Indirect effects of commercial fishing in the Marlborough Sounds on the foraging of king shag
Introduction
This is the final report for one component of BCBC2019-05: Understanding potential interactions and indirect effects between commercial fisheries and NZ king shag. Additional research on dietary and population trends is still underway. Published 2020.Download the publication
Summary
King shag (Leucocarbo carunculatus) are a nationally endangered species with a population numbering fewer than 900 individuals, breeding only in the Marlborough Sounds. This research investigated commercial finfish catch taken from a defined study-area in the Marlborough Sounds over the past 30-years. This provides essential information for use in future research and is part of a wider body of work to determine potential indirect effects of commercial fishing and the relationship between availability of prey species and changes to king shag population data over the past 30-years. Three effect indicators were identified and commercial fishing data were used to test for their presence between 1989–90 and 2018–19: namely, (1) large, short-term changes in harvest levels, (2) changes in fishing effort vs catch rates, and (3) decreased catch rates in one area resulting in increased effort in another.
There was no evidence of Indicator 1 in either the processed study-area dataset or the estimated catch and effort, and none for Indicator 3 in the distribution plots. There was evidence for Indicator 2 as increasing effort with a lower catch response in two of the study sub-areas; the distribution plots suggested that this could be related to the setnet fishery. No masking by chondrichthyans could be detected. Future work should examine the influence of fishing methods more closely, particularly their relative efficiency in terms of catch per unit effort. Interestingly, a feature in the stat-area data suggested a possible interaction between the two data reporting methods that is as yet unexplained.
Publication details
Taylor, P. 2020. Indirect effects of commercial fishing in the Marlborough Sounds on the foraging of king shag Leucocarbo carunculatus. Final report prepared by Statfishtics Ltd for the Conservation Services Programme, Department of Conservation. 47 p.