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The results from this study rely heavily on the assumption that survival rates of acoustically tagged smolts are similar to survival rates of PIT-tagged smolts. To rigorously test this assumption, a reasonable scientist would release two identical groups of tagged fish (i.e., reared in the same location, having similar length, and subsequently releasing those fish at the same time and at the same place), and then compare their resulting survival rates to assess whether the tag type has had an effect. This type of comparison controls for potentially confounding factors such as temporal effects (changes over time), size effects (differences in survival due to length), location effects (differences in survival between locations), and rearing type effects (differences due to hatchery versus wild rearing), leaving the tag type (acoustic versus PIT) as the only variable that is different between the groups.

The description in Welch et al. (2008) gives the misleading impression that this type of controlled comparison was conducted:
"We first compared survival of PIT and acoustically tagged smolts in the impounded section of the Snake and Columbia rivers to assess survival of animals implanted with these different-sized tags in 2006 (Figure 2; [21]). Survival of acoustically tagged Snake River spring Chinook smolts from the Dworshak Hatchery stock (tagged and released at Kooskia Hatchery) was statistically indistinguishable from the estimated survival of PIT-tagged Dworshak Hatchery Chinook in 2006 (p > 0.05), demonstrating that the PIT and acoustic tag methodologies provide similar survival estimates for freely migrating smolts in the impounded section of the river."

I characterize this as a misleading description because the authors elected to omit several relevant facts about the significant differences between the two groups of tagged fish that they compared. First, the PIT-tagged fish were released more than a month earlier than the acoustically tagged fish (PIT: March 27 & 29, 2006 versus acoustic: May 1 & 8, 2006). Second, the fish were released at different locations (PIT: released from Dworshak Hatchery versus acoustic: released from Kooskia Hatchery, which is 60 km upriver from Dworshak Hatchery). Third, the groups of tagged fish were likely of different lengths because of the release timing (over a month earlier for the PIT-tagged fish), even if the researchers attempted to starve or reduce feed levels to slow the growth of the acoustic-tagged fish. Fourth, fish from all hatcheries, along with wild PIT-tagged fish were combined for estimating survival of PIT-tagged fish in the lower river (McNary to Bonneville Dams). The Dworshak-based survival estimates from release to McNary appear to have been appended to these combined, all-hatcheries/all-wild fish estimates for survival in the McNary-Bonneville reach for comparison to the survival of acoustic-tagged Dworshak Hatchery stock fish released from Kooskia Hatchery.

The comparison between acoustic- and PIT-tagged fish in Welch et al. (2008) thus appears to be deeply compromised by many potentially confounding factors: differences in release timing, differences in release location, differences in length at release, and differences in rearing type along with variation among hatcheries for the lower river survival estimates. Because the authors did not openly disclose these relevant facts, I have to question the honesty and integrity of each of the researchers involved, as well as the peer-review process that occurred with this paper, which should have brought these issues to the forefront. Without first conducting a properly controlled, rigorous, field assessment of the two tag types, the Columbia-Fraser comparisons are meaningless. A properly controlled, rigorous, field assessment of the two tag types did not occur. As a scientist, I am ashamed by the complete failure of the peer-review process to identify and raise these issues. Furthermore, I feel the Kintama Research corporation should be ashamed of itself for misleading the scientific community and the general public by misrepresenting, perhaps deliberately, critical and relevant facts about the groups used for comparisons in this research.

posted 4 years, 6 months ago
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