Research Document 2024/003
Estimating Incidental Catch of Non-Target Species from the Commercial Fishery for Atlantic Halibut in Maritimes Region
By Bowlby, H.D., McMahon, M., Li, L., den Heyer, C.E., and Harper, D.
Abstract
This document provides an evaluation of bycatch from the 3NOPs4VWX5Z Atlantic Halibut (Hippoglossus hippoglossus) longline fishery in Maritimes Region, updating and extending work that was completed in 2014. Notably a new method for data extraction from regional databases was used to address previous limitations in identifying the fleet, which removed subjectivity and ensured consistency in the definition of the fleet. This had little effect on landings or the proportion of observed landings of Atlantic Halibut, yet had substantial implications for calculating observer coverage rates and understanding bycatch.
Observation rates have declined since the 2014 assessment, and effort was disproportionately allocated to Northwest Atlantic Fisheries Organization (NAFO) Divisions with relatively low fishing activity. Seasonal patterns show that the majority of fishing activity occurs between April and September (Q2: April to June–Q3: July–September), with less activity in the late fall and winter (Q1: January–March and Q4: October–December).The proportion of total catches that were Atlantic Halibut increased for essentially all NAFO Divisions and fishing quarters from the 2009–2013 to 2014–2020 time periods. The percentage of Atlantic Halibut catches that were discarded was twice as high in the 2009–2013 time period as it was in 2014–2020.
The catch profiles from fished sets (either combined catches or kept catches) were extremely variable among years, NAFO Divisions and fishing quarters. A diversity index suggested catches becoming more dominated by large amounts of specific species, which likely means bycatch is declining given that Atlantic Halibut landings are increasing. A log-linear regression was proposed as a way to predict total bycatch weight from kept Atlantic Halibut landings, accounting for differences among NAFO Division and time period. From 2009–2020, there are relatively few instances where bycatch of a particular species or species group seems to be increasing, and nearly all examples come from 4X. Calculating the mean proportion landed indicates there were several species or species categories that tended to be landed in conjunction with Atlantic Halibut, as would be expected under multi-species groundfish licences.
It is difficult to determine what these predictions imply for the status of individual bycatch species. Bycatch can decline due to factors such as improvements in the status of the target species, worsening status of the bycatch species, and/or changes in the distribution of effort or other operational characteristics of the fleet that influence catchability. This assessment represents general trends; the predictions should be taken as relative rather than absolute amounts. These patterns could be used to inform more targeted research on the status of individual bycatch species.
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