Marine Life - Fish Populations
There are hundreds of saltwater fish species found in NZ’s waters, yet you would be hard pressed to find many people who could name more than 20 or so. The “iconic” species of snapper, kahawai, kingfish, gurnard, terakihi, and trevally dominate popular consciousness.
Fishing plays an important part in the lives of many New Zealanders. Not only do fish provide kai, the experience of being on or by the water and connecting with nature contributes to our wellbeing.
Snapper (tāmure) is New Zealand's most popular recreational fish species and Kahawai are the second most commonly caught fish in New Zealand. Blue Cod (rawaru - primarily found in the South Island) and Kingfish (kahu) are particularly popular too.
Given that many of the changes in the Hauraki Gulf have been associated with fishing, we need to be aware of the facts and the scientific evidence for trends. Here we summarise some of the findings from the 2020 Fisheries Assessment Plenary from Fisheries New Zealand2 and the 2020 State of Our Gulf report1, focusing on Snapper.
Fish populations and their age structure are estimated by models using data from commercial catch reports, surveys of recreational catch and tracking tagged fish, including species, number, age, length and weight. These models focus on individual species, viewed as commercial fish stocks, and are designed to inform estimates of allowable catch in order to set quotas at sustainable levels. Thus data for the total number of fish in the Gulf are more difficult to find.
We do know that overall commercial fishing in the Hauraki Gulf has increased by more than 20% in the last 20 years. In 1996-99, the commercial catch was 42% snapper. However, in 2016-19, snapper only made up 23% of the commercial catch (Blue mackerel 36%, Jack mackerel 10%, Other species 31%). Nowadays, more snapper are caught by recreational fishers than by commercial boats.
The Baseline Stock (B0) is an estimate of the ‘unfished’ biomass of a particular species, around the year 1900. Because different species have differing resilience to fishing, the Maximum Sustainable Yield (MSY) varies by species. For a low productivity species with a high age of maturity, high longevity, slow growth rates or low fecundity (e.g. snapper), MSY is set at 40% B0, which is known as the ‘management target’. The ‘soft limit’, below which a population is considered to be ‘overfished’ is 20% B0, while stocks below 10% B0 are considered to be “collapsed”.
Snapper stocks in the Gulf are estimated to have been below 40% of the ‘unfished’ level (40% is the current management target) since the 1970s, reaching their lowest levels in the 1990s. Over the last decade, levels have recovered somewhat, likely due to the raising of the minimum length and lowering bag size for recreational fishers, as well as the lowering of commercial quota catch limits in 1997. However, stocks are still dangerously low.
Even though populations of snapper in the Gulf have been estimated to be fairly stable in the last decade, the recreational catch of snapper has been rising quite sharply, from an estimated 900 tonnes in 1991 to over 2,500 tonnes in 2012. Fisheries NZ suggest that this is likely due to a 50% rise in catch efficiency. As you can see in the graph above, snapper are back in the “overfished” category.
Sources;
1. State of Our Gulf 2020, p29, Hauraki Gulf Forum
2. Fisheries New Zealand (2020). Fisheries Assessment Plenary, May 2020 p 1435-6
There are many sections on fishing, fish stock sustainability, and notes on certain other notable species, in the 2020 SOTG report, and we urge you to read them here.