Squid and anchovy: Similar subjects, different schools
Abstract:Two species, anchovy Engraulis capensis and chokka squid Loligo vulgaris reynaudii, occupy similar ecological niches. The similar life-history characteristics of these species, e.g., fast growth, rapid onset of maturity and small adult size, spawning migrations and schooling, suggests that they have a similar strategy to maximizing reproductive potential. Current, detailed knowledge of anchovy reproduction is used to assess samples of chokka squid collected throughout their distributional range and comprising all life history stages. Examination of the ovaries of the two species confirmed histological similarities and allowed recognition and comparison of key structures present in both groups. It is confirmed that chokka squid, like the anchovy (both batch spawners) spawn a large number of eggs in each batch to hedge against environmental perturbations. This is achieved through continuous oocyte development in the ovary and by directing as much energy as possible into egg production, but being able to redirect that energy when under stress through resorption of oocytes. Like anchovy, post-ovulatory follicles are present in squid ovaries. The number and rate of resorption of post-ovulatory follicles are used to estimate batch fecundity in anchovy and it may be possible to use similar techniques to estimate batch fecundity in squid. Management of anchovy and the chokka squid share similar problems, such as suitable models to assess biomass in short-lived species and the need for within season assessment of recruitment. How these problems should be addressed are discussed. Although very different in many respects we should be careful not to ignore the obvious similarities between squid and fish, not only in our understanding of their position in marine ecosystems but in our advancement of knowledge of their life history strategies and management of exploited stocks.
Document Type: Research Article
Publication date: September 1, 2002
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