Abstract
New Zealand scampi (Metanephrops challengeri) is a commercially important deep-water lobster species that is caught by bottom trawling on areas of muddy seafloor on the continental shelf below 300 m. Efforts are being made to develop lower impact potting methods to harvest scampi, however, they can only be caught when out of their burrows and searching for food. This emergent food searching behaviour appears to be associated with periods of higher tidal flow. Such water flow will increase turbulence along the sea floor, which has been observed to improve the efficiency of chemosensory food searching in some lobster species. Consequently, this study examined the food search behaviour of scampi in response to odours from two types of bait (mackerel and mussel) in both turbulent and laminar flows. Scampi were more efficient at foraging in the turbulent flow than in the laminar flow, using shorter search paths in response to both types of bait. Scampi in the turbulent flow reached the mussel bait 44% faster and with lower mean heading angles than in laminar flow. However, there was no difference between the flow regimes for the mackerel bait. The pattern of orientation behaviour was similar under both flow regimes, suggesting that the scampi were using the same orientation strategy, but it was more accurate in turbulent flows. The results show that the foraging efficiency of scampi improves in turbulent conditions and that this may explain their increased emergent behaviour during periods of higher tidal flows.
Highlights
New Zealand scampi (Metanephrops challengeri) is a commercially valuable lobster species that lives in depths of 200–600 m around much of the New Zealand coast [1, 2]
Scampi search periods and total time to the mussel bait were both shorter in the turbulent flow compared to the laminar flow (Search period: t1,17 = 2.35, P = 0.046, 160.8 ± 32.5 vs 318.6 ± 60.3 s respectively; total time to bait: t1,17 = 2.39, P = 0.042, 567.8 ± 93.0 vs 1001.0 ± 130.3 s respectively) (Fig. 3)
Chemosensory food searching in New Zealand scampi is more efficient in turbulent flow as a result of adopting more direct search paths
Summary
New Zealand scampi (Metanephrops challengeri) is a commercially valuable lobster species that lives in depths of 200–600 m around much of the New Zealand coast [1, 2]. Scampi are the target of a deep sea trawl fishery which has an annual catch quota of 1191 t and generates an estimated NZ$11 million a year of sales [2, 3]. Deep sea bottom trawling for scampi damages the sea floor, has high levels of bycatch and uses large quantities of fuel [4,5,6]. Pots ( known as creels) are used in northern hemisphere fisheries to target the ecologically similar Norway lobster (Nephrops norvegicus) [1, 7]. Diffusion disperses chemicals in fluids that are not moving, which creates a concentration gradient away from the
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