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Possible effects of pollock and herring on the growth and reproductive success of Steller sea lions : insights from feeding experiments using an alternative animal model, Rattus norvegicus Donnelly, Carolyn Patricia


The decline of Steller sea lions (Eumetopias jubatus) in the Gulf of Alaska appears to have been associated with a switch of diet from one dominated by fatty forage fishes (such as herring - Clupea pallasi) to one dominated by low fat fish (such as pollock - Theragra chalcogramma). Observations made during the decline include reduced body size of sea lions, low pregnancy rates, poor fur quality and high mortality. I used the general mammalian model, Rattus norvegicus, to test whether changes in size and reproductive performance could be caused by a switch in the quality of prey consumed. I fed five groups of 12 female, weanling rats diets composed of herring (H), pollock (P), pollock supplemented with herring oil (PH), pollock supplemented with pollock oil (PP), or a semi-purified diet (ICN). Mean body weights were greatest for H , followed by PH, P, PP and finally ICN, although ICN was the only group significantly different from the others. Food intakes prior to mating were 10% higher for groups on the lower fat diets (P and ICN), resulting in similar caloric intakes in all groups. Efficiency of energy utilization was also similar for all fish diets. However, this efficiency was slightly reduced when pollock was supplemented with oil (PP and PH) compared to pollock alone. The protein efficiency ratio (PER) was highest for the H diet, slightly lower for all pollock diets, and significantly lower for ICN. Rats fed the low energy P and I CN meals did not compensate by consuming more during gestation. The fetal weights for mothers fed pollock (P) were significantly reduced. This study shows that the caloric content was a major limiting factor in the nutritional quality of pollock. If food intake was adjusted to meet energetic requirements, there were no detrimental consequences to eating pollock. However, supplementation of pollock meal with additional pollock oil may reduce growth and reproductive performance, although the reasons for this were not apparent.

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