Rick M. Rideout

Skipped Spawning in Fishes: More Common than You Might Think

Abstract The traditional view of iteroparity in fishes is one of an annual reproductive cycle that culminates each year in spawning. More recently, a more flexible view of fish reproduction has been adopted, including the potential for mature fish to skip spawning. Here, we review the abundance of recent research on skipped spawning, covering a broad range of fishes with diverse life history strategies. Evidence for skipped spawning has been collected by use of traditional histological techniques as well as modern technological advances, such as satellite tags and the ability to track fish movements based on elemental and isotope signatures. Skipped spawning is most commonly attributed to deficient diet and poor nutritional condition. Advances made in this field of study in recent years include descriptions of hormonal changes that precede and perhaps initiate skipped spawning, the development of life history models that incorporate the potential for skipped spawning, and estimates of the degree to which skipped spawning influences the reproductive potential of fish populations. In addition to summarizing this new research, we attempt to advance current knowledge by (1) providing the first review discussion of skipped spawning in males, (2) exploring skipped spawning in anadromous fishes by using the Atlantic salmon Salmo salar as an example, and (3) discussing the potential for and difficulties in identifying skipped spawning in species with indeterminate fecundity.

Growth and condition in relation to the lack of recovery of northern cod

Growth and condition in fishes have been taken as indicating levels of energy available for survival and reproduction, major components of a population’s productivity. After a rapid collapse in population size, northern (NAFO Division 2J3KL) cod (Gadus morhua) remained at a very low level of abundance for 20 years. We investigated the potential for poor growth and condition to have played a role in the collapse and lack of recovery of northern cod. Juveniles and adult males and females all showed similar patterns. Perceptions about the importance of growth and condition to population status depended on the metrics and area examined. When the northern cod population was declining, the northern areas of the population clearly had reduced growth and condition, while these metrics improved in the south. Results were equivocal as to the potential role of growth and condition in the continued low abundance of northern cod and, to some extent, depended on the nature of the metric being examined. Indices of condition, which included lipid storage in the form of liver weight, were generally lower in the north while the stock remained at a low level. Metrics associated with longer-term protein storage returned to precollapse levels quickly following the period of collapse. An index of food availability was more closely related to growth and condition than was temperature. These results point to the need both for studies of growth and condition in a population to have a comprehensive time-series of data covering the entire range of the population and the need for a better understanding of the causes and implications of changes in different metrics of condition.

Evaluating the use of the autodiametric method for estimating fecundity of Reinhardtius hippoglossoides, a species with an unusual oocyte development strategy

Evaluating the use of the autodiametric method for estimating fecundity of Reinhardtius hippoglossoides, a species with an unusual oocyte development strategy R. Dominguez-Petit*, R. M. Rideout, D. Garabana, Y. Lambert, M. Hermida, and M. J. Morgan Spanish Institute of Oceanography, Oceanographic Centre of Vigo, Vigo, Spain Institute of Marine Research-CSIC, Vigo, Spain Fisheries and Oceans Canada, Northwest Atlantic Fisheries Centre, St John’s, NL, Canada Spanish Institute of Oceanography, Oceanographic Centre of A Coru~na, A Coru~na, Spain Fisheries and Oceans Canada, Institute Maurice-Lamontagne, Mont-Joli, QC, Canada *Corresponding author: tel: þ34 98 646 2271; fax: 986498626; e-mail: rosario.dominguez@ieo.es.