Total fishing mortality affecting Porbeagle shark in Atlantic Canadian waters
Notice bibliographique
Résumé
Porbeagle Shark (Lamna nasus) are intercepted as bycatch from numerous fisheries in the Maritimes (MAR), Newfoundland and Labrador (NL), Gulf (GULF), and Quebec (QC) regions. From 2015 onwards, Porbeagle Sharks have been considered bycatch as there has been little incentive to land the species due to its low economic value. Given changes in fishing practices, these analyses considered data from 2015–2021. The three components of fishing mortality were considered: landings, at-vessel mortality (AVM), and post-release mortality (PRM) of discards. AVM represents animals that are dead upon gear retrieval, PRM represents animals that die following release. Most Porbeagle landings came from MAR, and landings were sporadic from all other regions. Within MAR, the majority was from benthic longline. However, landings make up a small component of total fishing mortality, as the majority of Porbeagle are discarded. Discard information was obtained from Canadian at-sea observer (ASO) data. Discards from observed trips represent a proportion of fishery-wide bycatch; therefore, they must be scaled up to represent fishery-wide values. Total discard weights from observed trips were highest in MAR, lower in NL, and lowest in GULF and QC. Fishery-wide estimates will be substantially higher due to low ASO coverage in numerous fisheries. Numerous statistical methods to estimate fishery-wide bycatch were identified and examined for ASO data from pelagic longline, given that this gear type was used historically to target Porbeagle. However, the quality and characteristics of the data precluded the use of these methods. For fisheries in MAR, total Porbeagle bycatch (kg) on observed trips was scaled up to fishery-wide estimates based on the proportion of trips that were observed. For fisheries in NL, total Porbeagle bycatch (kg) on observed trips was scaled up to fishery-wide estimates based on the proportion of target species landings that were observed. Bycatch weight on observed trips from fisheries in QC and GULF was not scaled up due to the lack of information on observer coverage levels and low levels of bycatch. There was information on AVM and PRM rates from few fisheries. Example scenarios applied different assumed AVM and PRM rates for fisheries in MAR and NL to estimate fishery-wide dead discards. The annual estimates varied by 6–20% among scenarios. Given demonstrated challenges and limitations of the available data, it is not possible to derive meaningful estimates of total annual fishing mortality of Porbeagle. Interpretation of the implications or impacts of observed increases or decreases in annual fishing mortality is not possible without information on underlying abundance and status of infrequently observed, discarded bycatch species (such as Porbeagle). This limits the utility of estimates of fishing mortality to address conservation or management goals, and warrants consideration of an alternate framework to quantify threats to bycatch species from fisheries.
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Comment cette classification a été obtenuedéplier
Prédiction machine sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Le volet Gemma est une étiquette directe du modèle pour chaque travail de la base, lue sur la notice réduite au titre. Le volet Codex est un classifieur appris des 10 348 étiquettes directes de Codex et calibré sur les taux pondérés de l'échantillon; les champs sans appui suffisant ne portent aucun appel Codex. Le mode candidate est l'union des deux volets; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont pas des étiquettes humaines.
Scores du classifieur distillé par catégorie (deux têtes)
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,001 | 0,002 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,001 |
| Bibliométrie | 0,001 | 0,002 |
| Études des sciences et des technologies | 0,001 | 0,001 |
| Communication savante | 0,001 | 0,000 |
| Science ouverte | 0,001 | 0,001 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,001 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule source (Gemma direct ou Codex distillé), pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».