Salish Sea Marine Survival Project

16 TECHNOLOGIES 1. Using microtrolling to understand salmon mortality Traditional methods to collect fish in the marine environ- ment use large vessels which cost thousands of dollars per day and are limited in their ability to access specific habitats and high-current areas. But, Will Duguid, (University of Victoria) and Kevin Pellett developed a method coined 'microtrolling' that uses personal boats and miniature recreational hook-and-line gear to non- lethally capture juvenile Chinook or Coho Salmon during their first marine summer. The method greatly reduces costs, allows sampling at fine habitat scales and provides fish with minimal injury (Figure 1). Mortality of juvenile Pacific Salmon in their first marine months is hypothesized to be a critical period in deter- mining the survival of salmon. But to test this hypothesis requires measuring survival during short time periods, which has been a major challenge in the past. Pilot studies of microtrolling in Cowichan Bay at the beginning of SSMSP showed that this method proved effective for systematically sampling juvenile Chinook Salmon in many micro-habitats. And when coupled with tagging methods that allow us to uniquely identify each tagged fish, these tagged "groups" provide a novel program to measure survival differences between these groups of juvenile salmon. Duguid uses microtrolling to investigate juvenile Chinook distribution, diet and growth in the southern Gulf Islands in late summer to early autumn. His study focuses on how juvenile salmon use their environment, and whether they are concentrated in biological 'hotspots' that support optimal rearing conditions for salmon. 2. Use of Passive Integrated Transponders (PIT) Tags Salmon biologists believe the mortality rate of juvenile salmon is very high for the first few months at sea and then declines as salmon grow. But, in reality, our ability to measure the mortality rate in a specific time period is very limited. Typically, it is measured by estimating the number of juveniles migrating to sea (or counted at release in hatcheries) and comparing that number to the estimated catch and spawning return of these fish. So we can estimate the total survival during the life span of a group of fish, but we don't know when the mortality events are occurring. However, SSMSP participant, Kevin Pellett, came up with a novel method to allow us to pinpoint the key periods of mortality and possible bottlenecks. By PIT tagging a large number of hatchery and wild Chinook at different time periods: in freshwater, at early ocean entry (collected by beach seines when fish are still very close to shore), when the juveniles are larger and have moved into the open bay (collected using purse seines) and later in their first summer and fall when they have moved offshore. In any of the periods/locations, these fish can be collected using micro- trolling, tagged, and released (Figure 2). The tags can be detected at a series of antennas located in the mainstem of the lower river and in side-channels. These can detect when juveniles leave freshwater and also when the adults return. Instead of having just one measure of total survival, we can thus create multiple "release" groups and compare their survival using the information from the PIT tags (which are unique to every fish). During SSMSP, the BC Conservation Foundation applied PIT tags to more than 56,000 juvenile Chinook in the Cowichan River to compare the survival of different groups of fish. USE OF NOVEL TECHNOLOGIES Microtrolling, a non-lethal, low-cost method of capturing juvenile salmon, was invented in the Strait of Georgia and is now being employed in Puget Sound by USGS. Coupled with the application of PIT tags to juvenile fish, microtrolling allowed for the first direct estimates of marine survival during the early marine rearing periods. Figure 1. Miniature gear used for microtrolling. Photo by Will Duguid.

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