Evidence accumulated over the last decade indicates that reproductive potential of marine fish stocks is not correctly represented by spawning stock biomass. Fundamental variables that affect reproductive potential of fish stocks (i.e. proportion mature at age, fecundity, and offspring size and viability) have found to vary with age, size, and condition of spawning fish, and/or spawn- ing experience. Modeling initiatives that attempt to describe reproductive potential by incorporating all available information on reproductive variables require extensive, high quality data of a temporal and spatial origin. In this study, we explored the influence of female age, size, and condition on sev- eral reproductive variables for the cod Gadus morhua, including maturity, fecundity, egg density and size, and larval size and growth. In addition, we described the potential for annual variation in these relationships to increase our knowledge of temporal stability for fundamental variables that influence reproductive potential.

/pdf/essential-relationships-incorporating-the-influence-of-age-116313lzwf.pdf

Essential relationships incorporating the influence of age, size and condition on variables required for estimation of reproductive potential in Atlantic cod Gadus morhua

East and West Greenland cod: From: ICES 2005 Spawning and life history information for North Atlantic cod stocks

Based on long-term investigations on sea temperature in Icelandic waters, five climatic periods are defined from the mid-1880s until today. These are a cold period between 1880 and 1920, a warm period between 1921 and 1964, a cold period between 1965 and 1971, one of intermediate conditions (alternating warm and cold) between 1972 and 1995, and finally a warm period from 1996 until today. Mackerel were first reported from Icelandic waters in 1895, were then found intermittently until 1996, and from then appeared almost every year and since 2007 in large numbers in many areas around Iceland. The occurrence of mackerel appears to be confined mainly to warm periods in the North Atlantic Ocean and around Iceland. The unprecedented occurrence and extended distribution of the species began at the onset of the recent warm period during the mid-1990s and, in recent years, 0-group and age 1 mackerel have also been observed in Icelandic waters. This expansion in distribution resulted initially in a bycatch fishery, which then developed into a direct fishery within the Icelandic Exclusive Economic Zone, increasing from 1700 t in 2006 to 120 000 t in 2009 and 2010.

/pdf/climate-related-variations-in-the-occurrence-and-4vbcn0q6qs.pdf

Climate-related variations in the occurrence and distribution of mackerel (Scomber scombrus) in Icelandic waters

Stomach content data collected from cod caught during offshore resource assessment surveys in three Arcto-boreal ecosystems (the Barents Sea and the shelves off Iceland and eastern Newfoundland) were examined to determine the prevalence of cannibalism, and to identify possible factors associated with variability in prevalence. Cannibalism provides a minor source of food, except for the largest predators. Cannibalism Increases with predator length. Most prey are less than 40 cm In length and less than 3 years old. In each region, cannibalism occurs over most of the area surveyed, but is most prevalent where the smallest cod have been found in bottom trawl surveys. The frequency of occurrence of cannibalism recorded in recent years (late 1970s to the present) has usually been low (<I%) in all regions. Much higher values were reported from the Barents Sea in 1949-1960. In the Barents Sea, the frequency of occurrence of cannibalism increased with the abundance of juvenile cod. There was little support for the hypothesis that the frequency of cannibalism increased when the abundance of capelin, the major prey of cod, was low. It can be demonstrated that cod eat large numbers of their young, especially those of ages 0-2, but the mortality rate imposed cannot be calculated without independent estimates of the abundance of young cod. Mortality imposed by cannibalism and competition is estimated without stomach content data for Icelandic cod. This is done by modelling the change in abundance from the pelaglc 0-group stage, as measured by pelagic trawl surveys, to age 3, as estimated by VPA.

Cannibalism and year-class strength in Atlantic cod (Gadus morhua L.) in Arcto-boreal ecosystems (Barents Sea, Iceland, and eastern Newfoundland)

[Extract] Identification of fish stocks is necessary to fisheries management for allocation of catch between competing fisheries, recognition and protection of nursery and spawning areas, and for development of optimal harvest and monitoring strategies (Kutkuhn, 1981; Grimes et al., 1987; Smith et al., 1990; Begg et al., 1999a). A fish “stock” can be considered to be a group of randomly mating, reproductively isolated individuals with temporal or spatial integrity (Ihssen et al., 1981),
which may exhibit differences in vital population or life history parameters compared to other stocks of the same species (Begg and Waldman, 1999). Differences in these life history parameters among groups of fish have long been used as a
basis for the identification of fish stocks because of the relative ease of assessing these parameters and their dual functionality as input into fisheries stock assessment and management strategies. In this chapter, I review and critique the range
of life history parameters that have typically been used in stock identification studies and provide guidance for the effective protocol of the use of life history parameters in fish stock identification.

Life history parameters

The main objective of this study was to improve the precision of stock assessments of demersal fish in Icelandic waters, with particular emphasis on cod. Sampling was carried out on approximately 600 stations in the Iceland shelf area in March 1985 and again in March 1986. Stations were distributed in the survey area through a semi-randomly stratified process. A standardized bottom trawl was designed for the sampling and the data collected included length measurements, otolith samples and sex determination, as well as information onthe environment and fishing gear. Results are presented for cod, haddock, saithe, redfish, catfish and long rough dab. The distributions of the different species indicate common nursery grounds in the northern part of the survey area. The youngest age-groups were generally not fully represented in the survey. Pronounced diurnal catch variations were observed for catfish and redfish. Age disaggregated stock indices of the gadoid species are well correlated with virtual population analysis (VPA) values. However, the total stock indices differ in their proportion of the VPA stock size. In comparison with previous surveys, the precision of stock indices has been increased markedly through this survey for all species except saithe. This is basically the result of an increased number of stations. Skipper-selected stations (non-random) generally gave higher aggregated indices than random ones, although statistically significant differences are exceptional. On a length disaggregated basis, however, a highly significant difference was observed for all species.

/pdf/icelandic-groundfish-survey-data-used-to-improve-precision-4o1bopodn8.pdf

Icelandic Groundfish Survey Data Used to Improve Precision in Stock Assessments

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Icelandic Groundfish Survey Data Used to Improve Precision in Stock Assessments