Summary of data collected during the southern squid-fishery mincing trial

Edward R Abraham

Citation

Abraham, E. R. (2007). Summary of data collected during the southern squid-fishery mincing trial. Unpublished report prepared for the Department of Conservation, Wellington, New Zealand.

Summary

This report gives a preliminary analysis of data collected to test whether mincing of waste and discards reduces the number of birds attending fishing trawlers. The trial was carried out on a Korean trawler, fishing in the southern squid fishery during April and March, 2007. The numbers of birds were counted in 40m and 10m semicircular sweep zones extending behind the vessel. Counts were made of five different species categories (large albatross, small albatross, giant petrel, other petrel and shearwater, and cape pigeon). The birds were also classified into three behavioural categories (flying, sitting on the water, and actively feeding).

Three different offal treatments were used (discharge without any processing, mincing all waste with continuous discharge, and mincing all waste with batched discharge). During the trip, the fisheries observer who was implementing the experimental protocol made a total of 85 observations. Of these, 35 were made when the factory was not operating and so when there was no discharge. These observations provide a control, but cannot be used for distinguishing between the different treatments. There were some problems with the minced and batched protocols. Early in the voyage there was a high volume of discards which could not be batched, as there was insufficient room in the factory. The batched protocol was then changed to minced. On one tow, when the vessel was targeting hoki, the bycatch clogged the mincer and an unprocessed treatment was substituted. In addition, there were sometimes rocks in the trawl and these could not be put through the mincer. Small numbers of rocks could be removed by hand by the crew, but large numbers meant the minced treatment had to be changed to unprocessed.

Despite these problems, the preliminary analysis suggests that there was a treatment effect, with fewer large and small albatross attending the vessel when the discharge was minced. The batched treatment also reduced the total numbers of large and small albatross within the 40m sweep zone. The significance of these results will be checked by statistical modelling.

The observer also made 100 strike observations, 50 of trawl warp strikes and 50 of strikes on the tori lines. There were no warp strikes observed during the voyage, and so only the tori line strikes are considered. The effect of treatment on the strikes is unclear. There are fewer large bird strikes when the discharge is minced, but more small bird strikes.


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