in two U.S.-managed longline fisheries, rates of sea turtle bycatch significantly declined after the regulations. In the Atlantic (all regions), rates declined by 40 and 61% for leatherback and loggerhead turtles, respectively, after the regulations. Within the NED area alone, where additional restrictions include a large circle hook (18/0) and limited use of squid bait, rates declined by 64 and 55% for leatherback and loggerhead turtles, respectively. Gains were even more pronounced for the Pacific shallow set fishery, where mean bycatch rates declined by 84 and 95%, for leatherback and loggerhead turtles, respectively, for the post-regulation period. Similar management approaches could be used within regional fisheries management organizations to reduce capture of sea turtles and to promote sustainable fisheries on a global scale.

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Section: Introductionmentioning

confidence: 99%

Sea Turtle Bycatch Mitigation in U.S. Longline Fisheries

et al. 2017

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“…As a result, swordfish fisheries have been the focus of dramatic management actions to reduce bycatch, most notably because of their interactions with loggerhead Caretta caretta and leatherback Dermochelys coriacea sea turtles. Both of these species are considered to be endangered in most oceans (Lewison et al 2004, Garcia-Cortes & Mejuto 2005, Watson et al 2005, Baez et al 2007, Gilman et al 2007, Petersen et al 2009, Piovano et al 2009). Loggerhead turtles were relisted as endangered in the North and South Pacific by the National Marine Fisheries Service and the US Fish and Wildlife Service in September 2011.…”

Section: Introductionmentioning

confidence: 99%

Modeling swordfish daytime vertical habitat in the North Pacific Ocean from pop-up archival tags

Abécassis¹,

Dewar²,

Hawn³

et al. 2012

Mar. Ecol. Prog. Ser.

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The daytime foraging depth of swordfish in the North Pacific was investigated with data from an 8 yr tagging program, using 28 Wildlife Computer pop-up archival tags deployed on swordfish in the North Pacific. The tags transmitted data from 1°S to 44°N latitude and from 206 to 249°E longitude. Five tags were recovered, providing a full archival record that showed that when swordfish did not engage in daytime basking behavior, they remained within a narrow range of light level during both day and night, suggesting swordfish stay within a soundscattering layer (SSL) to feed during both day and night. Daytime mean depth of non-basking swordfish ranged from 32 to 760 m. Seventy-seven percent of the daytime mean depth could be explained with a generalized additive model that used 3 environmental indices: satellite-derived surface chlorophyll as a proxy for light at depth, oxygen at 400 m obtained from the World Ocean Atlas, and temperature at 400 m inferred from the tag data. This model, when used in a predictive mode, generated a basin-wide map of swordfish daytime mean depth that showed depths exceeding 600 m to the north of Hawaii, shoaling to 300 m off the coast of California. This information could improve daytime swordfish catch by longliners and potentially allow them to switch from shallow night sets that result in interactions with sea turtles. This approach in effect defines the habitat of swordfish prey, giving us insight into the vertical behavior of those mid-trophic level organisms inhabiting the SSL. Our model could be easily applied to other deep-foraging species. KEY WORDS: Xiphias gladius · Swordfish · Satellite tracking · Generalized additive model · Habitat modellingResale or republication not permitted without written consent of the publisher

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“…To reduce the incidental capture of sea turtles, efforts are being conducted to test circle hooks as a mitigation measure, both in Uruguayan and Brazilian pelagic longline fisheries (for Uruguay see Domingo et al 2009, for Brazil the data are unpublished), which have been found to be successful in the reduction of sea turtle bycatch in other parts of the world (Cooke and Suski 2004;Watson et al 2005;Piovano et al 2009). At the same time, there are ongoing studies on distribution, habitat use and environmental preferences of juvenile loggerheads through satellite telemetry (unpublished data).…”

Section: Discussionmentioning

confidence: 99%

Standardization of CPUE of loggerhead sea turtle (Caretta caretta) caught by pelagic longliners in the Southwestern Atlantic Ocean

Pons¹,

Domingo²,

Sales³

et al. 2010

Aquat. Living Resour.

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-The population abundance estimates used in stock assessments or required to establish management measures, depend on the sampling of the entire demographic spectrum of a population resident in a given area. However, for sea turtles, most population estimates are based mainly on nesting beach survey data and only consider a fraction of the population. The Southwest Atlantic Ocean (SWA) is an important foraging and development area for juveniles of the loggerhead sea turtle Caretta caretta where reproductive stocks from various nesting beaches mix. Declines in C. caretta populations have been observed in many parts of the world and bycatch rates of this species in the SWA are among the highest worldwide. This study standardizes the catch rates of loggerheads caught by pelagic longline fisheries in the region, using data collected by observer programs from Brazil and Uruguay. Generalized linear models (GLM) with a delta lognormal approximation were used. The variables used in the model take into account spatial and temporal variations as well as the characteristics of the fleet. In total, 6 272 344 hooks were observed between 1998 and 2007, with minimum effort registered in 2000 (12 010 hooks) and maximum effort in 2005 (1 989 431 hooks). During this period 3778 loggerheads were incidentally captured. The catch rates of loggerheads by the Uruguayan and Brazilian pelagic longline fisheries show oscillations through the years without a clear tendency; however, a low negative trend was observed from 1998 to 2005 with an increase in the last two years (2006 and 2007). The capture per unit of effort (CPUE) values varied between 0.38 to 1.78 ind/1000 hooks in 2005 and 2007, respectively. Distinct zones with differential catch rates were identified, with the higher CPUE values over the continental slope of Uruguay and adjacent waters. The incidental catch rates of this species are influenced, not only by fishing area, but also by year, season, sea surface temperature and gear type. In consequence, these variables and other potential ones should be considered in bycatch estimates by different fisheries because the loggerhead sea turtles are not uniformly distributed. This study intends to contribute not only to the general knowledge of loggerhead sea turtles in the SWA but to a future assessment of their populations at a global scale.Key words: Sea turtle / bycatch / longline / GLM / Southwestern Atlantic Ocean Résumé -Les estimations d'abondance de population utilisées dans l'évaluation des stocks ou demandées pour établir des mesures de gestion, dépendent de l'échantillonnage du spectre démographique entier d'une population résidente dans une zone donnée. Cependant, pour les tortues de mer, ces estimations sont basées principalement sur des relevés des nids observés sur les plages et considèrent une fraction seulement de la population. L'Atlantique sud-ouest (SWA) est une zone importante de nourriture et de développement pour les juvéniles de la tortue caouanne Caretta caretta où des stocks de diverses plages d...

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Are circle hooks effective in reducing incidental captures of loggerhead sea turtles in a Mediterranean longline fishery?

Cited by 40 publications

References 19 publications

Sea Turtle Bycatch Mitigation in U.S. Longline Fisheries

Sea Turtle Bycatch Mitigation in U.S. Longline Fisheries

Modeling swordfish daytime vertical habitat in the North Pacific Ocean from pop-up archival tags

Standardization of CPUE of loggerhead sea turtle (Caretta caretta) caught by pelagic longliners in the Southwestern Atlantic Ocean

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