Appendix A

# Appendix A. Workshop Summary

Eighteen scientists from universities and federal laboratories (Appendix F) with research interests in zooplankton and fish ecology met in Denver during 16-17 June 1992 to outline the scientific issues and formulate a research plan for a U.S. GLOBEC program in the Arabian Sea. The charge to the group was to define the scientifically interesting questions, relative to zooplankton and fish ecology, posed by the unique conditions of the circulation of the northern Arabian Sea. The seasonally reversing monsoon winds cause massive changes in the physical and biological phenomena of the region. The group was also charged with producing a series of hypotheses about and a plan of research on the upper trophic levels of the Arabian Sea. Following background presentations on the physical circulation (Don Olson) and numerical modelling of the physics (Mark Luther) of the Arabian Sea, three working groups were formed to address questions associated with zooplankton, fish and technology. Reports of the working groups follow this summary.

Working group discussions centered around the question of how structure and dynamics of the pelagic biota differ between the coastal Arabian Peninsula and the central Arabian Sea upwelling regions. Structure includes species composition, distribution, abundance and genetics, and dynamics includes population dynamics, individual vital rates and trophic interactions. The two upwelling regions differ dramatically in scale as well as in the physical mechanism responsible for the upwelling.

Major questions to emerge from the workshop discussions were: What are the trophodynamic links between the high and sustained primary productivity of the southwest monsoon and the large populations and biomasses of midwater myctophids, especially Benthosema pterotum, in the Arabian Sea? What is the fate of the enhanced primary production associated with the southwest monsoon in the central Arabian Sea?

The zooplankton working group also considered these questions (Appendix B): What is the response of the zooplankton populations to the strongly seasonal physical forcing? How does the strong seasonality affect species composition and abundance and trophodynamic linkages among the higher trophic levels? How do the population dynamics (vital rates) of the zooplankton respond to changes in the physical environment associated with the southwest monsoon, northeast monsoon and transitional periods?

The fish working group focused on the large standing stocks of myctophids, especially of Benthosema pterotum, in the slope-water regions of the northern Arabian Sea (Appendix C). The group proposed as a general hypothesis that the large stocks of myctophid fish and their high growth rates in the north Arabian Sea are a function of regional physical conditions. Several specific hypotheses were formulated. Among them: Myctophids are protected from daytime predation at depth by descent into dysoxic waters. Rapid growth is promoted by the unusually high productivity associated with both coastal and open sea upwelling. Variations in myctophid abundance are related to topography.

Both the zooplankton and the fish working groups discussed preliminary sampling plans. Central to their discussion was an onshore-offshore transect across the northern Arabian Sea, with sampling sites within the Oman coastal upwelling domain, the offshore upwelling domain and the permanently oligotrophic, downwelling domain further to the southeast.

Discussion in the technology issues working group (Appendix D) focused on methods for rapid and quantitative description of the distribution and abundance of zooplankton and fish. Among the topics discussed were multiple frequency acoustics, optical imaging, conventional nets, pump samplers and molecular systematics. The group also discussed the measurement of population dynamical rates, such as consumption, birth and growth.