Appendix E. Alternative Viewpoint for Near-Term U.S. GLOBEC Myctophid Studies in the Arabian Sea

Laurence P. Madin, Stephen M. Bollens, James E. Craddock

As detailed in the Fish Working Group report and scientific review of fish biology sections, myctophids are very important in the Arabian Sea ecosystem. Their densities in the northern part of the Sea are higher than any observed elsewhere (Gjosaeter, 1984). They undergo diel migration down into the oxygen minimum zone, potentially accelerating vertical fluxes. Their biomass peaks in winter and spring, possibly in response to monsoon effects. The significance of the fish populations to U.S. JGOFS objectives seems clear: "If these (very high) fish biomass numbers are accurate, then any attempt to balance a carbon budget cannot fail to include a high level of effort at determining the biomass of mesopelagic fishes, their daily rations, and their impact on zooplankton" (Peterson, 1991 p. 105). The population dynamics of these organisms, and their likely responses to monsoonal forcing of production cycles make their biology equally central to any proposed U.S. GLOBEC efforts. The question is how best to sample the fish, and whether that sampling method is affordable and logistically compatible with other goals of U.S. GLOBEC or U.S. JGOFS. We agree with the desirability of the sampling equipment and approach recommended by the Fish Working Group. However, if use of chartered fishing vessels is not an economic possibility, we believe that information on midwater fish and macrozooplankton populations crucial to U.S. GLOBEC and U.S. JGOFS goals can be obtained using smaller and more manageable MOCNESS trawl and acoustic systems during process-oriented research cruises aboard a UNOLS vessel. We presume there will be coordination of planning and overlap of investigators between the U.S. JGOFS and U.S. GLOBEC efforts, and we want to argue for the importance and feasibility, in both programs, of sampling midwater fish and macrozooplankton with research-scale gear.

These observations lead us to conclude that a 20 m2 MOCNESS should be at least as accurate as a commercial trawl for estimating myctophid abundances, and much more effective for sampling vertical distribution and migration, and retrieving experimental specimens. The MOC-20 can be easily fished from a UNOLS vessel, along with other sampling work. It is towed from the stern, but launched and recovered over the side, so that the net frame is stabilized against the hull of the ship as it enters and leaves the water. Despite its size, the trawl is well suited to work in rough weather. The frequent and intensive sampling schedule recommended by the Working Group is clearly desirable for midwater fish (as it would be for zooplankton). But if it is not fiscally possible, we suggest that accurate, depth specific sampling with the MOC-20 and acoustic equipment should be carried out along with other pelagic process-oriented work aboard the UNOLS ship. We hope that U.S. GLOBEC will not dismiss or defer the study of myctophids in the Arabian Sea for simple logistic reasons. If the scientific questions surrounding the population biology and ecology of these fishes are of sufficient interest and importance -- as we agree they are -- then technology and expertise are currently available to sample these organisms in a quantitative and cost-effective manner.


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