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Research Data - Blue Cod14 September 2008
The Ministry of Fisheries has released the key data from research into blue cod stocks in the Marlborough Sounds.
The 2007 survey was conducted by fisheries scientists from the National Institute of Water and Atmospheric Research (NIWA). It consisted of 740 sample sites throughout the Sounds taken over a two week period.
This survey forms part of a time series of similar surveys dating back to 1995 that shows a dramatic decline in the size and abundance of blue cod, particularly amongst juvenile blue cod in the inner Sounds. Since the last major survey in 2004 there has been an average decline of 57% of juvenile blue cod within the inner Queen Charlotte Sounds.
“These findings have been independently peer reviewed and the research is of high quality. It shows that there has been a substantial decline in the abundance of blue cod in the Marlborough Sounds”, Ministry of Fisheries Chief Scientist Dr Pamela Mace said.
“While some fishers will no doubt be able to catch blue cod in the Sounds, overall numbers are low and dropping. Anecdotal reports of good catches in some areas are not the same thing as peer reviewed scientific research that assesses a fishery as a whole.”
Tag and release surveys have been undertaken on Marlborough Sounds blue cod to determine how far they move and if they migrate to spawn. This research shows that blue cod rarely move more than 900metres from their home reef throughout their entire life.
Blue cod live in small groups with one large dominant male fish living with a group of females. During September the fish spawn on their home reef amongst their group.
“There is significant evidence that blue cod do not migrate at any stage in their life cycle. This highly territorial nature of blue cod makes them susceptible to localised depletion, which is what we are currently seeing in the Marlborough Sounds” said Dr Mace.
In July the Minister of Fisheries announced that the enclosed waters of the Marlborough Sounds will be temporarily closed to all recreational blue cod fishing until 2012.
“This temporary closure will relieve the fishing pressure on blue cod stocks and allow time for Marlborough Community to develop a management plan that will allow fishing to occur now while making sure that blue cod stocks are protected for future generations” said MFish Inshore Fisheries Manager Scott Williamson.
Background:
The 2007 NIWA research survey
1. The survey was carried out from 1 – 16 September 2007 with 2 half days lost to bad weather conditions.
2. Four (4) areas were sampled each day, two in the morning, two in the afternoon (random allocation to avoid bias from tide).
3. The survey design was hierarchical; Region, Strata, Area, Station
4. There are 3 main Regions: Queen Charlotte Sound (QCS), Pelorus Sound (PS), and Tasman Bay (TB).
5. Each region was divided into Strata, QCS = 3, PS = 5 (Included D’urville East), TB = 2 (Includes D’urville West).
6. Each strata was divided into areas based on total area of the strata and blue cod habitat within the strata.
7. The number of areas per strata ranged from 3-12 (see Table below)
8. Within each area a series of Stations were carried out; nine pot stations and two handline stations, therefore each area had 11 stations .
9. These stations were fished for an hour, and the handline stations consisted of two lines, each consisting of two 6/0 hooks.
10. Additionally 46 gear trials were carried out including 42 pot stations and 4 line stations.
11. Total number of data stations for the 2007 survey was 770; 630 pot stations, 140 line stations.
12. From the 770 stations, 3685 blue cod were caught for the purposes of the survey.
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