Otolith shape and temporal stability of spawning groups of Icelandic cod (Gadus morhua L.)

Abstract

G. 2006. Otolith shape and temporal stability of spawning groups of Icelandic cod (Gadus morhua L.). e ICES Journal of Marine Science, 63: 1501e1512.During the past 5e10 years, studies exploring small-scale structure of cod populations have provided accumulating evidence for the existence of local populations. In Iceland, all cod have been thought to belong to a single management unit. Recent studies on genetic and life history variation have, however, indicated the existence of local populations. The main objective of this study is to explore the potential existence of local populations by use of otolith shape to discriminate between spawning groups of Icelandic cod. Otoliths were sampled from mature and spawning cod at spawning locations around Iceland in 2002 and 2003, and otolith shape was described using variables correlated with size (otolith area, length, width, perimeter, and weight) as well as shape (rectangularity, circularity, and 10 Fourier coefficients). Only standardized otolith variables were used so as to remove the effect of otolith size on the shape variables. Cod were on average larger and older south of Iceland, where ambient temperature was higher than northwest, north, and east of Iceland. Otolith shape effectively discriminated between cod north and south of Iceland, and it was also possible to discriminate among cod spawning below and above 125 m at spawning locations south of Iceland. Recent genetic and tagging studies have indicated differences between cod at these two depths. Correct classification of groups of cod at the different spawning locations ranged between 0% and 44%. Incorrectly classified cod were in most cases classified to adjacent spawning locations, and a high percentage of cod south of Iceland was classified to other southern locations and cod north of Iceland to other northern locations. The temporal stability of otolith shape was studied at seven spawning locations in two consecutive years. Otolith shape differences were greater between locations than among years within a location. The spawning groups are therefore likely to have remained separate during much of their lifetime.

Evidence of phenotypic plasticity and local adaption in metabolic rates between components of the Icelandic cod (Gadus morhua L.) stock

“…Previous studies have found differences in genetic structure (Pampoulie et al 2006), otolith morphology (Jónsdóttir et al 2006b;Petursdóttir et al 2006) and microchemistry (Jóns-dóttir et al 2006a), and growth and maturity (Jónsdóttir et al, 2008;Marteinsdóttir and Begg, 2002) between the two groups. Our results indicate that physiologically, northern and southern Iceland cod perform differently when reared in a common environment and exposed to the same experimental conditions and suggests a genetic basis for these differences (Reznick 1982;Imsland and Jónsdóttir 2002;Roff 2002;Roff 2002;Conover et al 2006;Hutchings et al 2007).…”

A comparison of otolith microchemistry and otolith shape analysis for the study of spatial variation in a deep-sea teleost, Coryphaenoides rupestris

“…Otolith shape analysis revealed low population differentiation and less than 50% classification accuracy. Shape analysis studies on deep-sea species have been relatively few compared to those of more coastal species (DeVries et al 2002;Jonsdottir et al 2006;Merigot et al 2007;Burke et al 2008;Hussy 2008). Those studies that have attempted to reveal stock structure in deep-sea species have been somewhat limited in their success (Stransky 2005).…”

Spatial and temporal trends in condition of Atlantic cod Gadus morhua on the Icelandic shelf

“…It is therefore important to remember that the environmental conditions in the locations in which the cod, particularly those that were mature, were caught during the spring groundfish surveys were not necessarily those that had the most influence on their condition. With that in mind, evidence of structure in the Icelandic cod stock is accumulating; recent studies of otolith shape and chemistry and of genetic markers have detected differentiation between cod from the northeastern and southwestern regions and also with depth (Jónsdóttir et al 2006a,b, Pampoulie et al 2006, Pétursdóttir et al 2006. Spawning cod on the northeastern spawning grounds seldom migrate to the southwestern spawning areas and vice versa (Pampoulie et al 2006).…”