Biology and Ecology of Blue CodBlue cod are found on all coasts of New Zealand, but are most abundant in the Marlborough Sounds, Foveaux Strait, and the Chatham Islands, especially over rough rocky ground with weed. Although blue cod live in waters down to about 80 m in depth, they are abundant right up to the shoreline, and in many localities are strongly territorial all year round (Doak 1972 ).
Press here for a picture of a blue cod, and here for a picture of a one being caught.
Blue cod were important to the pre-European Maori in many parts of New Zealand and were known variously as raawaru, paakirikiri, or paatukutuku (Williams 1971: 332).
Blue Cod in Archaeological Sites in New ZealandThe following table lists archaeological sites in New Zealand from which fish bones have been studied, and shows where blue cod have been identified and their relative abundance in the catch. "Blue cod MNI" is the minimum number of individual blue cod represented by bones in the site and "total MNI" is the minimum number of all fish represented. "Age of site" is explained at the bottom of the table.
Archaeological Site: blue cod Total % Age of
MNI: MNI: Site:
Breaksea Sound 1,Discovery Cove,(BSS/1) 118 1153 10.23 % 3
Breaksea Sound 2, Chatham Point 3, BSS/2 0 1 0.00 % 2
Cascade Cove, Dusky Sound (CC/1) 23 125 18.40 % 2
Chalky Is, Chalky Inlet, Southport CH/1 13 45 28.89 % 1
Coopers Island, Dusky Sound, (CI/1) 61 219 27.85 % 1
Davidson Undefended Site, Motutapu Is 0 54 0.00 % 2
Fox River, Te Onumata, Potikohua River 1 102 0.98 % 2
Foxton 0 270 0.00 % 1
Garden Island, Chalky Inlet, Southport 1 1 100.00 % 3
The Glen, Tasman Bay 0 179 0.00 % 1
Harataonga Bay W Midden, Gt Barrier Is 2 65 3.08 % 1
Hot Water Beach, Coromandel Peninsula 4 278 1.44 % 1
Hudson's Site, Goose Bay, Kaikoura 0 27 0.00 % 2
Te Ika a Maru, Eastern Flat 3 63 4.76 % 2
Te Ika a Maru, Flat at Base of Pa 4 199 2.01 % 2
Kahiti North, Hansons Bay, Chatham Is 34 95 35.79 % 2
Kahiti South, Hansons Bay, Chatham Is 41 159 25.79 % 2
Te Kiri Kiri, Ruapuke Island, (KK/1) 20 56 35.71 % 3
Lee Island Site, on Ruapuke Island, LI/1 3 8 37.50 % 1
Long Beach, Dunedin 5 5770 0.09 % 2
Long Island, Dusky Sound, (LI/1) 82 252 32.54 % 2
Leahy Undefended Site, Motutapu Island 0 12 0.00 % 2
Makara Beach Midden 2 50 4.00 % 2
Makara Terrace Midden 1 24 4.17 % 2
Milford 1 7 14.29 % 2
Te Ngaio, Petre Bay, Chatham Island 1 4 25.00 % 2
Ohinemamao, Petre Bay, Chatham Island 5 17 29.41 % 2
Omihi, Kaikoura 0 118 0.00 % 2
Papatowai, Catlins 0 27 0.00 % 1
Parangiaio, Ruapuke Island, (PP/1) 1 12 8.33 % 1
Paremata 3 147 2.04 % 2
Port Craig Cave, Foveaux Strait, (PC/1) 5 114 4.39 % 1
Port Craig Dry Rock Shelter 1, Foveaux 0 2 0.00 % 3
Port Craig Dry Rock Shelter 2, Foveaux 0 1 0.00 % 1
Port Craig Midden, Foveaux Strait, PC/4 0 28 0.00 % 1
Peketa Pa, Kaikoura 0 54 0.00 % 2
Port Jackson, Coromandel 0 45 0.00 % 1
Pokiakio, Petre Bay, Chatham Islands 6 7 85.71 % 2
Ross Rocks, Otago 27 144 18.75 % 1
Sandhill Point 1, Foveaux Strait, SHP/1 4 214 1.87 % 1
Sandhill Point 2, Foveaux Strait, SHP/2 0 2 0.00 % 1
Sandhill Point 3, Foveaux Strait, SHP/3 20 364 5.49 % 2
Sandhill Point 4, Foveaux Strait, SHP/4 6 105 5.71 % 1
Southport 1, Fiordland, (SP/1) 96 443 21.67 % 3
Southport 4, Cave Site, Fiordland, SP/4 18 86 20.93 % 1
Southport 5, Cave Site, Fiordland, SP/5 26 120 21.67 % 2
Southport 6, Fiordland, (SP/6) 17 185 9.19 % 3
Southport 7, Fiordland, (SP/7) 20 111 18.02 % 3
Southport 8, Fiordland, (SP/8) 4 10 40.00 % 2
Southport 9, Cave Site, Fiordland, SP/9 0 1 0.00 % 2
Station Bay Pa, Motutapu Island 4 156 2.56 % 2
Sunde Site, Motutapu Island 0 128 0.00 % 1
Taiaroa Head, Otago Peninsula 0 40 0.00 % 2
Takahanga Post Office Site, Kaikoura 0 130 0.00 % 2
Titirangi Cattleyards, Marlborough 1 14 7.14 % 1
Goose Bay Midden, Titirangi, Marlborough 1 2 50.00 % 2
Titirangi Pa, Marlborough Sounds 0 1 0.00 % 2
Titirangi Sandhills, Marlborough Sounds 2 47 4.26 % 1
Tiwai Point, Bluff Harbour 17 103 16.50 % 1
Tumbledown Bay, Banks Peninsula 0 42 0.00 % 1
Wakapatu, Western Southland 26 94 27.66 % 1
Parewanui Midden, Bulls, Manawatu 0 54 0.00 % 3
Shag River Mouth 155 2134 7.26 % 1
Kokohuia, Hokianga 4 844 0.47 % 1
Midden 8, Matakana Island 0 132 0.00 % 2
Washpool Site, Palliser Bay 29 771 3.76 % 1
Makotukutuku M3 Fort Site, Palliser Bay 1 9 11.11 % 2
Makotukutuku M1 Camp Site, Palliser Bay 0 5 0.00 % 2
Black Rocks BR2 Pond Midden, Palliser 8 58 13.79 % 2
Black Rocks BR3 Black Midden, Palliser 8 191 4.19 % 1
Black Rocks BR4 Crescent Midden Palliser 36 705 5.11 % 1
Black Rocks Fan 1 21 4.76 % 1
Mana Island South Midden R26/141A 35 596 5.87 % 1
Mana Island North Settlement R26/141 111 1206 9.20 % 2
Andrewburn, Fiordland 0 9 0.00 % 2
Huriawa Peninsula. Areas A,B,Salvage 1 453 0.22 % 2
Kelly's Beach, Stewart Island 2 13 15.38 % 2
Old Pier Point Avoca, Kaikoura 0 25 0.00 % 1
Omimi, Otago 0 27 0.00 % 1
Otokia Mouth, Brighton Beach, Otago 0 3 0.00 % 1
Pounawea, Otago 5 428 1.17 % 1
Purakanui Inlet, Otago 0 2745 0.00 % 1
Riverton, Southland 2 14 14.29 % 1
Rotokura, Tasman Bay 11 585 1.88 % 1
Waianakarua Mouth, North Otago 0 6 0.00 % 1
Harataonga Bay Pa, Great Barrier Island 0 231 0.00 % 2
Slipper Island, near Tairua Harbour 0 13 0.00 % 1
Tairua, Coromandel 1 70 1.43 % 1
Whangamata Wharf, Coromandel 0 6 0.00 % 1
Cross Creek Site 1 481 0.21 % 1
Waihora, Chatham Islands 1763 4197 42.01 % 2
CHA, Chatham Islands 602 884 68.10 % 2
CHB, Chatham Islands 3066 4978 61.59 % 2
CHC, Chatham Islands 1 3 33.33 % 2
Panau, Canterbury Peninsula 0 68 0.00 % 2
Twilight Beach, Northland 1 635 0.16 % 1
Aupouri Dune Middens 90 Mile Beach 1 18 5.56 % 2
Houhora 1 2425 0.04 % 1
Waipoua 0 329 0.00 % 2
Northland Harbour Board Site, Whangarei 0 5 0.00 % 2
Sunde Site Oyster lens 1 584 0.17 % 1
Sunde Site soft shore midden 1 401 0.25 % 1
Westfield N42/941 0 21 0.00 % 2
Hamlins Hill N42/137 0 12 0.00 % 2
Hahei N44/215 3 202 1.49 % 2
N44/97 0 9 0.00 % 1
Oruarangi N49/28 0 6 0.00 % 2
Raupa N53/37, T13/13 0 25 0.00 % 2
Aotea N64/25 0 35 0.00 % 2
Kohika N68/104 1 184 0.54 % 2
Awaroa N26/18 0 32 0.00 % 2
N26/214 0 261 0.00 % 2
Bark Bay 0 50 0.00 % 2
Taupo Point 1 11 9.09 % 2
Appleby 7 128 5.47 % 1
Haulashore Island 0 25 0.00 % 2
Bruce Bay 0 54 0.00 % 1
Tiromoana N135/1 0 6 0.00 % 2
Pararaki Wall, Pararaki North N168-9/41 3 36 8.33 % 1
Pleasant River (Anthropology) S155/8 7 54 12.96 % 1
Pleasant River (Smith) 22 145 15.17 % 1
Tumai, Pleasant River Mouth South 15 106 14.15 % 1
Mapoutahi S164/13 1 140 0.71 % 2
Pukekura Pa, Tairoa Head 0 105 0.00 % 2
Papatowai S184/5 1 29 3.45 % 1
West Point WP/1, Ruapuke Island 26 63 41.27 % 2
Age of Site: 1= Early Prehistoric. Before AD 1500, loosely
corresponding to what is referred to as the
Archaic period, or New Zealand East Polynesian
Culture.
2= Late Prehistoric. After AD 1500 and before
AD 1769, loosely corresponding to what is
referred to as Classic Maori Culture.
3= Post-European. After AD 1769 and before
AD 1840. Post-European Maori settlements.
Press here to see this distribution expressed graphically.
The Size of Prehistoric Catches of Blue CodA recent study ( Leach, Davidson and Horwood 1997) at the Archaeozoology Laboratory, Museum of New Zealand Te Papa Tongarewa, used a modern sample of 177 blue cod to establish the most reliable means of estimating live fork lengths and ungutted weights. Using the results of this study it is possible to estimate the live size of blue cod in archaeological sites, and to reconstruct the size frequency distribution of the catch.
Press here for a picture of the blue cod catch from Mana Island as an example.
Apparent Increase in Size over TimeCatches from both periods are dominated by small fish, less than 250 mm long, although very large fish were also obtainable. This suggests that people did not try to select fish according to size. They probably used some form of trap, such as pots, or nets with very small mesh, as it was very hard to make bone or shell hooks small enough to catch small fish. The people living at Mana probably considered small fish to be good food.
The increase in mean fish size over time at Mana (and other sites) challenges a widely held view that fishing pressure results in a lowering of mean size. It suggests the hypothesis that if people are permitted to take as many small specimens as they wish, sustained fishing of a species sensitive to human predation may lead to an increase in mean size. Polynesian people in the tropical Pacific are used to catching and eating small fish; they do not waste them by throwing them back. There is no reason to think that the first immigrants to New Zealand brought with them an idea that stocks are best preserved by taking the largest specimens and leaving the small ones alone. The "take everything" approach may not be as damaging to coastal ecology as is widely believed.
Biomass IssuesThe possible effects of intensive human predation can be investigated through studies of changes to the biomass of particular fish species. An important concept in these studies is the Maximum Constant Yield (MCY). This is defined as "the maximum constant catch that is estimated to be sustainable, with an acceptable level of risk, at all probable future levels of biomass" (Annala 1994: 10).
Blue cod may be a very good species in which to look for evidence of overfishing in the pre-European period. As previously mentioned, blue cod is strongly territorial all year round, and occurs in very shallow water and down to about 80 m. Although no estimates of blue cod biomass are available for different parts of New Zealand, estimates for MCY indicate that blue cod have very low values compared to barracouta and snapper ( Annala 1994).
Although we have been able to reconstruct live catch information on blue cod for quite a few archaeological sites, sufficiently large samples, representative of different time periods, have been more difficult to obtain. This is a significant ongoing area of study.
