Microtrolling: an Economical Method to Nonlethally Sample and Tag Juvenile Pacific Salmon at Sea

Abstract

AbstractMortality of juvenile Pacific salmon Oncorhynchus spp. in their first marine year is hypothesized to be a primary driver of variable recruitment in a changing ocean. Much contemporary research focuses on diet, distribution, growth, and survival during this period; however, existing methods of capturing juvenile salmon at sea are expensive and may be limited by topography and tidal currents. We assessed the feasibility of using a small vessel and modified recreational fishing gear (microtrolling) to nonlethally capture, sample, and tag juvenile Chinook Salmon O. tshawytscha during their first marine summer. Sampling was conducted in the Strait of Georgia, British Columbia, from August to October 2014. We captured 168 Chinook Salmon, 13 Coho Salmon O. kisutch, and 1 Chum Salmon O. keta in 72 h of active fishing; Chinook Salmon CPUE was greatest between 6 and 19 m and increased late in the afternoon and on the flood tide. To assess short‐term mortality related to capture, PIT tagging, and sampling, we maintained 66 microtroll‐captured Chinook Salmon (41 of which were PIT‐tagged) overnight in a net pen; only one mortality and one incidence of tag loss were observed. Microtrolling proved effective for systematically sampling juvenile Chinook Salmon across depths and habitats. Unlike alternative methods of sampling juvenile Pacific salmon (trawling and purse seining), the utility of microtrolling is likely limited to studies of Chinook Salmon and possibly Coho Salmon. The low cost of this method has potential to facilitate participation of frequently excluded stakeholders, including First Nations and community groups, in marine research on juvenile Pacific salmon.Received June 10, 2016; accepted November 1, 2016 Published online February 21, 2017