Chair: Robert Emmett
Rapporteur: Bruce McCain
The estuarine work group felt that many of the research needs identified by the Estuaries and Inlets Working Group during the 1983 meeting are still valid and perhaps even more necessary than a decade ago. In particular, the call for long-term data sets and a consistent research and monitoring program in estuaries in 1983 was not heeded. Participants identified the relation between salmonid mortality and timing and duration of estuarine residence as one of the most important unanswered questions critical to establishing the importance of estuarine areas to the health of salmon populations. The relative lack of knowledge about the importance of estuaries to salmonids became apparent as our group spent a considerable amount of time discussing the need to have a document that describes the value of estuaries to salmonids for managers and nonscientists. If managers and governments are going to put money into estuarine research and monitoring, they need to know how and why estuaries are an important life history stage for Pacific salmon. The role of estuaries in the life history of the various salmonid species and stocks needs to be described. A comprehensive review paper describing the relationship between estuaries and salmonid life histories, similar to that of Simenstad et al. (1982), would be valuable, although much essential information is still unavailable.
To begin our discussion, we revisited the hypotheses identified in 1983 and reviewed where the science has come since that time.
We still need data on how estuarine/ocean survival varies relative to the size of smolts and the number (densities) of smolts in estuaries. In particular, we need information on how the structure and functions of various habitats in estuaries affects salmonid survival. Information on dependent and independent variables, natural and anthropogenic factors affecting mortalities, and long-term databases are unavailable for any West Coast estuary, with the possible exception of San Francisco Bay.
A research program using salmon from hatcheries and net-pen operations (e.g., Youngs Bay, Columbia River estuary) focused on the effects of different smolt release strategies (timing, size, density) relative to various estuarine habitat parameters (food, temperature, predators, etc. ) on percent returning adults would be valuable. Of major interest would be how specific physical and biological factors in estuaries (food, temperature, predators, residence time, etc.) affect salmon mortalities.
Most research related to effects of habitat-specific factors has been conducted in fresh water, although some work has been done in Coos Bay, the Columbia River estuary, and the Campbell River estuary. Nevertheless, these estuarine studies simply identified that estuarine use enhanced survival but did not identify the mechanisms. The primary research issues are the differential uses of various estuarine habitats by juvenile salmonids and the mechanisms and functions of these uses with respect to salmonid mortalities. Research strategies recommended by the 1983 Working Group have not been undertaken.
The general feeling of the groups was that relatively more research has been done addressing this issue than H1 and H2. A variety of measures of smoltification and physiological status has been developed since 1983. Some physiological parameters in smolts may also be related to critical behavior (migration rates and location, feeding habits) that could affect survival. In addition, exposure of smolts to chemical contaminants in urban estuaries can affect the fitness of certain juvenile salmonid species. A key question was identified: How could fitness and physiological characteristics in hatchery reared and wild smolts affect differential mortalities? The feeling was expressed that hatchery fish are generally less fit than wild fish, and that the presence of hatchery fish in rivers and estuaries could potentially reduce the fitness of co-occurring wild fish. Recent advances in blood chemistry analysis (assays of endocrine growth factors) may assist with differentiating smolts that are growing slowly from those that are growing rapidly, and thus be able to tell us which smolts will survive and which estuaries/rivers are producing better smolts.
This was identified as one of the most important hypotheses we discussed. Several people expressed the opinion that natural and human-induced changes in estuaries can and have influenced the timing and duration of estuarine residence, and that the estuarine experience of smolts can determine ocean survival. For example, changes in regional and coastal ocean climate and associated circulation changes can affect estuarine productivity and availability of salmonid predators, and upwelling and freshwater inflow can affect estuarine primary productivity and food availability. Specific questions related to this hypothesis were: How do various salmonid species and stocks respond to various estuarine pulses in productivity, predators, and competitors? How is the timing and duration of estuarine residence linked to ocean conditions? How do increased salmonid densities influence timing and duration of estuarine residence? This last question relates to the effect of hatchery releases on estuarine use by wild salmonids.
It was the overall consensus of the group that much more information is needed on this topic. Ideally, researchers would gather timing and residence-time data from a range of estuaries, habitats, and salmon species, and from multiple years encompassing climate variability (e.g., regime shifts) and salmonid life history durations.
This is a difficult hypothesis to test because it is difficult to distinguish between oceanic and estuarine mortalities. Some research has been conducted, is being conducted, or is being proposed to address this question—including the work by Reimers (1973), the studies being conducted in the Skagit River in which smolts are being tracked from the river to salt marshes, and possible future retrospective studies. It was generally felt that scale studies would be valuable for determining the relative growth rates of different salmon stocks within estuaries (some agencies and Native American tribes have extensive scale collections).
Several factors were mentioned which could influence this hypothesis, including competition for food, attraction of predators (e.g., mammals and birds) by major pulses of hatchery fish, emigration timing, and disease transmission.
Several factors were mentioned which could influence this hypothesis, including temperature, salinity, dissolved oxygen, flow, turbidity, and chemical contamination.
Several factors were mentioned which could influence this hypothesis, including the abundance and distribution of certain species of marine mammals, birds, and fish, and the activities of commercial and recreational human fishers.
Because of limited time, no defining factors were discussed by the group. However, comparing the estuarine use and survival of salmonids in estuaries that include many exotic species with an estuary of few exotic species may not be easy to do because nearly all estuaries now have exotic species. Exotic species introductions into West Coast estuaries continues to be a problem, and we may be conducting this experiment without documentation.
The large and varied life history diversity and strategies of salmonids suggest that no single physical or biological factor may consistently determine overall salmonid survival. Through hatchery manipulation and reductions of wild populations, overall salmonid life history diversities have been greatly reduced. Because of this reduction, so called "environmental bottlenecks" may now have severe consequences.
There was a consensus that multidisciplinary, multiyear research programs are needed to assess the extent and mechanisms of juvenile salmonid mortalities in estuaries and the nearshore ocean. In particular, one major question needs to be addressed: Are physical, chemical, and biological factors in estuaries useful predictors of the health and survival of some life history stages of some salmonids species? Examples of suggested investigations included:
These estuary studies should be performed in concert with observations of nearshore and ocean conditions and with survival studies.
There was also a general feeling that the process of developing research strategies had to address funding sources. Examples of important research guidelines included an explanation of how the results would help guide management decisions about improvements to estuaries to protect and enhance salmon stocks, address the biggest gaps in our knowledge, and demonstrate the importance of estuaries to the recovery of depressed salmon stocks.
A number of participants expressed the feeling that estuaries are critical to the health and survival of certain life history stages of certain salmonid species, but more information is needed about the mechanisms. An idea was formulated to develop research programs in small coastal estuaries, such as the estuaries of the Salmon, Alsea, Yaquina, and Siletz Rivers in Oregon, to address some of these mechanistic questions.
Estuaries are valuable to salmonids, and research is needed to:
The mechanisms for various factors in estuaries affecting the health and survival of salmonids need to be determined. Only by conducting multiyear, multidisciplinary research, in a variety of estuaries, can the common estuarine mechanisms controlling salmonid estuarine/ocean survival be established.
Citations
Reimers, P. E. 1973. The length of residence of juvenile fall chinook salmon in Sixes River, Oregon. Oregon Fish Comm. Res. Rep. 4(2):3-42.
Simenstad, C. A., K. L. Fresh, and E. O. Salo. 1982. The role of Puget Sound and Washington coastal estuaries in the life history of Pacific salmon: an unappreciated function. In V. S. Kennedy (editor), Estuarine comparisons, p. 343-364. Academic Press, New York.