Reducing Discard Mortality of Cod in the Gulf of Maine
The recreational contribution to the total catch of Atlantic cod in the Gulf of Maine (GOM) has increased in recent years, with recreational discards outnumbering recreational landings by 2:1 from 2006-2011. However, the discard mortality rate of cod released in the recreational ﬁshery was poorly understood, thus contributing to the uncertainty in stock assessments and ﬁshery management decisions, such as a zero possession limit instituted in 2015.
To address this problem, members of the New England Aquarium, University of New England, Massachusetts Division of Marine Fisheries, and University of Massachusetts Dartmouth’s School for Marine Science & Technology set up a passive acoustic telemetry study on southern Jeffreys Ledge in the western Gulf of Maine to examine which capture-related factors influenced cod discard mortality in the recreational rod-and-reel ﬁshery.
“From June to October in 2013, our large team of collaborators captured and sampled 640 Atlantic cod under typical fishery scenarios,” said graduate student lead Connor Capizzano1. “We also tagged a subset of 136 cod with pressure-sensing VEMCO V9 transmitters and released them into an array of 31 Vemco acoustic receivers deployed to monitor survival for up to 94 days.”
The team angled cod using fishing gear representative of the local recreational fishery and visually assessed specimens for injuries according to a four-level injury score index to properly model discard mortality up to the ﬁshery-wide level.
“Mean tackle-speciﬁc discard mortality rates of 15.4 and 21.2% were estimated for bait- and jig-captured cod, respectively, with an overall 16.5% mean discard mortality rate for the 2013 Gulf of Maine recreational cod ﬁshery,” said Capizzano. “Twenty-nine cod tagged with acoustic transmitters were identiﬁed as dead, where 90% died within 16 hours of 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,” concluded Capizzano.
Study results will continue to inform the development of ﬁshery management plans and enhance cod survival through dissemination of recommended best practice techniques to ﬁshery stakeholders.
For more information on this study, access the complete paper here.
1 Connor Capizzano worked on this study as part of his MS degree at the University of New England. He is now at the University of Massachusetts where he continues to use acoustic telemetry to investigate groundfish discard mortality in the Gulf of Maine recreational fishery.