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Response to the Questions of the Implementation Team Regarding Juvenile Salmon Transportation in the 1998 Season
February 27, 1998 | document ISAB 98-2
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This report is the ISAB response to three questions raised by the National Marine Fisheries Services' Implementation Team in the letter of December 3, 1997 from Dr. Michael Schiewe, National Marine Fisheries Service, to Dr. Richard Williams, Chair of the ISAB concerning the possible consequences of juvenile transportation in 1998 on subsequent adult returns and straying of salmon and steelhead from the Snake River. During the course of preparing answers to the questions, the ISAB noted a mismatch between the questions and the available information. The method of transportation for which information is available is not the same as the current method of transport. The kinds of fish on which transport has been tested are not the same as those for which protection is most critical, the listed species. Therefore, drawing analogies between different modes of transportation and different species of fish introduces substantial uncertainty. Given the magnitude of uncertainty imposed by the nature and extent of available information, it continues to be prudent to exercise caution in weighing the possible risks against the perceived benefits of juvenile transportation. Here are brief answers to the questions.
1. " ... are there real and significant differences (differences that are both statistically significant and meaningful biologically) under the range of flow conditions for which data exists, in the survival to adult returns between salmon and steelhead that are transported as juveniles versus those left to migrate as juveniles in-river?"
Statistically significant differences have not been documented on a stock by stock basis. The present mixed-stock truck and barge transportation system probably would improve survival for some affected populations, given the same in-river survival levels present during the NMFS studies. However, the effect of transportation on any particular population is unknown. Barging juvenile stream type chinook (spring/summer) and steelhead should improve survival for some populations of these two types of fish, but it is not known which populations would benefit. It is important for managers to understand how individual populations fare under transport, because the combined effects of collection and transportation may decrease survival for some populations, life history types and species. With respect to the Snake River, the effects of barging have been systematically studied with modern (post-1982) tagging methods only for stream type chinook and steelhead taken as a single group. Although some portion of all emigrants is trucked, the effects of trucking juveniles from the Snake River have not been systematically studied. The effects of transport accrue only to those animals entrained (collected) in the bypass systems. Ample evidence is available to demonstrate that the collection efficiency of each bypass system varies by species, life history type and population. Within species and populations, the collection efficiency of the bypass systems is a function of the physiological state of the fish, time of year, and other factors.
2. " ... are there real and significant differences (differences that are both statistically significant and meaningful biologically) under the range of flow conditions for which data exists, in the straying rate between salmon and steelhead that are transported as juveniles versus those left to migrate as juveniles in-river?"
There are sometimes differences in the straying rate between salmon and steelhead that are transported as juveniles versus those left to migrate as juveniles in the river. Documented instances of transportation-related straying appear to be related to lack of adequate imprinting, and most often occurred in the course of truck transportation. Differences had no apparent relation to the range of flow conditions prevalent for the experimental lots of fish for which these differences were measured, but reviews on this subject have been limited. Whether or not the observed differences in straying rate are biologically meaningful is unknown. Without knowledge of whether the differences are biologically meaningful, questions concerning statistical significance are meaningless.
3. " Based on your comprehensive review and analyses of whether differences in survival to adult returns and straying rate are real and significant, what is the likelihood that collection and transportation of salmon and steelhead at the Snake River projects and McNary Dam in 1998 will result in an increased adult return compared to allowing those same fish to migrate in-river?"
Considering all species, life history types and populations together,
the effects of combined trucking and barging on adult return and
straying rates are uncertain. For the stream type chinook
(spring/summer) salmon and steelhead populations of some hatcheries and
watersheds, it is likely that collection and barge transportation in
1998 would result in an increased adult return compared to allowing
those same types of fish to migrate in-river, given that hydroelectric
operations in 1998 are representative of the past. However, the increase
in stream type chinook salmon and steelhead could be the result of
selective enhancement only of some stocks, and we have no basis for
knowing which stocks would benefit and which might be disadvantaged by
this action. We emphasize that the benefit of any single action, such as
smolt transportation, needs to be evaluated not only for its average
benefit, but also in regard to the variation in benefits within and
between populations.
RECOMMENDATIONS
1. We recommend a 1998 management approach that divides juvenile emigrants throughout the migration season between barging and natural emigration. In the long term,the result should be to apply mitigation measures evenly across all stocks. The 1998 management approach should work in concert with hydroelectric system operations that maximize survival of natural emigrants. The available information does not support taking the majority of emigrants of any stock into transportation. A spread the risk approach involving the use of barges, spill and other measures intended to enhance downstream passage survivals should be started each year as early as possible and continued as late as possible to protect the entire spectrum of the salmon and steelhead emigration.
2. We recommend that trucks not be used in the transportation program. There is a paucity of data on the effects of Snake River trucking on salmon and steelhead so that necessary information to guide management actions is absent. Most historical information on truck transportation shows lesser survival benefits and more problems with homing than have been experienced with barge transportation.
3. We recommend that management actions intended to protect salmon and steelhead be population specific to the maximum extent possible. Management decisions should be based on the expected outcomes of clearly defined actions on the spawning populations from specific watersheds, as opposed to extension of T/C comparisons of outcomes of mixed stocks resulting from unspecified actions. For the protection and enhancement of life history and stock diversity that is critical for recovery, it is important that comparisons of survival of transported and natural emigrants be assessed based on returns to, and spawning success within, the spawning grounds of individual stocks.