Mixing of populations or year class twinning in Norwegian spring spawning herring?

Abstract

In the present study, we question whether the mixing of autumn spawning herring with Norwegian spring spawning herring (Clupea harengus L.) in feeding and wintering areas is a result of year class twinning, that is, that they hatched in spring as products of the spring spawning stock, but ended up spawning in autumn. The otolith microstructure of the summer feeding autumn spawners (July 2001) was similar to the wintering autumn spawners (January 2002), stable and low in comparison with the sympatric spring spawners caught in the same two seasons. Hence, the otolith microstructure of the analysed larval herring seemed representative of their own spawning season. Data from 1982 to 2003 demonstrated that the fraction of autumn spawners by year class has been quite low at 1-14%, but relatively high in some of the weak year classes, indicating a different recruitment success between the spawning groups. Length at age and somatic weight at length did not differ between the spawning groups. In comparison, the neighbour North Sea autumn spawning herring were significantly smaller at the same age.

Otolith shape: a population marker for Atlantic herring Clupea harengus

“…Nearly 30 separate C. harengus populations have been defined in the North Atlantic Ocean (Hay et al, ) based on the location and timing of spawning. These populations have a wide range of life‐history strategies (Geffen, ), and some even show sub‐population structuring (Broch, ; Runnstrøm, ; Rasmussen, ; Aasen, ; Lie et al ., ; Hognestad, ; Husebø et al ., ; Johannessen et al ., ; K. E. Jørstad & S. A. Pedersen, unpubl. data).…”

“…: +354 694 3835; email: lisa.libungan@gmail.com based on the location and timing of spawning. These populations have a wide range of life-history strategies (Geffen, 2009), and some even show sub-population structuring (Broch, 1908;Runnstrøm, 1941;Rasmussen, 1942;Aasen, 1952;Lie et al, 1978;Hognestad, 1994;Husebø et al, 2005;Johannessen et al, 2009;K. E. Jørstad & S. A. Pedersen, unpubl.…”

“…Individuals from these stocks not only have the same external characteristics, but also grow to similar sizes, making it often problematic to separate them in mixed fisheries based on body features alone. The spatial distribution of the Norwegian spring and autumn spawners also overlap during most of the year and can thus be caught in the mixed fishery (Husebø et al, 2005). In Icelandic waters, Norwegian spring and Icelandic summer spawners are separated on the basis of maturity stage.…”

Stock structure of Atlantic herring Clupea harengus in the Norwegian Sea and adjacent waters

“…Three different management units are currently considered for stock assessment in the Norwegian Sea and adjacent waters: the Norwegian spring-spawning herring (NSSH), the Icelandic summerspawning herring (ISSH) and the North Sea autumn spawning herring (NSAH). In addition, the occurrence of Norwegian local spring-spawning herring (NLSSH) (Johannessen et al 2009, Silva et al 2013 mainly spawning in local fjords and of a Norwegian autumnspawning (NASH) herring has been mentioned (Husebo et al 2005). Moreover, the presence of a spring-spawning herring (FSSH) and an autumn-spawning (FASH) herring have been suggested in Faroese waters.…”

Otolith research and application: current directions in innovation and implementation

“…For example, Berg et al (2005) explored the accuracy and precision in distinguishing two cod (Gadus morhua) stocks in the north-east Atlantic based on otolith growth and shape morphometrics. Similarly, Husebø et al (2005) used otolith microstructure to discriminate spawning components of herring (Clupea harengus) and to estimate their relative contribution to overall year class strength.…”