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Vol. 46 No. 3, 2007
Different Spatiotemporal Distribution of Argentine Short-Finned Squid (Illex argentinus) in the Southwest Atlantic during High-Abundance Year and Its Relationship to Sea Water Temperature Changes
Chih-Shin Chen1, Wen-Bin Haung2, and Tai-Sheng Chiu3,*
1Institute of Fishery Biology, College of Life Science, National Taiwan University, Taipei 106, Taiwan
2Graduate Institute of Biological Resources and Technology, National Hualien University of Education, Hualien 970, Taiwan
3Institute of Zoology, College of Life Science, National Taiwan University, Taipei 106, Taiwan
Chih-Shin Chen, Wen-Bin Haung, and Tai-Sheng Chiu (2007)
The catch of Argentine squid (Illex argentinus) in the Southwest
Atlantic began in the early 1980s, reached a historical high in 1999,
and dropped thereafter. By using retrospective catch information
of Taiwanese jiggers to represent years of low (1996) and median (1998)
catches in contrast to the historical high, we outlined an ordinary
pattern of abundance for the winter cohort during the dominant fishing
phase from Mar. to May, and applied step-by-step generalized linear
models to look into possible causes for the high catch. The
variations in catch per unit of effort (CPUE) corresponding to the 5
variable effects of year, month, latitude, position on the continental
shelf, and body size were analyzed, and the findings were mapped
spatiotemporally. In the 1st step, we confirmed that the high
abundance of 1999 was significant at p
< 0.05 as compared to ordinary years (1996 and 1998). In the
subsequent intra-annual comparisons, effects of month, latitude, and
body size affected the CPUE in ordinary years, while only latitude and
body size were significant to the CPUE and monthly differences were
irrelevant in the high-abundance year (1999). The spatiotemporal
patterns in 1999 were unique; characterized by a significantly high
catch rate which was widespread over the fishing ground, relatively
small body sizes, a concentrated geographic distribution prone to
southern latitudes, and little signs of a northerly (pre-spawning)
migration. The cause of these characteristics could be explained by
deviations in subsurface water temperatures at fishing sites.
During the austral autumn of 1999, the thermal retention of waters on
the Patagonian Shelf experienced a rapid decrease. Specifically,
the temperature began to drop in Apr., becoming lower than in ordinary
years (supported by > 90% bootstrap possibility) in middle
latitudes. The lower water temperature in Apr. might have
retarded the growth of the squid, consequently causing the population
to remain on the nursery ground, and ultimately delaying the timing of
the northerly migration of the squid for spawning. The stagnation
of a high concentration of squid in the middle and southern latitudes
of the Patagonia Shelf may have resulted in extensive fishing practices
that further reduced the size of the potential spawning population.
Key words: Illex argentinus, Distribution, Migration, Temperature, Patagonian Shelf.
*Correspondence: Tel: 886-2-33662448. Fax: 886-2-23634014. E-mail:tschiu@ntu.edu.tw
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