Seasonal dynamics of growth and mortality suggest contrasting population structure and ecology for cod, pollack, and saithe in a Norwegian fjord

Heino M, Svasand T, Nordeide JT, & Ottera H (2012). Seasonal dynamics of growth and mortality suggest contrasting population structure and ecology for cod, pollack, and saithe in a Norwegian fjord. ICES Journal of Marine Science 69 (4): 537-546. DOI:10.1093/icesjms/fss043.

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Abstract

We study the dynamics of Atlantic cod (Gadus morhua L.), pollack (Pollachius pollachius L.), and saite (Pollachius virens L.) in Masfjorden, a small fjord in western Norway. Annually, cohorts of pollack and cod grow in size and decline in abundance, as expected of closed populations, whereas saithe virtually disappear before maturity. Seasonally, in contrast, the dynamics of cod and pollack differ. Pollack shows a regular growth pattern, with most of the growth taking place in summer. Its abundance-at-age shows strong seasonal variations, with a marked increase from spring to summer followed by a decline through autumn and winter. These patterns relate partly to seasonal changes in depth distribution and catchability. Combined with the observation that spawning-stage pollack are abundant in spring, we interpret these patterns to suggest that pollack in Masfjorden represent a dynamically independent unit. Seasonal changes in abundance are less marked for cod, and seasonal changes in depth distribution seem insignificant. However, cod shows an unusual pattern in length at age, with no apparent growth in summer and fast growth in autumn. These patterns suggest that the population structure of cod may be more open than that of pollack and may involve mixing of more than one population component.

Item Type: Article
Uncontrolled Keywords: Gadidae; Population ecology; Seasonal dynamics; Spatial population structure
Research Programs: Evolution and Ecology (EEP)
Bibliographic Reference: ICES Journal of Marine Science; 69(4):537-546 (May 2012) (Published online 13 March 2012)
Depositing User: IIASA Import
Date Deposited: 15 Jan 2016 08:46
Last Modified: 23 Feb 2016 12:10
URI: http://pure.iiasa.ac.at/9969

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