in horizontal haul 7-Tl-A, which we interpret as having sampled within a layer 

 of greater fish concentration. Thus, it is obviously necessary to invoke either 

 chance or discontinuities (patchiness or layering) in the distributional patterns 

 of the fish in order to adequately explain the observations. Many more samples 

 are required to adequately assess the comparative effectiveness of oblique versus 

 horizontal hauls, as well as the vertical and horizontal distributional patterns of 

 mesopelagic animals. 



Harrlsson (op.cit.) is undoubtedly correct in advocating a balanced 

 program of several different techniques for obtaining information about the 

 mesopelagic fauna. However, one great difficulty with a diversified sampling 

 program is in interpreting the data quantitatively. This must be done so that 

 biological measurements can be compared with quantitative acoustic measure- 

 ments of volume reverberation. It must also be done in order to assess the 

 importance of productivity as a criterion for predicting volume reverberation 

 conditions. 



Past measurements of productivity in the open ocean that appear in the 

 literature are subject to varying interpretations. This is particularly true where 

 the accuracy of finely detailed quantitative measurements is concerned. However, 

 the overall picture of productivity in the world ocean as shown by Fleming and 

 Laevastu (1956, p. 185), Steeman Nielsen and Jensen (1957), and Ebeling 

 (1962, p. 146), is not unreasonable. The classification of tropical and sub- 

 tropical waters by Steeman Nielsen and Jensen (op. cit., p. 89) is useful, 

 though perhaps an oversimplification, since they point out that there are no 

 definite boundaries between the regions. They distinguish four regions, based 

 on the rate of organic production as measured in grams of carbon produced per 

 square meter per day. The two of higher productivity, exemplified by the 

 southern part of the Benguela Current for Class I and the divergences caused by 

 the Equatorial Counter Currents for Class 11, do not really concern us here. 

 Class 111 with a daily organic production of 0. 1 - 0.2 g C/m^/day includes 

 most of the tropical and subtropical regions of the ocean, and probably both the 

 Gulf of Mexico and Area Bravo fit into this category. Class IV is exemplified 

 by the central part of the Sargasso Sea with a rate of organic production of about 

 0.05 g C/mvday. Riley's (1939) proposal that the Sargasso Sea may be 

 considered a productive area was discussed and refuted by Steeman Nielsen 

 (1954, p. 325). Since Area Bravo is at the western side of the Sargasso Sea, 

 it might more correctly be considered as being in a transitional region between 

 Class III and Class IV regions. There have been no primary productivity measure- 

 ments published from the central Gulf of Mexico, but the few papers (Riley, 

 1938; Marshall, 1956; Steele, 1964; Wood and Corcoran, 1966) that deal with 

 various aspects of productivity in the Gulf of Mexico, as well as studies of 

 current patterns (Armstrong and Grady, 1967) and the distribution of nutrients 



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