The effects of seasonal variation on the nutritional condition ofNephrops norvegicus(Astacidea: Nephropidae) from wild populations in the western Mediterranean

Abstract

The Norway lobster, Nephrops norvegicus is a target fishery species in European waters. The stock assessment of N. norvegicus is complicated because it is caught in commercial gear only when it emerges from its burrow. Landings are lower in winter, and feeding limitations have been hypothesized as the cause. Wild large-sized male lobsters were sampled each season (winter, spring, summer and autumn), and two groups of animals were kept in captivity for 90 d (fed and fooddeprived). The hepatopancreas and muscle were dissected, weighted, frozen for biochemical analyses (proximal analyses and DNA/RNA) and fixed in Bouin solution for microscopic observations. The oxygen consumption rates in the wild individuals caught in the spring and in the captive animals after the treatments were measured. Significant differences among the experimental groups were observed in the lipid concentration of the hepatopancreas and muscle, the water content in the hepatopancreas, and the numbers of vacuoles and pyknotic nuclei in the cells of the tubules of the hepatopancreas. The results showed that the wild Norway lobsters generally presented intermediate values between those observed in the fooddeprived and the fed lobsters kept in captivity, but the values were closer to those obtained for the fed animals. This finding indicates that the wild animals exhibit a good nutritional condition throughout the year. Therefore, the wild males of N. norvegicus do not face food deprivation during winter as is suggested by the pattern of commercial catches, the flow of organic matter, and the moulting period/reproductive behaviour of the species.

Importance of suspended particulate organic matter in the diet of Nephrops norvegicus (Linnaeus, 1758)

“…Although the sexes have similar diets, as shown in the present study, the overall opportunity for feeding may be reduced in females. However, starvation and sex-specific reduction in nutritional status has been previously examined and found to be absent 10 , with corroborating evidence from biochemical markers that suggest good nutritional condition throughout the year in females 38 . Although Clew Bay is a particularly shallow site, the same major food groups (i.e.…”

“…Due to their burrowing lifestyle and long breeding season in females, much effort has gone into investigating seasonal starvation in Nephrops 10,[37][38][39] . The ability to feed on particulate food sources would help to counteract starvation brought about by these lifestyle restrictions.…”

Lipid Composition of Oil Extracted from Wasted Norway Lobster (Nephrops norvegicus) Heads and Comparison with Oil Extracted from Antarctic Krill (Euphasia superba)

“…While in general GSI has been shown to clearly change seasonally in relation to the maturation state of the female gonads [5,24], HSI and the percentage of lipid in the hepatopancreas has been shown to be more variable. For instance, in some studies [25] lipid content in the hepatopancreas has been reported not to change significantly with season, while in other studies conducted in the Clyde Sea area [26] the lowest levels were obtained in the spring, which is similar to the present study. The earlier increase in HSI observed in females should then be explained by an increase in other constituents, such as water content [23] rather than an increase in lipid content.…”