Part of a proposal to do research on sperm whale dietary shifts as a consequence of fishing activity, just FYI (I'm trying to raise money and awareness for a student scholarship)......
Trawling is the most pervasive of marine activities to depths of 1200 m - a depth to which the sperm whale regularly dives. Many squid and octopus are retained as fisheries bycatch, trawled and discarded dead at sea. As a sperm whale can consume 800-1000 squid per day (Clarke 1980), it follows that any change in either the size-class composition or diversity of cephalopod fauna will be manifested in the diet of the whale. The squid fauna and size-class structure therefore act as environmental barometers, providing an index of environmental health from a whale’s perspective.
The threat of deep-sea trawling to the diet of the sperm whale is very real. Five species of large-bodied cephalopod are presently considered threatened or endangered in the DOC ‘Threat Classification System” (Hitchmough 2002) - each as a consequence of deep-sea bottom-trawling activity: Cirroctopus hochbergi, Opisthoteuthis mero, O. chathamensis, Octopus kaharoa, and Idioteuthis cordiformis. Other large-bodied squid not listed in this classification, for which concern is here expressed, are: Taningia danae, Taningia sp. nov., Octopoteuthis sp. nov. (giant), Lepidoteuthis grimaldi, Pholidoteuthis boschmai, Architeuthis dux, any of 7 locally occurring species of Histioteuthis, and any of three species of Moroteuthis. Two of the former, Opisthoteuthis mero and Idioteuthis cordiformis, and all of the latter are either a significant part of or component in the diet of sperm whales (Physeter catodon).
With the apparent decrease in both abundance and diversity of large-bodied cephalopod species in our waters, and the effective collapse of orange roughy stocks (reported from the stomachs of sperm whales by Gaskin & Cawthorn (1967)), it is likely that the diet of toothed whales, particularly sperm whales, has changed already, and worse still, has been forced to change as a direct consequence of deep-sea trawling. If unregulated, the long-term repercussions are devastating.
REFS:
Clarke, M.R. 1980: Cephalopoda in the diet of sperm whales of the Southern Hemisphere and their bearing on sperm whale biology. Discovery Reports 37: 1-324.
Gaskin, D.E. Cawthorn, M.W. 1967. Diet and feeding habits of the sperm whale (Physeter catodon L.) in the Cook Strait region of New Zealand. New Zealand Journal of Marine and Freshwater Research, 1(1[/i]): 156-179.
Hitchmough, R. (comp.) 2002. New Zealand Threat Classification lists - 2002. (Department of Conservation) Threatened species occasional publication 23: 210pp.
