Further analysis of the impact characteristics of the New Zealand Fisheries sea lion exclusion device stainless steel grid: final research report for Ministry of Fisheries

Abstract

This report documents the test methods, results and analysis used to create a ‘map’ of mild traumatic brain injury risk to sea lions interacting with the grid component of the Sea Lion Exclusion Device (SLED) used in the management of the New Zealand squid fishery. The risk was estimated by testing each of the grid bars within the area of the grid that could be struck by a sea lion during a trawl. The bars were tested at locations along their length at a consistent speed, impactor mass and impact angle. The impact severity was measured according to the head injury criterion (HIC). The results were generalised using a relationship that related the HIC to the speed and mass of the impact, and these were interpolated between locations tested points using curve fitting. Injury risk was estimated from information about human head injury risk modified using scaling methods. An injury risk map was generated that estimates the risk at all possible impact locations across the grid. This map can be modified to allow for variations in head impactor mass, impact speed and impact angle. The results can be used to determine the average impact severity (HIC) and the risk of mild traumatic brain injury (MTBI) at any location, and the average of these across the whole grid, for any set of impact conditions. Given a head mass of 4.8 kg, impact speed of 6 m/s and an impact angle of 90 degrees to the grid, the average HIC of the grid was 551, corresponding to an average risk MTBI of 18%.