Kahawai FAP

Kahawai Final Advice Paper

Ministry of Fisheries

29 June 2004

12. Non-Commercial Fishers submit that the best available estimate of natural mortality is not used in the 1996 stock assessment (refer to the section on the use of the 1996 stock assessment). Other submissions received did not raise any issues concerning the biological information for kahawai provided in the IPP (refer para 78-81).
13. Submissions from Non-Commercial Fishers, TOKM, NIFCL and Sanford referred to inaccuracies in the catch statistics reported in the IPP and Non-Commercial Fishers submitted that a longer time series of commercial catches should have been reported to indicate past trends in the commercial fishery.

14. Revised commercial catch statistics have been prepared and these cover a longer time period than that shown in the IPP. These are shown graphically in Figure 1 in the section outlining the trends in utilisation of kahawai.

15. Richard Pollock submits kahawai is an integral food source of a wide range of other carnivorous fish, dolphins and whales.
16. Non-Commercial Fishers believe that the decline in kahawai abundance is linked to anecdotal accounts of greater numbers of barracouta in northern waters since 1990. The submission quotes a charter boat skipper and ex-commercial fisher who believes that barracouta have extended their temperature preference and range northwards in response to a niche vacancy allowed for by the disappearance of kahawai schools.
17. Non-Commercial Fishers note that kahawai is one of the few inshore species that push krill and small fish to the surface where seabirds can reach them. While Non-Commercial Fishers states it is not aware of any study conducted to examine the relationship between food availability and nesting success of seabirds it submits that any reduction in the number of kahawai schools has the potential to impact on seabirds, particularly their ability to feed their offspring. Submissions consider that the most notable decline amongst seabirds has been in white fronted terns, which are known as “kahawai birds”. Non-Commercial Fishers submit that MFish have not adequately addressed the effect of declining kahawai stocks on associated and dependent species.
18. The BOPCB submission refers to a report that concludes that the lack of knowledge about marine species and their role in maintaining the integrity and resilience of marine ecosystems poses a serious risk for New Zealand [1]. It submits that kahawai have a unique role to play in terms of biodiversity and the interdependence of a broad range of other species and expresses concern regarding the impact of reduced kahawai stocks.

19. A number of submitters raise environmental issues that they consider are relevant to the determination of TACs for kahawai stocks. MFish notes that environmental issues and the related statutory considerations are addressed in the IPP at paragraphs 119-122 and paragraph 65 (a)-(g) respectively. In summary, MFish has identified the likely importance of kahawai in the food chain. This is a matter that you can take into account when determining a target biomass for kahawai and the setting of TACs for kahawai stocks.
20. In relation to specific submissions, MFish notes that stocks of barracouta and kahawai overlap their distributions throughout most of their respective ranges along the coastlines of both the North and South Island. They have broadly similar niche requirements and are often associated when forming summer feeding aggregations particularly around schools of juvenile jack mackerels or pelagic crustaceans. Tagged barracouta have moved considerable distances (up to 500 nautical miles). It is probably not surprising that at various times particularly when forming these summer feeding aggregations that barracouta are found further north (and kahawai are found further south) than is usual, depending on the movements of their prey. MFish considers this to be a more plausible explanation for the fisher’s observations than niche displacement of one exploited stock by another.
21. MFish notes that potential effects of reduced kahawai abundance on seabirds were addressed in the IPP at para 119. MFish is aware of one NZ research paper (Robertson 1992) on the effects of food supplies on seabirds. Contrary to the views of submitters, Robertson speculated that reduction of the populations of barracouta, kahawai, gemfish, skipjack and albacore tuna from commercial fishing may have allowed small pelagic species to increase in abundance and which may be contributing to the observed increase in the NZ gannet population during recent decades [2]. While the white fronted tern was once more abundant around the coast, its declining population is believed to be due to predation by stoats, dogs, rats and mustelids. Its accessible nesting habit makes this species particularly vulnerable to disturbance [3]. International research has concluded that only extreme food shortages cause significant adult bird mortality. However, poor to moderate availability of food can reduce adult body weight, clutch size, breeding success, colony attendance and the growth rates of chicks [4].
22. In summary, the literature suggests that the potential for impacts on other aquatic life is more complex that suggested by submitters. While the potential impacts of sustainable fisheries on seabird populations are likely to be minimal the potentially important role of kahawai in the ecosystem as both a pelagic predator and prey species emphasises the need for caution in management.
    

[1] Report of the Parliamentary Commissioner for the Environment, 1999: Setting Course for a Sustainable Future: The Management of New Zealand's Marine Environment.

[2] Robertson, D.A. (1992) Diet of the Australasian gannet (Morus serrator) around New Zealand New Zealand Journal of Ecology 16(2): 77-81

[3] Roberston C.J.R. editor (1985) The Complete Book of New Zealand Birds.

[4] Cairns, D.K. (1987) Seabirds as indicators of marine food supplies. Biological Oceanography. 5: 261-271 and Cairns, D.K. (1992) Bridging the gap between ornithology and fisheries science:use of seabird data in stock assessment models The Condor 94: 811-824