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Andy McKay @korimakoecology.bsky.social · 23/08/2026

Warmer spring/summers mean juvenile red cod have much higher mortality and don't go on to be caught as 2/3 year olds in the commercial fishery. This also means they are less available as prey for hōiho fs.fish.govt.nz/Doc/22595/RC...

The relationship between red cod recruitment
and environmental variables
Michael P. Beentjes & James A. Ren wick
Final Research Report for
Ministry of Fisheries Research Project RCO9801
Objective 3
National Institute of Water and Atmospheric Research
July 2000 Final Research Report

Consistently, the strongest correlations between commercial catch and explanatory
variables were with SST, over a wide range of time lags, for both RC03 and RC07.
Following SST, the next best "predictors" of catch variability were the frequencies of
southwest and northeast flow patterns. The correlations generally operate in the sense
that "colder is better": negative correlations (~ -0.75) with SST, positive with
southwest weather types (stronger southwesterlies are cooler over New Zealand),
negative with northeast weather types, and so on.
The maximum magnitude of the correlation occurs at 14-month lag for both fisheries,
corresponding to the period August-January of the year prior to the catch year. There
were often secondary maxima in the magnitude of the correlations two or three years
prior to the catch year. The commercial fishery is made up largely of two and three-
year-old fish, implying that juvenile fish (age ~ one year) are most sensitive to
environmental conditions.
The analyses suggest that enhanced catches since 1990 were largely due to a decrease
in SST, partly as a result of the dominance of El Nino conditions since that time.
Based upon SST values for August-January 1998/1999 and 1999/2000, catches in
both RC03 ,and RC07 fisheries for the current fishing year (1999/2000 and
2000/2001) are predicted to be very low, at levels not seen since the low years of the
mid-1980's.

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Andy McKay @korimakoecology.bsky.social · 23/08/2026

The core red cod habitats suffered extreme and/or severe heatwaves in Summer 2022/23 and 2023/24. This correlates with poor hōiho recruitment and high mortality. storymaps.arcgis.com/stories/0c24...

Figure 2: Observed Marine Heatwaves in each Fisheries Management Area (FMA) and over both depth ranges (0-200m and 200-1500m) in recent years. The colour represents the Marine Heatwave category and indicates by how much sea surface temperatures exceeded historical values (categories follow Hobday et al. 2018 )

Figure 1. Fisheries Management Areas of New Zealand's Exclusive Economic Zone. Red-highlighted regions indicate areas with water depths between 0–200 m, while blue regions represent areas with water depths between 200–1500 m. White regions have water depths greater than 1500 m.

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Andy McKay @korimakoecology.bsky.social · 23/08/2026

Moderate to strong heatwaves forecast in the core habitat this coming summer. www.moanaproject.org/recent-marin...

Charts showing heatwaves for Otago Peninsula and Stewart Island.

Charts showing heatwaves Banks Otago Peninsula.

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