scholarly journals Commercial viability of locating pelagic longline branchline weights at the hook to reduce seabird bycatch

2020 ◽  
Vol 43 ◽  
pp. 223-233
Author(s):  
E Gilman ◽  
S Beverly ◽  
M Musyl ◽  
M Chaloupka
Keyword(s):  
Economic Viability ◽  
Posterior Density ◽  
Commercial Viability ◽  
Catch Rates ◽  
Species Specific ◽  
Longline Fisheries ◽  
Alternative Designs ◽  
Highest Posterior Density ◽  
Pelagic Longline ◽  
Tuna Longline

Bycatch in pelagic longline fisheries threatens the viability of some seabird populations and reduces fishing efficiency. The mass of a branchline fishing weight and its distance from the hook significantly explain seabird catch risk during setting and hauling. We surveyed Hawaii tuna longline fishers to obtain their perspectives on the practicality, safety and economic viability of alternative designs which place weights adjacent to hooks instead of conventional designs with weighted swivels attached 0.6 m from the hook. We conducted experimental fishing to explore the commercial viability of a combination weighted swivel attached to the eye of the hook. We used a Bayesian random effects meta-analytic regression modeling approach to estimate pooled expected species-specific log relative risk of capture on conventional, as opposed to experimental, branchlines. There were significant decreases in catch rates on experimental branchlines of 54% (95% highest posterior density interval [HDI]: 34.3 to 73.8) for retained species and 28% (95% HDI: -7.5 to 93.3) for discarded species. For about 10% of experimental weighted hooks, the point of the hook tangled on the swivel, likely contributing to lower catch rates and making it more difficult for crew to coil branchlines. We identify possible factors explaining why the experimental gear reduced catch rates. The study demonstrates the benefits of stakeholder scoping to determine bycatch mitigation options with the highest promise for practicality, economic viability and safety, as well as benefits of conducting a pilot study to assess commercial viability to determine if a full experiment to assess bycatch mitigation efficacy is warranted.

scholarly journals A Comparison of Alternative Circle Hook (Kahle Hook) and J Style Hook Performance in Experimental Pelagic Longline Fishery in Turkey

2015 ◽  
pp. 19-27 ◽  
Author(s):  
Aytaç Özgül ◽  
Ali Ulaş ◽  
Altan Lök ◽  
F. Ozan Düzbastılar ◽  
Cengiz Metin
Keyword(s):  
Longline Fishery ◽  
Fish Catch ◽  
Study Circle ◽  
The Difference ◽  
Pelagic Longline Fishery ◽  
By Catch ◽  
Catch Rates ◽  
Longline Fisheries ◽  
Marine Wildlife ◽  
Pelagic Longline

In recent years, circle hooks have been encouraged as an alternative to traditional J-hooks in pelagic longline fisheries to minimize by-catch mortality and injury to sea turtles and other marine wildlife. Prior to this study, circle hooks had not been used by domestic commercial pelagic longliners in Turkey. The main objective of the study was to evaluate the efficiency of kahle hook comparing with J-style hook baited with sardine (Sardina pilchardus) in pelagic longline fishery in the Aegean coast of Turkey (Kuşadası Bay).We used conventional J-style hooks (Mustad 2315DT-4/0) and kahle hooks (Eagle Claw142A-6/0) for each fishing operation and compared catch rates, catch compositions of target and non-target species. The relative performance of kahle and traditional J-style hooks was tested during 22 valid pelagic longline fishing operations between August 2010 and December 2012. A total of 2200 hooks were used equally amongkahle and J-style hooks consecutively. Captured fish were identified, total and fork lengths were measured,weighed, the time of haulback, and hook type as well as by-catch fish were recorded. A total of 78 fish were caught belonging to 13 species during the samplings. The overall CPUE was 4.73 fishes per 100 hooks for kahle hooks and 2.46 fishes for J-style hooks. For the CPUE of all fishes, the difference was statistically significant (Z = -1.977; P<0.05), in favour of the kahle hook being almost two times greater than the J-style hook. Likewise CPUE was 17007.69 g per 100 hooks for kahle style hooks and 4807.27 g for J-style hooks (Z = -1.997; P<0.05). While no difference was found between two hook models on by-catch species, kahle hooks were more efficient in comparison to J hooks on discard species. Swordfish (Xiphiasgladius) had the highest CPUE (2.82) among all species for kahle hooks followed by silver scabbard fish (Lepidopuscaudatus), 0.64. For J-style hooks, silver scabbard fish catch had the highest CPUE (0.64) followed by swordfish (0.55).

Effect of bait on sea turtles bycatch rates in pelagic longlines: An overview

2011 ◽  
Vol 32 (4) ◽  
pp. 493-502 ◽  
Author(s):  
Imed Jribi ◽  
Abderrahmen Bouain ◽  
Khaled Echwikhi ◽  
Mohamed Nejmeddine Bradai
Keyword(s):  
Laboratory Experiments ◽  
Sea Turtles ◽  
Integrated Approach ◽  
Sea Turtle ◽  
Field Trials ◽  
Population Declines ◽  
Pacific Studies ◽  
Catch Rates ◽  
Longline Fisheries ◽  
Pelagic Longline

AbstractPelagic longline fishing has been identified as a significant threat to endangered sea turtle populations. Reducing sea turtle bycatch in pelagic longline fisheries, in concert with activities to reduce other anthropogenic mortality sources, may halt and reverse population declines. Here, we examine the effect of bait manipulation as a simple mitigation method that could reduce sea turtle interactions with longline fishing gear. We analyzed laboratory experiments and field trials conducted in the Mediterranean, the northeast Distant Area in the Atlantic and the Western North Pacific. Studies showed that turtles are more likely to feed on squid than on mackerel when both are used simultaneously as bait. The stingray, Dasyatis pastinaca, used as bait, was more effective than mackerel; this ray was vulnerable and stimulated much thought about other species to use as alternative bait. Effective in laboratory conditions with captive turtles, dyed and artificial bait did not seemed to be effective in reducing turtle bycatch in field conditions. Optimal mitigation measure must reduce incidence of hooking of threatened sea turtles to acceptable levels and also offer an economic advantage to fisheries. Studies concerning the effect of bait modification to reduce turtle bycatch highlight the importance of an integrated approach towards sensory deterrents, as both visual and chemical cues are likely to attract sea turtles to longline gear. Further research on the development of sensory-based deterrents can contribute to reduced sea turtle bait interactions and maintain catch rates of target species.

Seabird bycatch vulnerability in pelagic longline fisheries based on modelling of a long-term dataset

2021 ◽  
pp. 1-16
Author(s):  
CAN ZHOU ◽  
NIGEL BROTHERS
Keyword(s):  
Capture Event ◽  
Retrieval Rate ◽  
Competitive Environments ◽  
Global Concern ◽  
Competitive Species ◽  
Spatio Temporal ◽  
Longline Fisheries ◽  
Pelagic Longline

Summary The incidental mortality of seabirds in fisheries remains a serious global concern. Obtaining unbiased and accurate estimates of bycatch rates is a priority for seabird bycatch mitigation and demographic research. For measuring the capture risk of seabird interactions in fisheries, the rate of carcass retrieval from hauled gear is commonly used. However, reliability can be limited by a lack of direct capture observations and the substantial pre-haul bycatch losses known to occur, meaning incidence of seabird bycatch is underestimated. To solve this problem, a new measure (bycatch vulnerability) that links an observed interaction directly to the underlying capture event is proposed to represent the capture risk of fishery interactions by seabirds. The new measure is not affected by subsequent bycatch loss. To illustrate how to estimate and analyse bycatch vulnerability, a case study based on a long-term dataset of seabird interactions and capture confirmation is provided. Bayesian modelling and hypothesis testing were conducted to identify important bycatch risk factors. Competition was found to play a central role in determining seabird bycatch vulnerability. More competitive environments were riskier for seabirds, and larger and thus more competitive species were more at risk than smaller sized and less competitive species. Species foraging behaviour also played a role. On the other hand, no additional effect of physical oceanic condition and spatio-temporal factors on bycatch vulnerability was detected. Bycatch vulnerability is recommended as a replacement for the commonly used bycatch rate or carcass retrieval rate to measure the capture risk of an interaction. Combined with a normalized contact rate, bycatch vulnerability offers an unbiased estimate of seabird bycatch rate in pelagic longline fisheries.

The effect of light attractor color in pelagic longline fisheries

2021 ◽  
Vol 235 ◽  
pp. 105822
Author(s):  
André S. Afonso ◽  
Bruno Mourato ◽  
Humberto Hazin ◽  
Fábio H.V. Hazin
Keyword(s):  
Longline Fisheries ◽  
Pelagic Longline ◽  
Effect Of Light

Mitigating bycatch of threatened seabirds: the effectiveness of branch line weighting in pelagic longline fisheries

2018 ◽  
Vol 22 (4) ◽  
pp. 376-385 ◽  
Author(s):  
S. Jiménez ◽  
A. Domingo ◽  
R. Forselledo ◽  
B. J. Sullivan ◽  
O. Yates
Keyword(s):  
Branch Line ◽  
Longline Fisheries ◽  
Pelagic Longline ◽  
Threatened Seabirds
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