Estimating fishery-scale rates of discard mortality using conditional reasoning

Benoît, Hugues P.; Hurlbut, Thomas; Chassé, Joël; Jonsen, Ian D.

doi:10.1016/j.fishres.2011.12.004

Cited by 79 publications

(112 citation statements)

References 55 publications

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“…The uncertainty surrounding this DM rate was estimated via a combined empirical and parametric bootstrap routine that accounted for error in each component, as well as the clustered nature of both the injury score observations and the tackle survey data (e.g. Benoît et al, 2012). Each of the 1000 routine iterations proceeded in two phases.…”

Section: Estimating a Fishery-wide Cod Dm Ratementioning

confidence: 99%

Estimating and mitigating the discard mortality of Atlantic cod (Gadus morhua) in the Gulf of Maine recreational rod-and-reel fishery

Capizzano

Mandelman

Hoffman³

et al. 2016

ICES Journal of Marine Science

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In recent years, the recreational contribution to the total catch of Atlantic cod (Gadus morhua) in the Gulf of Maine (GOM) has increased with recreational discards outnumbering recreational landings by 2:1. However, the discard mortality (DM) rate of cod released in the recreational fishery remains poorly understood, thus contributing to the uncertainty in stock assessments and fishery management plans. The current study examined the capture-related factors most detrimental to cod DM in the GOM recreational rod-and-reel fishery. Atlantic cod (n ¼ 640; 26.0-72.0 cm) were angled from June-October 2013 on southern Jeffreys Ledge in the western GOM using fishing gear representative of the local recreational fishery. A subset (n ¼ 136) was also tagged with pressure-sensing acoustic transmitters before being released into an acoustic receiver array (n ¼ 31) deployed to monitor survival up to 94 days. To properly model DM up to the fishery-wide level, all cod were visually assessed for capture-related injuries according to a four-level injury score index. Mean tackle-specific DM rates of 15.4 and 21.2% were estimated for bait-and jig-captured cod, respectively, with an overall 16.5% mean DM rate for the 2013 GOM recreational cod fishery. Twenty-nine cod tagged with acoustic transmitters were identified as dead, where the majority ( 90%) died within 16 h post-capture. Upon evaluation with a specifically adapted parametric survival analysis, greater incidence of mortality was attributed to the capture and handling process (rather than release) for moderately and severely injured cod. Based on the capture-related factors associated with the highest injury rates, we recommend minimizing fight and handling times, avoiding areas with small cod, educating inexperienced anglers, and favouring bait over jigs to mitigate mortality. Results will continue to inform the development of fishery management plans and enhance survival through dissemination of "best practice" techniques to fishery stakeholders.

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Section: Estimating a Fishery-wide Cod Dm Ratementioning

confidence: 99%

Estimating and mitigating the discard mortality of Atlantic cod (Gadus morhua) in the Gulf of Maine recreational rod-and-reel fishery

Capizzano

Mandelman

Hoffman³

et al. 2016

ICES Journal of Marine Science

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“…Previous studies have shown that assessing condition upon capture is valuable because it can be a reliable predictor of post-release mortality (Hueter et al, 2006;Benoît et al, 2012). In the absence of tagging studies, capture condition indexing can be applied on a broad scale and to multiple species to estimate post-release mortality.…”

Section: Discussionmentioning

confidence: 99%

“…Consequently, these types of studies are limited to only a few shark species (Musyl et al, 2011;Dapp et al, 2015). In the absence of traditional post-release mortality estimation techniques, the externally visible condition (sometimes termed "vitality") of the animal when removed from fishing gear (e.g., "healthy, " "sluggish, " and "moribund") has been used as a proxy for post-release mortality (Hueter et al, 2006;Benoît et al, 2012;Braccini et al, 2012). The identification of variables that contribute to poor capture condition will allow researchers to better understand causes of post-release mortality during capture.…”

Section: Introductionmentioning

confidence: 99%

Moving from Measuring to Predicting Bycatch Mortality: Predicting the Capture Condition of a Longline-Caught Pelagic Shark

et al. 2016

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Incidental fisheries capture has been identified as having a major effect on shark populations throughout the world. However, factors that contribute to the mortality of shark bycatch during fisheries capture are not fully understood. Here, we investigated the effects of capture duration, sea surface temperature, and shark total length (snout to the tip of the upper caudal lobe) on the physiology and condition of longline-caught bronze whalers, Carcharhinus brachyurus. Plasma lactate and potassium concentration had a positive linear relationship with capture duration, indicating that this species experiences increasing physiological challenges while on fishing gear. Additionally, we used stereotype logistic regression models to determine variables that could predict the capture condition of sharks (categorized as "healthy," "sluggish," or "moribund or dead"). In these models, elevated plasma lactate concentration, plasma potassium concentration, and capture duration increased the likelihood of C. brachyurus being captured in a "sluggish" condition or in a "moribund or dead" condition. After plasma lactate concentration exceeded 27.4 mmol/L, plasma potassium concentration exceeded 8.3 mmol/L, or capture durations exceeded 293 min, the majority of captured sharks (>50%) were predicted to be "moribund or dead." We recommend that a reduction in the amount of time longlines are left fishing (soak time) will reduce immediate and post-release mortality in C. brachyurus bycatch and that our methods could be applied to identify causes of fisheries-induced mortality in future studies. The identification of operational, environmental, and biological variables contributing to poor condition will be necessary to implement conservation strategies that reduce mortality during capture.

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“…In contrast to a relatively high discard survival of invertebrates in beam-trawl fisheries, the survival rates of discarded undersized fish of commercial species are generally low: 0-50% for Pleuronectiformes, over 70% for Rajiformes and 0% for whiting and pouting (Van Beek et al, 1990;Benoit et al, 2012;Depestele et al, 2014), stressing the importance of minimizing the bycatch of undersized fish. The numbers given in Table 5 are therefore promising, and probably an underestimate because the in-liners used in the present study hamper the escape of undersized fish.…”

Section: Reduced Environmental Impactmentioning

confidence: 95%

Reducing bycatch in beam trawls and electrotrawls with (electrified) benthos release panels

Soetaert

Lenoir²,

Verschueren³

2016

ICES Journal of Marine Science

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Benthos release panels (BRPs) are known for their capacity to release large amounts of unwanted benthos and debris, which can decrease mortality on these animals and eases the on board sorting process aboard demersal beam trawlers. They can reduce the bycatch of undersized fish, which is desired once the European discard ban is implemented. However, unacceptable commercial losses of sole (Solea solea L.) and damage to the BRP as a consequence of suboptimal and unsuitable rigging in the traditional beam trawl with chain mat, is hampering a successful introduction in commercial beam-trawl fisheries. To eliminate these drawbacks, square-meshed BRPs with different mesh sizes (150, 200, and 240 mm) were rigged in a trawl with square net design as used in electrotrawls and tested for selectivity. In addition to this, the effect of electric stimulation at the height of the BRP to eliminate the loss of commercial sole was examined. According to our observations, no abrasion of the net attributable to suboptimal rigging occurred in any of the BRPs tested. The catch comparisons showed significant release of benthos and undersized fish in all panel mesh sizes, but there was always a significant loss of marketable sole in the 150, 200, and 240 mm BRPs. Adding a 80 Hz electric cramp stimulus to the BRP, resulted in equal catches of sole larger than 25 cm as the standard net, without negatively affecting the release of benthos and most undersized commercial fish. This clearly demonstrates the promising potential of electrified BRPs (eBRPs), but further optimization by using smaller BRP mesh sizes or optimized electric stimuli is warranted to retain all marketable sole.

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Estimating fishery-scale rates of discard mortality using conditional reasoning

Cited by 79 publications

References 55 publications

Estimating and mitigating the discard mortality of Atlantic cod (Gadus morhua) in the Gulf of Maine recreational rod-and-reel fishery

Estimating and mitigating the discard mortality of Atlantic cod (Gadus morhua) in the Gulf of Maine recreational rod-and-reel fishery

Moving from Measuring to Predicting Bycatch Mortality: Predicting the Capture Condition of a Longline-Caught Pelagic Shark

Reducing bycatch in beam trawls and electrotrawls with (electrified) benthos release panels

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