Abstract:To evaluate interstock differences in condition, it would be advantageous to develop stock-level condition indices from standardized databases on weight and length. This study describes a method for estimating stock-level condition when individual-level observations on length and weight are not easily accessible. For each year in a 56-year time series for Northeast Arctic cod (Gadus morhua), pseudo-observations of weight and length were generated by pairing the Norwegian and Russian values for weight-at-age provided annually to the assessment working group with estimates of length-at-age derived from the same databases. A weight-length relationship fit to each year was then used to predict weight-at-length, i.e., girth, for a range of standard lengths (30-120 cm). This index was uncorrelated with both the liver condition index and the abundance of Barents Sea capelin (Mallotus villosus), suggesting that at the stock level, the girth of cod is not necessarily indicative of the magnitude of stored energy reserves. Partitioning body size into length-at-age and girth revealed long-term trends in body size. In particular, large/old cod showed substantially higher values of both length-at-age and girth that could be the result of long-term increases in fishing mortality.

Maturity-at-age and length of Northeast Arctic cod was investigated based on survey data from the Barents Sea and Lofoten in 1989-97, applying the maximum likelihood method. The growth rate of immature fish is approximately the same for both sexes, but males mature at a younger age and smaller size, and age and length at 50% maturity are less in males than in females. The maturity analysis indicates considerable interannual variations both in 50% maturity-at-age and length, percentage mature by age and in the mean length of first time spawners in both sexes. Mean length of the first time spawners increases substantially with age for both sexes, but early maturation coincides with increased length-at-age indicating that the maturity is influenced by both age and length. The possible link between observed variation in maturation and the ratio of capelin consumption to cod biomass is discussed.

There is evidence of earlier maturation in males than in females and indications of higher mortality among mature males than mature females in the Northeast Arctic cod (Gadus morhua L.) stock. Both factors affect the composition of the spawning stock by sex and age. One possibility is that spawning mortality is involved. Spawning mortality may occur in both sexes, but observations indicate that it might be higher in males. The possibility of a spawning mortality is investigated by adding spawning mortality in calculations of the history of a year-class to see if this improves the fit with observed sex ratios in commercial landings from the Lofoten spawning fishery. The best fit was obtained for a spawning mortality of about 0.05 on the males. However, the results are not conclusive. Splitting the spawning stock into males and females shows that the earlier maturation in males has a larger impact on the sex ratio in the spawning stock than the spawning mortality rates. Increasing the fishing mortality rates will increase the surplus of male spawners. The results have implications for estimation of biological reference points and the way spawning stock biomass is used in management considerations. Estimation of the female SSB is necessary if maternal effects are to be taken into account.

The food habits of the goatfish, Parupeneus barberinus, from Aqaba were studied. A total of 166 fish over a range of 15 to 27.7cm and representing five age groups were examined. The major dietary components, based on occurrence, were crustaceans (82.6%), sand (71.1 Yy), foramniferans (%%), detritus (52.3%) and polychaetes (49%). Based on gravimetric analysis, crustaceans and sand were the major food components comprising 54.4% and 23.3% of the total food weight respectively. The food consumption decreased from 1.5% of body weight in the 2-year group to 0.3% of body weight in the 6-year group. Seasonal variations were observed in relation to food consumption, percentage weight composition and intensity of feeding.

Monthly changes in the gonadosomatic index indicate that the main spawning season of Parupeneus barberrnus in Aqaba extends from May to August for females and from May to June for males. Males in the 4 years age-group (63.4%) and the 5 years age-group (65.1%) are predominant. The von Bertalanffy growth equation parameters calculated from mean total length data are: L, =32.8 cm; K=0.225; to= -0.73 for males and L,=32,7cm; K=0.206; to= -0.82 for females. The length-weight regression coefficients for males (245) and females (2.8) are not significantly different and they indicate a negative allometric growth. There is no significant change in condition factor with age.