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The relation between spawning area and biomass of Japanese pilchard, Sardinops melanosticus, along the Pacific coast of Japan
Zenitani, H.; Yamada, S. (2000). The relation between spawning area and biomass of Japanese pilchard, Sardinops melanosticus, along the Pacific coast of Japan. Fish. Bull. 98(4): 842-848
In: Fishery Bulletin. US Government Printing Office: Washington, D.C.. ISSN 0090-0656; e-ISSN 1937-4518
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| Abstract |
When stocks are depleted, direct assessments of population levels are not only difficult but may be highly inaccurate. The work reported here was motivated by the need to manage the collapse of the far eastern sardine (Sardinops melanostictus) population. Spawning area was chosen as the first indicator of population size because the spatial spread of the stock increases when the spawning population increases. Our objective was to clarify the relation between spawning area and the spawning biomass of this species off the Pacific coast of Japan in order to estimate biomass with the spawning area data. The pilchard spawning area (A1) in a given year was calculated by summing the areas of 1° longitude x 1° latitude squares where early developmental stage eggs were present. The optimal relationship between A1 and the spawning biomass (B) was A1=2.518 B0.4610, not a simple linear relationship. One cause of the nonlinear relationship seemed to be that pilchard egg aggregations were distributed over space in a patchy manner. Finally, we introduced an approximate method for estimating the pilchard spawning biomass by using the inverted equation of the optimal relationship betweenA1 andB; (B=0.135A12.1691). |
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