Consequences of Fishery Gear Type and Handling Practices on Capture and Release of Wild Steelhead on the Bulkley River

Abstract

Steelhead Oncorhynchus mykiss are captured and released during spawning migrations by the commercial, subsistence (Indigenous), and recreational fishing sectors, though the consequences of these fisheries interactions on steelhead migration are poorly understood. This study evaluated injury, reflex impairment, behavior, and survival of released wild adult steelhead following capture in the subsistence dip-net, subsistence beach-seine, and recreational angling fisheries of the Bulkley River, British Columbia. Wild steelhead were captured using common handling practices employed in each fishery and were monitored postrelease using radiotelemetry. A greater proportion of steelhead captured by dip net and seine had impaired righting reflexes compared with angled fish, but only fish captured by dip net had notably higher incidence of injury (i.e., net marks, torn fins, flesh wounds, scale loss). Fish captured by dip and seine net had considerably faster peak migration rates (>4,000 m/d) than angled fish (<1,000 m/d), which likely reflects when the steelhead are encountered during their migration in these fisheries (earlier versus later stages). Air exposure (15-74 s) and water temperature (9.2-15.1°C) at the time of capture had significant negative relationships with 24-h fallback behavior (temperature only), intermediate-term (10-20 d after capture) migration rates, and peak migration rates in dip-net-captured steelhead. There were no significant effects of capture duration or fish length on injury, righting reflexes, or migratory behavior. Immediate mortality upon release was rare and occurred in only one fish captured by dip net. The 3-d survival was 88-97% for dip-net-caught steelhead, 96-100% for seine-caught steelhead, and 68-100% for angled steelhead. Despite inherent differences in timing and location between these fisheries, findings suggest that air exposure and water temperature can decrease steelhead migration rates. Fishers should look for opportunities to avoid or minimize these capture and handling conditions when releasing steelhead.

OUP accepted manuscript

“…Steelhead anglers almost exclusively target slow moving water or refuge sites where steelhead are known to hold prior to overwintering in the river (Keefer et al, 2009). These sampling groups therefore reflect fish in two different stages of migration and freshwater acclimation, which has been previously confirmed by telemetry (Twardek et al, 2019).…”

“…This study found one mortality (1.5% of fish) that could not be readily explained by the capture event itself, which indicates that infectious agent-induced mortality is minimal for fish upstream of the falls (Twardek et al, 2018). The notion of migratory culling is partly supported by the described telemetry work (Twardek et al, 2018, 2019), but future telemetry studies should additionally include gill agent-transcriptome analyses such as performed herein.…”

“…This is consistent with the elevated expression of CA4 and HBA in this group of fish which are important in the earlier stages of freshwater acclimation (Houde et al, in review) and higher expression of humoral immune genes (IgMs and IgT) and B2M, MHCIIB and IRF1 that tend to increase over the course of migration in sockeye salmon (Teffer et al, 2017). Radio telemetry work has indicated that steelhead upstream of Witset Falls represent successful migrants that are holding at or near spawning sites, while fish at Witset Falls are in the active stage of upstream migration (Twardek et al, 2019; Økland et al, 2001).…”

“…Witset Falls constitutes the most difficult hydraulic reach of the Bulkley River. Steelhead are known to delay their migration at this point, resulting in large densities of steelhead below the falls, and ~8–12% of steelhead that enter the canyon/falls area do not successfully migrate upstream of the falls (Welch et al, 2009; Twardek et al, 2019). Confinement of steelhead below this migratory barrier may increase exposure to infected individuals and correspondingly increase infectious agent prevalence and loads at this location (Bebak-Williams et al, 2002).…”

“…However, these sampling biases can be inconsistent across gears, species and environments making it difficult to develop generalizations (Hollins et al, 2018). There is also a small amount of capture-and-release mortality from the dip net fishery (<1% of the population) that could reduce the number of fish with high infectious burdens upstream of the falls (Twardek et al, 2019). Our data cannot evaluate the extent of fisheries selectivity towards fish with certain infectious agent profiles without downstream angled fish data for comparison, but we recognize that this selectivity may be occurring between gear types in our study.…”