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Figure 1. Microtrolling gear and set up. Graph provided by
Will Duguid.
WHAT IS MICROTROLLING?
QUESTIONS ADDRESSED DATA CONCLUSIONS
Do critical mortality period(s) exist
for juvenile Chinook Salmon?
Does juvenile Chinook Salmon
habitat quality and utilization vary
at scales below what is resolved by
current sampling programs?
How are diet and growth linked to
juvenile Chinook Salmon survival?
Catch per unit effort for over 30,000
georeferenced, depth-specific hook
deployments over 4 years (in most
cases including thermistor-derived
temperature-at-depth data).
Detailed biological data (diet, length,
genetic stock identification,
scale-based growth trajectories)
for over 1,600 juvenile Chinook
Salmon and 150 juvenile Coho
Salmon. Of these 1,333 Chinook
Salmon were tagged with PIT tags
allowing biological parameters to be
related to eventual survival.
Microtrolling is an effective, econom-
ical tool to sample juvenile Chinook
and Coho Salmon beginning in late
summer of their first year at sea, and
in specific environmental conditions.
Diet and growth of juvenile Chinook
Salmon varies predictably at fine
spatial scales with implications for
predation exposure and survival.
THE NEED FOR MICROTROLLING
As juvenile Chinook or Coho Salmon disperse from
estuaries and move deeper in the water column it
becomes more challenging to study them. While
midwater trawling with a large net can catch these
fish, vessel time is very costly. Trawl-caught fish are also
not landed in a condition where they can be used for
tagging studies. The Salish Sea Marine Survival Project
presented the need for an economical method to
non-lethally sample and tag juvenile Chinook Salmon
at the end of their first summer at sea. Microtrolling
was developed to fill this need.
WHAT IS MICROTROLLING
AND HOW WAS IT USED?
Microtrolling employs a small vessel and recreational
fishing gear (Scotty Electric Downriggers) to mimic the
methods of a commercial salmon troller at a minia-
turized scale. Up to 12 lines (6 per side) are deployed
simultaneously with very small lures (generally 2.5
cm or less) to target salmon in their first (~12-30 cm)
or second (~30-50 cm) year at sea. Gear is retrieved
frequently, generally every 10 minutes or less, and
salmon are landed into a live well. The location and
depth of capture is recorded for each fish.
