Chemoattraction in New Zealand scampi (Metanephrops challengeri): Identifying effective baits to develop a potting fishery

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 in areas around New Zealand. Bottom trawling is a fishing method that typically produces high levels of bycatch and is associated with extensive benthic habitat damage. Pots (also known as creels or traps) tend to have a lower environmental impact when used as an alternative harvesting method to trawling in a number of crustacean fisheries, and may have potential application for scampi. A key component of pot fisheries are effective and economic baits. Therefore, the aim of the research presented in this thesis was to identify effective baits for a scampi potting fishery, by firstly understanding the chemically-mediated food search behaviour of scampi. To achieve this aim the research followed a framework previously identified in the literature;1) characterising the phases of food search behaviour of scampi (presented in Chapter 2); 2) investigating the effect of different hydrodynamic regimes on this behaviour (presented in Chapter 3), and 3) utilising a binary-choice flume to compare the attractiveness of different potential baits (presented in Chapter 4). Additionally, a field experiment was undertaken to assess how baits influenced the operation of pots targeting scampi, especially in terms of their interaction with pot design and the resulting bycatch (presented in Chapter 5). The results of the research showed that the time scampi spent during each of the phases of chemically-mediated food search behaviour was highly variable regardless of the bait tested. However, scampi are more efficient at searching for food in turbulent versus laminar flow conditions. The New Zealand pilchard (Sardinops neopilchardus) baits were identified as being more attractive to the scampi than a number of alternative natural seafood baits. Homogenised pilchard tissue that was diluted (1 & 10% by wet weight) and set in an alginate binder were as attractive to scampi as both the natural pilchard tissue and a positive control to which scampi have previously been conditioned to respond to. This suggests that artificial baits utilising diluted fish tissue may be a practical approach for reducing the amount of fish that would be required for baits in developing a potting fishery for scampi. The advances in the understanding of scampi behaviour made by this research highlight that scampi are likely to feed on a range of food items, and are likely to be more efficient searching for food during periods of higher tidal flow associated with greater turbulence near the seafloor. The results of the potting study showed that the type of bait used did not affect the quantity of composition of the bycatch caught in pots, and that bycatch can be reduced in pots through appropriate pot design and spatially targeted fishing. Overall the results of this research provide a valuable foundation for advancing the potential for developing a more environmentally benign potting fishery for New Zealand scampi.