Discussion

No problems were encountered with the Simrad ER60 data acquisition software or the EK60 echosounder system throughout the sampling period. Once installed, the Starband system also performed very well. The data upload was automated to expedite quality control of the acoustic data. Installing a second computer on the network to upload the data through the Starband system allowed the data collection and analysis computer to operate smoothly throughout the year.

As in 2001, 2002 and 2004, acoustic sampling conditions at Flag Point Channel were very good in 2005. Consistent display settings and the high quality of acoustic data made it easy to distinguish salmon from eulachon tracks. Having no threshold applied to data collection meant that data could also be viewed at lower display thresholds than in the past, which sometimes helped in the interpretation of the data. Review of angle color echograms indicated that very few salmon were moving downstream.

The total number of salmon counted, the good seperation of salmon and eulachon, and fish behaviour were compared to the first two years of the pilot study, and the first year of the current study. After the difficulties experienced in 2003, there was concern that the low-water conditions in Flag Point Channel were related to the Copper River shifting towards its eastern channels to an extent that would make Flag Point Channel unsuitable for sampling. Results from 2004 and again in 2005 indicated that, for the time being, Flag Point Channel is still suitable for acoustic sampling. The highly dynamic delta remains, of course, unpredicatable and the site will need to be reassessed every year before sampling.

Fishery managers recognize two broad but useful levels of precision for "indexing" in-river escapement from the commercial fishery in the Copper River District: presence/absence and a more quantitative measure such as: more than a few hundred fish, less than 20,000 fish, etc. Each year, in the earliest stages of the salmon run (mid-May), managers simply want to know whether or not there are fish present in the river upstream of the commerical fishery. This is sometimes enough information to influence management decisions. In 2005, as in every year since its inception, with the exception of 2003, the Lower RIver Test Fishery accomplished the goal of determining when fish first entered the river in significant numbers.

However, it has also become clear that the number of salmon sampled at Flag Point Channel does not represent a fixed percentage of the number of salmon counted at the Miles Lake sonar site. This is not surprising since Flag Point Channel is only one of several alternative migration routes, and we sampled just one side of the channel. Nevertheless, as long as there is a systematic component in how the percentage sampled at Flag Point Channel varies, it will still be possible to establish an index that is more precise than mre presence or absence. The trend observed in 2005 is consistent with the data from 2002 and 2004, with the exception that the catch efficiency in 2002 and 2004 started at more than 20% while in 2005 the efficiency started at 10%., then gradually declining, leveling out at around 5% all three years. Only data collected over additional years will tell how consistent this pattern is from year to year and how precise the index will be in the medium and long term. The decline in the relative number of fish sampled at Flag Point Channel is consistent with the sequence in which the channels of the Copper River Delta break up in spring and reports from local fishermen who observed that, early in the run, salmon tend to aggregate (and presumably enter the river) on the west side of the delta and only later shift towards the east. Channels in the vicinity of Flag Point are amoung the first channels to become ice-free. Early fish may therefore be more likely to migrate through Flag Point Channel than fish entering later when more alternative routes become available.

The systematic variation in the percentage of fish sampled at Flag Point Channel was also reflected by the general alignment of peaks and troughs in the Flag Point Channel and Miles Lake counts observed throughout the 2005, 2004, 2002, 2001, and in the second half of the 2003 sampling period. Again, this suggests that it may be possible to obtain an index that goes beyond mere presence or absence.

The speed at which fish migrated from Flag Point Channel to Miles Lake (1-3 days for app. 30km) was similar to the apparent speed of migration from the commercial fishing district to Flag Point Channel (1-2 days for approximately 20km). Given the speed of migration, the Flag Point Channel index provided information on the number of fish entering the river that was 1 - 3 days more up-to-date than the Miles Lake sonar counts.

An advantage of the Lower River Test Fishery project arises from the early start-up date. In 2005, acoustic sampling at Flag Point Channel began on 5 May, one week before the Miles Lake sonar site was clear of ice and fully operational and 11 days before the first commercial fishing period. It is early in the season, when high fish prices add to the pressure on managers to open the commerical fishery, when up-to-date information on whether and how many fish have entered the river is especially important.

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